Assessment & Optimization of Influence of Some Process Parameters on Sheet Metal Blanking

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 04 Issue: 10 | Oct -2017 www.irjet.net p-ISSN: 2395-0072
© 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 266
Assessment & Optimization of Influence of some Process Parameters
on Sheet Metal Blanking
Vikrant J. Jadhav 1, Mr. B.R. Shah 2
1 ME - Mechanical Engineering (Computer Aided Design, Manufacture & Engineering)
2 M.E- Mechanical Engineering Design
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Abstract - Metal blanking is a widely used process in high
volume production of sheet metal components. Blanking
consists of a metal forming operation characterized by
complete material separation. Low carbon steel is a very
common material used in fabrication of sheet metal
components. The experimental studies were conducted under
varying sheet thickness, clearance and wear radius and shear
angle. The main objectives are to present thedevelopment ofa
model to predict the shape of the cut side. The model
investigates the effect of potential parameters influencing the
blanking process their interactions. This helped in choosing
the process leading parameters for two identical product
manufactures from two different materials blanked with
reasonable quality on the same Tool/Die.
Optimization is one of the techniques used in
manufacturing sector to arrive for the best manufacturing
condition. This is an essential need of industries towards
manufacturing of quality product at lower cost. The main
objective of this study is to treasure optimal parameters such
as sheet thickness, clearance and wear radius in blanking to
find out the variations in three performance characteristic
such as burr height, accuracy and circularity value for
blanking of medium carbon steel. Based on experiments are
conducted on L-9 orthogonal array, analysis has been carried
on by using Grey Relational Analysis, a Taguchi method.
Response tables and graphs were used to find optimal level of
parameters in blanking process. The obtained results shows
that the Taguchi Grey Relational Analysis is being effective
technique to optimize the parameters for blanking process
Key Words: Blanking, GRA, GRG, Taguchimethod, Orthogonal
Array, Finite Element Analysis (FEA)
1. INTRODUCTION
Die design is a large division of tool engineering, is complex,
fascinating subject. It is one of the most existing of all the
area of tool design. Stamping presses and stamping dies are
tools used to produce high volume sheet metal parts. These
parts achieve their shapes through the effectofthedie.Sheet
metal stampings have now replaced many components,
which were cast or machined. material economy and the
resultant reduction in weightandcost,highproductivity, use
of unskilled labor, and a high degree of possible precision
have rendered press work indispensable for many mass
produced goods.
For the manufacturing of the die,theselectionofappropriate
material selection of manufacturing process and highly
precise mating of the upper and lower half of the die is
significant. The proper heat treatment of die blocks, and
prevents warping. Also, manufacturing withinthetolerances
limits provided is important forproperfunctioningofthe die
and obtaining dimensional accuracy in the product. Also
while designing and manufacturing of die the factor of
economy is also kept in mind. Press working may be defined
as a chip less manufacturing process by which various
components are made from sheet metal. The machine used
for press working is called a press. The main features of a
press are: a frame which supports a ram or a slide and a bed,
a source of mechanism for operating the raminlinewithand
normal to the bed. The ram is equipped with a suitable
punch and a die block is attached to the bed. A stamping is
produced by downward stroke of ram when the punch
moves towards and into the die block.
1.1 Components of the Die and the Press
A simple cutting die used for punching and blanking
operation is shown in fig. Below the definition of main
components of the press are given.
Bed
The bed is the lower part of press frames that serves as a
table to which bolster plate mounted.
Bolster plate
This is a thick plate secured to the press bed, which is used
forlocating and supporting the dieassembly. Itisusually5to
12.5 mm thick.
Die-set
It is unitassembly, which incorporatesloweranduppershoe,
two or more guideposts and guideposts bushings.

Die
The die may be defined as a female portion to complete tool
for producing work in a press. It is alsoreferredtoacomplete
tool consisting of a pair of members for producing work in a
press.
Lower shoe
The lower shoe of dieset is generally mounted on the bolster
plate of the press. The dieblock is mountedonthelower;also
the guide post is mounted in it.
