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Die Design
Part 2-Cutting Operations
J5811 - Tool Design
(Based on notes of Prof Dr Simin Nasseri,
Southern Polytechnic ...
2MET3331, Prof Simin Nasseri, Part 2
Southern Polytechnic State University
Summary:
 Die-cutting operations
 Clearance i...
3MET3331, Prof Simin Nasseri, Part 2
Southern Polytechnic State University
Die Cutting Operation
 Cutting and forming ope...
4MET3331, Prof Simin Nasseri, Part 2
Southern Polytechnic State University
Die Cutting Operation
 Punching (Piercing): ro...
5MET3331, Prof Simin Nasseri, Part 2
Southern Polytechnic State University
Die Cutting Operation
 Lancing: combines bendi...
6MET3331, Prof Simin Nasseri, Part 2
Southern Polytechnic State University
Die Cutting Operation
 Notching: cuts off vari...
7MET3331, Prof Simin Nasseri, Part 2
Southern Polytechnic State University
Die Cutting Operation
 Cut-off: achieves compl...
8MET3331, Prof Simin Nasseri, Part 2
Southern Polytechnic State University
Die Cutting Operation
 Shearing of sheet metal...
9MET3331, Prof Simin Nasseri, Part 2
Southern Polytechnic State University
Die Cutting Operation
 Shearing of sheet metal...
10MET3331, Prof Simin Nasseri, Part 2
Southern Polytechnic State University
Clearance in Sheet Metal Cutting
 Die size de...
11MET3331, Prof Simin Nasseri, Part 2
Southern Polytechnic State University
Punching-die Design
 Single-station
piercing ...
12MET3331, Prof Simin Nasseri, Part 2
Southern Polytechnic State University
Punching-die Design
 A punch holder mounted t...
13MET3331, Prof Simin Nasseri, Part 2
Southern Polytechnic State University
Blanking-die Design
 The piercing punch is re...
14MET3331, Prof Simin Nasseri, Part 2
Southern Polytechnic State University
1- Simple Blanking Die
 Die is mounted to the...
15MET3331, Prof Simin Nasseri, Part 2
Southern Polytechnic State University
2- Inverted Blanking Die
 Used for producing ...
16MET3331, Prof Simin Nasseri, Part 2
Southern Polytechnic State University
2- Inverted Blanking Die
 On the upstroke of ...
17MET3331, Prof Simin Nasseri, Part 2
Southern Polytechnic State University
Compound Blanking & Piercing Die
 A compound ...
18MET3331, Prof Simin Nasseri, Part 2
Southern Polytechnic State University
Compound Blanking & Piercing Die
 The sheet m...
19MET3331, Prof Simin Nasseri, Part 2
Southern Polytechnic State University
 What type of
blanking die is
this? (Simple
o...
20
Design Elements
21MET3331, Prof Simin Nasseri, Part 2
Southern Polytechnic State University
Systems of Length, Area, & Force measurements
...
22MET3331, Prof Simin Nasseri, Part 2
Southern Polytechnic State University
Die Block General Design
 Overall dimensions ...
23
Mathematical Calculation
24MET3331, Prof Simin Nasseri, Part 2
Southern Polytechnic State University
Center of Pressure
 Irregularity in the shape...
25MET3331, Prof Simin Nasseri, Part 2
Southern Polytechnic State University
Center of Pressure
 Calculate the distance X,...
26MET3331, Prof Simin Nasseri, Part 2
Southern Polytechnic State University
Center of Pressure, Example
 In the following...
27MET3331, Prof Simin Nasseri, Part 2
Southern Polytechnic State University
Peak Cutting Force
Important for determining p...
28MET3331, Prof Simin Nasseri, Part 2
Southern Polytechnic State University
Shear strength and
tensile strength of
various...
29MET3331, Prof Simin Nasseri, Part 2
Southern Polytechnic State University
Stripping Force
 A properly designed tool nee...
