ACKNOWLEDGEMENT I express my gratitude to chairman, project Review Committee, JNTU College of Engineering, for their valuable recommendations and for accepting this project work. I express my deep sense of gratitude towards my able and acknowledge guide, Mr. P.Srinivas, Asst. Professor, Mechanical Engineering , GRIET, Hyderabad, to whom I owe the credit of being the moving spirit behind this project, whose guidance and constant inspiration led me towards its completion. I convey my sincere thanks to Mr.K.G.K MURTHY, Head of the Mechanical Engineering Department & Mr.P.S.V.KURMA RAO Professor, GOKARAJU RANGARAJU INSTITUE OF ENGINEERING AND TECNOLOGY, HYDERABAD for his kind cooperation in the completion of the project. At this juncture, I feel that, I am grateful to Mr.SUNIL JAJU, PROPIETOR OF OMEGA INDUSTRIES, BALANAGAR, HYDERABAD, for assistance in completion of project work. Finally, I extend my sense of gratitude to all my friends, teaching and non teaching staff, who directly or indirectly help me in this endeavor.
L.Dinesh Reddy
(07241A0304)
R.shiva Kumar
(07241A0319)
B.Tharun Gautham Vishnu (07241A0323)
1
ABSTRACT
PRESS TOOLS The process of designing and developing auxiliary equipment, methods, and techniques required to improve efficiency and productivity of manufacturing, production with large production volumes and higher production speeds require special helper tools known as press tools. Manufacturing of dust cap is accompanied by two types of press tool operation namely blanking and drawing.
BLANKING It is a metal stamping operation by which the sheet metal is punched to get the required outer profile of the sheet metal component. During the blanking process the blanking punch penetrates into the sheet metal and forces the material into the blanking die. The portion of the sheet metal which comes out through the blanking die opening is the component with the required profile.
PIERCING Piercing operation consists of simple hole punching. It differs from blanking in that the punching (or material cut from stock) is the scrap and the strip is the work piece. Piercing is nearly always accompanied by a blanking operation before, after or at the same time.
DRAWING Drawing is a metal forming process involving pulling a workpiece (cold or hot) through a die providing reduction of the cross section of the workpiece.As the cross section decreases after passing each die, the length of workpiece increases, requiring corresponding increase of the speed.
2
S.no List of figures
Page no
1
Blanking die
24
2
Top view of die plate
25
3
Top view of punch plate
26
4
Front view of tool
27
5
Tool fixed in press machine
28
6
Metal sheet feeding into press
29
7
c-type(open back inclined press)
30
8
Metal planning diagram for drawing die
31
9
Tool plan for drawing die
31
10
Top view of drawing die
39
11
Bearing cup
43
12
Metal sheet for component
52
13
Strip layout
53
14
Bearing cup
59
15
3D model of bearing cup in catia
58
3
S.no List of figures
Page no
1
Bill of materials for blanking die
45
2
Bill of materials for piercing die
47
3
Bill of materials for drawing die
49
4
Blanking die manufacturing costs
54
5
Piercing die manufacturing costs
54
6
Drawing die manufacturing costs
54
7 8
54
Cost analysis
S.no
APPENDIX
Page no
1
Bush
25
2
Die plate
25
3
Pillar
25
4
Pillar set1
25
5
Pillar set2
26
6
Punch
26
7
Punch bottom holder
27
4
8
Punch holder
27
9
Standard Punch
27
10
Stripper plate
15
5
NOMENCLATURE
S no
Name
Symbol
1
Bend radius
2
Punch radius
R r
3
Bend allowances
A
4
Die clearance
C
5
Perimeter of the blank
L
6
Stock thickness
T
7
Shearing strength
S
8
Bend angle
N
9
Span
L
10
Shearing constant
K
11
Ultimate tensile strength
Su
12
Maximum deflection
U
6
INDEX S.NO
TITLE
PG-NO
Acknowledgement
1
ABSTRACT
2
List of figures
3
Nomenclature
6
Introduction 6-7 1
Introduction To Die Elements
9
1.1 Die to Press Relationship
10
1.2 Die Sets
11
1.3 Strippers
15
1.4 Blanking operation
17
1.5 Piercing operation
23
1.6 Drawing operation
31
2
Spring Back Forces
40
3
Statement of problems
43
4
Design calculations
45
5
Drawing calculations
45
6
Strip Layout
53
7
Cost analysis
54
8
Conclusion
55
9
Appendix
56
7
INTRODUCTION PRESS TOOL Press Tool is a set of plates with a relief, or depth-based design, in them. The metal is placed between the plates, and the plates are pressed up against each other, deforming the metal in the desired fashion. This may be blanking or piercing or drawing or forming or coining etc. There are different types of press machines: Some of them are 9 C-type( fixed type & open back inclinable press) 9 Single action straight side press 9 Typical Hydraulic press
BEARING CAP A bearing cap can be described as a number of things, but the most common reference is the part of the engine block which contains the main bearings of a crankshaft. In an engine block, the part of the engine that the crankshaft runs through is split. Once the main caps are removed, the crankshaft can be set in the block on top of one-half of the main bearings. The other half of the main bearings are in the bearing cap and are placed in order onto the crankshaft and the corresponding other half of the main saddle. The bolts are then torque to specification, thereby holding the crankshaft in place.
