Frequently used for automotive components such as engine blocks, transmission cases, and suspension parts, the VRC/PRC casting process with permanent molds can achieve high-quality, near-net shape castings with minimal machining required. It’s also ideal for producing complex geometries with good dimensional accuracy because of the foundry’s ability to control the filling of the mold cavity. 

This process uses a vacuum to remove trapped air and gases during pouring, which allows for thinner wall sections and eliminates the need for additional risers to compensate for shrinkage––material waste is reduced, which improves production efficiency. In addition, because VRC/PRC produces near-net shape parts with close tolerances, extensive post-casting machining is not required, which saves time and cost.

This Ford F150 Lightening Battery Electric Vehicle Semi Trailing Arm, VRC (Vacuum Riserless casting) /PRC (Pressure Riserless Casting) permanent mold 356 T6 aluminum casting was converted from a steel stamping fabrication, which saved the customer 9.7 lbs. It took the foundry more than 130 design iterations over the course of four years to achieve this safety-critical structural part with optimized design and performance at lower weight.

Optimum parting plane allowing as-cast insert placements (1)

• Parting plane determination is the very first critical decision-making step for design engineers to achieve streamlined liquid metal passages with uniform wall thickness, thereby promoting directional solidification to reduce the tendency for primary shrinkage. This in turn makes for a sounder casting with reduced residual stresses in the final casting for better dimensional stability and  tighter tolerances.  

• Optimization is an iterative design and manufacturing validation process, and casting process simulation is a very valuable tool to reduce the number of tooling and casting iterations.

Lightening pockets, cored holes and stiffeners [2}

• Myth: Making a casting solid and heavier always makes it stronger.  

• Fact: The key is in making it as light as possible with hollow sections to get the same or better stiffness, which will help make it sounder with overall reduced weight. Thinner walls in aluminum have better mechanical properties than thicker due to faster local cooling rates, which leads to finer grains and shorter dendrite arm spacings. 

• The size and location of the cored holes determine whether to make it as-cast or cast solid and drilled out.
Generous corner radii and fillets [3}

• Generous radii and corner fillets allow smooth transitions for complex structural casting shapes, which would not be possible with any other manufacturing process. Smooth transitions drastically reduce the stress-concentrating factor, allowing directional solidification and less turbulent liquid metal entry into the mold cavity. These features create cleaner castings by eliminating sharp corners. Reducing heat concentration in the corners leads to longer mold life.