Technical Information

Vol. 28TECHNICAL COUNSELING FAQThis time, we will introduce the prevention of warping (curvature)
during blank punching.

WARPING PREVENTION OF BLANKING OUT
Ｑ

ＡAlthough processing a blank out, the removed product may be warped or partially twisted.
Currently, leveler corrects, but is there any good way?

When the plate is punched out, the scraps aregenerally curved. (See Fig.1)
This is because the material is subjected to bending
and bending at the same time as punching, whichcauses plastic deformation of the material. (See Fig.2)
Therefore, if the slug is a product like a blank tool,
it may be necessary to make adjustments such as
passing through a leveler in a later process.
As this measure,
1. Slitting the outline (Periphery).
This method is generally adopted as a method ofpunching out the outer periphery (contour) of theproduct rather than punching out the product.
In this case, products are connected by micro joints
and separated after processing. (See Fig.3)
2. Reduce the die clearance.
As the clearance increases, the bending force applied
to the material increases and the curvature increases.
In the case of a blank type, we recommend a clearance
slightly smaller than the appropriate clearance.
However, if the clearance is too small in the case of a
thick plate, the burden on the tooling will increase andit may also cause damage to the tooling.
3. Re-grind early.
Even when punched with a worn cutting edge, thebending force is increased and the curvature is greater.
We recommend re-grinding early and punching with asharp cutting edge.

Continue to the next pageFig.1 Curved slug when punchingCurved slug
Fig.2 Applied force to the punching time
Shearing
force

Shearing
force

Bending
stressFig.3 Micro joint processing

ProductProductProductProductTECHNICAL COUNSELING FAQWARPING PREVENTION OF BLANKING OUT
4. Adjust the output length of the urethane kicker.
Even in the case of the blank type, a urethane
kicker may be attached to the punch dependingon the shape and size of the cutting edge,in order to prevent the phenomenon that the blankproduct is lifted without being dropped out(It is called slug pulling).
As a result, depending on the material and thicknessof the workpiece, it is possible that deformation suchas warpage may occur in the blank product.(See Fig.4)

Fig.4 Adjust the length of slug ejector
Cut slug ejector toadjust the length

ORPunchSlug ejector

5. Back pressure
his is a method of correcting the curvature of the material
by applying reverse pressure to tool and applying back pressure.
(See Fig.5)
Half sheared is done in this process, and it is pierced in anotherprocess.
6. To strengthen the holding force.
By using 1 bigger station size and increasing the plate pressing
force, the bending force of the workpiece is suppressed anddeformation is reduced.
7. If there is a hole inside the product (in the form of a washer),a greater curvature will occur. Also, if there is a hole closer
to the product's outer periphery (outline), there may be distortionin the area between the outer periphery and the hole. (See Fig.6)
Do the drilling in a post process other than punching, or pierce theoutline near the hole first

Take outslug ejector

Fig.5 Tooling with back pressure

Back pressure
Fig.6 Holes close to the edge ofproduct outlinePunch
Material
Product HoleDie

Twist occurs

8. Do not attach shear angles to the blank type.
When punching with a punch with a shear angle, the blank isdeformed by the shear angle. Always grind the punch surface(the surface that the material hits) flat.

For More information,please contact
CONIC tool sales desk.

Do not attach shear
angle to the blank tool !