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

Spritzgießen

Kunststoffverarbeitung: Verfahren

Spritzgießmaschinen, allgemein

Kunststoffverarbeitung: Maschinen und Komponenten

Spritzgießmaschinen

Spritzgießsimulation

Software

Simulation

Schnecken und Plastifiziersysteme

All about Plasticizing Screws

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

Schaumspritzgießen

Künstliche Intelligenz für die Qualitätssicherung

Industrie 4.0

Industrie 4.0 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

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

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

Smart Factory

Energieeffizienz

Mikrospritzgießen

Fließpressen

Handling, Handhabungstechnik für die spanende Fertigung

Automatisierungstechnik

Handling, Handhabungstechnik

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

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

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.

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

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.

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.

A Process Monitoring Platform Monitors Several Hundred Parameters Simultaneously

Steuerungen (Hardware und Software)

Prozessvisualisierung

Condition Monitoring / Prozessüberwachung

Instandhaltung

IoT-Plattformen für die Kunststoffverarbeitung

An Eye on the Process –  a Handle on Quality

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

“Mold Strategy 2.0 – New Ideas for Reducing Costs”

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

Kennzahlen

Qualitätsmanagement

Kennzahlen, Q-Leitstand, Q-Monitor

Kühlelemente, aktive

Kühlkörper

Elektromechanik

Management-Informationssysteme

Medizintechnik

Mehrfarben-Spritzgießmaschinen

Mikrobauteile

Montage

Mischer

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

Haitian International, the Chinese manufacturer of injection molding machines, is consolidating its growth of the last ten years while its European business flourishes. New locations and additional investments will support its foreign activities. On the program for the K 2019 is the introduction of what is now their third generation technology.

Haitian’s Success Story Continues with Big Plans

Doriat, Clemens, Dr.

Elektrische Antriebe für Spritzgießmaschinen

Antriebe

Elektrische Antriebe

Plans for Further Expansion

Investment strengthens Arburg´s expertise and electric drives portfolio. AMK has been Arburg‘s development partner in electric drives for decades.

Kunststoffverarbeitung

Dienstleistungen

Lohnfertigung

Unternehmen

kunststoffe.de

Arburg Acquires AMK‘s Drives & Automation Division

Weld lines reduce the strength of injection molded parts – a problem that can hardly be avoided in product development. Therefore, an integrative calculation method was developed at IKV in Aachen, Germany, to predict the weld line strength of amorphous thermoplastics at an early stage. The method was successfully tested for polystyrene.

Prediction of the Weld Line Strength in Amorphous Thermoplastics  by Integrative Simulation

Prozesssimulation

How Strongly Does a Weld Line Weld?

SIMCON – Our solutions help you make better plastic injection molding decisions, faster – for better parts, molds, and an optimized injection molding process!

simcon kunststofftechnische Software GmbH  

https://www.simcon.com

Analysetools, FEM

Beratung und Consulting

Logistiksysteme Software

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

A Special Process that Is Becoming a Sustainable Normal Case

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

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.

Which injection molding machine is the right one for which application? Is fast also powerful – and at what price? Anyone trying to answer these questions by comparing brochure data will be disappointed. This is because different manufacturers sometimes measure under different conditions and specify parameters so different from each other it is like comparing apples and oranges. In addition to injection volume and speed, filling time and component weight are also crucial factors when selecting a machine. Below we will demonstrate why performance is not always performance, but physics is always physics.

What this means can be illustrated using the example of a car driver: suppose someone wants to drive over the Alps on holiday. A powerful SUV, a sporty convertible and a tandem trailer are available. Both vehicles have roughly the same power output of 250 kW, i. e. around 350 hp. Which of the two vehicles will drive in a relaxed manner over the Alps to the destination, and which one would it be more fun to cruise through the various passes in? Should the driver load the SUV onto the trailer and drive the sports car to the destination – or would the other way around be better, so as to enjoy the bends of the landscape in the convertible? This is a decision that everyone will probably make intuitively in the same way.

If we transfer this analogy to the forming process world of injection molding, the answers are not particularly clear at present. One reason is the change in drive technology and in suppliers, who are increasingly coming from the machine tool sector. As a result, the injection speed for the injection axis is specified in some cases linearly in mm/s, and in others volumetrically in cm3/s. Other conventional brochure data relates to screw diameter, shot volume and injection pressure. Recognized substantiated values are those which are actually achieved under full load at 2000 bar counter pressure and 1 D screw stroke. Most (European) molds and screws are also adapted to this mechanical load.

