PUNCHING AND BLANKING PROCESS Presented By: Presented To: Nilabrata Bera Dr. Biswanath Dolui Anupam Halder

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.

Application:

Automobile industries.

Aerospace industries.

Kitchen appliances.

Mass production of sheet metal components.

Cutting Tool & 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.

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.

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.

Drive Type of Punch Presses:

Flywheel Drive

Mechanical Punch Press

Hydraulic Punch Press

Servo Direct Turret Punch Press

Different Zones of Blanked Part:

Rollover Zone (Zr)

Shear Zone (Zs)

Fracture Zone (Zf)

Burr Zone (Zb)

Depth Of Crack Portion (Dcp)

Secondary Shear

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.

Die diameter(d1)=d2+2c d2-punch diameter, c-clearance

Deformation of Workpiece:

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.

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.

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.

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).

Process Variants:

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

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.

Notching:

In notching, material is removed from the side of a sheet material.

Lancing:

Lancing process makes partway through the metal without producing any scrap.

Slitting:

It is an operation to cut a coiled sheet metal lengthwise to produce narrower strips.

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.

Trimming:

Trimming process refers to the removal of excess material in a flange or flash.

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.

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.

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.

References:

Manufacturing Science(Amitabh Ghosh, Asok Kumar Mallik)

www.wikipedia.org

www.nptel.ac.in

www.slideshare.net

Degarmo’s Manufacturing Science

Thank You