MAULANA AZAD NATIONAL INSTITUTE OF TECHNOLOGY BHOPAL (M.P.)
DEPARTMENT OF MECHANICAL ENGINEERING MANIT, BHOPAL [M.P.] 2011-2012 A Major Project report on
“Design and Fabrication of DIE for compaction of Metal Powder in Powder Metallurgy” Metallurgy ” for the degree of
BACHELOR OF TECHNOLOGY IN MECHANICAL ENGINEERING
Submitted By: Mohit Assudani Assudani
Under the Guidance of: (081116052)
Asst. Professor Dr. Rajesh Purohit
Mirza Amir Ahmed Beg (081116058)
Asst. Professor R.S. Rana
Pranay Vyas
(081116081)
Aditya Pagare
(081116086)
ACKNOWLEDGEMENT
Words shall never be able to pierce through the gamut of emotions that are suddenly exposed during the routine of our life. They shall never be able neither to describe the spirit with which we worked together nor shall they ever be able to express the feeling we felt towards our guides.
This project was a struggle that was made much more difficult due to several reasons. Sometimes we were like rudderless boat without knowing what to do next. It was then the timely guidance of them that has seen us through all these odds. We would be very grateful to them for their inspiration, encouragement and guidance in all phases of the discretion. Sarvaiya, HOD of Mechanical Engineering for his It is our pleasure that Dr. R.M. Sarvaiya, constant encouragement and valuable advice during the course of our project. We would also thank Associate Professor Dr. Rajesh Purohit & Asst. Professor R.S. Rana who has tremendously contributed to this project directly or indirectly, gratitude from the depths of our heart is due for them.
Mohit Assudani Mirza Amir Ahmed Beg Pranay Vyas Aditya Pagare
MAULANA AZAD NATIONAL INSTITUTE OF TECHNOLOGY BHOPAL (M.P.)
CERTIFICATE This is to certify that Mr. Mohit Assudani, Mr. Mirza Amir Ahmed Beg, Mr. Pranay Vyas and Mr. Aditya Pagare students of final year B.Tech Mechanical Engineering in the academic year 2011-12 of this institute have completed major project work entitled “Design and Fabrication of DIE for compaction of Metal Powder in Powder Metallurgy” based on the syllabus and have submitted a satisfactory report on it as a partial fulfillment for the degree of Bachelor of Technology in Mechanical Engineering.
Project Guide
Head of theDepartment theDepartment
Associate Professor Dr. Rajesh Purohit
Dr. R.M. Sarvaiya
& Asst. Professor R.S. Rana
Department of Mechanical
Department of Mechanical
Engineering, MANIT Bhopal.
Engineering, MANIT Bhopal.
CONTENTS S. No.
Topic
1.
Introduction
Page No.
1
1.1 What are we aiming to do!
2.
Die
3
2.1 Introduction 2.2 Die Forming 2.3 Components for Die Toolsets 2.4 Die Operation & Types
3.
Die Material (High Carbon High Chromium Steel)
7
3.1 Available Options for Die Material 3.2 Properties and Technical Data for High Carbon High Chromium Steel 3.3 Applications
4.
Design of Die 4.1 Introduction 4.2 Calculations 4.3 Die Design in PRO E
13
5.
Die Fabrication
20
5.1 Turning 5.2 Drilling 5.3 Boring 5.4 Internal Grinding 5.5 Oil Quenching
6.
Aluminum (Metal Powder)
26
6.1 Introduction 6.2 Properties of Aluminum 6.3 Why Aluminum? 6.4 Aluminum - Product Applications 6.5 Aluminum Alloys - Heat Treatment & Welding 6.6 Aluminum Supply
7.
Specimen Manufacturing (Powder Metallurgy) 7.1 Introduction 7.2 History 7.3 Powder Manufacturing or Atomization 7.4 Zinc Stearate as Lubricant 7.5 Powder Blending 7.6 Powder Compaction 7.7 Sintering 7.8 Powder Metallurgy using Aluminum
30
7.9 Aluminum comparison to other P/M materials
8.
Testing of Specimens
44
8.1 Introduction to Universal Testing Machine 8.2 Indirect Tensile Test 8.3 Compression Test 8.4 Density Comparisons 8.5 Hardness Test
9.
Scope of Improvement
58
10.
Final Conclusions
60
11.
References
61
1.Introduction The word "die" is a very general one and it may be well to define its meaning as it will be employed in our work. It is used in two distinct ways. When employed in a general sense, it means an entire press tool with all components taken together. When used in a more limited manner, it refers to that component which is machined to receive the blank, as differentiated from the component called the punch which is its opposite member. The initial data needed to design metal powder compaction die are: compact shape and density, powder mix composition, compaction and radial pressure, part number and tool materials. The design targets are: diameters of insert and ring, sometimes number of rings and interference or interferences. The constraints include: no tensile stresses on the insert, no risk of relative motion at part ejection, no unwanted alteration of material microstructures and maximum stresses always below the allowable limits. Usually the design is based on engineering experience, company knowhow, and approximated the analytical calculations and cost considerations. This study is focused on the use of numerical methods to determine the design parameters of dies for powder compaction. Both room temperature and warm compaction have been investigated. Numerical algorithms, implemented into FEM calculation codes, enable one to optimize the common diameter of insert and ring, corresponding to the lowest stresses on both items, or to find the minimum value of the outer diameter. A wide range of compaction pressures, die materials and geometries, interferences and allowable stresses have been explored. To compare the results, based either on analytical or numerical methods, circular dies have been investigated. The differences among the results depend on the consideration of the actual stressed length, or compact height, and total die length. The calculations by analytical methods overestimate the stresses. The report presents some suitable nomograms for the comparison of results of calculations performed either by Lame’s Formula or by sophisticated numerical methods.
Two-piece designs were considered in order to make the dies easier to assemble than the five-piece dies that were previously used. The two areas of concern were the stresses at the interior corner of the die cavity and the distortion of the cavity wall due to the interference fit between the two pieces and the pressure exerted on the die during the compaction process. A successful die design would have stresses less than the yield stress of the material. Design factors that were investigated include the compaction force, the size of the cavity, and the outer radius. Adding a FACTOR OF SAFETY of 3 to the compaction force tends to lead to conservative estimates of the stresses but not for the wall distortion. However, when the FACTOR OF SAFETY of is removed, the wall distortion is not affected enough to discard the design.
1.1
What Are We Aiming To Do !
Learn about the working of dies.
Selection of a material for die manufacturing based on working conditions & the type of product to be created using this die.
Calculations for design of die i.e. calculating thickness of the shell to bear the load to be applied on die in the process.
Fabrication of die by using different processes i.e. turning, drilling, boring etc.
Preparing specimens using this die & testing them.
2.DIE 2.1 Introduction of Die A die is a specialized tool used in manufacturing industries to cut or shape material using a press. Like molds, dies are generally customized to the item they are used to create. Products made with dies range from simple paper clips to complex pieces used in advanced technology.
2.2 Die forming Forming dies are typically made by tool and die makers and put into production after mounting into a press. The die is a metal block that is used for forming materials like sheet metal and plastic. For the vacuum forming of plastic sheet only a single form is used, typically to form transparent plastic containers (called blister packs) for merchandise. Vacuum forming is considered a simple molding thermoforming process but uses the same principles as die forming. For the forming of sheet metal, such as automobile body parts, two parts may be used, one, called the punch, performs the stretching, bending, and/or blanking operation, while another part, called the die block , securely clamps the work piece and provides similar, stretching, bending, and/or blanking operation. The work piece may pass through several stages using different tools or operations to obtain the final form. In the case of an automotive component there will usually be a shearing operation after the main forming is done and then additional crimping or rolling operations to ensure that all sharp edges are hidden and to add rigidity to the panel.
Components for Die Toolsets The main components for Die Toolsets are:
Die block - This is the main part that all the other parts are attached to. Punch plate - This part holds and supports the different punches in place. Blank punch - This part along with the Blank Die produces the blanked part. Pierce punch - This part along with the Pierce Die removes parts from the blanked finished part. Stripper plate - This is used to hold the material down on the Blank/ Pierce Die and strip the material off the punches. Pilot - This is used to keep the material being worked on in position. Guide / Back gage / Finger stop - These parts are all used to make sure that the material being worked on always goes in the same position, within the die, as the last one. Setting (Stop) Block - This part is used to control the depth that the punch goes into the die. Blanking Dies - See Blanking Punch
Pierce Die - See Pierce Punch. Shank-used to hold in the presses. it should be align and situated at the center of gravity of the plate.