Brochure Data for a Comparison  of Machines

Footnotes in the technical data sheets that quote “theoretical” idle speeds without the pressure factor or with limited holding pressure times are less significant. Whether such theoretical values in the brochure or on the control system screen are actually sufficient to realize the desired injection times with the machine in the actual process cannot be deduced from this. For example, a “theoretical” idling speed of 1000 mm/s simply means: according to the data sheet, the motor can rotate fast enough that the specified speed is theoretically achieved over the entire screw stroke – but without taking into account the counter pressure in the mold, into which the plastic does not “voluntarily” flow. The faster the injection, the higher the counter pressure and consequently the pressure required for injection. In addition, it is of course not possible to drive into the holding pressure at full speed because the mold would inevitably become completely overloaded if there was no slowing down. This value is therefore never reached in the actual process.

Hydraulic versus  Electric Injection Units

Modern hydraulic injection units require relatively little superimposed system pressure in order to be able to use the full injection pressure (2000 bar) at maximum programmed speed. At least that is how current data sheets for hydraulic injection units are designed. For fast and precise injection, hydraulically driven injection units are usually equipped with a servo valve and barely differ in terms of dynamics. While stored energy and high peak performance can be used here, the performance required for electric drives is always supplied directly from the mains to the injection axis and screw tip. In addition, with commercially available hydraulic injection units, the inertial mass of the construction plays virtually no role, in contrast to electromechanical solutions.

Intrinsic inertia is another crucial factor in electro-mechanical systems. This needs to be overcome in order to accelerate the drive components spindle or gearbox and servomotor to the required final speed. As a rule, at least 50 % of the installed drive power and the available torque must be used for this purpose. The dynamics of servo-electric direct drives depend heavily on the mechanical design. Arburg develops and manufactures its own planetary roller screw drives for its Alldrive and Hidrive series machines, which are particularly load-resistant and durable (Title figure).

Without getting lost in technical details, the mechanical design and the construction principle and consequently the target design play a key role in electric injection units. The dynamics and peak performance that can be achieved with these machines have a significant influence on the machine price and the technical possibilities in the injection molding process. Or to stay with the analogy mentioned at the beginning: an 800-kg sports car that needs to get a trailer with a 2.5 t SUV moving can no longer accelerate from 0 to 100 km/h in 3 s. That is, if it can even still pull it on a 15 % incline without the wheels spinning.

All Good Things Come in Threes – Different Performance Classes

Based on the filling time, the applications and injection molding machines suitable for them can currently be roughly divided into three classes (Table 1). The majority of all applications are technical injection molded parts with a filling time of 0.3 s and well above. Directly driven hydraulic standard machines are generally designed and ideally suited for this area.

Applications with extremely short filling times of less than 0.1 s are more of a niche for specially adapted injection molding machines, which by no means every manufacturer offers. These include, for example, thin-walled high-temperature components made of PEEK for the classic consumer goods and electronics industries. One example is charging plugs for smartphones.

Classic applications with filling times of approx. 0.1 to 0.3 s here are the processing of polyolefins into thin-walled packaging parts such as cups (Fig. 1.), buckets or screw caps with flow path to wall thickness ratios of 100 to 300:1. Such thin-wall applications require high dynamics. Therefore, hydraulic machines with hydraulic accumulator technology have been used to a large extent in this segment up to now. However, the trend here is also towards directly driven electric or hybrid high-performance machines. This is where the wheat is separated from the chaff, because the term “high performance” is elastic and relative.

The achievable injection speed in mm/s is one of the characteristic indicators for the technical performance of an injection molding machine. The use of mm/s actually comes from the machine tool industry, which describes the linear feed rate of an axis. In the dimension of km/h, this approach is a suitable SI unit for the maximum achievable movement speed of a motor vehicle, but not for injection. The situation here is fundamentally different. This is because the machine’s injection unit does not fill in millimeters, but injects a volume in the form of a fluid plastic melt into the mold cavities. This is where the screw size comes into play (Fig. 2).

Three-Dimensional Thinking:  Screw Size as an Influencing Factor

The same injection molding machine can be equipped with different screws. At the same feed rate, this results in different flow volumes per unit of time until the required volume has been injected. In addition, in Europe diameters are usually graduated in 5 mm steps, i. e. 25, 30, 35 mm, etc. Other manufacturers prefer a standard series with diameters of, for example, 28, 32 and 46 mm, so a direct comparison, in terms of process capability, based on feed rate alone is not meaningful.

