1. International Journal of Industrial Engineering
and Development (IJIERD),
INTERNATIONAL JOURNAL 4,ResearchSeptember - December (2013),ISSN 0976 –
OF INDUSTRIAL ENGINEERING
6979(Print), ISSN 0976 – 6987(Online) Volume Issue 3,
© IAEME
RESEARCH AND DEVELOPMENT (IJIERD)
ISSN 0976 – 6979 (Print)
ISSN 0976 – 6987 (Online)
Volume 4, Issue 3, September - December (2013), pp. 01-12
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IJIERD
©IAEME
A DETAILED STUDY ON PROCESS FAILURE MODE AND EFFECT
ANALYSIS OF PUNCHING PROCESS
J. Arun1, S. Pravin Kumar2, M. Venkatesh3, A.S. Giridharan4
1
UG Graduate, Department of Mechanical Engineering, Government College of Technology,
Coimbatore.
2
UG Graduate, Department of Mechanical Engineering, Government College of Technology,
Coimbatore.
3
UG Graduate, Department of Mechanical Engineering, Government College of Technology,
Coimbatore.
4
UG Graduate, Department of Mechanical Engineering, Government College of Technology,
Coimbatore.
ABSTRACT
An FMEA (Failure Mode and Effect Analysis) is a systematic method of identifying
and preventing product and process problems before they occur. FMEAs are focused on
preventing defects, enhancing safety, and increasing customer satisfaction. Ideally, FMEAs
are conducted in the product design or process development stages, although conducting an
FMEA on existing products and processes can also yield substantial benefits. FMEA is used
in the manufacturing industry to improve production quality and productivity by reducing
potential reliability problems early in the development cycle where it is easier to take actions
to overcome these issues, thereby enhancing reliability through design. It is a method that
evaluates possible failures in the system, design, process or service. In this paper, Failure
mode and Effect Analysis is done on the process of Punching. A series of punching operation
is done on various work pieces and the defects are found. Based on the evidence found, the
ratings are given and risk priority number is given. Based on the RPN, the preventive
measures are given. The FMEA is a proactive approach in solving potential failure modes.
These works serve as a failure prevention guide for those who perform the punching
operation and works towards effective punching operation.
KEYWORDS: Failure Modes, Punching, Risk Priority Number, FMEA Table, Chipping.
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2. International Journal of Industrial Engineering Research and Development (IJIERD), ISSN 0976 –
6979(Print), ISSN 0976 – 6987(Online) Volume 4, Issue 3, September - December (2013), © IAEME
1.
INTRODUCTION
In today’s market, the expectancy of the customer towards high quality, reliable and
cost effective products is really high. So this expectancy proves a burden for the
manufactures as they strive to satisfy the customers with defect free, reliable product. So the
manufacturers switch to a newer technique which helps them to achieve the expected
standards. The challenge is to design a quality and reliability product early in the
development cycle. Such challenges are met with latest techniques and strategies
implemented in both the design and product manufacturing. One such technique is Failure
Mode and Effect Analysis (FMEA). Failure Mode and Effect Analysis (FMEA) is used to
identify potential failure modes, determine their effect on the operation of the product, and
identify actions to mitigate the failures [1-2].
1.1
FAILURE MODE & EFFECT ANALYSIS
FMEA is a tool originated by SAE reliability engineers. It continues to be associated
by many with reliability engineering. It analyzes potential effects caused by system elements
ceasing to behave as intended. The purpose of FMEA is to identify possible failure modes of
the system, evaluate their influences on system behavior and propose proper countermeasures
to suppress these effects. FMEA enhances further improvisation of both the design and
manufacturing processes in the future as it serves as a record of the current process in
formations [4-5]. FMEA is an engineering technique used to identify, prioritize and alleviate
potential problems from the system, design, or process before the problems are actualized
(According to Omdahl, 1988). What does the term “Failure Modes” imply? Lots of
definitions for this term can be obtained. According to the Automotive Industry Action Group
(AIAG), a failure mode is “the way in which a product or process could fail to perform its
desired function” (AIAG, 1995). Some sources define “failure mode” as a description of an
undesired cause-effect chain of events (MIL-STD-1629A, 1994). Others define “failure
mode” as a link in the cause-effect chain [3] (Stamatis, 1995: Humphries, 1994). To conclude
with we consider the term failure mode as any errors or defects in a process, design, or item,
especially those that affect the customer, and can be potential or actual. The term “Effect
Analysis” also invites various definitions. The effect analysis is “the analysis of the outcome
of the failure on the system, on the process and the service” (Stamatis, 1995: Humphries,
1994) [2-5]. To put it simply Effects analysis refers to studying the consequences of those
failures.
