Investment casting, in which molten metal is poured into an expendable ceramic mold, is one of the world’s oldest manufacturing processes, dating back thousands of years. The mold is formed by using a wax pattern or model—a disposable piece in the shape of the desired part.

 

The wax model or pattern can be used by itself to cast a single piece or attached to a wax “casting tree” (or gating system), with multiple other pieces for higher volume production. The wax model or casting tree is first dipped into a ceramic slurry, then into a ceramic powder, multiple times, until a thick coa forms around the model and/or tree. The resulting ceramic mold is then cured to achieve the required hardness that finally becomes the mold for the investment casting process.

 

Investment casting is often referred to as “lost-wax casting” because the original wax pattern is melted out of the mold after the ceramic has cured. The base metal being used is then poured into the remaining cavity, filling the inside shape.

With over 20 years of foundry casting expertise, XHX Precision Industry offers you the reliability and quality assurance needed for custom investment castings. As a performance-driven supplier, we utilize top-quality equipment that enables us to efficiently manufacture your large volume castings at a competitive price. In addition to investment castings, we also provide several value-added services. By decreasing supply chain issues and potential project derailment, XHX Precision can save you time and money.

Our capabilities encompass more than just casting expertise. We employ a technical team and sales support team with extensive experience with engineering, metallurgy, and manufacturing. If you have questions regarding our investment casting process, please discuss your concerns with one of our experts.

 

While investment castings made using the lost-wax process are often produced one part at a time, most of the investment castings XHX Precision Industry creates are produced in multiples for larger volume production. Investment castings with complex geometries and intricate details can be created with little worry about die wear or dimensional changes.

 

Other advantages of investment castings include:

Excellent surface finish

High dimensional accuracy

Extremely intricate parts can be cast

Almost any metal can be used

No flash or parting lines

A good investment casting foundry like XHX Precision can produce near-net castings from nearly any metal. The most commonly used materials for investment castings are aluminum alloys, bronze alloys, magnesium alloys, cast iron, carbon steels, stainless steel, and other nickel alloys.

Investment casting requires the use of a metal die (usually aluminum), wax, ceramic slurry, furnace, molten metal, and any machines needed for sandblasting, vibratory tumbling (with or without a grinding or polishing media), cutting, and grinding. Like any good investment casting foundry, we follows a process that includes the following steps:

Pattern creation: Wax patterns are typically produced by injecting molten wax into an aluminum alloy die, and are formed as a single piece. Cores may be used to form internal features of the pattern if any. Several of these patterns are attached to a central wax gating system (sprue, runners, and risers), to form a tree-like assembly. The gating system forms the channels through which the molten metal will flow into the mold cavity.

Mold creation: The “pattern tree” is dipped into a slurry of fine ceramic particles, coated with medium to coarser particles, generally in powder form, and then dried to form a ceramic shell around the patterns and gating system. This process is repeated until the shell is thick enough to hold the weight and heat of the poured metal. The shell is then cured and, once set, is placed into an oven where the wax is melted out, leaving a hollow ceramic shell that acts as a one-piece mold—hence the name “lost wax casting.”

Pouring: The mold is preheated in a furnace to approximately 1,000°C (1,832°F) before molten metal is poured from a ladle into the gating system of the mold, filling the mold cavity. Pouring metal for investment casting is typically done manually under the force of gravity, but other methods such as vacuum or pressure are sometimes used.

Cooling: After the mold has been filled, the molten metal is allowed to cool and solidify into the shape of the final casting. Cooling time can vary depending on the thickness of the investment castings, the thickness of the mold, and the metal used.

Casting removal: After the metal has cooled, the mold is broken and the casting removed. The ceramic mold is broken either manually or with water jets, though several other methods may be used. Once removed, the investment castings are separated from the grating system by either sawing or cold breaking parts from the tree.

Finishing: Operations such as grinding, sandblasting, or vibratory tumbling is used to smooth the joints at the gates. Heat treatment is also sometimes used to harden the final investment castings. Once this is completed, the parts are ready for any additional processing, such as machining.

Investment casting is generally more expensive per unit than die casting or sand casting, but has lower tooling costs. An experienced investment casting foundry can produce complicated shapes that would be difficult or impossible to create via die casting, yet, like that process, investment casting typically requires little surface finishing and only minor machining.
 

For industrial applications, the size limits of investment castings are typically between 3 g and 5 kg Cross-sectional limits are generally from 0.6 mm to 75 mm. Typical tolerances are 0.1 mm for the first 25 mm (0.005” for the first inch) and 0.02 mm for each additional centimeter (0.002” for each additional inch). A standard surface finish is 1.3 to 4 micrometers RMS. All measurements, of course, depend on the design and complexity of the part.
 

 

Investment castings are used in the power generation industries to produce turbine blades with complex shapes or cooling systems. Blades produces via investment casting can include single-crystal (SX), directionally solidified (DS), or conventional equiaxed blades.

No matter what the part application, any investment casting foundry worth their salt is capable of producing a near-net shape with very high dimensional accuracy in small castings, although tolerances tend to increase somewhat with casting size.

Because of the relatively high tooling costs and higher than average total costs, investment castings are usually produced in relatively large production runs.
 

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