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Sand, shell, investment or die casting: choosing the route for a machinery part

How quantity, alloy, tolerance grade and machining stock decide the casting process, and who owns the pattern, core box or die.

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Start from the part, not the foundry's favourite process

Most construction-machinery castings could be made more than one way. The right route depends on four things you can state before asking for prices: the alloy, the annual and lifetime quantity, the as-cast tolerance you can accept, and which surfaces will be machined afterwards. ISO 8062-3:2023 links the last two: it gives casting tolerance and machining allowance grades that vary with the manufacturing process, so the process choice and the drawing note have to agree.

On this site, the Henao profile compares water-glass and coated-sand routes, JW Casting describes investment and shell moulding, and Muyang combines casting, forging and machining. All three work from the buyer's drawing, which is why the drawing has to carry the decision.

Sand, shell and investment routes

Sand moulding has low tooling cost and suits large or low-volume steel and iron parts; the trade-off is a coarser tolerance grade and more machining stock. Coated-sand (shell) moulding gives better surface and repeatability at moderate quantities. Investment casting reproduces fine detail and thin sections and is common for smaller steel parts such as brackets and levers.

Compare how each supplier frames the order. The Henao construction casting page asks for alloy, delivered state and first-article definition; the JW0020 casting page asks for alloy, heat treatment and drawing acceptance; the Muyang bracket page separates rough and finished supply. Wear castings are a special case, because hardness and toughness matter more than appearance; see the Lingfeng profile.

Die casting and the tool that comes with it

High-pressure die casting suits aluminium and zinc housings in larger quantities. The steel die is expensive and slow to make, but each part repeats closely. The Zonzao die-development profile and its reducer-housing die case show what the buyer actually orders: a die design, trial castings and a die that must suit the receiving machine's tonnage and platen size.

Sand routes have tooling too. Patterns and core boxes from Yingda and Zhongfa are made before any metal is poured; the Yingda lift-part tooling and the Zhongfa core box are examples. Settle who owns the tooling, where it is stored and whether it can be moved to another foundry. Production equipment for die-cast or brazed parts is listed under manufacturing process equipment.

Machining stock and the finished part

A casting quote and a finished-part quote are different products. If you buy castings and machine them yourself, the as-cast drawing needs datums and machining allowance; if the foundry delivers machined parts, the finished drawing with general tolerances to ISO 2768-1 and individual limits on fits applies, as explained in our guide to tolerances and dimensional reports.

Machining can also be bought separately; Wenlin machines to drawing. Whichever route you choose, ask for the first casting to be sectioned or X-rayed where internal soundness matters, and write the result into the approval. More castings and finished parts are grouped under construction components.

Sources

  1. ISO 8062-3:2023 Tolerances and machining allowances for castings
    Casting tolerance and machining allowance grades for all cast metals and processes.
  2. ISO 2768-1:1989 General tolerances — Part 1
    General tolerances for machined features of the finished part.

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