FMEA is a tool that allows us to:
•
•
•
•
•
Discover potential failures in a system, product or process
Prioritize actions that decrease risk of failure
Evaluate the system/design/processes from a new vantage point
Guide design evaluation and improvement
Troubleshoot and monitor the performance of systems
1.2 IMPORTANCE OF FMEA IN PUNCHING
Punching process is a stamping or pressing type of metal removal process in which
the product is formed by pressing the work between die [7]. The metal removal is by shearing
force between the work and the die. Various components contribute to the accuracy,
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3. International Journal of Industrial Engineering Research and Development (IJIERD), ISSN 0976 –
6979(Print), ISSN 0976 – 6987(Online) Volume 4, Issue 3, September - December (2013), © IAEME
reliability of the product. When these components are defective, this leads to the failure of the
product. Some of the failures in the punching process are like Punch chipping, Slug jamming,
Galling etc. [7]. These result in unfavorable consequences like failure of the system or
production of inaccurate products. Hence it is essential to conduct a FMEA in this process so
that the failure is avoided totally or reduced. Prior notification of these failures can prevent
them by following control measures.
2.
IMPLEMENTATION OF FMEA
The purpose of performing an FMEA is to analyze the product's design characteristics
relative to the planned manufacturing process and experiment design to ensure that the
resultant product meets customer needs and expectations. When potential failure modes are
identified, corrective action can be taken to eliminate them or to continually reduce a
potential occurrence [3-4]. In FMEA, failures are prioritized according to how serious their
consequences are, how frequently they occur and how easily they can be detected. Ideally,
FMEA begins during the earliest conceptual stages of design and continues throughout the
life of the product or service. Results can be used to identify high-vulnerability elements and
to guide resource deployment for best benefit. An FMEA can be done any time in the system
lifetime, from initial design onwards. The various steps in Process Failure and Effect
Analysis are as follows
•
Reviewing the process
•
List the potential effects and modes of failure
•
Assign a severity rating
•
Assign an occurrence rating
•
Assign a detection rating
•
Calculate the risk priority number (RPN) for each mode of failure
•
Take action to eliminate or reduce the high-risk failure modes
•
Calculate the resulting RPN as the failure modes are reduced or
eliminated [4].
2.1 STEP 1: PROCESS REVIEW
The blueprint (or engineering drawing) of the product and a detailed flowchart of the
operation are reviewed. The process parameters of the conducted tests are as follows:
Capacity
: 60 Ton
Maximum stroke
: 6"
Bed Area
: 42" X 32"
Speed
: 40 Strokes per minute
Floor to Bed
: 33"
Dimensions
: 10'10" High, 8'6" RL, 6' FB
Weight
: 15,000 Lbs
Tool used
: Tungsten steel
Work piece material : Silicon steel
Several trials are to be conducted with the above mentioned parameters.
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4. International Journal of Industrial Engineering Research and Development (IJIERD), ISSN 0976 –
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Fig 1: High Speed Press
Fig 2: Defective product from punching process
Burr formation
Fig 3: Burr formation in the punched product
2.2 STEP 2: POTENTIAL EFFECTS & FAILURE MODES
Based on the trials conducted the failures are listed. In this, previously recorded
failures are also added. The effects of these failure modes are also tabulated. These failure
modes and their effects are charted separately for the sake of calculating and assigning the
ratings and risk priority numbers. With the failure modes listed on the FMEA Worksheet,
each failure mode is reviewed and the potential effects of the failure should it occur are
identified. For some of the failure modes, there is only one effect, while for other modes there
may be several effects. This step must be thorough because this information will feed into the
assignment of risk rankings for each of the failures. It is helpful to think of this step as an ifthen process: If the failure occurs, then what are the consequences [4].
