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.

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

Spritzgießen

Kunststoffverarbeitung: Verfahren

Spritzgießmaschinen, allgemein

Kunststoffverarbeitung: Maschinen und Komponenten

Spritzgießmaschinen

Schnecken und Plastifiziersysteme

All about Plasticizing Screws

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.

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

Spritzgießsimulation

Software

Simulation

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 Principle of Starve Feeding: Injection Molding Ultrahigh Purity Light Guides

Farbmessgeräte

Messtechnik

Optische Mess- und Prüftechnik

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

Industrie 4.0 für die Qualitätssicherung

Industrie 4.0

Energieeffizienz

Handling, Handhabungstechnik

Automatisierungstechnik

Kennzahlen

Qualitätsmanagement

Kennzahlen, Q-Leitstand, Q-Monitor

Qualitätssicherung

Kühlelemente, aktive

Kühlkörper

Elektromechanik

Management-Informationssysteme

Medizintechnik

Mehrfarben-Spritzgießmaschinen

Mikrobauteile

Montage

Montagetechnik

Mikrospritzgießen

Mischer

Kunststoff-Aufbereitung

NE-Metalle

Metall Werkstoffe

Partikelschäumen

Schäumen / Reaktive Verarbeitung

Produktionssystem

PUR-Schäummaschinen

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

Industrie 4.0 für die spanende Fertigung

A year to forget is nearing its completion. To brighten up this dreary fall season without a major event like Fakuma, injection molding machine builders have concocted various strategies.

Injection Molding Machine Builders Are Discovering New Ways to Reach Their Customers

Vernetzung / Cloudlösung für die Kunststoffverarbeitung

Industrie 4.0 für die Kunststoffverarbeitung

Biokunststoffe

Kunststoff Werkstoffe

Nachhaltigkeit

Umweltmanagement

Schneidmühlen

Silikonkautschuk

Kautschuk / Elastomere

What Can You Do at Fall Fairtime,  When There Aren’t Any?

Once again, the K 2019 in Düsseldorf, Germany, lived up to its claim to be the leading trade show for plastics technology. At least in the field of injection molding, there were exciting global innovations to see – if you looked closely.

Injection Molding Trends at K 2019

Schaumspritzgießen

Smart Factory

Mehrkomponenten-Spritzgießen

Spritzgießwerkzeuge

Werkzeuge für die Kunststoffverarbeitung

Fließpressen

Handling, Handhabungstechnik für die spanende Fertigung

Spritzgieß-Sonderverfahren

Elastomer-Spritzgießen

Linearroboter für die Kunststoffverarbeitung

Industrieroboter

Montage-Spritzgießen

Knickarmroboter

Co-Injektion (Barriere-/Sandwich-Spritzgießen)

Hybrid-Spritzgießen (Metall / Kunststoff)

Ressourcenmanagement

Produktion

Technical Excellence thanks  to Digital Assistance

Infrared heating technology has become established as the standard in the processing of thermoplastic composite materials. The focus is on process control. On the one hand, it is important that the heating process is fast, on the other hand, the material must not be overheated. It is also important to achieve excellent temperature homogeneity. Simultaneous processing of blanks with different thicknesses is a particular challenge.

Efficient and Precise Heating up of Thermoplastic Composites

Steuern, Regeln

Infrarotstrahler

Verbundwerkstoffe / Werkstoffverbunde

Organobleche (gewebeverstärkte Thermoplast-Halbzeuge)

Halbzeuge und Zwischenprodukte

Kunststoff-Halbzeuge

Software-Based Control of IR Ovens

The new injection-molding machine Engel duo speed combines productivity and efficiency with short cycle times in a high clamping force range. The two-platen machine is thus making inroads into a range of packaging applications that were formerly the domain of toggle machines.

Engel Duo Speed Expands the Machine Portfolio for Packaging Applications

High-Speed Machine with a  Small Footprint

The Wilhelm Böllhoff GmbH & Co. KG employs Arburg’s ALS host computer system as a uniform MES at locations all over the world. Not only all their injection molding machines are networked with information technology via ALS, but hundreds of machines and turnkey systems for metalworking and assembly, as well. Some 3000 injection molds are also managed. This generates transparency in everything from order planning and process optimization to maintenance.

