Casting shape design directly affects the forming quality, process feasibility, and subsequent processing costs of castings. A reasonable structural design can effectively reduce defects such as porosity, shrinkage, cracks, and deformation, improving yield. The following are key considerations for casting shape design, systematically summarized by design dimension:
External Shape Design: Simplify the Shape for Easier Demolding
Strive for simplified external shape. Avoid unnecessary curved surfaces, concave areas, and complex contours. Reduce the use of parting surfaces and cores to lower the difficulty of molding.
Reduce the number of parting surfaces. Fewer parting surfaces result in higher mold assembly accuracy and reduce defects such as misalignment and flash.
Set structural draft angles (mold draft angles). Non-machined surfaces perpendicular to the parting surface should be designed with appropriate draft angles to facilitate mold removal and prevent sand mold damage.
Avoid large and thin horizontal surfaces. Large horizontal planes are easily baked by high-temperature molten metal for extended periods during pouring, leading to defects such as sand inclusions and porosity. It is recommended to design them as inclined or corrugated surfaces.
Set casting fillets. All corners should be rounded to avoid stress concentration, improve metal fluidity, and prevent hot cracking.
Casting Fillets: All corners should be rounded to avoid stress concentration, improve metal fluidity, and prevent hot cracking.
Wall Thickness Design: Uniform Transition to Prevent Defects
The wall thickness should be as uniform as possible. Uneven wall thickness leads to inconsistent cooling, causing shrinkage cavities, porosity, and internal stress, resulting in deformation or cracks.
Smooth Transitions at Thickness Changes: Use gradual transitions at thickness junctions to avoid abrupt changes and reduce hot spots.
Inner Wall Thickness Should Be Slightly Smaller Than Outer Wall Thickness: The inner wall cools more slowly; excessive thickness can easily cause shrinkage cracks at the joint. Generally, the thickness should be 0.6 to 0.7 times the outer wall thickness.
Avoid Excessive Thinness or Thickness: Excessive thinness can lead to incomplete filling and cold shuts; excessive thickness can cause shrinkage porosity and coarse grains. The specific minimum wall thickness needs to be determined based on the alloy type and casting dimensions.
