2. Introduction:
Punching and blanking processes are sheet metal forming
processes.
In these two processes a finite volume of metal from a
sheet is removed by using die and punch.
The shape and size of the portion removed depends on
the geometry of die and punch.
Also the operation cost and time depends on die and
punch design.
4. CuttingTool & Job Material:
The cutting tool(punch and die) are made of hardened
steel or tungsten carbide.
The sheet metal to be machined is generally made of
aluminium, brass, copper, stainless steels.
In some cases plastic is also used.
5. Difference:
In the punching process the final product is the metal
sheet from which metal is removed.
In blanking process the final product is the removed
portion from the sheet.
6. Punching Press:
It is a type of machine press used to cut the material.
Can be very simple and manually controlled or very
complex and CNC controlled.
8. Different Zones of Blanked Part:
Rollover Zone (Zr)
Shear Zone (Zs)
Fracture Zone (Zf)
Burr Zone (Zb)
Depth Of Crack Portion (Dcp)
Secondary Shear
9.
10. Process:
The job is held by job holders to prevent distortion.
A clearance is provided between the punch and die.
Force is given on the job by the punching tool.
A finite portion of metal is removed from the sheet.
12. Deformation ofWorkpiece:
The job bends and is pulled down by the punch
movement.
The grains elongate at A,B & D.
When the elongation reaches a limiting value , rupture
occurs.
13. Working Force:
The maximum force required to create a complete
rupture is, Fmax=σf Co L (σf -true rupture stress, Co -
optimum clearance. L-length of cut).
The maximum force required can be reduced by avoiding
the simultaneous failure of the total area.
This is done by providing an angle to the punch edge.
But the total energy requirement remains same.
14. Effective Clearance:
The amount of clearance given is very important.
As the velocity of propagation of fracture lines is very
high, they may miss each other without optimum
clearance.
In optimum clearance, a clean edge is obtained.
In case of too little or too large clearance, secondary
deformation takes place.
15. Stripping Force
Two actions take place in the punching process-punching
and stripping.
A stripping force develops due to spring back of the
punched material that holds the punch.
This force is generally expressed as a percentage of the
force required to punch the hole.
The value of stripping force is generally given by the
equation,
SF = 0.02 L * t( L-length of cut , t-thickness of material).
16. ProcessVariants:
Depending on the shape of the metal removed or process,
there are some special types of Blanking processes-
Fine Blanking
Notching
Lancing
Slitting
Nibbling
Trimming
17. Fine Blanking Process:
A special type of blanking process.
Fracture zone does not form while shearing.
Very tight tolerance is achieved by this process.
Aluminium , brass, copper ,stainless steels are the metals
that can be fine blanked.
20. Slitting:
It is an operation to cut a coiled sheet metal lengthwise
to produce narrower strips.
21. Nibbling:
In nibbling operation, complicated shapes are cut out from
a sheet metal by producing overlapping notches.
Without using any special tools, a simple, round or
triangular punch is reciprocated at a fixed location.
The sheet metal is guided to obtain the desired shape of
cut.
23. Advantages:
Punching and blanking are quick processes.
The slug produced may be reused or recycled(depending
on material).
It is often the cheapest and most cost effective method
for medium to high volume of production.
It can create multiple shaped holes or same shaped holes
very fast.
24. Disadvantages:
Equipment and tooling costs are high.
Often needs secondary finishing operations to smooth
out burrs along the bottom edge.
Fine blanking process is a slow process.
25. Conclusion:
Punching and blanking process is very cost effective
process.
Though the initial equipments cost may be high but it is
very useful for mass production.
Very closer dimensional tolerance can be achieved by fine
blanking process.
