Short fiber-reinforced plastics are used for many technically demanding applications. For efficient development processes and high product quality, their anisotropic material properties must be factored into the design cycle. A simple approach often taken is to reduce the material stiffness. However, a more accurate approach is to consider the effective fiber orientation. This article discusses the pros and cons of both approaches.

Water pump bFlow C as an example of a part manufactured with short glass fiber-reinforced plastic.

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Universal-Prüfmaschinen für Zug, Druck und Biegung

Messtechnik

Werkstoffprüfung

Simulation

Software

Spritzgießsimulation

Analysetools, FEM

Faserverbundwerkstoffe

Andere Werkstoffe

Modellierung

Methoden und Werkzeuge

Qualitätssicherung Kunststoff

Qualitätssicherung

Anisotropic Simulation of  Short Fiber-Reinforced Plastics

SimpaTec: Material charts from a CAE software supplier lab offer a more reliable basis for product development than “family values” of similar materials.

Spritzgießen

Kunststoffverarbeitung: Verfahren

Compound

Kunststoff Werkstoffe

Thermoplaste

Rheologie

Similar and Yet Completely Different

Automotive supplier Friedrich Deutsch Metallwerk has combined the die casting of a metal insert and its overmoulding with plastic in a single tool.

A new combination of conventional processing methods – high-pressure die-casting and injection molding – could lead to a more efficient process.

Simulative combination for the production of metal-polymer-composite parts

Hybridtechnik

Mehrkomponenten-Spritzgießen

Spritzgießwerkzeuge

Kunststoffverarbeitung: Maschinen und Komponenten

Werkzeuge für die Kunststoffverarbeitung

Gusswerkstoffe

Metall Werkstoffe

Stähle

High-Pressure Die-Casting  and Injection Molding in One Mold

The crystallization of the plastic is an important criterion for the warpage of components. This can be determined inline using a special sensor.

Picture of the IR combi sensor in comparison with a 2 euro cent coin: In the background the sensor (red circle) is integrated in an injection mold.

Materialcharakterisierung

Determining Crystallization Inline

A case study for microphone manufacturer Lewitt shows how simulation software can influence the development of a product without delaying the launch date.

“Connect 2” audio interface: The top housing (upper and bottom view, left) and a set-up example (right).

Weld Lines and Sink Marks – Just a Question of Visual Appearance?

Moldex3D has opened a new office in Jakarta, Indonesia. With the new location, the company aims to cater to the rapidly developing Indonesian market and offer a more localized service.

The new office in Jakarta is one of three in Southeast Asia.

Moldex3D Opens New Office in Jakarta

StrömungsRaum Framework cloud-based platform from Ianus Simulation makes it possible to carry out simulations without the need for prior knowledge or hardware.

Various process steps in plastics processing combined in a single cloud framework – StrömungsRaum.

Extrusion

Extrusionswerkzeuge

Heißkanalsysteme

Komponenten für die Kunststoffverarbeitung

KI (Künstliche Intelligenz)

A Pioneer in Digital  Process Optimization

The so-called ColorForm process combines injection molding and painting, which are separate operations in the conventional technique, into a one-step process. This results in a variety of quality and cost advantages. The completely solvent-free and release-agent-free paint systems used for this purpose are available in almost all conceivable color combinations and have successfully withstood all the relevant tests for use in large series. 

Polyurea Lacquers Permit the Production of Flawless Surfaces in a Combined Injection Molding and Reaction Process 

Spritzgieß-Sonderverfahren

Schäumen / Reaktive Verarbeitung

Oberflächentechnik

Lackieren

Form- / Oberflächenmesstechnik

An Affordable Alternative to Conventionally Painted Parts 

An innovative evolution of the ColorForm process from KraussMaffei is on its way: one-step injection molding of sophisticated design parts flow-coated directly in the mold with a fast-reacting polyurea coating. While the process already established in the market creates high-gloss, matte or textured full-tone color surfaces, the enhanced process creates new freedom in design in the area of high-quality metal effect surfaces that are also more durable. 

