The resource-economical determination of an optimized operating point in injection molding is still a challenge. Machine learning offers great potential for re-using knowledge from a flow simulation that has already been generated.

Significant reduction of the effort for determining the optimum operating point by machine learning

Machine Learning: Combining Simulation and Experimental Test Data

Spritzgießen

Kunststoffverarbeitung: Verfahren

Spritzgießsimulation

Software

Simulation

DOE-Software

Qualitätsmethoden

Industrie 4.0 für die Kunststoffverarbeitung

Industrie 4.0

Digitaler Zwilling

Quicker Evaluation of the Optimum Operating Point

In the realm of virtual product development, the idea of the cycle has been around for many years. But where does the cycle begin? When we take a closer look at this concept, new aspects rightly start to emerge.

Fig. 1. Stress-strain diagram as a function of microstructure. Shown are three different porosities (5 to 15 %) relative to the compact material

When Traditional Approaches Meet their Micromechanical Counterparts

Schaumspritzgießen

Werkstoffprüfung, mechanisch

Messtechnik

Werkstoffprüfung

Analysetools, FEM

Produktentwicklung(sprozess)

Qualitätsmanagement

Cracking Product Development

In the second part of the series, calculations were carried out on the throughput behaviour, pressure build-up capacity and the melting process on the basis of an exemplary geometry. These results are now to be examined in more detail and subsequently optimized.

Through empirical tests and simulation-supported test series, a screw can be designed in a tailor-made manner for the respective application 

Part 3 of the Series Deals with the Tests to Optimize the Screw Geometry

Spritzgießmaschinen, allgemein

Kunststoffverarbeitung: Maschinen und Komponenten

Spritzgießmaschinen

Schnecken und Plastifiziersysteme

All about Plasticizing Screws

The fifth broadcast by arburgXvision was all about the exciting question of how productivity can be optimized by bringing together technology, organization and digitalization in the ideal manner.

Christoph Kiefer, Team Manager Technical & Commercial Sales Support (left), and Dr Thomas Walther, Head of Application & Process Development (center), had a discussion with presenter Guido Marschall on how to increase production efficiency by taking advantage of “hidden benefits“

Automatisierungstechnik

5. arburgXvision: „Savings through Hidden Benefits!“

iQ process observer, the new process monitoring platform from Engel monitors hundreds of parameters from the injection molding cell in the background.

The injection molder is truly not a friend of changes – if they occur in the running process. The iQ process observer helps him to keep an eye on the process and thus keep a handle on the quality

A Process Monitoring Platform Monitors Several Hundred Parameters Simultaneously

Steuerungen (Hardware und Software)

Industrie 4.0 für die Qualitätssicherung

Prozessvisualisierung

Condition Monitoring / Prozessüberwachung

Instandhaltung

IoT-Plattformen für die Kunststoffverarbeitung

An Eye on the Process –  a Handle on Quality

With Moldex3D 2021, the supplier of software in German-speaking countries SimpaTec, by its own account, succeeded in improving both prediction accuracy and tailored solutions. Thus, for shrinkage and warpage predictions, which are frequently required in injection molding, the new version now combines the material and stress properties of the plastic at the phase-switchover to the holding pressure phase.

Moldex3D 2021 offers users improvements that make routine workflows easier

Messe Fakuma

kunststoffe-international.com

Virtual Product Development – Precise and Tailor-Made

Over past months, many in-house workflows and development processes have slowed down and also changed. Nevertheless, time has not stood still, also not in injection molding technology. The debate and development have been shaped by two themes: digitalization and the circular economy. Below are some examples of developments and projects that underpin this trend.

Two displays are seamlessly integrated into the continuously 3D-formed instrument panel

Innovative Injection Molding in Times of Pandemic

Künstliche Intelligenz für die Qualitätssicherung

Steuern, Regeln

Mehrkomponenten-Spritzgießen

Folientechnik (IMD, IML, FIM, u.a.)

