In-mould process data is essential for high quality injection moulding processes due to its high correlation to multiple quality criteria, such as part weight, dimensions and surface properties. To take advantage of the high correlation of cavity pressure and part quality, we developed a phase-unifying model-based cavity pressure control. This approach allows an approximate prediction and realisation of cavity pressure curves in real-time by calculating the optimal screw velocity adjustment based on a process model. The phase-unifying process control approach avoids discontinuities by eliminating the switch-over point and enables thereby a smooth transition from filling to packing.

Besides the process control concept, the specification of a suitable process setting is the second key factor in achieving high part quality. A process adaption is always required, if process disturbances occur. For example, production interruptions can occur in the injection moulding process when parts are demoulded incorrectly. Furthermore, process disturbances can influence the injection moulding process such that the process parameters leave a predefined monitoring window and cause a machine interruption. During these interruptions, the thermal household of the mould and polymer melt changes. This causes rejection of parts during the subsequent start-up process due to the changed process conditions. The start-up of the process takes a long time until quality criteria can be again fulfilled.

The study aims to shorten the start-up process as use-case for phase-unifying process control. For this purpose, injection moulded parts were produced for various interruption times. The part quality of the first five parts of start-up process was determined by weight measurements. Additionally, we carried out injection moulding trials for different cavity pressure references to quantify the correlation between cavity pressure characteristics and part weight as quality criteria.

Quantitative correlations between cavity pressure characteristics and part quality were determined by calculating an ideal cavity pressure reference for inline process control for the start-up process. This allows high process stability under the occurrence of production interruptions with fast mould filling.

The quality consistency of part weight was increased by 35 % for the first five produced parts. This leads to a highly reproducible process and fewer rejected parts during the production start-up. Part weight fluctuations are significantly lower compared to conventional process control, which shows the high potential of a combined inline and online phase-unifying process control for injection moulding.

1.
C.
Gornik
,
Using Derived Process Characteristics for Optimization
,
Kunstst. Internat.
,
99
(
9
)
15
18
, (
2009
).
2.
G.
Pillwein
,
J.
Giessauf
,
G.
Steinbichler
,
Switch over to Consistent Quality
,
Kunstst. Internat.
,
102
(
9
)
13
16
, (
2012
).
3.
D.
Kazmer
,
Plastics manufacturing systems engineering
, (
Cincinnati
,
Hanser Publications
,
2009
).
4.
D.
Kazmer
,
S.
Westerdale
,
The effects of temperature and relative humidity on injection molded part quality
,
Society of Plastics Engineers Annual Technical Conference
,
Milwaukee
, (
2008
).
5.
Y.
Yang
,
X.
Chen
,
N.
Lu
,
F.
Gao
, Injection Molding Process Control,
Monitoring, and Optimization
, (
München
,
Carl Hanser Verlag
,
2016
).
6.
D.
Kazmer
,
S.
Westerdale
,
A model-based methodology for on-line quality control
,
J. of Adv. Manuf.
,
42
(
3
)
280
292
, (
2009
).
7.
N.
Kudlik
,
Reproducibility of the plastic injection moulding process
, Dissertation,
RWTH Aachen, Institute for Plastics Processing
(
1997
).
8.
A.
Schötz
,
Abmusterung von Spritzgießwerkzeugen, 3. Auflage
, (
München
,
Carls Hanser Verlag
,
2016
).
9.
M.
Bichler
,
Prozessgrößen beim Spritzgießen. Analyse und Optimierung
, (
Berlin
,
Beuth Verlag
,
2012
).
10.
K.
Hornberg
,
C.
Hopmann
,
M.
Vukovic
,
S.
Stemmler
,
D.
Abel
,
Effects of cyclical process influences on the cavity pressure curve and part quality in the injection moulding process
.
J. of Plastics Technol.
,
17
(
3
)
179
203
, (
2021
).
11.
C. C.
Davis
,
J.C.
Hudson
,
Injection Molding Process Variation before and after Interruption
,
Paper presented at the 49th Annual Technical Conference, Montréal
, 5--9 May
1991
.
12.
I. J.
Čatić
,
Cavity temperature-An Important Parameter in the Injection Molding Process,
Poly. Eng. & Sci.
,
19
(
13
)
893
899
, (
1979
).
13.
D.O.
Kazmer
,
S.
Velusamy
,
S.
Westerdale
,
S.
Johnston
,
R.X.
Gao
,
A Comparison of Seven Filling to Packing Switchover Methods for Injection Molding.
Polymer Engineering & Science
50
(
2010
)
10
, S.
2031
2043
.
14.
R.
Schiffers
, N.
Topic, Mehr Stabilität erhöht die Attraktivität – Optimierte Prozessführung beim Spritzgießen duroplastischer Formmassen, Kunststoffe 7/2017
, (
München
,
Carl Hanser Verlag
,
2017
).
15.
R.
Schiffers
,
S.
Moser
,
S.
Kruppa
,
M.
Busl
, Patent DE 102015117237B3 (
2017
).
16.
M.
Gergov
,
C.
Huang
,
S.A.
Burns
,
R.A.
Pollard
, U.S. Patent 20190105826A1 (
2019
).
17.
B.
Collins
,
G.M.
Altonen
,
C.
Huang
,
B.M.
Birchmeier
,
B. M.
Burns
, Patent WO2019213380A1 (
2019
).
18.
E.D.
Stiefel
,
B.
Collins
,
G.M.
Altonen
,
B.M.
Burns
,
B.M.
Birchmeier
, Patent WO2019245794A1 (
2019
).
19.
D.
Djurdjanovic
,
L.
Mears
,
F.A.
Niaki
,
A.U.
Hao
,
L.
Li
,
State of the art review on process, system, and operations control in modern manufacturing.
Journal of Manufacturing Science and Engineering
140
(
6
), (
2018
).
20.
M.
Finn
,
J.
Hernandez
,
R.
Dubay
,
Cavity peak pressure control during packing using model predictive control theory
. In
Proceedings of ANTEC
, vol.
3
, pp.
2408
2412
, (
2011
).
21.
M. G.
Forbes
,
R.S.
Patwardhan
,
H.
Hamadah
,
R.B.
Gopaluni
,
Model predictive control in industry: Challenges and opportunities.
IFAC-PapersOnLine
48
(
2015
)
08
, S.
531
538
.
22.
A.
Maxim
,
D.
Copot
,
C.
Copot
,
C.M.
Ionescu
,
The 5W’s for Control as Part of Industry 4.0: Why, What, Where, Who, and When – A PID and MPC Control perspective
.
Inventions
4
(
2019
)
01
, S.
10
23.
S.
Stemmler
,
M.
Ay
,
M.
Vukovic
,
D.
Abel
,
J.
Heinisch
,
C.
Hopmnn
,
Cross-phase Model-based Predictive Cavity Pressure Control in injections Molding
.
Proceedings of the 3rd IEEE Conference on Control Technology and Appplications CCTA2019
,
HongKong, China
,
2019
.
24.
M.
Vukovic
,
S.
Stemmler
,
K.
Hornberg
,
D.
Abel
,
C.
Hopmann
,
Adaptive model-based predictive control for cross-phase cavity pressure control in injection molding,
Journal of Manufacturing Processes
77
(
2022
)
730
742
.
25.
F.
Johannaber
,
W.
Michaeli
,
Handbuch Spritzgießen
(
Carl Hanser Verlag
,
München
,
2004
)
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