An INDUSTRIAL TRAINING REPORT On Automation and Maintenance
At JCB India, Ballabgarh Final Semester Training Submitted for the partial fulfillment for the award of Degree of Bachelor of Technology In Electronics and Communication Engineering Maharshi Dayanand University, Rohtak Session (2010-2014) Submitted By:Pushpesh Sharma 10/EL078
Under the Guidance of
(Mr. Prem Nandan Yadav)
Training and Placement Head
(Mr. Rajeshwar Sahai)
Submitted to
(Wg. Cdr. Indrash Babbar)
B.S. ANANGPURIA INSTITUTE OF TECHNOLOGY & MANAGEMENT, ALAMPUR, FARIDABAD
i
CERTIFICATE
This is to certify that Mr. Pushpesh Sharma of Bachelor of Technology (B.Tech Electronics and Communication Engineering), has successfully
completed Industrial Training in maintenance
department from JCB India, Ballabgarh for partial fulfillment for the award of degree of Bachelor of Technology in Electronics and Communication Engineering. The Industrial Training report being submitted by him is genuine work done by him and the same is being submitted for evaluation.
Signature
Company Executive with Seal
ii
PREFACE Practical training in an industry is an essential part of an engineering curriculum towards making a successful engineer, as in an industry only as student can realize the theory thought in classroom and it also gives an exposure to modern technology. In the field of Electronics Computer engineering there has been rapid development to support the ever increasing volume information, so Electronics students has an opportunity during Training period to knowledge about the latest technologies. The training period of 6/4 months is not much sufficient to take complete knowledge of technology used but one is expected to identify components, the process flow in an industry for high efficiency and about the knowledge of product technology. Practical knowledge means the visualization of the knowledge, which we read in books. For this we perform experiments and get observations. Practical knowledge is very important in every field. One must be familiar with the problems related to that field so that we may solve them and became successful person. After achieving the proper goal of life an Engineer has to enter in professional life. According to this life he has to serve an industry, may be public or private sector or self-own. For the efficient work in the field he must be well aware of practical knowledge as well as theoretical knowledge. To be a good Engineer, one must be aware of the industrial environment & must know about management, working in industry, labor problems etc., so we can tackle them successfully. Due to all the above reasons & to bridge the gap between theory and practical, our engineering curriculum provides a practical training course of 6/4 months. During this period a student in industry and gets all type of experience and knowledge about the working and maintenance of various types of machinery. Since time immemorial, a man has tried hard to bring the world as close to himself as possible. His thirst for information is hard to quench so he has continuously tried to develop new technologies, which have helped to reach the objective. The world we see today is a result of the continuous research in the field of automation. All these technologies have come to existence because man continued its endeavor towards the objective. This project report of mine on automation and maintenance has been a small effort in reviewing the trends technologies prevailing. For this purpose, no organization other than JCB India could have been a better choice. I have undergone 6 months of training (in 8th semester) at JCB India, Ballabgarh. This report has been prepared on the basis of the knowledge which I acquired during my 6/4 months (10-02-2014 to 10-06-2014) training at Company.
iii
ACKNOWLEDGMENT
This training cannot be realized without help from numerous sources and people in the organization. I take this opportunity to express my profound sense of gratitude and respect to all those who helped me throughout the duration of this training. Without the bliss and euphoria of the accompany successful completion of any task would complete without the expression of appreciation of simple gratitude to the people who made it possible. So, with reverence and veneration honor, I acknowledge all those who’s guidance and encouragement has made this training successful. This project report is the result of the dedication and encouragement of many individuals. My sincere and heartfelt appreciation goes to all of them. Firstly I would like to thank my Director of our college B.S.Anangpuria Institute of Technology and ManagementMr. SS Tyagiand Head of our Department Wg. Cdr. Indrash Babbarfor giving us useful t ips for our exposure to the corporate world. I would
also like to show my sincere gratitude to our training guide Mrs. Anju for giving us the useful guidelines for making the report. I would also like to thank Mr. Prem Nandan Yadav, under whose guidance I have successfully completed this report. I have endeavored to present this in most clear and interesting way. I express my heartfelt thanks and gratitude to JCB India for giving me an opportunity to undertake this project and providing me with crucial feedback that influenced the development of this project.
iv
LIST OF TABLES
Table No.
Title
Page No.
5.1
Preparatory commands (G-code)
26
5.2
Miscellaneous commands (M-code)
27
6.1
4-Bit gray and natural binary codes
34
v
LIST OF FIGURES
Figure No.
Title
Page No.
3.1
A typical numerical control system for a milling machine
15
3.2
Right-hand coordinate system used in drill press and lathe
16
4.1
Cutter path between holes in a point-to-point system
17
4.2
(a) Continuous path cutting and (b) Position error caused by the velocity error Schematic illustration of drilling, boring, and milling with various paths Types of interpolation (a) linear, (b) continuous path approximated by incremental straight lines, and (c) circular (a) Absolute versus incremental; in absolute positioning, the move is specified by x = 6, y = 8; in incremental, the move is specified by x=4, y=5 for the tool to be moved from (2, 3) to (6, 8) (b) Drilling 5-holes at different locations
18
4.6
Open loop control system
20
4.7
Closed loop control system
21
4.3 4.4
4.5
4.8 4.9
18 19
19
22
Optical Encoder (a) Device (b) Series of pulses emitted Diagram showing the difference between accuracy and repeatability
23
5.1
Direct Numerical Control (DNC) Machine
29
6.1
A rotary optical encoder
33
6.2
4-Bit binary code absolute encoder disk track patterns
34
6.3
Incremental encoder disk track patterns
35
6.4
Quadrature direction sensing and resolution enhancement. (CW=clockwise, CCW=counter-clockwise)
36
7.1
PM sheet of Makino machine
45
8.1
Figure showing five-s
14
8.2
The PCDA cycle
56
vi
CONTENTS Front Page
I
Certificate
II
Preface
III
Acknowledgement
IV
List of Tables
V
List of Figures
VI
Contents
VII
Chapter 1 1.1
Chapter 2
INTRODUCTION About JCB
1
CNC MACHINE
2.1
Different components related to CNC machines
11
2.2
Application
14
Chapter 3
ELEMENTS OF A CNC
3.1
Part program
15
3.2
Machine Control Unit (MCU)
15
3.3
Machine tool
16
Chapter 4
PRINCIPLES OF CNC
4.1
Basic Length Unit (BLU)
17
4.2
Point-to-Point Systems
17
4.3
Continuous Path Systems
18
4.4
Interpolator
18
4.5
Incremental and Absolute systems
19
4.6
Open Loop Control Systems
20
4.7
Closed-loop Control Systems
21
4.8
Chapter 5
Precision in CNC Machining 4.8.1
Resolution
4.8.2
Accuracy
4.8.3
Repeatability
PART PROGRAMMING FOR CNC
22
5.1
Introduction
24
5.2
Machine Control Panel
28
5.3
Other Peripheral Devices
28
5.4
Direct Numerical Control (DNC)
29
5.5
Advantages and Disadvantages
30 vii
5.6
Chapter 6
Environmental Control for CNC Machines
32
Digital Encoders
6.1
Absolute encoder
33
6.2
Incremental encoder
35
Chapter 7
Theory of Maintenance
7.1
Total Productive Maintenance
37
7.2
Types of Maintenance
38
7.3 7.4
TPM History OEE
40 42
7.5
Introduction of TPM in an organization
42
Chapter 8
Pillars of TPM
8.1
5S
44
8.2
JISHU HOZEN
46
8.3
KAIZEN
48
8.4
Planned Maintenance
50
8.5
Quality Maintenance
50
8.6
Training
52
8.7
Office TPM
52
8.8
Safety. Health and Environment
55
CONCLUSION
58
REFERENCES
59
viii
Chapter 1
“
JOSEPH CYRIL BAMFORD FOUNDER 1916-2001 You know my motto from my initials J.C. - Jamais Content that's very, very much me. I am never content.
”
THE JCB HERITAGE What began in a garage of 12 feet by 15 feet back in 1945, today manufactures over 300+ models of construction and agricultural equipment’s on 4 different continents with bases in the UK, the US, India, China and South America. JCB's world headquarters JCB IN INDIA is one of the finest engineering factories in Europe and sells a full A subisdiary of J
C Bamford
range of equipment in over 150 countries. A family run business Excavators Limited (JCB), JCB India, is the largest founded by Joseph Cyril Bamford more than 65 years ago, is in known today for its unique products that exceed customers' construction
equipment
expectations worldwide. Backed by an innovative and efficient manufacturer in India. support system, JCB offers brilliant engineering solutions, superb service with reliable back up and great ideas. They all combine to create a guaranteed JCB worldwide performance standard.
JCB India is growing at an enviable pace and surging ahead with ambitious development and
Today JCB is one of the world’s largest construction equipment expansion plan. manufacturers. All this has been made possible through the launching of revolutionary products and adherence to world-class JCB corporate identity norms. Today in India, JCB has machine park of over 1, 25,000 machine and one out of every two equipment’s sold in India is a JCB.JCB in India has 3 modern manufacturing facilities in India:
JCB India headquarters- Ballabgarh, Haryana.
