What is Investment Casting ?
Investment casting, also known as lost-wax casting, is a manufacturing process used to manufacture complex parts with high precision by using expendable patterns made of wax-like materials. The process is valued for its ability to produce components with tight tolerances, accuracy, exceptional surface qualities, repeatability, versatility and integrity in a variety of metals and high-performance alloys. It is ideal for the production of precision castings with thin walls and fine surface finishes, which can reduce the need for secondary machine processes. The article will discuss the process of die casting in detail, and go over its materials, advantages, disadvantages, and applications.
The Investment Casting Process
The investment casting process consists of several steps:

  • Create the Pattern

    • An original pattern is created from wax, clay, wood, plastic, or another material. Patterns are typically made of wax using a metal injection die. A more recent development has been the production of patterns using 3D printing for relatively small wax parts. Volume production can be made without the cost of a wax casting tool. The pattern used in the process have the same details as the finished part, and the only difference is its allowance for thermal contraction (i.e. shrinking).

  • Mount the Wax Patterns And Create the Tree

    • Any area that may be poorly ventilated will require the addition of air passage features. After the wax pattern is created, it is assembled with other wax components, which then can form the gate and runner metal delivery system. Multiple wax patterns can be handled with one tree according to the size and configuration of the desired finish component.

  • Make a Mold Shell

    • Dip the wax pattern assembly into the ceramic slurry, which then is covered with sand stucco and given sufficient time to dry. Repeat the cycles of wet dipping and stuccoing until a shell of the desired thickness is developed all over. After being completely dried, the ceramic shell can become firm and rigid, helping to retain the molten metal during the casting process.

  • Remove the Wax

    • Put the assembly inside a steam autoclave to remove the wax and fully integrate the refractory coating. The residual wax is burned off, and the moisture content is evaporated. Therefore, the ceramic mold still retains a cavity with the shape of a desired cast part. Meantime, the the strength and stability of the ceramic material can be improved.

  • Melt and Cast

    • Preheat the mold to a specific temperature,which allows the metal to stay liquid longer. Then , the mold can be filled with molten metal better, creating the metal casting with high dimensional accuracy.

  • Finalize the Castings

    • The mold shell is broken away from the casting in a knockout operation when the cast has cooled. The removal of cast material from sprue, vents, and supports will have a negative effective on the casting, which can be repaired with die grinding,sandblasting, sawing,clipping, sanding and polishing. In addition,machining operations like milling and drilling are performed to finish holes and surfaces.
Different Types of Investment Casting Materials
Investment casting works well with a wide range of materials, both ferrous and non-ferrous materials.

  • Carbon Steel

  • Stainless Steel Alloys

  • Aluminum

  • Ductile Iron

  • Beryllium Copper

  • Nickel-Based

  • Cobalt-Based

  • Copper-Based

  • Glass

Surface Finishing for Investment Cast Parts
The followings are surface finishing treatments available to achieve the desired surface quality, including:

  • Anodizing

  • Polishing

  • Painting

  • Powder Coating

  • Passivation

Advantages of Investment Casting
Large Parts
Mold Design Versatility
Versatile And Intricate Shapes
Fine Surface Finish
Great Dimensional Accuracy
No Flash or Parting Lines
Wide Material Selection
Numerous Types of Metal Alloys Can Be Used
Less Material Waste
Produce Numerous Types of Products
Fewer Environmental Hazards from the Foundry Process
Disadvantages of Investment Casting
The High Cost for Short-run Productions
Need A Lot of Labor
Be Difficult to Cast Objects Requiring Cores
Limited to Small Casting
Holes cannot be smaller than 1/16 in. (1.6 mm) and should be no deeper than about 1.5 times the diameter.
Require Longer Production Cycles
More Time Consuming
Applications of Investment Casting
Investment casting can create complex parts with excellent as-cast surface finishes and superior dimensional accuracy. It has applications in a variety of industries, including:

  • Military

    • Firearm receivers, triggers, hammers

  • Aerospace

    • Gas turbine components ( turbine blades, and fuel components)

  • Automotive

    • High-performance parts like drive train components, rocker arms, and power train elements

  • Marine

    • Strong, corrosion-resistant metallic panels for ships and submarines

  • Industrial

    • Components for heavy goods/construction equipment and tractors

  • Agricultural

    • Components for agricultural machinery

  • Medical

    • Parts for MRI machines, prosthetics, implants,wheelchairs, hospital beds, operating room equipment, and surgical tools

  • Jewelry

    • Jewelry and decorative items in one-off and limited production

  • Golf clubs

    • Clubheads
FAQs
1.Is Investment Casting Better Than Die Casting?
What is the difference between investment casting and sand casting ?

  • Weight

    • Investment casting can be used to make small and intricate parts with high tolerance and surface finishes, which is smaller than 1lb . In contrast, sand casting is economical for high-volume production of huge parts.

  • Cost

    • The cost of investment casting is higher than that of sand casting due to the complexity and preparation needed.
2.Is Investment Casting Expensive?
Investment casting is generally expensive than other processes like sand casting,especially dealing with a low volume of production. This is because of the costs and labor with the molds. However, the cost can be compensated through the reduction of machining achieved through as-cast near-net-shape tolerances.
3.What Type of Tooling is Required for Investment Casting?
A split aluminum tool or die. It is used to create a wax pattern of the part where a ceramic mold is built. This contributes to the process of investment casting .
4.What dimensional tolerance can be expected from investment casting?
Investment casting can be utilized to produce extremely tight dimensional tolerances on a variety of alloys. Depending on the size and complexity of the part, a linear tolerance of +/- 0.005 inches per inch is standard for investment casting. Generally speaking, the smaller the part, the tighter the dimensional tolerances that can be maintained.
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