Press Tool for mechanical and manufacturing.pptx

press tool for manufacturing

1. Press Tool

2. Press

3. Topic to be covered: • • • • • • • • • • • • • Classification of presses, Classification of dies, Cutting actions in dies, Clearance, Cutting forces, Methods of reducing cutting forces, Minimum Diameter of Piercing Center Blanking, Piercing, Drawing, Bending and Progressive Die design, Scrap reduction, Strip layout. of Pressure,

4. In t roduction: • Press working has been defined a s a chipless manufacturing process metal. by which various components are made from sheet • Press working m e t a l f o r m i n g c o m p o n e n t b y operations are carried out with the help of a machine called applying force. press which shears or forms the • The main features of the press include a frame which supports a ram or a slide, a bed and source of power with a mechanism for operating the ram inline or at right angles to the bed. • The ram is equipped with sha p e o f t h e j o b t o t h e b e d . a punch or a set of punches which have the attached to be produced while a die block is

5. In t roduction: Workpieces are • produced or formed as the punch descends onto the die block. • Processed sheet metal components find extensive industrial and household applications such a s in manufacture of automobile and aircraft bodies, office appliances, kitchen ware, storage cabinets, furniture items, mechanical toys etc. • Press tool operation of sheet metal is by far the cheapest and fastest method of complete manufacture of components.

6. Advantages o f P r ess Working : Use of presses for sheet metal operations has the following advantages. 1. 2. 3. 4. 5. 6. 7. 8. 9. High productivity. Better accuracy. Uniformity of parts produced. Possibility of using lesser skilled labour. Low scrap losses. Predictable strength characteristics of the Reduction of weight. Considerable cost reduction. Possibility of automation. components.

7. Press Working Operations

8. Cutting Operations: I n c u t t i n g o p e r a t i o n s , t h e w o r k p i e c e i s u l t i m a t e s h e a r s t r e ng t h an d c u t o f f i n t o • stressed beyond its pieces. • The stresses involved in the process are shearing stresses • The common cutting operations u s in g dies and punches include the following : 1. 3. 5. 7. 9. Blanking T r i m m i n g N o t c h i n g N i b b l i n g P a r t i n g 2. 4. 6. 8. Punching or Shaving Lancing Perforating piercing 10. Shearing

9. Cutting Operations: 1.Bla n ki n g : contd ... • Blanking is the operation of cutting out flat intermediate shapes called blanks which are to be further processed to produce desired parts. • The sheet metal from which the blank is to be cut is to properly located over produce the required the die and a punch lowered into it cut. • Neglecting the small amount of spring-back that occurs when m a d e p i e c e the shearing force is removed, the s i z e of the hole in the sheet is the size of the punch while the cut out has a size equal to the die opening.

10. Cutting Operations: contd ... - P u nch h older c Fasten i ng bolts Metal stri p relief ang l e Die geed ~,a±us±EK[ S tri p p e r m t ! ! I I i ' L I l C ut off blank ' ' I \ '- Bol st er pla te of the pre ss Blanking set-up

11. Cutting Operations: 1.Bla n ki n g : contd ... • The die opening will be made of the required size of the blank while the punch will be made smaller by a n amount equal to twice the clearance between the punch and die. • The punch and die should be made of hard wear resistant m a t e r i a l s s u c h a s hardened high carbon steel, high chromium die steel or tungsten carbide. with a die relief angle or draft about 3 ° • The die is provided to 4° so that the cut piece falls freely through the die opening. The actual value of the draft used depends on the material thickness and shape.

12. Cutting Operations: 1.Bla n ki n g : contd ... • A stripper plate is provided to release the metal from the sides of the punch as it rises after completing the stroke. The sheet metal sticks on the punch due to the spring-back. • While p l a nn i n g a blanking operation between it is necessary to provide suitable clearances the adjacent blanks and the edge of the blank and the edge of the strip. • When a number of blanks are required to be cut from a given strip of metal a proper layout of such blanks may be helpful area. in determining the maximum utilization of sheet

13. Cutting Operations: contd ... - P u nch h older c Fasten i ng bolts Metal stri p relief ang l e Die geed ~,a±us±EK[ S tri p p e r m t ! ! I I i ' L I l C ut off blank ' ' I \ '- Bol st er pla te of the pre ss Blanking set-up

14. Cutting 2.Punchi n g Operations: or p i e r ci ng : contd ... • Piercing or punching is similar to piercing blanking except that the metal pieces cut out in are scrap. The interest in piercing is to produce a hole of a desired shape in the workpiece. • The size of size the of punch us e d in piercing is equal to the required the hole while the die opening is made larger by twice the desired clearance between the punch and die.

15. Cutting 2.Punchi n g Operations: contd ... or p i e r ci ng : hea r S hea r nu lh P u n ch jg (a) B l a n k i ng (b) Pierc i ng

16. Cutting Operations: contd ... 3.Trimmi n g : • Trimming remains is the process of removing excess metal which around parting lines metal after o p e r a t i o n s l i k e die casting, forging and sheet drawing. • Trimming is done by forcing the parts to be trimmed through trimming dies with a suitable punch. The operation is similar to a blanking operation. • The p r e ss e s us e d for trimming normally have a larger bolster plate area compared to those used for blanking.