Fabrication -India Business Unit, Pune
Heavy line -India Business Unit, Pune
JCB in India has India's largest Parts & Technical Training Centre and India Design Centre also Pune.Through these facilities, JCB offers a diverse range of unmatched Backhoe Loaders, 11
JCB BACKHOE LOADER RANGE
JCB's advanced range of Backhoe Loaders include the 2DX, 3DX, 3DX-Xtra, 3DX Super and 4DX. These are the machines that promise versatility and high performance with their fuel-efficient engines and superb manoeuvrability. They epitomize strength and durability backed by powerful loader performances and state-of-the art operator cabins.
2
JCB TRACKED EXCAVATOR RANGE
JCB India's finest Excavator range includes the JS81, JS 120 JS 140, JS200, JS200HD and JS210HD all of which are suited to diverse weight requirements. Backed by powerful engines ranging from 76hp to 138hp, JCB excavators are suited to work on all terrains with powerful excavator ends and smooth swing systems to enhance the performance on dual advantage of low fuel consumption and high productivity.
3
JCB WHEEL LOADER RANGE The options available for Wheeled Loaders are 3DXL, 430ZX and 432ZX. These powerful machines are backed by engines ranging from 76hp to 150hp, promising superior performance with state-ofthe-art operator cabins and excellent loader options. These loaders are designed to economize on fuel consumption and for higher productivity.
4
JCB TELEHANDLER RANGE JCB Telescopic Handlers for material handling is symbol of power, performance and style. JCB Telescopic handlers are specifically designed and tailored to operate with the high level of productivity economically. It is a machine that features safety, reliability, operator's comfort, better visibility and durability, making it a masterpiece that has captured the trust of customer’s world over. Its versatile function facilitates various material handling applications and has high fuel economy making it suitable machine for Indian Market.
5
JCB VIBROMAX-VIBRATORY COMPACTOR RANGE The first vibratory soil compactor invented in Dusseldorf, Germany has come a long way since 1934.This machine became the first of a line of vibratory compaction rollers, plates and tampers known around the world as JCB Vibromax. The name itself spells out its meaning- "Maximum Vibration". The heavy equipment such as single drum compactors and vibratory tandem rollers has been a success in the market, representing the majority of Vibromax sales while the light equipment range is customized to offer its customers variety. Vibromax is a combination of high performance and reliability with high operating economy and efficiency. Backed by best dealer network support in the country, JCB Vibromax is set to create a benchmark and meet with success.
6
JCB LIFTALL- PICK 'n' CARRY CRANE Yet another champion from the makers of India's most loved range of Backhoes-JCB Liftall. Liftall offers an unmatched lifting capacity upto 12T. With a Load Movement of 22.8Tm and maximum horizontal reach of 10.2 m, Liftall sets a new landmark. That’s not all. Kirloskar BSIII Diesel Engine makes it a super-efficient machine as it offers excellent performance consuming the least fuel.
7
JCB ROBOT: SKID STEER RANGE Robot Skid Steer Loader, 170 which come with a wide range of attachments to suit specific customer needs. Easy to maintain and full service access at the ground level features the best manoeuvrability options with high productivity and performance that spell convenience and reliability on wheels and on tracks.
8
Hues of JCB in India JCB India, with support of Lady Bamford Trust of UK, has been actively supporting the economically weak people of the country. In the year 2000, the Trust adopted a Government school at Jharssaintli, Haryana. Lady Bamford has taken personal interest in improving the condition of the school and providing financial assistance as well as trained teachers. This noble gesture has increased the number of students from 450 to 730 with remarkable decline in drop-outs. JCB recently adopted 2 villages, Ladhiapur village in Haryana & Ambi village in Pune. The Trust centers to the basic living requirements like drinking water, sanitation, primary health centers, schools and source of livelihood. JCB Joined global relief effort In India and Pakistan by donating £500,000 worth of machines to help the rescue and clearing work after the disastrous earthquake wreaked havoc In the region In the year 2005. JCB has a history of making significant contribution to the quake relief expeditions, playing a major role after Gujarat quake during 200l, and also in Izmit, Turkey in 1999 that claimed over thousands of lives.
JCB helps in Leh rebuilding JCB India had pledged two 3DX Backhoe Loaders and other supports to help in clean-up operation following a devastating flood in Northern India, which claimed the lives of dozens of people. Heavy rains led to flash floods and mudslides in the mountains of Leh .This is the North West of the country. Besides the two Backhoe Loaders pledged to the Indian Ministry of Defence, JCB India also donated 500 blankets to the disaster region and set up several free JCB Service Camps to ensure the machines working on the Relief Camps were operational. The two Backhoes were used to repair The Drukk School at Leh and to build new housing for victims of the disaster.
9
JCB Corporate Mission
Our mission is to grow our company by providing innovative, strong and high performance products and solutions to meet our global customers’ needs. We will support our world class products by providing superior customer care. Our care extends to the environment and the community. We want to help build a better future for our children, where hard work and dedication are given their just reward.
10
Chapter 2 CNC MACHINE
Different components related to CNC machine tools Any CNC machine tool essentially consists of the following parts: 1) Part program:
A part program is a series of coded instructions required to produce a part. It controls the movement of the machine tool and on/off control of auxiliary functions such as spindle rotation and coolant. The coded instructions are composed of letters, numbers and symbols. 2) Program input device:
The program input device is the means for part program to be entered into the CNC control. Three commonly used program input devices are punch tape reader, magnetic tape reader, and computer via RS-232-C communication. 3) Machine Control Unit:
The machine control unit (MCU) is the heart of a CNC system. It is used to perform the following functions:
•
To read the coded instructions.
•
To decode the coded instructions.
•
To implement interpolations (linear, circular, and helical) to generate axis motion commands.
•
To feed the axis motion commands to the amplifier circuits for driving the axis mechanisms.
•
To receive the feedback signals of position and speed for each drive axis.
To implement auxiliary control functions such as coolant or spindle on/off and tool change. The CPU is the heart of a CNC system. It accepts the information stored in the memory as part program. This data is decoded and transformed into specific position control and velocity signals. It also oversees the movement of the control axis or spindle and whenever this does not match with the programmed values, a corrective action was taken. All the compensation required for machine acquires (like lead screw pitch error, tool wear out, backlashes.) are calculated by CPU depending upon the corresponding inputs made available to the system. The same will be taken 11
care of during the generation of control signals for the axis movement. Also, some basic safety checks are built into the system through this unit and continuous necessary corrective actions will be provided by CPU unit. Whenever the situation goes beyond control of the CPU, it takes the final action of shutting down the system and in turn the machine. 4) Drive System:
A drive system consists of amplifier circuits, drive motors, and ball lead-screws. The MCU feeds the control signals (position and speed) of each axis to the amplifier circuits. The control signals are augmented to actuate drive motors which in turn rotate the ball leadscrews to position the machine table. The decoded position and velocity control signals, generated by the CPU for the axis movement forms the input to the servo control unit. This unit in turn generates suitable signals as command values. The command values are converted by the servo drive units which are interfaced with the axes and the spindle motors. The servo control unit receives the position feedback signals for the actual movement of the machine tool axes from the feedback devices (like linear scales, rotary encoders, revolvers, etc.) 5) Machine Tool:
CNC controls are used to control various types of machine tools. Regardless of which type of machine tool is controlled, it always has a slide table and a spindle to control of position and speed. The machine table is controlled in the X and Y axes, while the spindle runs along the Z axis. 6) Feed Back System:
The feedback system is also referred to as the measuring system. It uses position and speed transducers to continuously monitor the position at which the cutting tool is located at any particular instant. The MCU uses the difference between reference signals and feedback signals to generate the control signals for correcting position and speed errors. The present day computer can be considered as a direct consequence of the progress in the field of numerical control of machine tools. A real breakthrough was achieved around 1965 when numerical control machines were fitted with minicomputers which introduced the name Computer Numerical Control. The first step in the process of implementing automation in any industry is to manufacture parts or components through automation using machines and machine tools with little human intervention. In order to meet the increasing demand to manufacture complicated components of high accuracy in large quantities, sophisticated technological equipment and machinery have been 24 CNC Machines developed. Production of these 12
components calls for machine tools which can be set up fairly rapidly without much attention. The design and construction of Computer Numerically Controlled (CNC) machines differs greatly from that of conventional machine tools. This difference arises from the requirements of higher performance levels. The CNC machines can be operated automatically using computers. A CNC is specifically defined as “The numerical control system where a dedicated, stored program computer is used to perform some or all of the basic numerical control functions in accordance with control programs stored in read & write memory of the computer” by Electronic Industries Association (EIA). CNC is a microprocessor based control system that accepts a set of program instructions, processes and sends output control information to a machine tool, accepts feedback information acquired from a transducer placed on the machine tool and based on the instructions and feedback, assures that proper motion, speed and operation occur. The information stored in the computer can be read by automatic means and converted into electrical signals, which operate the electrically controlled servo systems. Electrically controlled servo systems permits the slides of a machine tool to be driven simultaneously and at the appropriate feeds and direction so that complex shapes can be cut, often with a single operation and without the need to reorient the work piece. Computer Numerically Control can be applied to milling machines, Lathe machines, Grinding machines, Boring machines, Flame cutters, Drilling machines etc. A CNC system basically consists of the following:
a) Central processing unit (CPU) b) Servo control unit c) Operator control panel d) Machine control panel e) Programmable logic controller f) Other peripheral devices. Some of the important parts of CNC machines are Machine structure, guide ways, feed drives, spindle and Spindle bearings, measuring systems, controls, software and operator interface, gauging, tool monitoring. Computer Numerical Control (CNC) is one in which the functions and motions of a machine tool are controlled by means of a prepared program containing coded alphanumeric data. CNC can control the motions of the work piece or tool, the input parameters such as feed, depth of cut, speed, and the functions such as turning spindle on/off, turning coolant on/off.
