INVESTMENT CASTING PROCESS
An expendable wax pattern is first produced for each casting from a pattern die. Pattern dies are manufactured Castco's in-house tool room equipped with CAD/CAM and CNC machining capability. Selection of materials for pattern dies and die manufacturing techniques are dictated by the casting part design requirements and the quantity required. Pattern die materials range from epoxy resin to multi cavity, automatically operating machined metal dies. Machining of metal pattern dies is most feasible when a repeated production is required with complex shapes. An investment casting pattern die shown is for an impellor casting such as shown on photo.
A number of wax patterns, depending on size and complexity, are attached to a wax frame or sprue to form a wax cluster, or assembly. This process also incorporates in-gate and feeding requirement of the part.
At this step of the operation assemblies are immersed or “invested” into ceramic slurry. The properties of slurry are controlled to an extent to give a uniform coverage of wax assembly. Whilst this coat is still wet, a rather coarse refractory material coat is applied onto it. The coated assembly is then let to dry. After drying of the assembly number of successive coats of slurry and studco (5 to 8 times) is applied.
The removal of expendable wax, i.e. de-waxing, is accomplished in a steam autoclave. Following the de-waxing, ceramic shells are fired at high temperature.
The pouring of ceramic shells with liquid metal is a fundamental part of any casting operation. At this step pouring and solidification of molten metal in a ceramic shell takes place hence forming a 3 dimensional object with a very fine surface finish and precision. The melting of metal can be done at different furnaces depending on the metal type and the chemistry and properties of liquid metal must be controlled to achieve required properties of the casting part.
Ceramic shell is removed from cast assembly by mechanical means which may require sand or shot blasting. This process also incorporates removal of sprues and in-gates from the casting part.
The casting part inspection is a function of quality requirements of the design. All of the parts will go through visual and sample approval inspection. More complex castings may require full dimensional check, x-ray radiography, crack and or leak tests, and mechanical test. The carefully prepared quality plans will ensure only certified casting will be shipped to customers.