NOTES TO GUIDE THE DESIGNER ON PRESS TOOL DESIGN

1. These notes' are to guide the designer, to design a practical press tool, to get an acceptable component from the tool and are very valuable points, to produce a perfect tool design drawing.
2. The press tool designer should keep these points in mind or should refer to these notes, before starting a fresh press tool design.
3. Depending upon the type of press tool, to be designed for the particular operation/stage of the components, the designer shall apply the relevant points of these notes.
4. These notes are grouped under the following headings of the tool design. .
A. Most important press dimensions to be considered,
B. Miscellaneous notes to the designer,
C. Planning and layout,
D. Punches and Dies,
E. Cutting clearance,
F. Shearing and shear,
G. Locating of work,
H. Shedders and strippers,
J. Progressive and automatic tools,
K. Compound and combination tools,
L. Forming and drawing tools,
M. Tool materials and craftsmanship,
N. Die try-out and operation.
A. MOST IMPORTANT PRESS DIMENSIONS TO BE CONSIDERED:
5. Before starting a tool design, the designer should know the specifications of the press on which the tool shall be used during the production run. The following factors of the press specification must be considered:
5.1 SHUT HEIGHT WITH/WITHOUT BOLSTER AND BOLSTER PLATE THICKNESS,
5.2 ROLL FEED HEIGHT,
5. 3 SHANK DIAMETER AND LENGTH,
5.4 HOLE IN PRESS BED/BOLSTER (WIDTH AND LENGTH),
5. 5 STROKE LENGTH AND ITS STEPS -DETAILS LIKE FIXED OR ADJUSTABLE STROKE,
5.6 DOES GATE GO UP IN TO THE WAYS? GATE-TOP RAM,

5.7 IF THE GATE GO UP IN TO THE WAYS, CHECK THE OPENING BETWEEN THE WAYS,

5.8 WHICH WAY SHOULD DIE FEED?
5 .9 TONNAGE OF THE PRESS,
5.10 ADDITIONAL HOLES FOR CLAMPING PUNCH HOLDER TO THE TOP RAM (GATE),
5.11 TAPPED HOLE CENTERS IN PRESS BOLSTER-TEE-SLOT POSITIONS AND ITS SIZE,
5.12 THE DISTANCE ABOVE THE BOTTOM OF THE STROKE WHERE THE PRESSURE FIRST OCCURS,
5 .13 ANY ADDITIONAL PRESSURE REQUIRED DUE TO ATTACHMENTS SUCH AS THE BLANK
HOLDER, IRONING WRINKLES OR STRETCHING THE MATERIAL IN DRAWN WORK,



5.14 DIE CUSHION DETAILS AND ITS MOUNTING POSITIONS.PRESSURE TRANSFER PINS POSITIONS IN THE BED/BOLSTER.
B. MISCELLANEOUS NOTES TO THE DESIGNER:
6. SHOULD PART BE MADE PROGRESSIVE OR COMPOUND –This should be given due consideration before proceeding with the die layout. In general, precision stampings can be made more accurately in compound dies.
7. LAY-OUT CORRECT FOR BURR SIDE -many stampings have a right burr side, which the part print may not specify. This point should be checked before starting the die lay- out.
8. STARTING AND AUTOMATIC STOPS -Care should be taken in establishing the position of starting stops to avoid cutting half slugs or blanks.
9. BACKING UP PUNCHES WITH SIDE STRAIN -Punches cutting on one side only should be heeled, the heel entering the die for support before any cutting takes place. The same condition may arise with forming or shaving or bending punches. Shaving on one side only should be avoided and a forming punch, which has all the pressure on one side, must be backed up solid in some manner. Dowels as a rule, are not sufficient.