Digitale Transformation

Wirtschaft

Innovationen und neue Technologie

Spritzgießwerkzeuge

Werkzeuge für die Kunststoffverarbeitung

Biokunststoffe

Kunststoff Werkstoffe

Spritzgieß-Sonderverfahren

Nachhaltigkeit

Umweltmanagement

Machine Learning / Künstliche Intelligenz für die spanende Fertigung

Industrie 4.0 für die spanende Fertigung

Kunststoff-Recycling

Kunststoff-Aufbereitung

Lasermarkieren

Oberflächentechnik

Laserbearbeitungen

Inline- / Online-Messsysteme

Qualitätssicherung

Qualitätssicherung Kunststoff

Kreislaufwirtschaft

There Is More beyond the Horizon

MS-Schramberg has a track-record of developing precision polymer parts for the automotive industry. The example of a gear wheel demonstrates how the efficiency of component optimization can be boosted through the use of simulation.

After component optimization, the gear wheel lay within the desired tolerance as soon as it went into series production

16:9

Optimizing a Tricky Component Geometry Using Sigmasoft Virtual Molding

Magnete

Maschinenelemente

Mechanische Konstruktionselemente

Systematic Approach to a Precision Polymer Gear Wheel

Which injection molding machine is the right one for which application? Below we will demonstrate why performance is not always performance, but physics is always physics.

Direct drives such as planetary roller screw drives are very precise and durable

How Feed Rate, Injection Volume and Filling Time Correlate with Injection Unit Performance

Kugelgewindetriebe

Getriebe

Elektrische Antriebe für Spritzgießmaschinen

Antriebe

Elektrische Antriebe

Elektromechanische Maschinen

A Question of Class

The ninth broadcast by arburgXvision was about strategies for significantly increasing the utilization rate of injection molding machines.

Moderator Guido Marschall and Arburg experts Christian Homp and Christoph Blöchle (from right) discussed how the right mold strategy pays off for injection molding companies

“Mold Strategy 2.0 – New Ideas for Reducing Costs”

Guido Frohnhaus has been Managing Director Technology & Engineering at Arburg for a good two years now. The pandemic restrictions meant that he has made very few appearances outside the company so far, but, as he says himself, he spent the time getting to know the in-house processes at all levels and in great detail. In this interview with Kunststoffe, the 52-year-old talks about the course he plans to set and how crucial the high level of in-house manufacturing and programming expertise is for the company’s independence.

Doriat, Clemens, Dr.

“Gestica Will Be the Fixed Star in the Customer’s Universe”

The digital shadow is the core concept of the Cluster of Excellence “Internet of Production” at RWTH Aachen University. It represents the data trace of an asset to describe its real behavior. In the Plastics Innovation Center 4.0 (PIC 4.0), digital shadows, e.g. the data trace of a sensor, are used to optimize processes taking into account real behavior and to determine simulation quality.

The construction of the PIC 4.0 proceeds and throws its shadow on the Campus Melaten.

Part 7 of the Series: How the Digital Shadow Enlightens Real Processes in the PIC 4.0

Sensorik für Kunststoff-Verarbeitungsmaschinen

Out of the Shadow into the Light

Internal pressure loads are typical for fiber-reinforced plastic components. To increase the burst strength of components, the fiber orientation can be modified in a targeted way during injection molding by means of a rotating mold core. A newly developed simulation method allows this modified fiber orientation to be taken into account at the design stage.

Practical implementation of a mold system with rotating core.

Mold System with Rotating Core Improves Mechanical Properties

Verbundwerkstoffe / Werkstoffverbunde

Faserverbundwerkstoffe

Andere Werkstoffe

Design Methodology for Parts Subject to Internal Pressure

CoreTech System announced the appointments of Dr. David Hsu as its new Chairman, and Dr. Venny Yang as the new CEO. Dr. Rong-Yeu Chang, founder of CoreTech System, announced his resignation and assumed new roles.