2.3 Die operations and types Die operations are often named after the specific type of die that performs the operation. For example a bending operation is performed by a bending die. Operations are not limited to one specific die as some dies may incorporate multiple operation types:
Bending: The bending operation is the act of bending blanks at a predetermined angle. An example would be an "L" bracket which is a straight piece of metal bent at a 90° angle. The main difference between a forming operation and a bending operation is the bending operation creates a straight line bend (such as a corner in a box) as where a form operation may create a curved bend (such as the bottom of a drink can).
Blanking: A blanking die produces a flat piece of material by cutting the desired shape in one operation. The finish part is referred to as a blank. Generally a blanking die may only cut the outside contour of a part, often used for parts with no internal features. Three benefits to die blanking are:
1. Accuracy. A properly sharpened die, with the correct amount of clearance between the punch and die, will produce a part that holds close dimensional tolerances in relationship to the parts edges. 2. Appearance. Since the part is blanked in one operation, the finished edges of the part produce a uniform appearance as opposed to varying degrees of burnishing from multiple operations. 3. Flatness. Due to the even compression of the blanking process, the end result is a flat part that may retain a specific level of flatness for additional manufacturing operations.
Broaching: The process of removing material through the use of multiple cutting teeth, with each tooth cutting behind the other. A broaching die is often used to remove material from parts that are too thick for shaving.
Bulging: A bulging die expands the closed end of tube through the use of two types of bulging dies. Similar to the way a chef‟s hat bulges out at the top from the cylindrical band around the chefs head.
1. Bulging fluid dies: Uses water or oil as a vehicle to expand the part. 2. Bulging rubber dies: Uses a rubber pad or block under pressure to move the wall of a work piece.
Coining: is similar to forming with the main difference being that a coining die may form completely different features on either face of the blank, these features being transferred from the face of the punch or die respectively. The coining die and punch flow the metal by squeezing the blank within a confined area, instead of bending the blank. For example: an Olympic medal that was formed from a coining die may have a flat surface on the back and a raised feature on the front. If the medal was formed (or embossed), the surface on the back would be the reverse image of the front.
Compound operations: Compound dies perform multiple operations on the part. The compound operation is the act of implementing more than one operation during the press cycle.
Compound die: A type of die that has the die block (matrix) mounted on a punch plate with perforators in the upper die with the inner punch mounted in the lower die set. An inverted type of blanking die that punches upwards, leaving the part sitting on the lower punch (after being shed from the upper matrix on the press return stroke) instead of blanking the part through. A compound die allows the cutting of internal and external part features on a single press stroke.
Curling: The curling operation is used to roll the material into a curved shape. A door hinge is an example of a part created by a curling die.
Cut off : Cut off dies are used to cut off excess material from a finished end of a part or to cut off a predetermined length of material strip for additional operations.
Drawing: The drawing operation is very similar to the forming operation except that the drawing operation undergoes severe plastic deformation and the material of the part extends around the sides. A metal cup with a detailed feature at the bottom is an example of the
difference between formed and drawn. The bottom of the cup was formed while the sides were drawn.
Extruding: Extruding is the act of severely deforming blanks of metal called slugs into finished parts such as an aluminum I-beam. Extrusion dies use extremely high pressure from the punch to squeeze the metal out into the desired form. The difference between cold forming and extrusion is extruded parts do not take shape of the punch.
Forming: Forming dies bend the blank along a curved surface. An example of a part that has been formed would be the positive end(+) of a AA battery.
Cold forming (cold heading): Cold forming is similar to extruding in that it squeezes the blank material but cold forming uses the punch and the die to create the desired form, extruding does not.
Roll forming: a continuous bending operation in which sheet or strip metal is gradually formed in tandem sets of rollers until the desired cross-sectional configuration is obtained. Roll forming is ideal for producing parts with long lengths or in large quantities.
Swaging: Swaging (necking) is the process of "necking down" a feature on a part. Swaging is the opposite of bulging as it reduces the size of the part. The end of a shell casing that captures the bullet is an example of swaging.
Trimming: Trimming dies cut away excess or unwanted irregular features from a part, they are usually the last operation performed.
3. Die Material (High Carbon High Chromium Steel) 2
Powders are usually compacted with pressures between approx. 300 and 650 N/mm .All dies of the compacting tool have to withstand these high loads not only once but several 100 000 to 1 000 000 times without breaking or getting plastically deformed. Neither may they under these loads expand elastically to such an extent that they jam in the punch. Even an ever so small amount of plastic deformation during one compacting cycle would, after a number of cycles, lead to a sizable shortening and thickening of the punch. It does not take much imagination to realize the consequences: As the punch gets shorter, the height of the compacts increases correspondingly, and as the punch gets thicker, it eventually jams in the die and breaks and possibly damages the entire tool. Thus, punches must possess high compressive yield strength, high toughness and high fatigue strength. In cases where punches form part of the side walls of the compacting tool, they must, in addition to the mentioned properties, have a sufficiently high surface hardness. Surface-hardening of punches, if necessary, has to be carried out with great care, in order to avoid embrittlement and surface cracking. Only the toughest types of tool steels are suitable for punches. Ideally, they should combine the following properties: • Good machinability when soft-annealed. • Highest possible toughness and fatigue strength after hardening.
• Highest possible dimensional stability and lowest possible susceptibility to cracking in the
hardening procedure. • Highest possible wear resistance.
3.1 Available Options for die material:
O1 tool steel
D2 tool steel
D3 tool steel
D6 tool steel
A2 tool steel
General purpose oil hardening tool steel which hardens at a relatively low temperature with minimum distortion.
High carbon high chromium tool steel giving a good hardness with added toughness. This steel can be vacuum hardened when minimum distortion is required.
Similar steel to D2 tool steel, this steel attains a slightly higher hardness and has good abrasion resistance.
Popular European high carbon high chromium tool steel, with high hardness achievability and good abrasion resistance, akin to D3 tool steel.
Air hardening tool steel which is easier to machine than D2 or D3 but offers high abrasion resistance with good toughness.
H13 tool steel
5% chromium hot work tool steel. This steel is air hardening with very little distortion. H13 tool steel can be vacuum hardened and may be water cooled in service.
S1 tool steel
Excellent tough and shock resisting tool steel, with good abrasion resistance. When hardened S1 has a good cutting ability with great toughness
P20 tool steel
Pre-hardened high tensile steel which is readily machinable. P20 can also give a higher hardness than its supply condition and can be nitrided.
1.2767 tool steel
4.25% nickel steel, which achieves a good through hardness. 1.2767 is capable of taking a good polish and is commonly used as a plastic mould steel.
M2 high speed steel 420 stainless steel
1.2842 tool steel
General purpose high speed steel. M2 which offer good wear resistance and superior toughness and machinability.
13% chromium stainless steel which will achieve a high hardness. 420 stainless steel gives a good polish and is resistant to attack from corrosive plastics. A cold work tool steel which has high dimensional stability when heat treated, with good resistance to cracking.
M42 high speed steel
A high quality cobalt molybdenum high speed steel, suitable core components that require high hardness and superior cutting performance.
3.2 Properties and Technical Data for High Carbon High Chromium Steel
Chemical Composition:
Typical Analysis
C.
Si.
Cr.
Mo.
V.
1.50%
0.30%
12.00%
0.80%
0.90%
Physical Properties:
Temperature: 20°C
200°C
400°C
Density (kg/dm³) Coefficient of thermal expansion (per °C from 0°C)
7.70 -
Thermal conductivity (cal/cm.s °C)
40.9 x 10-3
Specific heat (cal/g °C) Modulus of elasticity: Kp/mm² N/mm²
7.65 7.60 11.0 x 10- 10.8 x 106 6 50.4 x 10- 55.2 x 103 3
0.110 19 700 193 000
19 200 188 000
17 650 173 000
Forging: Heat slowly and uniformly to 700°C then more rapidly to 900/1040°C. After forging cool slowly.
Annealing: Anneal at 850°C and slow furnace cool. Hardness after annealing will be approx. 225 brinell.
Hardening: Pre heat slowly to 750/780°C and thoroughly soak. Continue heating to the final hardening temperature of 1000/1030°C and allow the component to be heated through. Quench in oil or cool in air.
Tempering: Heat uniformly and thoroughly at the selected tempering temperature and hold for at least one hour per inch of total thickness. Double tempering should be carried out with intermediate cooling to room temperature.
Tempering °C HRc
150
200
250
300
350
400
62/61 61/60 60/59 57/56 56/55 56/55
Stress Relieving:
If machining operations have been heavy or if the tool has an unbalanced section, remove stresses before hardening by heating up to 700°C, equalize then cool slowly.
Hard Chromium Plating:
After hard chromium plating tempering of D2 tool steel is recommended at 180°C for 4 hours to avoid hydrogen embrittlement. Tempering is to be performed immediately after chromium plating.
Welding:
Due to the high risk of crack formation welding of D2 tool steel should be avoided, if possible.
