Press Tool Design For Blanking

Design procedure for blanking and piercing tool :-

Blanking and piercing is Punching operation in which a flat metal piece is cut out from the primary metal strip or sheet. In this tool entire outer profile of flat metal piece is cut in single stroke of punch.The design of these tools are similar except the sizes of punch and die.

Here we learn about design and development procedure for simple blanking and piercing tool.

Steps for design and development of simple blanking tool:

Know about your customer requirement.
Identify the type of operation.
Select the required tool for that operation.
Check the best strip layout and economy factor.
Make the Conceptual drawing for the tool.
Calculate the cutting clearance and sizes of punch and die.
Calculate the required cutting force.
Calculate the required press tonnage.
Selection of fasteners.
Calculate the die plate thickness.
calculate the other plates thickness.
Working area calculation.
Select standard die set based upon working area.
Height of punch.
Determine center of pressure (optional).
Calculate the m/c and tool shut height .
Recalculate and re-adjust tool shut height.
Bill of material.
Press tool data.
Final assemble tool drawing with required views.
Detail part drawing.

Example:-

Design and develop simple blanking tool for the given component.

Step 1. Customer requirement.

Before designing any tool we should know about the customer needs for that tool.

We should discuss with customer about functionality of component, accuracy grade, burr side, grain flow direction, production rate, tool life etc.

Step 2. Identify the type of operation.

In this step we have to read the customer component carefully and identify the type of operations required to make that component.

For given example we only need Blanking Operation.

Step 3. Select required tool.

In this step we have to select the type of tool required for that component which fulfills the customer needs.

For given example we select the Simple Blanking Tool.

Step 4. Strip layout and economy factor.

Designer should try all possible strip layouts and select the best strip layout which should have atleast 60% economy factor and fulfill the customer needs.

For given example we select the single row single pass strip layout.

scrap bridge = 2.6 mm

pitch = 102.6 mm

width of strip = 105.2 mm

Step 5. Conceptual drawing.

Here designer draw the roughly drawing of tool to exploring the initial ideas for design.The drawing are not intended to be accurate but show the layout of tool.

Step 6. Cutting Clearance and sizes of punch and die.

Here designer calculate the optimum cutting clearance which justify tool life, production rate & part quality.

Cutting clearance C :-

_________

C = c x t x √ T max/10 mm /side

where,

c = constant

c = 0.01 (for normal work)

t = sheet thickness in mm

T max = ultimate shear strength in N/mm^2

_____

C = 0.01 x 2 x √400/10

= 0.126 mm

Sizes of punch and die:

Since this is a blanking tool so the responsible member is die.

therefore, the size of die = size of blank.

= 100 mm

Size of punch = size of die - cutting clearance all around

= 100 - 2 x 0.126

= 99.748 mm

Step 7.Cutting force

Fsh = l x t x T max

where, l = perimeter / circumference in mm.

t = thickness of sheet in mm.

T max = ultimate shear strength of strip material in N/mm^2.

Fsh = 314 x 2 x 400

= 251200 N/mm^2

= 25.12 tonne

Step 8. Press Tonnage

minimum required press tonnage = 1.2 x Fsh

= 1.2 x 25.12

= 30.14 tonne.

Step 9. Selection of fasteners.

Fasteners should have enough strength, so that it can withstand with cutting force.

stripping force

strength of fasteners = ____________

no. of bolts

Let we need four bolt to fastened the die or stripper.

= 25120 N/ mm^2

strength of fasteners = 25120 / 4

= 6280 N

Selecting bolt is M16 from the table.

Size of dowel is generally equal to the size of bolt.

size of dowels = dia.16

Safe load for fasteners

Step 10. Die plate thickness.

Td = cube root of Fsh. (cm)

Td = cube root of 25.12

= 2.92 cm

= 29.2 mm = 30 mm

Step 11. Other plate thickness.

Thickness of top plate and bottom plate = 1.5 to 2 times of die plate thickness.

Top plate thickness = 45 mm

bottom plate thickness = 50 mm

Thrust plate = 6 to 8 mm

(if it is made of OHNS i.e oil hardened non shrinkage steel)

Thrust plate thickness = 8 mm.

Stripper & punch holder plate thickness = 0.8 to 1 times of die plate thickness.

Stripper plate thickness = 30 mm

Punch holding plate thickness = 30 mm.

Step 12. Working area

Calculate the working area of tool with enough wall thickness so that it can be withstand with the cutting force.

Thickness of wall should be 1.5 to 2 times of die block thickness.

working area = a x b

= 220 x 200 mm

Step 13. Select the standard die set.

we can also select the standard die set from FIBRO, MISUMI etc. on the basis of working area or we can also work with our above calculated die set.

Step 14. Height of punch

Height of punch is generally taken 60 to 80 mm. but it also depends upon cutting force and shape / geometry or size of component.

Step 15. Shut Height

To fit the tool or proper working of tool on machine it is necessary to calculate the shut height of machine and tool.

Tool shut height : It is the distance between top of top plate to the bottom of bottom plate, when tool is in closed condition.

M/c shut height : It is the distance between press ram and table when ram is completely down stock and screw adjustment is completely upward.

maximum tool shut height = m/c shut height - 10 mm (10 mm for setting)

minimum tool shut height = maxi. tool shut height - screw adjustment (for movement)

optimum tool shut height = mini. shut height + 20 mm ( 20 mm for regrinding allowances)

Step 16. Recalculate and re-adjust tool shut height

On the basis of practical conditions, adjust the tool shut height for proper working of tool.

Step 17. Bill of material and press tool data.

Prepare the bill of material for the tool and all necessary press tool data.

Step 18. Final assemble drawing with required view.

Release the final assembled tool drawing with all necessary views in production department.

Step 19. Detail part drawing

Prepare and release the detail drawings of each component.

I hope this article will helped you.