Dr David Hsu (left) and Dr Venny Yang (right) have taken over the roles of chairman and CEO, respectively, from Dr Rong-Yeu Chang (centre)

CoreTech System Appointed New Chairman and CEO

Methods of statistical experimental planning can be selectively employed for optimizing machine parameters in the production of optical components. In comparison with normal injection molding practice application of this theoretical approach reduced the necessary run-in time and demonstrably produced two-shot components having very good properties. 

Statistische Methoden

Optische Komponenten / Baugruppen

Design of Experiments: Overtaken by Statistics 

Simulation as a Tool for Weighing Process Options before Producing Optical Components

Making the production of optical lenses economical while maintaining a certain level of product quality poses a huge challenge. Aside from the need to modify the geometry of the molded part, there is often a debate about the right production strategy. Injection-compression molding may offer an alternative to injection molding in terms of quality, but it is also cost-intensive. This is where simulation can serve as a decision-making aid.

Making the production of optical lenses economical while maintaining a certain level of product quality poses a huge challenge. Aside from the need to modify the geometry of the molded part, there is often a debate about the right production strategy.

Lenses have played an important role in people’s lives since long before the 17th century, when the Laterna magica or magic lantern was developed [1]. The first optical products made by humans are considerably older. In early times, they were made by grinding or polishing mostly quartz to produce the desired properties.

Today, it is hard to imagine everyday life without lenses. Glasses, cameras and projectors are obvious examples, but metrology and automotive engineering are other areas in which they play a major role. A corollary of this wide range of applications is that the mechanical manufacture of lenses is constantly being presented with new challenges, and so not only the manufacturing process but also the underlying material, quartz, is in need of alternatives.

Back in 1933, Röhm & Haas AG launched a polymethyl methacrylate (PMMA) under the brand name Plexiglas [2]. A good seven years later, in 1940, Heinrich Wöhlk developed a product whose forerunner had first been proposed by René Descartes back in 1636 [3] – the contact lens [4]. A whole series of developments followed, but the example of the contact lens illustrates for how long and to what extent lenses have fascinated mankind.

Injection Molding or  Injection-Compression Molding?

A decisive, portentous step was ultimately taken when plastics started to be used in the manufacture of products that possess optical properties. Injection molding, the process by means of which the two components – plastic and lenses – are combined, is capable of producing large volumes with reproducible results. However, it also has to contend with technical hurdles such as uneven shrinkage, stresses and sink marks.

Since the requirements imposed on products with optical properties are much higher than those on technical products [5], a further manufacturing process that merits consideration is injection-compression molding. Combining injection molding and compression molding affords a way of optimizing both process-related (e. g. filling pressure) and component-related properties [6]. The main focus here is on homogenizing both material and component properties.

Injection-compression molding delivers superior component quality compared to injection molding but can incur considerable costs. This is where process simulation steps in. Not only can each process be modeled in the same way as for technical components, but optical properties such as birefringence, refractive index, fringed pattern, and retardation can also be simulated. Thus, simulation is a tool that optimizes the production of optical parts and also provides criteria for a well-informed decision as to which process is best suited to which product from a qualitative and an economic point of view.

Process simulation is a long-established tool for garnering knowledge about genuine errors – and not just the kind suggested in the context of troubleshooting. It is also used in product development to identify and, if possible, rule out potential problems from the outset. Furthermore, simulation can be used to evaluate alternative processes and materials. However, in many cases, process simulation is just one part of the development chain, and that is why the coupling together of different simulation methods is growing in popularity. For instance, in many companies it is standard practice to couple process simulation with structural simulation as a way of transferring additional data such as anisotropic material properties, weld lines, etc.

Such coupling methods are also available when it comes to designing lens products. For example, the refractive index or even the deformation can be exported from Moldex3D to Code V, a software for optical design. This approach yields more meaningful results, e.g. in terms of possible imaging errors, and lends itself to both injection molding and injection-compression molding.

