30120140501011 2-3

International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING
6340(Print), ISSN 0976 – 6359(Online) Volume 5, Issue 1, January (2014), © IAEME

AND TECHNOLOGY (IJMET)

ISSN 0976 – 6340 (Print)
ISSN 0976 – 6359 (Online)
Volume 5, Issue 1, January (2014), pp. 108-115
© IAEME: www.iaeme.com/ijmet.asp
Journal Impact Factor (2013): 5.7731 (Calculated by GISI)
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IJMET
©IAEME

OPTIMIZATION OF CRITICAL PROCESSING PARAMETERS FOR
PLASTIC INJECTION MOLDING OF POLYPROPYLENE FOR ENHANCED
PRODUCTIVITY AND REDUCED TIME FOR NEW PRODUCT
DEVELOPMENT
Mr. A.B. Humbe(1),
(1)

Dr. M.S. Kadam(2)

Student, M.E. Manufacturing, Mechanical Engineering Department,
J.N.E.C. Aurangabad, Maharashtra, India
(2)
Professor, Mechanical Engineering Department,
J.N.E.C. Aurangabad, Maharashtra, India

ABSTRACT
Injection molding has been a challenging process for many plastic components manufacturers
and researchers to produce plastics products meeting the requirements at very economical cost. Since
there is global competition in injection molding industry, sousing trial and error approach to
determine process parameters for injection molding is no longer hold good enough. Since plastic is
widely used polymer due to its high production rate, low cost and capability to produce intricate
parts with high precision. It is much difficult to set optimal process parameter levels which may
cause defects in articles, such as shrinkage, war page, line defects. Determining optimal process
parameter setting critically influences productivity, quality and cost of production in plastic injection
molding (PIM) industry. In this paper optimal injection molding condition for minimum cycle time
were determined by the DOE technique of Taguchi methods. The various observation has been taken
for material namely Polypropylene (PP).The determination of optimal process parameters were based
on S/N ratios.
Keywords: Injection Molding, DOE, Taguchi Optimization.
PROCEDURE
• Set the parameters based on historical data and experience
• Fine tune the process parameters for the component which can be considered for evaluation and
observe the trend while setting each process.
108

•
•
•
•
•

Document the data for research and analysis further using DOE (Taguchi Method/ Minitab)
Derive a standard based on the material and the configuration
Optimize the setting time and validate the process Injection Molding Machine Sectional view
Document the data for research and analysis further using DOE (Taguchi Method/Minitab)
Derive a standard based chart on the material and the configuration.

EXPERIMENTATION
In the analysis part we have analyzed 4 important parameters like Melting Temperature,
Holding Pressure, Cool Time and Injection pressure at three levels, The response for this considered
is cycle time.
Table No.1 Large Component
SR. PART NAME/ MT IP(MPa) HP(MPa) COOL
CYCLE
NO. PARAMETERS (°c)
TIME
TIME
(sec)
(Sec)

1

2

3

Large
component
with size: 525
X 320 X 80mm

Large
component
with size: 600
X 200 X
195mm

Size of Large
component is:
500 X 275 X
175mm

PSNRA1

PMEAN1

225
225
225
228
228
228
229
229
229

81
84
85
81
84
85
81
84
85

55
52
56
52
56
55
56
55
52

20
22
23
23
20
22
22
23
20

39
38
42
40
39
42
44
48
42

-31.8213
-31.5957
-32.465
-32.0412
-31.8213
-32.465
-32.8691
-33.6248
-32.465

39
38
42
40
39
42
44
48
42

219
219
219
220
220
220
225
225
225

76
71
79
76
71
79
76
71
79

50
48
51
48
51
50
51
50
48

26
25
22
22
26
25
25
22
26

35
34
35
36
39
39
41
34
40

-30.8814
-30.6296
-30.8814
-31.1261
-31.8213
-31.8213
-32.2557
-30.6296
-32.0412

35
34
35
36
39
39
41
34
40

204
204
204
205
205
205
217
217
217

44
50
56
44
50
56
44
50
56

25
30
33
30
33
25
33
25
30

16
23
27
27
16
23
23
27
16

66
67
69
69
70
77
78
79
79

-36.3909
-36.5215
-36.777
-36.777
-36.902
-37.7298
-37.8419
-37.9525
-37.9525

66
67
69
69
70
77
78
79
79

109

Analysis of the S/N Ratio
SN ratio (Smaller is Better)

