Category:Diecast metal toys

The diecasting process involves injecting molten metal (usually a zinc-based alloy) into a mould made from hardened (usually tool-grade) steel. Diecasting became a significant feature of British toymaking with the introduction of Dinky Toys in the mid-1930s, cast using the recently-developed Mazac zinc alloy.

Advantages

High casting pressures allow high detail
High casting pressures allow the use of "sludgy" metal alloys

Limitations

Diecasting has certain limitations:

The use of tool-grade steel makes the dies very expensive, so the process is most suitable for the mass-production if large numbers of identical parts - if making huge numbers of a piece, the initial cost of the die becomes less important. This makes diecasting very much an "industrial" process.
There is typically a maximum size that can be cast per "shot", which limits the size of parts, and also the number of smaller parts that can be cast per "shot".
The shapes of parts need to be reasonably simple to make it easy for the cast pieces to detach from the mould
The process usually results in tiny amount of trapped air inside the final piece ("porosity"), which prevents further heat-treating processes (such as case-hardening) being applied to the parts, as this would encourage the tiny pockets of air to expand and form micro-cracks in the metal.

Some manufacturers had early problems with the disintegration of zinc alloy diecast items ("Zinc pest") caused by additional "foreign" metals ending up in the alloy before casting ... but these were solved by improved quality control.

Process characteristics

Diecasting usually involves non-ferrous metals, to limit metal migration between the melt and the tooling.

Diecasting usually involves the use of channels in the die to guide the liquid metal to the cavities for multiple parts, which then energe connected together by "sprues" or "runners" similar to those found in injection-moulded plastic model kits (eg traditional Airfix kits). In a variant called heated-manifold direct-injection die casting, the die has separate heated inlet nozzles for each chamber in the die, which reduces the amount of waste metal.

The properties make diecasting ideal for the production of smallish "chunky" toy vehicle bodies, where the castings don't have to have any particularly demanding properties, other than the ability to hold high levels of detail, to support thinnish window-frame details, to be able to hold springy steel axles, and to be able to be thudded repeatedly into furniture without cracking.

Alternatives

Lead

Prior to the appearance of diecasting, British cast metal toy vehicles were typically made from lead. Lead casting was a well-understood process but resulted in soft castings that might have trouble coping with being stood on, and had "weak" detailing – window frames and bumpers were prone to bending and breaking, wheels were prone to bucking and bending. The softness of the body metal meant that special care was needed when designing how wheels attached to springy steel axles, and how the axles attached to the body.

Ferrous metals

In the United States, some manufacturers of early metal toys in the late C19th and early C20th used cast iron as a material (eg for the bodies of toy railway locomotives).

This was again a known ("low-tech") material, but resulted in toys that were very heavy, somewhat crude and clunky, and had a tendency to break if dropped onto a hard surface, due to the brittleness of the material

White metal

For very small production runs, smaller companies might use "white metal" casting. This typically involves using very low melting-point metals and gravity-fed (or centrifugally fed mould made from special vulcanised rubber). White metal casting was typically only used by specialist "one-man" manufacturers producing low production run products such as niche metal kits.

The rubber moulds are far cheaper to make, but have very restricted lifespans: once a "cottage industry"'s products become popular it often becomes worth the company migrating their designs to diecasting (or plastic injection moulding).

Plastic injection moulding

After World War Two, the injection moulding of plastics became popular for lightweight toys where strength wasn't an issue.

Evolution

The production of small cast lead figures typically migrated from lead to plastic, as the additional strength of diecast alloys wasn't needed. Diecasting is still popular for small robust toy vehicles, and for larger vehicle models where some detailing may be plastic, but the rigid bodyshell uses diecast metal, typically painted to take a high-gloss finish.

Modern diecast toy vehicles typically also incorporate a variety of plastic parts, for windows (where transparency can't be recreated in metal), for seating and upholstery (where the soft appearance of plastic can add realism), and for fine protruding complex details. Moulded windscreen wipers flex when made from plastic where a metal casting would tend to break off at the root, and complex three-dimensional radiator grilles can often be injection-moulded in plastic and successfully extracted from the moulds due to plastic's flexibility, where an attempt to make the same shape in metal would result int the part and its mould ending up locked together.