Piston rods also use a bearing cap to hold the piston rod onto the crankshaft. Like the main bearings, the piston rod is split into two pieces: the rod and the cap. The rod bearings are divided into two pieces, with one half of the bearing going into the bottom of the rod and the other half going into the rod cap. The rod is slid into location onto the crankshaft rod through the journal. The rod bearing cap is placed onto the bottom of the rod and around the crankshaft, completing the union of the piston rod and the crankshaft with the connecting rod bolts being torque to specification. 8
INTRODUCTION TO DIE ELEMENTS
Die: A Die is an assemblage of parts used for producing different sheet metal components . The Die is also called press tool as the dies are used on different types of presses based on the cutting forces required for the component. In this project a blanking die , piercing die , drawing die is produced for production of Bracket used in supporting the fuel tank of an automobile. Before venturing into making of die , the die making depends on many factors . Below given are the important points regarding die to press relationships , die sets , strippers.
2.1 Die to press relationships: Press Shut height: The press shut height is always measured with the press stroke with the bottom dead center position. In considering maximum shut heights, the ram adjustment is up at its highest stroke down position. In considering minimum shut heights, the ram adjustment is down with the ram extended to its lowest position.
Capacity of press: The force in kilo new tons indicates the capacity of press ram can exert on work piece safely. If the capacity of force is expressed in tones of force, then it is referred as ‘press tonnage.
Feed Height: For dies, which are fed manually, the fed height is not critical. How ever, when dies are used in conjunction with automatic feeding devices, the height of the stock line of the die must be with in the range permitted by feeding device.
2.2 Die sets: Die sets were introduced by the mass production manufacturers such as automotive appliance, and business machine companies. 9
The die set is one of the basic tools of the stamping industry, and while not a glamour product, such as numerical controls, electrical discharge machines, and exotic metals, it is as vital to metal working as the tool bit, drill, reamer, and a grinding wheel
DIE SET The industries which manufacture die sets commercially compromises six national and eight to ten regional companies whose overall volume is relatively small in contrast to the importance of its product to metal working mass production. The die set industry operates through assembly branches or distributors on a national scale or locally with independent special die set manufacturers on a small scale.
Role of die sets in industry: A die set can be considered as a sub unit considering of an upper shoe and lower shoe, together with guideposts and brushings by means of which the shoes are aligned .The punch and die components are mounted on the inner surface of the die set to complete the finished punch-press tool. A component is secured to a sidewall of one or both of the shoes. Such cases usually require special machining of the sidewall to provide a mounting surface. 10
Purpose of die sets: The purpose of the die set is to utilize the entire die assembly. Some of the advantages realized by assembling die components to a properly selected die sets are: 1.
Accuracy of the setup: The die can be installed in the press as a self-contained unit, assuring proper alignment of the various punch and die members.
2.
Improved piece-part quality: The quality of the work produced is enhanced by the assured setup accuracy.
3.
Increased die life: This is a result of proper alignment.
4.
Minimum setup time: Setup time is kept to minimum because the die is installed as a unit.
5.
Facilitation of maintenance: Die components can be removed and reassembled without disturbing their relationship to each other. Cutting components can be sharpened in assembly, as units without removing them from die set. This can be distinct advantage over removing the components and sharpening them as separate pieces.
6.
Alignment of punch and die members: A die set can be a means of keeping the punch and die members properly during the working process. However, a die set cannot be expected to compensate foe a punch press, which is not in good condition. Neither should a die set be expected to operate satisfactorily if heavy, unbalanced work forces exist. Such loads should be compensated for in the design of the die; they should not be transferred to the guide posts and bushing of the die set.
7.
Facilitation of storage: On completion of the production run, the die can be stored as a unit ready to be replaced in production again immediately. 11
Industrial uses and applications: 1.
Primarily foe mental working in “capacitive” pressrooms and contract job-shops.
2. 3.
Also used in plastics, die casting, paper and fiber, and other industries.
12
Terminology pertinent to die sets: The following terms are either directly pertinent or closely related to die sets:
1.
