How Investment Casting Works
Investment casting is a metal casting process used to create complex and intricate metal parts with high dimensional accuracy and fine surface finishes. This casting method is ideally suited to producing relatively high-quality components with intricate details, delicate features, and tight tolerances.
Investment casting is commonly used in industries such as: aerospace, automotive, jewelry, and medical devices, in which high precision and intricate designs are essential. It also produces castings with very tight tolerances and high dimensional accuracy. Investment castings typically have smooth and fine surface finishes. Investment casting can be used with a variety of materials, including various metals and alloys. It can also produce parts with complex shapes, internal cavities, and thin walls that are challenging for other casting methods.
Key Steps In The Investment Casting Process
Investment casting involves several precise steps to produce high-quality metal components. Here’s a breakdown of the process:
Step 1. Pattern Creation
You begin with a wax pattern that matches the desired component’s design. This pattern forms the foundation of the entire process. Wax patterns are typically produced using injection moulding, ensuring consistent dimensions across multiple components. For larger batches, patterns are attached to a wax tree, making them ready for subsequent steps.
Accuracy during this phase is essential. Any imperfections will directly affect the final casting. Equipment like dies and moulds used for wax injection must be precise to prevent flaws in the wax model.
Step 2. Mould Creation
Next, the wax pattern is coated with ceramic slurry to create a durable mould. You dip the pattern into the liquid ceramic, covering every surface, then sprinkle it with fine sand to strengthen the shell. Repeating this process several times builds up the mould’s thickness and resilience.
Once the layers are complete, the mould dries and solidifies. Environmental conditions like humidity and temperature play a big role here, as they influence how quickly and evenly the ceramic hardens.
Step 3. Wax Removal
After drying, you heat the mould in a furnace to melt and remove the wax, leaving a hollow cavity inside. This process, known as dewaxing, ensures the mould is clean and ready for metal pouring.
Here, precision heating is key. Using controlled temperatures prevents cracking or distortion of the ceramic shell, ensuring integrity for the next stages.
Step 4. Metal Pouring
In this step, molten metal is poured into the ceramic mould. The metal fills every detail of the cavity, capturing the intricate design of the pattern. Pouring must be done carefully to avoid introducing air pockets or defects.
The mould can withstand high temperatures, ensuring compatibility with metals like aluminium or steel. Metal cooling time depends on the alloy used, affecting the final casting’s properties.
Step 5. Finishing
Once cooled, you break away the ceramic shell to reveal the casting inside. Finishing includes removing excess material, surface cleaning, and any post-cast treatments like heat treatment or machining to refine the component.
If necessary, you can also inspect or test the casting to confirm it meets design and quality standards. This final step ensures the part is ready for use or further assembly.
Investment Casting Materials
There is a large selection of alloys to choose from during the material selection process for investment casing. These include:
Stainless Steel
Stainless steels feature superior durability in comparison with many other materials. The potential of the material has led to increased use in investment casting by designers and engineers. Applications for stainless steel casting include gearbox parts in automotive applications, various gears, camp components, and golf club heads.
Low Alloy Steel
Low alloy steels are among the most frequently used steels in the mechanical world due to their affordability and beneficial mechanical properties. Specialized heat-treating processes make it possible to engineer parts that have differing properties in different areas of the same workpiece. For example, varying heat treatments can be used to make one surface tough and impact-resistant, while another surface becomes wear-resistant.
Aluminum Alloy
Aluminum alloy is the most used material in investment casting. Industries that use aluminum casting most frequently include aerospace, avionics, electronics, and military.
Castings are now offered for demanding applications like airframe components thanks to the material’s improved strength and the availability of quality castings made from aluminum-silicon-magnesium alloy.
Carbon Steel
Carbon steel is a common low-cost material that comes in a variety of grades, with the classifications varying based on the amount of carbon content. The strength, ductility, and performance of carbon steel can be improved in industrial applications through heat treatment. Its ferromagnetic properties make carbon steel useful in motors and electrical appliances. It is safe, durable, and has a high structural integrity, making it one of world’s most frequently used alloys.
Super Alloy
Super alloys based in nickel and cobalt have common uses in the aerospace, energy, medical, chemical, and marine industries. Nickel-based alloys are stronger at high temperatures and cobalt-based alloys have superior corrosion, oxidation, and wear resistance over their nickel-based counterparts. Super alloys increasingly replace sheet metal because they provide high rigidity and superior service characteristics while remaining a cost-effective option.
Copper Alloy
Copper-based alloys are corrosion-resistant and feature low rates of wear. They are frequently used in applications such as ship or pump propellers, electrical components, and plumbing components. A versatile material, there are more than 400 different alloys featuring a wide variety of properties.
6 Advantages of Investment Casting
Complex Geometries: Investment casting can produce parts with intricate details, undercuts, and thin walls that are difficult or impossible to achieve with other casting methods.
Precision and Accuracy: The process offers excellent dimensional accuracy and surface finish, reducing the need for extensive machining.
Material Versatility: A wide range of metals can be cast, including ferrous metals (stainless steel, cast iron, carbon steel) and non-ferrous metals (aluminium, brass, bronze, copper, nickel alloys, and titanium).
Minimal Machining: Investment castings often require minimal or no machining, reducing costs and lead times.
Net Shape Production: Parts can be produced close to their final shape, minimizing waste.
Mass Production: Investment casting is well-suited for mass production of intricate components.
Investment Casting vs. Die Casting: What Are The Differences?
Strengths of Investment Casting: Investment casting can produce parts with superior surface finish, fine details, and complex geometries. It allows for a wide range of material options, including high-performance alloys. It is well-suited for small to medium production volumes and provides good design flexibility.
Limitations of Investment Casting: Die casting offers higher production rates and cost efficiency for large production volumes. The dimensional tolerances of investment castings may not be as tight as die castings. Investment casting is not suitable for parts requiring thick sections or heavy load-bearing capabilities.