13
Applications The applications of CNC include both for machine tool as well as non-machine tool areas. In the machine tool category, CNC is widely used for lathe, drill press, milling machine, grinding unit, laser, sheet-metal press working machine, tube bending machine etc. Highly automated machine tools such as turning centre and machining centre which change the cutting tools automatically under CNC control have been developed. In the non-machine tool category, CNC applications include welding machines (arc and resistance), coordinate measuring machine, electronic assembly, tape laying and filament winding machines for composites etc.
Advantages and Limitations The benefits of CNC are
1) High accuracy in manufacturing 2) Short production time 3) Greater manufacturing flexibility 4) Simpler fixturing 5) Contour machining (2 to 5 –axis machining) 6) Reduced human error. The drawbacks include high cost, maintenance, and the requirement of skilled part programmer.
14
Chapter 3 ELEMENTS OF A CNC A CNC system consists of three basic components (Figure 2):
1. Part program 2. Machine Control Unit (MCU) 3. Machine tool (lathe, drill press, milling machine etc.) Part program The part program is a detailed set of commands to be followed by the machine tool. Each command specifies a position in the Cartesian coordinate system (x,y,z) or motion (work piece travel or cutting tool travel), machining parameters and on/off function. Part programmers should be well versed with machine tools, machining processes, effects of process variables, and limitations of CNC controls. The part program is written manually or by using computer assisted language such as APT (Automated Programming Tool).
Figure 3.1: A typical numerical control system for a milling machine
Machine Control Unit The machine control unit (MCU) is a microcomputer that stores the program and executes the commands into actions by the machine tool. The MCU consists of two main units: the data processing unit (DPU) and the control loops unit (CLU). The DPU software includes control 15
system software, calculation algorithms, translation software that converts the part program into a usable format for the MCU, interpolation algorithm to achieve smooth motion of the cutter, editing of part program (in case of errors and changes). The DPU processes the data from the part program and provides it to the CLU which operates the drives attached to the machine lead screws and receives feedback signals on the actual position and velocity of each one of the axes. A driver (dc motor) and a feedback device are attached to the lead screw. The CLU consists of the circuits for position and velocity control loops, deceleration and backlash take up, function controls such as spindle on/off.
Machine Tool The machine tool could be one of the following: lathe, milling machine, laser, plasma, coordinate measuring machine etc. Figure 3 shows that a right-hand coordinate system is used to describe the motions of a machine tool. There are three linear axes (x,y,z), three rotational axes (i,j,k), and other axes such as tilt (9) are possible. For example, a 5-axis machine implies any combination of x,y,z,i,j,k and Ɵ.
Figure 3.2: Right-hand coordinate system used in drill press and lathe
16
Chapter 4 PRINCIPLES OF CNC
Basic Length Unit (BLU) Each BLU unit corresponds to the position resolution of the axis of motion. For example, 1 BLU = 0.0001" means that the axis will move 0.0001" for every one electrical pulse received by the motor. The BLU is also referred to as Bit (binary digit). Pulse = BLU = Bit
Point-to-Point Systems Point-to-point systems are those that move the tool or the work piece from one point to another and then the tool performs the required task. Upon completion, the tool (or work piece) moves to the next position and the cycle is repeated (Figure 4). The simplest example for this type of system is a drilling machine where the work piece moves. In this system, the feed rate and the path of the cutting tool (or work piece) have no significance on the machining process. The accuracy of positioning depends on the system's resolution in terms of BLU (basic length unit) which is generally between 0 .001" and 0.0001”.
Figure 4.1: Cutter path between holes in a point-to-point system
Continuous Path Systems (Straight cut and contouring systems ) These systems provide continuous path such that the tool can perform while the axes are moving, enabling the system to generate angular surfaces, two-dimensional curves, or three-dimensional contours. Example is a milling machine where such tasks are accomplished (Figure 5). Each axis might move continuously at a different velocity. Velocity error is significant in affecting the positions of the cutter (Figure 5). It is much more important in circular contour cutting where one
17
axis follows sine function while the other follows cosine function. Figure 6 illustrates point-topoint and continuous path for various machines.
Figure 4.2: (a) Continuous path cutting and (b) Position error caused by the velocity error
Figure 4.3: Schematic illustration of drilling, boring, and milling with various paths.
Interpolator The input speed of l in/sec in example 2 is converted into the velocity components by an interpolator called the linear interpolator whose function is to provide the velocity signals to x and y directions. Similarly we have circular and parabolic interpolators. See Figure 7.
18
Figure 4.4: Types of interpolation (a) linear, (b) continuous path approximated by incremental straight lines, and (c) circular
Incremental and Absolute systems CNC systems are further divided into incremental and absolute systems (Figure 8). In incremental mode, the distance is measured from one point to the next. For example, if you want to drill five holes at different locations, the x-position commands are x + 500, + 200, + 600, - 300, -700, -300. An absolute system is one in which all the moving commands are referred from a reference point (zero point or srcin). For the above case, the x-position commands are x 500,700, 1300, 1000, 300, and 0. Both systems are incorporated in most CNC systems. For an inexperienced operator, it is wise to use incremental mode.
Figure 4.5: (a) Absolute versus incremental; in absolute positioning, the move is specified by x = 6, y = 8; in incremental, the move is specified by x=4, y=5 for the tool to be moved from (2, 3) to (6, 8) (b) Drilling 5-holes at different locations
19
The absolute system has two significant advantages over the incremental system: •
Interruptions caused by, for example, tool breakage (or tool change, or checking the parts), and would not affect the position at the interruption.
If a tool is to be replaced at some stage, the operator manually moves the table, exchanges the tool, and has to return the table to the beginning of the segment in which the interruption has occurred. In the absolute mode, the tool is automatically returned to the position. In incremental mode, it is almost impossible to bring it precisely to that location unless you repeat the part program •
Easy change of dimensional data
The incremental mode has two advantages over the absolute mode. •
Inspection of the program is easier because the sum of position commands for each axis must be zero. A nonzero sum indicates an error. Such an inspection is impossible with the absolute system.
•
Mirror image programming (for example, symmetrical geometry of the parts) is simple by changing the signs of the position commands.
Open Loop Control Systems The open-loop control means that there is no feedback and uses stepping motors for driving the lead screw. A stepping motor is a device whose output shaft rotates through a fixed angle in response to an input pulse (Figure 9). The accuracy of the system depends on the motor's ability to step through the exact number. The frequency of the stepping motor depends on the load torque. The higher the load torque, lower would be the frequency. Excessive load torque may occur in motors due to the cutting forces in machine tools. Hence this system is more suitable for cases where the tool force does not exist (Example: laser cutting).
Figure 4.6: Open loop control system
20
The stepping motor is driven by a series of electrical pulses generated by the MCU. Each pulse causes the motor to rotate a fraction of one revolution. The fraction is expressed in terms of the step angle,
, given by = 360/N, degrees where N = numberfopulses required for one revolution If the motor receives "n" number of pulses then the total angle, A = n (360/N), degrees
In terms of the number of revolutions, it would be (n/N) If there is a 1:1 gear ratio between the motor and the lead screw, then the lead screw has (n/N) revolutions. If the pitch of lead screw is p (in/rev), then the distance travelled axially, say x, x = p*(n/N) can be used to achieve a specified x-increment in a point-to-point system. The pulse frequency, f, in pulses/sec determines the travel speed of the tool or the work piece. 60 f = N (RPM) where N = number of pulses per revolution, RPM = RPM of the lead screw The travel speed, V, is then given by V = p (RPM) where p pitch in in/rev
Closed-loop Control Systems Closed -loop NC systems are appropriate when there is a force resisting the movement of the tool/work piece. Milling and turning are typical examples. In these systems (Figure 10) the DC servomotors and feedback devices are used to ensure that the desired position is achieved. The feedback sensor used is an optical encoder shown in Figure 11. The encoder consists of a light source, a photo detector, and a disk containing a series of slots. The encoder is connected to the lead screw. As the screw turns, the slots cause the light to be seen by the photo detector as a series of flashes which are converted into an equivalent series of electrical pulses which are then used to characterize the position and the speed. The equations remain essentially the same as openloop except that the angle between the slots in the disk is the step angle, Both the input to the control loop and the feedback signals are a sequence of pulses, each pulse representing a BLU unit. The two sequences are correlated by a comparator and gives a signal, by means of a digital-to-analog converter, (a signal representing the position error), to operate the drive motor (DC servomotor).