Die shoe: The die set base is called the die shoe. This remains true even though punches are sometimes mounted on this lower shoe. The great majority of standardized die sets have the guideposts in the die shoe.
2.
Punch holder: The die set type member is called punch holder. This remains true even though die blocks are sometimes mount on this top member. The great majority of standardized die sets have the guide bushings mounted in the punch holder.
3.
Shank: Most punch holders in the smaller sizes are made with the shank, which fits the clamping hole in the lower end of the punch press holder to ram. These shanks are generally an internal part of the punch holder.
4.
Guideposts: Guideposts are cylindrical pins, which provide a means of alignment for the die set.
5.
Guidepost bushings: These are installed in the opposing whole and engage the guide posts with a closing fit. The posts and bushings, acting together, align the die sets.
6.
Flange: A ledge which is flush with the bottom surface of a die shoe or the top surface of a punch holder. The ledge extends beyond the die area to provide a means for clamping the choke member to the bolster plate or press ram, which is appropriate. Flanges are more commonly provided on the die shoes on the punch holders.
7.
Die area: The area is available on the top surface of the die whole and the lower surface of the punch holder for the mounting of punch and dies components. The die set guideposts and bushings are normally located outside this area.
Materials from which die sets are made: 1.
HCHC
2.
Mild steel CR. 13
Types and styles of die sets: Die sets are generally classed in two categories.
1. Catalog sets: Advances in die sets design have brought about an almost endless choice of catalog types and styles within a limited size rang which are produced by commercial manufacturers of die sets and stocked for fast assembly with pins bushings. In addition to these catalog sets, die set manufacturers can produce any practical type and size of die set the die designer specifies, usually at lower cost than would result from in plant manufacturing.
a.
Back post: Two guideposts are located toward the back of the set.
b.
Center post: Two guideposts at the left and right sides of the set on the shank centerline. The two guideposts should differ in diameter in order to foolproof the set.
c.
Diagonal post: Two guideposts, one located at the right corner and the other at the left corner. These sets can be supplied with reversed guidepost locations, the two guidepost diameters must differ in order to foolproof this type of set also.
d.
Four post: One guidepost located at each of the four corners of the die set. One guidepost center must be offset for fool proofing.
2. Special sets: A special die set is one, which differs in anyway from the standard catalog specifications. Special die sets are made to order. They may be similar to catalog sets, or they may be radically different. Special die sets may have pockets, slots, or cutout areas. These may be rough in or completely finished by the die set manufacturer.
Die sets are [through] stress relieved by the manufacturers before finishing rough machining of deep pockets cut outs etc should be done by the die set manufacturer before the stress relieving 14
operation, if residual stresses are not removed, they will be gradually released in service. This can be the source of distortion and dimensional changes, which can have serious consequences.
Surface finishes on die set components: 1.
Punch and die holders: Top and bottom surfaces of these parts are usually ground, with
some manufacturers finishing surface – ground finish for ease of layout on the working areas where shank are cast integral or welded, the shanks have a smooth turned finish. 2.
Guide pins: Most guide pins are ground with a 20in. finish, but major manufacturers of the
die sets now improve this finish to 9in., which is ideal for wear and lubrication qualities required in the operating die sets. 3.
Bushings: Press fit or slip fit diameters on bushings are also ground with a fine finish, but
only to simplify insertion into holes in the punch holders. The ID of the bushing is ground smooth but always honed or lapped to a smooth finish when fitted to the guide pins.
2.3 Strippers: Strippers is the act of removing the work from the punch or punches. A stripper is a device for stripping.
STRIPPER PLATE 15
Materials required for stripping plates:
Choice of material for stripper plate depends upon the cost and quality factors pertaining to each specific instance. In the majority of box stripper applications, the stripper plate is made of low-carbon steel, left soft. Both cold drawn and hot rolled steel are used.Plain stripper plates are often made from cold drawn steel, because it is well suited to this type of stripper construction and because its initial cost is low. Also, machining time is minimized. Channeled plates and offset plates are also often made from cold drawn steel The following materials listed in descending order of quality and durability are commonly employed for making stripper plates,
1.
Tool steel, hardened
2.
Pretreated alloy steel
3.
Tool steel, left soft
4.
High strength, low alloy steel
5.
Hot rolled low carbon steel, including low carbon ground stock
6.
Cold drawn low carbon bar stock, commonly called cold rolled steel
Stripping Force for Blanking and Piercing: Accurate calculations of stripping force requirements can be made. There are so many visible factors involved that an accurate calculation must be a highly specialized computation for a specified job.
16
Important factors which affect stripping force: 1.
Stock material: Material, which have a high friction value and material, which tend to cling more and more difficult to strip.