Punch
This is the male components of the assemblies, which is
directly or indirectly moved by and fastens to the press ram
or slide.
Punch plate
The punch plate or the punch plate retainer fits closely over
the body of the punch and holds in proper relative position.
Upper shoe
This is the upper part of the die, which contains guidepost
bushing and guidepost assembly.
Back up plate
Back up plate or pressure plate is placed so that the intensity
of pressure does not become excessive on punch holder. The
plate distributes the pressure over a wide area and the
intensity of pressureon the punch holder is reduced to avoid
crushing.
Stripper
It is the plate which used to strip the metal strip from a
cutting punch or die it may also guide the strip.
Knock-out
It is mechanism usually connected to and operated by the
press ram for pressing a work piece from die.
1.2 Press Working Operations
The sheet metal operations done on a press may be grouped
into two categories, cutting operations and forming
operations. In cutting operations, the work piece is stressed
beyond its ultimate strength. The stresses caused in the
metal by the applied forces will be shearing stresses. In
forming operations, the stresses are below the ultimate
strength of the metal. In this operation, there is no cutting of
the metal but only the contour of the work piece is changed
to get the desired product. The cutting operations include:
blanking, punching, notching,perforating,trimming,shaving,
slitting and lancing etc. the forming operations include:
bending, drawing, redrawing and squeezing. The stresses
induced in the metal during bendinganddrawingoperations
are tensile and compressive and during the squeezing
operations these are compressive
1.3 Working of Cutting Dies
As it is clear in the figure, the punch holder (upper shoe) is
fastened directly to the ram of the punch press, and the die
shoe (lower shoe) is fastened to the bolster plate of the
press. Guide posts may be used to better align the punch
holder with the die shoe. These main components (Punch
holder, Die shoe and Guide Posts) constitute what is known
as the die set. A die set can be had with two guide posts
located at the rear of the die set (Known as back post),
diagonally, one at the die set. The lower ends of the guide
posts are press fitted into the die shoe. At the upper end, the
guide posts have a slip fit with the guide bushings. The
punch is fastened to the punch holder and the die block is
fastened to the die-shoe. The punch is aligned with the
opening in the die-block. Since, both the punch and the die-
block act as cutting tools, they are hardened.
Fig.1: Press working operations
The cutting action takesplaceduringthedownward
movement of the punch into the die block. After the cutting
action, the elastic recovery takes place in strip material. Due
to this, the size of the blank (Cut portion from the strip)
increases and that of the hole in the strip decreases. So, at
the end of the cutting action, when the punch starts to move
upwards the scrap strip clings to the punch and the blank
gets clogged in the die-opening. To remove the scrap strip
from the punch surface, a striper is used. In fig, a simplest
type of striper is used. It strips off the scrap strip from the
punch surface when the scrap strip strikes the bottom
surface of the stripper during the upward movement of the
punch. To avoid clinging of the blank in the die opening, the
walls of the die-opening are tapered

2. Blanking Process
Blanking is a manufacturing operation as old as the
technology itself. Its applications range from components of
very light to heavy appliances and machineries. Blanking is
defined as the cutting of a work piece between two die
components to a predetermined contour. During blanking,
the part is subjected to complex solicitations such as
deformation, hardeningandcrackinitiationandpropagation.
The theoretical modeling of such processes is very difficult
due to the complexity in describing the different stagesofthe
whole shearing process starting with the elastic stage and
ending with the total separation of the sheet metal.
Blanking process, which is also referred to as
shearing, or punching process, is illustrated in Fig. . A metal
sheet is pressed on a die by a blank holder and perforated by
a punch. Four characteristic dimensionscanbedistinguished
on the blanked edge such as the roll over depth, the fracture
depth, the smooth sheared depth, the burr formation and
fracture angle.
Fig.: Geometry of the sheared work piece.