17. Cutting Operations: S h avi n g : contd ... 4. • Shaving is similar to trimming except a ro un d that the amount of metal r e m ove d is much less 10% of the metal thickness. • S h av i n g i s do n e o n blanked or pierced work pieces to o b t a i n smooth, square edges with c l o s e r d i m e n s i o n a l tolerances. • Shaving dies use much lower clearances than blanking or punching dies.

18. Cutting Notc h i n g Notching Operations: : contd ... 5. • is the operation of making indentations at the edge of the work piece as shown in Fig. • A die and a notch. punch of a suitable shape are used to make the

19. Cutting Operations: L a n ci n g : contd ... 6. • In lancing as shown in Fig. a hole is partially cut in a sheet and the cut metal is bent on one side. Punch Dia

20. Cutting Operations: Nibb l i n g : contd ... 7. • Nibbling is the process of cutting irregular shapes from sheet m e t a l w i t h o u t us i n g a die and punch o f t h e corresponding shape. • When the number ar e s m a l l of pieces of a given shape to be produced production and the possibility of a repeat run is remote it becomes very uneconomical to corresponding shape. use dies and punches of the • Such jobs are handled on a n i b b l e r which uses a s m a l l round or triangular punch that reciprocates vertically in and out of a corresponding die producing a series of overlapping holes.

21. Cutting Operations: Nibb l i n g : contd ... 7. • The sheet metal is guided through the machine along the path desired. • The process is slow and the cut edges may need to be further dies. finished but it eliminates the need for costly special I I I I

22. Cutting Operations: contd ... 8. Perforating : i s t h e p r o c e s s o f m a k i n g a l a r g e n um b e r o f ve r y c l o s e t o e a c h o t h e r i n f l a t w or k p i e c e s . • Perforating small holes

23. Cutting Operations: contd ... 9 . P a r ti n g : • Parting is the operation in which metal is cut simultaneously along two parallel lines or contours in such a say that the side thrust is neutralised.

24. Cutting Operations: 1 . She a ri n g : contd ... • Shearing straight is a g en e r a l purpose shearing o p e r a t i o n a l o n g lines mostly for cutting small pieces from large sheet stock. • G e n era l p u r p o s e shearing operations u se straight line shearing for cutting. • The machines used for the purpose can be divided into 1.Square shear 2.Rotary shear

25. Cutting Operations: contd ... 1 . She a ri n g : • The square Fig. shearing operation is shown schematically in • The work piece is sheared between two blades. The lower moves blade is fixed to the machine while the upper blade up and down with the ram of the machine. St o p Wor k piece L owe r bl ade

26. Cutting Operations: 1 . She a ri n g : contd ... • Rotary shearing is shown in Fig. In this c a s e shearing is done with rotating disc blades. T h e f o r c e s in vo l ve d ar e l o w e r i n t h i s c a s e • and the length of the sheet does not pose any problem. Up p er d i sc blad e I ' W or kpiece w , l- w , -+- w , . l w , 4 -- - O ri g in al width of the stri p ....,._ - L ower d i sc bl a d e

27. Bending Operations : • T h e operations for bending can b e divided into four categories: 1.Angle bends 2.Roll bending 3.Roll forming 4.Seaming - single, double or straight

28. Bending Operations: A n g l e bendi n g : contd ... 1. • Angle bending is the process in which the sheet is bent through an angle. • If the angle of bend is less than 90°, the bend is called single bending. • For 90° angle the bend is called straight bending. • If a n angle less than 90° is produced at two places, the operation as called double bending.

29. Bending Operations: 2. Rol l bendi n g : contd ... • Roll bending is the process in which sheet is bent in the form of rolled edges.

30. Bending Operations: Rol l formi n g : contd ... 3. • Roll for m i n g is the process of bending the sheet between rolls. • The process may also be used to form any impression in the form of a bend.

31. Bending Operations: Sea m i ng: contd ... 4. • S e a m i n g i s the process of providing a mechanical lock between the edges of two different workpiece. • The edges of the two workpiece are bent in appropriate direction, assembled and pressed to from the seal.

32. Bending Operations: D i e B en d i n g : contd ... • Die bending is used for long straight line bends on press brakes. It may be further divided • into- 1. 2. V-bending and Edge bending.

33. Bending Operations: V-ben din g : V-bending is done with a wedge shaped punch contd ... 1. • pressing the sheet into a V-shaped die as shown in Fig. type • The die. die us e d may be of the air bend or a bottoming D i e • The process is used to produce sharper and more accurate bends i n t h i n n e r s h e e t s . V-bending c a n b e us e d for producing included angles which are acute, 90° or obtuse.

