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 at least two months to around ten working days. This process is called Rapid Casting.
The most time-consuming process in an iron foundry is modeling. 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 leads to time-critical bottlenecks. To avoid this problem, many customers used to weld their prototypes from sheet metal or even manually carve them from the solid material. This leads to the loss of freeforms and up to 80 % of the material. Until now, these were the only options available for all those who, despite late orders from end customers or delays in the design process, still required the real components on time for the next trade fair, the announced start of series production or the start of a field test. But that’s not a satisfying solution. In order to quickly obtain prototypes made of the series-material and manufactured in the process used in series production, the time required for modeling must be reduced.
Compared to the actual costs for series-raw casting, the additive production of molds and cores is considerably more expensive. However, prototypes or small series can be delivered within ten working days, if complex quality tests are skipped. One beneficiary of this process is the MAN foundry in Augsburg, which now produces many spare parts for the shipping industry in printed molds. At first glance, the costs of 20,000 to 30,000 Euros for the molds seem to be absurd. But when a ship is waiting for spare part in port, the costs quickly climb to 50,000 Euros per day.
How Rapid Casting Works
The iron foundry Brechmann-Guss also uses this advantage for development 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 the 3D data supplied without consideration of drafts and undercuts;
- 4S prototyping: series-identical prototypes in series material, under series production conditions, in series geometry, and, if necessary, in series test 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. Against the background that in conventional production the construction of the core boxes takes the longest and, on the other hand, subsequent modification requests of customers mostly concern the internal geometries, changes to the geometry can be quickly implemented. In this way, the foundry can produce prototypes within ten working days.
Finally, Brechmann-Guss supplies series-produced prototypes suitable for series production using the "series process of machine mold 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 in parallel. 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 costs just as much time as
- complex measurements and tests required by the customer after the casting is finished.
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, for example, a 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 dataset. 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 that 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 was first published by Schweizer MaschinenMarkt
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