Lightweight parts, energy-saving processing or the practice of combining several process steps into one can all be subsumed under one current buzzword: sustainability. A technology that is highly promising in this regard is thermoplastic foam injection molding.

In physical foam injection molding, a blowing gas is injected into the polymer melt during plasticizing

New Developments in Thermoplastic Foam Injection Molding

Spritzgießen

Kunststoffverarbeitung: Verfahren

Schaumspritzgießen

Künstliche Intelligenz für die Qualitätssicherung

Industrie 4.0

Industrie 4.0 für die Qualitätssicherung

Schnecken und Plastifiziersysteme

Kunststoffverarbeitung: Maschinen und Komponenten

Spritzgießmaschinen

A Special Process that Is Becoming a Sustainable Normal Case

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

Steuern, Regeln

Software

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

Spritzgießsimulation

Simulation

Industrie 4.0 für die Kunststoffverarbeitung

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

With the MicroJect Advanced, Faurecia, a company of the Forvia Group, is presenting a new manufacturing process for foam injection molding.

Single-source component: the door panel comes directly from the injection-molding machine as a ready-to-install visible component with different grains.

16:9

New Injection Molding Technology for Foamed Parts with Class A Surfaces

Werkzeugbeschichten

Dienstleistungen

Dienstleistungen in der Metallbearbeitung

Design Surfaces thanks to Innovative Mold Coating

Under the motto “It‘s all Wittmann”, Wittmann Battenfeld is presenting its machines and systems in the new Wittmann design for the first time.

Automation cell with SmartPlus 90 for manufacturing a spirit level.

Messe K-Kunststoffmesse

kunststoffe-international.com

kunststoffe.de

Spritzprägen

Energieeffizienz

Naturmaterialien

Verstärkungsstoffe

Kunststoff-Rezyklat

Green DC Current for the Injection Molding Machine

This year, the world’s leading trade show K has succeeded in presenting practical solutions for greater resource efficiency on a broad front. A first foray through the trade show grounds.

K 2022 gave numerous practical examples showing visitors how recyclates can be reliably processed with digital aids.

State-of-the-Art Injection Molding Solutions for Greater Resource Efficiency.

State-of-the-Art Injection Molding Solutions at K 2022

Doriat, Clemens, Dr.

Solar / PV

Energieerzeugung

Erneuerbare Energie

Temperiertechnik

Condition Monitoring / Prozessüberwachung

Instandhaltung

Handling, Handhabungstechnik

Automatisierungstechnik

Elastomer-Spritzgießen

Digitalisierung

Silikonkautschuk

Kautschuk / Elastomere

Compoundieren

It Can Be Done!

In foam injection molding by the ZiFoam principle, gas is added to the pellet stock while it is still in the solid range.

Small pores, big difference (micrograph): Foaming makes the manufactured parts much more lightweight, consumes less resources and improves the CO2 balance.

Flexible Retrofit Set for Thermoplastic Foam Injection Molding

Leichtbau

Physical Foaming Made (More) Easy

Material and manufacturing process optimized, CO2 saved: recycled wash cap from Pöppelmann K-Tech closes the loop.

Material and manufacturing process optimized, closed loop: Recycled wash cap for the automotive industry. 

Sustainable Wash Cap

A ceramic CeraShibo coating can significantly improve the surface quality of foamed molded parts compared to conventional mold inserts.

Surface defects can be significantly reduced by using the coating on the aluminum tool.

Keramik

Andere Werkstoffe

Beschichtungen

Chemisches Bearbeiten (Auftragen)

Attractive Surfaces through  Foam Injection Molding

The aim of the present work is to establish the necessary scientific basics for the processability of the combination of co-injection molding and FIM for complex material systems.

Thermoplastische Elastomere

Thermoplaste

Polypropylen

Co-Injection Molding: Sandwich Parts with foamed core and soft skin

Investigations show the positive effects resulting from the combination of thermoplastic foam injection molding with post-consumer recyclate.

Double benefit: Reducing part weight and processing recyclate by the MuCell process.

Werkstoffprüfung, mechanisch

Messtechnik

Werkstoffprüfung

Saving CO2 Twice Over

In cars, LEDs are taking over ever more applications and are increasingly used as differentiating design elements. In order to ensure a high luminous efficiency even with complex geometries and elongated structures, Engel has developed a new plasticizing process for manufacturing light guides.

The transformation of the automobile also strongly affects the vehicle interior. Light is gaining in importance as a design element

The Principle of Starve Feeding: Injection Molding Ultrahigh Purity Light Guides

Farbmessgeräte

Optische Mess- und Prüftechnik

Spritzgießmaschinen, allgemein

LED / OLED-Systeme und Faseroptik

Lichttechnik

Less Granules  Stock Means More Quality

ARBURG is one of the world‘s leading manufacturers of plastic processing machines. The product portfolio encompasses ALLROUNDER injection moulding machines with clamping forces of between 125 and 6,500 kN, the freeformer for industrial additive manufacturing, plus robotic systems, customer and industry-specific turnkey solutions, and further peripheral equipment.