34. Bending Operations: Edg e B en d i n g : contd ... 2 . • Edge bending shown in Fig. is a cantilever type of bending operation in which the punch forces the sheet metal over the edge of a supporting die. • A spring loaded pad clamps the sheet against the die block lifted before during the the punch contacts punch travel. it to prevent is from being Pessure p e d - Punch Die ] W or kpiece j+ Die undercu t to a l low ove r bendin g

35. Press Working Terminology : • - Ba ck up plat e . • _- Punch pad . .. Punch p late • G u de b usn n g - -- -- --- Punch -- G uid e p o st --- ------ - - -- s , _ -" " w _--- S t o ck gui de • _ --- Blank .c Packi n g ---• D i e sho e . " - B olster Die ret ain er -• hdtell [yg t lff} _ h , hbh • p l a t e 19t ' BHase ar bed ot t he press

36. Press Working Terminology: Bed : contd ... 1. • w.a _-- Sh ank ~ - Back u p plat e hyvyhhfww - Linh pgtd Bed is p r e s s . w h i c h the lowest part of the It acts as a table plats on is the bolster .c _- Punch .,.,.-·· Punch p late ---' I .,-• mounted. " - _--- S t o ck gui de - G uid e post - == s ,, [ _ - _.-- Blank S tr p per + Pac kin g --7 B olster plat e l Ba se or bed o t t he press

37. Press Working Terminology: contd ... 2 . • B ol s ter pl a te : w.a _-- Shank ~ - Backup plate hyvyhhfww - Linh pgtd It is a thick plate attached to the bed of the press. .c .,.,.--· _- Punch , " -- stoe ouie Punch plate -- - ' I .,-• • It is used for locating the and die - Guide post 59 ,,I - aee l supporting assembly. Strpper + usually 50 to It is Packing --7 150 mm thick. Bolster plate l Base or bed ot t he press

38. Press Working Terminology: Die h ol der: contd ... 3 . • w.a _-- Shank ~ - Backup plate hyvyhhfww - Linh pgtd Also called die retainer or die shoe it is u s e d to hold the die block in proper .c .,.,.--· _- Punch , " -- stoe ouie Punch plate -- - ' I .,-• alignment with the punch. - Guide post 59 ,,I - aee l Strpper + • It is mounted on the bolster plate. Packing --7 Bolster plate l Base or bed ot t he press

39. Press Working Die block: Terminology: contd ... 4 . • _-- Sh ank w.a It is the female part of the ~ - Back up plat e hyvyhhfww - Linh pgtd die set having an suit the punch. It opening to i s ma d e o f r e s i s t a n t h a r d e n e d .c .,.,.--· _- Punch , " -- st oe oui e Punch p late -- - ' I .,-• a hard wear - G uid e post 5 9 ,,I - aee l material such a s S tr p per + high carbon steel, steel high or Pac kin g --7 chromium die tungsten carbide. B olster plat e l • The die die is provided with a B a se or bed o t t he press relief angle or draft about 0.75° p i e c e s f a l l so that the cut freely through the die opening.

40. Press Working Stripper: Terminology: contd ... 5 . • w.a _-- Sh an k ~ - Ba ckup plat e hyvyhhfww - Linh pgtd Strippers prevent are the u s e d to sheet metal from coming up with the .c .,.,.--· _- Punch G uid epost , see o de Punch p late -- - ' I l_ ., - • punch when it returns after • 82 ,] the working stroke. aee l Str p per + Packing --7 • Strippers may be fixed or spring loaded and may also Bolster plate guide the sheet. I Base or bed ot t he press

41. Press Working Terminology: Stock guides and packing: contd ... 6 . • _-- Sh ank w.a T h e s e a r e u s e d to ensure ~ - Back up plat e hyvyhhfww - Linh pgtd that during feeding between e a c h operation the stock is .c .,.,.--· _- Punch " , -- s oc @vi e Punch p late -- - ' I .,-• guided properly to ensure - G uid e post 5 9 ,,I - aee l accurate location fo r ea c h S tr p per + successive component. Pac in g -- • Stock o f t e n after strip stops u s e d ea c h and pilots are t h a t t h e B olster plat e to ensure l operation B a se or bed o t t he press is moved through correct distance and located properly operation. for the next

42. Press Working Terminology: contd ... 7 . • P u n ch P u n c h o f t h e : w.a _-- Sh ank ~ - Back up plat e hyvyhhfww - Linh pgtd is the male member die set which forces the sheet strip down to .,., . - - · - - .c _- Punch Punch p late -- - ' I .,-• pierce or form it. , " -- st oe oui e - G uid e post 5 9 ,,I - aee l S tr p per + • Like the die it is also made Pac kin g --7 of a hard wear resistant material. B olster plat e l • It is attached to the ram B a se or bed o t t he press through holders devices design. suitable and depending punch fastening upon its

43. Press Working Terminology: contd ... 8 . • Punch r eta i ne r o r punch pad Punch retainer or punch pad : i s in w.a _-- Shank ~ - Backup plate hyvyhhfww - [In pgtd u s e d for holding the punch Gude busnn Punch plate -- - ' its proper relative position. .c .,.,.--· _- Punch I .,-• " - Guide post 59 ,,I ,-- stoe ouie - aee l • It may be holder. bolted to the punch Strpper + Packing --7 Bolster plate l Base or bed ot t he press

44. Press Working Terminology: P r essure pl ate : contd ... 9 . • w.a _-- Sh ank ~ - Back up plat e hyvyhhfww - Linh pgtd A p r e ss u r e p l a t e or backup provided plate is usually t h e p u n c h G u de bu snn Punch p late -- - ' between and the .c .,.,.--· _- Punch , " -- st oe oui e I .,-• punch holder to provide some - G uid e post 5 9 ,,I - aee l cushioning effect. S tr p per + Pac kin g --7 • It distributes the pressure over a wider area of the punch B olster plat e holder reducing any possibility l of i t s g e t t i n g crushed under B a se or bed o t t he press heavy load.

