An introduction to Lost Wax Casting process.
Lost Wax Casting also known as investment casting or precision casting, is a manufacturing process in which a wax pattern is used to shape a disposable ceramic mold. A wax pattern is made in the exact shape of the item to be cast. This pattern is coated with a refractory ceramic material. Once the ceramic material is hardened, it is turned upside-down and heated until the wax melts and drains out. The hardened ceramic shell becomes an expendable investment mold. Molten metal is poured into the mold and is left to cool. The metal casting is then broken from of the spent mold.

The term investment casting is derived from the process of “investing” (surrounding) a pattern with refractory materials. Investment casting is often selected over other molding methods because the resulting castings present fine detail and excellent as-cast surface finishes. They can also be cast with thin walls and complex internal passageways. Unlike sand casting, investment casting does not require a draft.

The ancient art and science of investment casting is also known as the lost wax process.
Investment casting was developed over 5500 years ago and can trace its roots back to both ancient Egypt and China. Parts manufactured in industry by this process include dental fixtures, gears, cams, ratchets, jewelry, turbine blades, machinery components and other parts of complex geometry.

Due to its complexity and labor requirements, investment casting is a relatively expensive process – however the benefits often outweigh the cost. Practically any metal can be investment cast. Parts manufactured by investment casting are normally small,but the process can be used effectively for parts weighing 130 lbs or more.

Investment casting is capable of producing complex parts with excellent as-cast surface finishes. Investment castings do not need to have taper built in to remove the components from their molds because the ceramic shells break away from the part upon cooling. This production feature allows castings with 90-degree angles to be designed with no shrinkage allowance built-in, and with no additional machining required to obtain those angles.

The investment casting process creates parts with superior dimensional accuracy; net-shape parts are easily achievable, and finished forms are often produced without secondary machining. Each unique casting run requires a new die to produce wax patterns. Tooling for investment casting can be quite cheap; depending on the complexity, tooling costs can run anywhere between $500 and $1,500.

For high volume orders, the time and labor saved by eliminating or decreasing secondary machining easily makes up for the cost of new tooling. Small casting runs are less likely to make up for the investment. Generally, investment casting is a logical choice for a run of 100 parts or more.

It usually takes 15 days to go from a fresh wax pattern to a complete casting; the majority of that time is taken up by creating and drying the ceramic shell mold. The time and labor-intensive nature of investment casting doesn’t only effect cost, so longer lead times for investment casting are common.

There are many benefits associated with lost wax investment casting. The enhanced flexibility of being able to utilize nearly any metal material makes this process suitable for a variety of industries and applications, including aerospace, energy, automotive and more. There’s also a great deal of room for flexibility, as investment casting can be executed using many different alloys, including tool steel, stainless steel, carbon steel. and low-alloy steel.

In addition to producing parts of intricate shapes and sizes, lost wax investment casting helps minimize material waste and conserve energy. It also provides manufacturers the ability to cast complex parts with superb surface finishes, greater dimensional accuracy, and no flash or parting lines.

1. Metal die construction The wax pattern and ceramic mold are destroyed during the investment casting process, so each casting requires a new wax pattern. Unless investment casting is being used to produce a very small volume (as is common for artistic work or original jewelry), a mold or die from which to manufacture the wax patterns is needed. The size of the master die must be carefully calculated; it must take into consideration expected shrinkage of the wax pattern, the expected shrinkage of the ceramic material invested over the wax pattern, and the expected shrinkage of the metal casting itself.

2. Wax pattern production he number of wax patterns always equals the number of castings to be produced; each individual casting requires a new wax pattern. Hot wax is injected into the mold or die and allowed to solidify. Cores may be needed to form any internal features. The resulting wax pattern is an exact replica of the part to be produced. The method is similar to die-casting, but with wax used instead of molten metal. Wax pattern of a wheel Hot wax is injected into a mold or die and allowed to solidify, resulting in a wax pattern that is an exact replica of the part to be produced.

3. Mold creation A gating system (sprue, runner bars, and risers) is attached to the wax mold. For smaller castings, several wax patterns are attached to a central wax gating system to form a tree-like assembly. A pouring cup, typically attached to the end of the runner bars, serves to introduce molten metal into the mold. The assembled “pattern tree” is dipped into a slurry of fine-grained silica. It is dipped repeatedly, being coated with progressively more refractory slurry with each dip. Once the refractory coating reaches the desired thickness, it is allowed to dry and harden; the dried coating forms a ceramic shell around the patterns and gating system. The thickness of the ceramic shell depends of the size and weight of the part being cast, and the pouring temperature of the metal being cast. The average wall thickness is approximately 0.375 in. (9.525 mm). The hardened ceramic mold is turned upside down, placed in an oven, and heated until the wax melts and drains away. The result is a hollow ceramic shell. Numerous ceramic molds used in investment casting Once the coating of slurry reaches the desired thickness, it is left to dry and harden, forming a ceramic shell around the pattern.

4. Pouring The ceramic mold is heated to around 800-900°C. The heating process further strengths the mold, eliminates any leftover wax or contaminants, and evaporates water from the mold material. Molten metal is poured into the mold while it is still hot – liquid metal flows into the pouring cup, through the central gating system, and into each mold cavity on the tree. The pre-heated mold allows the metal to flow easily through thin, detailed sections. It also creates a casting with improved dimensional accuracy, as the mold and casting will cool and shrink together.

5. Cooling After the mold has been poured, the metal cools and solidifies. The time it takes for a mold to cool into a solid state depends on the material that was cast and the thickness of the casting being made.

6. Shakeout Once the casting solidifies, the ceramic molds break down, and the casting can be removed. The ceramic mold is typically broken up manually or by water jets. Once removed, the individual castings are separated from their gating system tree using manual impact, sawing, cutting, burning, or by cold breaking with liquid nitrogen.

7. Finishing Finishing operations such as grinding or sandblasting are commonly employed to smooth the part at the gates and remove imperfections. Depending on the metal that the casting was poured from, heat treating may be employed harden the final part.

Investment casting is one option for creating intricate parts and components. There are several specific steps in the entire process to design and create the desired workpieces. It is named such because the workpieces are created around a shelled casting, which is later removed once the workpieces have been poured into the mold and are set.

Investment casting can produce a wide variety of products and prototypes, but it is important to choose the correct investment casting material for your application. The right material helps you get the desired functionality, save on the cost of materials, eliminate unwanted casting defects, and limit the need for secondary processes after the casting is complete.
Investment Casting also known as precision casting or Lost wax casting, is a manufacturing process in which a wax pattern is used to shape a disposable ceramic mold. A wax pattern is made in the exact shape of the item to be cast. This pattern is coated with a refractory ceramic material. Once the ceramic material is hardened, it is turned upside-down and heated until the wax melts and drains out. The hardened ceramic shell becomes an expendable investment mold. Molten metal is poured into the mold and is left to cool. The metal casting is then broken from of the spent mold.

Final parts can display smooth surfaces and dimensional precision while allowing for lower weight, thin walls, or other beneficial properties. Determining which properties can be successfully incorporated into your part largely depends on material choice.

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 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 it 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.
Many part types can be investment cast from copper-based alloys. More common types of copper-based alloys include bronze and brass. The strongest copper alloy is beryllium-copper, which has similar properties to high-strength alloy steels but with a higher corrosion resistance over longer periods.

Cast Iron
Iron castings, which often include gray iron and ductile iron, are known for their high accuracy and an affordable price tag. Ductile iron has high strength, heat-resistance, and toughness, but it has a more complex production process than other steels. This leads to a higher production cost than cast steel.