Mechanical Properties Conditions
Properties
T (°C)
Density (×1000 kg/m3)
7.7-8.03
25
Poisson's Ratio
0.27-0.30
25
Elastic Modulus (GPa)
190-210
25
Tensile Strength (Mpa)
1158
Yield Strength (Mpa)
1034
Elongation (%)
15
Reduction in Area (%)
53
Hardness (HB)
335
Treatment
25
oil quenched, fine grained, tempered at 425°C
25
oil quenched, fine grained, tempered at 425°C
Thermal properties
Properties
Conditions
T (°C)
Treatment
Thermal Conductivity (W/m-K)
42.7
100
Specific Heat (J/kg-K)
477
50-100
Physical Properties
Quantity
Value
Unit
Thermal expansion
16 - 17
e-6/K
Thermal conductivity
16 - 16
W/m.K
500 - 500
J/kg.K
Melting temperature
1370 - 1400
°C
Service temperature
0 - 500
°C
8000 - 8000
kg/m3
0.7 - 0.7
Ohm.mm2/m
Specific heat
Density Resistivity
3.3 Applications They can be heat treated to be both tough and hard. They are used for tooling applications like blocks in stamping dies (particularly when the dies will be used on stainless blanks) and blocks in draw dies for forming. High carbon High Chromium tool steel gives a good hardness with added toughness. This steel can be vacuum hardened when minimum distortion is required. Typical Applications for high carbon high chromium steel
Stamping and Forming Dies Punches Forming Rolls Knives, Slitters, Shear Blades Tools Scrap Choppers Tyre Shredders
4. Design of Die 4.1 Introduction DESIGNING THE DIE Before a designer begins to draw, there are a number of things which he must seriously consider. It is now possible to list all the items which will be required before he can begin designing intelligently. They are: 1. The part print 2. The operation sheet or route sheet 3. The design order 4. A press data sheet.
In addition, he may have a reference drawing of a die similar to the one he is to design or a sketch of a proposed design prepared by the chief tool designer or group leader suggesting a possible approach to solution of the problem. Let us consider further the information required: Part Print: The part drawing gives all necessary dimensions and notes. Any missing dimension must be obtained from the product design department before work can proceed.
Operation Sheet: The operation sheet or route sheet must be studied to determine exactly what operations were performed upon the work piece previously. This is very important. When the views of the stamping are laid out, any cuts which were applied in a previous operation must be shown. The Design Order: This must be studied very carefully because it specifies the type of die to be designed. Consider particularly the operation to be per formed, the press in which the die is to be installed, and the number of parts expected to be stamped by the die. The latter will establish the class of die to be designed. The Machine Data Sheet: The die to be designed must fit into a particular press and it is important to k now what space is available to receive it and what interferences may be present. In time you will come to realize the importance of careful and repeated study of the part print, operation sheet, and design order because there can be no deviation from the specifications given. DRAWING If the information on a drawing is complete, concise, and presented in the simplest possible manner, the die maker can work to best advantage. The first step in originating plans for a new die is the preparation of a sk etch or sketches of significant features of the proposed die. These will become a guide for beginning the actual full-size layout on tracing paper. However, 13 it is a mistake to spend too much time in this phase of the work or to try to develop the entire design in sketch form because then decisions can become too arbitrary and inflexible. Always keep your mind open to possible improvements as you develop the design in layout form. You will find that, often, the first or second idea sketched out can · be considerably improved by alteration as work progresses. Often the first idea proves entirely impractical and another method of operation must be substituted. Before beginning the sketch, place the part print, operation sheet, and design order before you on the drawing table. The three must be studied together so that a complete and exact understanding of the problem will be realized. This study will form the basis for the creation of a mental picture of a tool suitable for performing the operations - one which will meet every requirement. The sketch you make may be a very simple one for simple operations or it may be more elaborate. In fact, a number of sketches may be required for more complex operations and intricate designs. In any event, the sketch will clarify your ideas before a formal layout is attempted. In addition, it will form the basis for a realistic estimate of the size of the finished die so that you may select the proper sheet size for the layout. LAYOUT Laying out the die consists of drawing all views necessary for showing every component in its actual position. In the layout stage, no dimensions are applied and neither is the bill of material nor the record strip filled out. After the die has been laid out, the steps necessary for completing the set of working drawings are more or less a routine.
A properly prepared assembly drawing contains six general features: 1. All views required for showing the contour of every component including the work piece. 2. All assembly dimensions. These are dimensions which will be required for assembling the parts and those for machining operations to be performed after assembly.
3. All explanatory notes. 4. Finish marks and grind marks to indicate those surfaces to be machined after assembly. 5. A bill of material listing sizes, purchased components, materials, and number required for all parts. 6. A title block and record strip with identifying information noted properly.
4.2 Calculations Lame‟s Equation for calculating the thickness of Thick Cylindrical Shells
-
( √ ) Where d = internal diameter of shell (mm) 2
P = internal pressure (MPa or N/mm ) 2
= tangential stress (MPa or N/mm ) =
(where S = ultimate tensile stress)
We design the thick cylindrical shells to be safe against tangential stress, since for thick cylindrical shells, Tangential Stress > Longitudinal Stress > Radial Stress
For High carbon High Chromium Steel,
Ultimate Tensile Stress, S = 1757 MPa Designing for a factor of safety = 3 Tangential Stress,
= =
= 585.67 MPa Therefore,
Aluminum Powder,
For compacting of Al powders, P = 300 MPa
= 585.67 MPa
For compacting various Al alloys, P = 500 MPa (maximum)
Hence designing for P = 500 MPa
Internal diameter chosen for specimens, d = 19.5 mm
Final Calculations,
(√ ) (√ ) Therefore, t = 24.9587 mm t
25 mm
Hence, Outer diameter, D = d + 2t D = 19.5 + 2*25 D = 69.5 mm
70 mm
Final Dimensions as per our Design are:
Dimension
Value (mm)
Internal Diameter, d
19.50
Thickness of cylindrical shell, t
25.00
Outer Diameter, D
70.00
Note- This DIE will be safe for maximum internal pressures of 500 N/mm
4.3 Die Design in PRO E
1. Die-
2
2.Punch-
5. Die Fabrication 5.1 Turning Turning is a form of machining, a material removal process, which is used to create rotational parts by cutting away unwanted material. The turning process requires a turning machine or lathe, work piece, fixture, and cutting tool. The work piece is a piece of pre-shaped material that is secured to the fixture, which itself is attached to the turning machine, and allowed to rotate at high speeds. The cutter is typically a single-point cutting tool that is also secured in the machine, although some operations make use of multi-point tools. The cutting tool feeds into the rotating work piece and cuts away material in the form of small chips to create the desired shape. Turning is used to produce rotational, typically axi-symmetric, parts that have many features, such as holes, grooves, threads, tapers, various diameter steps, and even contoured surfaces. Parts that are fabricated completely through turning often include components that are used in limited quantities, perhaps for prototypes, such as custom designed shafts and fasteners. Turning is also commonly used as a secondary process to add or refine features on parts that were manufactured using a different process. Due to the high tolerances and surface finishes that turning can offer, it is ideal for adding precision rotational features to a part whose basic shape has already been formed.
5.2 Drilling Drilling is a cutting process that uses a drill bit to cut or enlarge a hole in solid materials. The drill bit is a multipoint, end cutting tool. It cuts by applying pressure and rotation to the work piece, which forms chips at the cutting edge.
Drilling is the most common machining process whereby the operation involves making round holes in metallic and nonmetallic materials. Approximately 75% of all metal-cutting process is of the drilling operation. Drills usually have a high length to diameter ratio that is capable of producing deep hole, however due to its flexibility, necessary precaution need to be taken to maintain accuracy and prevent drill from breaking. Drilled holes can be either through holes or blind holes (see Figure 4.1). A through hole is made when a drill exits the opposite side of the work; in blind hole the drill does not exit the work piece.
5.3 Boring In machining, boring is the process of enlarging a hole that has already been drilled (or cast), by means of a single-point cutting tool (or of a boring head containing several such tools), for example as in boring a cannon barrel. Boring is used to achieve greater accuracy of the diameter of a hole, and can be used to cut a tapered hole. Boring can be viewed as the internal-diameter counterpart to turning, which cuts external diameters. There are various types of boring. The boring bar may be supported on both ends (which only works if the existing hole is a through hole), or it may be supported at one end. Lineboring (line boring, line-boring) implies the former. Backboring (back boring, back-boring) is the process of reaching
through an existing hole and then boring on the "back" side of the work piece (relative to the machine headstock).