2.
Conditions for cutting edges: When the cutting edges are sharp, less stripping effort is required.
3.
Surface condition of side walls: A punch which has a smooth finish on its side walls strips more easily than a punch which is not as smooth.
4.
Distance between punches: More effort is required to strip punches that are close together.
17
2.4 Blanking die:
Blanking : Blanking is used to produce blanks of desired contour and size by cutting them out of the stock strip. Blank is the desired ‘piece part’ made by Blanking Die. The material. remaining after blanking is called as ‘scrap’.
Introductory Terminology:
Piece part: A piece part is the product of a Blanking Die. It may be complete product or it may be only the component of a product consisting of many and different parts. Stock material: It is the raw sheet metal from which the piece part is produced.
Die: The word Die has different meanings. * A complete Production Tool, the purpose of which is to produce piece parts consistently to required specifications. * The female part of a complete Die.
Punch: A punch is the male member of a complete die, which mates in conjunction with female die to produce a desired effect upon the material being worked. .A Die can be a simple Tool composed of punch, die block and stripper or float.
Stripper: Stripper is a device, which is used for stripping the piece part from the punch as the punch traverses in the reverse direction. 18
Pilot: Pilot is a locating device, which position the work or stock strip accurately for die working. When the pilots bring the work into the required position, it is said to be registered.
Shedder & Knockout: Shedder is a device, which acts to expel the work piece from the die cavity. Shedder actuation is done by means of Knockouts bars.
Nest gage: The next gage is a device, which is used to locate and position the work piece properly in the die.
Pushers: Pushers are installed for the purpose of holding the required edge or edges of the work securely in contact with the appropriate gauging member.
Die stops: Die stops are installed in dies for the purpose of arresting the feeding movement of the stock strip.
Shearing action: The result of the forces imposed on the stock material by the working of the blanking dies is a shearing action. The shearing action may be considered in three stages, which are important to the Die maker because of their direct relationship to the dimensional qualities and appearance of piece parts. They are also related to the effective working and life of the die.
19
Critical stages of shearing action
First stage – Plastic Deformation: The stock material has been placed on the die, the press has been tripped, and the punch is being driven toward the die. The punch contacts the stock material and exerts pressure upon it. When the elastic limit of the stock material is exceeded, plastic deformation takes place.
Second stage – Penetration: As the driving force of the ram continues, the punch is forced to penetrate the stock material, and the blank or slug is displaced into the die opening a corresponding amount..
Third Stage – Fracture: Further continuation of the punching pressure causes fractures to start at the cutting edge of the punch and the die. These are points of greater stress concentration. Under the proper cutting conditions the fractures extend toward each other and meet. When this occurs, the fracture is complete and the Blank or Slug is separated from the original stock material. The punch then enters the die opening pushing the blank or slug slightly below the die cutting edge.
Cutting Clearance:
20
Cutting clearance is the space between a side of the punch and the corresponding side of the die opening at the cut edge when the punch is entered in the die opening. Cutting clearance should be thought of and expressed as the amount of clearance per side. Proper cutting clearance is necessary to the life of the die and the quality of the piece part. Excessive cutting clearance results in objectionable piece-part characteristics. Insufficient cutting clearance causes undue stress and wear on the cutting members of the tool because of the greater punching effort required.
Angular clearance: Angular clearance is a draft or taper applied the side walls of a die opening in order relieve internal pressure of the blank slug as it passes through the opening. In any Blanking or Piercing operation where the blank passes through die, it is imperative that angular clearance be provided on the sidewalls of the die opening. The importance of angular clearance cannot be over emphasized. The ‘Blank-through’ type of the die will not run successfully unless there is relieve for the pressure developed with in the die opening by the blanks or slugs as they are through. This pressure can build up rapidly. Failure to relieve it causes distortion and burring the material passing through the die opening and culminates in pressure accumulations so great that punches break and die blocks burst.
Angular clearance should be expressed in terms of the amount of clearance per side. The optimum angular clearance for any die opening depends upon the type of material to be run, production requirements and the method of die construction. The strength of cutting members also influences the amount of angular clearance to be used.
Typical Appearance Characteristics: 21
The appearance characteristic of material that has been blanked or pierced depends on the amount of clearance between the punch and die and alignments of punch with die opening.
Optimum cutting clearance: The blank or slug has been made under optimum cutting conditions. The edge radius is the result of the initial plastic deformation, which occurred during the first stage of the shear action. The highly burnished band, resulting from the second stage of the shearing action the cut band. The width of the cut band is approximately 1/3 the thickness of the stock material. The balance of the cut is the brake, which results from the third stage of the shearing action.
