# Designing a progressive die to make a blank on a thick steel sheet

Suggest and Design a progressive die to make a blank with a 2 mm thick steel sheet as shown in Fig. The ultimate shear strength of the material is 480 MPa. Calculate press capacity assuming 75% efficiency. Like I know if we have to design a progressive die washer then we calculate shear force as= shear stress x Area to be sheared. area to be sheared in washer= 3.14 x (D+d) x t where D is outer diameter and d is inner diameter and t is thickness. And then press capacity is calculated as F/0.75 as 75% is efficiency

and if we need to design die a punch for a single blanking operation we calculate fore as = 3.14 x D x t x shear strength.

But I'm not able to tackle this problem as it is not similar two either of the case I described above, how do we tackle such problems, kindly looking for help. Thank you

• what is your question? ... you described a school assignment, but you did not ask anything ... akso, please describe what difficulty you are having Oct 13, 2021 at 7:35
• @jsotola sir basically I need to suggest a die design for my question means including shear force and a suitable die size, type with dimensions Oct 13, 2021 at 7:45
• I don't know anything about metal punching but I would think that the force depends on the length of the cut, not the area. Oct 13, 2021 at 12:07
• Any presses I have seen have substantially more capacity than needed for a particular job. No one would design a press for a single job. Oct 13, 2021 at 14:17

The cutting blanks equation is,

$$F=l*t*s$$

• L=length mm
• t+thickness mm
• s =shear N/mm^2

We measure the perimeter of the blank and then add the circumference of the two holes.

$$\text{The straight sides are 2*70mm =140mm and 2*( 70-40-20=10)mm=20mm =160mm}$$

$$\text{half circles are 2*pi*20=125.66mm, inner holes 2*2*pi*15=188.49mm}$$

$$\text{ Total 188.49+124.66+160= 473.15mm}$$

$$F= 473.15mm*2mm*S*\frac{1}{0.75}$$

So why not calculate the cut length ie perimeter and use that with the thickness - the cut length is what you get with pi * D in your single blanking example.