5.4 Internal Grinding Internal cylindrical grinding is a machining process used to finish machine internal diameters to a high degree of accuracy with a fine finish. Materials can be ground unhardened or hardened. Internal cylindrical grinding is used to finish machine internal diameters such as bearing journals, seal surfaces, bushes, plain bearings, cutting tool guides, jig bushes, or any internal diameter that needs to be finished to a high level of accuracy. In the case of materials that are hardened or coated in hard materials such as hard chrome, hard facing alloys or ceramic, internal cylindrical grinding is often the method of choice to finish machine the diameter to final size. Particularly in the case of intermittent cuts which can easily break ceramic cutting tools. Internal grinding provides an easy solution.
5.5 Oil Quenching Rapid cooling of a material results in high internal stresses. The transformation from austenite to martensite involves some volumetric expansion. This adds further stresses particularly in parts of varying cross section. These stresses together with the hard, brittle nature of martensite can be sufficient to cause cracking. To avoid this, the steel is reheated to an intermediate temperature D to soften the part to the desired hardness level. This operation known as tempering or drawing also serves to relieve those residual stresses which otherwise would cause brittleness in the steel. If quenching is not rapid enough, the austenite reverts to ferrite and carbide E, and high hardness is not obtained. The rate of quenching required to produce martensite depends primarily on the alloy content. Low alloy steels require rapid cooling in water or oil, while highly alloyed steel usually can be air-quenched at a much slower rate. Throughout all these heat-treating reactions, most die steels retain excess or undissolved carbides, which take no direct part in the hardening. The high carbon high-chromium steels, for example, have large quantities of excess iron-chromium carbide, which give them in large measure the high degree of abrasion resistance possessed by this class of steel. Influence of Heat Treatment on Die Life
Each type of die steel must be handled slightly differently from any other for optimum results. Different temperatures, different heating and cooling rates and variable tempering procedures must
be used as recommended. In general, it may be said that the harder a given die, the longer it will wear, while the softer a die is, the tougher it becomes. Assuming the proper die steel is being used, dies which are wearing out too quickly should be made harder for improved life and dies which are breaking or cracking should be made softer. Within limits, heat treatment can be used to adjust these variables to best advantage. Oil-hardening steel may work best on one application at Rockwell C62 and on another involving higher stresses and shock at Rockwell C58. Adjustments of the drawing temperature easily produce the hardness desired. Double drawing and in some instances triple drawing is desirable for tools in severe applications. This is because steels retain austenite when quenched. The first temper affects the martensite formed during quenching and conditions the austenite so that it transforms upon air-cooling from the draw. Double drawing is necessary to affect the martensite, which forms after the first draw. Triple drawing eliminates nearly all retained austenite, further increasing toughness. Process
Quenching metals is a progression; the first step is soaking the metal, i.e. heating it to the required temperature. Soaking can be done by air (air furnace), or a bath. The soaking time in air furnaces should be 1 to 2 minutes for each millimeter of cross-section. For a bath the time can range a little higher. The recommended time allotment in salt or lead baths is 0 to 6 minutes. Uneven heating or overheating should be avoided at all cost. Most materials are heated from anywhere to 815 to 900 °C (1,500 to 1,650 °F). The next item on the progression list is the cooling of the part. Water is one of the most efficient quenching media where maximum hardness is acquired, but there is a small chance that it may cause distortion and tiny cracking. When hardness can be sacrificed, whale, cottonseed and mineral oils are used. These often tend to oxidize and form a sludge, which consequently lowers the efficiency. The quenching velocity (cooling rate) of oil is much less than water. Intermediate rates between water and oil can be obtained with water containing 10-30% Ucon, a substance with an inverse solubility which therefore deposits on the object to slow the rate of cooling. To minimize distortion, long cylindrical work pieces are quenched vertically; flat workpieces are quenched on edge; and thick sections should enter the bath first. To prevent steam bubbles the bath is agitated. Effect of Oil Quenching
Before the material is hardened, the microstructure of the material is a pearlite grain structure that is uniform and laminar. Pearlite is a mixture of ferrite andcementite formed when steel or cast iron are manufactured and cooled at a slow rate. After quench hardening, the microstructure of the material form into martensite as a fine, needle-like grain structure. Before using this technique it is essential to look up the rate constants for the quenching of the excited states of metal ions.
Equipment
There are three types of furnaces that are commonly used in quench hardening: salt bath furnace, continuous furnace and box furnace. Each is used depending on what other processes or types of quench hardening are being done on the different materials. Quenching media
When quenching, there are numerous types of media. Some of the more common include: air, brine (salt water), oil and water. These media are used to increase the severity of the quench. Quenching Distance
Quenching distance is an important property in the study of combustion. It is defined as the smallest hole a flame can travel through. For example hydrogen has a quenching distance of 0.64 mm.
6. Aluminum (Metal Powder) 6.1 Introduction The element aluminum (Al) has a specific gravity of 2.7, placing it among the light-weight structural metals. It is used as a base for die casting alloys with three primary constituents: silicon, copper and magnesium. Eight available aluminum die casting alloys give the designer the widest choice among the four primary alloy groups, and they account for the majority of die castings in terms of tons of components produced. Seven of the eight alloys are based on the aluminum-silicon system. The eutectic (system) composition, 11.7% silicon, is a convenient reference point for grouping them. The seven alloys are further grouped as either controlled copper content or restricted copper content. Other major alloying elements in the aluminum-silicon system are magnesium and iron. Some constituents are considered impurities, and maximum limits, expressed as a single number, are imposed.
6.2 Properties of Aluminum: Mechanical and Performance Properties of Powder Metal Aluminum:
Powder metal aluminum parts can be produced with a range of property levels. Mechanical properties such as tensile strength can vary from 20 ksi (130 MPa) to 50 ksi (330 MPa) depending upon the composition and density of the alloy, sintering practices and thermal treatments. Further secondary processing such as hot or cold forming can yield properties approaching those of conventional wrought aluminum materials. Powder metallurgy aluminum mechanical properties are very good and typically are a significant factor in the material selection process.
Base powder
Alloying powder
YS, MPa
UTS, MPa
Elong. %
RA, %
Oxygen content, %
Al
Al-V alloy
master
ASM Standard
850-930
960-990
10-12.5
23-29
0.11-0.25
828
897
10
20
0.20
6.3 Why Aluminum? Aluminum is: Light in weight - about a third as heavy as copper or steel. Highly resistant to corrosion Strong, and it can be made stronger by alloying and heat treatment An excellent conductor of heat and electricity Nonmagnetic, a valuable property around sensitive electronics Outstanding in cryogenic properties - strong, not brittle, in intense cold Good machinability Good response to a variety of finishing processes, such as anodizing Completely recyclable (and, therefore, energy-efficient) The combination of aluminum's light weight and moderate strength give it an excellent strength-toweight ratio. Aluminum offers product forms and alloys that surpass any other material. The design flexibility of aluminum is unparalleled, allowing designers to engineer optimum shape and performance for each specific application. Powder metal aluminum can compete successfully with less costly materials because of the advantages it brings in primary and secondary weight savings, structural performance and design flexibility. When you link the usual advantages of powder metallurgy to the attributes of an exceptional material like aluminum, you have a winning combination. Aluminum powder metallurgy offers a number of additional advantages related to the specific properties of basic aluminum. Light Weight
Lighter weight is a distinguishing characteristic of powder metal aluminum. In fact, aluminum enjoys better than a 3 to 1 weight advantage over iron, nickel, and copper. Conductivity
Excellent conductivity, both electrical and thermal, is also a hallmark of powder metal aluminum. Aluminum powder metallurgy parts are comparable to their wrought counterparts and can be utilized as heat sinks or electrical conductors. See Figure 2 (next page) for a comparison.
Corrosion Resistance
Powder metal aluminum alloys have excellent resistance to corrosion. In particular, the Al-Mg-Si alloys exhibit extremely high resistance to general corrosion, when compared to ferrous-based products. Parts may also be chromate conversion coated or anodized for increased resistance to corrosion. Hard type anodize finishes can be applied for water-resistant applications. Appearance
The natural appearance of powder metal aluminum parts is suitable for most applications where good appearance is a requirement. In addition, a wide range of decorative finishes is available. Many of the decorative and protective treatments currently employed for wrought and cast aluminum alloys can also be applied to aluminum powder metallurgy parts. These include mechanical finishing and etching to achieve textures, coloring for decorative or functional purposes, electroplating, and painting. Machining
Powder metallurgy aluminum parts also offer many of the important advantages of wrought aluminum in machining operations, including high cutting speeds, smooth surface finish and superior tool life. Joining and Bonding
Powder metal aluminum lends itself to a variety of joining and bonding techniques. Sintered aluminum parts can be successfully fastened by adhesive bonding, although the use of threaded fasteners is a more conventional method of joining multiple parts. Excellent thread characteristics can be obtained in powder metallurgy aluminum parts above the 90% density level. The ductility of parts in the upper density range is also sufficient for self-tapping fasteners.