Finishing within the Mold Meets the Highest Demands for Surface Design 

Polyurethan

Beschichten von Kunststoffen

Metal Effect Design in the Injection Molding Process 

In the automotive industry, many injection molded plastic components are painted with multi-layer coating systems. After suitable surface pretreatment, at least one layer of primer, a basecoat, and a clearcoat are applied. A new polypropylene compound now fulfills all technical criteria without application of a primer, so saving time and money. However, this achievement does not depend on the material alone. 

Right Material and Processing Parameters for Primerless Painting of Polypropylene  

Polypropylen

Lackiermaschinen für Kunststoff

So the Paint never Comes off 

The design versatility of a polyurethane coating on part surfaces, including metallic effects and a fine grain with matt and glossy sections, is being illustrated with a steering wheel cover at the K trade fair. In contrast to  injection molding with separate spray painting, this prototype is produced using an integrated process. Flooding the injection mold with the coating was simulated in advance. 

A Steering Wheel Cover Produced with the DirectCoating Process Illustrates  the Varied Design Possibilities for the Automobile Interior  

Oberflächenveredelung

Vis-à-vis with the Driver 

For several years a quartet of developers has been working on a new technology for painting thermoplastic parts in the injection mold. The process of flow coating in the injection mold using reaction system technology has now started into series production for the first time. The new Peugeot SUV 3008 is the first car in the world to feature elegant deep piano black A-pillar trims with a mirror finish – manufactured in a fast one-step process that does not require either solvents or release agents. 

Painting without Runs – Cycle Time Less than One Minute 

KFZ-Zulieferer

Mirror-Finish Painting in the Mold 

Whether automobiles, shower bath fittings, or furniture handles: Surfaces with a metallic appearance are found everywhere. Mostly, the items are made of plastic that has been given the corresponding look – frequently by means of galvanizing, but also by means of modern chrome substitute procedures such as PVD, in-mold labelling or spray painting. For different component geometries, one or the other process is recommended.  

Kunststoff Helmbrechts Gives an Overview of all Available Surface Treatment Technologies and their Advantages 

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

Beschichten (CVD, PVD)

Chrome or Not Chrome? 

Pearlescent pigments produce striking effects in thermoplastics. However, the natural photoactivity of TiO¿ influences the stability of the polymer matrix. Unlike off-the-shelf organic stabilizations, the inorganic "Way" technology significantly reduces the photoactivity of effect pigments, which in turn opens up new design possibilities for plastic products with high UV exposure. 

Special Encapsulation Makes Metallic Effects Inert and Weather-Resistant 

Additive

Farbstoffe

Pigmente

Effects without Drawbacks 

In a joint project, seven companies developed a combination of technologies for manufacturing electronically functionalized high-quality surfaces, e. g., for applications in and on the car. Demo parts were shown in public for the first time at Fakuma 2018.  

Combination of Technologies for Manufacturing Electronically Functionalized Plastic Parts 

HMI, Bedienelemente, Displays

Laserstrukturieren

Premium Surfaces by the  One-Shot Process 

Predicting the Surface Finish of High-Gloss Plastic Parts

Skilful application of the evaluation and analytical options afforded by process simulation, including designing the best temperature-control system and making comparisons with alternative manufacturing processes, smoothes the way to efficient product development and manufacturing. Doing this from the very start of a project enables investments to be weighed and qualified, and technical, economic or environmental concerns to be taken into account, as exemplified here by a part with a high-gloss surface.

Whether it be in automotive engineering, the furniture industry or consumer electronics – high-gloss products are in demand, and are sure to grab attention, win customers over, and so secure market share. The commonplace perception of plastic as a cheap material has changed and it is now seen as a lifestyle material with maximum demands on its surface finish and under pressure to keep meeting new requirements. This process of change is also being influenced by other aspects that need to be addressed, such as economic factors and steps to reduce the carbon footprint.