Burr side: The burr side is adjacent to the break. Burrs should be practically non-existent if the cutting clearance between the punch & the die is correct and if the cutting edges are sharp. In fact, when a die is running in production, the degree of burr on the piece part is an indication whether the die is ready for sharpening. The burr side of a blank or slug is always toward the punch. The burr side of a punched opening is always toward the die opening.
Excessive cutting clearance: The comparatively large space between the punch and die cutting edges allows the stock materials to react to the initial punch pressure in a manner approaching that of forming rather than cutting. The stock material has been forced into the clearance space, and when the break occurs, large burrs are present at the break edge.
22
2.5 Piercing die:
Piercing: This operation consists of simple hole punching. It differs from blanking in that the punching (or material cut from stock) is the scrap and the strip is the work piece. Piercing is nearly always accompanied by a blanking operation before, after or at the same time.
23
Introductory Terminology:
Piece part: A piece part is the product of a Blanking Die. It may be complete product or it may be only the component of a product consisting of many and different parts. Stock material: It is the raw sheet metal from which the piece part is produced.
Die: The word Die has different meanings. * A complete Production Tool, the purpose of which is to produce piece parts Consistently to required specifications. •
The female part of a complete Die.
Punch: A punch is the male member of a complete die, which mates in conjunction with female die to produce a desired effect upon the material being worked. .A Die can be a simple Tool composed of punch, die block and stripper or float.
Stripper: Stripper is a device, which is used for stripping the piece part from the punch as the punch traverses in the reverse direction.
24
TOOL DIAGRAMS FOR COMPOUND DIE
TOP VIEW OF THE COMPOUND DIE
25
FRONT VIEW OF DIE PLATE
26
TOP VIEW OF PUNCH PLATE
27
FRONT VIEW OF THE COMPOUND DIE
28
DIE PLACED IN MACHINE
29
METAL STRIP PLACED IN A DIE
30
OPEN BACK INCLINED PRESS 31
Drawing Fundamentals of Drawing • A flat blank is formed into a cup by forcing a punch against the center portion of a blank that rests on the die ring. • The progressive stages of metal flow in drawing a cup from a flat blank are shown schematically in Fig. 1.
• During the first stage, the punch contacts the blank (Fig. 1a), and metal section 1 is bent and wrapped around the punch nose (Fig. 1b). Simultaneously and in sequence, the outer sections of the blank (2 and 3, Fig. 1) move radially toward the center of the blank until the remainder of the blank has bent around the punch nose and a straight-wall cup is formed (Fig. 1c and d). • During drawing, the center of the blank (punch area, Fig. 1a) is essentially unchanged as it forms the bottom of the drawn cup. The areas that become the sidewall of the cup (1, 2, and 3, Fig. 1) change from the shape of annular segments to longer parallel-side cylindrical elements as they are drawn over the die radius.
• Metal flow can occur until all the metal has been drawn over the die radius, or a flange can be retained.
Fig. 1 Progression of metal flow in drawing a cup from a flat blank 32
Types of drawing •
Drawing is a method of forming under compressive and tensile conditions whereby a sheet metal blank is transformed into a hollow cup, or a hollow cup is transformed into a similar part of smaller dimensions without any intention of altering the sheet thickness.
Single draw drawing
Redrawing
Reverse drawing
Hydro mechanical drawing
1) Using the single-draw drawing technique it is possible to produce a drawn part from a blank with a single working stroke of the press (Fig).
Fig: Single-draw drawing with blank holder
2) In case of large deformations, the forming process is performed by means of redrawing, generally using a number of drawing operations.(Fig)
33
Fig: Re-drawing with telescopic punch 3)This can be performed in the same direction by means of a telescopic punch or by means of reverse drawing, which involves the second punch acting in opposite direction to the punch motion of the previous drawing operation
(Fig).
Fig: Reverse Drawing •
The most significant variation of drawing is done with a rigid tool.
•
This comprises a punch, a bottom die and a blank holder, which is intended to prevent the formation of wrinkles as the metal is drawn into the die.
•
In special cases, the punch or die can also be from a soft material.There are drawing methods which make use of active media and active energy.
•
Drawing using active media is the drawing of a blank or hollow body into a rigid die through the action of a medium. Active media include formless solid substances such as sand or steelballs, fluids (oil, water) and gases, whereby the 34
forming work is performed by a press using a method similar to that employed with the rigid tools. 4) The greatest field of application of this technique is hydro mechanical drawing, For example for the manufacture of components from stainless steel .(Fig.)
Fig-Hydro mechanical drawing
Materials for Drawing
•
Sheet steels and other sheet metals with higher strengths and better formability have recently become available.