2.3 STEP 3: ASSIGN SEVERITY RATING
The severity ranking is an estimation of how serious the effects would be if a given
failure did occur. In some cases it is clear, because of past experience, how serious the
problem would be. In other cases, it is necessary to estimate the severity based on the
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5. International Journal of Industrial Engineering Research and Development (IJIERD), ISSN 0976 –
6979(Print), ISSN 0976 – 6987(Online) Volume 4, Issue 3, September - December (2013), © IAEME
knowledge of the process. There could be other factors to consider (contributors to the overall
severity of the event being analyzed) [4]. Calculating the severity levels provides for a
classification ranking that encompasses safety, production continuity, scrap loss, etc. user.
Each effect is given a severity number (S) from 1 (no danger) to 10 (critical). A failure mode
with severity number of 10 results in severe dissatisfaction of the customer and may even
result in the physical injury due to the failure. Severity ratings in the range of 4-6 result in
mild dissatisfaction of the customer whereas those in the range of 1-3 are not so severe and
may even be not detected [2-6]. Table 1gives the guidelines based on which severity ratings
were given.
3-5
Table 1: Severity Ratings
Description
Failure is of such minor nature that the customer (internal or
external) will probably not detect the failure.
Failure will result in slight customer annoyance
and/or slight deterioration of part or system performance
6-7
Failure will result in customer dissatisfaction and annoyance
and/or deterioration of part or system performance.
Severity Rating
1-2
Failure will result in high degree of customer
dissatisfaction and cause non-functionality of system
Failure will result in major customer dissatisfaction and cause
non-system operation or non-compliance with regulations
8-9
10
2.4 STEP 4: ASSIGN THE OCCURANCE RATINGS
Occurrence ratings denote how often such failures occur. In this step it is necessary to
look at the number of times a failure occurs. This can be done by looking at similar products
or processes and the failure modes that have been documented [4]. A failure mode is given an
occurrence ranking (O), again 1–10. If a failure is inevitable or occurs often, then it is given a
rating in the range of 8-10. Those with mild occurrences are given 4-6 whereas those with
low or eliminated failure have 1-3 occurrence ratings [2-6]. Table 2 gives the occurrence
ratings based on which FMEA table is designed in this paper.
Occurrence Rating
1
2,3
4,5,6
Table 2 Occurrence Ratings
Meaning
Failure eliminated or no know occurrence
Low or very few
Moderate or few occasional
7,8
High or repeated failure occurrence
9,10
Very high rate of failure or inevitable failures
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6. International Journal of Industrial Engineering Research and Development (IJIERD), ISSN 0976 –
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2.5 STEP 5: ASSIGN DETECTION RATING
This section provides a ranking based on an assessment of the probability that the
failure mode will be detected given the controls that are in place. The proper inspection
methods need to be chosen. The probability of detection is ranked in reverse order. For
example, a "1" indicates a very high probability that a failure would be detected before
reaching the customer; a "10" indicates a low – zero probability that the failure will not be
detected [2-6]. Table 3 shows the guidelines based on which the detection ratings of a product
are given.
Detection Rating
1
2-4
5-6
7-8
9
10
Table 3: Detection Rating
Description
Very certain that the failure will be detected
High probability that the defect will be detected
Moderate probability that the failure will be detected
Low probability that the failure will be detected
Very Low probability that the defect will be detected.
Fault will be passed to customer undetected
2.6 STEP 6: CALCULATE THE RISK PRIORITY NUMBER
The risk priority number (RPN) is simply calculated by multiplying the severity
ranking times the occurrence ranking times the detection ranking for each item.
Risk Priority Number = Severity × Occurrence × Detection
The total risk priority number should be calculated by adding all of the risk priority
numbers. This number alone is meaningless because each FMEA has a different number of
failure modes and effects. The small RPN is always better than the high RPN. The RPN can
be computed for the entire process and/or for the design process only. Once it is calculated, it
is easy to determine the areas of greatest concern. There could be less severe failures, but
which occur more often and are less detectable. These actions can include specific inspection,
testing or quality procedures, redesign (such as selection of new components), adding more
redundancy and limiting environmental stresses or operating range. Once the actions have
been implemented in the design/process, the new RPN should be checked, to confirm the
improvements [1,2,6].
Table 4: FMEA Table for Punching Process
S.