6.4 Aluminum Alloys - Heat Treatment & Welding Aluminum alloy die castings are not usually solution heat treated. Low-temperature aging treatments may be used for stress relief or dimensional stability. A T2 or T5 temper may be given to improve properties. Because of the severe chill rate and ultra-fine grain size in die castings, their “as-cast” structure approaches that of the solution heat-treated condition. T4 and T5 temper results in properties quite similar to those which might be obtained if given a full T6 temper.
As stated above aluminum alloy die castings are not usually heat treated; however, there are heat treatable specialty alloys available for structural applications, such as the Silafonts. Die castings are not generally gas or arc welded or brazed; however, developments in high integrity die casting processes coupled with specialty alloys has enabled the successful welding of die castings in specific applications. Contact your die caster or alloy producer for more information.
6.6 Aluminum Supply Aluminum die casting alloys are made from recycled metal. Secondary (recycled) aluminum is more economical to produce than primary because it requires only 5% as much energy to produce a pound. Current projections indicate that the supply of recycled aluminum will be adequate to meet the needs for aluminum die casting into the foreseeable future. Used beverage cans (UBC) comprise a large portion of the aluminum available recyclers. The supply has been enhanced by the 1 widespread recycling of beverage cans. Aluminum smelters are widely dispersed across internationally.
7. Specimen Manufacturing (Powder Metallurgy) 7.1 Introduction Powder metallurgy is concerned with the production of metal powders and converting them to useful shapes. It is a material processing technique in which particulate material are consolidate to semi finished and finished products . Generally the emphasis is on the metallic material but the principal of the process apply with little modification to ceramic, polymers and a variety of composite
materials
composed
of metallic and non
metallic phases.
Nowadays
powder metallic techniques are increasingly used to provide exceptional properties that are required in highly sophisticated aerospace electronic and nuclear energy industries. However an automobiles industry is the major consumer of powder metallurgy product today. There are two
important reasons to use powder metallurgy by industries. Products like tungsten filament, tungsten carbide, porous self lubricating bearings etc. are either difficult or impossible to make by other methods. The other reason is that powder metallurgy process of manufacturing structural components competes with other manufacturing products such as casting machining and forging. Powder metallurgy process minimizes or eliminates the machining, and scrap losses at the same time is suited to high volume production of components. The process offers economy, savings in energy and raw materials along with mass production of quality precision components.
Powder metallurgy is the process of blending fine powdered materials, pressing them into a desired shape (compacting), and then heating the compressed material in a controlled atmosphere to bond the material (sintering). Compacting is generally performed at room temperature, and the elevatedtemperature process of sintering is usually conducted at atmospheric pressure. Optional secondary processing often follows to obtain special properties or enhanced precision.
Two main techniques used to form and consolidate the powder are sintering and metal injection molding. Recent developments have made it possible to use rapid manufacturing techniques which use the metal powder for the products. Because with this technique the powder is melted and not sintered, better mechanical strength can be accomplished.
The powder metallurgy process generally consists of four basic steps:
Powder manufacturing.
Powder blending.
Compacting.
Sintering.
Finishing operations.
7.2 History Powder metallurgy principle of shaping metallic objects without melting from powdered materials can be traced back to the early civilizations. These include the ancient Egyptian iron implants which date from at least 3000 B.C. In Greece the manufacture of iron components were widespread in 800-600 B.C. The manufacture of large objects were known to Indians as early as 300A.D. and the famous Delhi iron pillar weighing more than six tons is a typical master piece indeed . These are processed by direct reduction of iron oxide without melting, since the technology to obtain temperature high enough to melt pure iron was not available until about 1800. The significant development in the use of the powder metallurgy principle took place during the early part of nineteenth century for processing platinum and the credit to this is to be given to Wollaston in England and Sobolevskiy in Russia. These developments ultimately led to the modern renaissance of powder metallurgy in the beginning of twentieth century with the manufacture of tungsten filaments for the incandescent lamp industry. The invention of electric lamp by Thomas Edison and Swan a century ago has contributed substantially to the rapid progress of this field. Powder metallurgy emerged as a new dimension in materials technology in twentieth century particularly during the world war period and subsequent years. Today the technology is used advantageously to process advanced material for the nuclear, electronics and aerospace industries. But in modern India the progress made in this field is mainly during the past two decades. Thus, powder metallurgy has behind it a long and anything but straight road. However, as can be seen from the present review, its history has received little study. The historical notes in the books considered above provide merely a background or introduction to the analysis of each specific topic. Yet it is precisely today, when the role of powder metallurgy has grown so enormously, that
it is particularly important to discover links between present-day practice and historical experience. A thorough study should be made of all the relevant facts, events, and scientific ideas of the past, involving their objective interpretation, precise documentation, and full analysis.
Basic Flow chart of Powder Metallurgy
START
Metal Powder Preparation
Blending
Compaction
START
Auxiliary Operations
Sintering
7.3 Powder Manufacturing or Atomization Atomization is accomplished by forcing a molten metal stream through an orifice at moderate pressures. A gas is introduced into the metal stream just before it leaves the nozzle, serving to create turbulence as the entrained gas expands (due to heating) and exits into a large collection volume exterior to the orifice. The collection volume is filled with gas to promote further turbulence of the molten metal jet. On Earth, air and powder streams are segregated using gravity or cyclonic separation . Most atomized powders are annealed, which helps reduce the oxide and carbon content. The water atomized particles are smaller, cleaner, and nonporous and have a greater breadth of size, which allows better compacting.
7.4 Zinc stearate as Lubricant Zinc stearate (Zn(C18H35O2)2) is a zinc soap that repels water. It is insoluble in polar solvents such as alcohol and ether but soluble in aromatic hydrocarbons (e.g., benzene and chlorinated hydrocarbons) when heated. It is the most powerful mold release agent among all metal soaps. It contains no electrolyte and has a hydrophobic effect. Its main application areas are the plastics and rubber industry where it is used as a releasing agent and lubricant which can be easily incorporated.
Structural Formula:
Applications of Zinc Stearate:
As a synergic stabilizer for Ba/Cd and Pb stabilizer systems.
As a gloss imparting agent in paint industry.
As a metal release agent in rubber, polyurethane and polyester processing system.
As a die release agent in powder metallurgy.
As a chief ingredient in "fanning powder", used by magicians performing card manipulation to decrease the friction between the cards.
As a lubricant in cosmetics to improve texture.
As an activator system for rubber vulcanization by sulfur and accelerators.
Specifications:
Characteristics
Properties
Appearance
White Fine Powder
Melting Point
120ºC - 124ºC
Solubility
Insoluble in Water, Ethanol & Ether
Moisture Content
Less than 2%.
Total Ash Content
Between 14-16%.
Free Stearic Acid
Less than 3%.
Zinc Content (as ZnO)
13-15 %
Bulk Density
App.0.10 Gm/CC
Fineness through 240 mesh
99% passes
pH
6.5 – 7.5
7.5 Powder Blending Blending and mixing are carried out to achieve uniformity of the product manufactured. Distribution of properly sized particles is attained by mixing elementary powder with alloy powders to obtain a homogeneous mixture. Lubricants are also mixed with powders to minimize the wear of dies and reduce friction between the surfaces of dies and the particles of powder during compaction. Mixing time depends upon the results desired, and over-mixing should be prevented, or otherwise the size of particles will be decreased, and they will be hardened.
Horizontal Ball Mill (Tumbler ball mill): Specifications: Diameter: 320 mm (Approx.) Width: 120 mm (Approx.) Speed: 100 rpm (Approx.) (With speed regulator) Material of the ball mill: Stainless steel Material of Balls: Stainless steel. Two or three different diameter balls should be provided. Extra balls should be provided to replace for the worn out balls. Hose pipes for filling Argon gas should be provided. Provision for filling Argon gas for creating inert atmosphere through non return valves in the ball mill is available.
7.6 Powder Compaction Powder compaction is the process of compacting metal powder in a die through the application of high pressures. Typically the tools are held in the vertical orientation with the punch tool forming the bottom of the cavity. The powder is then compacted into a shape and then ejected from the die cavity. In a number of these applications the parts may require very little additional work for their intended use; making for very cost efficient manufacturing. The cavity of the die is filled with a specified quantity of blended powder, necessary pressure is applied, and then the compacted part is ejected. Pressing is performed at room temperature; the pressure depends upon the material, properties of the powder used, and the density required of the compaction. Friction between the powder and the wall of the die opposes the pressure applied; the pressure decreases with depth and causes uneven density in the compact. Thus the ratio of length and diameter is kept low to prevent substantial variations in density.
There are four major classes of tool styles: single-action compaction, used for thin, flat components; opposed double-action with two punch motions, which accommodates thicker components; doubleaction with floating die; and double action withdrawal die. Double action classes give much better density distribution than single action. Tooling must be designed so that it will withstand the extreme pressure without deforming or bending. Tools must be made from materials that are polished and wear-resistant.