PATRT-1

PART-2

PART-3

Part -1:-The main effect plot for SN ratio graphs above depicts certain characteristics of each
parameter. The Melting Temperature graph indicates the steep slope when compared to other
parameter graph curves. This also means that it is holding the first rank in control parameters among
the chosen ones. The Melting Temperature curve slope starts very shallow slope from 225 to 228 and
after that its slope is very steep till 229. The slope of this graph is very steep, which means that we
need to attack or act on this parameter first to reduce our cycle time.
the chosen ones. The Melting Temperature curve slope starts very steep slope from 219 to 220 and
after that its slope is very flat till 225. This means that the best temperature to work upon is around
220 and not above that, as the slope becomes flat, there is no much effect on cycle time. The slope of
this graph is very steep, which means that we need to attack or act on this parameter first to reduce
our cycle time. The Cool Time graph is also equally steep in nature so the second closest ranking is
this and so we need to attack this after Melt temperature. This graph also depicts that the slope of
curve is very flat after 25 sec. So our best cycle time would be achieved below 25 sec.
Part -3:-The main effect plot for SN ratio graphs above depict certain characteristics of each
parameter. The Melting Temperature graph indicates the very steep slope when compared to other
parameter graph curves.. The Melting Temperature curve slope starts very steep slope from 204 to
205 and after that also its slope is very steep till 217. This means that the best temperature to work
upon is around or above 217 and not below that, as the slope continues further, as there will be much
effect on cycle time. The slope of this graph is very steep, which means that we need to attack or act
on this parameter first to reduce our cycle time.

110

Table No.2 Small Component
SR. PART NAME/
NO. PARAMETERS

4

5

6

Size of Small
component is:
80 X 50 X 45
mm

Size of Small
component is:
70 X 35 X 25
mm

Size of Small
component is:
35 X 35 X 15
mm

MT
(°c)

IP(MPa)

HP(MPa)

COOL
TIME
(sec)

CYCLE
TIME
(Sec)

PSNRA1

PMEAN1

201
201
201
199
199
199
204
204
204

58
56
60
58
56
60
58
56
60

24
20
19
20
19
24
19
24
20

15
19
14
14
15
19
19
14
15

23
26
25
26
27
28
27
21
24

-27.2346
-28.2995
-27.9588
-28.2995
-28.6273
-28.9432
-28.6273
-26.4444
-27.6042

23
26
25
26
27
28
27
21
24

200
200
200
196
196
196
207
207
207
196
196
196
192
192
192
198
198
198

49
56
51
49
56
51
49
56
51
45
40
47
45
40
47
45
40
47

21
20
19
20
19
21
19
21
20
30
28
35
28
35
30
35
30
28

21
18
22
22
21
18
18
22
21
14
20
12
12
14
20
20
12
14

29
31
34
33
37
40
39
37
33
24
31
33
36
38
31
37
32
39

-29.248
-29.8272
-30.6296
-30.3703
-31.364
-32.0412
-31.8213
-31.364
-30.3703

29
31
34
33
37
40
39
37
33

-27.6042
-29.8272
-30.3703
-31.1261
-31.5957
-29.8272
-31.3840
-30.1030
-31.8213

24
31
33
36
38
31
37
32
39

Analysis of the S/N Ratio
SN ratio (Smaller is Better)

PATRT-4

PART-5
111

PART-6

Part -4:-The main effect plot for SN ratio graphs above depict certain characteristics of each
after that its slope is little flat till 204. This means that the best temperature to work upon is around
201 and not above that, as the slope becomes little flat, there is no much effect on cycle time. The
slope of this graph is very steep, which means that we need to attack or act on this parameter first to
reduce our cycle time. The Hold Pressure is also very steep from 19 till 24. So this parameter also
play important role as second player.
The Cool Time graph is also equally steep in nature so the third closest ranking is this and so
we need to attack this after Melt temperature. This graph also depicts that the slope of curve is less
steep till 15 sec, after that the steep increases till 19. So our best cycle time would be achieved
around 19 sec.
after that its slope is changing direction till 207. This means that the best temperature to work upon is
around 200 and not above or below that, as the slope changes direction, and there is no much effect
on cycle time. The slope of this graph is very steep, which means that we need to attack or act on this
parameter first to reduce our cycle time.
The Hold Pressure is also very steep from 19 till 20 and after that it is changing its direction
of slope till 21. So this parameter also play important role as second player. The best cycle time will
be achieved if this parameter is kept around 20.
The Cool Time graph is also equally steep in nature so the third closest ranking is this and so
we need to attack this after Melt temperature. This graph also depicts that the slope of curve is
changing at 21. So our best cycle time would be achieved around 21 sec.
Part 6:-The main effect plot for SN ratio graphs above depict certain characteristics of each
parameter. The Hold Pressure graph indicates the steep slope when compared to other parameter
graph curves. This also means that it is holding the first rank in control parameters among the chosen
ones. The Melting Temperature curve slope starts very steep slope from 28 to 30 and after that its
slope is changing direction till 35. This means that the best pressure to work upon is around 30 and
not above or below that, as the slope changes direction, and there is no much effect on cycle time.
The slope of this graph is very steep, which means that we need to attack or act on this parameter
first to reduce our cycle time.
The Melting Temperature is also very steep from 192 till 196 and after that it is changing its
direction of slope till 198. So this parameter also play important role as second player. The best cycle
time will be achieved if this parameter is kept around 196.
The Cool Time and Injection pressure graph does not play a major role in the Cycle time.
CONCLUSION
Taguchi method stresses the importance of studying the response variation using the signalto-noise (S/N) ratio, resulting in minimization of quality characteristics variation due to
uncontrollable parameter. The procurement process was considered as the quality characteristics with
the objective of minimizing the Costs involved in the process of procurement.