It must be pointed out that the simulations for both injection-compression molding and optical properties differ noticeably in some aspects from the routines actually employed in injection molding, namely process control and treatment of the simulation model. The simulation is performed in 3D and, for both processes, is broken down into the various phases of filling, compression, packing, and cooling.

Thus, not only can properties such as birefringence and residual stresses be simulated, but a distinction can also be made between thermally induced and flow-induced properties.

A special situation arises in connection with compression. In order that the compression stroke may be simulated, the mesh is deformed as a function of time. Consequently, the domain changes during the course of the simulation. Plastics are often described by parameters such as viscosity, pvT behavior, thermal conductivity and specific heat capacity, coefficient of linear thermal expansion (CLTE), Poisson’s ratio and Young’s modulus. In order that the specific results concerning the optical properties may additionally be obtained for both processes, a knowledge of the viscoelastic properties of the plastic is needed.

Multi-Layer Injection Molding  Shortens Cycle Time

Plastic optical parts that serve as attachment lenses for defined light distribution, for example, can have wall thicknesses of up to 60 mm. In traditional injection molding, the quality of the lenses is assured by having cycle times lasting in some cases more than 20 min. The need to address this and thus enable series production inspired the development of multi-layer injection molding for thick-walled lenses. Multi-layer injection molding is similar to multi-component injection molding and consists in producing the finished lens over a number of molding processes, thereby shortening the cycle time to an economically acceptable level.

Both core-back technology and transfer and turntable technology, which are already established concepts for manufacturing multi-component parts, can be used in multi-layer injection molding. Furthermore, more uniform cooling and thus lower levels of residual stress can be obtained by using a conformal temperature control system and/or adopting a dynamic temperature control strategy. The production of optical lenses in multi-layer injection molding by the core-back technique, and its simulation, are explained below.

Simulation Model and Simulation Sequence for a Biconvex Lens

The geometry employed [7] was supplied by the Institute for Plastics Processing (IKV) at RWTH Aachen University, Germany. A two-layer, aspherical, biconvex lens was simulated. The overall view of the simulation model (Fig. 1) shows the mold (WZ), the general cooling system (aKS), the conformal cooling system (kKS), the hot runner (HK) and the cold runner (KK). Shown below this are the pre-molded part (VS) and post-molded part (NS) and the compression zone (KZ) for the injection-compression molding process. There is no compression zone in the injection molding process.

The chosen material was PMMA (type: Plexiglas 7N; manufacturer: Evonik Performance Materials GmbH, Darmstadt, Germany). The shape geometry was created with the aid of a mold incorporating core-back technology [8]. This mold design makes it possible to produce pre-molded and post-molded parts in the same cavity by means of a hydraulic core-retraction system. The compression stroke of the compression zone is executed via a compression frame construction and the clamping movement of the injection molding machine.

In the injection molding simulation, the first shot fills the cavity of the pre-molded part. If this meets the pre-determined demolding criteria, the physical condition of the part is transferred for the second shot. The mold core on the clamping side is retracted to expose the cavity of the post-molded part. Then, in the second shot, the post-molded part is given its shape. In the injection-compression molding simulation, the pre-molded part is created and transferred in the same way as in the injection molding. When the post-molded part is being filled, the compression core closes under a defined compression force and speed profile as soon as a pre-determined filling volume has been reached.

The IKV conducted a filling study for the post-molded part made by injection molding, so that it could be compared with a simulation performed by SimpaTec. The three selected time steps (t1 – t3) clearly show the good agreement between the simulated flow front and the real flow front (Fig. 2).

The results of the injection molding and injection-compression molding simulations were compared. The pressure distribution at the end of the packing phase (injection molding simulation) and after the compression phase (injection-compression molding simulation) shows a pronounced pressure gradient starting from the gate location in the case of injection molding. In contrast, the pressure distribution on the optical functional surfaces of the lens made in the injection-compression molding simulation is more homogeneous (Fig. 3).