Die compaction represents the most widely used method and is considered as the conventional technique. This involves rigid dies and special mechanical or hydraulic presses. Densities of up to 90 % of full density can be achieved following the compaction cycle, the duration of which may be of the order of just a few seconds for very small parts. Powders do not respond to pressing in the same way as fluids and do not assume the same density throughout the compact. The friction between the powder and die wall and between individual powder particles hinders the transmission of pressure. A high uniformity in green parts can be achieved depending on: – the kind of compacting technique – the type of tools – the materials to be pressed and the lubricant.
The compacting techniques used may be characterised by references to the movement of the individual tool elements – upper punch, lower punch and die relative to one another. Pressing within fixed dies can be divided into: – Single action pressing – Double action pressing In the former the lower punch and the die are both stationary. The pressing operation is carried out solely by the upper punch as it moves into the fixed die. The die wall friction prevents uniform
pressure distribution. Compact has a higher density on top than on the bottom. In the latter type of pressing only the die is stationary in the press. Upper and lower punches advance simultaneously from above and below into the die (Fig.5.1). The consequence is high density at the top and undersides of the compact. In the centre there remains a „neutral zone‟ which is relatively weak. Pressing Operation:
The pressing operations can be sequenced as follows: 1. Filling of the die cavities with the required quantity of powder. 2. Pressing in order to achieve required green density and part thickness. 3. Withdrawal of the upper punch from the compact: Here the risk of cracking of green parts is felt. As the upper punch withdraws, the balance of forces in the interior of the die ends. In the case of parts with two different thicknesses, e.g. flange with a hub, the elastic spring back of the lower punch is the greatest danger. Other problems are protrusions required on the upper face of the part. In the case of thin parts with large projected area, cracking is common due to elastic spring back of the lower punch and the part itself. The former pushes the part still lying in the die cavity upwards, while the latter tends to expand the part. Ejection:
The tooling must be done in such a manner so that the ejection of part is feasible. Ejection of a part of complex forms is rather problematic, as it involves friction between the green part and tool walls. The green strength must be high to resist the bending stresses introduced by the ejection force. There is another type of compaction involving upper punch pressing with floating die. This is characterized by a stationary lower punch the upper punch moves into a die supported by spring. As soon as the friction between the powder and the die wall exceeds the spring power, the die wall is carried down. The friction will vary slightly from stroke to stroke. It also depends on the degree of wear in the tools so that a constant density distribution is difficult to maintain over a period. During second world war another tooling method was developed in Germany, known as „withdrawal tooling‟ . In this case, the lower punch does not move during compacting cycle. After the upper punch has entered the die cavity, both upper punch and die plate move downwards. After the compact has been pressed, the upper punch moves up but the die plate and lower coupler move further down until the top of the die plate is flush with the lower punch. The compact is ejected and can be moved out of the way by the loading shoe. Die plate and lower coupler then move back into the filling position and the cycle repeats. The major advantage of withdrawal system of tooling is that the lower punches are relatively short and are well supported during compaction and ejection. When there are multiple lower punches, as many of them as possible rest directly on the base plate. Withdrawal tooling can be built for very complex parts. On the other hand, in the tooling system with ejection by the lower punches the motions of the punches are built into the multiple action presses. In many cases no tool holders are required.
7.7 Sintering Solid state sintering is the process of taking metal in the form of a powder and placing it into a mold or die. Once compacted into the mold the material is placed under a high heat for a long period of time. Under heat, bonding takes place between the porous aggregate particles and once cooled the powder has bonded to form a solid piece. Sintering can be considered to proceed in three stages. During the first, neck growth proceeds rapidly but powder particles remain discrete. During the second, most densification occurs, the structure recrystallizes and particles diffuse into each other. During the third, isolated pores tend to become spheroidal and densification continues at a much lower rate. The words Solid State in Solid State Sintering simply refer to the state the material is in when it bonds, solid meaning the material was not turned molten to bond together as alloys are formed.
One recently developed technique for high-speed sintering involves passing high electrical current through a powder to preferentially heat the asperities. Most of the energy serves to melt that portion of the compact where migration is desirable for densification; comparatively little energy is absorbed by the bulk materials and forming machinery. Naturally, this technique is not applicable to electrically insulating powders. To allow efficient stacking of product in the furnace during sintering and prevent parts sticking together, many manufacturers separate ware using Ceramic Powder Separator Sheets. These sheets are available in various materials such as alumina, zirconia and magnesia. They are also available in fine medium and coarse particle sizes. By matching the material and particle size to the ware being sintered, surface damage and contamination can be reduced while maximizing furnace loading.
CONTROLLED ATMOSPHERE FURNACE SPECIFICATIONS:
1. Maximum temperature: 1500 C 2. Dimension of Heat Zone: Diameter = 100 mm, Length = 180 mm 3. Length of Furnace = 500 mm (Approx.) 4. Arrangement to remove the air by vacuum pump and purge the inert gas (Argon). 5. Provision to run the furnace at vacuum, without purging inert gas, with vacuum pump continuously „on‟ while heating. 6. Cooling arrangement for gas or air before entering the vacuum pump. -3
7. Suitable vacuum pump (10 torr vacuum). 8. Provision to measure the vacuum. 9. The furnace should be programmable to control the rate of heating and cooling.
10. Arrangement to set at maximum desired temperature. 11. One Argon cylinders (for inert gas supply). 12. One argon regulator for Argon cylinder and Hoses. 13. Outside skin temperature of furnace should be as low as possible (not more than 60
C).
14. Guarantee of 3 years.
7.8 Powder Metallurgy using Aluminum Increased demand for light weight components, primarily driven by the need to reduce energy consumption in a variety of societal and structural components, has led to increased use of aluminum. Additionally, the cost of fabrication coupled with a need to improve part recovery has led to significant growth in the net-shaped component manufacturing processes. Aluminum Powder Metallurgy (P/M) offers components with exceptional mechanical and fatigue properties, low density, corrosion resistance, high thermal and electrical conductivity, excellent machinability, good response to a variety of finishing processes, and which are competitive on a cost per unit volume basis. In addition, aluminum P/M parts can be further processed to eliminate porosity and improve bonding yielding properties that compare favorably to those of conventional wrought aluminum products. The primary driver for the use of aluminum P/M is the unique properties of aluminum coupled with the ability to produce complex net or near net shape parts which can reduce or eliminate the operational and capital costs associated with intricate machining operations. Aluminum P/M can replace other P/M in certain applications on a direct basis. However, in terms of the potential for ferrous based product substitution, each potential application needs to be considered on a case by case basis. Typical economics tend to favor iron parts but the unique characteristics of aluminum such as strength, weight, corrosion resistance, and machinability can make the aluminum parts economically viable .
The aluminum P/M process consists of three basic steps: 1. Aluminum powders of controlled purity and particle size are mixed with alloying metal powders in precisely controlled quantities. Generally a powdered lubricant is added to permit the consistent production of high density parts without seizing of the punches or cold welding to the die walls. This lubricant is carefully chosen to ensure that there is no residual ash to interfere with bonding during sintering. 2. The premix is compacted using precision metal dies in specially designed P/M presses to yield a green compact. Aluminum premixes exhibit excellent compressibility and yield high density parts at low compaction and ejection pressures. Premixes can be compacted to 90% density at only 12 tsi
and 95% at 25 tsi. Typical green strengths range from 450 to 1500 psi which is sufficiently strong to withstand normal handling without chipping or breaking. 3. The green compacts are sintered in a controlled atmosphere furnace at closely regulated temperatures. This process metallurgically bonds the powder particles together and develops the desired physical and mechanical properties. Aluminum powder sintering is difficult to achieve because the aluminum oxide is not reduced by common furnace atmospheres at sintering temperatures. However, successful sintering is accomplished in environments containing hydrogen, nitrogen and dissociated ammonia as long as the following conditions are observed: The lubricant is essentially free of moisture and low in ash contact. Atmospheres contain low levels of moisture and oxidizing gases. Alloying elements having a high solubility in aluminum are added to generate low melting phases.
Most aluminum P/M alloys are sintered between 1000 and 1200°F with a sintering time of 7 to 20 minutes. The recommended atmosphere is nitrogen with a furnace dew point range of -40 to -60°F. Higher dew points yield reduced properties and very high dew points can result in gross expansion of the compact.
