DIE CASTING DESIGN
There are many sources for information on die casting design. These include text books, technical papers, literature, magazines, seminars and courses conducted by engineering societies, trade associations and industry. Often, the die caster selected to produce a component part is an excellent source for information.
To gain maximum advantage of the die casting process, it is always a good idea to draw upon the wide ranging experience of a custom die caster. New designs should be reviewed during the early stage of development. Significant savings may be realized during this interchange of ideas.
GUIDES FOR DESIGN
Advice on designing die castings is usually based upon desirable practices or situations to avoid. However, like most rules, there are exceptions. These affect either costs, appearance and/or quality of final products. Listed below are guides which should be considered when designing for die casting:
- Specify thin sections which can easily be die cast and still provide adequate strength and stiffness. Use ribs wherever possible to attain maximum strength, minimum weight.
- Keep sections as uniform as possible. Where sections must be varied, make transitions gradual to avoid stress concentration.
- Keep shapes simple and avoid nonessential projections.
- A slight crown is more desirable than a large flat surface, especially on plated or highly finished parts.
- Specify coring for holes or recesses where savings in metal and overall costs outweigh tooling costs.
- Design cores for easy withdrawal to avoid complicated die construction and operation.
- Avoid small cores. They can be easily bent or broken necessitating frequent replacement. Drilling or piercing small holes in die castings is often cheaper than the cost of maintaining small cores.
- Avoid use of undercuts which increase die or operating costs unless savings in metal or other advantages fully warrant these extra costs.
- Provide sufficient draft on side walls and cores to permit easy removal of the die casting from the die without distortion.
- Provide fillets at all inside corners and avoid sharp outside corners. Deviation from this practice may be warranted by special considerations
- Die casting design must provide for location of ejector pins. Take into consideration the effect of resultant ejector marks on appearance and function. The location of ejector pins is largely determined by the location and magnitude of metal shrinkage on die parts as metal cools in the die.
- Specify die cast threads over cut threads when a net savings will result.
- Die castings which affect the appearance of a finished product may be designed for aesthetics, and to harmonize with mating parts.
- Inserts should be designed to be held firmly in place with proper anchorage provided to retain them in the die casting.
- Design parts to minimize flash removal costs.
- Never specify dimensional tolerances closer than essential. This increases costs.
- Design die castings to minimize machining.
- Where machining is specified, allow sufficient metal for required cuts.
- Consider contact areas for surfaces which are to be polished or buffed. Avoid deep recesses and sharp edges.
Dies can be produced for simple and complex parts. Parts having external undercuts or projections on side walls often require slides which increase costs. In many cases, however, resultant savings of metal or other advantages such as uniform wall sections, offset the extra cost or effect a net economy in overall costs. This is especially true when large quantities are involved.