45. Press 1 . P u nc h Working h o l d e r: Terminology: contd ... w.a _-- Sh ank ~ - Back up plat e hyvyhhfww - Linh pgtd • Punch holder is provided to it hold the punch and connect G u de bu snn Punch p late -- - ' to the ram of the press. .c .,.,.--· _- Punch , " -- st oe oui e I .,-• - G uid e post 5 9 ,,I - aee l • On its top it ends up in a shank S tr p per + that exactly fits into the ram Pac kin g --7 opening for proper positioning and aligning of the punch. B olster plat e l B a se or bed o t t he press

46. Press 1 1 . Guide Working Terminology: posts : contd ... w.a _-- Shank ~ - Backup plate hyvyhhfww - Linh pgtd • Guide provide posts are u s e d to proper alignment Gude busnn between the die shoe and the punch holder. .c .,.,.--· _- Punch - Guide £o Punch plate -- - ' I .,-• l 59 ,,I , " -- stoe ouie - aee l Strpper + • Guide bushes are provided at Packing --7 the top of the guide posts. Bolster plate • These bushes are mounted on l t h e p un c h holder and slide Base or bed ot t he press over the guide posts.

47. Types of Presses

48. Types of Presses : 1.Based o n source of power Presses: Manually operated presses are the hand, • Manual ball or fly presses. Power presses: Power presses can be further mechanical or hydraulic presses. classified into •

49. Types of Presses : 2.Based o n method of act u ation of s l ides : contd ... • Based o n t h e d ev i c e s use d in mechanical presses for converting rotary motion of the main shaft to linear motion of the crank the presses can be divided into 1.Crank operated press 2.Cam press 3.Eccentric press 4.Screw press 5.Rack and pinion press 6.Knuckle joint press 7.Toggle joint press.

50. Types of Presses : contd ... 3.Based o n n u mber of s l ides : 1.Single action press 2.Double action press 3.Triple action press

51. Types of Presses : 4.Based o n Type of frame used contd ... : 1.Back inclinable C Frame 2.Gap bed press 3.Adjustable bed press 4.Horn Press 5.Straight side press 6.Arch press 7 .Tie rod type press 8.Pillar type press

52. Types of Presses 5.Based o n E n d use : : contd ... • Most machines are capable of doing a variety of work. • Only some job. machines are designed for a particular type of • These machines are known by their end use

53. Types F l y P ress : of Presses : contd ... F l y weight er b all B a ll / A rm S t o p • Typical press. example of a mechanical Handle for o pera ting th e press Nut S c rew - Joint o f screw with ram G u i d e Fra m e hand • This press is operated by [ arm T Punch - B l ank ~mp, Di e _- - - Base and can be used for performing most of the sheet metal operations on a small scale. • The press essentially consists of a scr e w o p e r a t i n g in a nut formed in the upper part of a rigid F-type frame.

54. Types of Presses : contd ... Rann Bed Adjustable bed Incdinab le C-frame -P fa Ram ---- Hor -wl4{gr Hom Solid stra i ght side Arch Crown Movable p la te or ram P i llar Column Bed Tie rod Pilla r Types of press frame

55. Ejecting Mechanisms

56. Ejecting Mechanisms : • Ejectors are the devices used for ejecting the components from die after completing the operation. • Simple components ca n b e e j e c t e d easily but heavy components need external help for ejection. • Automatic pressure completed ejection mechanisms may employ air or oil the or mechanical apparatus to remove part from a press. • Ejection mechanisms may be interlocked with the operating controls to is accomplished. prevent operation until part ejection

57. Ejecting Mechanisms : contd ... 1.lnjector pin inserted through a hole in the punch: • Fig. shows a set up for a curling operation. • After the operation is c o m p l e t e d a n ejector pin inserted through the hole in the punch cavity. helps in pushing the workpiece out of the punch H ol e fo r eje c tor pir - l u nger

58. Ejecting Mechanisms : contd ... 2.Knockout pin through the Die: • In this case die platen is at the top while the punch is at the bottom constituting an inverted punching Top ejector or k nockout operation. ht - L t @pi a [ef Die . · . A Bottom ejector o r pressure pad Punch • The descending die first shears the workpiece and then forces, the platen further down on the pressure plate (or the bottom ejector).

59. Ejecting Mechanisms : contd ... 2.Knockout pin through the Die : • When under the the die moves up, the work-plate is knocked up spring pressure. Top e jector or k nockou t ht - L t @pi a [ef D ie A Bottom ejecto r o r pressure pad P unch • The top ejector within the die knocks out the the die cavity. blank held in

60. Ejecting Mechanisms : contd ... 3.Ejection with the help of a lever: • The lever is operated manually by the worker after the press work is completed with the upward motion or of may be connected the press ram. mechanically / L ever l Eject

61. Ejecting Mechanisms : contd ... 4.Ejection with hooks in top tool: • In this arrangement the top tool of the press is provided with hinged hooks. • The hooks when the slide smoothly over the surface of the workpiece ram is descending but when ram starts going them back the hooks engage in grooves provided for thereby ejecting the finished workpiece.

