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

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

Industrie 4.0 für die Kunststoffverarbeitung

Biokunststoffe

Kunststoff Werkstoffe

Nachhaltigkeit

Umweltmanagement

Schneidmühlen

Kunststoff-Aufbereitung

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

Energieeffizienz

Mikrospritzgießen

Mehrkomponenten-Spritzgießen

Spritzgießwerkzeuge

Werkzeuge für die Kunststoffverarbeitung

Fließpressen

Handling, Handhabungstechnik für die spanende Fertigung

Automatisierungstechnik

Handling, Handhabungstechnik

Spritzgieß-Sonderverfahren

Elastomer-Spritzgießen

Linearroboter für die Kunststoffverarbeitung

Industrieroboter

Montagetechnik

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

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

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

The area of application of cube molds has expanded to take in the production of technical parts. The new Allrounder Cube 1800 from Arburg with a clamping force of 1800 kN is providing the response to this trend. With its compact cube, this machine completes the portfolio of products at the lower end of the range.

Arburg Expands Hybrid Cube Series

After a year’s forced break of Fakuma, Wittmann Battenfeld is announcing the new servohydraulic SmartPlus machine as the highlight of this year’s trade show. It is claimed to be characterized by high economic and energy efficiency and repeat accuracy.

Messe Fakuma

kunststoffe-international.com

Spritzprägen

Injection Molding Innovations In-House, Live and in Color

Emilio López has been appointed as the new managing director of Engel de Mexico SA de CV. He succeeds Peter Auinger, who retired on 1st September 2021.

New Managing Director in Mexico

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.

Innovative Injection Molding in Times of Pandemic

Künstliche Intelligenz für die Qualitätssicherung

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

Digitale Transformation

Wirtschaft

Innovationen und neue Technologie

Machine Learning / Künstliche Intelligenz für die spanende Fertigung

Industrie 4.0 für die spanende Fertigung

Kunststoff-Recycling

Lasermarkieren

Oberflächentechnik

Laserbearbeitungen

Inline- / Online-Messsysteme

Qualitätssicherung

Qualitätssicherung Kunststoff

Kreislaufwirtschaft

There Is More beyond the Horizon

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.

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

Kugelgewindetriebe

Maschinenelemente

Getriebe

Elektrische Antriebe für Spritzgießmaschinen

Antriebe

Elektrische Antriebe

Elektromechanische Maschinen

A Question of Class

Arburg will be showing the hybrid high-performance Hidrive series on its stand no. 21B25 in Hall 2, with an Allrounder 520 H producing 32 pipette tips in around 6 s cycle time.

High-Tech for Medical Technology

From 25 to 28 January, the OOO Engel team presents its booth in Moscow again. The injection molding machine manufacturer and system solution provider headquartered in Austria is making the huge potential of digital solutions tangible by producing technical parts live on a tie-bar-less victory injection molding machine.

The Benefits of Tie-Bar-Less Technology

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

Wittmann Battenfeld GmbH  

https://www.wittmann-group.com

Ausgabenartikel

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

16:9

20:7

Fig. 1. Schematic diagram of a 3-zone screw with number of screw flights i = 1

Fig. 2. Pressure curve along the screw at 50 mm stroke position

Fig. 3. Melting process curves for the screw at stroke position 50 mm towards the end of the cycle

Name - Hauptartikel

<b> Filipp Pühringer</b> heads the Process Engineering Development Department at Wittmann Battenfeld GmbH in Kottingbrunn, Austria.

Part 1 of the series was devoted to the basic design of a plasticizing unit and the correct choice of injection unit and was published in Kunststoffe international (<a ext="tango:{45D59CEA-6DC5-4DBA-A9B4-CA287D7F7E2F}">issue 10/2020, p. 27–29</a>). In the 3rd part of this series of articles, the calculation results will be analyzed, and first steps towards optimization of the geometry will be outlined. It will appear in one of the next issues.