Force required for cutting process

[Ali Durrani]

hello brothers and sisters, i have got a project on making an agriculture shredder, i am having difficulty in finding the general equation for the force required to perform cutting operation can anyone help me out

 

[Tom.G]

The value you are looking for is the Shear Strength of the material you are shredding. In the U.S. it is generally given in pounds force to shear a one-inch cube of the material. Multiply the listed value by the length of the cut and the thickness of the material.

EDIT: This is applicable to punch press type operations. Hopefully someone else here can help with the torque required for a shredder operation.

 

[Ali Durrani]

but i am starting for raw i only know the chip size should not be more than 10 mm in width and 10 mm in length the thickness should not exceed 5 mm,
would this be correct ?
F=Ssu*t*w
F=Cutting force
Ssu=Shear ultimate strength
t=thickness
w=width
now force for each shaft is
F1=F*i*k
F2=F*i*k
F1&F2=cutting force on the shafts
F=cutting force on each blade
i=number of blades
k=number of cutting edges
torque would be
T=F1*R1+F2*R2
where R1&R2 are the radius (from the center to the tip of the cutting edge)
Power=
P=T*omega
T=torque
Omega= Angular velocity=2*pie*n/60 so it becomes
P=T*2*pie*n/60

 

[Baluncore]

This is a very complex situation. Scissors or shears are velocity independent, but if the cutters are independent and “on the fly”, then there will be a minimum velocity at which they will cut. This is related to all sorts of things, like the speed of sound in the material being cut, and the material's tendency to be pushed out of the way of the cutter.

What type of cutter geometry are you considering ?

 

[Ali Durrani]

This is similar to my cutting geometry, i have got less than a month the design is due by 20th of the next month and i don't have any knowledge regarding this thing and my supervisor is not helping me infact he is doing such thing for the first time, can you please refer me any book or literature so that i can get knowledge about it?

 

[Baluncore]

See if you can find a library copy of “The Science and Engineering of Cutting”, by Tony Atkins.

Google; 'mulcher design analysis' and you will get blade design optimisation references.

Google terms; Chipper, Shredder, Mulcher, Slasher, Mower.
With; Design, Analysis, analysis of design, Design analysis, shredder design calculations ...

 

[Nidum]

'forces in rotary shears'

 

[Ali Durrani]

Thanks Alot let's see if i could find some useful stuff in there

 

[Nidum]

http://www.mymachineinfo.com/2015/06/paper-shredder-design.html

 

[Ali Durrani]

http://www.mymachineinfo.com/2015/06/paper-shredder-design.html

I have read that The First Equation doesn't seem dimensionally correct to me, secondly, it does not say anything about the cutting speed or the blade design the blade material etc so i mean i can't go with it as baluncore said it's a complex thing

 

[Ali Durrani]

But thanks for your help :)

 

[Baluncore]

There is a big difference between restrained and unrestrained cutting. Shears restrain the material during cutting. Slashers and strimmers do not restrain the material, they have blunt cutters and so rely on the high speed of the cutter and the high inertia of the material. Fundamentally the difference is between shearing and shattering.

Attached is a two page extract from; “The Science and Engineering of Cutting”, by Tony Atkins.

 

[Nidum]

'Agricultural shredder' is too loose a specification for starting a project design .

Questions :

Materials to be handled ?
Range of incoming shapes and sizes ?
Throughput ?

Power source ?
Portable/fixed ?

Like something that already exists or original design ?
Technology level ?

 

[Ali Durrani]

Material to be handled is vegetable peel, fruit peel, fruits vegetables, household organic waste, sugarcane bagasse, some small plants etc
as its an organic waste shredder so the shapes would be random, sizes range from a small peel of any vegetable to as large as a watermelon
power source is electricity
Fixed
it's same as garbage shredder available in the market