Addditively manufactured casted spare parts
The application of Benninger Guss AG demonstrates how a digital process chain can be com-bined with binder jetting and sand casting to produce spare parts in a fast and cost-efficient manner for complex and large geometries.
Long-lasting components have the requirement to operate over a long period without failure. In the event of damage, the manufacturer usually guarantees the supply of spare parts – in some cases for decades. Fast production of spare parts is essential to continue operations as quickly as possible. Particularly for larger components with complex geometries, it is important to supply spare parts quickly and cost-efficiently. With older cast components, there is often no longer a model (tool) available and drawings are no longer valid or not available anymore. Nevertheless, the spare part should meet today’s quality requirements.
Production of spare parts for turbochargers
Such a scenario applies, for example, to turbochargers of marine diesel engines. For this application, Benninger Guss AG was commissioned to produce spare parts for turbochargers. In this particular case, the original component was produced in the early 1980s using a conventional sand casting process with a model. The dimensions of the component are 1200 X 800 X 640 mm with a mass of approximately 200 kg. For the part, the customer provided a reference part as well as 3D data created from the original drawings. On this basis, Benninger Guss AG was commissioned to produce a completely machined, ready-to-install spare part. In order to solve this problem quickly and cost-effectively, Benninger Guss AG applied the following process.
The existing drawings and the 3D model from the customer served as a starting point for the reconstruction of the part geometry. Using a contactless and portable 3D scanner, Benninger Guss AG captured the geometry of the reference part without having to destroy the component. For reverse engineering, the 3D model generated from the scan data and the 3D model provided by the customer were superimposed and compared to each other. The deviations and inaccuracies displayed with a color map were compared and corrected in several steps. The 3D model resulting from this process was released by the customer for production.
Based on the reconstructed part geometry, the casting technician created the mold filling and feeding system. The challenge was to produce a flawless casted part right the first time. For this purpose, mold filling and solidification simulations were carried out to analyze the casting process for the complex geometry. The obtained results led to the final design of the casting system. Based on the part geometry and the final casting system, the individual molded parts were then designed. In this case, four partial molds were necessary, a base plate, an intermediate piece, a lid and a core.
An ExOne S-Max printer with a maximum build volume (job box) of 1,800 X 1,000 X 700 mm was used for the production of the individual partial molds employing binder jetting of silica sand. In this additive manufacturing process, a binding agent is applied to selected areas of the silica sand through a print head. After the printing process, the individual molded parts were removed from the build volume and the molded parts had to be separated from loose powder material.
The cleaned molded parts were then joined together and assembled to form a complete mold. The subsequent production steps are the same as those of the conventional sand casting process. Melt was poured into the prepared molds. A special temperature-re-sistant alloy is used for turbocharger parts. For the final treatment, the raw castings were blasted, plastered, primed and mechanically processed. The ready-to-install spare part could then be delivered together with the test certificates.
Advantages of the additive process - time savings and lower costs
The described process offers many advantages in the production of spare parts. The use of the binder jetting process makes it possible to fabricate components with complex geometries quickly and cost-effectively. In the above example, the lead time was reduced by 26 working days to 70 working days compared to the conventional procedure. This time saving is particularly important when it comes to the supply of spare parts. In this particular case, a cargo ship could be put back into service much earlier.
Assuming that a model (tool) is no longer available for the production of a complex component, the described additive process offers considerable cost advantages compared to the conventional manufacturing process. In the present case, the savings amount to CHF 54,000.00 compared to the conventional method (total CHF 80,000.00, of which the model costs CHF 67,500.00). The break-even point, i.e. the quantity at which the conventional process becomes cheaper, would in this case occur with approxi-mately 16 spare parts!