Frequently Asked Questions
FAQ Category: Recyclability
What is the recyclability status of die cast parts?
Die casting alloys offer the designer concerned with post-consumer recyclability one of the most advantageous material options. Die castings and the die casting process provide the product engineer who is designing for the environment: (1) Components that can maintain their integrity through disassembly, repair, remanufacturing and reassembly; (2) Product recyclability, at the end of useful life, with the potential for return to high-performance applications; (3) Knowledge that a proven recycling infrastructure is in place to reclaim recycled die cast parts. Engineering Bulletin (No. 024), "Designing for Servicing & Recyclability," presents an outline of the current die casting alloy recycling infrastructure that enables designers to meet today's "design for recyclability" mandates. This bulletin is available for instant download in the Resource Center.
With the growth of plastic recycling, aren't molded plastic parts being recycled at rates comparable to die cast parts?
Widespread recycling of plastic injection moldings remains in its infancy, with handling of scrap molded plastic still uneconomic to the established recycling infrastructure. Virtually all engineered molded parts continue to be produced from virgin raw materials. Over 95% of the aluminum die castings currently produced in North America, including the most sophisticated applications, are made from post-consumer reclaimed alloy.
Can the die casting engineer make a direct conversion from a part design produced in another process to a die cast design?
While product designers often call for an exact conversion of an existing non-die cast part to a die casting for reasons of package size and mating parts, dramatic savings can often be made if the part and its mating components are reconceptualized as a single die casting. Costly assembly and post-casting operations can often be eliminated, with greater product integrity over an assembly of components. Sufficient redesign time must, of course, be allowed for such a conversion with close die caster consultation to attain the maximum cost savings.
How close are the tolerances the die casting process can achieve?
The tolerances that can be specified on a part design intended for die casting will vary with the precise configuration of the part, the alloy being cast, and whether a dimension is contained entirely in one half of the die, or falls across a parting line or is formed by a moving die component. Casting accuracy will also depend on the die casting machine being used and its control systems. As an approximation, the tolerance on a dimension between features formed in the same die part can be held to from +/-0.002 to +/-0.014 (+/-0.051 mm to +/-0.356 mm) , dependent on the additional qualifications mentioned above. For specific dimensional tolerancing guidelines, consult the 223-page NADCA Product Standards Manual, available from CWM at a special discount. The Standards Manual provides guidance on such questions as draft, radii, and flatness, among other design characteristics, and can be consulted prior to discussions with CWM engineering. E-mail email@example.com or call 630-595-4424 for more information.
What are the thinnest walls that can be specified on a die cast part?
Typical wall thicknesses for a die cast design range from 0.040 in. (1.016 mm) to 0.200 in. (5.08 mm), depending on alloy, part configuration, part size and application. In specific instances for smaller die castings, wall sections as thin as 0.020 in. (0.50 mm) can be cast, with CWM consultation. For extremely small zinc parts, micro-miniature die casting technology (commonly called Miniature Die Casting) can be used to cast still thinner walls.
Can a design that has undercuts be produced as a die casting?
For lowest-cost die cast production, undercuts should be avoided in a part design; such parts would most often require post-casting machining operations. To produce a die cast part with an undercut, as cast, requires the construction of special die members, such as retractable core slides. The increased tooling cost and reduced cycle time would be offset by savings on secondary machining costs. Consultation with CWM can often result in a feasible part redesign that eliminates the need for these core slides or the post-casting machining that would be involved.
Can external threads be die cast, without secondary operations?
In many parts, external threads can be die cast on cylindrical features. The threads can be formed across the parting line of dies, with either slides or with solid die components. When threads are formed across the parting line, or when slides are used, some flash is usually left in the threads, and this is difficult to remove. If the flash is not severe, and if conditions of assembly and use permit, the first installation of the nut can serve as a flash removal operation. It is also possible, if some thread strength can be sacrificed, to cast "flats" on the parting line at the root of the threads. The flash is formed on the flats where it is easily trimmed off.
Can internal threads be die cast, without secondary operations?
It is possible to cast internal threads in die castings by employing spin-out cores or by unscrewing the casting from the core. However, practical considerations such as the increase in cycle time and required draft (which weakens the threads) usually make it more feasible to economically tap the threads in a separate, post-casting operation.
What are the limits on complex features that can be designed in a part to be die cast?
Intricate features and the most complex shapes are common to die castings, with the basic limitation being that a part feature must not prevent removal of the casting when the die halves are parted. With the use of a variety of core slides (or pulls), special features are cast in place, with the slides retracting to permit rapid ejection. Such moving die parts may require the use of a larger machine and rule out the use of a multiple-cavity die or unit die. These considerations will raise die casting production cost, plus a more complex die will add to die investment, but the result can be a net-shape casting with substantial cost reductions. The CWM Engineering Dept. should be consulted at the preliminary part design stage.
What are the advantages and disadvantages of specifying textured surfaces cast into a die cast part?
Textures, from delicate stipples to deep grain patterns photoengraved into the die surface, can be cast into the surface of a part during die casting production, with no further texture treatment other than final painting, if required. In addition to providing a unique decorative surface, many of these textures enable parts to maintain their appearance through rough handling in use as well as providing a better grip for hand-held products. These advantages will entail added maintenance of the die surface nears the end of the die's normal life, to reinstate the textured die surface.
What are the highest temperatures that die castings can be expected to withstand?
Die cast parts can generally withstand continuous temperatures in use between 300 degrees and 400 degrees F, which make them effective substitutes for plastic parts in many applications.
Is the Geometric Dimensioning & Tolerancing System recommended for product designs intended for die cast production?
The functional dimensioning scheme, basic to GD&T, helps the designer examine and better analyze product function in the design stage and establishes part tolerances based on functional requirements. With geometric dimensioning, the designer has the best opportunity to balance optimum function and lowest part cost through his or her engineering drawings. By enabling the designer to determine the maximum allowable tolerance that will not adversely affect product function, significant manufacturing savings can result. When manufacturing produces parts to the dimensions and tolerances on a GD&T print, there is the highest degree of confidence that the parts will function as intended. GD&T is the preferred dimensioning system for die cast part drawings as well as for any of today's precision manufacturing processes. A special chapter outlines the GD&T scheme as it applies to die cast part prints in the NADCA Product Standards Manual which is available from CWM. E-mail firstname.lastname@example.org or call 630-595-4424 for more information.