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International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 3, Issue 3, March 2013)

390

An Overview Of Factors Affecting In Blanking ProcessesAmol Totre1, Rahul Nishad 2, Sagar Bodke3

1,2,3 B.E. student

Abstract — During the past decade, two clear trends have

been observed in the production of metal components. Firstly,

time-to-market needs to be shortened in order to introduce

new products competitively. Secondly, ongoing

miniaturization forces product dimensions to decrease. Of all

forming processes employed in high volume production,

blanking is one of the most widely used separation techniques.

Still, analysis of blanking is mainly based on

phenomenological knowledge. Since, also in blanking

processes, requirements concerning product dimensions are

becoming more severe so we focus on what are the factors that

will affect in blanking process.

Keywords — Blanking, Burr, Clearance, Factors, Tool

wear

I. I NTRODUCTION

Blanking and piercing are both shearing operation. The

difference is only in the scrap. In blanking what you cut out

is of interest. In punching what you cut from is of interest.

For example: You cut a hole in a sheet metal. If you are

interested in the disc that is cut out, then the process is

called blanking. The sheet metal with a hole through it is

the scrap. If you are interested in the sheet metal that now

has a hole through it, then the process is called piercing.The disc is the scrap shown in fig 1

Figure 1. blanking & piercing

Blanking and piercing is used in almost all sheet

forming operation. The size of hole can be vary from less

than 1 to 100 mm or more. In this paper we focus on the

blanking process and factors affecting the blanking

product.

A. Characteristics of the blanking process include:

1. Its ability to produce economical metal work pieces in

both strip and sheet metal during medium or high

production processes,

2. The removal of the work piece from the primary

metal stock as a punch enters a die,

3. The production of a burnished and sheared section on

the cut edge,

4.

The production of burred edges,

5.

The control of the quality by the punch and die

clearance,

6.

The ability to produce holes of varying shapes –

quickly

B. The blanking process has some downside effects. These

include:

Generating residual cracks along the blanked

edges,

Hardening along the edge of the blanked part or

work piece, and

Creating excess roll-over and burr if the clearance

is excessive.

The most common materials used for blanking include

aluminum, brass, bronze, mild steel, and stainless steel.

Due to its softness, aluminum is an excellent material to be

used in the blanking processes

II.

BLANKING PROCESS

Blanking process can be considered to include series of

phases in which sheet metal undergoes deformation and

separation as seen in fig 2

Contact of punch

The punch first touches the fixed sheet .at impact a

compressive stress rapidly builds on the punch and sends a

shock wave through it

Elastic and plastic deformation

The punch penetrates into the sheet .first causing an

elastic and then plastic deformation

Shearing and crack formation

When the stresses increase shearing occurs followed by

fracture .fracture begins from both the punch end and die

end of the sheet they usually meet and complete fracture of

the material takes place

Breakthrough

If the sheet material has a high strength or is thick. A

large force is required for blanking process. During fracture

compressive forces are stored in the tool.





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When complete fracture occurs there is an instant release

of the compressive forces these generate shock, which can

lead to breakage of the punch in some cases.

Stripping

The punch move down to the bottom dead centre and

ejects the part.

At the bottom dead centre direction of the punch motion

is reversed. Due to the friction between the stock and the

surface of the punch, the surface pressure intensifies. Astripper or blank holder strips the blank from punch

Figure 2 Steps in blanking process

A. Forces and stresses

The cutting force do not act linearly along the cutting

edge instead, the vertical force Fv and horizontal force FH

act in small area near the cutting edge as shown in fig 3

The distribution of those compressive forces are non

uniform. The distance, l, between the forces FH and FV’

cause bending movement must be compensated for by

counter bending moment that is created by bending stresses

and horizontal normal stresses between work piece and tool

fig also shows the resulting frictional forces µ.FH and µ. FV

these frictional forces increases total blanking forces.

The blanking process can be investigated by monitoring

the change in the blanking force during the cutting process

the force varies with the punch displacement , punch entry

time or crank angle.

Figure 3 Stresses in blanking

Because part quality is evaluated in terms of region

formed along the part edge ,it is preferred to present.

The load versus punch displacement. In addition the

cutting work can be calculated by integrating the forces

over the stroke .the theoretical load-stroke curve in a

blanking process can be described schematically as seen in

fig 5

Step 1: The sheet metal deforms elastically.

Step 2: The limit of elastic deformation is reached and the

material starts to deform plastically. The material flows

along the cutting edge in the direction of the punch

penetration and into the gap between the punch and die.

The material floe causes strain hardening which result in an

increase of the cutting force up to the maximum load. At

this time the cross section is not reduced and shearing is not

started.

Step 3: the increase cutting force at cutting edge prevent

the material from flowing and shearing start. Due to a

decreasing cross section the blanking force decreases

deposit the strain hardening of the material.