ARBURG GmbH + Co KG  

https://www.arburg.com

Abkantmaschinen, -pressen, -bänke

Blechbearbeitungsmaschinen

Maschinen für die spanlose Fertigung

Additive Fertigung

Anlagen für die Additive Fertigung

Antriebselemente

Lineartechnik

Maschinenelemente

Ceramic-Injection-Moulding, CIM

Condition Monitoring für die Qualitätssicherung

Kennzahlen

Qualitätsmanagement

Kennzahlen, Q-Leitstand, Q-Monitor

Kühlelemente, aktive

Kühlkörper

Elektromechanik

Management-Informationssysteme

Medizintechnik

Mehrfarben-Spritzgießmaschinen

Mikrobauteile

Montage

Montagetechnik

Mikrospritzgießen

Mischer

NE-Metalle

Metall Werkstoffe

PUR-Schäummaschinen

Schäumen / Reaktive Verarbeitung

Partikelschäumen

Produktionssystem

Rapid Manufacturing

Rapid Prototyping

Reinraumsysteme / -technik

Reinraumtechnik

Betriebsausrüstung / Betriebsmittel

Reporting-Tools

Rückverfolgbarkeit, Traceability

Schnecken und Zylinder

Spanneinrichtungen

Systemperipherie

Spritzgieß-Zubehör und Einzelteile

Stetigförderer

Fördertechnik

Logistik

Trockner

Vorbeugende Instandhaltung für die spanende Fertigung

The required screw diameter can be ascertained on the basis of the shot volume. The formula for the average residence time can be used to estimate the degree of utilization and the thermal load on the material.

Various shapes of plasticizing screws. The correct design is approached in several steps

Part 1 of the Series Discusses the Basic Design of a Plasticizing Unit and the Correct Choice of Injection Unit

All about Plasticizing Screws

To be able to carry out the practical test in a resource-saving manner, the designers use simulation tools to assess the screw geometry. What is important here is explained using a 3-zone screw as an example.

The screw geometry is finely optimized in several calculation steps until the desired result is achieved. Subsequently, test screws are manufactured in original size and tested in practical tests with various material types

20:7

Part 2 of the Series Deals with Basic Methods for Evaluating a Screw Geometry

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

KraussMaffei has offered physical foaming of plastics for over 20 years. Now, the team has examined all the screw types available on the market and, for almost two years, investigated their strengths and weaknesses regarding different materials. The result is a new universal foam screw with a 30 percent higher plasticizing rate plus a knowledge toolbox that allows custom production for special projects.

The “HPS-Physical Foaming” screw model improves the plasticizing rate for physical foam injection molding by up to 30 percent.

Physical foam injection molding is a wide field – applications of the MuCell process (supplier: Trexel), in particular, are a growing market. In the course of the generally sought-after conservation of resources and the reduction of the carbon footprint required by politicians and customers, it is being used ever more frequently, since it allows lightweight construction applications to be easily implemented. In thermoplastic foam injection molding (TFIM), a physical blowing agent (often nitrogen) is added to the melt, which forms a cellular structure in the cavity. Compared to non-foamed parts, this can make significant material savings and reduce the part weight [1]. Since the gas reduces the viscosity of the melt, longer flow paths are possible for thin-walled parts. Due to foaming, the holding pressure can be eliminated and low-warpage parts are produced. If the part design is tailored for plastics, the cycle time can also be shortened by eliminating the holding pressure. Because of the lower pressure demand, the clamping force can also be reduced – the energy consumption of the injection molding machine is decreased [2, 3].

To understand the central role of the screw in this, and why there was a need to improve KraussMaffei’s plasticizing unit development, it is appropriate to consider the process in detail.

Before the blowing agent can be injected, the material must be completely melted and homogenized. For this purpose, the MuCell screw has the familiar three-zone geometry. Nitrogen is an inert gas that can only be dissolved in the plastic melt in extremely small amounts. To obtain precise metering and good solubility, it must be in the form of a supercritical fluid. This is achieved under conditions above both the critical pressure and the critical temperature. In the case of nitrogen, these values are 33.9 bar and –147 °C. Since the thermoplastic injection molding process always takes place in the range above the aforementioned temperature, it is only necessary to keep the pressure value above 33.9 bar for as long as the melt is in the plasticizing chamber. It is only due to the pressure drop occurring in the cavity during the injection phase that the melt is supersaturated with blowing agent and the foaming process starts [4, 5].