•
Other metals and alloys that can be deep drawn include aluminum and aluminum alloys, copper and alloys, some stainless steels, and titanium.
•
Low-carbon sheet steels are the materials that are most commonly deep drawn and are commonly used, for example, in the Automotive industry. Materials such as 1006 and 1008 steel have typical yield strengths in the range of 172 to 241MPa (25 to 35 ksi) and elongations of 35 to 45% in 50 mm (2 in.). These materials have excellent formability and are available cold or hot finished in various quality levels and a wide range of 35
thicknesses. Table 4 lists mechanical properties of the various qualities of carbon steel sheet.
Types of drawing •
Drawing is a method of forming under compressive and tensile conditions whereby a sheet metal blank is transformed into a hollow cup, or a hollow cup is transformed into a similar part of smaller dimensions without any intention of altering the sheet thickness.
Single draw drawing
Redrawing
Reverse drawing
Hydro mechanical drawing
1) Using the single-draw drawing technique it is possible to produce a drawn part from a blank with a single working stroke of the press (Fig).
Fig: Single-draw drawing with blank holder
36
2) In case of large deformations, the forming process is performed by means of redrawing, generally using a number of drawing operations.(Fig)
Fig: Re-drawing with telescopic punch 3)This can be performed in the same direction by means of a telescopic punch or by means of reverse drawing, which involves the second punch acting in opposite direction to the punch motion of the previous deep-drawing operation (Fig).
Fig: Reverse Drawing
• The most significant variation of deep drawing is done with a rigid tool.
37
• This comprises a punch, a bottom die and a blank holder, which is intended to prevent the formation of wrinkles as the metal is drawn into the die. • In special cases, the punch or die can also be from a soft material.There are deep drawing methods which make use of active media and active energy. • Deep drawing using active media is the drawing of a blank or hollow body into a rigid die through the action of a medium. Active media include formless solid substances such as sand or steelballs, fluids (oil, water) and gases, whereby the with the rigid tools. 4) The greatest field of application of this technique is hydro mechanical drawing, For example for the manufacture of components from stainless steel .(Fig.)
Fig-Hydro mechanical drawing
38
Materials for Drawing •
Sheet steels and other sheet metals with higher strengths and better formability have recently become available.
•
Other metals and alloys that can be deep drawn include aluminum and aluminum alloys, copper and alloys, some stainless steels, and titanium.
•
Low-carbon sheet steels are the materials that are most commonly deep drawn and are commonly used, for example, in the Automotive industry. Materials such as 1006 and 1008 steel have typical yield strengths in the range of 172 to 241MPa (25 to 35 ksi) and elongations of 35 to 45% in 50 mm (2 in.). These materials have excellent formability and are available cold or hot finished in various quality levels and a wide range of thicknesses. Table 4 lists mechanical properties of the various qualities of carbon steel sheet.
39
TOP VIEW OF DRAWING DIE 40
Spring back:
Variation of bend-stresses causes spring back after drawing. The largest tensile stress occurs in the outside surface metal at the bend. The tensile stress reduces toward the centre of the sheet thickness and becomes zero at neutral axis. The pie shaped sketch in figure depicts the changing tensile and compressive stresses in the bend zone. Since the tensile stresses go from zero at point O on the neutral axis to a maximum value at point X on the outside surface, the stress-strain curve developed is the standard tensile test may be used for analysis of drawing.
Figure 17 Spring back forces
The metal nearest the neutral axis has been stressed to values below the elastic limit. The metal creates a narrow elastic band on both sides of the neutral axis, as shown in above figure. The metal farther away from the axis has been stressed beyond the yield strength, however, and has been plastically or permanently deformed when the doe opens, the elastic band tries to return to the original flat condition but cannot, due to restriction by the plastic deformation zones. Some slight return does occur as the elastic and plastic zones come to equilibrium, and this return is known as spring back. 41
The spring back forces about point O as created by the elastic metal are also depicted. Actually, plastically deformed metal has a very small elastic return characteristic, which adds to the spring back.
Overcoming Spring back: Several methods are used to overcome or counteract the effects of spring back. These are 1. Over drawing 2. Bottoming or setting 3. Stretch drawing
The sheet metal is often over bent an amount sufficient to produce the desired degrees of bend or bend angle after spring back. Over drawing may be accomplished by using cams, by decreasing the die clearance, or by setting the punch and die steels at a smaller angle than required in the case of a V-die. When the clearance is reduced below the sheet metal thickness, the burnishing action wipes the metal against an undersize punch or die steel. Over drawing is illustrated in following figures. Bottoming or setting consists of striking the metal severely at the radius area. This places the metal under high compressive stresses that set the metal past the yield strength. Bottoming is accomplished by placing a bead on the punch at the bend area. In a Wiping die or U-die, the pad must bottom against the shoe or backing plate so that the punch may set the metal at the bend. I t would be useless to bottom against the flat areas of sheet metal, since they are not stressed and do not cause spring back. Also, bottoming against these larger areas would require extremely high press tonnage.