62. Ejecting Mechanisms : contd ... 5.Ejection by hydraulic and pneumatic cushions • Hydraulic or p n e u m a t i c c u s h i o n s throughout the stroke using length. oil/air provide uniform force The force can • also be varied suitably by adjusting the oil/air pressure and the movement is smoothly. A noe • D i e H opper • Pneumatic ejectors however tend to be noisier.

63. Ejecting Mechanisms : contd ... 6.Robots : • Robots are us e d in many organisations f o r l o a d i n g , unloading, assembly of parts. • When a robot is required to remove the finished work it is important to ensure that the movements of the robotic arm is not obstructed by any part of the set up.

64. The Metal Shearing Process: • When the punch is forced down into the sheet metal the punch first draws the stock in a circular bend over the cutting edge. • The and grains elongate die corner D. near the cutting edge A of the punch C l earance ] Penet ra t ion (a) S h ea r i n g ope r ation ( b ) Rup tur e

65. The Metal Shearing Process: contd ... • As the punch descends further t h i s l o c a l deformation increases and when local strain in the s u r f a c e f i b r e s reaches the limiting value for the work material the fibres rupture. • The crack starts just ahead of the punch corner but with the advancement of the punch, the inner fibres also get sides ruptured and the crack starts advancing from both C l earance ] Penet ra t ion (a) S h ea r i n g ope r ation ( b ) Rup tur e

66. The Metal Shearing Process: contd ... • If the clearance between the die and punch is correct the cracks started at the two ends spread towards each other till they meet causing separation with a clean edge . · · ¢ T o¢ l i ttle cle ar ance C or rect clea r an ce Ta o m uch ' ea ran ce • The t h e t h i s amount of clearance depends upon the thickness of sheet and ductility of the work material. For steels, clearance varies from 5 to 8 percent of the thickness to 10 of the sheet. Larger clearances up percent are required for aluminium.

67. The Metal Shearing Process: contd ... • If the clearance between the punch and die is too large or too small the cracks started meet as shown. at the punch and die do not • Additional bands of metal must be sheared in such cases to complete the separation. This leads to higher cutting forces and cut edges are generally not smooth. • E x c e s s i v e c l e a r a n c e also c a us e s a l a r g e r a d i u s to be formed at the corners of the slug and work piece.

68. The Metal Shearing Process: contd ... • An approximate value of the correct clearance to be used for a shearing operation on each the following relationship. c = side may be obtained by 00021 [f Where, C = clearance, mm [on each side] t = sheet thickness, mm fs = shear strength of the material, MPa

69. The Metal Shearing Process: contd ... engi • neeri • ng • Values of shear strength for common materials Shear strength MPa Material Partially cold worked 400 55 700 Annealed 300 44 540 47 L o w c a r bo n s t ee l C . 2 % C = 4% M ed carb o n st ee l Stain l ess steel Br a ss Copper B ronze Al um i num C = 0.6 3 4 4 24 - 300 4 00 -- 600 2 1 300 1 7 -2 00 3 00 -- 4 00 7 -- 1 00 180 -2 00 1 30 16 Aluminium all o y 22 -4 00

70. The Metal Shearing Process: contd ... • Clearance values normally used for punching Ma t erial Cleara n ce p erce nt of s t oc k th ic kn ess 2- 3 3 5 2- 6 2- 3 3 5 4- 8 Aluminum less than I mm thick Alumnum more Copper all o y s L o w ca r b o n s t ee l H ar d s t eel S tainless steel mm t han t hick I

71. of Shear Angle Effect

72. Effect of Shear Angle : • Shear is provided on the punch or die to reduce the forces required o pe r a t i o n s h o p . on on the punch often to accommodate the the a lower capacity c machine available .7 in (a) N o ( b ) Unba l a n ced s h ear ( e) B a l an c ed s h ea r s h ea r • The purpose of the shear is to distribute the shearing action over a period of time so that the punch does not contact the time. work piece over its entire length at the same

73. Effect of Shear Angle : contd ... • The provision of shear, work as mentioned earlier, does in no way affect the total required to complete the shearing operation. c .7 (a) N o s h ea r ( b ) Unba l a n ced s h ear ( e) B a l an c ed s h ea r • The total work done in shearing with or without the shear is the same. • The total travel of the punch to complete the operation in however increased with the provision of shear.

74. Stripping Force

75. Stripping Force : • The force required for stripping depends primarily on the thickness of the sheet, size and number of the holes and the location of the holes. • Small holes in the middle of a sheet or holes holes in in thicker material require more stripping force than a thin sheet or holes located near the edge of the workpiece. • A number of punches located close to each other or punches with rough walls are comparatively more difficult to strip than single punches with smooth walls.

