Perhaps you are working on a new part fabrication and do not want to commit to the tooling costs of die casting. Or maybe you are increasing production and are ready for a cost-effective manufacturing option. This article does a deep dive comparing investment casting and die casting so you can better understand your production options.
Investment Casting Process
Investment casting is a metalworking process that produces precise parts and components with excellent finishes while also limiting material waste. It is also called precision and lost wax casting.
This name comes from the initial steps of the process where a wax pattern is created, then dipped into a ceramic slurry until it hardens. The wax is then melted, leaving a sturdy mold that is used to cast metal parts.
- Create Wax Pattern: A pattern of the desired part is made either by 3D printing or building a wax injection die. Dies can have a single cavity or a complex multi-cavity structure.
- Wax Assembly: Wax patterns are attached to a sprue and constructed into a tree. Imperfections are removed so the wax resembles the finished part as closely as possible.
- Ceramic Coating: The entire assembly is dipped into a ceramic slurry that creates a shell around the wax. Fine material preserves small details on the first pass; coarser material adds strength in subsequent dips.
- Dewaxing: When the ceramic mold has completely cured, it is placed in a furnace where the wax melts or evaporates. Most mold failures occur at this step as expanding wax places stress on the mold.
- Casting: Metal is poured or forced under pressure into the mold and allowed to solidify.
- Divesting: The ceramic shell is removed by vibration, hammering, media blasting, or water ejection to release the final part.
- Finishing: Grinding and hand tooling remove any remaining impurities.
- Testing: Parts are inspected for surface and sub-surface defects using visual, fluorescent penetrant, and optional x-ray inspections.
Die Casting Process
Die casting is different from investment casting in that it uses a permanent mold or die that does not need to be remade for each casting cycle. This method is considered the most efficient method for producing precise non-ferrous metal parts.
A steel die containing the pattern for a part is created in two or more sections, mounted on a machine, and held tightly together. Molten metal is injected into the die where it can cool, the die halves are pulled apart, and the casting is ejected. The dies can withstand up to 150,000 to over 1,000,000 cycles before needing replacement or repairs.
Hot Chamber Method
Hot chamber die casting is used for metal alloys with low melting points. Metal is heated in a furnace attached to the machine and fed into the die via a gooseneck. Cycle times vary from under a second for small parts to thirty seconds for castings weighing several pounds.
Cold Chamber Method
Cold chamber machines use a separate furnace for metals with higher melting points, which would erode hot chamber machinery. Molten metal is poured into a cold chamber by hand or automatic ladle before injection, making the process somewhat less efficient than hot chamber casting.
Applications
Investment casting applications span nearly every industry. The power generation and aerospace industries use it to create turbine blades with intricate shapes and complex cooling systems.
Firearm manufacturers produce hammers, triggers, and precision parts. The oil and gas industry creates pressure relief and safety components. Automotive, food service, defense, medical, and agriculture industries also benefit from investment cast parts.
Die casting is the most popular technique for mass-producing commercial, consumer, and industrial products such as vehicles, construction materials, gears, and heavy machinery. The automotive industry uses die casting for transmission and engine components as well as GPS and entertainment system housings.
Recreation and landscaping industries create RV chassis, outboard gear cases, and marine undercuts. Hospital equipment such as blood analysis machines and surgical devices are also produced using die casting.
Advantages of Die Casting
- Cost-effective in higher volumes.
- Capable of producing near-net-shape parts with little secondary machining required.
- Rapidly produces consistent and reliable parts.
- Die-cast parts have excellent dimensional tolerance.
Disadvantages of Die Casting
- Subject to high porosity, making it less ideal for parts that require high hardness.
- Cannot be heat treated due to porosity.
- High cost for smaller production runs.
- Difficult to cast parts that require cores.
- Limited to non-ferrous metals.
Advantages of Investment Casting
- Ideal for parts and components with complex geometries.
- Parts and components achieve high tolerances.
- Superior surface finishes without requiring secondary operations.
- Economical way to produce parts that would otherwise require welding or other secondary processes.
- Ideal for low-volume production or fabrication.
- Can cast both ferrous and non-ferrous metals.
Disadvantages of Investment Casting
- Longer cycle times to create new ceramic molds, which adds to overall cost.
- Difficult to cast parts that require cores.
- Costly binders and refractory materials for making molds.
Which Method is Best for My Parts?
When selecting which method best suits your production, consider the following variables:
- Material: If you need non-ferrous metals, both methods work. For copper or stainless steel alloys, investment casting is the better option.
- Budget: Investment casting is more labor-intensive, driving up cost. Die casting requires more tooling and secondary machining, making it more cost-effective for longer production runs.
- Design Complexity: Investment casting offers greater flexibility in design complexity and allows product numbers and logos to be incorporated directly. Die casting cannot provide this level of detail.
- Part Size: Investment casting accommodates parts from one ounce to about 200 pounds. Die casting has fewer size restrictions, though larger parts mean higher tooling costs.
- Cycle Time: Die casting can produce upwards of 45 shots per minute and can be fully automated. Investment casting requires additional labor.
- Surface Finish: Investment cast parts achieve a standard 125 micro finish, superior to die casting.
- Tolerance: Die cast parts up to 25mm start at +/- 0.050mm. Investment cast parts of the same size start at +/- 0.250mm. Both tolerances increase as part size increases.
Investment Casting vs. Sand Casting
Sand casting pours molten metal into a sand mold. Molds are created by mixing sand and clay with a binder, forming a pattern around the final part. The sand is then reused to create another mold. Several of the same parts can be produced simultaneously, or a range of parts that share a mold can be cast.
| Factor | Investment Casting | Sand Casting |
|---|---|---|
| Mold material | Ceramic slurry (single-use) | Sand and clay (reusable) |
| Design flexibility | Almost any shape; complex internal features possible | Parts typically need draft angles; internal voids require cores |
| Surface finish | Excellent; little or no post-processing | Rough texture from sand; demarcation lines require additional processing |
| Run size | Hundreds of small parts at once up to single large components | Better suited for moderate runs; limited precision on very small parts |
| Cost | More expensive due to process complexity | Generally less expensive |
| Design changes | Complex; may require modifying metal pattern or new wax versions | Relatively simple to change a sand mold |