2.1 Deformation and Rupture Mechanism
During sheet metal shearing operation, the part is subjected
to complex solicitations such as deformation, hardening and
crack initiation and propagation. The theoreticalmodelingof
such processes is very difficult due to the complexity of
describing the different stages of the whole shearing process
starting from the elastic stage and ending to the total
separation of the sheet metal Fig.6. Accurate knowledge of
the failure process is essential for the selection of a suitable
damage model. In the case of sheet blanking by shearing
processes, numerous authors have studied the different
physical mechanisms leading to the final rupture, and
proposed their own models.
1. Elastic stage
2. Elastoplastic stage
3. Elastoplastic stage in which damage occurs.
4. Initiation propagation of crack leading to final rupture.
Fig.: Different stage of the blanking process
A set of formulae taking into account the material
characteristics of the sheet, the geometry of the operation
and the wear state of the tool has been developed allowing
for the prediction of the characteristic zone heights of the
blanked part such the heights of the burr the roll-over, the
sheared and the fractured zones. The punch penetration
curve can also be plotted which allowsforthecomputationof
the maximum blanking force and the blanking energy.
2.1 Main Objective of this Project
The main aim of this study is to evaluate the influence of tool
clearance, friction, sheet thickness, punch /die size and
blanking layout on the sheet deformation. Hence for
optimizing various blanking process parameters following
objectives are decided
1. To review the literature on blanking process.
2. To design the die for selected blanking operation.
3. Select various process parameters for in-depth analysis.
4. To optimize selected blanking process parameters.
5. Studyactual stress concentrationonsheetduringblanking.
6. Study of deformation on punch and die using Analysis.
3. EXPERIMENTATION
This experimentationwasconductedusingtheMachines and
Equipment’s listed in Table 1 on press machine as shown in
figure at Indo-German Tool Room, P-31, MIDC Chikalthana,
Aurangabad-431006 (M. S.). A blanking die having Ø10 cut
profile manufactured in same organization. After
experimentation output variables / Parameters are
measured at Micronics Calibration Center, Plot 12, Cidco
service industrial zone, opp. A. P.I. Ltd,Aurangabad-431210.

Table: Hardware List
Fig.: Video measuring machine (VMM)
3.1 Selection of Blanking Parameters
The methodology that is followed to attain the research
objectives is divided into the following work phases:
1) Classify the blanking parameters into controllable and
uncountable. The identified controllable parameters are
clearance, blank holder force, sheet metal thickness, and
material type. While, the uncountable parameters are
material properties, inconsistency and conditions (shape,
defects and internal stresses), friction and wear state of the
tool, stroke rate or blanking speed,andpunch-diealignment.
2) Choose the controllablefactorsthatinfluencetheblanking
process.
Select an appropriate working range for each potential
factor. It is found that the working range of clearance fall
within the range (0-15%) of the sheet metal thickness and
the working range of the thickness of the used material fall
within the range (0.3-0.5) mm.
3) Prepare to use of Design of Experiments (DOE) technique
by selecting the experimental levels for each selected factor,
i.e. the clearance to be in three levels (5, 10, 15 %) of the
sheet metal thickness i.e.0.3, 0.4, 0.5 mm.
Fig.: Blanking process parameters
A) Influence of Blanking Clearance
Dm, Dp, and t are, respectively, the die diameter, the punch
diameter, and the sheet thickness.
In order to study the influence of this design parameter,
three tools have been designed corresponding to four
different clearances, 5%, 10%, a n d 15%. These values
correspond to the most used clearances in industry.
B) Influence of the sheet thickness
For a given material, the energy requirement in blanking is
influenced by the sheet thickness. It has been observed that:
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.
3. To study the effects of the interactions between the
clearances and the sheet thickness, a series of experiments
have been carried out with four thickness values of sheeti.e
0.30, 0.40, and 0.50.
C) Influence of the tool wear / wear radius
The design of the tool is one of the main features in the
industrial process. Therefore it is necessary to study the
effects of tool wear on the blanking force and the sheared
profile variations. The quality of the work piece is governed
by the state of the tool wear.
