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I have cropping/cutting wedges with a thickness of 4 mm cutting either side of a round mild steel bar (17.5 mm). Imagine two wedges being driven together with a round mild steel bar in the middle (similar to the design of bolt cutters) These wedges are operated using 2 hydraulic cylinders (6" diameter, 2 1/2 travel) (one for each cutting wedge) to force them together (against the mild steel). The cropping wedges are made from BS 970 304S12 steel.

How can I determine the force required to crop this round bar? What equations/formulas are relevant?

Chris Mueller
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J Lancastle
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2 Answers2

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This is a simple shear force problem. However there are a few considerations.

  1. You don't need 2 hydraulic cylinders. One should be mobile, the other should be stationary. Below is a simple and quick figure to show how they should align. Shear mechanism

You should check Sheet Metal Shears they will give you an idea.

  1. Below is the simple equation for shear. T is shear stress, it is around 400MPa for 0.3%C steels. If you don't have shear stress values you can use ultimate tensile stress values and multiply by 0.6-0.7, for an approximation. Use cross section area of your bar for A.
    Shear force equation

  2. 304 steels aren't a great idea for this kind of work. It can't be hardened by heat treatment, just by cold working. So you won't have long life from your tool. Consider a martensitic stainless steel such as 410, you can harden it and have much higher life. If you don't need corrosion resistance then consider a heat treatable steel. However if you must use 304, try hardening it by hammering, or if you have rolling. That will increase tool life.

Gokce Mehmet AY
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Here is the formula: https://www.researchgate.net/post/how_to_calculate_cutting_force_required_by_hacksaw_for_particular_work_piece_for_particular_hardness

Fc = zckzA*f

Where:

Fc = cutting force in kg.

Zc=number of contact teeths (this number is maximun when the saw reach the diameter of the bar.

kz=especific pressure of cutting in kg/mm2 (this value depend of the cutting material).

A=width of saw in mm.

f = feed per stroke in mm.

Visit website for more info - https://www.acealloysllp.com/stainless-steel-bending.php

Hope this helps

Rahul Verma
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