Calculation of force for shearing with rotating blades

[Pina87]

Hi,
can anyone help me with defining the force that is needed for shearing of sheet steel (st.37) with 2 rotating blades? The principle can be seen on this video: [URL unfurl="true"]https://www.youtube.com/watch?v=da99re5O0Rc[/url].

I need to define the force for penetration (blades going down) and for rotation of the two blades (see image).

Thank you,

P

 

[Pina87]

Ok, I see noone is answering.

Let's say we got a 4 mm thick sheet and we want to cut out a diameter of 800mm. The rolling knife has a diameter of 110 mm.

I only need the formulae for the forces acting on the knife...please.

Thank you,

 

[jlnsol]

To me it's a wedge principle to divide steel sheet without metal removal.
So if you transfer the formulas on this page:

http://en.wikipedia.org/wiki/Wedge_(mechanical_device)

to the circular knife motion, that will be a good starting point.
Guess it will require a lot of force.

 

[Pina87]

Thank you jlnsol, I will check it up.

P

 

[gruntguru]

Looks more like a shearing action to me - like tin snips or a guillotine. The tricky bit will be determining the area of the cross section being sheared. This will depend on the depth setting of the knife.

eg if the section being sheared is 20mm long, the area will be 20 x 4 = 80 sq mm. Force will be area times average shear stress across the section (somewhere between 50% and 100% of ultimate shear stress for the material).

USS = about 0.75 x UTS for steels. So a 400 MPa steel would have USS of 300 MPa and the force in the example would be
300 x 80 = 24,000 N per wheel. This is the normal force - the vertical (press force) and horizontal (spindle torque) force components will depend on the angle of the Normal force vector (a line through the shering section and the axis of the cutting wheel)

je suis charlie

 

[hydtools]

If you have a Machinery's Handbook, look up the section on the shearing process.

Ted

 

[Pina87]

Hi, hydtools. Which version of MH do you have. I have the 27th and 28th but I can't find the shearing process.

 

[jlnsol]

A condition for shearing is a counterdisc underneath the plate being cut. (Plus narrow tolerances between top and bottom disc. In the video it doesn't look like that.

 

[Pina87]

Hmm, so you say this is a cutting process and not shearing?

 

[jlnsol]

Indeed.

 

[gruntguru]

My eyesight isn't all that good but I am pretty sure there is a counterbore in the reaction bed. So yes - shearing.

je suis charlie

 

[jlnsol]

gruntguru, you're right, shearing, I looked once more to the video and yes there is a table with counterbore underneath the plate.