The key to ensuring that a product will possess a given level of quality is to coordinate the various analytical and evaluation options afforded by process simulation, and then to heed and utilize the resulting insights with a view to enhancing the process engineering. Adopting such an approach from the outset makes it possible to evaluate manufacturing processes expediently and to define the most suitable range of applications.

There is no denying that the injection molding of high-gloss plastic parts is very challenging. All it takes for a sub-standard finish to result, for example, is a mold insert with a poor surface finish, an unsuitable material, or the wrong process parameters [1, 2]. In certain circumstances, the desired level of high gloss may still be achieved by painting the surfaces in a downstream process [3]. The problem then is that the energy consumed in that painting process contributes from 5 to 15 % of the overall cost of parts manufacture [4]. Against a backdrop of growing demand for greater production efficiency and a need to combine the lowest-possible manufacturing costs with high product quality, alternative processes must be found [3].

Weighing the Costs and Benefits of Variothermal Temperature Control

The three major factors governing the quality of high-gloss surfaces made by injection molding are injection speed, holding pressure, and mold temperature, with the last of these having the greatest impact [5]. Although high mold temperatures can yield nearly ideal high-gloss surfaces, the long cooling times necessarily give rise to long cycles. These can be avoided by employing variothermal temperature control, which represents a practicable alternative for the production of high-gloss parts [5]. In this connection, the use of simulation to predict part quality at an early stage, ideally during product design, is recommended with a view to forestalling unforeseen costs and part defects [6].

In the course of close collaboration on the design of a manufacturing process for a high-gloss part, Contura MTC GmbH and SimpaTec GmbH compared the use of both conventional thermal and variothermal control. They used the same injection mold with conformal cooling for both processes (Title figure). Premec S.p.A., Toolax and Contura MTC played a substantial role in the development and manufacture of this mold. The customized temperature-control system exerts a strong influence over the mold-wall temperature (Fig. 1).

The comparison consisted in evaluating the surface finish of the respective parts and estimating the cost and energy requirements of both processes, while making allowance for any necessary additional painting. Process simulation was used to assess whether the molded part’s surface finish could be predicted early in the design stage, thus making it possible to consider  the costs that might arise from a painting <a href="http://process.The" target="_blank">process.The</a> use of different materials was also analyzed; e.g. the reference part was made from a PC+ABS in one case and from a polyamide 6 with 30 % glass fiber content (PA6-GF30) in another.

The PC+ABS reference part yielded a high-gloss surface in both process variants. Dynamic alternating temperature control produced an ideal piano-black finish (Fig. 2, right), free of streaks, weld lines and similar defects, and with no need for downstream painting. The conventional temperature-control process also yielded a streak-free finish at first glance. However, weld lines are clearly visible on closer inspection (Fig. 2, left), with the result that a downstream coating process is necessary for achieving the desired piano-black surface finish.

Comparison of Energy Consumption: Variothermal versus Painting

The integration of a downstream process step, such as painting, not only necessitates more outlay on resources in terms of organization, transport, packaging and handling of the part during post-treatment. It also leads to greater energy consumption and thus incurs higher costs that must also be taken into account. That being said, injection molding with variothermal control also consumes more energy. So, how great is the additional outlay in reality? This is what has to be compared.

To this end, measurements were made of the energy consumption of an injection molding machine (type: Si-180-6s; manufacturer: Toyo Machinery & Metal Co.), including all additional temperature control units, in the production of 40 reference parts by both methods. The conventional method consumed 2.882 kWh over the course of the 40 cycles, rising to 7.868 kWh when the dynamic temperature control was added. This represents a 2.7-fold increase in energy consumption. Given an electricity price of 20 cents per kWh (as of 2020), the extra cost per part is thus just under 2.5 cents [7].

This is a small increase compared with the cost of the downstream painting process needed for conventional mold-temperature control, where the extra cost per part for a batch of 25,000 units and a single coat of paint works out at more than 45 cents. And that figure excludes handling, possible one-time costs and coating waste of approx. 2 %.