Bottoming must be carefully controlled when adjusting the press ram or the forces involved will rise at a rapid rate. Also, if two blanks are accidentally placed in a drawing die that bottoms, press or die breakage may result. Stretch drawing consists of stretching the blank so that all the metal is stressed past the yield strength. The blank is then forced over the punch to obtain the desired contour. Very little spring back occurs due to this pre-stressing before drawing. Only relatively large radii are bent by this method, since sharp radii would take the pre-stressed metal beyond the ultimate tensile strength. The sheet metal must be uniform in strength. Stretch drawing is most frequently done with a special hydraulic machine rather than a die in a press.
42
Effects of burr side: The location of the burr side of the work piece can have an undesirable effect on drawing and forming dies. It is undesirable for the burr side to be located on the outer surface of the formed piece part, because the burr drags around the drawing radius and into the die opening. This condition causes excessive wear on the die members. In short order, the burrs wear grooves in the surface of the drawing radius and into the walls of the die opening. If however, the work piece is inverted so that the burr side is located on the inner surfaces of the formed piece part, the burrs will face toward the punch. Since there is no drag between the workpiece and the punch, the burr cannot erode the punch. This is, obviously, the desired condition, to be sought whenever possible. It is the source of the following expression, which may be considered a good rule to remember. When permissible, locate the burr side toward the inside of a form (or bend). Z dies and the like, which produce reverse bends in a single operation, are excepted from the rule.Important! In the above rule the emphasis is on the works when permissible. This is because the burr side of the piece part is often predetermined in accordance with the functional requirements of the piece part in relation to the end product. In such a case, the burr side is specified on the piece part drawing. It is then the normal obligation of the die maker to examine his die design drawings and verify that the die he is about to make will produce the piece part to specification. A burr side specification on the part drawing supersedes the possible deleterious effects of the burr on drawing or forming dies.
Edge condition of the work piece is known to be a factor, which can affect the degree of drawing possible for a given type of material. Smooth edges permit more severe drawing than rough edges. The burr side of a blank is contiguous to the break, and therefore, if the burr side is on the outer surface of the bend (tension side), the stock material will be more susceptible to the initiation of edge fractures in the bend area. While it is true that this condition is primarily concern of the product engineer, the die maker should recognize it also. In some cases where drawing is relatively severe, burr side location can be difference between fracturing and not fracturing. In doubtful cases, the burr side effect on the bend should be verified in advance, in order to assure compatibility of the cutting and forming (drawing) operations. 43
STATEMENT OF THE PROBLEM
3.1 Statement of the problem : To design and manufacture the dies (Blanking die, Piercing die, Drawing die) required for producing a bearing cup which is used for in asbestos sheet which we use as roof, for production of this bearing cup four materials (AISI 410, AISI 1300, Duralumin, High Brass) are chosen. . Cost analysis is proposed.
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DESIGN CALCULATIONS Blanking calculations : Shearing force for blanking operation: Shear force F= (K*L*T*S)/1000 TONS K =1.2 for normal clearance L = perimeter of the blank = 188.4 mm T =thickness of the stock strip = 1 mm S =shearing strength of mild steel = 21 kg/sq.mm Shearing force = (1.2*188.4*1*21)/1000 TONS = 4.7 TONS
Thickness 0f the die plate: Thickness of the die plate T = cube root of shearing force F = cube root of 4.7 = 1.68 cm = 16.8 mm = 17 mm
Thickness of the punch holder plate: Thickness of the punch holder plate = 0.75 T = 0.75 (17) = 12.75 mm = 13 mm 45
Thickness of the fixed stripper plate: Thickness of the fixed stripper plate = 0.5 T = 0.5(17) = 8.5 mm = 9 mm
Thickness of the top bolsters plate: Thickness of the top bolster plate = 1.25T = 1.25(17) = 21.25 mm
Thickness of the bottom bolster plate: Thickness of the bottom bolster plate = 1.75T = 1.75(17) = 29.75 mm
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Piercing Calculations: Shearing force for piercing operation: Shear force F= (K*L*T*S)/1000 TONS K =1.2 for normal clearance L = perimeter of the hole = 78.5 mm T =thickness of the stock strip = 1 mm S =shearing strength of mild steel = 21 kg/sq.mm Shearing force = (1.2*78.5*1*21)/1000 TONS = 2.6 TONS