Böllhoff Uses ALS as a Uniform Global MES for Injection Molding and Metalworking

Big Data für die Qualitätssicherung

Qualitätssicherung Kunststoff

Energiemanagement

Completely Joined to the Host Computer System

Munich-based mechanical engineering group KraussMaffei is repositioning itself and uniting all divisions under a single brand. At a time of accelerated technological change, the company is increasing its efforts to develop new products for digital solutions and new business models – and that includes plastics recycling.

KraussMaffei Consolidates Three Divisions and the Previous Group Brands under a Single Brand

Extrusion

Doriat, Clemens, Dr.

Digitale Transformation

Wirtschaft

Innovationen und neue Technologie

Kunststoff-Recycling

Compoundieren

Moving with the Times

The injection molding system supplier Husky is launching its HyPET HPP5e. This is a refinement of the proven HPP platform, which, as a fully integrated system for the manufacture of PET preforms, is intended to obtain greater energy savings, system reliability, preform quality and user friendliness than its predecessor.

Husky: Advances in the Injection Molding of PET Bottle Preforms

Polybutylenterephthalat

Thermoplaste

Refining a Proven Platform

The new head of the Asia-Pacific region (excluding Greater China) will be responsible for sales, service and project management.

Spritzgießmaschinen, Spritzpressen

Kunststoffverarbeitungsmaschinen

New Vice President of Asia-Pacific Region

The company Leonhard Kurz is a specialist in the development and production of decorative and functional coatings for plastics applications, which are applied by means of carrier foils during injection molding. Essential objectives of the company are technology and process development as well as the optimization of the 3D foil forming around corners and the contours of the plastic parts. For this purpose, Kurz operates an extensive injection molding technology center. New in the machinery: two production cells based on servo-hydraulic injection molding machines from Wittmann Battenfeld.

Leonhard Kurz Has Extended its Development Capacities with Injection Molding Systems from Wittmann Battenfeld.

Kapazitive Sensoren

Sensoren / Messwertaufnehmer

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

From the Roll to the Third Dimension

According to the company, the UltraShot Injection System provides part design freedom, while improving part quality and speed of mold qualification.

Husky introduces the UltraShot Injection System

Kunststoffverarbeitung allgemein

Kunststoffverarbeitung

Normalien und Heißkanaltechnik

Komponenten für die Kunststoffverarbeitung

Heißkanalsysteme

Next Generation Melt Delivery and Control System

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.

New Developments in Thermoplastic Foam Injection Molding

Künstliche Intelligenz für die Qualitätssicherung

A Special Process that Is Becoming a Sustainable Normal Case

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

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.

Once the basic layout of a plasticizing unit has been determined and the appropriate injection unit has been selected, the development of the screw geometry enters its decisive phase. 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 basic design of a plasticizing unit and the correct choice of the injection unit were discussed in the first part of this series. The way to determine the required screw diameter on the basis of the shot volume was also explained. By applying the formula for the mean residence time, the utilization rate and the thermal material load can be estimated; the latter needs to be kept low to achieve high end product quality. The maximum injection pressure and the available screw torque are additional key variables for successful injection molding production.

These considerations (see <a ext="tango:{45D59CEA-6DC5-4DBA-A9B4-CA287D7F7E2F}">Kunststoffe international 10/2020, pp. 27-29</a>) form the basis for the choice of the barrel-and-screw combination and also the starting point for further optimizations. In the second part of this series of articles, the basic methods for simulative assessment of the geometry of a given screw are presented – using the example of a 3-zone screw.

Before All Experiments Comes  the Simulation

The first question to be answered is what objectives should be pursued in developing a screw geometry. Often the goal can be clearly defined, such as increasing the flow rate, reducing the melt temperature, improving the quality of the blend, etc. The requirements become more complex as soon as the desired results are only indirectly linked to the screw geometry, or when they can be attributed to several causes, for example, when it is desired to reduce the formation of plaques, or when the wear behavior and conveying stability need to be improved.

Such multiple demands on screw aggregates often conflict with each other. Careful balancing of the layout is necessary to resolve such conflicts between several different objectives.

It has become common practice to optimize the geometry of a screw by way of simulation before the first tests are carried out with real experimental screws. With PSI/REX, Wittmann Battenfeld GmbH, Kottingbrunn, Austria, has a special software at its disposal for calculating the screw design. This software is ultra-modern and subject to continuous updates by targeted research carried out at Paderborn University, Germany.