21
Figure 4.7: Closed loop control system
Figure 4.8: Optical Encoder (a) Device (b) Series of pulses emitted
PRECISION IN CNC MACHINING The combined characteristics of the machine tool and the control determine the precision of positioning. Three critical measures of precision are: •
Resolution
•
Accuracy
•
Repeatability
Control resolution (BLU) is the distance separating two adjacent points in the axis movement
(the smallest change in the position). The electromechanical components of the positioning system that affect the resolution are the lead screw pitch, the gear ratio, and the step angle in the stepping motor (open loop) or the angle between the slots in the encoder (closed-loop). The control resolution for a 1:1 gear ratio of a stepped motor is, Resolution = p/N where p = pitch, and N = 360/a 22
Features smaller than the control resolution could not be produced. The programming resolution can not exceed the control resolution.
Accuracy of a CNC system depends on the resolution, the computer control algorithms, and the
machine inaccuracies. The inaccuracy due to the resolution is considered to be (1/2) BLU on the average. The control algorithm inaccuracy is due to the rounding off the errors in the computer which is insignificant. The machine inaccuracy could be due to several reasons (described below). The designer minimizes this inaccuracy to be under (1/2) BLU and hence Accuracy = (1/2) Resolution + Machining inaccuracy = BLU
Repeatability is a statistical term associated with accuracy. It refers to the capability of a
positioning system to return to a programmed point, and is measured in terms of the errors associated with the programmed point. The deviation from the control point (error) usually follows a normal distribution in which case the repeatability may be given as +/- 3a where a is the standard deviation. The repeatability is always better than the accuracy. The mechanical inaccuracy can be considered as the repeatability. Figure 12 shows the difference between the accuracy and the repeatability.
Machining Inaccuracy Cutting tool deflection, machine tool chatter, mechanical linkage between the lead screw and the tool, and thermal deformations are the chief contributing factors. The lead screw transmits the power to the table or tool holder by means of a nut that engages the lead screw. This will create what is known as "backlash “due to the friction between the screw and the nut. If the nut consists of ball bearings, the friction is reduced. Thermal deformations are significant. For example, a temperature difference of 1 °C along 1000 mm can cause an error of 0.01 mm.
Figure 4.9: Diagram showing the difference between accuracy and repeatability
23
Chapter 5 PART PROGRAMMING FOR CNC The transfer of an engineering blueprint of a product to a part program can be performed manually using a calculator or with the assistance of a computer language. A part programmer must have an extensive knowledge of the machining processes and the capabilities of the machine tools. In this section, we describe how the part programmers execute manually the part programs. First, the machining parameters are determined. Second, the optimal sequence of operations is evaluated. Third, the tool path is calculated. Fourth, a program is written. Each line of the program, referred to as a block, contains the required data for transfer from one point to the next. A typical line for a program is given below. N100 G91 X -5.0 Y7 .0 F100 S200 T01 M03 (EOB) The significance of each term is explained below.
Sequence Number, N
Consisting of typically three digits, its purpose is to identify the specific machining operation through the block number particularly when testing a part program.
Preparatory Function, G
It prepares the MCU circuits to perform a specific operation. The G-codes (some) are shown in Table 1. G91 implies incremental mode of operation.
Dimension Words
1. Distance dimension words, X,Y,Z 2. Circular dimension words, I,J,K for distances to the arc centre 3. Angular dimensions, A,B.C While (1) and (3) are expressed either by incremental or absolute mode, (2) is always in given in incremental mode. All angular dimensions are specified in revolutions or degrees. In the above block, X moves a distance of 5 in. in the negative direction while Y moves a distance of 7 in. in the positive direction. Other axes remain stationary. In some systems, actual distances are used. In others, the dimension words are programmed in BLUs.
24
Feed rate, F
It is expressed in in/min or mm/min and, is used in contouring or point-to-point or straight cut systems. For example, a feed rate of F100 implies 100 in/min or 100 mm/min. Feed rates are independent of spindle speed. In linear motions, the feed rate of the cutting tool is not corrected for the cutter radius. But in circular motions, the feed rate should be corrected for the tool radius as follows: F = [(part contour radius ± tool radius)/part contour radius] (required feed rate) For cutting around the outside of a circle, the plus sign in the above equation is used, and the feed rate is increased. For cutting around the inside of a circle, the minus sign is used, and the feed rate is decreased.
Spindle speed, S
Programmed in rev/min, it is expressed as RPM or by a three-digit code number that is related to the RPM.
Tool word, T
Consisting of a maximum of five digits, each cutting tool has a different code number. The tool is automatically selected by the automatic tool changer when the code number is programmed in a block.
Miscellaneous Function, M
Consisting of two digits, this word relates to the movement of the machine in terms of spindle on/off, coolant on/off etc. shown in Table 2.
EOB
The EOB character is used at the end of each block to complete a line.
25
Pr epar ator y commands (G-code) G00
Point-to-point positioning
G01
Linear interpolation
G02
Clockwise circular interpolation
G03
Counter-clockwise circular interpolation
G04
Dwell
G05
Hold
G33
Thread cutting, constant lead
G40
Cancel tool nose radius compensation
G41
Tool nose radius compensation - left
G42
Tool nose radius compensation - right
G43
Cutter length compensation
G44
Cancel cutter length compensation
G70
Dimensions in inches
G71
Metric dimensions
G90
Absolute dimensions
G91
Incremental dimensions
G92
Datum offset Table 5.1: Preparatory commands (G-code)
26
M iscellaneous commands (M -code) M00
Program stop
M01
Optional stop
M02
End of program
M03
Spindle start clockwise
M04
Spindle start counter-clockwise
M05
Spindle stop
M06
Tool change
M07
Mist coolant on
M08
Flood coolant on
M09
Coolant off
M10
Clamp
M11
Unclamp
M13
Spindle clockwise, coolant on
M14
Spindle counter-clockwise, coolant on
M30
End of tape, rewind Table 5.2: Miscellaneous commands (M-code)
27
Operator Control Panel The Operator Control Panel provides control panel provides the user interface to facilitate a two way communication between the user, CNC system and the machine tool. This consists of two parts are Video display unit and Keyboard.
Machine Control Panel It is the direct interface between the operator and the NC system, enabling the operation of the machine through the CNC system. During program execution, the CNC controls the axis the motion, spindle function or tool function on a machine tool, depending upon the part program stored in the memory. Prior to the starting of the machining process, machine should first be prepared with some specific takes like, establishing a correct reference point, loading the system memory with the required part program, loading and checking of tool offsets, zero offsets, etc. Programmable Logic Controller (PLC)
A PLC matches the NC to the machine. PLC’s were basically as replacement for hard wired relay control panels. They were basically introduced as replacement for hard wired relay panels. They developed to be re-programmed without hardware changes when requirements were altered and thus are re-usable. PLC’s are now available with increased functions, more memory and larger input/output capabilities. In the CPU, all the decisions are made relative to controlling a machine or a process. The CPU receives input data, performs logical decisions based upon stored programs and drives the output connection to a computer for hierarchical control are done through CPU.
Other Peripheral Devices These include sensor interface, provision for communication equipment, programming units, printer, tape reader interface, etc.
CNC Concept A CNC system may be characterized in terms of three major elements: hardware, software and information.
Hardware Hardware includes the microprocessors that effect control system functions and peripheral devices for data communication, machine tool interfacing and machine tool status monitoring.
Software 28
Software includes the programs that are executed by the system microprocessors and various types of software associated with CNC.
Information Information regarding the dynamic characteristics of the machine and many other information pertaining to the process. When any of these unreliable components fails, the diagnostics subsystem would automatically disconnect the faulty component from the system and activate the redundant component in place of faulty one so that newly installed component can perform its function.
DIRECT NUMERICAL CONTROL (DNC) MACHINES Direct Numerical Control can be defined as a type of manufacturing system in which several NC or CNC machines are controlled remotely from a Host/Main frame computer or direct numerical control (DNC) – control of multiple machine tools by a single (mainframe) computer through direct connection.
Figure 5.1: Direct Numerical Control (DNC) Machine
A DNC is specifically defined as “A system connecting a set of numerically controlled machines to a common memory for part program or machine program storage with provision for on-demand
29
distribution of data to machines” by Electronic Industries Association (EIA). In DNC, several NC machines are directly controlled by a computer, eliminating substantial hardware from the individual controller of each machine tool. The part-program is downloaded to the machines directly (thus omitting the tape reader) from the computer memory. The basic DNC system requires following basic component are Main frame computer, Memory, Communication network, NC machine tool. The communication network can be done either through connecting the remotely located computer, with lengthy cables to the individual machine control directly or connecting the main frame computer with a small computer at individual operator’s station known as satellite computer. DNC system is expensive and is preferably used in large organizations. The combination of DNC/CNC makes possible to eliminate the use of programme as the input media for CNC machines. The DNC computer downloads the program directly to the CNC computer memory. This reduces the amount of communication required between the central computer and each machine tool.