No
1
Occurrence
Rating
6
Detection
Rating
8
Leading to
downtime
5
6
Additional
die damage
3
Problem
Effects
Punch
Chipping &
Point
Breakage
Deformation
Severity
Rating
7
3
6
Causes
Solutions
RPN
High impact
or
compressive
failure
Misalignment
resulting in
lateral forces
Part material
movement
Change
punch
materials and
diameter
336
210
Check overall
die alignment
Use a retainer
or punchmounted
stripper
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7. International Journal of Industrial Engineering Research and Development (IJIERD), ISSN 0976 –
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1
3
6
2
2
1
1
8
2
7
Poor material
control
Excessive
stripping
force
Punch point
hardness too
low
Improper
punch
material
selected
Sharpening
damage
1
Regrind burr
1
1
Tight die
clearance
6
2
Sharp corners
on shaped
punches
6
4
Flat punch
face
3
4
4
3
7
2
Excessive
burr
7
2
7
2
Stress
concentration
at edges
7
Improper
heat
treatment
Improper
punch
stagger
Improper
finish on
punch point
and/or punch
face
Incorrect
clearance
Review die,
press, &
feeder setup
Reduce
punch-to-die
entry
Increase
punch-to-die
button
clearance
Consider
coatings to
add lubricity
35
126
28
Verify
hardness
7
Change
punch
material
Use Coolant,
correct speeds
and feeds for
grinding
Remove
regrind burr
Increase
clearance
Change
material
Use Coatings
and surface
treatments
Increase
clearance in
the corners of
die button
Use shear
angles and
use edge
breakers
Triple
tempered for
high-speed
and follow
the guided
speeds
Cut-off
operation &
large point
first to enter
112
49
7
84
168
84
84
98
Ensure there
are no harsh
grinding
Restore
correct
clearance
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Decreases
resistance to
fracture
Shortens
fatigue life
5
1
Worn tools
Sharpen or
replace tools
Misalign
components
Check
alignment
8
Tight die
clearance
Excessive
land length
Increase die
clearance
Change relief
from counter
bore to taper
Land length
should not
exceed four
times material
thickness
Verify there
is no reverse
taper in the
land of the
die button
1
1
3
Taper in the
land of the
die button
6
Punch
breakage
1
5
Slug
Jamming
1
6
3
4
2
Inadequate
taper relief in
die button
Worn die
button
Punch point
deformation
9
2
9
3
Worn or
chipped
punch
Rough land
in die button
5
3
Slug
Pulling
Punch point
deformation
Excessive
wear on
punch and
die
6
2
Slug tipping
7
4
1
1
Obstruction
in slug relief
hole
9
1
Bell mouth
wear in die
button
8
28
8
48
120
96
Increase per
side taper
Sharpen,
replace,
and/or change
die button
material
144
216
Sharpen or
replace punch
Use die
buttons with
smooth wire
cut, or ground
land
Check
lubrication—
consider
lubricating
both sides of
part material
Examine slug
path
Consider
increasing the
size of the
relief hole in
lower plate
Increase die
clearance
Check
alignment
Change die
button
material
Surface
defects
35
40
48
56
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Broken
punches and
dies
8
2
Punch entry
too deep
3
3
Punch entry
not deep
enough
Excessive die
clearance
Slug not held
in the land
9
3
Reduced die
performance
Reduced
punch and
die life
Requires
heat
treatment of
parts
High stress
concentration
in parts
7
1
3
Punch
Wear
and/or
Galling
2
3
5
1
4
9
1
Tight die
clearance
6
2
Use slug
control
system
Reduce punch
entry
54
Increase
punch entry
Reduce die
clearance
Use slug
control
system
Use vacuum
slug sucker
Blow air
through
center hole in
punch
Use negative
taper in land
Check
lubrication
Increase taper
relief or use
counter bore
die
Punch entry
too deep
Sticky
lubricants
Not enough
relief on die
3
2
Misalignment
4
2
Regrind burr
6
1
Improper
sharpening of
punch
3
1
5
1
Improper
punch
material
Sharp corners
on shaped
punches
4
1
9
Punch
surface too
rough
96
Increase die
clearance
Change
punch
materials
54
36
18
72
63
84
Reduce punch
entry
Check die &
press
alignment
Remove
regrind
burr—break
sharp
Use flood
coolant, and
correct
grinding
wheel speed
& feed for
steel type
Change
punch
materials
Increase
clearance in
the corners of
the die button
Consider
punch finish
improvements
42
56
42
21
35
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5
6
3
Insufficient
chamfer in
retainer
4
7
Backing plate
too hard
3
6
Head is too
hard
4
High impact
or high
compressive
load on head
