Permanent Mold Aluminum Casting: Process Fit and Standards

# Permanent Mold Aluminum Casting: Process Fit and Standards

Permanent-mold casting, gravity die casting and gravity casting commonly describe a route in which molten aluminium fills a reusable metal mold without the high-pressure injection used in HPDC. It can suit repeat production that needs a heat-treatable alloy, machined features and project-defined quality evidence, but the drawing must drive the decision.

What the process does

The supplier prepares and conditions the metal mold, places any approved cores or inserts, fills the cavity, controls feeding and solidification, removes and trims the part, and completes the agreed heat treatment, machining, finishing and inspection.

A metal mold generally extracts heat faster than a sand mold, which can refine the local solidification structure. The result still depends on section thickness, gating, feeding, mold temperature, local cooling and alloy preparation. Permanent-mold casting does not guarantee zero porosity, a fixed surface finish or a universal tolerance.

When to compare it with another route

Evaluate permanent mold when the program needs:

• •reusable tooling for repeat orders;
• •an alloy and temper compatible with the required properties;
• •machining of datums, bores, threads or sealing faces;
• •pressure-tightness or internal-integrity controls defined by the buyer;
• •traceability and approval records tied to production lots.

Sand casting may be more practical for very low volume, large geometry or frequent design changes. HPDC may be more practical for thin-wall, very high-volume parts when its alloy, porosity and heat-treatment constraints fit the function. LPDC may be evaluated when controlled bottom filling and feeding suit the geometry. Do not select a process from an annual-volume threshold alone.

Standards: keep the scopes separate

• •ASTM B108/B108M is a material specification for aluminium-alloy permanent-mold castings. It is not a generic dimensional-tolerance table for every design.
• •ASTM B557/B557M defines tensile test methods. Mechanical-property requirements come from the controlling material specification and drawing.
• •ASTM E505 contains reference radiographs for aluminium and magnesium die castings. Do not assign its levels to a gravity casting without a documented scope review and buyer-manufacturer agreement.
• •IATF 16949 is a quality-management-system standard. It does not define the strength of an A356 casting.

Where radiographic inspection is required, the drawing or inspection plan should identify an applicable reference, material and thickness range, image method, areas to inspect, sampling frequency and acceptance severity.

Pressure-tight and machined parts

For housings, manifolds and valve or pump components, mark the pressure boundary and every surface opened by machining. Define test medium, pressure, hold time, allowable leakage, test stage and sampling or 100% requirement. Also define whether impregnation or weld repair is allowed.

Machining can reveal subsurface discontinuities that were not visible in the as-cast surface. The DFM review should therefore connect casting stock, datum scheme, feeding, inspection zones and final leak-test stage.

RFQ checklist

Send:

• •revision-controlled 2D drawing and 3D model;
• •alloy, temper and controlling specification with edition;
• •prototype and annual quantities;
• •machined datums, bores, threads and sealing faces;
• •heat-treatment and finishing scope;
• •dimensional, mechanical, NDT and pressure-test acceptance criteria;
• •traceability, PPAP or other approval requirements;
• •destination, Incoterm and target first-article timing.

Request a drawing-based permanent-mold review.

*The purchased standards, customer drawing and approved control plan govern acceptance. This guide does not replace them.*