Permanent Mold Casting

Permanent mold casting forms repeatable metal parts by gravity- or low-pressure-filling reusable metal molds, delivering good surface finish and moderate tolerances at medium volumes.

Overview

Permanent mold casting pours molten metal into a reusable steel or iron mold (often with cores) to produce near-net-shape parts. Compared to expendable molds, the rigid tooling holds dimensions better, improves surface finish, and supports higher repeatability across runs.

Choose it for aluminum or magnesium parts in medium volumes where you want casting geometry without the cost or complexity of high-pressure die casting. It fits housings, covers, brackets, and structural shapes with consistent wall thickness and sensible draft.

Tradeoffs: you pay upfront for permanent tooling and process development, and design freedom is more limited than sand or investment casting (parting lines, draft, coring constraints). Section thickness must be controlled to avoid shrinkage and hot spots; very large parts and extreme thin walls are challenging. Critical features often still need machining, so plan datum surfaces and stock allowance.

Common Materials

  • Aluminum A356
  • Aluminum 319
  • Magnesium AZ91
  • Zinc Zamak 3
  • Brass C86300

Tolerances

±0.005" to ±0.015"

Applications

  • Automotive transmission housings
  • Pump and valve bodies
  • Electric motor end bells
  • Gearbox covers
  • Compressor housings
  • Industrial brackets and mounts

When to Choose Permanent Mold Casting

Permanent mold casting fits medium-volume production when you need repeatable dimensions and better surface finish than expendable-mold casting. It works best for non-ferrous parts with controlled wall thickness, simple-to-moderate complexity, and clear parting/draft. Plan for secondary machining on sealing faces, bores, and precision datums.

vs Sand Casting

Choose permanent mold casting when you need better repeatability, tighter as-cast tolerances, and cleaner surfaces across a production run. It’s a good fit when the part size and geometry can justify permanent tooling and you expect enough volume to amortize it.

vs Die Casting

Choose permanent mold casting when you want lower tooling cost and less process risk than high-pressure dies, and when moderate wall thickness and lower porosity risk matter. It’s often preferred for structural aluminum shapes that don’t need ultra-thin walls or very high annual volumes.

vs Investment Casting

Choose permanent mold casting when the geometry is not highly intricate and you can accept a parting line and draft in exchange for lower piece price at medium volumes. It’s also a strong option for larger non-ferrous parts where investment casting cost rises quickly.

vs Centrifugal Casting

Choose permanent mold casting for non-axisymmetric parts or features that require coring, bosses, and complex external geometry. It’s better suited to housings and brackets than ring/tube shapes where centrifugal casting excels.

vs Shell Mold Casting

Choose permanent mold casting when you want a reusable tool and higher repeatability over many cycles, and when the part can be designed around metal-mold constraints. It can reduce variability and finishing time compared to thin-shell expendable molds.

Design Considerations

  • Use consistent wall thickness and generous radii to reduce hot spots and shrink porosity
  • Add draft on external and internal walls (typically 1–3°) to support release and tool life
  • Place parting lines on non-cosmetic, non-critical surfaces and keep sealing faces off the parting line when possible
  • Design cores to be simple, robust, and well-supported; avoid long, thin, floating cores without clear prints
  • Specify machining stock and clearly define datums for post-cast operations on bores, gasket faces, and bearing seats
  • Call out cosmetic expectations (as-cast finish, allowable flash/parting witness) so the shop can quote realistic finishing steps