7.9 Aluminum comparison to other P/M materials
A direct comparison of mechanical properties of aluminum P/M with ferrous based products reveals that, like its wrought aluminum counterpart, has lower, but competitive, strength levels. However, there are many major property advantages associated with aluminum P/M alloys. A major advantage is the density of aluminum which is translatable into many property, processing and economic benefits. Parts will weigh less and relatively small changes in part dimensions can yield bulk properties comparable to the ferrous based parts while still maintaining an overall weight advantage. This is a major benefit in today‟s energy conscious world. In addition, because of the lower density, the relatively high cost per pound of aluminum P/M raw materials becomes less significant and more competitive with typical P/M materials, when considered on a cost per unit volume or individual part weight basis. This lighter weight can also be translated into a potentially higher volume of parts per inch of belt in the sintering operation (i.e., greater productivity), and also lowers shipping costs. Other significant property advantages associated with aluminum P/M include corrosion resistance, conductivity and finishing characteristics. The excellent corrosion resistance of aluminum alloys has been well established through years of experience in marine, aerospace and chemical industry applications. In normal outdoor exposure aluminum P/M alloys will provide corrosion resistance equivalent to brass, bronze and stainless steel P/M parts and significantly better than ferrous based products. This corrosion resistance also means that no special coatings are necessary for normal shipping and storage. Aluminum has excellent conductivity values, both thermal and electrical. Aluminum P/M is comparable to it‟s wrought cou nterparts and significantly better than brass, bronze and ferrous based materials. The natural appearance of aluminum P/M parts after chemical or mechanical cleaning is suitable for most applications where good appearance is a requirement. In addition, a wide range of decorative and functional finishes are available with aluminum P/M that are not possible with other P/M materials. Aluminum P/M also offers economic advantages in the parts fabrication area. These blends exhibit excellent compressibility and yield high density parts at low compaction and ejection pressures. Aluminum P/M blends can be compacted to 90% theoretical density at only 12 tsi and 95% at 25 tsi which is much lower than comparable ferrous based materials. These lower pressures permit the use of smaller, faster presses to produce larger parts and in some cases allow the use of multiple cavity tooling. Lower compaction pressures reduce the possibility of damage in fragile tool designs and tool breakage is less likely with aluminum. Sintering temperatures for aluminum P/M parts are much lower (1100°-1200°F) than other P/M parts (>2000°F). This yields significant energy savings in the production process. The sintering in presence of atmospheric gases for aluminum part production also tends to be more economical. The atmosphere of choice for aluminum tends to be low dew point nitrogen while other P/M parts use a combination of hydrogen (5-15%) and nitrogen. Since hydrogen gas is 3-4x more expensive than nitrogen, the use of nitrogen alone can translate into further cost savings. Aluminum P/M parts offer many advantages over other P/M products. In addition to properties such as low density, thermal and electrical conductivity, finishing characteristics and corrosion resistance not available with other P/M products, aluminum can be economically viable on a direct part replacement basis. An analysis of a hypothetical P/M flange
part with a flange diameter of 1 inch and the length of 0.06 inches coupled with an overall length and body OD of 0.75 inches suggests a 30% lower cost than 316L SS, a 20% lower cost than Bronze 9010 and a comparable cost with FC0008 at a density of 6.6.
8. Testing Of Specimens 8.1 Introduction to Universal Testing Machine (UTM): A universal testing machine, also known as a universal tester, materials testing machine or materials test frame, is used to test the tensile stress and compressive strength of materials. It is named after the fact that it can perform many standard tensile and compression tests on materials, components and structures.
Components:
Load frame - usually consisting of two strong supports for the machine. Some small machines have a single support. Load cell - A force transducer or other means of measuring the load is required. Periodic calibration is usually called for. Cross head - A movable cross head (crosshead) is controlled to move up or down. Usually this is at a constant speed: sometimes called a constant rate of extension (CRE) machine. Some machines can program the crosshead speed or conduct cyclical testing, testing at constant force, testing at constant deformation, etc. Electromechanical, servo-hydraulic, linear drive, and resonance drive are used. Means of measuring extension or deformation- Many tests require a measure of the response of the test specimen to the movement of the cross head. Extensometers are sometimes used. Output device - A means of providing the test result is needed. Some older machines have dial or digital displays and chart recorders. Many newer machines have a computer interface for analysis and printing. Conditioning - Many tests require controlled conditioning (temperature, humidity, pressure, etc.). The machine can be in a controlled room or a special environmental chamber can be placed around the test specimen for the test. Test fixtures, specimen holding jaws, and related sample making equipment are called for in many test methods.
Use: The set-up and usage are detailed in a test method, often published by a standards organization. This specifies the sample preparation, fixturing, gauge length (the length which is under study or observation), analysis, etc. The specimen is placed in the machine between the grips and an extensometer if required can automatically record the change in gauge length during the test. If an extensometer is not fitted, the machine itself can record the displacement between its cross heads on which the specimen is held. However, this method not only records the change in length of the specimen but also all other extending / elastic components of the testing machine and its drive systems including any slipping of the specimen in the grips. Once the machine is started it begins to apply an increasing load on specimen. Throughout the tests the control system and its associated software record the load and extension or compression of the specimen. Machines range from very small table top systems to ones with over 53 MN (12 million lbf) capacity. Normally, universal testing machines have a moveable structure which can vertically move up and down to realize both tensional and compression tests. Tensional tests include tensile, tear and peel tests Compression tests include compressive, shearing, bending and flexural tests
Universal testing machines can be classified into two categories according to their driving methods: servo-hydraulic drive and electromechanical drive.
Servo-hydraulic: it has a tensile structure mounted on a oil cylinder which is used to drive the tensile structure up and down, and the oil feeding rate to oil cylinder is controlled by a servo valve. such as HUALONG servo-hydraulic universal testing machine Electromechanical: it has two screws and a moveable crossbeam, the crossbeam could move up and down to achieve tensile and compression tests, a servo motor which is controlled by a servo drive to drive the crossbeam up and down.
8.2 Indirect tensile strength test : A cylindrical specimen is loaded diametrically across the circular cross section. The loading causes a tensile deformation perpendicular to the loading direction, which yields a tensile failure. By registering the ultimate load and by knowing the dimensions of the specimen, the indirect tensile strength of the material can be computed. Below is a figure showing the load fixture and a principal picture of the loading.
Calculations of the indirect tensile strength of specimen are as follows:
where St = Indirect tensile strength, kPa P0 = Maximum load sustained by the specimen, N t = Specimen thickness, mm D = Specimen diameter, mm
Figure 2: Proper alignment of specimen within the loading strips for the indirect tensile test.
Figure 3. Chart for visual percentage estimation.
Calculate the numerical index of the asphalt mixture's response to the detrimental effect of water as follows:
where Yd = average tensile strength of dry subset Yc = average tensile strength of conditioned subset.
TSR values near one are indicative of mixtures which will have very low susceptibility to stripping after exposure to moisture and freeze-thaw conditions. Calculate the Relative Variation in Strength (RVS) as follows:
where: CVc = coefficient of variation for conditioned subset (S c /Yc) CVd = coefficient of variation for dry subset (S d /Yd) where Sc and Sd are calculated using the following equations:
where Stc1 = tensile strength of the first conditioned specimen Stc2 = tensile strength of the second conditioned specimen Stc3 = tensile strength of the third conditioned specimen Yc = (Stc1 + Stc2 + Stc3)/3 and
where Std1 = tensile strength of first dry specimen Std2 = tensile strength of second dry specimen Std3 = tensile strength of third dry specimen Yd = (Std1 + Std2 + Std3)/3
8.3 Compression Testing Compressive strength is the capacity of a material or structure to withstand axially directed pushing forces. When the limit of compressive strength is reached, materials are crushed. Compressive strength is often measured on a universal testing machine; these range from very small table top systems to ones with over 53 MN capacity. Measurements of compressive strength are affected by the specific test method and conditions of measurement. Compressive strengths are usually reported in relationship to a specific technical standard. the compressive strength of a material is that value of uniaxial compressive stress reached when the material fails completely. The compressive strength is usually obtained experimentally by means of a compressive test. The apparatus used for this experiment is the same as that used in a tensile test. However, rather than applying a uniaxial tensile load, a uniaxial compressive load is applied. As can be imagined, the specimen (usually cylindrical) is shortened as well as spread laterally.
Load Vs Displacement
Stress Vs Displacement
Stress Vs Strain
8.4 Density Test Observations :
S.No.
Before Sintering Volume 3 (mm )
Weight (gms)
After Sintering
Speci men No.
Length (mm)
Diameter (mm)
1.
10.36
19.48
3086.809
7.6799
0.002488
10.22
19.12
2932.893
7.6186
0.002597
2.
23.88
19.48
7113.476
18.0627
0.002539
23.40
19.15
6736.325
18.0398
0.002676
3.