Thickness of the die plate: Thickness of the die plate T = cube root of shearing force F = cube root of 2.6 = 1.38 = 1.4cm =14mm
Thickness of the punch holder plate: Thickness of the punch holder plate = 0.5 T = 0.5 (14) = 7mm
Thickness of the floating stripper plate: Thickness of the floating stripper plate = 0.75 T 47
= 0.75(14) = 10.5mm
Thickness of the top bolsters plate: Thickness of the top bolster plate = 1.25T = 1.25(14) = 17.5 mm
Thickness of the bottom bolsters plate: Thickness of the bottom bolster plate = 1.75T = 1.75(14) = 24.5 mm
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Drawing calculations : Shearing force for drawing operation: Shear force F= (K*L*T*S)/1000 TONS K =1.2 for normal clearance L = perimeter of the hole = 78.5 mm T =thickness of the stock strip = 1 mm S =shearing strength of mild steel = 21 kg/sq.mm Shearing force = (1.2*78.5*1*21)/1000 TONS = 1.2 TONS
Thickness of the die plate: Thickness of the die plate T = cube root of shearing force F = cube root of 3.6 = 1.54 = 1.5cm =15mm
Thickness of the punch holder plate: Thickness of the punch holder plate = 0.5 T = 0.5 (15) = 7.5mm
Thickness of the floating stripper plate: 49
Thickness of the floating stripper plate = 0.75 T = 0.75(15) = 11.25mm
Thickness of the top bolsters plate: Thickness of the top bolster plate = 1.25T = 1.25(15) = 18.75 mm
Thickness of the bottom bolsters plate: Thickness of the bottom bolster plate = 1.75T = 1.75(15) =26.25mm
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Compound tool calculations Total force required for the compound tool=shearing force for blanking operation+ shearing force for piercing operation+ total load required for drawing operation =4.7+2.5+1.2=6.21tons
STRIP LAYOUT Strip layout plays an important role especially in the case of the design of the press tool. Strip decides the economic utilization of the work piece and helps in the decrease of cost of the job and reduction in the production time by increasing the number of components. First method: Length of the stock strip = 684 mm Width of the stock strip = 115 mm Area of the stock strip = 684*115 = 78660 sq.mm Number of blanks obtained = 22 Area of one blank = 2826 sq.mm Area of 22 blanks = 22*2826= 62172 sq.mm Stock strip efficiency = area of all blanks obtained/ area of the stock strip = 62172/ 78660 = 0.79 = 79%
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Before Blank
52
Second method: length of the stock strip = 684 mm width of the stock strip = 64 mm area of the stock strip = 684*64 = 43776 sq.mm number of blanks obtained = 11 area of one blank = 2826 sq.mm area of 11 blanks = 11*2826 = 31086 sq.mm stock strip efficiency = area of all blanks obtained/ area of the stock strip = 31086/43776 = 0.71 = 71%
The FIRST method is chosen as it has higher stock strip efficiency. 53
COST ANALYSIS COMPUND DIE
Manufacturing time in hours
Manufacturing cost per hour
Amount in Rs
Conventional milling
12
100
1200
Grinding
10
100
1000
Jig Boring, Drilling and tapping
10
100
1000
CNC wire cut
5
320
1600
Lathe turning
6
100
600
Cylindrical Grinding
3
200
600
Total cost
6000
Other cost Allen screw, dowel pins, high tension rubber material are purchased from markets, including the raw material for making the die and the heat treatment of the material has been charged = Rs 3000 Total cost of the compound die = 6000 + 3000 = Rs9000
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CONCLUSIONS
1) The Bearing cup can be manufactured in 3 operations namely blanking operation, drawing operation, piercing operation. If we use unit dies, the total cost will be more and the time taken to manufacture will be more. So a compound die is used to manufacture the product where all the operations are performed in one stroke of the press. 2)
The total manufacturing cost of the Compound die is Rs 9000.
3)
The Compound die is used in the batch operation of 6000 units of bearing cup.
4) After the batch production of 6000 units, then the compound die is sent for machining so that it can be used again for the next batch production. 5)
The unit cost of the bearing cup is Rs 3.
6) The life of the compound die can be increased by machining the vital parts of the compound die which are the punch and the die. 7) The impact plate which is placed between the bottom bolster and punch holder is replaced if necessary to improve the die life. Also the high tension rubber material can be replaced if required.
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APPENDIX
DRAWING DIE 56
DRAWING PUNCH 57
BEARING CAP
58
BEARING CAP 59
BOTTOM PILLAR PLATE WITH PUNCH INSIDE STRIPPER 60
UPPER PILLAR PLATE AND DIE PLATE 61
STRIPPER PLATE
62
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