The outcome is that the variothermal variant is more cost-effective than the conventional variant (including the outlay needed for the painting process) by a factor of at least 18.

Simulation for the Purpose  of Cost Estimation

A piano-black finish can therefore be two things at once: an inexpensive and an expensive lifestyle look, the deciding factor being the manufacturing process. However, this information on its own is only valuable and useful if it is possible to estimate in advance whether or not variothermal temperature control can add value to the product to be manufactured.

Injection molding simulation is not just useful for identifying the direction in which the future quality of the part’s surface is trending. Moldex3D was used to simulate the injection molding process under both conventional and dynamic temperature control. Aside from the usual results, e.g. about flow properties, temperatures, pressure and deformation, it also returns information about weld lines and shear stresses, inter alia, which can assist with assessing how the surface finish is trending.

The temperature of the weld lines at the time of their formation can be used to infer how pronounced they are. When melt fronts converge at elevated temperatures, the mixing is more extensive because the melt viscosity is lower, and so the weld lines are less pronounced. In the variothermal variant, this manifests itself on the variothermally controlled side of the part, i.e. the visible surface of the top side. There, the temperature is still so high that the real part shows no signs of weld lines at this point (Fig. 2, right).

The simulation reveals the different temperatures of the weld lines. In the variothermally controlled visible surface (top side) of the part, the temperature of the potential weld line is so high that the data points indicating even higher temperatures can be ignored as far as weld lines are concerned (Fig. 3, right). In the absence of variothermal control, weld lines of lower temperatures are formed which can be detected with the help of the data points (Fig. 3, left). Aside from the weld lines, it is also important to compare the shear stresses induced on the part’s surface by the two temperature-control variants. For the rest of this article, the focus here will be on the glass fiber-reinforced material.

Comparison of the simulation results produced by both variants reveals clear differences in the parts’ surface quality. However, in the case of the variothermal variant, this must not be construed as a definitive guarantee of a perfect finish or of the elimination of an entire painting step. That would require further tests that provide insights into additional influencing variables, such as the surface finish of the mold. Nevertheless, the results do reveal a visible improvement in surface finish of the variothermal part, a fact which should be highly influential in the decision as to which manufacturing process is suitable.

All or Nothing: High Gloss  on Glass Fiber

Parts made from polyamide 6 with 30 % glass fiber content illustrate the difficulty of achieving a glossy finish without recourse to any coating at all. The finishes resulting from conventional temperature control were so critical that in some cases there was no point in considering painting to a high gloss finish due to a lack of feasibility (Fig. 4, top left). Such a situation would not be acceptable in in a real-life product-development process. The choice of dynamic alternating temperature control managed to salvage what was still salvageable: an acceptable surface finish (Fig. 4, top right) that would lend itself to downstream painting and still be capable of producing the desired high-gloss surfaces. Notwithstanding the need for downstream painting, in this case, it was the use of variothermal control that made it possible to produce a high-gloss surface in the first place.

Comparison of these Moldex3D simulation results with the real part surfaces reveals parallels which allow of the possibility that the debacle described above may be predictable (Fig. 4). The simulation shows the maximum shear stresses at the end of the filling phase in both variants (Fig, 4, bottom). The gradients of the shear stresses suggest a non-uniform part surface, a fact which is emphatically confirmed in the case of conventional temperature control (Fig. 4, left).

The less-pronounced shear stress gradients in the variothermal simulation coincide with a higher-quality surface on the real part (Fig. 4, right). As was the case earlier for the weld lines, the shear stress simulation can also indicate the direction in which the downstream surface quality of the real part is trending. This test on PA6-GF30 also underscores the important contribution that injection molding simulation can make to predictions as to the feasibility of part production.