While using the computer to calculate the screw geometry, the geometry can be varied extremely flexibly, and the resulting change can be immediately visualized on the screen. By running systematically through a pre-defined series of tests, it is possible to analyze the emerging trends. Finally, the results of all calculations are combined and compared. From the sum of this information, the corresponding screw geometry is developed and further optimized down to the last detail – until the desired result comes into view.

Only then are experimental screws produced in original size and used in practical tests. Depending on the complexity of the task, several different experimental screws may be used to approach the objective from various angles. If these tests prove successful, the optimization process is completed. Where there is still room for improvement, the development loop is re-run.

Model Case for the Optimization fo the Screw Geometry

Next, the parameters of a standard 3-zone geometry shall be discussed, and their influence on the manufacturing process shall be illustrated by an example. In order to give a full description of such a geometry in terms of process technology, the following parameters must be known (Fig. 1).

From the number of geometry parameters for only a relatively simple standard 3-zone screw, it is already apparent that there is basically a multitude of possible variants even for this type of screw. In the case of more complex geometries, such as those found in barrier screws, screws with shearing and mixing sections or shearing/mixing screws, the number of geometry parameters is many times higher. Starting basically from the recommendations available in the relevant professional literature [1], the optimization of the geometry for a screw with a diameter of 50 mm (DSC) is calculated below as an example.

It is assumed that the length of the feed zone is 50 % of the total length of the screw and the lengths of the compression zone and metering zone should each be 25 % of its total length. We set the feed zone depth at 0.1 D, i. e. 5 mm. The flight depth ratio between the feed zone and the metering zone should be 2. The L/D ratio is assumed to be 22.

A variety of different calculations can be performed for a screw with these pre-defined parameters. The present discussion focuses on the melt throughput, the pressure curve or pressure build-up capacity and the melting process.

Basic Assumptions and  Throughput Behavior

Further assumptions include the metering stroke of 85 mm and the cycle time of 35 s. The back pressure is set at 80 bar. To simulate moderate and realistic metering conditions for the material polystyrene (grade:PS 454N; manufacturer: Styrolution), a circumferential screw speed of 300 mm/s is assumed. The barrel temperature profile is slightly rising from the filling opening to the antechamber. All calculations are carried out for the 50 mm screw position (Figs. 2 and 3).

For the previously selected cycle parameters, the average metering performance is calculated at about 12.49 g/s for the present screw geometry. This means that the machine transports 12.49 g/s in the metering phase and thus takes about 12.7 s to plasticize 158 g of material. With a residual cooling time of more than 12.7 s, the machine can start a new metering stroke on time. But if plasticizing takes longer than the residual cooling time, the timing of metering impacts the total cycle time and thus reduces productivity.

The total output of 16,25 kg/h determines the amount of material consumption in the course of production. Since the screw does not dose during most of the cycle time, this output falls below the figure suggested by the average metering performance. The total output is the decisive parameter in dimensioning auxiliary equipment (dryers, material loaders, etc.).

Pressure Build-up Capacity and Melting Process Curves

During the metering phase, the pressure inside the screw channel increases from the feed opening to the back pressure in the antechamber. Depending on the screw geometry, there may be one or more pressure peaks in between.

Figure 2 shows the pressure curve over the screw length. In this particular case, the pressure curve begins to rise at about L/D = 2 and reaches the peak pressure of about 160 bar at about L/D = 14.25. In the last zone of the screw, the metering zone, the pressure drops continuously up to the check valve.

The melting process (MP) is visualized via two curves (Fig. 3): the solid bed width (green) is shown for the corresponding screw channel section, and the proportion of molten material (red) during the metering process. In addition, the development of these two parameters towards the end of the cycle is illustrated (in orange and beige).

From the results, it can be concluded that this melting process promises good melting of the material, since the proportion of melt has already reached 100 % at about L/D = 8 (proportion of melt MP = 1). In other words, the solid bed width has been reduced to 0.

It can be seen that even with a “simple” 3-zone screw, the designer has a large number of geometric parameters at his disposal to achieve the development goal. With the simulation software, the actual experimental effort can be reduced significantly. However, the results of the simulation cannot replace the practical experiments, since not all boundary conditions can be considered or are known. In a closed environment they show trends and possible need for action.

[1] Johannaber, F.; und Michaeli, W.: Handbuch Spritzgießen. Carl Hanser Verlag, München 2014

[2] Gornik, C.: Neue Erkenntnisse zur Plastifiziereinheit von Spritzgußmaschinen basierend auf experimentellen Untersuchungen, Dissertation, Montanuniversität Leoben 2007