33.46
19.48
9967.207
24.2578
0.002433
32.64
19.12
9366.893
24.2157
0.002585
Ave rage
Density 3 (gm/mm )
Length (mm)
Diameter (mm)
Volume 3 (mm )
0.002486
3
Average Density before Sintering
= 0.002486 gm/mm
Average Density after Sintering
= 0.002619 gm/mm
Change in Density
= (0.002619 - 0.002486) gm/mm
3
3
3
= 0.000133 gm/mm = 5.3499 %
Density 3 (gm/mm )
0.002619
Calculations :
Percentage Change in Density
Weight (gms)
8.5 Hardness Testing Hardness is the measure of how resistant solid matter is to various kinds of permanent shape change when a force is applied. Macroscopic hardness is generally characterized by strong intermolecular bonds, but the behavior of solid materials under force is complex; therefore there are different measurements of hardness: scratch hardness, indentation hardness, and rebound hardness.
Hardness is dependent on ductility, elastic stiffness, plasticity, strain, strength, toughness, viscoelasticity, and viscosity. Common examples of hard matter are ceramics, concrete, certain metals, and superhard materials, which can be contrasted with soft matter. There are a large number of hardness testing methods available e.g. Vickers, Brinell, Rockwell, Meyer and Leeb). Although it is impossible in many cases to give an exact conversion, it is possible to give an approximate material-specific comparison table. The Vickers hardness test method consists of indenting the test material with a diamond indenter, in the form of a right pyramid with a square base and an angle of 136 degrees between opposite faces subjected to a load of 1 to 100 kgf. The full load is normally applied for 10 to 15 seconds. The two diagonals of the indentation left in the surface of the material after removal of the load are measured using a microscope and their average calculated. The area of the sloping surface of the indentation is calculated. The Vickers hardness is the quotient obtained by dividing the kgf load by the square mm area of indentation.
F = Load in kgf d = Arithmetic mean of the two diagonals, d1 and d2 in mm
HV = Vickers hardness
When the mean diagonal of the indentation has been determined the Vickers hardness may be calculated from the formula, but is more convenient to use conversion tables. The Vickers hardness should be reported like 800 HV/10, which means a Vickers hardness of 800, was obtained using a 10 kgf force. Several different loading settings give practically identical hardness numbers on uniform material, which is much better than the arbitrary changing of scale with the other hardness testing methods. The advantages of the Vickers hardness test are that extremely accurate readings can be taken, and just one type of indenter is used for all types of metals and surface treatments. Although thoroughly adaptable and very precise for testing the softest and hardest of materials, under varying loads, the Vickers machine is a floor standing unit that is more expensive than the Brinell or Rockwell machines
9. Scope Of Improvement This report addresses the problem of finding the radial stress within a powder body undergoing plastic deformation by confined compression, motivated by the compaction test for powdered materials. Small deformation, elastoplastic behavior is assumed, with porosity as the parameter governing the evolution of material properties. An elliptic yield surface is selected, whose aspect ratio approaches zero as full density is neared, so as to recover the Von-Mises criterion of plastic yield in ductile metals. The results were used to track the radial stresses on a notional compaction process, and applied to the design of an instrumented closed die.
A crucial point is the determination of an appropriate value for die wall thickness: too thin and it would collapse upon loading of the powder specimen; too thick and hoop strains could not be properly gauged. In the light of this, it is clear that some estimation of radial stress exerted by the powder body, which is undergoing uniaxial confined compression, is to be done in advance. In a first approximation to this problem the analysis of seemingly influential factors, such as die-wall friction and Non-uniformities within the specimen thereof – both in axial and radial directions-, is relinquished on behalf of mathematical tractability. That said, it was decided to turn to a yield surface expression devised for aluminum foams, deeming it as makeshift powdered material. The end result is a solution to the problem of uniaxial confined compression of a specimen of increasing relative density, where elastic stresses are stored up until plastic onset, dictated by the mentioned material model, occurs.
CLOSED DIE DESIGN Common constitutive equations for mechanical behaviour of granular bodies imply a joint evolution of axial stress, radial stress and porosity within the specimen, which must be traced out so that the resulting plots convey the desired material parameters. This is actually the problem whose solution is sought when designing a parameter identification rig. It will be henceforth regarded as Measuring Instrument, or just MI.
The upper punch load conveys an axial stress axial to the powder body. The die wall is rigid so that it is a kinematic constraint and a radial stress radial is developed. These two stresses allow for computing stress invariants p and q. Upper punch displacement data permits volumetric strain computation in turn.
Symmetrical Load Distribution on Punches:
The tool assembly on the press should be carefully centered, to warrant the punches being loaded as symmetrically as possible during compacting. For punches with circular or regular cross-section, their cross-sectional center of gravity can easily be brought in line with the center line of the press, and frictional forces act symmetrically upon their lateral faces. Achieving a symmetrical load distribution, on punches with unsymmetrical crosssections, is a more complicated affair. Their cross-sectional center of gravity can certainly be brought in line with the center line of the press, but frictional forces do not act symmetrically upon their lateral faces. Since those frictional forces cannot be calculated very accurately in beforehand, the optimal centering of the tool assembly on the press may constitute a serious problem. In a badly centered tool, punches get out of parallel with die and core rods when subjected to the compacting load. They scrape hard on die and core rods, causing excessive local wear which, if not detected and corrected in time, leads to a complete break-down of the tool. When loaded asymmetrically, thin and sleeve-like punches tend to bend elastically to such a degree, that clearances between them and the die wall get out of concentricity. At places of enlarged clearance, powder is being extruded into the gap, forming excessive burrs on the face of the compact. At places of narrowed clearance, punches scrape hard on die walls and core rods. This leads to excessive tool wear and increases the risk of jammed punches and broken core rods. An uneven density distribution adds to this effect.
Influence of Profiles:
For good functionality and long life of the various tool members it is important, not only to choose the right tool material but also to avoid profiles that provoke high stress peaks under load. Photo-elastic stress analysis with plexi-glass models can help to avoid unsuitable shapes and profiles. In particular, the following points shou ld be observed: • Avoid sharp corners and edges on the cross-sectional profiles of die, punches and core rods. • Avoid sharp-edged protrusions or incisions on punch faces. • Avoid core rod diameters smaller than 1/3- to 1/5 the length of the core rod‟s portion in contact with the powder. In order to avoid kinking under load, keep unguided portions of core rods and connecting rods as short as possible.
10. Conclusions
The Die which is designed as per our requirements can withstand a maximum pressure of 500 MPa and it will be safe under any value of tangential stresses upto 500 MPa.
The designed die can be used for the compaction of Aluminum powders, Aluminum powdered alloys as well as Ferrous Powders which require compaction pressure of about 450 MPa.
The fabrication process of the die which includes Turning, Drilling, Boring and Oil Quenching Processes has been carried out very carefully taking into consideration proper tolerances and allowances to each dimensions.
The calculated compressive strength of aluminum is 51 MPa which is very close to the data given in DESIGN DATA BOOK. Hence the designed die is efficient and produces close to exact results.
11. References
Höganäs Data Sheets. G. Bockstiegel, The Porosity-Pressure Curve and its Relation to the Size Distribution of Pores in Iron Powder Compacts, Proceedings of the 1965 International Powder Metallurgy Conference, New York, NY, USA. W. Schatt, Pulvermetallurgie, Sinter - und Verbundwerkstoffe, Dr. Alfred Hüthig Verlag, Heidelberg 1988. G. Bockstiegel, Einfluß des Vor - und Nachpressdruckes sowie der Sintertemperatur auf die Eigenschaften von Sinterteilen aus Eisenpulvern, Archiv für das Eisenhüttenwesen 28 (1957) 3, S.167 -177. W. M. Long, Powder Metallurgy, No. 6, 1960. G. Bockstiegel, Höganäs 1967. G. Bockstiegel und J. Hewing, Verformungsarbeit, Verfestigung und Seitendruck beim Pressen von Metallpulvern, 2. Europäisches Symposium über Pulvermetallurgie, Stuttgart 1968. G. Bockstiegel und J. Hewing, Verformungsarbeit, Verfestigung und Seitendruck beim Pressen von Metallpulvern, 2. Europäisches Symposium über Pulvermetallurgie, Stuttgart 1968. G. Bockstiegel, Höganäs 1967). Example: the yield point s0(T) decreases with increasing temperature T (T3 > T2 > T1). G. Bockstiegel, Höganäs 1967. G. Bockstiegel, Höganäs 1964. Höganäs Data Sheets. Courtesy: Dorst Maschinen- und Anlagenbau, Kochel a. See. Courtesy: Dorst Maschinen- und Anlagenbau, Kochel a. See. Courtesy: Dorst Maschinen- und Anlagenbau, Kochel a. See Illustration No. 6.16 in: W. Schatt, Pulvermetallurgie , Sinter- und Verbundwerkstoffe, Hüthig Verlag, Heidelberg (1988). H. Fischmeister and E. Exner, Metall 18, p. 113, (1965).
