Investment Casting Process: Ancient process is CAST AS the future
It’s a process that dates back more than 5000 years, used for art and jewelry production over the centuries from China to India, Africa and Europe. But investment casting is now being seen as the future by many industries seeking lightweight thin-wall metal components.
The investment casting or lost wax process produces high-strength components with fine detail, thin walls, and greater dimensional accuracy than sand and other casting methods. Investment castings have excellent “as-cast” surface finish, reducing or even eliminating the need for machining, and that means huge reductions in cost and lead times.
THE INVESTMENT CASTING PROCESS WAS primarily used for art until the development of the jet turbine engine at the end of World War II. Since that time it has become an enabling technology in today’s top industries:
- Aerospace and Defense
- Power Generation
- Oil and Gas
- Space Exploration
- Medical / Orthopedics
When to use Investment Casting:
- Shaped or non-symmetrical parts
- Smaller parts with fine details
- Parts that have internal structures
- Tight tolerances and thin walls
It ’s normal for investment castings to cost more than castings produced using other, simpler methods, such as sand casting. The benefits achieved, however—including intricacy, reliability, reproducibility, surface finish, and others—more than make up for the difference in cost.
Investment Casting Process at Barron Industries
Step 1: Creation of a wax pattern
The process begins with the production of a one-piece heat disposable pattern. Wax patterns are typically made by injecting wax into a metal tool or “die”. But since the early 90’s, Barron Industries has also produced patterns through 3D printing technology. Today, Barron can produce rapid prototype castings from most 3D printed materials AND DELIVER A FINISHED MACHINED CASTING IN TEN DAYS.
Step 2: Wax Tree Assembly
Because it is uneconomical to make small parts one at a time, wax patterns are typically attached to a wax tree or “sprue”. The wax between the pattern(s) and the sprue are called “Gates. These solid wax branches also guide molten metal in the casting operation to form each final product. Larger parts can also be cast on their own.
Step 3: Shell Building
The wax tree is dipped into a ceramic bath or “slurry”. Barron’s six-axis dipping robot ensures consistency and uniformity of shell production in intricate and complex parts. After dipping, fine sand or “stucco” is applied to the wet surface. The mold is allowed to dry, and the process is repeated a number of times resulting in a layered ceramic mold, capable of withstanding the stresses of the casting process.
Step 4: Dewax/Burnout
Before pouring metal into the mold, the wax is removed using a flash fire oven, which melts and burns off the wax. Flashfire burns off residual wax and cures the shell, preparing it for casting.
Step 5: Pouring of Ferrous and Non-ferrous metals
Before the metal is poured into the ceramic mold or “shell”, the mold is preheated to a specific temperature to prevent the molten alloy from solidifying or “freezing off” before the entire mold is filled.
Alloy is melted in a ceramic crucible using a process known as induction and electric resistance melting. A high-frequency electric current creates a magnetic field around the alloy, generating electric fields inside the metal. When the alloy reaches its specified temperature, it is poured into the mold, and the mold is allowed to cool.
Step 6: Shell Knock Off
Once cool, the shell material is removed from the metal. This is typically done via mechanical means using a hammer or high-pressure water blast.
Step 7: Cut Off
Once the shell material has been removed, the parts are cut off the sprue and the gates are ground off.
Step 8: Finished Castings
Once the parts are removed from the sprue, and the gates removed, the surface can be finished using a number of means including vibratory/media finishing, belting or hand grinding, or polishing. Using a ceramic mold, the lost wax process produces a smooth finish, averaging 125Ra surface finish as cast and a.005”/inch tolerance for the majority of applications. Depending on the application, investment castings can be used in their “net shape” or undergo machining for precision mating surfaces.
Barron’s In-House CNC Machining
If needed, Barron can perform any required machining using the highest quality equipment including Makino, Mori Seiki and Mazak. Our 13 CNC machining centers include 5 horizontal and 5 vertical milling, as well as 3 lathes, combined with grinding, brazing, welding, assembly and fabrication.
We are experienced in the challenging machining of alloys such as 17-4phstainless steel, 90/10 copper, armor steel, cobalt, nickel and S7tool steel.
Inspected, Packaged and Shipped around the Globe
Barron Industries is AS9100D Certified, and our investment casting process is closely controlled at every point of production. NADCAP accredited for non-destructive testing, our lab is equipped to perform Dye Penetrant Testing, Magnetic Particle Testing, x-ray inspection, tensile and physical properties tests, and chemical and structural analysis. All testing results in a formal certification report. Barron offers real-time work-in-process tracking with our PLEX ERP system, laser engraving serialization and barcode/RFID tag tracking. All of our manufactured components are inspected, marked (if required), packaged and shipped around the globe.