Permanent Mold Casting

Permanent mold casting uses reusable metal molds to produce nonferrous castings with good surface finish, repeatability, and moderate tooling cost at medium to high volumes.

Overview

Permanent mold casting pours molten metal into reusable steel or iron molds under gravity (or low pressure) to create repeatable, near-net-shape parts. It targets nonferrous alloys like aluminum, magnesium, and brass, delivering better surface finish and tighter tolerances than sand casting with shorter cycle times once tooling is built.

Use permanent mold casting for medium to high annual volumes where you can justify dedicated tooling but don’t need the extreme production rates and pressures of high-pressure die casting. Expect good dimensional control, consistent mechanical properties, and decent thin-wall capability, but plan for moderate draft, uniform wall thickness, and machining of critical features. Tooling lead time and cost are higher than sand casting, and very complex internal passages or extreme undercuts may require sand or soluble cores, adding cost and complexity.

Common Materials

  • Aluminum 356
  • Aluminum 319
  • Aluminum 380
  • Magnesium AZ91
  • Zinc ZA-12
  • Brass C85700

Tolerances

±0.005" to ±0.010"

Applications

  • Automotive brackets and housings
  • Engine pistons and cylinder components
  • Hydraulic and pneumatic valve bodies
  • Pump and compressor housings
  • Marine hardware and fittings
  • Small wheels and pulleys

When to Choose Permanent Mold Casting

Choose permanent mold casting for nonferrous parts with moderate complexity, stable designs, and medium to high production volumes where you can amortize tooling cost. It fits parts needing better surface finish and repeatability than sand casting, without the very high tooling cost and pressures of die casting. It works well for relatively simple cores, moderate wall thickness, and features you’re willing to finish by machining.

vs Sand Casting

Pick permanent mold casting when you need tighter tolerances, better surface finish, and more consistent properties than sand can deliver at recurring medium to high volumes. Tooling costs more and design freedom is a bit lower, but cycle times and part-to-part repeatability are significantly better for stable, repeat-production parts.

vs Die Casting

Choose permanent mold casting when volumes are not high enough to justify expensive die-casting tooling or when you want lower porosity and better structural integrity. Permanent mold uses gravity or low pressure, so it suits thicker sections and structural parts where mechanical properties matter more than ultra-high production rates.

vs Investment Casting

Use permanent mold casting when you can accept simpler geometry and slightly looser tolerances in exchange for lower per-part cost at moderate to high volumes. Investment casting wins on intricate features and very thin walls, but permanent mold is more economical and faster for repeatable, moderately complex nonferrous parts.

vs Centrifugal Casting

Select permanent mold casting for prismatic or irregular shapes that are not dominated by a rotational axis. Centrifugal casting excels at cylindrical, hollow parts; permanent mold is better for housings, brackets, and complex external profiles where gravity fill and reusable tooling provide adequate quality and throughput.

vs Shell Mold Casting

Choose permanent mold casting when you want better productivity and part-to-part consistency once tooling is built, and you can tolerate less design flexibility. Shell molding can handle more intricate geometries with lower tooling commitment, but permanent mold offers longer tool life, faster cycles, and lower part cost at sustained volumes.

Design Considerations

  • Aim for uniform wall thickness where possible; transition between sections with generous radii to reduce thermal stress and shrinkage defects
  • Provide adequate draft on all pull directions, typically 2–3° on external surfaces and 3–5° on internal surfaces, to ease ejection and extend mold life
  • Avoid heavy isolated sections; if unavoidable, work with the foundry to add chills, feeders, or design changes to control solidification and porosity
  • Specify realistic tolerances and flatness, and allow machining stock on sealing, bearing, and datum surfaces that must be tightly controlled
  • Place the parting line to simplify tooling, minimize sliding cores, and keep critical surfaces away from gate and overflow regions
  • Communicate expected annual volume, alloy, heat treatment, and critical-to-function features in the RFQ so the foundry can design appropriate gating and cooling for your part