When the local flow-induced residual stresses in the XX direction are displayed as false-color diagrams, clear differences also emerge at this point between the simulated lenses made by both types of simulation, as was the case for the pressure results (Fig. 4). In contrast to the injection-molded lens, the injection-compression molded lens is characterized by a lower residual stress gradient, resulting in better optical properties.

There are clear differences in the flow-induced and thermally induced fringed patterns of the simulated lens; both effects may also be superposed (Fig. 5).The simulation results can be used to conduct defect analysis as part of a quality assurance regime, with the aid of real polarized images. The separation of the flow and thermally induced fringed patterns can also be used for targeted root cause analysis.

Injection molding or injection-compression molding? Conformal versus conventional cooling layout? These are just two out of a whole range of questions that can be answered in advance by conducting a simulation. There is no question that traditional injection molding simulation provides many answers. However, the coupling methods described above show that the possibilities are now much greater, yielding in advance an enhanced product under process conditions which have been optimized from both technical and economic aspects.

[1] Burkart, L.: Bewegte Bilder – sichtbares Wissen: Athanasius Kircher und die Sichtbarmachung der Welt. In: Bredekamp, H.; Kruse, C.; Schneider, P.(Publ.): Imagination und Repräsentation: zwei Bildsphären der Frühen Neuzeit. Munich 2010, p.335–352

[2] Evonik Industries AG: Die Geschichte der Röhm GmbH. URL: https://history.evonik.com/sites/geschichte/de/gesellschaften/roehm/, retrieved on 06.04.2020

[3] Efron, N.: Contact Lens Practice. 3rd edn., Elsevier, Amsterdam 2018

[4] Wöhlk Contactlinsen GmbH: History: URL: https://www.woehlk.com/historie.html, retrieved on 06.04.2020

[5] Forster, J.D.: Vergleich der optischen Leistungsfähigkeit spritzgegossener und spritzgeprägter Kunststofflinsen. Dissertation RWTH Aachen 2006

[6] Chen, S.-C.; Lee, G.-H.; Tseng, C.-Y.; Chen, T.-C.; Chiu, H.-S.; Hsu, C.-C.: Investigation on Warpage Behavior of DVD Disk in Injection-compression Molding. ANTEC, Orlando, Florida/USA 2011

[7] Röbig, M.: Multi-layer-Spritzgiessen und -Spritzprägen für eine hochpräzise und wirtschaftliche Fertigung dickwandiger Kunststofflinsen. Dissertation RWTH Aachen 2019

[8] Hopmann, C.:Multi-layer injection molding of thick-walled optical plastics parts. Institut für Kunststoffverarbeitung in Industrie und Handwerk, RWTH Aachen, Concluding Report on IGF Project No.16862 N, 2014

SimpaTec Simulation & Technology Consulting GmbH  

https://www.simpatec.com

Ausgabenartikel

Fig. 1. Two-layer injection molding: visualization of the simulation model for the first and second component, including mold and temperature control

Fig. 2. The filling study shows the high level of agreement between injection molding reality and simulation

Fig. 3. The pronounced pressure gradient that occurs during injection molding (left) contrasts with the homogeneous pressure distribution arising in injection-compression molding (right)

Fig. 4. Flow-induced residual stress in the XX direction is more pronounced in injection molding (left) than in injection-compression molding (right)

Fig. 5. Flow-induced and thermally induced fringed patterns and the superposition of both effects for the simulated lens using injection molding as an example

Simulated production of a two-layer, aspherical, biconvex lens. Here, mold filling is superimposed with the fringed pattern of the final lens

Name - Hauptartikel

<b>Cristoph Hinse</b> is Managing Director of SimpaTec GmbH, Aachen, Germany.

<b>Nuno Ribeiro Simões</b> is an employee at SimpaTec.

The authors would like to thank Dr. Malte Röbig (IKV) for supplying information.