Advantages of DNC a) The computer can be remotely located, even a thousand miles away.
b) The computer can program simultaneously many NC machines. ADVANTAGES OF CNC MACHINES
a) High Repeatability and Precision, e.g. Aircraft parts. b) Volume of production is very high. c) Complex contours/surfaces need to be machined, e.g. Turbines. d) Flexibility in job change, automatic tool settings, less scrap. e) Safer, higher productivity, better quality. f) Less paper work, faster prototype production, reduction in lead times. g) Easier to program. h) Easy storage of existing programs. i) Avoids human errors. j) Usually generates closer tolerances than manual machines. k) Program editing at the machine tool. l) Control systems upgrades possible. m) Option -resident CAM system at machine tool. n) Tool path verification.
30
DISADVANTAGES OF CNC MACHINES
a) b) c) d)
Costly setup, skilled operators. Computers, programming knowledge required. Maintenance is difficult. Machines have to be installed in air conditioned places.
PARTS SUITABLE FOR CNC MACHINES The following parts are usually made in practice on the CNC Machines:
a) Aerospace equipment. b) Automobile Parts. c) Complex shapes. d) Electronic industry uses CNC e.g. Printed circuit board. e) Electrical industry uses CNC e.g. Coil winding. f) For small to medium batch quantity. g) Where the set-ups are very large. h) Where the tool storage is a problem. i) Where much metal needs to be removed. j) When the part geometry is so complex. k) The operations are very complex. l) For parts subjected to regularly design changes. m) When the inspection is required 100%. n) When lead time does not permit the conventional tooling manufacture. o) When the machining time is very less as compared to down. p) Where tool storage is a problem. q) Where repetitive operations are required on the work.
31
ENVIRONMENTAL CONTROL FOR CNC MACHINES There are various factors, which are very much important to maintain proper environmental conditions. CNC machines are very costly and complex in design, so great care is necessary for these machines in handling as well as up keeping. For proper working of these machines, the following environmental conditions are to be maintained Well air circulation.
a) Working temperature should be within control limits. b) Space should not be congested but should be quite open. c) Electrical power supply should be regulated. d) There should be proper disposal point for scrap. e) There should not be presence of noisy source near to the machine. f) There should not be presence of harmful chemicals near to the machine. g) Proper lighting to the system. h) The machine should be protected from the moisture. i) There should not be presence of vibrating source near to the machine. j) Power supply should be regulated. k) Floor should be cleaned free from oily and greased. l) Trained person should operate the machine. m) Dust free floor space and environment. n) Sufficient supply of coolant required during machining.
32
Chapter 6 Digital Encoders A digital optical encoder is a device that converts motion into a sequence of digital pulses. By counting a single bit or by decoding a set of bits, the pulses can be converted to relative or absolute position measurements. Encoders have both linear and rotary configurations, but the most common type is rotary. Rotary encoders are manufactured in two basic forms: the absolute encoder where a unique digital word corresponds to each rotational position of the shaft, and the incremental encoder, which produces digital pulses as the shaft rotates, allowing measurement of relative position of shaft. Most rotary encoders are composed of a glass or plastic code disk with a photographically deposited radial pattern organized in tracks. As radial lines in each track interrupt the beam between a photo emitter-detector pair, digital pulses are produced.
Figure 6.1: A rotary optical encoder
Absolute encoder The optical disk of the absolute encoder is designed to produce a digital word that distinguishes N distinct positions of the shaft. For example, if there are 8 tracks, the encoder is capable of producing 256 distinct positions or an angular resolution of 1.406 (360/256) degrees. The most common types of numerical encoding used in the absolute encoder are gray and binary codes. To illustrate the action of an absolute encoder, the gray code and natural binary code disk track patterns for a simple 4-track (4-bit) encoder are illustrated in Fig 2 and 3. The linear patterns and associated timing diagrams are what the photo detectors sense as the code disk circular tracks rotate with the shaft. The output bit codes for both coding schemes are listed in Table 1.
33
Figure 6.2: 4-Bit binary code absolute encoder disk track patterns
Decimal code
Rotation range (deg.)
Binary code Gray code
0
0-22.5
0
0
1
22.5-45
1
1
2
45-67.5
10
11
3
67.5-90
11
10
4
90-112.5
100
110
5
112.5-135
101
111
6
135-157.5
110
101
7
15.75-180
111
100
8
180-202.5
1000
1100
9
202.5-225
1001
1101
10
225-247.5
1010
1111
11
247.5-270
1011
1110
12
270-292.5
1100
1010
13
292.5-315
1101
1011
14
315-337.5
1110
1001
337.5-360
1111
1000
15
Table 6.1: 4-Bit gray and natural binary codes
34
The gray code is designed so that only one track (one bit) will change state for each count transition, unlike the binary code where multiple tracks (bits) change at certain count transitions. This effect can be seen clearly in Table 1. For the gray code, the uncertainty during a transition is only one count, unlike with the binary code, where the uncertainty could be multiple counts. Since the gray code provides data with the least uncertainty but the natural binary code is the preferred choice for direct interface to computers and other digital devices, a circuit to convert from gray to binary code is desirable. Figure 4 shows a simple circuit that utilizes exclusive OR gates (XOR) to perform this function.For a gray code to binary code conversion of any number of bits N, the most signficant bits (MSB) of the binary and gray code are always identical, and for each other bit, the binary bit is the exlcusive OR (XOR) combination of adjacent gray code bits.
Incremental encoder The incremental encoder, sometimes called a relative encoder, is simpler in design than the absolute encoder. It consists of two tracks and two sensors whose outputs are called channels A and B. As the shaft rotates, pulse trains occur on these channels at a frequency proportional to the shaft speed, and the phase relationship between the signals yields the direction of rotation. The code disk pattern and output signals A and B are illustrated in Figure 5. By counting the number of pulses and knowing the resolution of the disk, the angular motion can be measured. The A and B channels are used to determine the direction of rotation by assessing which channels "leads" the other. The signals from the two channels are a 1/4 cycle out of phase with each other and are known as quadrature signals. Often a third output channel, called INDEX, yields one pulse per revolution, which is useful in counting full revolutions. It is also useful as a reference to define a home base or zero position.
Figure 6.3: Incremental encoder disk track patterns
35
Figure 14 illustrates two separate tracks for the A and B channels, but a more common configuration uses a single track with the A and B sensors offset a 1/4 cycle on the track to yield the same signal pattern. A single-track code disk is simpler and cheaper to manufacture. The quadrature signals A and B can be decoded to yield the direction of rotation as shown in Figure 6. Decoding transitions of A and B by using sequential logic circuits in different ways can provide three different resolutions of the output pulses: 1X, 2X, 4X. 1X resolution only provides a single pulse for each cycle in one of the signals A or B, 4X resolution provides a pulse at every edge transition in the two signals A and B providing four times the 1X resolution. The direction of rotation (clockwise or counter-clockwise) is determined by the level of one signal during an edge transition of the second signal. For example, in the 1X mode, A= with B =1 implies a clockwise pulse, and B= with A=1 implies a counter-clockwise pulse. If we only had a single output channel A or B, it would be impossible to determine the direction of rotation. Furthermore, shaft jitter around an edge transition in the single signal would result in erroneous pulses.
Figure 6.4: Quadrature direction sensing and resolution enhancement. (CW=clockwise, CCW=counter-clockwise)
36
Chapter 7 Theory of Maintenance Total Productive Maintenance (TPM) It can be considered as the medical science of machines. Total Productive Maintenance (TPM) is a maintenance program which involves a newly defined concept for maintaining plants and equipment. The goal of the TPM program is to markedly increase production while, at the same time, increasing employee morale and job satisfaction. TPM brings maintenance into focus as a necessary and vitally important part of the business. It is no longer regarded as a non-profit activity. Down time for maintenance is scheduled as a part of the manufacturing day and, in some cases, as an integral part of the manufacturing process. The goal is to hold emergency and unscheduled maintenance to a minimum.
Why TPM? TPM was introduced to achieve the following objectives. The important ones are listed below:
Avoid wastage in a quickly changing economic environment.
Producing goods without reducing product quality.
Reduce cost.
Produce a low batch quantity at the earliest possible time.
Goods send to the customers must be non-defective.
Similarities and differences between TQM and TPM: The TPM program closely resembles the popular Total Quality Management (TQM) program. Many of the tools such as employee empowerment, benchmarking, documentation, etc. used in TQM are used to implement and optimize TPM. Following are the similarities between the two:
Total commitment to the program by upper level management is required in both programmers.
Employees must be empowered to initiate corrective action, and
A long range outlook must be accepted as TPM may take a year or more to implement and is an on-going process. Changes in employee mind-set toward their job responsibilities must take place as well. 37
The differences between TQM and TPM is summarized below:
Category TQM TPM Object Quality (Output and effects) Equipment (Input and cause)
Mains of attaining goal systematize the management. It is software oriented Employees participation and it is hardware oriented Target Quality for PPME limitation of losses and wastes.
