Aluminum Die Cast Parts in Product Design
856 words
The choice of product design and engineering professionals for manufacturing woodworking tools and fixtures are alloys such as aluminum and zinc, two of the best non-ferrous materials for the die casting of thin wall product parts. Combinations of those alloys are used as well. When a product must be robust to the point it can withstand more functional force than needed, yet light enough to prevent fatigue and accidents when being used, aluminum or zinc die cast parts are the alternative over thin wall aluminum extrusions and the injection molding of plastic parts with a glass-filled polymer. The parts being able to withstand reasonable heat enters the equation as well.
The innovative dovetail jig shown here is a good example. The jig is intended to clamp to project boards securely held in a bench vice. It must be repositioned for each router cut, suggesting it doesn't want to be heavy and difficult to move. Yet it must be robust enough to withstand excessive clamping forces that might bow the base, which would cause unsatisfactory machining results.
Die cast parts are rarely solid in cross-section. Solid cross sections lead to unwanted weight, excessive material, and sink marks caused by non-uniform cooling of the part. The cross sections of the parts are usually designed with uniform wall thicknesses. Many ribs projected ninety degrees from the main surface walls provide more than sufficient strength. Optimizing all cross sections comes from the experience of the engineer as well as from proven and tested finite element computer programs. All die cast parts have draft on any surface that must be pulled from the confines of a cavity. The part walls look parallel but are not. A home example is a tray of ice cubes. With outside taper, the ice cubes can be dumped out. It's important to hire an engineering and design service that has proficiency in molding and casting technology.
Die cast parts, like injection molded parts, should be designed and engineered so they can be ejected from the molds with only one action, the opening of the mold. Undercuts in piece part design usually result in additional slide actions, which can be costly with the construction of the dies, especially multi-cavity dies. Higher tooling costs can be absorbed with high volume products that might run for several years or more. With low volume parts, an engineering and design service should strive to keep piece parts free of features that require slides. or what the profession calls action.
Where threads are needed, steel inserts can be inserted into the die between cycles for the aluminum to flow around and capture, or the knurled inserts can be pressed into the piece part at a later stage. Parts must be ejected from die cavities with push pins. The pins will always produce a footprint, usually under the part. They are always round and not very deep. The feed gate, or the entrance of the molten aluminum into the die cavity usually must be machined off after ejection of the part.
All plastic molded and die cast parts of all processes have flash, material that flows between tool halves, each side of the parting line. When it exceeds the specification, it must be removed. Tumbling deburring is a process used to do this. The process can also be used to enhance the surface finish of the part. If the flash is excessive, it must be machined off as a secondary operation.
Secondary operations, whether intention or not, are costly and in many cases requires the design and construction of fixtures. With modern mold making technology, die castings can have a smooth surface that otherwise might be expected from only aluminum plate or extrusions. Burning of the cavity instead of machining them produces smooth cavity walls that in turn transfers to smooth surface piece parts.
Very fine detail should always be discussed with the molder. This is something the product design service can't assume they can automatically have. The molten aluminum, even under pressure, can't always fill tight volumes with the same performance as polymers, although the fill capability is above other lower cost casting alternatives, such as sand castings.
Products not only have to be innovative, but the processes also to produce them need to be as well, especially with challenging cost goals.
Die cast parts do not accept anodizing to the degree of satisfaction aircraft aluminum does. Often, die cast parts can have an intentional rough surface, providing adequate draft is provided, that accepts paint applications. After painting, working surfaces of the tool or jig are machined flat, and left free of paint. This is a process used with large parts from sand cast moldings.
Aluminum alloys used for diecasting are usually formulated with a small amount of zinc and magnesium that adds strength and improves flow characteristics of the alloy. Naturally, engineering data is available for choosing the best formula for any product application.