At Euro PM 2015, organized by the European Powder Metallurgy Association (EPMA) in Reims, France, between October 4th and 5th, Sigmasoft Virtual Molding Chief Technical Officer Timo Gebauer will give a presentation describing how the correct viscosity can be calculated for MIM (Metal Injection Molding) feedstocks.
Sigmasoft Virtual Molding is able to predict shear heating and particle segregation, and to couple these effects to predict the real feedstock viscosity. This accurate modelling delivers a better description of the flow behavior and a far more precise pressure demand prediction, a key parameter to determine proper machine size and processing profitability.
Sigmasoft Virtual Molding is already a well-established tool in MIM processes, to predict feedstock molding behavior and its thermal interaction with the mold. To simulate the feedstock flow behavior inside the cavity, viscosity is a key parameter. However, the methods used to characterize viscosity in thermoplastic materials may not be suitable for the characterization of MIM feedstocks.
There is no testing device available to directly measure the viscosity; the values are always calculated indirectly. The most common way to determine the viscosity of polymers at high shear rates is the high pressure capillary rheometer (HCR). The measurements are corrected with theoretical models, but the temperature increase produced by heat dissipation is assumed to be low enough to be neglected. This assumption is accurate enough for thermoplastic materials at low shear rates. However, as the shear rate increases, the heat dissipation due to molecular friction (a phenomenon known as shear heating) starts to be important.
In MIM feedstocks, besides the high shear heating, the rheological behavior can be even more complex, because the shear field leads to particle segregation . Since
viscosity is a function of the powder concentration in MIM feedstocks, this segregation leads to significant differences in local viscosity and thus in local flow deformation. “One way to get the right viscosity for a MIM feedstock is to measure it with different particle concentrations. Once the viscosity based on the concentration is known, it is possible to use Sigmasoft Virtual Molding to calculate the correct viscosity”, states Gebauer.
The Fakuma 2014 went exceptionally well for Arburg. The Lossburg-based machine manufacturer was the only exhibitor to present the entire spectrum from additive manufacturing to injection moulding. The main focus was on the next step in the production efficiency strategy: the cost-effective production of plastic parts – from one-off parts, multiple-variant small and medium batches, through to mass-produced items.
“The trade fair in Friedrichshafen has traditionally been an excellent platform for high-quality discussions, intensive exchanges of ideas and good business. The exhibition stand was extremely well frequented throughout, and we received numerous specific enquiries,” says Michael Hehl, Managing Partner and Spokesperson for the Arburg Management Team, summing up the trade fair. “With eleven exhibits on our own stand and a further eight on partner stands, we presented numerous technical innovations, exciting processes and pioneering applications, positioning ourselves as the trendsetter of the industry.”
High level of interest in additive manufacturing
Particular interest was generated by the Arburg Plastic Freeforming (AKF) technology with the Freeformer, the German sales launch of which took place at the Fakuma. The ability to process standard granulates using an additive technique, and to build up the desired plastic part layer-by-layer from tiny droplets using 3D CAD data is unique. Using the production of a pair of office scissors as an example, Arburg offered a clear demonstration of the flexible customisation of plastic products under the Industry 4.0 heading by combining injection moulding and additive manufacturing.
Positive expectations for 2015
For the entire industry, the Fakuma 2014 was an important trend indicator of the coming months. The positive response and positive mood among visitors – including many international guests – at Europe’s major trade fair of 2014, has given Arburg a positive outlook on the year to come.
The completely redesigned “Evolution” exhibit at the company’s headquarters in Lossburg (northern Black Forest) brings Arburg’s history to life. Covering around 770 square metres, the exhibition area offers visitors an interactive approach to the company’s history – from its founding in 1923 to the present.
The exhibition includes injection moulding machines the Freeformer for additive manufacturing and many more innovations, historic milestones and product examples from the last 90 years. Accounts of historical events and wide-ranging multimedia content complement the exhibition.
How did Arburg become the worldwide leading manufacturer of injection moulding machines? Who are the heads of the family-owned company? Why was the first machine built from a bombed-out railway bridge? How has the brand developed over the decades? How will plastic materials be processed in 2040? – Customers will find answers to these and many more questions when they visit the modern “Evolution” exhibition at Arburg, which includes numerous exhibits and interactive touchscreen monitors.
From medical devices to the Freeformer
For example, visitors will see the first medical products made in 1923, consumer goods manufactured during the Second World War, flash units from the period of the Economic Miracle and, of course, the company’s milestones in injection moulding machine technology, right up to today’s Allrounder machines and the brand new Freeformer for additive manufacturing.
For everyone interested in injection moulding
The presentation is rounded off with an exhibit wall containing around 600 plastic parts, videos and so-called thematic and vision spheres. Visitors can call up detailed information on various levels, covering topics such as injection moulding processes, automation, corporate development, the brand, trade fairs and historical events, as well as taking a glimpse into the future.
To coincide with the 27th International Colloquium Plastics Technology, the Institute of Plastics Processing (IKV) in Industry and the Skilled Crafts at RWTH Aachen University put a new electric Allrounder 270 A injection moulding machine from Arburg, Lossburg, into operation. At the heart of this system is a micro injection moulding unit, the plasticising cylinder of which has been developed jointly by Arburg and the IKV.
The innovative plasticising unit, a so-called “inverse screw” is characterised by its special geometry. In distinction to conventional three-zone screws, the thread turns necessary for plasticising and melting the material are incorporated in the cylinder.
Micro injection moulding machine with new plasticising unit
The necessary relative movement is generated by means of an internal rotating piston. As the forces acting upon the piston are lower compared to plasticising screws, a significantly more compact plasticising system can be implemented, which is ideal for use in micro injection moulding. In addition to a reduced dwell time of the melt in the plasticising cylinder, the injection process can be controlled more effectively due to the smaller piston diameter. The mass fluctuations can thereby be reduced and the repeat accuracy of the injection cycle improved considerably. This has a positive effect on the achievable part quality.
Influence of geometry investigated and optimised
The effectiveness of the process has been evidenced through extensive joint studies carried out by Arburg and IKV. The influence of the geometry on the achievable feed rate and the melting characteristics in particular were investigated in order to progressively optimise the geometry. With the transfer of the geometry to a commercial injection moulding machine, use in a fully-automated injection cycle and consequently the potential of the technology in industrial application is now to be demonstrated.
At the Swiss Plastics trade fair, which will take place from 21 to 23 January 2014, ARBURG (Hall 1, Stand C1061) will present a cost-effective injection moulding solution for technical precision parts.
Visitors to the Luzern show will be able to discover an electric Allrounder 370 E injection moulding machine with servo-electric Integralpicker
Cost-efficient entry into the world of electric machines “All factors that increase energy efficiency, reduce cycle times and optimise production organisation help to improve the cost-efficiency of part production,” explains Marcel Spadini, ARBURG’s subsidiary manager in Switzerland. This is precisely what will be demonstrated by the exhibit, an electric Edrive series Allrounder with a servo-electric Integralpicker V. The machine will use a Stamm mould to produce two 8.5 g housings for knife sharpeners in a cycle time of 23 seconds. The robotic system offers low-cost entry into automated part removal.
Additive manufacturing with the freeformer
Furthermore, visitors to the Swiss Plastics fair in Lucerne will have an opportunity to see the new freeformer for themselves as part of a specialist presentation. This unique system for additive manufacturing will be introduced by one of its creators, Arburg Managing Director Technology & Engineering Herbert Kraibühler.