Investment Casting to Produce Prototype Metal Components
21 Jan 11
Many designers are familiar with the investment casting process also known as the 'lost wax' casting process or when foam is used for the pattern it is known as the 'lost foam' process. The basic principle is that a wax pattern is produced that replicated the final design. Wax runners and risers are added to the pattern to enable pouring of the molten metal and expulsion of the air. The wax pattern is then encased in fireclay or dipped in a ceramic slurry (multiple times to build up some thickness). The whole thing is then fired which solidifies the fireclay and melts the wax. The melted wax is poured out and the molten metal poured in. The fireclay is then simply broken away to leave the cast product ready for finishing.
Investment casting has literally been used for centuries to produce one-off castings with the most well known examples being bronze statues. The original statue is typically modeled using wax then cast using the procedure described above. Another well known example is in jewellery manufacturing and investment casting is used to produce finely detailed designs in precious metals.
Modern investment casting has come along in leaps and bounds in terms of accuracy and features that can be molded. These days producing near-net-shape castings requiring little finishing or machining is almost a given. Many investment casting foundries are also setup with small, efficient furnaces to enable them to cast in almost any material you need. Investment casting for one-offs and short runs requires no tooling and is ideal for producing your prototype metal components.
Because investment casting uses no cores, the pattern is not pulled from a sand box not the casting pulled from a die, the designer has a large amount of freedom to design their parts. Undercuts and complex internal features are easily achieved. The only real design constraints are firstly to make sure the melted wax has a path to be poured out and that wall sections are not too thin. Design considerations also need to be given to the removal of air and additional risers may need to be attached to some area to remove the air. These are cut off and dressed after casting, but the designer simply needs to consider the aesthetics of the dressed area.
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For prototyping metal components using investment casting as the process, the real advances now are in how simple it is to produce the wax patterns. Wax printing is a technology similar to the well known 3D printing technologies used to produce plastic parts. Your components can be directly printed in wax from your 3D models, ready to be cast. Wax printed patterns have good strength also so they hold their shape accurately while being prepared in the fire clay. Using wax printing to produce you components in metal is fast and accurate.
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If wax printing is unavailable, there are other techniques that can be used. Some polymers printed using FDM or 3D printing can also be melted although not as efficiently as wax. So a pattern can also be printed using 3D printing techniques. Of course a pattern made with draft to be pulled from a sand box using conventional sand casting techniques can also be readily produced. 3D printing can also be used to produce a mould into which wax can be poured and solidified. Thus the 3D print is used to cast the wax pattern first.
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Investment casting wax also comes in different grades. There are grades that are quite stiff when solid and can be readily machined using simple techniques such as CNC routing or CNC machining. 3D hot wire carving machines as used for shaping foam can be used to CNC carve the wax. CNC routers and CNC hot wire foam carving machines can also be used to make foam patterns enabling casting of your designs using the lost foam process.
For simple shapes and designs, you can of course shape wax and/or foam using hand tools, hand modeling and hand carving techniques. Less high-tech than the other options presented, but for an item such as a bronze statue, it works very well.
Wax printing, investment casting, CNC routing, 3D printing and foam cutting are some of the many processes that can be directly sourced through ManufactureLink's online sourcing system. Submitting RFQs takes only a few minutes and it is free-of-charge to do.
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