Designing Permanent Mold Castings More Efficiently
Casting offers an ideal solution for efficiently manufacturing complex parts, often meeting all stability and weight requirements. The casting process generates minimal waste compared to machining and involves significantly lower tool costs than manufacturing components from carbon-fiber-reinforced plastic. Traditional trial-and-error methods or energy-intensive sample production can result in long development times, making them unsuitable, particularly when time and cost-efficiency are of the essence. This is where casting process simulation provides a competitive advantage. An experienced and skilled user can reduce both development time and number of energy-intensive prototype castings, thus enabling foundries to meet even the tightest schedules and achieve cost-effective production.
Time constraints are a common challenge in foundries. In this example, manufacturer Rosenbauer aimed to develop and produce a hybrid-powered fire engine within two years. The vehicle needed to be lightweight, while maintaining structural integrity to meet both safety and hybrid vehicle standards. A lighter fire engine increases the battery driving range and improves agility, which is particularly beneficial in urban traffic.
The development team opted for utilizing a casting process to manufacture the door frames. They rejected milling due to its excessive material waste and slow processing speed. They also ruled out carbon-fiberreinforced plastic because of prohibitive tooling and manufacturing costs.
Mettec faced the challenge of meeting tight manufacturing tolerances within a very narrow time frame. To address this and ensure cost-effectiveness, and given the limited production volume, the team decided to use a permanent mold casting process for the doors. They used a CAD model of the previous door design as the basis for the new manufacturing process.
Closing Old Doors – Adjusting Both Design and Risering
The original frame design featured an X-shaped element for stabilization, but initial simulations showed it was unsuitable for casting due to significant porosity (Fig. 1), which would jeopardize the door's structural integrity and would have increased the scrap rate during production.
Fig. 1: The initial simulation of the original door design shows porosity issues.
Mettec had the opportunity to modify the design, provided that both stability and weight of the part were still ensured and, more importantly, that they would be able to adhere to the tight schedule.
The experts proposed an S-shaped design (Fig. 2) to create more efficient feeding paths in the part, leading to reduced porosity. This design change maintained the component's structural integrity, while saving material, making the doors lighter, more cost-effectiveand still stable.
Fig. 2: The new design saved material, while still maintaining door stability.
Next, the team focused on optimizing the risering. They simulated solidification with two different configurations (Fig. 2, left: pouring position 1; right: pouring position 2). For both variants, however, the simulation results revealed porosity in the casting, risking increased scrap rates or compromised stability of the component.
To reduce porosity, the foundrymen combined both feeder designs, placing a total of 16 feeders along the frame. They increased the feeder size at the locations where most of the porosity had previously occurred, particularly where the inner S intersects with the frame. The solidification simulation with this feeder configuration showed significant improvement, though some areas in the casting still had potential porosity (Fig. 3).
Fig. 3: The feeder configurations from Fig. 2 were combined and individual feeders were increased in size. However, the experts were not completely satisfied with the result.
To completely eliminate porosity and thus meet the stability requirements, the foundrymen added an additional feeder on each of the wider struts of the S-shaped structure (Fig. 4). The simulation results confirmed that this final feeder configuration would effectively prevent porosity in the casting in the long term. With this knowledge, the experts at Mettec produced a mold using the optimized feeding system.
Fig. 4: The final feeder design ensures long-term porosity prevention.
Adjusting the New Doors – Eliminating Casting Defects, Ensuring Quality
The foundry team could already use the first series castings for sampling successfully, but they had to reject individual castings due to misrun (Fig. 5). To identify the defect, determine its root causes, and define countermeasures, Mettec simulated the entire process with the real process parameters. The mold filling simulation (Fig. 4) revealed a cold metal front forming in the middle strut area, leading the team to initially suspect a cold shut defect.
Fig. 5: Under real casting conditions, scrap occurred.
Further investigations ruled out too low mold temperatures or a too slow filling as causes of this defect. Instead, inadequate mold venting caused the rejects, with the supposed cold shut turning out to be entrapped air. To prevent the defect, Mettec integrated a wafer pattern and added additional vents to the mold (Fig. 6), resulting in defect-free series production.
Fig. 6: A wafer pattern and additional vents eliminated defects, allowing defect-free production.
Rapidly Eliminating Defects – and Preventing Them in the Long Run
Initially, the vehicle developers had feared that robustly designing or even manufacturing a casting within such a narrow time frame would be impossible. However, these concerns were unfounded: The foundrymen managed to quickly adjust the casting design, ensuring that the part remained stable, while using less material. They developed a robust casting process and eliminated unexpected defects without jeopardizing the schedule. This allowed the vehicle developers to benefit from a manufacturing process that saves both cost and time.
Eventually, the team successfully produced a lightweight cast part that now elps firefighters reach scenes more quickly. Casting process simulation was crucial for rapidly achieving a robust production process.