Types of maintenance: 1. Breakdown maintenance: It means that people waits until equipment fails and repair it. Such a thing could be used when the equipment failure does not significantly affect the operation or production or generate any significant loss other than repair cost. 2. Preventive maintenance (1951): It is a daily maintenance (cleaning, inspection, oiling and re-tightening), design to retain the healthy condition of equipment and prevent failure through the prevention of deterioration, periodic inspection or equipment condition diagnosis, to measure deterioration. It is further divided into periodic maintenance and predictive maintenance. Just like human life is extended by preventive medicine, the equipment service life can be prolonged by doing preventive maintenance. a.
Periodic maintenance (Time based maintenance - TBM):
Time based maintenance consists of periodically inspecting, servicing and cleaning equipment and replacing parts to prevent sudden failure and process problems. b. Predictive maintenance: This is a method in which the service life of important part is predicted based on inspection or diagnosis, in order to use the parts to the limit of their service life. Compared to periodic maintenance, predictive maintenance is condition based maintenance. It manages trend values, by measuring and analyzing data about deterioration and employs a surveillance system, designed to monitor conditions through an on-line system.
38
Figure 7.1: PM sheet of Makino machine
39
3. Corrective maintenance (1957): It improves equipment and its components so that preventive maintenance can be carried out reliably. Equipment with design weakness must be redesigned to improve reliability or improving maintainability 4. Maintenance prevention (1960): It indicates the design of a new equipment. Weakness of current machines are sufficiently studied (on site information leading to failure prevention, easier maintenance and prevents of defects, safety and ease of manufacturing) and are incorporated before commissioning a new equipment.
TPM - History: TPM is an innovative Japanese concept. The srcin of TPM can be traced back to 1951 when preventive maintenance was introduced in Japan. However the concept of preventive maintenance was taken from USA. Nippondenso was the first company to introduce plant wide preventive maintenance in 1960. Preventive maintenance is the concept wherein, operators produced goods using machines and the maintenance group was dedicated with work of maintaining those machines, however with the automation of Nippondenso, maintenance became a problem as more maintenance personnel were required. So the management decided that the routine maintenance of equipment would be carried out by the operators. (This is Autonomous maintenance, one of the features of TPM). Maintenance group took up only essential maintenance works. Thus Nippondenso which already followed preventive maintenance also added Autonomous maintenance done by production operators. The maintenance crew went in the equipment modification for improving reliability. The modifications were made or incorporated in new equipment. This lead to maintenance prevention. Thus preventive maintenance along with Maintenance prevention and Maintainability Improvement gave birth to Productive maintenance. The aim of productive maintenance was to maximize plant and equipment
effectiveness to achieve optimum life cycle cost of production equipment. By then Nippon Denso had made quality circles, involving the employee’s participation. Thus all employees took part in implementing Productive maintenance. Based on these developments Nippondenso was awarded the distinguished plant prize for developing and implementing TPM, by the Japanese Institute of Plant Engineers (JIPE). Thus Nippondenso of the Toyota group became the first company to obtain the TPM certification.
TPM Targets: I.
Obtain Minimum 80% OPE.
40
II.
Obtain Minimum 90% OEE (Overall Equipment Effectiveness)
III.
Run the machines even during lunch. (Lunch is for operators and not for machines!)
IV.
Operate in a manner, so that there are no customer complaints.
V. VI. VII.
VIII.
Reduce the manufacturing cost by 30%. Achieve 100% success in delivering the goods as required by the customer. Maintain an accident free environment. Increase the suggestions by 3 times. Develop Multi-skilled and flexible workers.
Motives of TPM •
Adoption of life cycle approach for improving the overall performance of production equipment.
•
Improving productivity by highly motivated workers which is achieved by job enlargement.
•
The use of voluntary small group activities for identifying the cause of failure, possible plant and equipment modifications.
Uniqueness of TPM •
The major difference between TPM and other concepts is that the operators are also made to involve in the maintenance process. The concept of "I (Production operators) Operate, You
(Maintenance department) fix" is not followed. TPM Objectives Achieve Zero Defects, Zero Breakdown and Zero accidents in all functional areas of the organization. •
Involve people in all levels of organization.
•
Form different teams to reduce defects and Self Maintenance.
Direct benefits of TPM •
Increase productivity and OPE (Overall Plant Efficiency) by 1.5 or 2 times.
•
Rectify customer complaints.
•
Reduce the manufacturing cost by 30%.
•
Satisfy the customer’s needs by 100 % (Delivering the right quantity at the right time, in the required quality).
•
•
Reduce accidents. Follow pollution control measures.
Indirect benefits of TPM •
Higher confidence level among the employees.
•
Keep the work place clean, neat and attractive.
•
Favorable change in the attitude of the operators. 41
•
Achieve goals by working as team.
•
Horizontal deployment of a new concept in all areas of the organization.
•
Share knowledge and experience.
•
The workers get a feeling of owning the machine.
OEE (Overall Equipment Efficiency) OEE can be defined by the equation given below: OEE = A x PE x Q Where, A - Availability of the machine. Availability is proportion of time machine is actually available out of time it should be available. A = (MTBF - MTTR) / MTBF. MTBF - Mean Time between Failures = (Total Running Time) / Number of Failures. MTTR - Mean Time to Repair. PE - Performance Efficiency. It is given by RE X SE. Rate efficiency (RE): Actual average cycle time is slower than design cycle time because of jams, etc. Output is reduced because of jams Speed efficiency (SE): Actual cycle time is slower than design cycle time machine output is reduced because it is running at reduced speed. Q - Refers to quality rate. Which is percentage of good parts out of total produced sometimes called "yield".
Steps in introduction of TPM in an organization: A. Step - PREPARATORY STAGE 1. Announcement by Management to all about TPM introduction in the organization:
Proper understanding, commitment and active involvement of the top management in needed for this step. Senior management should have awareness programmes, after which announcement is made to all. Publish it in the house magazine and put it in the notice board. Send a letter to all concerned individuals if required.
42
2. Initial education and propaganda for TPM:
Training is to be done based on the need. Some need intensive training and some just an awareness. Take people who matters to places where TPM already successfully implemented. 3. Setting up TPM and departmental committees:
TPM includes improvement, autonomous maintenance, quality maintenance etc., as part of it. When committees are set up it should take care of all those needs. 4. Establishing the TPM working system and target:
Now each area is benchmarked and fix up a target for achievement. 5. A master plan for institutionalizing:
Next step is implementation leading to institutionalizing wherein TPM becomes an organizational culture. Achieving PM award is the proof of reaching a satisfactory level. B. STEP - INTRODUCTION STAGE
This is a ceremony and we should invite all. Suppliers as they should know that we want quality supply from them. Related companies and affiliated companies who can be our customers, sisters concerns etc. Some may learn from us and some can help us and customers will get the communication from us that we care for quality output. C. STAGE - IMPLEMENTATION
In this stage eight activities are carried which are called eight pillars in the development of TPM activity. Of these four activities are for establishing the system for production efficiency, one for initial control system of new products and equipment, one for improving the efficiency of administration and are for control of safety, sanitation as working environment. D. STAGE - INSTITUTIONALISING STAGE
By all their activities one would has reached maturity stage. Now is the time for applying for PM award. Also think of challenging level to which you can take this movement. Organization Structure for TPM Implementation:
43
Chapter 8 Pillars of TPM 1. PILLAR - 5S: TPM starts with 5S. Problems cannot be clearly seen when the work place is unorganized. Cleaning and organizing the workplace helps the team to uncover problems. Making problems visible is the first step of improvement. Japanese Term
English Translation Equivalent 'S' term
Seiri
Organisation Sort
Seiton Seiso
Tidiness Systematise Cleaning Sweep
Seiketsu
Standardisation Standardise
Shitsuke
Discipline Self – Discipline
SEIRI - Sort out:
This means sorting and organizing the items as critical, important, frequently used items, useless, or items that are not need as of now. Unwanted items can be salvaged. Critical items should be kept for use nearby and items that are not be used in near future, should be stored in some place. For this step, the worth of the item should be decided based on utility and not cost. As a result of this step, the search time is reduced. Priority Frequency of Use How to use Low Less than once per year, Once per year
44
Store together but offline High Once Per Day Locate at the workplace.
Figure 8.1: Figure showing five-s
SEITON - Organise:
The concept here is that "Each items has a place, and only one place". The items should be placed back after usage at the same place. To identify items easily, name plates and coloured tags has to be used. Vertical racks can be used for this purpose, and heavy items occupy the bottom position in the racks. SEISO - Shine the workplace:
This involves cleaning the work place free of burrs, grease, oil, waste, scrap etc. No loosely hanging wires or oil leakage from machines. SEIKETSU - Standardization:
Employees has to discuss together and decide on standards for keeping the work place / Machines / pathways neat and clean. This standards are implemented for whole organization and are tested / inspected randomly. SHITSUKE - Self-discipline:
45
Considering 5S as a way of life and bring about self-discipline among the employees of the organization. This includes wearing badges, following work procedures, punctuality, dedication to the organization etc.
