What is Investment Casting?
The investment casting or "lost wax" process of forming metal originated with ancient artisans making jewelry and works of art.
Wax patterns were made of the article to be cast and then dipped into a ceramic slurry that when dried, turned into a shell. The shell was then baked, causing the wax to melt out. Molten metal was then poured into the hollow shell, allowed to cool, and the ceramic shell broken away.
The result was a metal casting that had the detail and precision of the original wax pattern.
This process was commercialized in the early 1900's for dental and medical applications and now extends into many different industries, including aerospace, automotive, chemical, food, medical, military, and OEMs.
Benefits of Investment Casting.
Looking for ways to reduce your costs and increase your productivity? Investment casting by ODP is a great way to save money and increase your production.
Why is investment casting a great choice? First, investment casting is usually more affordable than weldments, fabrications, and machined components. It is not uncommon for customers to save up to 50% of production costs by partnering with ODP. Investment casting does more than reduce costs - it also provides you with tremendous design flexibility.
By choosing investment casting, you'll benefit from:
- Near Net Shape - On average, investment castings offer 90% or more of the requirements of the finished part in an as-cast state. Investment casting can incorporate complex undercuts, slots, holes, lettering, and bevels into the design. By working closely with ODP engineers, you can determine whether it is more cost effective for you to build desired features into the die.
- Design Freedom - Since virtually any shape or configuration can be investment cast, ODP investment casting affords your engineers considerable freedom to design the part for maximum function. Because of the various coring systems that can be incorporated into the pattern, investment casting can even produce internally complex parts.
- Weight Reduction - We can work with you to eliminate unnecessary metal and weight from non-functional areas of the part.
- Tooling Economy - Our tooling is usually much less expensive than tooling for other "hot" casting methods, because dies are built to withstand plastic injection rather than metal injection.
- Close Tolerance - Investment casting promises tight tolerances ranging +/- .0002", with even more exact tolerances depending on the part size and complexity.
- Surface Finish - Depending on the alloy chosen, the as-cast product of the mold is smooth and free of surface defects.
- Wide Alloy Choice - Even alloys that cannot be cast by other methods or which are difficult to machine can be investment cast at ODP.
Process of Investment Casting
ODP uses centrifugal investment casting, or spin casting, which rotates the mold at high speed as the melted metal fills the mold. This enhances the metal filling characteristics, allowing us to create small parts with detailed features of superior quality. Here's how the process works:
- Tooling construction (one time event) - Plastic injection molds are normally constructed from high grade stainless steel for extremely long life. The customer can supply tooling or, in most cases, ODP will coordinate the mold build through our mold makers. Cost and lead-time for tooling depends on the casting geometry and complexity, number of cavities, and other factors.
- Plastic Injection - Specially formulated plastic is injected into the mold and allowed to harden into an exact replica, or pattern, of the finished metal part. ODP uses multi-cavity tooling to produce many identical parts per injection. Multiple plastic patterns are ganged together on a single expendable wax sprue which, when completed, is referred to as a "tree."
- Investment - Once the tree is complete, it proceeds to the Investment room. The tree is placed inside a flask container, and ceramic slurry is poured into the flask. Once filled, it remains in a temperature and humidity controlled environment to allow it to cure.
- Dewax - After a tree is cured, the plastic pattern and wax sprue inside must be removed to leave behind the hardened ceramic shell. The entire flask is placed in a kiln to melt out the wax.
- Burnout - After the kiln, residual plastic and moisture remains in the ceramic shell. In order to inject molten metal in the ceramic shell, it must be preheated to a precise temperature to accept the molten alloy it will receive.
- Pour - When the shell reaches the correct temperature in the preheat furnace, it is quickly removed and positioned in the centrifugal machine so that molten metal can be injected into the shell.
- Finishing - In general, several tasks are completed during finishing. After cooling, the ceramic mold is broken away and disposed of, leaving behind the tree of metal parts. The parts are removed from the tree in a process called "break off." The parts are then cleaned to a high luster finish with a variety of chemicals and polishing processes.