The application that ARBURG presented at Fakuma 2015 in partnership with Swiss-based company Trelleborg Sealing Solutions Stein am Rhein AG represented a quiet revolution: an electric two-component ALLROUNDER 470 A was used to produce buttons for car interiors from two liquid silicones. Bonds like this offer a wide range of benefits.
Having collaborated for over 30 years, the partners decided to pool their expertise for the application shown at the exhibition: the 32+32-cavity mould with integrated electric rotary unit, the removal module and the material selection system came from Trelleborg, while the essential swift and precise machine and robot technology came from ARBURG. The LSR components were prepared by two all-electric dosing systems from Reinhardt Technik.
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At the Fakuma show, buttons weighing just 0.09 grams were produced from two LSR components with a 32 +32-cavity mould. Almost 4,000 parts were produced per hour. |
0.09 gram LSR-LSR parts
The shot weights are especially small at just 2.04 and 0.98 grams. Moulding takes place directly via a cold runner and the cycle time is around 30 seconds. Parts are removed and set down automatically by means of a verticallyoperating MULTILIFT V robotic system. This removes the finished 0.09 g parts from the mould, conducts a visual inspection using a thermal imaging camera and sets them down according to cavity.
This button mould demonstrates what can be achieved with current state-of-the-art technology. Because of material and demoulding requirements, comprehensive expertise is particularly important when dealing with small shot weights in combination with a high number of mould cavities. Because silicones, unlike thermoplastics, do not perish or turn yellow, they enable a particularly pleasant texture and unvarying appearance to be achieved on buttons.
A cold runner system is essential
“Because of the material price, direct injection using cold runner needle shut-off systems is the ideal solution,” says Jakob Bleiker, Technical Director at Trelleborg Sealing Solutions. “In turn, this makes symmetrical mould filling and the balancing of high-cavity moulds, in other words the even volumetric filling of all cavities, very important indeed. That’s why we develop, design and produce our cold runner systems in-house in Stein am Rhein itself.”
Automated removal
Because the rubber elasticity of the LSR moulded parts means they are not dimensionally stable and because burr formation may be favoured by further mould separation, it is not possible to use ejector pins for demoulding purposes. This means that automatic removal is more or less inevitable in batch production.
Nonetheless, Jakob Bleiker does not regard LSR-LSR injection moulding as a competitor process, but rather as a complementary process to the overmoulding of thermoplastic inserts: “The choice of a soft/soft or hard/soft combination is primarily determined by the application of the part.
The market potential exists
Even though the greatest market potential lies in high-volume production, smaller volumes can also pay off. This requires technical feasibility in combination with cost efficient applications.” However the complexity of mould technology is increasing exponentially with the number of cavities. For this reason it is important to relate development times and product life cycles to the number of parts, so as to be able to produce in a cost efficient way.
The process itself will gain significantly in importance in the future. The automotive industry in particular is calling out increasingly for ready-to-use moulded parts, according to Jakob Bleiker. However, there are also significant applications in the areas of pressure-sensitive mats (electronics), healthcare (e.g. multi-coloured pacifiers) and medical technology (e.g. catheters or respirator masks).