2. PILLAR - JISHU HOZEN (Autonomous maintenance): This pillar is geared towards developing operators to be able to take care of small maintenance tasks, thus freeing up the skilled maintenance people to spend time on more value added activity and technical repairs. The operators are responsible for upkeep of their equipment to prevent it from deteriorating policy:
Uninterrupted operation of equipment.
Flexible operators to operate and maintain other equipment.
Eliminating the defects at source through active employee participation.
Stepwise implementation of JH activities.
JISHU HOZEN Targets:
Prevent the occurrence of 1A / 1B because of JH.
Reduce oil consumption by 50%
Reduce process time by 50%
Increase use of JH by 50%
Steps in JISHU HOZEN:
Preparation of employees.
Initial clean-up of machines.
Take counter measures
Fix tentative JH standards
General inspection
Autonomous inspection
Standardization and
Autonomous management.
Each of the above mentioned steps is discussed in detail below.
Train the Employees:
Educate the employees about TPM, Its advantages, JH advantages and Steps in JH. Educate the employees about abnormalities in equipment.
Initial clean-up of machines:
46
Supervisor and technician should discuss and set a date for implementing step1. Arrange all items needed for cleaning. On the arranged date, employees should clean the equipment completely with the help of maintenance department. Dust, stains, oils and grease has to be removed. Following are the things that has to be taken care while cleaning. They are Oil leakage, loose wires, unfastened nits and bolts and worn out parts. After clean up problems are categorized and suitably tagged. White tags is place where problems can be solved by operators. Pink tag is placed where the aid of maintenance department is needed. Contents of tag is transferred to a register. Make note of area which were inaccessible. Finally close the open parts of the machine and run the machine.
Counter Measures :
Inaccessible regions had to be reached easily. E.g. If there are many screw to open a fly wheel door, hinge door can be used. Instead of opening a door for inspecting the machine, acrylic sheets can be used. To prevent work out of machine parts necessary action must be taken. Machine parts should be modified to prevent accumulation of dirt and dust.
Tentative Standard :
JH schedule has to be made and followed strictly. Schedule should be made regarding cleaning, inspection and lubrication and it also should include details like when, what and how.
General Inspection :
The employees are trained in disciplines like Pneumatics, electrical, hydraulics, lubricant and coolant, drives, bolts, nuts and Safety. This is necessary to improve the technical skills of employees and to use inspection manuals correctly. After acquiring this new knowledge the employees should share this with others. By acquiring this new technical knowledge, the operators are now well aware of machine parts.
Autonomous Inspection :
New methods of cleaning and lubricating are used. Each employee prepares his own autonomous chart / schedule in consultation with supervisor. Parts which have never given any problem or part which don't need any inspection are removed from list permanently based on experience. Including good quality machine parts. This avoid defects due to poor JH. Inspection that is made in preventive maintenance is included in JH. The frequency of clean-up and inspection is reduced based on experience.
Standardization:
Up to the previous stem only the machinery / equipment was the concentration. However in this step the surroundings of machinery are organized. Necessary items should be organized, such that there is no searching and searching time is reduced. Work environment is modified such that there is no 47
difficulty in getting any item. Everybody should follow the work instructions strictly. Necessary spares for equipment is planned and procured.
Autonomous Management:
OEE and OPE and other TPM targets must be achieved by continuous improve through Kaizen. PDCA (Plan, Do, Check and Act) cycle must be implemented for Kaizen.
3. PILLAR - KAIZEN: "Kai" means change, and "Zen" means good (for the better). Basically kaizen is for small improvements, but carried out on a continual basis and involve all people in the organization. Kaizen is opposite to big spectacular innovations. Kaizen requires no or little investment. The principle behind is that "a very large number of small improvements are more effective in an organizational environment than a few improvements of large value. This pillar is aimed at reducing losses in the workplace that affect our efficiencies. By using a detailed and thorough procedure we eliminate losses in a systematic method using various Kaizen tools. These activities are not limited to production areas and can be implemented in administrative areas as well. Kaizen Policy:
Practice concepts of zero losses in every sphere of activity. Relentless pursuit to achieve cost reduction targets in all resources. Relentless pursuit to improve over all plant equipment effectiveness. Extensive use of PM analysis as a tool for eliminating losses. Focus of easy handling of operators. Kaizen Target:
Achieve and sustain zero loses with respect to minor stops, measurement and adjustments, defects and unavoidable downtimes. It also aims to achieve 30% manufacturing cost reduction. Tools used in Kaizen:
PM analysis
Why - Why analysis
Summary of losses
Kaizen register Kaizen summary sheet.
The objective of TPM is maximization of equipment effectiveness. TPM aims at maximization of machine utilization and not merely machine availability maximization. As one of the pillars of TPM activities, Kaizen pursues efficient equipment, operator and material and energy utilization that is extremes of productivity and aims at achieving substantial effects. Kaizen activities try to thoroughly eliminate 16 major losses. 48
16 Major losses in an organisation:
Loss
Category
Failure losses - Breakdown loss
Setup / adjustment losses
Cutting blade loss
Startup loss
Minor stoppage / idling loss.
Speed loss - operating at low speeds.
Defect / rework loss
Scheduled downtime loss
Losses that impede equipment efficiency Management loss
Operating motion loss
Line organization loss
Logistic loss
Measurement and adjustment loss
Loses that impede human work efficiency Energy loss
Die, jig and tool breakage loss
Yield loss.
Loses that impede effective use of production resources Classification of losses:
Aspect
Sporadic Loss
Chronic Loss
Causation Causes for this failure can be easily traced. Cause-effect relationship is simple to trace.
This loss cannot be easily identified and solved. Even if various counter measures are applied
Remedy Easy to establish a remedial measure
This type of losses are caused because of hidden defects in machine, equipment and methods.
Impact / Loss A single loss can be costly A single cause is rare - a combination of causes trends to be a rule
Frequency of occurrence:
The frequency of occurrence is low and occasional. The frequency of loss is more. Corrective action usually the line personnel in the production can attend to this problem. Specialists in process engineering, quality assurance and maintenance people are required.
49
4. PILLAR - PLANNED MAINTENANCE: It is aimed to have trouble free machines and equipment producing defect free products for total customer satisfaction. This breaks maintenance down into 4 "families" or groups which was defined earlier.
Preventive Maintenance
Breakdown Maintenance
Corrective Maintenance
Maintenance Prevention
With Planned Maintenance we evolve our efforts from a reactive to a proactive method and use trained maintenance staff to help train the operators to better maintain their equipment. Policy:
Achieve and sustain availability of machines.
Optimum maintenance cost.
Reduces spares inventory.
Improve reliability and maintainability of machines.
Target:
Zero equipment failure and break down.
Improve reliability and maintainability by 50 %
Reduce maintenance cost by 20 %
Ensure availability of spares all the time.
Six steps in planned maintenance:
Equipment evaluation and recoding present status.
Restore deterioration and improve weakness.
Building up information management system.
Prepare time based information system, select equipment, parts and members and map out plan.
Prepare predictive maintenance system by introducing equipment diagnostic techniques and
Evaluation of planned maintenance.
5. PILLAR - QUALITY MAINTENANCE: It is aimed towards customer delight through highest quality through defect free manufacturing. Focus is on eliminating non-conformances in a systematic manner, much like Focused Improvement. We gain understanding of what parts of the equipment affect product quality and begin to eliminate current quality concerns, then move to potential quality concerns. Transition is from reactive to proactive (Quality Control to Quality Assurance). 50
QM activities is to set equipment conditions that preclude quality defects, based on the basic concept of maintaining perfect equipment to maintain perfect quality of products. The condition are checked and measure in time series to very that measure values are within standard values to prevent defects. The transition of measured values is watched to predict possibilities of defects occurring and to take counter measures beforehand. Policy:
Defect free conditions and control of equipment.
QM activities to support quality assurance.
Focus of prevention of defects at source
Focus on poka-yoke. ( fool proof system )
In-line detection and segregation of defects.
Effective implementation of operator quality assurance.
Target:
Achieve and sustain customer complaints at zero
Reduce in-process defects by 50 %
Reduce cost of quality by 50 %.
Data requirements:
Quality defects are classified as customer end defects and in house defects. For customer-end data, we have to get data on:
Customer end line rejection
Field complaints.
In-house, data include data related to products and data related to process
Data related to product:
Product wise defects
Severity of the defect and its contribution - major/minor
Location of the defect with reference to the layout
Magnitude and frequency of its occurrence at each stage of measurement
Occurrence trend in beginning and the end of each production/process/changes. (Like pattern change, ladle/furnace lining etc.)
Occurrence trend with respect to restoration of breakdown/modifications/periodical replacement of quality components.
Data related to processes:
The operating condition for individual sub-process related to men, method, material and 51
machine.
The standard settings/conditions of the sub-process
The actual record of the settings/conditions during the defect occurrence.
6. PILLAR - TRAINING: It is aimed to have multi-skilled revitalized employees whose morale is high and who has eager to come to work and perform all required functions effectively and independently. Education is given to operators to upgrade their skill. It is not sufficient know only "Know-How" by they should also learn "Know-why". By experience they gain, "Know-How" to overcome a problem what to be done. This they do without knowing the root cause of the problem and why they are doing so. Hence it become necessary to train them on knowing "Know-why". The employees should be trained to achieve the four phases of skill. The goal is to create a factory full of experts. The different phase of skills are: 1. Phase: Do not know. 2. Phase: Know the theory but cannot do. 3. Phase: Can do but cannot teach 4. Phase: Can do and also teach. Policy:
Focus on improvement of knowledge, skills and techniques.
