Press tool Design cutting force calculation FORCE.ppt

Press tool Design cutting force calculation

1. Calculation of cutting force:
CUTTING FORCE
•Cutting force is the force which has to act on the stock material
in order to cut out the blank or slug.
• This determines the capacity of the press to be used for the
particular tool.

2. RELATIONSHIP BETWEEN SHEARING ACTION
AND CUTTING FORCE
•The three critical stages of shearing action are related to cutting
force.
• Resistance begins when the punch contacts the stock material.
• The load builds up rapidly during the plastic deformation stage.
• It continues to increase while penetration takes place.
• The accumulated load is suddenly released when fracture
occurs.
The curve levels off near the bottom.
• The last portion of the load curve represents frictional
resistance developed,
As the punch travels through the stock material
As the blank or slug passing through the die.
• If proper cutting clearance condition exists between the punch
and the die fracture will occur when cutting force
equals the shear strength of the material.

3. RELATIONSHIP BETWEEN SHEARING ACTION
AND CUTTING FORCE

4. METHODS OF REDUCING PRESS FORCE
• In some cases it will be necessary to reduce cutting force to
prevent over loading press
• A method to reduce press force is to grind the face of the punch
or die at a small shear angle with reference to the horizontal
plane.
• This reduces the area of contact during shear at anyone time.
• Providing shear angle also reduces shock to the press and
smoothens out the cutting operation.

5. • The shear angle should provide a change in punch length from
1 to 1.5 times the sheet thickness.
• Double shear angle is preferred over single shear angle
because it does not create lateral forces.
• Double shear angled punches should be concave to prevent
stretching the material before it is cut.
METHODS OF REDUCING PRESS FORCE

6. METHODS OF REDUCING PRESS FORCE
• To prevent distortion on the stock material for blanking operation
the shear angle will be on the die member for piercing operation
the shear angle will be on the punch member.
• Another method to reduce cutting force is to step punch lengths.
• Punches or groups of punches are made progressively shorter.
by about one sheet thickness.

7. WORKED OUT EXAMPLE -1

8. WORKED OUT EXAMPLE -2

9. WORKED OUT EXAMPLE -3

10. WORKED OUT EXAMPLE -4

11. ASSIGNMENTS -1
CALCULATE THE PRESS FORCE RQUIIRED TO PRODUCE
THE FOLLOWING COMPONENTS

12. CALCULATE THE PRESS FORCE RQUIIRED TO PRODUCE
THE FOLLOWING COMPONENTS
ASSIGNMENTS -2

13. CALCULATE THE PRESS FORCE RQUIIRED TO PRODUCE
THE FOLLOWING COMPONENTS
ASSIGNMENTS -3

14. CALCULATE THE PRESS FORCE RQUIIRED TO PRODUCE
THE FOLLOWING COMPONENTS
ASSIGNMENTS - 4