30MET3331, Prof Simin Nasseri, Part 2
Southern Polytechnic State University
Stripping Force
 Stripping force depends on:
...
31MET3331, Prof Simin Nasseri, Part 2
Southern Polytechnic State University
Press Tonnage
 The sum of all the forces requ...
32MET3331, Prof Simin Nasseri, Part 2
Southern Polytechnic State University
Reducing Cutting Forces
 Cutting forces are c...
33MET3331, Prof Simin Nasseri, Part 2
Southern Polytechnic State University
Reducing Cutting Forces
Two methods reduce cut...
34
Cool Design!
Yummy!!
Versus bad design
35MET3331, Prof Simin Nasseri, Part 2
Southern Polytechnic State University
Test yourself!
 Name the major
components of ...
36MET3331, Prof Simin Nasseri, Part 2
Southern Polytechnic State University
Test yourself!
1. Relative motion of the strip...
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Transcript of "Dies Design - Cutting Operations Part 2"

  1. 1. 1 Die Design Part 2-Cutting Operations J5811 - Tool Design (Based on notes of Prof Dr Simin Nasseri, Southern Polytechnic State University) Sources:  Handbook of Die Design, Suchy  Sheet Metal forming Knowledge base, SME  Fundamentals of Tool Design, SME
  2. 2. 2MET3331, Prof Simin Nasseri, Part 2 Southern Polytechnic State University Summary:  Die-cutting operations  Clearance in sheet metal cutting  Piercing die design  Blanking die design  Compound blanking & piercing  Design elements  Die block general design  Center of pressure  Peak cutting force  Stripping Force  Press Tonnage  Reducing Cutting Forces
  3. 3. 3MET3331, Prof Simin Nasseri, Part 2 Southern Polytechnic State University Die Cutting Operation  Cutting and forming operations performed on relatively thin sheets of metal  Thickness of sheet metal = 0.4 mm (1/64 in) to 6 mm (1/4 in)  Thickness of plate stock > 6 mm  Operations usually performed as cold working Thickness= 0.4 to 6 mm (1/64 to 1/4 in)
  4. 4. 4MET3331, Prof Simin Nasseri, Part 2 Southern Polytechnic State University Die Cutting Operation  Punching (Piercing): round punch cuts a hole in the work material.  The material (slug) cut from the sheetmetal is often scrap.  Blanking: differs from piercing only in that the part cut from the work material is usable. Blanking Punching or Piercing
  5. 5. 5MET3331, Prof Simin Nasseri, Part 2 Southern Polytechnic State University Die Cutting Operation  Lancing: combines bending and cutting along a line in the work material, leaving a bent portion or tab attached to the work material. Lancing
  6. 6. 6MET3331, Prof Simin Nasseri, Part 2 Southern Polytechnic State University Die Cutting Operation  Notching: cuts off various shapes from the edge of the workpiece material (a blank or a part).
  7. 7. 7MET3331, Prof Simin Nasseri, Part 2 Southern Polytechnic State University Die Cutting Operation  Cut-off: achieves complete separation of the work material by cutting it along straight or curved line.  Shaving: secondary shearing or cutting operation in which the surface of a previously cut edge of a workpiece is finished or smoothed (punch and die clearance is small). Cut-off
  8. 8. 8MET3331, Prof Simin Nasseri, Part 2 Southern Polytechnic State University Die Cutting Operation  Shearing of sheet metal between two cutting edges: (1) just before the punch contacts work; (2) punch begins to push into work, causing plastic deformation;
  9. 9. 9MET3331, Prof Simin Nasseri, Part 2 Southern Polytechnic State University Die Cutting Operation  Shearing of sheet metal between two cutting edges: (3) punch compresses and penetrates into work causing a smooth cut surface; (4) fracture is initiated at the opposing cutting edges which separates the sheet.