Wear is defined as a slow degradation of the blanking tool
caused by the friction involved between tool and sheet
metal. The rate of wear is affectedbyparameterssuchastool
material, blanked part material, punch–die clearance,punch
velocity, lubrication, and material thickness.Generally,wear
takes place on the external surface of the tool. It causes the
cutting edges to be rounded. Therefore, the influence of the
tool wear can be accounted for by changing the values of the
edge radii Rwp and Rwd. Experimental investigationintothe
blanking process was carried out using punches with
different wear states. The aim was to define the relationship
between the sheared profile of thecomponentandtheforces
applied to the tool evolutions versus thetool wear evolution.

Three wear states of the tool were chosen corresponding to:
A new die with: Rwd= 0.01 mm.
A new punch with: Rwp= 0.01 mm.
Two “worn out” punches with different edge radii Rwp=
{0.15, 0.3} mm.
4. GREY RELATIONAL ANALYSIS
In a blanking operation, many factors simultaneously
influence on blanking process to determine the state of
development of the system Usually, we want to know which
factors influences the system more and which factor
influences the system little. However, the relationship
between various factors is usually grey where the
information is unclear, incomplete and uncertain.Moreover,
practical and experimental data was difficult to obtain and
too much scatter to analyze. Two conventional statistical
methods frequently used on the relationship between
independent and dependent factorswerefactoranalysisand
regression analysis methods. Comparing to regression
analysis and factor analysis in mathematic statistics, grey
relational has some merits such as small sample, having no
use for typical distribution, no requirement for
independency and small amount of calculation.Additionally,
GRA analysis is already proved to be simple and accurate
method for selecting factors especially for those problems
with unique characteristic. Grey relational grade (GRG) can
be used to describe the relationships among the factors and
to determine the important factors that significantly
influence some defined objectives. GRA can provide a
ranking scheme that rank the order of the grey relationship
among dependent and independent factors andthisallowus
to decide which input factors need to be considered more
precisely. In the case when experiments are ambiguous or
when the experimental method cannot be carried out
exactly, grey analysis helps to compensate for the
shortcoming in statistical regression .Grey relation analysis
is an effective means of analyzing the relationship between
sequences with less data and can analyze many factors that
can overcome the disadvantages of statistical method.
Taguchi method or Taguchi approach is a DOE technique
with new experimental strategy where the qualityisdefined
in general terms. The method could be used not only to
improve quality, but also to quantify the improvements
made in terms of saving money. The experimental design
and analyze of the results can be done with less effort and
expenses by using the Taguchi approach. Since the method
enormously reduces the number of experiments.
4.1 Flowchart of the Taguchi method
The first step of Taguchi method requires the knowledge
about the domain that is examined, since the main function,
side effects and failure modes have to be identified. A wrong
decision in this step makes all other steps useless. The
second step is to find control factors and their levels. To
reduce the number of experiments, only the most important
factors should be considered
Two or three factor levels can be chosen. In the latter case,
the levels should be evenly distributed. The factor levels
should be placed very carefully, since the Taguchi method
defines the significant and optimal parameters only within
the levels. The orthogonal arraythatdefinestheexperiments
is selected in the third step. The fourth step is to performthe
experiments. Optimal factors are predicted in the fifth step.
And in the last step of Taguchi method optimal parameters
should be tested to confirm or reject optimal parameters
found by Taguchi method.
4.2 GREY RELATIONAL ANALYSIS
In Grey relational analysis, experimental data i.e., measured
features of quality characteristics are first normalized
ranking from zero to one. This process is known as Grey
relational generation. Next, based on normalized
experimental data, Grey relational coefficientiscalculatedto
represent the correlation between the desired and actual
experimental data. Then overall Grey relational grade is
determined by averaging the Grey relational coefficient
corresponding to selected responses. The overall
performance characteristic of the multipleresponseprocess
depends on the calculated Grey relational grade.
4.3 Process Parameters
The control parameters at three different levels and three
different response parameters considered for multiple
performance characteristics.

In this work, L-9 Orthogonal Array design matrix is used to
set the control parameters to evaluate the process
performance. The next table shows thedesignmatrixusedin
Experimentation.
