A Guided Tour Through the Investment Casting Process
LeanWerks Provides Machined Investment Casting Solutions from Prototype to Production
LeanWerks is one of America’s leading providers of CNC machined investment casting solutions backed by aerospace precision, quality and consistency. We specialize in custom-machined complex castings and forgings, while also delivering expertise in GD&T, workholding and custom fixture design.
Our responsive manufacturing services combined with our utilization of multi-axis CNC machining technology makes LeanWerks the ultimate source for machining expensive and critical investment castings
We strive to be your single-source provider of manufacturing excellence and engineering expertise.
What Is the Investment Casting Process?
This versatile casting method begins in the pattern shop. Once a custom pattern is created for your products, the pattern is surrounded (or “invested”) by a refractory material, thus creating a unique mold of the product.
After the mold is created, molten metal or other materials (such as glass and ceramics) are poured into the mold to create a quality casting. The result is an extremely accurate duplicate of your custom component design. When it comes time to CNC machine the finished casting into even more complex, close-tolerance designs, LeanWerks’ precision machine shop
is up to the challenge.
An Overview of How the Investment Casting Process Works
- Pattern wax is injected into a tool (mold).
- Pattern wax is designed to have a specific melting point and has a filler material that has minimal shrink for good stability.
- It is molded into the exact shape and size of the finished casting.
Soluble Wax Injection
- Soluble wax is used to create cavities inside of castings.
- Once pattern wax is injected around a soluble core the part is placed in an acidic solution and the white soluble wax is dissolved, leaving a cavity in the pattern wax.
Wax Injection with Ceramic Cores
- Ceramic cores are also used to create cavities inside of castings.
- Once pattern wax is injected around a ceramic core, the core is then left in during the shelling process and removed after the metal is poured.
SPC – Statistical Process Control
After the pattern is injected, various measurements are taken to ensure that the pattern is dimensionally correct. This process is called statistical process control, or SPC.
Wax Assembly is the second major step in the investment casting process. In wax assembly, the injected wax patterns are assembled onto a setup that is designed to both “fill” and “feed” the part during the pouring operation. All set-ups have a pour cup, back-up(or support) runners, gates and a wax pattern(s). Most set-ups use an injected base as part of the set-up.
- Here are some examples of some pre-formed bases that are used in both steel and aluminum castings:
The Shell Process
The shell room produces a ceramic covering over wax setups using multiple layers of slurry and sand.
- Aluminum castings are all dipped using a robot controlled system.
- Steel castings are all dipped manually without using a robot controlled system.
- Steel castings require 7 to 12 dips while aluminum castings require 4 to 5 dips.
- Castings can be dipped either manually or robotically.
- The setup is dipped into a slurry tank.
- Once removed from the tank, the operator will allow the setup to drip for a couple minutes to allow excess slurry to drain.
- The slurry is then coated with sand. The setups will be placed on a rack or back on the conveyor line to dry for a minimum of 8 hours. After drying, the setup will repeat the dipping process until the desired shell strength is achieved.
Dewaxing via Autoclave
After the shell process is complete, an autoclave is used to melt out the wax from the molds using steam to generate pressure and heat simultaneously. The autoclave is pressurized to prevent the molds from cracking from wax expansion when the wax melts.
Preheat will burn out all remaining wax residue from the shell molds and heat the mold up in preparation for pouring the metal into it. Molds will be loaded into the preheat oven prior to pouring in the foundry.
The Foundry Process
Each mold will be filled with the desired molten metal alloy. A probe stick is used to evaluate the temperature of the melt. Once the desired temperature of the melt is met, pouring may begin.
An alloy is melted in either an induction furnace for steel or an electric melter for aluminum and brought to the desired pour temperature.
Aluminum Metal Treatment:
The molten metal goes through a fluxing and degassing operation to clean the metal prior to pouring.
Steel Metal Treatment:
With steel casting, aluminum is added to remove oxygen in the melt. Silicon Zirconium then is added to remove any remaining oxygen, nitrogen, or hydrogen in the melt.
Once the metal has been cleaned, several tests are performed to verify the quality of the melt. These tests include chemistry, gas check etc.
After full analysis is complete, the shell is removed from the metal casting through a variety of carefully controlled processes. These methods include:
- Knockout: Using a hammer, some of the shell material is removed by striking the pour cup or base several times (Note, striking an aluminum part will damage the part).
- Water Blasting: In aluminum the remaining shell will be removed by water blast which uses high pressure water to blast the shell away.
- Sand Blasting: Sand blasting is sometimes used to remove the remaining shell after the shot blast or water blast process.
- Kolene: When the shell cannot be completely removed with any or all of the blasting process, the parts are placed into a caustic salt bath to chemically remove the remaining shell material.
Cutoff and Grinding
Once the shell has been completely removed, the gates and runners are cut off from the part(s).
In steel, a chop saw is used to remove the base and cup from some of the casting. A friction or band saw is used to remove the remaining gates and runners.
Gates will be cut off as close to the casting as possible without causing damage. The remaining bulk of the gate is removed through precision grinding processes.
Finishing and Welding
Finally, the remaining gate witnesses are machined to match the surfaces of the part. If customer specifications allow for it, any defects found while finishing will be repaired through welding. The defect that was welded will then be blended to meet all dimensional requirements.
The Advantages of LeanWerks’ Precision-Machined Investment Casting Services
Wide Range of Part Sizes
- Steel Castings: Our precision CNC machine shop can machine custom steel castings in a variety of alloys, with part sizes ranging up to 1 cubic feet.
- Aluminum Castings: We specialize in custom-machined aluminum castings in a range of aluminum alloys, with part sizes ranging up to 3 cubic feet.
Complex Close-Tolerance Geometry
- Our CNC facility is capable of machining custom investment castings with +/- .01mm dimensional accuracy. Our state-of-the-art machine shop outputs close-tolerance, geometrically complex machined investment castings required by modern aerospace applications and other precision commercial/industrial sectors.
Premium Surface Finishes
- Our machined investment castings exhibit exceptionally smooth surface finishes for superior fit and aesthetics.
LeanWerks Is Your Single-Source Provider of Superior Machined Investment Casting Solutions
At LeanWerks, we provide responsive and sustainable production solutions that will optimize the machined investment casting supply chain of your enterprise. From design and prototype to production, we offer precision-machined investment casting solutions manufactured for the unique needs of your application. Backed by one of the American manufacturing industry’s most rigorous quality control systems, our facility is certified to AS9100D
, ISO 9001:2015 and DDTC/ITAR standards.