  10. 10. 10MET3331, Prof Simin Nasseri, Part 2 Southern Polytechnic State University Clearance in Sheet Metal Cutting  Die size determines blank size Db  Punch size determines hole size Dh  c = clearance Distance between punch cutting edge and die cutting edge: Depends on hardness and thickness of materials Thickness of metal c  Typical values range between 4% and 8% of stock thickness
  11. 11. 11MET3331, Prof Simin Nasseri, Part 2 Southern Polytechnic State University Punching-die Design  Single-station piercing die: A complete press tool for cutting two holes in work material at one stroke of the press. ngle dimple Single dimple (clean hole bottom) Double dimple clean hole top & bottom
  12. 12. 12MET3331, Prof Simin Nasseri, Part 2 Southern Polytechnic State University Punching-die Design  A punch holder mounted to the upper shoe holds the punch (guided by bushings inserted in the stripper).  A sleeve, or quill, encloses the punch to prevent its buckling under pressure. 1. Top die shoe 2. Bottom die shoe 3. Guide plate 4. Top back-up block 5. Bottom back-up block 6. Guide pin 7. Punch 8. Punch holder with adjusting plate 9. V-Ring plate 10. Guide bushing 11. Adjusting plate 12. Punch retainer with adjusting plate 13. Ejector 14. Die 15. Piercing punch holder 16. Guide bushing
  13. 13. 13MET3331, Prof Simin Nasseri, Part 2 Southern Polytechnic State University Blanking-die Design  The piercing punch is replaced by the blanking punch.  There are two types of blanking dies: 1- Simple or conventional blanking die 2- Inverted blanking die
  14. 14. 14MET3331, Prof Simin Nasseri, Part 2 Southern Polytechnic State University 1- Simple Blanking Die  Die is mounted to the lower shoe and punch is mounted to the upper shoe.  Drop-through design: finished blanks drop through the die. Angular clearance in needed to remove the part.
  15. 15. 15MET3331, Prof Simin Nasseri, Part 2 Southern Polytechnic State University 2- Inverted Blanking Die  Used for producing larger blanks,  The die is mounted to the upper shoe,  The punch is mounted to the lower shoe,  No need for angular clearance as part is removed by hand.  The spring-loaded stripper is mounted on the lower shoe (travels upward in stripping the stock from the punch fastened to the lower shoe). 4th ed, page 363 die die rod punch
  16. 16. 16MET3331, Prof Simin Nasseri, Part 2 Southern Polytechnic State University 2- Inverted Blanking Die  On the upstroke of the ram, the upper end of the knockout rod strikes the arm on the press frame, which forces the lower end of the rod downward, through the die.  It ejects the finished blank from the die cavity Backing plate Die An arm of the press frame Knockout rod Backing plate Die Finished blank upstroke  Part removal:
  17. 17. 17MET3331, Prof Simin Nasseri, Part 2 Southern Polytechnic State University Compound Blanking & Piercing Die  A compound blanking and piercing die is used to pierced blanks, eg a washer.  Here both piercing punch and the blanking punch are attached to the upper-die shoe.  The piercing punch contacts the material slightly ahead of the blanking die.  The center hole is cut and outer diameter trimmed in a single-die station in one press stroke.  The material is usually 0.015 in (0.38 mm) cold-rolled steel strip.
  18. 18. 18MET3331, Prof Simin Nasseri, Part 2 Southern Polytechnic State University Compound Blanking & Piercing Die  The sheet material is lifted off the blanking punch by a spring- actuated stripper.  The blanks normally remains in the upper die, and is usually removed by knockout (which occurs at the top of stroke).  No angular clearance is needed (results in simpler die construction).  In some cases, a piercing punch is attached to the upper-die shoe and the blanking punch to the lower-die shoe. Disadvantage:  The part must be removed from the upper die at the top of each stroke. In case of small parts, once knocked out of the upper die, they may be ejected by a timed blast of air.