9
1
Incorrect
clearance
2
Lack of
lubrication
5
1
6
1
Tough
materials
Ineffectual
extraction
system
10
1
Incorrect
clearance
2
2
Lack of
lubrication
6
Wear
6
3
9
Punch
pumping
5
Work part
deformation
2
Deflection of
punch head
8
5
Excessive
shear on
punches and
die
Punch does
not extract
Increase in
punch-to-die
clearance
1
Holes too
close in
sequence
6
8
Speed too
fast
Increased
delay
Imprecise
components
Reduced tool
life
10
Lack of
lubrication
on part
and/or
incorrect
lubrication
Punch
breakage
7
Punch Head
Breakage
2
10
10
6
10
70
Check
lubrication
Verify head
thickness is
properly fit in
the retainer
counter-bore
Chamfer
retainer to
clear head
fillet on
punch
Draw back
backing plate
to reduce
hardness—
RC 40-50
Draw back
head of punch
to lower RC
Increase head
diameter and
thickness
Increase
shank
diameter
Restore
correct
clearance
Use proper
lubrication or
coated
punches
Revise
clearance
Replace with
a spring or
reloaded
assembly
100
180
280
180
200
90
60
50
60
Restore
correct
clearance
Use proper
lubrication or
coated
punches
Reprogram
alternate
punching
sequence
100
Slow down,
use more
coolant
288
40
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3
High cost
4
5
Improper
feed rate (too
slow)
Improper
punch-die
angle
4
Reduced
tool life
8
4
10
Hard material
4
Dimensional
inaccuracies
7
5
7
6
5
6
4
6
Improper
clearance
angle
Too much
shearing
force during
punching
Tough work
material
Frequent
resharpening
of tool
Use higher
grade tool
material, add
surface
treatment
Increase feed
rate
Change to
correct
punching
angle
126
192
120
120
Give proper
clearance
angle
168
Select proper
tool materials
Select
premium tool
Resharpen the
tool
periodically
120
96
3. RESULTS & DISCUSSIONS
From the table 4, which shows FMEA table for punching process, it is observed that
the punch chipping and point breakage due to the high impact or compressive force has the
highest risk priority number. This can be minimized by the proper selection of punch-die
materials and by maintaining the correct clearance between punch and die. The burr and slug
formations also have detrimental effect on the overall quality of the final product. These
undesirable developments can be curtailed by varying the feed rates and speed of the
machine. To reduce the breakage of tool and burr formation due to excessive feed rate and
high cutting speeds, we have to perform the process in rated speed and acceptable feed rates.
In order to produce the punched products without any deformations or distortions, better tool
and work holding devices are to be used. To reduce metal chipping, initial speed has to be
minimum and proper cutting speeds should be employed. The tool life can be increased by
proper lubrication, minimizing the wear and other parameter perfection has to be achieved.
4.
CONCLUSION
Thus the high speed punching process in motor manufacturing section has been
analyzed and the expected failure modes have been noted. From the results of the critical
analysis made on the punching process, the failure modes with greater risk priority number
has been selected. The causes, effects and possible alternate solutions are given along with
the ratings and priorities of action that decrease risk failure. The risk priority numbers are
specified which indicates the necessity of care for producing defect-free punching process
and its products. Thus this process analysis will serve as a helpful tool to detect the failure
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modes occurring in the punching process and also assures in the effective functioning of the
process.
This study provides a documented method for selecting a design with a high
probability of successful operation and safety. As a result of this approach, the system
development cost and time, the possibility of occurrence of same kind of failure in future are
reduced along with improved quality, reliability and safety of process/product. Consequently,
the productivity of the product is also increased. This approach can be well suitably applied
to consumer products like automotives, home appliances, etc., and other fields such as
manufacturing, aerospace, instrumentation, medical, chemical processing, etc.
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