Experiments were conducted as per L-9 orthogonal array,
assigning various values of the levels to the process
parameters. After individual experiments for each set of
values were conducted on medium carbon steel sheet for
Ø10mm Blank, burr height, Accuracy and Circularity are
calculated using video measuring machine (VMM) and the
final results.
Following Table and fig shows experimental results and
individual effect of process variables on burr height.
Assembly Model – A
Sheet / strip thickness 0.30mm, Blanking punch diameter
9.97mm (with the clearance 5 % of sheet thickness) In all
loading conditions, the maximum deformation on sheet. at
the region where actual force is applied and on die plate
contact area of punch and die with sheet / strip.
4.4 Conformation of Results
The Confirmation for the optimal process parameters with
its level has conduct to evaluate quality characteristics for
Blanking of medium carbon steel sheet. Table 14 shows
highest grey relational grade, indicating the initial process
parameters set of A1B1C1 for the best multipleperformance
characteristics among the nine experiments.Table14shows
the comparison of the experimental results for the
conditions (A1B1C1) with predicted result for optimal
(A1B1C1) Blanking process parameters.
Predicted Response=Average of A1 + Average of B1 +
Average of C1 – 2 x Mean of response (Yij)
The response value obtained from the experiment are
Minimum Burr height = 0.039 mm, Accuracy of Blank =
10.012 mm, and Circularity of Blank = 10.008mm. The
comparison is shows the good agreement between the
predicted and experimental values.
4.5 FINITE ELEMENT ANALYSIS [FEA]
FEA consists of a computer model of a material or design
that is stressed and analyzed for specific results. It is used in
new product design, and existing product refinement. A
company is able to verify a proposed design will be able to
perform to the client's specifications prior to manufacturing
or construction. Modifyinganexistingproductorstructureis
utilized to qualify the product or structure for a new service
condition. In case of structural failure, FEA may be used to
help determine the design modifications to meet the new
condition.
Methodology of work
Step-I: Received Idea about Stress distribution and punch,
die deformation.

Step-II: With the help of Literature survey and Technical
Knowledge Preparing CAD Model Blanking tool (Punch and
Die)
Step-III: With the help of 3-D Model from CAD System
Preparing Meshed 3-D Model for Analysis
Step-IV: Extracting Results from CAE Software
5 CONCLUSIONS
The developed experimental investigationofthesheetmetal
blanking process makes it possible to study the effects of
process parameters such as the material type, the punch-die
clearance, the thickness of the sheet and the blank holder
force and their interactions on the geometry of the sheared
edge especially the burrs height.Ingeneral,clearanceplaysa
key role in both product quality and the service life of dies. A
good clearance design not only increases the quality of
product manufactured, but also reduces product’s burr.Asa
result, the wear of punches and dies can be greatly reduced
and the life expectancy of punching dies increased. More
punching times is positively related to bigger wear, while
less punching times is related to smaller wear.
The numerical FEAsimulationshowsthedeformationduring
shearing on punch ranging from 0.074mm to 0.139mm, die
0.000051µ to 0.017µ. These values increase for greater
frictional coefficient. The blankingprocesscanbeconsidered
as cold working process due tothemaximumtemperatureof
365 K (92˚ C) Attained in the sheet shear region.
ACKNOWLEDGEMENT
I wish to express my profound gratitude to the almighty god
for guiding us to successfully complete this work. I take this
opportunity to express my deep sense of gratitude to my
guide, Prof B.R. Shah for his continuous guidance and
encouragement throughout the courseofthisstudy.Without
his valuable suggestion and encouragement this would not
have been possible. It is because of his experience and
wonderful knowledge; I could fulfill the requirement of
completing the Project report II within the stipulated time.
I would also like to thank Dr.Atul Padalkar,
Principal, Flora Institute of Technology,Khopi, Punefortheir
through valuable support.
I acknowledge with thanks, the assistance provided
by the departmental staff and library staff. I thank all my
colleagues for their valuable cooperation and coordination
which was available from time to time.
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