  19. 19. 19MET3331, Prof Simin Nasseri, Part 2 Southern Polytechnic State University  What type of blanking die is this? (Simple or inverted)  Although the finished blanks do not drop through the die, but the main feature is that the punch is mounted to the upper shoe and the die to the bottom shoe. So this is a ....  So this seems to be a simple blanking die. Notice that there is a piercing punch at the bottom as well. So this is in fact a compound blanking and piercing die! Test yourself!
  20. 20. 20 Design Elements
  21. 21. 21MET3331, Prof Simin Nasseri, Part 2 Southern Polytechnic State University Systems of Length, Area, & Force measurements  In North America, engineering calculations for stamping are carried out using measurements based on the following units: For length and thickness: Inch, For shear and yield strength: Pounds per square inch or psi, For press force: 2000 lb.  Throughout most of the world: For length and thickness: Meter, centimeter and millimeter For shear and yield strength: KPa (K N/m2 ) or MPa For press force: Tons or 1000kg (sometimes KN & MN).
  22. 22. 22MET3331, Prof Simin Nasseri, Part 2 Southern Polytechnic State University Die Block General Design  Overall dimensions will be determined by:  Minimum wall thickness required for strength,  by the space needed for screws and dowels and for mounting the stripper plate.  Depends upon the thickness of the stock to be cut. Die thickness per ton of pressure Stock Die Stock Die Thickness in (mm) Thickness in (mm)* Thickness in (mm) Thickness in (mm) 0.1 (2.5) 0.03 (0.8) 0.6 (15.2) 0.15 (3.8) 0.2 (5.1) 0.06 (1.5) 0.7 (17.8) 0.165 (4.19) 0.3 (7.6) 0.085 (2.2) 0.8 (20.3) 0.18 (4.6) 0.4 (10.2) 0.11 (2.8) 0.9 (22.9) 0.19 (4.8) 0.5 (12.7) 0.13 (3.3) 1.00 (25.4) 0.20 (5.1) * For each ton per sq in of shear strength
  23. 23. 23 Mathematical Calculation
  24. 24. 24MET3331, Prof Simin Nasseri, Part 2 Southern Polytechnic State University Center of Pressure  Irregularity in the shape of a blank, may result in a bending moment in the press ram and undesirable deflections and misalignment.  This is because the summation of shearing forces on one side of the center of the ram may greatly exceed the forces on the other side.  Center of pressure= Center of gravity of the perimeter of the blank, not the area  A point about which the summation of shearing forces will be symmetrical. Why is it important to find this point? G Perimeter of the blank The press tool will be designed so that the center of the pressure will be on the central axis of the press ram when the tool is mounted in the press.
  25. 25. 25MET3331, Prof Simin Nasseri, Part 2 Southern Polytechnic State University Center of Pressure  Calculate the distance X, of the center of pressure C from the axis Y-Y by: 1 1 2 2 3 3 4 4 1 2 3 4 L x L x L x L x X L L L L + + + = + + +  Calculate the distance Y, of the center of pressure C from the axis X-X by: 1 1 2 2 3 3 4 4 1 2 3 4 L y L y L y L y Y L L L L + + + = + + +
  26. 26. 26MET3331, Prof Simin Nasseri, Part 2 Southern Polytechnic State University Center of Pressure, Example  In the following figure, the elements are shown and numbered 1, 2, 3, etc. Find the center of the gravity. 3 4 2 5 6 1 0.5 D 2.5 1.5 3 2 1.5R 4.25 Element L x y Lx Ly 1 4 0 6.25 0 25 2 4.71 1.5 9.25 7.05 43.33 3 3.21 4.00 7.00 12.80 22.4 4 2.5 4 5 10 12.5 5 3 1.5 4.25 4.5 12.75 6 1.57 1 0 1.57 0 Total 18.98 35.92 115.98 2 For semicircle 2: 35.92 1.89 (48 ) 18.98 115.98 6.11 (155 ) 18.98 r y X in mm Y in mm π = = = = = 1
  27. 27. 27MET3331, Prof Simin Nasseri, Part 2 Southern Polytechnic State University Peak Cutting Force Important for determining press size (tonnage) Fs = Ss . L . t Where Fs = Shear force Ss = shear strength of metal L = length of cut edge t = stock thickness Ss ≈ 0.7 St St = Tensile strength (F = Stress x Area of material cut = σ. A) Thickness t Length of cut edge or L = perimeter of this rectangular shape
