3D Printing with Sand Rapid casting for shorter delivery times of prototypes

By printing prototypes in 3D with sand, a foundry reduces delivery times from about two months to around ten working days - by a process called rapid casting.

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The most time-consuming process in an iron foundry is modelling. This is because the path from data processing and milling of the outer models and the core forming geometries to the assembly of the core boxes is time consuming and often lead to time-critical bottlenecks. To avoid this problem, many customers used to weld their prototypes from sheet metal or even manually carve them from solid material, which led to the loss of free forms and up to 80% material loss. But until now, these were the only options available. Despite late orders from end customers or delays in the design process, these clients still required the real components on time for the next trade fair or the announced start of series production or the start of a field test. It was an unsatisfactory solution. In order to quickly obtain prototypes made of series material and manufactured in the process used in series production, the time required for modelling had to be reduced.

Compared to the actual costs for raw casting series, the additive production of moulds and cores is considerably more expensive. However, prototypes or small series can be delivered within ten working days, if complex quality tests are skipped, which benefits this process as the Man foundry in Augsburg actually does. It now produces many spare parts for the shipping industry in printed moulds. At the first glance, paying € 20,000 to 30,000 for these moulds seem to be absurd. But when a ship is waiting for a spare part while at port, the cost can very quickly rise to € 50,000 per day.

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How rapid casting works

The iron foundry Brechmann-Guss also uses this advantage for developing projects of its customers. The time saved in shorter product development or thanks to the penalty-free handling of a development project very quickly compensates for the higher costs of the process. In order to keep costs and deadlines under control, the East Westphalian iron foundry pursues two strategies:

• Rapid casting: the fastest possible casting based on 3D data supplied without consideration of drafts and undercuts;

• 4S prototyping: series-identical prototypes in terms of material and geometry under series production conditions and, if necessary, in test series status.

The ideal conception is that Brechmann-Guss produces the outer geometry of the castings conventionally by means of a milled outer model, but the core-formed inner geometries consist of 3D-printed sand cores. For the background, of which the construction of the core boxes in conventional production takes the longest, and, while, subsequent modification requests by customers mostly concern the internal geometries, changes to the geometry can be quickly implemented. As a result, the foundry could produce prototypes within ten working days.

Finally, Brechmann-Guss supplies series-produced prototypes suitable for series production using the "series process of machine mould casting". If the component then goes into series production, pilot series requirements – or a small series for field trials – can still be produced with 3D-printed cores, while series core boxes are produced simultaneously. The hurry that occurred during new part start-ups is a thing of the past. There are only two aspects to consider:

• machining the 3D data provided by the customer (fillets, draft angles, graduation planes, feed and so on) ready for series production takes just as much time as

• complex measurements and tests required by the customer after the casting is finished

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Not everything has to be measured

Under the first aspect, rapid casting is suitable for the fastest possible production of a few prototypes. From the practical point of view, the second aspect raises the question of whether complete 3D measurement is really necessary for a field test before the delivery of prototypes. Ultimately, it is sufficient to measure five main masses as long as the entire manufacturing process is focused on the 3D data set. Because if the model built according to the 3D dataset is accurate, either all values are correct or all values are wrong. The measurement of 80 instead of five masses provides little or no further information in this context.

Various projects, which have already been carried out, have delivered further advantages: All of a sudden, parts that couldn’t be cast at all became castable. In conventional processes, complex core packages consisting of several individual cores are often bonded; the tolerance chain becomes longer with each additional bonded core and the scrap that accrues in the foundry increases to the same extent. The Brechmann foundry therefore considers the use of printed cores for complex internal geometries as a real alternative.

This article first appeared on www.maschinenmarkt.ch.

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