Step 4: fracture starts after the formability limit of thematerial is exceeded. As soon as the initial cracks meet

each other slug and skeleton are completely separated. The

cutting force decreases rapidly during this phase.





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Excessive clearance will result in tapered cut edge

because for any cutting operation, the opposite side of the

material that the punch enters after cutting, will be the samesize as the die opening.

The width of the burnish zone is an indication of the

hardness of the material. Provided that the die clearance

and material thickness are constant, the softer the material

the wider will be the burnish zone.

Harder metals require large clearance and permit less

penetration by the punch than ductile materials; dull tool

(punch and die) create the effect of too small a clearance aswell as bur on the die side of the stock. Clearance is

generally expressed as a percentage of the material

thickness, but some authorities recommend absolute values.

C = Dm -d p/2 from fig 7

Table 1

Value of clearance as the percentage of the thickness of material

MATERIALS MATERIAL THICKNESS T(MM)

<1.0 1.0 TO 2.0 2.1 TO 3.0 3.1 TO 5.0 5.1 TO 7.0

LOW CARBON STEEL 5.0 6.0 7.0 8.0 9.0

COPPER AND SOFTBRASS

5.0 6.0 7.0 8.0 9.0

MEDIUM CARBON

STEEL 0.2% TO 0.25%

CARBON

6.0 7.0 8.0 9.0 10.0

HARD BRASS 6.0 7.0 8.0 9.0 10.0

HARD STEEL 0.4% TO

0.6% CARBON

7.0 8.0 9.0 10.0 12.0

Table illustrate the value of the shear clearance in percentage depending on the type and the thickness of the material

Figure 7 punch and die

B.

The eff ect Punch geometry

Punch geometry affects the punch stresses and

temperature as well as punch life. Figure shows the

maximum forces by using different punch shapes when

blanking a round part. The punch forces differ because the

area of contact with the sheet at given instant in the

penetration length is not the same.

Figure 8 force Vs time digram

Shear angles/chamfers on the punches are also used for

easy stack up of the slugs. The slugs, when bent, become

neatly stacked over and one another fig 8 shows the various

punch shapes





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Figure 9 effect of tool wear and blanking force on part edge quality as

predicted by simulation .58mm thick copper alloy

C.

The effect of tool wear

Tool wear leads to the Formation of burrs and increases

burr length. Burr length is generally an important criterion

in the industry to evaluate part quality. Burr length in-

dicates when the tool should be reground to obtain the

sharp die-and-punch radius. It has also been observed that

the effect of tool wear is more pronounced at higher

blanking clearances. The effect of tool wear on part edge

quality is significant. Tool wear leads to the formation of

buns and increases burr where the effect of tool wear was

simulated by assuming different punch corner radii insimulations. It has also been observed that the effect of tool

wear is more pronounced at higher blanking clearances

from fig 9 &10

Figure 10 tool wear

D. The Effect of the Sheet Thickness

For a given material, the energy requirement in blanking

is influenced by the sheet thickness. It has been observedthat:

1. The blanking energy decreases with increasing

clearance-to-sheet thickness ratio c/t and increases

with increasing sheet thickness.

2.

The proportions of the different depth characteristics

of the sheared profile are affected by the thickness.

E.

The Effect of Material

The part edge quality also depends on the mate-rial

being blanked. Materials with large ductility, low yield

strength, and homogeneity will have better blanked edge

quality, dimensional tolerances, and longer tool life

IV. CONCLUSION

In the present paper we see the factors affecting in the

blanking process like the

A. Clearance

B. tool wear

C.

Sheet Thickness

D.

Material

E.

Punch geometry

Also by the help of the various fig we see the what are

importance of this factors in the blanking process out of

which clearance, thickness & tool wear is important factors

clearance value of the various material is given in the table

1 like brass, steel, carbon steel etc.

REFERENCES

[1]

R. Hambli, (2002), ―Design of Experiment Based Analysis for Sheet

Metal Blanking Processes Optimization‖. The International Journal

of Advanced Manufacturing Technology, Vol.19, Page No.403-410.

[2] F. Faura, A. Garcia, and M. Estrems, (1998), ―Finite element

analysis of optimum clearance in the blanking process‖. Journal of

Materials Processing Technology, Vol.80-81, Page no.121-125.

[3]

R. Hambli, S. Richir, P. Crubleau, and B. Taravel, (2003),

―Prediction of optimum clearance in sheet metal blanking processes‖. International Journal of Advanced Manufacturing

Technology, Vol. 22, page no. 20-25.

[4]

Emad Al-Momani, Ibrahim Rawabdeh, (Mar. 2008), ―AnApplication of Finite Element Method and Design of Experiments

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[5]

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[6]

R. Hambli, (2003), ―BLANKSOFT: a code for sheet metal blanking processes optimization‖. Journal of Materials Processing

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[7]

Ridha Hambli, (June 2005), ―Optimization of blanking process using

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