The melt-gas mixture is very low-viscosity, so that the critical pressure can only be maintained with the aid of a shut-off unit (e.g. a non-return valve). This shut-off element has the function of preventing excessive pressure drop. It is located directly in front of the gas injector position on the screw and separates the three-zone region from the mixing and gassing range (Fig. 1). At the end of the metering process, this shut-off element, for example a central non-return valve (C-NRV) closes, and ensures a reproducible pressure level, which is the prerequisite for a stable and reproducible process with the same degree of foaming and the lowest possible shot-weight tolerance.

Since the KraussMaffei’s MuCell customers implement very different applications with different materials, the demand was clear: to create a new universal foam screw. At the beginning of the two-year analysis and test phase, there were two main questions:

<ul><li>How can the plasticizing performance be improved?</li><li>And can we perhaps do without the C-NRV?</li></ul>

Until now, it was necessary to use larger screw diameters for MuCell applications than for non-foamed injection molding, since, due to the gassing zone and C-NRV, the entire screw length was not available for melting and homogenization. Where otherwise an 80 mm screw was sufficient, 90 or 100 mm was required – resulting in higher costs. The C-NRV, in turn, was often called into question by users as a constriction (shearing and damage to the plastic) and as a wear point of the plasticizing system.

To be able to selectively investigate all regions of the screw, KraussMaffei developed a modular concept, in which various designs of the mixing and gassing range, C-NRV and three-zone range can be interchanged and combined by screwing. The analyses were performed on two three-zone regions, two mixing geometries and four central non-return valves (C-NRV), consisting of shearing elements of different gap widths, the standard ball check and an annular C-NRV. The existing foam screw served as a reference parameter for the results (Fig. 1). The tests were performed by the developers with seven different materials (Table 1).

At first, the aim was to optimize the plasticizing performance and the three-zone range for this. Its length was 15 times that of the screw diameter (15D). However, analyses showed that the mixing and gassing range (6D until now) could be reduced by 2D without loss of quality. Thus, the melting and homogenizing range could be increased to 17D, which also had a favorable effect on the wear behavior.

With the single-flight three-zone range, the plasticizing rate increased by about 20 % compared to the previous screw geometry. With a two-flight three-zone range, it even increased by a further 20 % for a glass-fiber-filled polyamide 6. However, an unfilled PP MFI 11 showed a decrease in the plasticizing rate, depending on the level of the backpressure (Fig. 2). With the use of low-viscosity plastics, the effect turned even more negative and led to a severe collapse of the plasticizing rate. For the sought-after new universal foaming screw HPS-Physical Foaming, it was therefore necessary to choose the single-flight option.

Another focus of the laboratory work was the C-NRV, since there are a large number of fundamentally different solutions on the market, four of which were taken into account here (Fig. 3). The main function of the C-NRV is to keep the pressure above the critical value (for nitrogen 33.9 bar) during the time between metering and injection, and so prevent backflow of the gas-charged melt towards the feed point. In principle, this function can be performed by a non-moving resistance element (such as a spiral shearing element) or a moving non-return valve (such as a ball check). In addition, the plastic melt should be able to pass easily through the C-NRV during metering to ensure high plasticizing rates and short metering times with as little shear as possible.

The results for the C-NRV show a differentiated picture: The fixed resistance elements in the form of the spiral shearing element and the cylindrical shearing gap offer an acceptable seal together with good plasticizing performance for high-viscosity polymers. In the case of PA6-GF30, the pressure in the phase between the end of plasticizing and the beginning of injection in the next cycle fell to about 60 bar (Fig. 4). The gap width did not have a significant influence on the pressure level reached.

However, with low-viscosity plastics, such as mineral-filled PP, the resistance elements reached their functional limits. Thus, until the beginning of injection in the next cycle, the pressure fell below the critical value (Fig. 4), which led to bubble growth in the plasticizing unit and made a stable process difficult to impossible to achieve. Strictly speaking, the gap between the resistance element and cylinder edge would thus have to be adapted to the viscosity of the particular plastic, or at least there would have to be several variants.

The ball check, on the other hand, showed good sealing behavior for both high-viscosity and low-viscosity polymers, and kept the pressure in the mixing section constant and reproducible above the critical value (Fig. 4). To ensure process reliability under a variety of background conditions and to reliably prevent the separation of gas and melt in the plasticizing unit, this option was chosen for the new foam screw.

New Universal Foam Screw with 30 Percent More Plasticizing Rate

The result of the development work is the “HPS-Physical Foaming” model, which is suitable for a wide variety of materials and improves the plasticizing performance by up to 30 % compared to the previous screw geometry (Fig. 5). Due to the extended three-zone range, the residence time until C-NRV is increased, which has a favorable effect on the melt quality and wear behavior of the entire screw. The non-return valve at the screw tip was retained, which proved advantageous for high shot-weight constancy.