10. INDICATE CLASS OF WORKMAN SHIP -Some working surfaces can be left as they come from furnace or machine and some should be ground and some lapped or stoned. The designer should indicate what is required.
11. SELECTION OF PROPER STEELS -To day there are steels for every purpose and some thought should be given to what is expected of the die, what material is being punched or formed and choose the best material for the particular job.
12. SPRING STRIPPERS: -Make the spring stripper of ample width and length to provide room for additional springs if necessary. Also make it thick enough to properly take care of the stripper bolts which some times loosen up. If some of the punches are to be guided in the stripper, it must be supported on guide posts/pillars and accurately held in line. When punches are not guided in the stripper, ample clearance must be allowed around all the smaller punches to avoid the possibility of their being thrown out of line. If they are one or two good sturdy punches in the die, fit the stripper close to these punches (0.001" to O. 005" clearance) and allow 0.010" to 0.015" clearance on the smaller punches.
13. HIGH NESTS FOR HAND FED SECOND OPERATION:- If possible, make locating nests 3 to 4 times the blank thickness with the top well rounded to receive the part. The proper condition here will increase production 10% to 25%.
14. PROVISION FOR WEAR ON FORMING TOOLS:- Some forming dies wear fast from the abrasion action and usually provision can be made to adjust or replace this portion at little, if any, added cost.
15. STRIPPER WELL DOWELLED:- In some dies, the stripper is depended upon to do a lot of heavy guiding and it is easy to overlook the importance of large dowels to keep the stripper from shifting.


16. INDICATE HARDNESS:- Having each part the proper hardness is important. Frail parts must be drawn back perhaps to Rockwell 55C and other parts possibly should be left as high as 65C. "
17. CONSIDER LENGTH OF PILOTS: - pilots must be long enough to accurately locate the strip before any punch starts cutting or trimming or forming otherwise their purpose is defeated.




18. STAMP THE FEED DISTANCE ON THE DIE:- This dimension should be plainly stamped on roll feed jobs to save the set-up man the trouble of checking it up.
19. GIVE INSTRUCTION ON THE ASSEMBLY DRAWING TO STAMP THE FOLLOWING DETAILS:- These details should be stamped on the tool bolster plate, to assist the tool shop personnel to maintain the tool and for easy follow up of the production.
19.1 TOOL ORDER NUMBER
19.2 COMPONENT NAME AND DRG NUMBER,
19.3 MATERIAL, STRIP WIDTH,
19.4 SHEET THICKNESS AND TOLERANCE,
19 .5 CLEARANCE,
19 .6 REQUIRED TONNAGE,
19.7 DETAILS OF PRESS ON WHICH THE TOOL SHALL BE LOAD
19 .8 TOOL DESIGN DRAWING NUMBER,
19 .9 SHUT HEIGHT OF THE TOOL,
19.10 ROLL FEED HEIGHT,
19.11 PITCH OF STAGE FOR PROG TOOL.
20. Always check the die drawings with part prints to make certain that the tool will produce the part correctly, relation of grain direction to forms, shear forms, embossments, spurred holes, blanking pressure required and strength of fragile projections.
21. Dimension the detail drawing with information in the form required by the toolmaker, so that he has a minimum amount of translation to do, in understanding the tool design drawing.
22. As soon as the design of a die is decided upon order material/arrange to issue the material details to planning, so that there are no unnecessary delay. Order try-out material at the same time.
23. Always confirm to customers/company's specification for the type of tool construction, kind of steel, die set standard if possible and standardized sizes of die sets.
24. Whenever possible, specify the standard parts as per the international nomenclature/standards and other parts of the tool should be referred as per the standard nomenclature followed in national/international standards for tools.
25. Design all tool parts so as to be easily removable with minimum of disassembly.

26. Consider in the design, the safety and the relation of efficiency to fatigue of the press operator.





27. On detail drawings vitally important working dimensions must not mingle with less important details like location of screws, spring holes, dowels etc.
C. PLANNING AND LAYOUT:
28. Always determine if a more satisfactory design can be obtained by the use of an inverted tool.
29. Draw/Drawing tools are usually inverted.
30. The blank usually follows the shape of the punch.
31. On a blanking tool, the burr is to wards the punch i.e. the clearance shall be given to punch dimension in the case of a blanking tool.
32. Burrs from piercing and contouring are on the same side of the blank taken from a compound tool.
33. In progressive tools, the burrs of the piercing and the blank profile are on the opposite sides.
34. A compound piercing and blanking type of tool is usually to be preferable to a progressive type tool for the same operation.
35. If the part drawing of a blank calls for a close flatness, it is preferable to design an inverted blanking tool instead of a conventional design.
36. On complicated forms always use a template to check the parts and the layout of the punch and die.
37. It is often good practice to use a shaving tool after a blanking tool operation on heavy stock to get clear, sharp edges and to hold close tolerance and to get perfect right angle edge through-out the thickness of the' sheet.
38. Shaving tools as the name implies, are used to remove the die roll or rough edges caused by the shear fracture or break through characteristics in blanking tools. In effect, the shaving tool action is a trimming or squaring up action. Shaving tools are similar to blanking or piercing tools, except little or no clearance is left between the punch and die. Usually no shear is added to either the punch or the die. Often it is necessary to shave a blank only at important functional areas.