  28. 28. 28MET3331, Prof Simin Nasseri, Part 2 Southern Polytechnic State University Shear strength and tensile strength of various materials are written in this table. Peak Cutting Force
  29. 29. 29MET3331, Prof Simin Nasseri, Part 2 Southern Polytechnic State University Stripping Force  A properly designed tool needs to have a method for holding the work while the punch is pulled back through the material.  This stripping procedure can be either by a fixed-bridge or spring-loaded stripper.  Thinner material deforms easily when punch is withdrawn from a hole, so the spring loaded stripper should be used. Length of cut edge or L = perimeter of this rectangular shape t http://www.diesupplies.com/catalog/accessories/35bbr_a.html
  30. 30. 30MET3331, Prof Simin Nasseri, Part 2 Southern Polytechnic State University Stripping Force  Stripping force depends on:  Type of material being cut,  Area of the cut,  Clearance between punch & die,  Spring position, etc.  Rough empirical equation: F = 1.5L t L and t are in in and F in ton. F = 20,600L t L and t are in mm and F in kN.
  31. 31. 31MET3331, Prof Simin Nasseri, Part 2 Southern Polytechnic State University Press Tonnage  The sum of all the forces required to cut and form.  In many cases, the stripping forces must be added to the cutting force. This is while the spring- loaded stripper is used. Because, the springs are compressed while cutting the material. Any other spring forces for forming, draw pads, etc will have to be added. Fixed or tunnel strippers will keep the press load to a minimum, but they will not control the stock as well as spring-loaded ones.
  32. 32. 32MET3331, Prof Simin Nasseri, Part 2 Southern Polytechnic State University Reducing Cutting Forces  Cutting forces are characterized by very high forces exerted for very short periods. It is desirable to reduce these forces.  The likelihood of design difficulties and outright tool failure increases if:  we have punch contours of large perimeters,  we have many smaller punches,  high tonnage requirements are concentrated in a small area.
  33. 33. 33MET3331, Prof Simin Nasseri, Part 2 Southern Polytechnic State University Reducing Cutting Forces Two methods reduce cutting forces and smooth the shock impact of heavy loads: 1- Adding shear to the die or punch equal to one-third of the material thickness reduces the tonnage required by 50% for that area being cut with shear applied. 2- By adjusting the height of the punches so they differ in length by one-third the material thickness. (they can cut in sequence rather than all at once). This reduces the tonnage to one-third!
  34. 34. 34 Cool Design! Yummy!! Versus bad design
  35. 35. 35MET3331, Prof Simin Nasseri, Part 2 Southern Polytechnic State University Test yourself!  Name the major components of this die and mention how many relative motions exist.  The entire die is actuated by a mechanical press that moves the die up and down. The press is also responsible for feeding the material through the die, progressing it from one station to the next with each stroke.  Clicking on the picture will open the progressive die animation.
  36. 36. 36MET3331, Prof Simin Nasseri, Part 2 Southern Polytechnic State University Test yourself! 1. Relative motion of the stripper backup & guide pins with respect to the lower shoe, 2. Relative motion of the stripper backup with respect to the upper shoe, 3. Relative motion of the smaller guide pins (for the workpiece) with respect to the stripper, 4. Relative motion of the workpiece and the supporting guides (shown in yellow) with respect to the lower shoe.
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