What is ultimately relevant for the respective practical application is the volume of plastic melt that can be injected per unit of time, i. e. the time during which the “cake is baked” before the material solidifies. This filling process is characterized by the filling time, on which filling simulations are also based. The relevant variable is therefore the injection volume per unit of time, known as the injection flow volume (Q). Ever since the development of the first control systems at the end of the 1970s, Arburg has been specifying the associated injection molding physical unit as the injection flow volume in cm3/s and has been using this as a data sheet parameter for decades. A milestone in more recent times was the introduction of the Gestica control system in 2016 (Fig. 3.). The data for a filling simulation can also be transferred to this. A filling simulation can be done directly on the screen with the help of the “aXw Control FillAssist” function (Fig. 4).

Most machines can operate with a maximum screw stroke of 3.5 to 4.5 D, but this is only relevant for thick-walled components and for filling times in the seconds range. Particularly in the thin-wall sector, around 1 D of screw stroke can usually be used as injection volume with common three-zone screws and a usable throughput design. The filling time, which is achieved in the injection molding process with 1 D screw stroke, is therefore a great classification feature, irrespective of the abundance of materials and the width of the part spectrum. During this time, more than 95  % of the liquid plastic melt must have been injected into the mold by the injection unit.

For the filling process, the crucial factor for the given injection unit and machine is how much melt volume arrives in the mold during the available filling time. This constitutes another reason to state the injection flow volume in cm3/s instead of the feed rate in mm/s in data sheets relating to plastics. This value is therefore standardized with the corresponding screw diameter and can be easily calculated in your head for a desired plastic part: assuming a density of 1 g/cm3, a part volume of 50 cm3 and a required filling time of 0.1 s. This initially results in an injection flow volume of at least 500 cm3/s. With electric drives, which have to be accelerated and actively braked with not inconsiderable inertial masses, this value must be multiplied by a factor of 2 (triangular operation). So in this case the value in the data sheet suitable for this application – without a footnote – should be around 1000 cm3/s.

If it has been a while since GCSE physics for you: for a given feed rate and screw diameter (converted into cm), the injection volume flow (Fig. 5) can be calculated as follows:

Q = π · ¼ D2 · v

<ul><li>Q = injection flow volume [cm3/s];</li><li>π ≈ 3.14;</li><li>D = diameter [cm];</li><li>v = velocity [cm/s]</li></ul>

If the feed rate is, e. g., 200 mm/s (= 20 cm/s), the following injection flows result for screws with diameters of 35 and 28 mm:

In order to also achieve an injection flow volume of 192 cm3/s with a 28 mm screw, the feed rate would have to be 313 mm/s instead of 200 mm/s – around 1.5 times that of the 35 mm screw. Conclusion: the smaller the screw, the higher the feed rates [mm/s] required to inject the same volume of liquid plastic melt [cm3/s].

In order to estimate which injection unit is suitable for the respective application, the filling time, the part or shot weight and, if necessary, the material density should be known. For this reason, almost every injection molding engineer has a small spring scale in their pocket. This is because, in contrast to the specific weight of the plastic melt, the actual weight of the cured component can be easily determined. By rule of thumb, this can be equated with the volume to be injected at a density of 1 g/cm3 (e. g. for polyolefins) in order to roughly estimate the suitability according to the data sheet (the exact calculation according to the PvT diagram is carried out by the control system in modern machines).

Selection of the Appropriate  Injection Unit

Again, a simple calculation example: assume that a ballpoint pen to be produced weighs 5 g. Multiply this component weight by the number of cavities (e. g. 8) and add the sprue weight (e. g. 30 g). In the example, this results in a shot weight of 70 g. A filling time of 0.5 s results in an injection flow volume of around 70 cm3 in 0.5 s, which corresponds to around 2 x 70/0.5 = 280 cm3/s for electric drives according to the above rule of thumb. Now it is easy to see from the technical data sheet which injection unit achieves a shot volume of 70 cm3 and an injection flow volume of at least 280 cm3/s with a 1 D screw stroke. In this way, the suitable injection unit can be determined in an uncomplicated manner. However, you will need to use a calculator if the brochure indicates speeds in mm/s instead of injection flows.

Euromap: Standardized Injection  Unit Sizes

The designation for injection units proposed in accordance with Euromap 1 has become established as a near standard data sheet. This is the product of the maximum stroke volume in cm3 and the maximum spray pressure in kbar. This classification number is then also used for price/performance comparisons. Example: an injection unit 800 according to Euromap has, in many cases, a screw diameter of 50 mm, a stroke of 200 mm and a maximum injection pressure of 2000 bar.

Given that stroke is more cost-effective than force for electric drives, various manufacturers use smaller screw diameters for a given Euromap index. The consequence of this is that, in accordance with the square area ratio, more stroke, L/D ratio and correspondingly higher feed rates need to be realized in order to obtain the same part in the mold for a given injection volume and filling time.