Interview with Grunewald Additive Production in an Aluminum Foundry

| Editor: Alexander Stark

More and more foundries are dealing with additive manufacturing, especially in prototype construction. The Grunewald Foundry in Bocholt is also looking into the new technology. In an interview, Sales Manager Dr. Joachim Gundlach tells us why Grunewald uses the sand printing process, what the process looks like, and what advantages and disadvantages are associated with it.

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The picture shows a printing plant in Grunewald's foundry unpacking moulds.
The picture shows a printing plant in Grunewald's foundry unpacking moulds.
(Source: Grunewald GmbH & Co. KG)

Grunewald has been manufacturing aluminum castings for more than 40 years. Now you are installing a new 3D sand printing system. Why did you choose this method and what are its advantages and disadvantages?

Dr. Joachim Gundlach: As one of the first companies, Grunewald started using sand sintering technology at the end of the 90s. In the beginning we had difficulties with the quality of castings from laser-sintered molds. The high binder content in the molding sand system led, for example, to outgassing and thus to casting defects. Also, the machine technology of sand sintering was not yet fully developed. This is different with sand printing. Since this method allows the use of near-production molding sand systems right from the start, fewer quality problems arise. Nowadays the quality of sand printed parts is almost similar to conventionally produced molds and cores. Essentially, the use of printed molds and cores has two advantages: Time savings due to the elimination of model construction and model making and an extended design freedom of the casting geometries and the casting system. Sand casting can also give rise to new ideas and provide impetus for adjustments in series casting. This is also possible with regard to other casting processes, since die casting or gravity die-casting geometries can also be produced using sand casting. Speed, flexibility and quality are ultimately the main arguments that contributed to the decision.

Dr. Joachim Gundlach is Head of Sales at Grunewald GmbH & Co. KG.
Dr. Joachim Gundlach is Head of Sales at Grunewald GmbH & Co. KG.
(Source: Grunewald GmbH & Co. KG)

When does additive manufacturing start to pay off?

Dr. Joachim Gundlach: For complex cast parts or even cast parts in multiple cavities, for certain quantities, when things have to go fast and, for example, also for core-containing cast parts, when model-making and 3D printing of cores can be combined. And of course, with not yet fully developed geometries, which cannot be formed conventionally. If we compare sand printing with the process of conventional mold design, in my experience a few years ago the break even for more complex components was about 10 parts. Depending on the size and complexity of a geometry, it is now possible to multiply this amount. However, this must be considered individually in each case.

What does the low-pressure sand-casting process look like in additive mold production?

Dr. Joachim Gundlach: Usually the process starts with a 3D CAD model as well as the design of the print form and the cores. The most important thing in mold design is that by designing the mold and casting system appropriately, time can be saved during printing and subsequent processes in the foundry. This influences the entire production process. At this point, however, a great deal of know-how and creativity is required in order not to remain stuck in conventional construction approaches. In the second step, the CAD data is transferred and the installation space in the print system is used intelligently. After the printing process, the box is emptied. At this point, the printed sand is hardened so that the loose sand can be extracted. Depending on the binder system and plant technology, the further curing process takes place, for example, in a further furnace process. . Then the molds and cores are ready and fed into the casting process. All further steps (casting, emptying, cleaning, blasting, heat treatment, straightening, NC machining, etc.) are then identical with conventional processes.

What are the mechanical properties of such a product?

Dr. Joachim Gundlach: In general, we orient ourselves on the wishes of the customer and the specific requirements. In this example, we processed and heat-treated an aluminum-silicon-magnesium alloy for a thin-walled crash- and strength-relevant part. At an elongation of > 10 %, the tensile strength is > 180 MPa and the yield strength is 0.2 Rp is > 120 MPa. At an elongation of > 7 %, the tensile strength is > 230 MPa and the yield strength is > 180 MPa. That means: The higher the elongation, the lower the strength and vice versa. These are general and exemplary values. Higher values can also be achieved locally through casting technology and cooling.

Can you give a cost example?

Dr. Joachim Gundlach: Forms and cores were printed using the example of a typical shock tower. We were able to determine that the use of additive manufacturing is worthwhile if a maximum of 25 castings are required. With milled model halves and printed cores, the use of additive manufacturing was profitable for up to 32 castings. From a quantity of 33 castings, model halves and core boxes were to be milled and everything formed conventionally. This means that additive production methods of sand printing can pay off in the production of small quantities, but conventional methods are even more economical for larger quantities - in our case 33.

What degree of quality do 3D-printed parts achieve? How much post-processing is necessary compared to conventionally cast parts?

Dr. Joachim Gundlach: We examined the quality in both procedures as part of a master's thesis and concluded that the quality is indeed almost identical. According to the results, the geometric tolerances and the component properties are almost identical. In the subsequent processes, reworking, such as cleaning and deburring, can even be significantly reduced by an innovative design.

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