Investment Casting or Lost Wax denotes the mechanical manner of obtaining a mold rather than the material used. It is the process completely investing a three dimensional pattern in all of its dimensions to produce a one-piece destructible mold into which molten metal will be poured.
The principle feature of investment casting molding is that a fluid mixture flows around the wax pattern providing excellent detail. This mixture sets with the aid of a hydraulic bond. These wax patterns are assembled on a tree and invested with a ceramic slurry. The tree is then immersed in a fluidized bed of refractory particles to form the first layer of the ceramic shell. The mold is allowed to dry and the process repeated with a coarser material until sufficient thickness has been built up to withstand the impact of hot metal. The wax is then melted out for subsequent recovery and the molds are fired prior to casting. Most materials can be molded by this process but the economics indicate that the shape and complexity of the casting should be such that savings are made by eliminating machining. Unless advantages can be taken of this feature it is unlikely that investment casting will compare favorably with other processes. Accuracy of investment castings is totally dependent on the accuracy of the die and extremely fine tolerances can be achieved with an exceptionally wide range of materials.
Advantages
Extreme accuracy and flexibility of design. Useful for casting alloys that are difficult to machine. Exceptionally fine finish. Suitable for large or small quantities.
Disadvantages
Limitation on size of casting. Casting cost make it important to take full advantage of the process to eliminate some or all machining.
Precision Molding
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Investment Casting
Typical dimensional tolerances, inches± .010, ± .020Relative cost in quantityHighestRelative cost for small numberMediumPermissible weight of castingOunces to 100 lbs.Thinnest section castable, inches1/16Relative surface finishVery GoodRelative ease of casting complex designBestRelative ease of changing design in productionFairRange of alloys that can be castUnlimitedParting Line Influence
When Parting lines are considered, very close tolerances are difficult to obtain. A parting line absorbs fractions of inches per inch. A foundry is doing well to hold a parting line to 0.015 inch. Additional measurement is added to the casting tolerance.
When mentioning lost wax casting, most people associate it to the investment casting process. In fact, the two terms are sometimes used interchangeably. However, when people start talking about lost foam casting, these metal casting processes start to sound confusing. The confusion may lie with the fact that lost foam casting is remarkably similar to investment casting. When evaluating all these processes, we can determine both similarities as well as differences between them. Here is a straightforward guide to understand each one.
Lost wax casting is a metal mold casting process that has been in use for thousands of years. This process involves creating a wax pattern of the intended part. This wax pattern becomes coated in a ceramic slurry and allowed to harden. The wax is later removed, and molten metal is poured into the ceramic shell to create the part.
Investment casting is another term for the lost wax casting method. It uses the wax patterns that are later melted or burned out of the hardened ceramic mold. The process allows for near net-shape of parts with exceptional surface finishes. Often, the metal part does not need additional machining and surface finishing details. A major advantage to investment casting is that the customers can select a wide variety of metals to use with this process. Also, investment casting tighter dimensional tolerances creates simple and complex parts in a range of sizes.
Lost foam casting processes involve making a pattern made from expanded polystyrene. The polystyrene pattern becomes coated in the refractory slurry as the shell hardens. Then the shell has sand compacted around it to provide extra stability and support. Molten metal is poured into the shell as the polystyrene becomes vaporized inside. Customers may select lost foam casting methods when looking for a process that accepts a wide variety of ferrous and non-ferrous metals while gaining simple and complex parts that may require additional machining after casting.
Both investment casting and lost foam casting processes are similar where they use patterns to make ceramic shells that will hold the molten metal to produce parts. The produced parts seldom require additional machining and both processes can be used for simple and complex parts manufacturing. Both processes can cast parts made from non-ferrous and ferrous metals.
Searching for the right manufacturing method allows you to obtain parts that are high quality, dimensionally accurate, and meet project deadlines. For more information about these processes, contact Impro.
Contact us to discuss your requirements of lost wax investment casting. Our experienced sales team can help you identify the options that best suit your needs.