Painting Needed or Even Possible?  Use Empirical Values

A better interpretation of the absolute values of the shear stresses and the temperatures of the weld lines can be obtained with the aid of the Moldex3D iSLM platform. Among other things, this interactive platform for data management for companies in the plastics industry can store knowledge that has already been gained – such as the size of model features, gate sizes, gate types, cooling systems, sampling parameters and CAE simulation results – so that it can be used for comparisons in subsequent projects.

The approach described here is transferable to other product-development processes, such as the manufacture of foamed parts. Although achieving the optimum temperature control needed for a high-quality part surface poses a particular challenge in this case, it also offers huge potential for process optimization.

[1] Kerkstra, R.: Solving Issues with Gloss. Plastics Technology (2016), available online at <a href="https://www.ptonline.com/news/solving-issues-with-gloss" target="_blank">https://www.ptonline.com/news/solving-issues-with-gloss</a>, last checked on April 5, 2022

[2] Berger, G.; Friesenbichler, W.; Reitter, M.; Jutz, S.; Langecker, G.: Hochglanzoberflächen beim Spritzgießen. Materials Testing 52 (2010) 4, pp. 211–221

[3] Schulz, D.: Ausschussarmes Lackieren von Kunststoffen. Plastverarbeiter (2018), available online at <a href="https://www.plastverarbeiter.de/markt/ausschussarmes-lackieren-von-kunststoffen.html" target="_blank">https://www.plastverarbeiter.de/markt/ausschussarmes-lackieren-von-kunststoffen.html</a>, last checked on April 5, 2022

[4] Bundesministerium für Wirtschaft und Energie: Luftstromregelung und Wärmerückgewinnung im Lackierprozess. (2021), p. 1, available online at <a href="https://www.wettbewerb-energieeffizienz.de/WENEFF/Redaktion/DE/Artikel/Projekte/Projektideen/energieeffizienz-in-lackieranlagen.html" target="_blank">https://www.wettbewerb-energieeffizienz.de/WENEFF/Redaktion/DE/Artikel/Projekte/Projektideen/energieeffizienz-in-lackieranlagen.html</a>

[5] Gim, J.; Han, E.; Rhee, B.; Friesenbichler, W.; Gruber, D.: Causes of the Gloss Transition Defect on High-Gloss Injection-Molded Surfaces. Polymers 12 (2020) 9, pp. 1–16

[6] Sánchez, R.; Martinez, A.; Mercado, D.; Carbonel, A.; Aisa, J.: Rapid heating injection moulding: An experimental surface temperature study. Polymer Testing 93 (2021) 106928, pp. 1–7

[7] Homann, J.; Mundt, A.: Monitoringbericht Energie 2020. Bundesnetzagentur für Elektrizität, Gas, Telekommunikation, Post und Eisenbahnen, Bonn (2021), pp. 27–28

SimpaTec Simulation & Technology Consulting GmbH  

https://www.simpatec.com

CONTURA MTC GmbH  

https://www.contura-mtc.de

Ausgabenartikel

3D CAD view of the conformal temperature-control system for injection molding a fascia with a high-gloss surface.

Fig. 1. The view of the mold interior in the simulation model shows the temperature difference  at the end of the filling stage: variothermal control on the top side leads to higher mold temperatures than on the conventional temperature-controlled side (below).

Fig. 2. The PC+ABS reference part had a high-gloss surface in both process variants, but weld lines were absent only in the variothermal variant (right). 

Fig. 3. Particle tracking shows the temperature of the weld lines as they form. In the variothermal variant (right), the temperature of the melt fronts on the visible surface (top side) is still so high that they do not show up as weld lines.

Fig. 4. The simulation of the shear stresses (bottom) indicates the direction in which the downstream surface quality of the PA6-GF30 real part is likely to trend – shown here is the higher-quality surface produced by variothermal temperature control (right).

Name - Hauptartikel

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

<b>Paula Hohoff</b> is an engineer at SimpaTec; <a href="mailto:sales@simpatec.com">sales@simpatec.com</a>