76. Stripping Force : contd ... • In general, stripping force but forces vary from 2.5 to 20 percent of in the punch 5 to 10 percent is quite satisfactory most cases. • A formula generally used · t for finding the stripping force is, Fs = k · L Where, Fs = s t r i p p i n g f o r c e , kN L t = perimeter of the cut, mm = stock thickness k = stripping constant depending upon the material, and size and location of the cut

77. Stripping Force : contd ... • The value of k is given in Table. S t ock t hickness k 0.0 1 03 . 0145 . 0207 0. 0241 S t ock ma t erial Ca rb o n st e el C u t e dg e o r near a pr e ce d ing O th e r cuts Any cut - A t t he 1. 5 < 1 . 5 > 1 . 5 - mm mm mm cut Ha r d er mat eria l • The press selected for the shearing operation must h a v e enough capacity, not only to provide for maximum punch force and the stripping force but also to account for friction and other losses during the process.

78. Working Dies : Press

79. Press Working Dies: contd ... (a)Based on type of press operation: 1. Shearing n o t c h i n g t h e s e a r e Dies: Dies used for blanking piercing, punching, perforating, trimming, shearing and parting. All known as cutting dies. 2. Bending dies: Dies used for bending, curling, forming etc. 3. Drawing bulging. dies: Dies used for curling, flanging, embossing, 4. Squeezing f I a tter i n g. dies: Dies used for coining, sizing, swaging,

80. Press Working Dies: contd ... (b)Based on type o f d i e construction: 1. 2. 3. 4. 5. 6. Simple dies Progressive Compound dies dies Combination dies Transfer dies Multiple or gang dies

81. Press Working Dies: Simple dies : contd ... 1. • Simple dies are dies designed to perform only one specific operation like blanking, punching, notching, trimming etc. • The die may be pins provided with all the usual elements including stop the metal strip. which are us e d for proper indexing of

82. Press Working Dies: Progressive dies: When the quantity of pieces to be produced is large, more contd ... 2. • complex dies are often used to increase production rate. Dies included in this category are progressive, compound and combination dies. • A progressive die us e s two or more punch and die sets located a t d i f f e r e n t stations to perform a n u m b e r of operations simultaneously in one stroke of the ram. • The sheet is moved progressively from one station to the other till at the last station a complete job is obtained.

83. Press Working Dies: contd ... 2. Progressive dies: Ba n k in g I pun ch Pi e r cing p u nch [ j] g t r S t ri ppe r Sto p F i n al p r od u ct •

84. Press Working Dies: Progressive dies: A si m pl e t w o - s t a g e p r og r e s s i v e p un c h and bl a nk i n g di e us e d f o r m a k i n g w a s h e r s is i n f i g . contd ... 2. • Bla n ki n g p unch Pier c i ng pu nch p j[ a t -[ • The metal strip i s i n t r o d u c e d - Sri pper from one end and is advanced till the first is punched the ram. station where a hole · in the first stroke of Di e S top ' • The the metal next is now advanced to ~%a l stage, t h e c o r r e c t distance shown. being set by the stop

85. Press Working Dies: Progressive dies: contd ... 2. • As the ram moves down for its next stroke the pilot on the blanking punch enters the hole Blanking puna pilot vl pierced at the previous station - Piercing punch to locate the sheet. r Stripper _{a. s1o:- ' ~ The working punch itself moves down to remove the completed washer. • t_ I I / ' Ft n a l p r o o u c t / ' • In the mean time a at new the hole first \ I S lug h a s been pierced stage.

86. Press Working Dies: Progressive dies: contd ... 2. • In the each subsequent stroke of are ram two operations performed one at each station B lanking puna and one job is completed at last station. the P iercing punch Pilot -] r Stripper _ {l, • Straight pieces of metal are fed y = manually pressure maintaining a slight " «»w ( /i/fit '+' on t h e s t r i p a s it p passes through the die. / Final product '

87. Press Wo r ki n g D i e s: contd ... _ - upp e r d ie i ,- B l a n ki ng die Str i ppe r f o r pierci ng p u n ch p j e nt ing u nit/ -..I P i e rc i n g die B l an k i n g pu n S t ripp er f or b l a nk i ng pun ch Stri p 3. Compound dies: Di o more • In compound die two or functions are performed at the same station of the die. • Fig. shows a simple compound die for producing washers. • It combines a blanking and a shearing operation at one station.

88. Press Working Dies: contd ... Compound dies -- B l ank i ng die S tr i pp er f o r pierci ng p u n ch Pi erc i n g p unch Strip P i e rc i ng {d i£ El sn k ing pu nch S t ripp e r f o r bl a nk i n g pu nch ;--1 .I Lc we r di e I Di

89. Press Wo r ki n g D i e s: contd ... _ - upp e r d ie i ,- B l a n ki ng die Str i ppe r f o r pierci ng p u n ch p j e nt ing u nit/ -..I P i e rc i n g die B l an k i n g pu n S t ripp er f or b l a nk i ng pun ch Stri p 3. Compound dies: Di o blanking • The ram. piercing punch and the die the are bolted to the The spring loaded stripper for piercing punch is located within the blanking die. • The edge lower di e ha s cutting edges on the both sides. The inner serves a s a piercing die for piercing punch while the outer edge serves as a blanking punch.