Creating a training environment for self-learning based on felt needs.
Training curriculum / tools /assessment etc. conductive to employee revitalization
Training to remove employee fatigue and make work enjoyable.
Target:
Achieve and sustain downtime due to want men at zero on critical machines.
Achieve and sustain zero losses due to lack of knowledge / skills / techniques
Aim for 100 % participation in suggestion scheme.
Steps in Educating and training activities:
Setting policies and priorities and checking present status of education and training.
Establish of training system for operation and maintenance skill up gradation.
Training the employees for upgrading the operation and maintenance skills.
Preparation of training calendar.
Kick-off of the system for training.
Evaluation of activities and study of future approach.
7. PILLAR - OFFICE TPM:
52
Office TPM should be started after activating four other pillars of TPM (JH, KK, QM, and PM). Office TPM must be followed to improve productivity, efficiency in the administrative functions and identify and eliminate losses. This includes analysing processes and procedures towards increased office automation. Office TPM addresses twelve major losses. They are:
Processing loss (Cost loss including in areas such as procurement, accounts, marketing, sales leading to high inventories)
Communication loss
idle loss
Set-up loss
Accuracy loss
Office equipment breakdown Communication channel breakdown, telephone and fax lines Time spent on retrieval of information on availability of correct on line stock status Customer complaints due to logistics Expenses on emergency dispatches/purchases
How to start office TPM?
A senior person from one of the support functions e.g. Head of Finance, MIS, Purchase etc. should be heading the sub-committee. Members representing all support functions and people from Production & Quality should be included in subcommittee. TPM co-ordinate plans and guides the subcommittee. Providing awareness about office TPM to all support departments. Helping them to identify P, Q, C, D, S, and M in each function in relation to plant performance. Identify the scope for improvement in each function. Collect relevant data. Help them to solve problems in their circles. Make up an activity board where progress is monitored on both sides - results and actions along with Kaizens. Fan out to cover all employees and circles in all functions. Kobetsu Kaizen topics for Office TPM:
Inventory reduction
Lead time reduction of critical processes
Motion & space losses
Retrieval time reduction.
Equalizing the work load
Improving the office efficiency by eliminating the time loss on retrieval of information, by achieving or breakdown of office equipment like telephone and fax lines.
Office TPM and its Benefits:
Involvement of all people in support functions for focusing on better plant performance
Better utilized work area
Reduce repetitive work 53
Reduced inventory levels in all parts of the supply chain
Reduced administrative costs
educed inventory carrying cost
Reduction in number of files
Reduction of overhead costs (to include cost of non-production/non capital equipment)
Productivity of people in support functions
Reduction in breakdown of office equipment
Reduction of customer complaints due to logistics
Reduction in expenses due to emergency dispatches/purchases
Reduced manpower
Clean and pleasant work environment.
P Q C D S M in Office TPM:
P - Production output lost due to want of material, Manpower productivity, Production output lost due to want of tools.
Q - Mistakes in preparation of cheques, bills, invoices, payroll, Customer returns/warranty attributable to BOPs, Rejection/rework in BOP's/job work, Office area rework.
C - Buying cost/unit produced, Cost of logistics - inbound/outbound, Cost of carrying inventory, Cost of communication, Demurrage costs.
D - Logistics losses (Delay in loading/unloading)
Delay in delivery due to any of the support functions
Delay in payments to suppliers
Delay in information
Safety in material handling/stores/logistics, Safety of soft and hard data.
M - Number of kaizens in office areas.
How office TPM supports plant TPM:
Office TPM supports the plant, initially in doing Jishu Hozen of the machines (after getting training of Jishu Hozen), as in Jishu Hozen at the Initial stages machines are more and manpower is less, so the help of commercial departments can be taken, for this Office TPM can eliminate the lodes on line for no material and logistics. Extension of office TPM to suppliers and distributors:
This is essential, but only after we have done as much as possible internally. With suppliers it will lead to on-time delivery, improved 'in-coming' quality and cost reduction. With distributors it will lead to accurate demand generation, improved secondary distribution and reduction in damages during storage and handling. In any case we will have to teach them based on our experience and
54
practice and highlight gaps in the system which affect both sides. In case of some of the larger companies, they have started to support clusters of suppliers.
8. PILLAR - SAFETY, HEALTH AND ENVIRONMENT: Target:
Zero accident
Zero health damage
Zero fires In this area focus is on to create a safe workplace and a surrounding area that is not damaged by our
process or procedures. This pillar will play an active role in each of the other pillars on a regular basis. A committee is constituted for this pillar which comprises representative of officers as well as workers. The committee is headed by senior vice President (Technical). Utmost importance to Safety is given in the plant. Manager (Safety) is looking after functions related to safety. To create awareness among employees various competitions like safety slogans, Quiz, Drama, Posters, etc. related to safety can be organized at regular intervals.
Kaizen Kaizen (改善), Japanese for "improvement" or "change for the best", refers to philosophy or practices that focus upon continuous improvement of processes in manufacturing, engineering, business management or any process. It has been applied in healthcare, psychotherapy, life-coaching, government, banking, and other industries. When used in the business sense and applied to the workplace, kaizen refers to activities that continually improve all functions, and involves all employees from the CEO to the assembly line workers. It also applies to processes, such as purchasing and logistics that cross organizational boundaries into the supply chain. By improving standardized activities and processes, kaizen aims to eliminate waste (see lean manufacturing). Kaizen was first implemented in several Japanese businesses after the Second World War, influenced in part by American business and quality management teachers who visited the country. It has since spread throughout the world and is now being implemented in environments outside of business and productivity.
55
The Toyota Production System is known for kaizen, where all line personnel are expected to stop their moving production line in case of any abnormality and, along with their supervisor, suggest an improvement to resolve the abnormality which may initiate a kaizen. The cycle of kaizen activity can be defined as: •
Standardize an operation and activities,
•
Measure the operation (find cycle time and amount of in-process inventory).
•
Gauge measurements against requirements.
•
Innovate to meet requirements and increase productivity.
•
Standardize the new, improved operations.
•
Continue cycle ad infinitum.
This is also known as the Shewhart cycle, Deming cycle, or PDCA. Other techniques used in conjunction with PDCA include 5 Whys, which is a form of root cause analysis in which the user
Figure 8.2: The PCDA cycle
asks "why" a failure occurred five successive times, basing each subsequent question on the answer to the previous. There are normally a series of root causes stemming from one problem, and they can be visualized using fishbone diagrams or tables. Masaaki Imai made the term famous in his book Kaizen: The Key to Japan's Competitive Success. Apart from business applications of the method, both Anthony Robbins and Robert Maurer have popularized the kaizen principles into personal development principles. In the book One Small Step Can Change Your life: The Kaizen Way, and CD set The Kaizen Way to Success, Maurer looks at how individuals can take a kaizen approach in both their personal and professional lives. In the Toyota Way Fieldbook, Liker and Meier discuss the kaizen blitz and kaizen burst (or kaizen event) approaches to continuous improvement. A kaizen blitz, or rapid improvement, is a focused activity on a particular process or activity. The basic concept is to identify and quickly remove waste.
56
Another approach is that of the kaizen burst, a specific kaizen activity on a particular process in the value stream.
57
Conclusion Today, with competition in industry at an all-time high, TPM may be the only thing that stands between success and total failure for some companies. It has been proven to be a program that works. It can be adapted to work not only in industrial plants, but in construction, building maintenance, transportation, and in a variety of other situations. Employees must be educated and convinced that TPM is not just another "program of the month" and that management is totally committed to the program and the extended time frame necessary for full implementation. If everyone involved in a TPM program does his or her part, an unusually high rate of return compared to resources invested may be expected.
58
REFERENCES
Introduction to Mechatronics and Measurement Systems, Histand & Alciatore, 1999 McGraw Hill.
http://nptel.ac.in/
http://www.jcb.com/
http://www.jcbindia.com/
http://www.makino.com/horizontal-machining-4-axis/a81/ http://www.makino.com/engineering-services-automation/
http://www.makino.com/engineering-services/machining-application-services/
http://www.makino.com/engineering-services/machine-tool-automation/
http://www.makino.com/customer-support/training/online-training/
http://www.automation.siemens.com/mcms/mc-systems/en/automation-systems/cncsinumerik/sinumerik-controls/sinumerik-840/sinumerik-840d/pages/sinumerik-840d.aspx
http://www.automation.siemens.com/mcms/mc-systems/en/automation-systems/cncsinumerik/sinumerik-controls/sinumerik-840/sinumerik-840d-sl/pages/sinumerik-840dsl.aspx
http://www.industry.usa.siemens.com/drives/us/en/cnc-for-machine-tool-solutions/cnccontrollers/sinumerik-840d/pages/sinumerik-840d.aspx
59