39. The amount of metal to be removed by a shaving operation is proportional to the blank thickness and varies with the stock. From 8 to 10% of the thickness of mild steel stock is a good average. For two shaving allow 10% and take off 2/3 with the first and 1/3 with second operation.
40. SHAVING DIRECTION: 1'he cutting direction for a shaving operation should be the same as the cutting direction of the previous cutting operation i.e. for shaving a blank profile, the burr side of the blank should face the shaving punch.
41. STRIPPING IN SHAVING: - Be certain that stripping provisions are adequate. The amount of stripping force required in shaving operation may be double or even triple the force required for equivalent blanking or piercing type of cutting operation.
42. When the thickness of the stock is more than 3mm, it is preferable to have more than one sharing operation. The No. Of shaving operation also depends on the profile to be shaved and the cleanliness of the cut band and the needed accuracy of the profile of component.
43. CLEARANCE BEFORE SHAVING: -cutting clearance for the prior cutting operation (before shaving operation) should be made at least normal or larger than normal if necessary. Most common error is to use too little cutting clearance for those cutting operation, which precede shaving operation.
44. CLEARANCE IN SHAVING: Cutting clearance for shaving dies may be practically non-existent. It is common practice to use fits between punches and die opening which are as close as possible without interference. However, in cases where the shave allowance is quite large, a cutting clearance (in shaving) equal to 5 percent of the shave allowance will be generally acceptable.
45. ALLOWANCE FOR SHAVING:- The width of the scrap web removed by the shaving operation is the shave allowance.
A -Shave allowance for the first shave or for single shave operation
A1 -Shave allowance for second shave operation
T -Stock material thickness
C -cutting clearance used for previous cutting operation (prior to shaving)





For steel A = C+O-O4T A = o.075mm mini
Al=c/2 Al= o.035mm mini
For Brass, Copper, German silver
A = 2c A = o.075mm mini
Al = C Al = o.035mm mini.
46. RECOMMENDED SHAVING CLEARANCE:
First shaving clearance = 5% of first shaving allowance
First shaving allowance = A = c+o.04T
T -Stock thickness
C -Piercing or blanking clearance in % of sheet thickness prior to shaving.
Second shaving allowance = Al = c/2

Second shaving clearance = 5% of second shaving allowance.
47. PINCH TRIMMING: Pinch trimming (should be done) can be attempted, when the sheet thickness of the material is less than 1.5mm (1/16”)



48. DRAWING OF SHEETS: In drawing of sheets, the blanks holder pressure is normally considered between 10 to 20% of the drawing load.
49. DRAWING PRESSURE: To find out the drawing pressure in draw tools, the formula is: -
= (Yield points + ultimate tensile strength) cross sectional area
2
50. DRAWING SPEED: Drawing speed shall depend on the material that is to be drawn. Normally 30 feet per minute is considered for steel material. For brass material the draw speed can be little more i.e. 40 feet per minute draw speed can be considered.

51. HARDENED BACK PLATE: When the compressive stress of the punch (behind the shoulder of punch) on the top bolster plate increases beyond 24.5 kg/mm2 (35000 psi), the designer should provide a (52 RC) hardened back plate behind the punch holder. Keep a minimum of 6mm thick back plate.
52. SPRING ACTUATED STRIPPERS: If the stock or strip is thin(less than 0.5mm), it is good practice to use movable strippers (spring actuated floating stripper) which simultaneously act as a blank holder that firmly grip the stock or strip during cutting. This especially true, when the cutting contour (profile) is irregular.
53. BACK TAPER IN DIE: For thin strip or stock, a back taper of 1/20 right from the die surface, has been found to give good results. The cutting angle 'B' is then large enough to allow sufficient re-sharpening without appreciable change in size of the blank.

Hyperthreading in autocad

Hi guys i thik this may be useful for you .

The autocad can be enabled hyperthreading this will be used while redraw,regen,zoom in zoom out and pan, I felt increase in speed while working with large die designs of size more than 30MB

The command is Whipthread set its value to 3,in many cases i seen it is set to 1 (the value makes it off).

This will be felt only when your processor is hyperthreaded (like I3,I5 etc.,)