112

3 different experimentations carried out to study the interaction of each parameter on the
other. Many times it becomes very difficult to separate out the contribution of each factor as whole
on to the final response. The 3 experiments conducted were for Large size components. Out of the 3
components, all the components exhibit same with respect to its top ranking parameter, that is Melt
Temperature. It is can unanimously said that in large size parts the Melt temperature play in
important role in deciding the cycle time. There is no pattern seen in other parameters behavior in the
experimentation The 3 experiments conducted for small size components reveal a varied ranking. For
2 parts Melt temp was important and last part it was not. When we closed analyzed the reason for
such behavior and found out the complexity of part, in term of intricate shape, fine features was
driving this change.
Design of Experiments is a statistical method and Taguchi method is very proven and robust
so we have used this technique. It is important to remember that statistical methods are based on
assumptions and iterations, which means the results obtained are to some percentage level of
confidence and not 100%. Taguchi claims that his technique is 90% confident on the results.
Also, once we act upon / attach on one parameter of any experimentation, we need to run DOE to see
the results and find out the ranking of the parameter again. Because when the readings / observations
change, the ranking may change depending on its portion of influence on the response parameter. If
the ranking remains same, you can carry out next set of experiments by only changing the parameter
ranked first. If the ranking changes then our experimentation should attached the next parameter
which is ranked. So like this, we can continue to go on, till we receive a satisfactory level of
outcome.
DOE also gives use some empirical relationships in the form of equation that can be used as a
quick reference or guideline while we need to take major decisions like deciding cycle time quickly
when a new customer is asking for basic quotation OR while making major decision like buying of
additional Injection molding machine, which costs in cores of rupees, etc.
We had carried out 3 large and 3 small components experimentations with different
parameters. Out of the 9 runs per component, we have chosen the top 2 best SN ratio values from
each Large size components and small size component and carried out a regression analysis.
With the available parameters, we have a regression equation for all the 6 experiments. By
properly substituting the values of the parameters, we can take decisions for future projects.

113

REFERENCE CHART
Material
Polypropylene(PP)
Large Sized
Volume range-600cm cube to 1200
cm cube
Polypropylene(PP)
Small Sized
Volume range-up to 650cm cube

MT (°c)

IP( MPa)

HP(MPa) CT(sec)

209

52

30

23

202

54

19

20

The reference chart standardized with the values for the process variables will be validated
for the upcoming automotive components that are awaiting pilot run of production. The process
would be repeated for the variants to ensure consistency in the physical characteristics of the
component produced. Validation will be carried out by bring out actual development of two
components. Trials and testing would address the phase of validation as the mould would be tried out
for checking the nature of the physical components as an outcome of the development process. The
study has evolved reference values for the significant factors suitable for each category of the
material. Following is the compilation for the conclusions drawn.
Material : PP – Small
For small Polypropylene parts, cycle time increased with increase in cooling time & also PP melt
temperature Coolant flow & temperature could be controlled to reduce cycle time. It was observed
that PP melt temperature in the range of 200-206 degcel. & cooling time of 19 to 21 sec produced
consistent parts with optimum cycle time.
Material : PP Large
For large Polypropylene parts, cycle time increased with increase in cooling time & also PP melt
temperature. It was observed that PP melt temperature in the range of 203-209 degcel. & cooling
time of 23 to 25 sec produced consistent parts with optimum cycle time.
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