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Injection moulding: Possibility of earlier test run with samples

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The production of tools for prototype injection moulding is extremely complicated and costly, especially when steel or aluminium is used for the production. The tools must therefore be milled and hardened, which means that not only is their production relatively expensive, it may well take a week. But the time pressure on companies is increasing. In order to provide tools in a significantly more time and cost-effective manner, Hans Geiger Spritzgießtechnik GmbH recently tested the process of additive manufacturing for production. With this method, the first tools can be made available for viewing in just under six hours. The printing process uses a special synthetic resin that is much cheaper to buy than the materials used so far, which reduces production costs by up to 70 per cent. By eliminating milling and hardening, the prototype can be tested in just a few hours instead of several days – up to 90 per cent time savings.

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Injection moulding tools have to withstand enormous loads. For this reason, mainly resistant metals are preferred in production, which requires an expensive and time-consuming manufacture. This is not a problem for mass production – thousands of operations mean investment costs pay off shortly. But the fixed costs are out of proportion in particular for small batch sizes or individual pieces needed to produce prototypes – especially if the prototype does not lead to the order acquisition. In addition, time is playing an increasingly important role. An alternative is 3D printing. Initial tests have already been carried out at Hans Geiger Spritzgießtechnik GmbH, resulting in significant advantages for the manufacturer and the customers.

Acceleration of the development and test phases
Previously, manufacture at Geiger took several days. With the help of additive manufacturing, it was possible to shorten the duration to just 6 hours: “That significant reduction in time has made it much easier to test whether an object can actually be injection-moulded as planned,” explains Hans Kolb, process engineer at Geiger. Consequently, tool manufacturers can test quickly whether a prototype is fully functional or if any improvements are necessary. “3D printing even makes a functional test, an early test run with series-like moulds, possible quite quickly,” adds Kolb. This means that not only can prototypes be tested for their functionality, it is also possible to choose a design and materials early on. With the accelerated process comes a cost minimisation of up to 70 per cent, which greatly reduces the financial risk involved in prototype manufacture and makes it possible to offer more attractive prices: “It is easy to demonstrate quickly how certain requirements can be met without any great time and money expenditure,” says Kolb. This is a significant advantage in the tendering phase, for instance.

Fast and efficient: PolyJet process with synthetic resin
There are several ways to make tools using 3D printing: a liquid starting material can be hardened layer by layer, or a powder can be selectively melted. With the PolyJet process, as used by Geiger, the workpiece is built up in layers. First, tiny droplets are sprayed onto a building platform and crosslinked via UV light. “We use synthetic resin for printing. The best results have been achieved with Digital ABS, especially for complex geometries,” explains Kolb. Following the UV curing, the support material is removed in a water bath or with a jet of water. If necessary, the printed workpiece is reworked by hand.

The components can be used directly from the 3D printer – post-curing is not necessary. This has the advantage of generating less waste than milling, cutting or casting, which keeps material costs down and makes disposal easier. The precision of the prints is about 1/10 mm. “Not every little detail can always be accurately represented; occasionally you have to reprocess a part mechanically,” explains Kolb. “But for prototypes, the focus is not primarily on exact details but on the option of testing different solution procedures.” It is also possible to print finished parts directly for viewing – in this case, Geiger uses polyamide with glass fibre reinforcement.

Suitable for thermoplastic injection moulds
In principle, 3D printing is suitable for all thermoplastic injection moulding tools, but it may be advisable to reinforce the workpieces in part with steel or aluminium. At Geiger, components can be printed up to a size of 165 ccm. The injection moulding machines, which are suitable for 3D printing processes, range between 100 and 800 kN. “Certain concessions to draft angles, radii or geometry of the parts may need to be made,” explains Kolb. “After all, these are prototypes that are produced for testing and with a focus on low-cost and fast manufacturing, not durable tools.” Depending on the material used, the prototypes last about 20 cycles. The parts are manufactured according to CAD plans submitted by the customer and converted to STL. This allows the customer to gain an idea of what his work piece looks like and how it fulfils its functional purpose within a very short time. “If a tool does not meet the manufacturer’s expectations, the manufacturer has not invested large sums of money and valuable time, but can use this knowledge to make immediate improvements to the product – and re-test it a little later thanks to 3D printing,” concludes the process engineer from Geiger. “For our customers, this means faster processes with reduced risk: a clear verdict for the new technology.”

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