In the Product Design & Development Brainstorm we talk with industry leaders to get their perspective on issues critical to the design engineering marketplace. In this issue, we ask:
Casting 101: What do you do? Why should I use it? What should I look for when choosing a casting service? What new materials and alloys are available to design engineers?
Val Zanchuk, President, Graphicast
Graphicast casts parts made from ZA12 — a zinc aluminum alloy — in graphite permanent molds. Our services include casting design assistance, mold making, casting, CNC machining and CMM-based inspection.
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Design engineers should consider Graphicast for several reasons: If you need quick turnaround, we can usually turn a CAD design into a production part in six weeks. If you need to produce tight tolerance parts, our in-house CNC machining centers and CMM-based inspection systems produce machined castings for stringent requirements, such as medical diagnostic equipment. If your production demands are from 100 to 10,000 parts per year, our process can be the most economical way of manufacturing your parts.
When looking for a casting service, you should ensure that your supplier can help you with designing your part for casting from the start of your design effort. This lowers the cost of the part by capturing as many features as possible in the cast part, reducing secondary machining.
The supplier should also be able to provide several types of prototypes to help in design evaluation. Additionally, the supplier should be able to provide as complete a part as possible, including machining, finishing and assembly to reduce lead times and costs.
For many designers, we’ve found that ZA12 is a new material to them. Once they recognize the excellent physical properties of the alloy and the lower costs of graphite permanent mold castings, they apply this knowledge to many cost saving projects and new designs.
Ron Jr (Reg) Gustafson, Project Manager, Clinkenbeard
Clinkenbeard specializes in time-critical delivery for turnkey machined prototype and small lot metal castings. Typical quantities fall between 1 to 100 pieces; typical lead times are one to four weeks.
Our patented, pattern-less Clinkenbeard Process is of particular interest to engineers who require a small quantity of castings and castings which are likely to experience design changes.
This process lets us machine sand cores and molds without the time and expense of tooling, which can reduce lead time for castings up to 90 percent. If you’re close to production launch and discover an issue, modification of production sand cores and sand molds allows engineering changes to be implemented into castings using molds and cores made using qualified production foundry tooling.
Our employees are part of a corporate culture that is based on a healthy sense of urgency. After all, our company slogan is 'Fasterestest'.
The Clinkenbeard Toolingless Process is industry renown for producing metal castings efficiently, affordably and extremely fast. Development hardware which is likely to experience design changes, testing multiple design iterations in parallel and spares are all perfect applications.
Our process emulates the production sand casting in every way. We tailor the following process parameters to emulate the foundry process: foundry sand type and grain size, foundry binder type and percentage level and custom mixing sand and chemicals. In house 5-axis machining, CMM inspection, and pressure testing is the icing on the cake.
Because our customers typically want to emulate production processes and materials with their prototype castings, we are not exposed to engineers looking for new alloys.
John Gode, Sales & Marketing Manager, Prototype Casting
Prototype Casting has been in business for over 15 years, working with aluminum, magnesium and zinc. We specialize in rapid casting, getting castings for testing form, fit and function in as little as three to seven days — depending on geometry and complexity.
This helps design engineers get a new product to market faster, with less development expenses. We employ rubber plaster molding (RPM), investment casting and precision sand casting.
We have recently added a ProJet CP3000 wax pattern production system [3D Systems] with a print envelope of approximately 11” x 7” x 7”. After a pattern is printed, it is connected to a tree and covered with slurry. The slurry-covered mold and tree are placed into a furnace to burn out the wax pattern and molten metal is poured into the void created. This investment casting process allows us to ship a small number of castings in as little as three days, depending on geometry and complexity.
Casting tolerances vary depending on part geometry and metal being used, the minimum casting wall thickness for stainless steel is .125”, aluminum is approximately .040” and the minimum wall thickness for magnesium is .080”.
The expansion of our precision or “No Bake” sand casting process allows us the ability to create high tolerance master patterns and sand molds for larger castings, up to 20 pounds, in stainless steel and mild steel. First article castings can ship in five to seven days, depending on the amount of post cast machining required.
The minimum casting wall thickness for stainless steel is .250”, aluminum is .150” and magnesium is approximately .200”, depending on part geometry. We also offer finishing options, such as dye pen, chemfilm, inspection reports, liquid paint and powder coating.
Howard Mullin, Vice President , Control Plastics
Control Plastics supplies products from the component level through packaged goods. Casting, of all sorts, is part of the service we offer, including sand cast, gravity cast, investment cast and die cast among others.
Sand cast uses most metals. It is slower, but has the least tooling costs, lowest precision and mediocre finish. Automated sand cast includes higher tooling costs, much higher production capacity, better precision and surface finish and better strengths, though it is limited to grey and ductile iron. Gravity cast has lower tooling costs than die casting, but the tooling life similar to die casting with lower internal stresses on the parts. Gravity cast typically uses aluminum alloy 356.
Investment casting (IC) uses a wide variety of metals and allows for larger build sizes than metal injection molding (MIM). IC holds better tolerance than MIM with lower tool costs, but the part costs are similar. Die casting is the most expensive tooling, but offers the best part costs. The tool life is more limited than injection molding (plastics), and there may be issues with uniformity. Choose a process determined by quantity; materials for the final parts; and tooling versus part cost.
Choose a vendor based on service, attitude, delivery and price, typically in that sequence. Will your vendor help tweak the design for process and materials, secondary operations, tooling requirements and end-of-life issues?
Vendors should have a can/will do attitude and go above and beyond to warn of pitfalls, help with specifications and work to get into production as fast as possible. Though, there are no free lunches and if the deal is too good to be true, it likely isn’t. We have seen a lot of quotes that didn’t cover material costs for the molds or parts and we can’t (won’t) compete with those.