90. Press Wo r ki n g D i e s: contd ... -- upp er d i e Bla n k i ng di e S tri ppe r for p ier c i n g pu n ch Pien ing u nit/ S tri p -..I Pi e rc i ng die Bl a n k ing pun ch S t ripper f o r b l ank i n g pu nch 3. Compound dies: Lowe r di e Di is so located that as the ram • The blanking punch is lowered the blanking operation is completed earlier than the piercing operation. • This ensures that the metal strip is firmly held before the relatively weaker piercing punch contacts it. • The spring loaded stripper plates help in knocking out the washer produced.

91. Press Working Dies: Combination dies: contd ... 4. • A combination die set up is - D rawi n g p u nc h shown in Fig. Blank i ng pun ch • It combines blanking and M w l e r k Kn p , l i ! e - c . e . drawing operations. - D i e • The drawing punch is located inside the blanking punch while the die blank h a s two working surfaces one for each punch.

92. Press Working Dies: Combination dies: contd ... 4. • As the blanking punch descends - D rawi n g p u nc h it cuts a blank of required si ze Blank i ng pun ch from the metal using the outer working surface of the die. M w l e r k Kn p , l i ! e - c . e . • The inner drawing punch now t h e p a r t - D i e descends and draws out metal to form the required while the blanking punch serves as a pressure pad. • The drawn cup is then ejected from the die.

93. Press Working Dies: Transfer dies : contd ... 5. • Transfer dies are similar to progressive dies in that the stock i s t r a n s f e r r e d p r o g r es s i ve l y f r o m on e s t a t i o n t o t h e n e x t t i l l a t t h e l a s t s t a t i o n t h e j o b i s c o m p l e t e d . • Generally pre-cut blanks are used in these dies.

94. Press Working Dies: contd ... 6. Multiple or gang dies : • In these dies, number of simple die that and two punch sets are grouped together in such a way or more work pieces are produced in each stroke.

95. Sheet Metal Layout: • An important requirement in planning sheet metal operations is to prepare a proper layout design. • A proper stock layout is essential in order to decide how the blanks will be cut from the sheet stock in the best way. • While planning a blanking operation, for example, it is necessary to provide suitable clearances between adjacent blanks and the edge of the last blank or the edge of the strip to prevent the metal being drawn between the punch and the die.

96. Sheet Metal Layout: • Fig. strip shows some of the terms that are us e d in relation to layout. I Scra p bri dg e ( b ) B a c k sc ra p ( a) Advanor ( c ) --4' 1 • I ' I I I t W I ' h I \ " -h- t S hee t t hi ckn ess -h» L ead end F ront s crap ( a) S cra p bridg e ( b ) ~ ------- L ------- - Fee d dir ec t io n

97. Sheet Metal Layout: contd ... • • t a = stock thickness = distance between edge of strip and the blank called front and back scrap I Scra p bri d ge ( b ) scrap ( a) Adva n or ( c ) Back --4' 1 • I ' I I I t W I ' h I \ " -h- t S hee t t hi ckn ess -h» L ead e n d F ront s crap ( a) S cra p bridg e (b ) ~ ------- L ------- - Fee d dir ec t io n

98. Sheet Metal Layout: contd ... • b = distance between the nearest points of the blanks and also the distance between the edge of the blank and the edge of the strip, called scrap bridge. I Scra p bri d ge ( b ) scrap ( a) Adva n or ( c ) Back --4' 1 • I ' I I I t W I ' h I \ " -h- t S hee t t hi ckn ess -h» L ead e n d F ront s crap ( a) S cra p bridg e (b ) ~ ------- L ------- - Fee d dir ec t io n

99. Sheet Metal Layout: contd ... • c = die advance or lead of to the the die. It is the distance from a point on one blank corresponding point on the next blank. I Scra p bri d ge ( b ) scrap ( a) Adva n or ( c ) Back --4' 1 • I ' I I I t W I ' h I \ " -h- -h» L ead e n d t S hee t t h i c k n e s s F ront s crap ( a) S cra p bridg e (b ) ~ ------- L ------- - Fee d dir ec t io n

100. Sheet Metal Layout: contd ... • • h = height of the blank or diameter in c a s e of circular blank + W = width of the strip= h 2 a I Scra p bri d ge ( b ) B a c k scrap ( a) Adva n or ( c ) --4' 1 • I ' I I I t W I ' h I \ " -h- t S hee t t hi ckn ess -h» L ead e n d F ront s crap ( a) S cra p bridg e (b ) ~ ------- L ------- - Fee d dir ec t io n

101. Sheet Metal Layout: contd ... • L = length of the strip for a given number of blanks I Scra p bri dg e ( b ) B a c k sc ra p ( a) Advanor ( c ) --4' 1 • I ' I I I t W I ' h I \ " -h- t S hee t t hi ckn ess -h» L ead end F ront s crap ( a) S cra p bridg e ( b ) ~ ------- L ------- - Fee d dir ec t io n

102. Sheet Metal Layout: contd ... • The distance a is generally a= t + 0.015 h given by the equation I Scra p bri dg e ( b ) B a c k sc ra p ( a) Advanor ( c ) --4' 1 • I ' I I I t W I ' h I \ " -h- t S hee t t hi ckn ess -h» L ead end F ront s crap ( a) S cra p bridg e ( b ) ~ ------- L ------- - Fee d dir ec t io n

