Investment casting (or lost wax casting) refers to the formation of ceramic around the wax patterns to create a multi or single part mold to receive molten metal. This process utilizes an expendable injection molded wax pattern process to achieve complex forms with exceptional surface qualities. Precision investment castings can achieve exceptional accuracy for products both small and large, in a wide range of materials.
Investment castings date back over 6,000 years and are one of the oldest metal forming techniques in existence. To create a mold, a wax pattern, or cluster of patterns, is dipped into ceramic material several times to build a thick shell. Once the ceramic dries, it is placed in an autoclave which causes the wax center to melt and run out under pressure. The wax-less ceramic shell is then placed in a high temperature oven to cure. Once cured, molten metal is then poured into the ceramic shell cavities or cluster, and once solid and cooled, the ceramic shell is broken off to reveal the final cast metal object.
Investment Casting Advantages
Due to its extreme versatility, accuracy and production value, investment casting is a highly touted way of producing a wide range of metal parts and components. The advantages precision investment castings can provide your company includes:
- High dimensional accuracy
- Excellent surface finish
- Mold and part versatility
- Can cast nearly any metal
- No flash or parting lines
- Can cast extremely intricate parts
The Investment Casting Process
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. The investment casting process involves the following steps:
- Pattern Formation – Lost wax casting patterns are created by injecting molten wax into an aluminum alloy die.
- Assembly – Single molds can be created, or tree-like precision investment casting molds can also be created for larger scale production runs.
- Shell Building – The investment castings outer shell casing is built up through dipping into a ceramic bath and then immediately coated with sand several times.
- Dewaxing – The inner cavity of precision investment casting is then dewaxed, which leaves a hollow outer ceramic shell layer.
- Pouring & Solidification – The ceramic cavity is then heated and cured. This prevents shock and the ceramic shell from cracking once the liquid metal is poured into the casing.
- Sawing/Cutting – Once the metal has cooled, the cast part(s) is then removed from the sprue or tree cluster via a radial blade cutting or friction sawing off the individual cast part.
- Customization – The part is then fully customized through grinding or additional heat treatments. Secondary machining may also be required depending on the requirements of the part.
- Finish – The part can be supplied with a standard 125 RMS sand blasted finish, media polished, plated, painted, or coated.
Investment Casting Alloys
Precision investment castings can be created from an almost limitless variety of investment casting alloys. The metals we work with include but are not limited to the following materials.
The base alloy elements of any nickel-base or stainless steel investment casting are chromium, nickel, and molybdenum (or “moly”). These three components will determine the casting’s grain structure and mechanical properties and will be instrumental in the casting’s ability to combat heat, wear, and/or corrosion.
Stainless steel has a minimum chromium content of 10.5%, making it more resistant to corrosive liquid environments and to oxidation. However, this is not an absolute. Stainless steel investment castings are “corrosion-resistant” when used in liquid environments and vapors below 1200°F (650°C) and “heat-resistant” when used above this temperature.
Ductile iron offers design flexibility and reduced manufacturing costs versus welded fabrications and forgings. Ductile iron castings have many “best in class” characteristics, however, are not always the most cost-effective alternative to other ferrous alloys. Additionally, ductile irons are widely used in numerous manufacturing industries, including the agricultural, automotive and aerospace industries.
Carbon steel, low alloy steel, and tool steel castings are used in several industries and are widely used materials for a range of applications and environments. It is economical, accessible in numerous grades, and can be heat-treated to improve its yield and tensile strength; and, adjust hardness or ductility to the engineer’s application needs or desired outcome.
Beryllium copper casting alloys with 2.0% to 2.75% beryllium content provides outstanding wear, toughness, and anti-galling characteristics. In challenging geometric shapes with thin walls and detailed internal passages, beryllium copper provides excellent replication of finer details while not foregoing any of the characteristics of copper, like conductivity.
Nickel-based alloys, beyond Stainless Steel, are known for their oxidation and corrosion resistant properties in harsh environments and high-temperature applications. Choosing the right nickel-based alloy is dependent on several factors, including the environment the nickel-based castings will be exposed to while in service.
Aluminum investment casting alloys are generally used for aerospace and industrial applications. They feature moderate strength, excellent castability, weldability and pressure tightness. Typically used for more complex shapes with tighter specifications and lower volumes.
Cobalt alloys are corrosion-resistant, heat-resistant, and wear-resistant. This makes cobalt-based alloy castings useful in numerous industries, including medical, aerospace, automotive, military, and other applications where oxidization is problematic and high strength is critical in high heat environments.
Like many other alloys, copper and copper-based alloys can be formed into highly complex parts, making them ideal for the investment casting process. Constant cost fluctuations can make these materials very price sensitive, making waste very costly, especially when considering CNC machining and/or forging as a manufacturing process to produce your production part. Pure copper is not usually cast.
The Aero Metals Advantage for Precision Investment Casting
There are several reasons to choose Aero Metals as your source for investment castings, these include:
- We’re engineering centric with a metal casting focus
- We design and build your tools in house
- We have extensive experience with complex geometries and hard-to-manufacture parts
- We work with a broad range of materials, including ferrous and non-ferrous alloys
- We have in-house CNC machining capabilities to complete your metal castings
- We’re a one-stop shop for investment castings and casting-based assemblies
- We guarantee consistent quality
- Our team is comprised of highly-skilled, very experienced toolmakers, engineers, foundry and production technicians you won’t find anywhere else.