103. Sheet Metal Layout: contd ... • Distance b must be large enough to prevent the scrap twisting and wedging between the punch and die. from • A rule of thumb is to make it at least equal to 1.St. I Scra p bri d ge ( b ) scrap ( a) Adva n or ( c ) Back --4' 1 • I ' I I I t W I ' h I \ " -h- t S hee t t hi ckn ess -h» L ead e n d F ront s crap ( a) S cra p bridg e (b ) ~ ------- L ------- - Fee d dir ec t io n

104. Sheet Metal Layout: t h a t p e r m i t contd ... • Other factors it to be thinner are strip thickness, h a r d n e s s o f the material, type of operation, shape of blank etc. I Scra p bri d ge ( b ) scrap ( a) Adva n or ( c ) Back --4' 1 • I ' I I I t W I ' h I \ " -h- t S hee t t hi ckn ess -h» L ead e n d F ront s crap ( a) S cra p bridg e (b ) ~ ------- L ------- - Fee d dir ec t io n

105. Sheet Metal Layout: contd ... • The commonly used values of bare given in Table Ma t erial t hickness . 8 8 t o 3 2 > 3 .2 mm b mm 0. 8 t 3 . 7 t I Scra p bri dg e ( b ) sc ra p ( a) Advanor ( c ) Back --4' 1 • I ' I I I t W I ' h I \ " -h- t S hee t t hi ckn ess -h» L ead end F ront s crap ( a) S cra p bridg e ( b ) ~ ------- L ------- - Fee d dir ec t io n

106. Factors Affecting t he Strip 1.Grain direction : l ayout : • The strips are usually available in coils. • An important point that has to b e considered is the grain direction or the direction in which rolling was done. • T h e strip should always b e f e d a n d processed in the direction of the grains.

107. Factors Affecting the Strip Cost of tooling : Layout : contd ... 2. • The tooling needed for presswork is quite long time to design and manufacture. costly and takes a • A compromise between reasonable tool cost and optimum layout i s o f t e n required. For high production rates, however, tool cost per piece becomes less important and more attention should be paid for economy of material and ease of operation.

108. Factors Affecting the Strip 3.Ease of operation : Layout : contd ... • T h e strip has to be planned in such a way that actual f e e d i n g i n t o t h e d i e holes is accurate. is as simple as possible a n d location of • T h e strip m a y get ja m m e d i f there ar e a n y projecting contours. • The strip may also need to be turned over when different passes. feeding for

109. Factors Affecting the Strip Layout : contd ... 4.Availability of standard strip widths : • Strips are available in standard sizes only. • As far as possible only these sizes should easily and faster. b e used because they are available • Un com m o n sizes have to be ordered specially a n d ar e usually costlier and have longer delivery periods.

110. Factors Affecting 5.Strip or coiled stock the : Strip Layout : contd ... • The available stock may be in the form of a coil or a strip. • A strip may be b u t t h e c o i l e d once. Coiled stock is passed through the die stock is usually passed any number of times die only through the • used when production volumes are high and metal thickness is low. • The feed in this case is usually automatic. • Strip stock is used with low production volumes and thicker metal sheets. The stock feed is mostly manual.

111. Factors Affecting the Strip 6.Direction of burr : Layout : contd ... • A burr is produced on the die the punch side of the blank. side of the scrap strip and on • Sometimes i t m a y be desirable to keep t h e b u r r on a pa rt i cu I a r side. • It is however, not a very important point in most cases.

112. Factors Affecting the Strip 8.Narrow run or wide run : Layout : contd ... • If the length of a component is more than keep its the width length it is necessary to make a choice whether to side or width side towards the feeding direction. ill Fee d fl[f f; [ [ f f] ' ' (a) N arrow r un (b ) Wide run • As s h o w n i n F i g . if the narrow side is towards feeding direction run. it is called a narrow run, otherwise it is the wide

113. Materia l U ti liza t io n Facto r : • The economy of material used is usually expressed in terms of Material U t i l i z a t i o n F a c t o r ( M U F ) d e f i ne d a s MF /Area . o fblanks.cut Ar ea of sh e ets us ed • Thus if one blank of dimensions w x h is b) x (h + 2a) and produced the sheet used will be (w + M UF = 7 W { + b) . +2 . a a

114. Materia l U ti liza t io n Facto r : contd ... • Quite often it is possible to improve the material utilization by rearranging the layout. • Fig (a). with one punch but it is not the best arrangement from area utilization point of view. -557 l=7ll (b) Double r ow ( a ) Si n gle row (c ) S i ng l e row double pass

115. Materia l U ti liza t io n Facto r : contd ... • Quite often it is possible to improve the material utilization by rearranging the layout. • Fig (a). with one punch but it is not the best arrangement from area utilization point of view. -557 l=7ll (b) Double r ow ( a ) Si n gle row (c ) S i ng l e row double pass

116. Centre of Pressure : contd ... • Quite often it is possible to improve the material utilization by rearranging the layout. • Fig (a). with one punch but it is not the best arrangement from area utilization point of view. -557 l=7ll (b) Double r ow ( a ) Si n gle row (c ) S i ng l e row double pass