Investment casting

What is Investment casting?
Investment casting is a manufacturing process used to produce a wide range of lightweight industrial parts. Investment casting takes its name from the ceramic slurry that is used to form a ceramic shell around a wax pattern. Because it yields such precise and reliable results, this process is also sometimes known as precision casting. In addition, it is also called a "lost-wax process," "lost wax casting," or even just "wax casting." This is because, after the wax cast part is ready, the remaining wax is melted down, or "lost."
In non-industrial terms, lost wax casting and precision investment casting both refer to a method in which a duplicate copy of a metal sculpture is made. However, in industrial terms, the investment casting process is not about sculptures; it is solely about creating machine parts following the practices of wax cast sculpturing.
Many manufacturers depend on the investment casting process to produce dimensionally accurate precision cast parts. Investment casting is a diverse process that allows for the usage of all sorts of alloys and specifications. Investment castings can be found in the aerospace, automotive, chemical, defense, food processing, electrical, railroad, mechanical, marine, electronic, textile and engineering industries.

The History of Investment Casting
Investment casting is a very old industrial process. In fact, it’s the oldest known industrial process, and the earliest known description of investment casting was written around 1100 A.D. by a monk who wrote under the pseudonym Theophilus Presbyter. By 1100 A.D., though, it had already been around for a long time. In practice for over 5,000 years, the earliest examples of castings hail from the tombs of King Tut and the ancient civilizations of Harappa, Mesopotamia, Aztec and Mayan Mexico and the Benin civilization of Africa.
Originally, people used natural honeycomb or beeswax for the wax pattern, clay for the molds. They manually operated bellows as stoking furnaces. In contrast, today, people make the wax pattern using a variety of pure and synthetic waxes, and they make molds using a variety of refractory material types and alloys. Instead of handheld bellows, they use a cast foundry.
Investment casting entered the modern era in the late 1800s. At that time, dentists were beginning to use it to make crowns and fillings. The investment casting process was ushered into the industrial world during World War II, when it was used with alloys and other materials in precision net shape and near-net shape manufacturing.
Today, investment casting is a staple of industrial manufacturing.

What is Investment Casting Used For?
The investment casting process is most beneficial for casting metals with high melting temperatures that cannot be forged, pressure casted, or molded in plaster or sand. Typical investment castings include parts with complex geometries, such as turbine blades, firearm components, marine parts, and other industrial components.

Advantages of Investment Casting
Choosing to make investment cast parts has a host of advantages. These include its low production costs, efficiency, lack of waste, reliability and environmental friendliness. In addition, investment cast parts have superior tolerances, excellent surface finishes, no seams and no lines. Also, the investment process allows manufacturers to create complex parts with extra fine details that match the exact specifications of the original design.
Low Production Costs
Investment casting has lower production costs than many comparable methods, such as metal fabrication. Requiring less manpower, it slashes capital-consuming labor costs. It also requires the use of fewer resources, and it takes less time. Precision investment casting also saves money because it does not require welding, assembly or finishing work. All of these factors add up to lower production costs that allow you to earn a substantial margin.
Low Wastage and Fewer Time Delays
Investment cast parts are much better than machined parts for a number of reasons. For example, if you are considering using machines to prepare your parts, then there are chances that it will lead to a great deal of wastage. Wastage also adds to your production cost, and subsequently, your losses. Furthermore, machining processes can easily become prolonged and delay on-time delivery. On the contrary, investment casting prevents the waste of material and time.
High Reliability
Investment casting, along with other similar techniques such as brass investment casting, aluminum investment casting, and forging, stands as one of the most reliable methods of creating machining parts. Engineers have strong control over the process throughout the process.
Environment Procurement
Last but not the least, investment casting offers great environmental procurement. In other words, investment casting takes and uses resources in a way that is sustainable for the environment. For example, manufacturers can make most investment cast parts using just 9 wax patterns, most of which can be used time and time again.
Complexity, Details, and Quality
Investment casting is effective at producing lightweight, complex and detailed parts that other methods cannot. It allows for a greater design flexibility and metal alloy selection, as well as a superior surface finish. In addition, because the part is made as one whole piece, investment cast parts have no joints or flash lines. This means investment cast parts are more durable and less susceptible to breakage than other products.

What Are the Disadvantages of Investment Casting Products?
Investment casting is not a perfect process. Limitations and restrictions must be taken into account, including:
Non-automated process costs are higher than for sand casting.
Volume component costs are always higher than for die casting.
The many steps in the process leave wide scope for error.
The size and weight of one-piece castings are much more limited than for sand casting.
The per-component cost is higher than for sand casting at the one-off level, with the differential eroding quickly with increased automation and volume of parts.
Material limitations are not significant but must be taken into account.

How Accurate Is Investment Casting?
The investment casting process is very accurate in creating precise reproductions of the pattern when the flask has been prepared with skill and care. Pattern accuracy is highly dependent on the manufacturing process used to make it. A range of techniques can be used to improve the precision of the wax pattern. For example, if the pattern is molded in a tool, the injection pressure of the wax can be adjusted to moderate dimensional errors. Parts of the pattern requiring high precision can also be post-machined or “coined” (press molded with a precise steel cavity in two parts.

Investment Casting Process
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.
Steps 1: Creating the Die/Pattern
The first step in the process is to create the die or pattern of the desired workpiece. The pattern is made from wax. It can be poured into a die using injection molding, carved by hand from a block of wax, or printed using a 3D printer and the appropriate wax material.
Step 2: Mounting the Wax Patterns
Investment casting tooling involves creating multiple wax patterns and attaching these onto a “gate” device. This device is where metal or other materials will be poured to eventually create the desired workpieces.
Step 3: Tree Assembly
The tree assembly finishes the mounting of the wax patterns on the “gate” device. It is called a tree at this step because each individual wax pattern is essentially a “branch” and will be one finished workpiece once the process is finalized. You may have seen tree assemblies in new board games that need to have pieces detached before use.
Step 4: Shell Molding
Once the tree is assembled, the next step is to add the shelled casting around it. First, the tree is dipped into a ceramic slurry. Then it is dipped into a stucco of fine sand. The molding must fully dry before it can be used. These two processes can be completed multiple times until the mold is thick enough to handle casting stresses.
Step 5: Wax Removal
Before the desired material can be poured into the newly shelled mold, the wax patterns have to be removed first. This is often done by heating the wax inside an oven. Steam can also be used to heat the wax. The mold is placed upside down so that the liquid wax can flow out of it and be reused to create new wax patterns.
An alternative process of wax removal is to heat the wax so that it “burns” off and is fully removed from the shelled casting.
Step 6: Mold Casting
After the wax has been removed, there will be open spaces inside the shelled casting in the shape of the formal wax patterns. Molten metal or another liquid material is poured into the casting. The material remains in the casting until it has fully cooled and solidified.
Step 7: Removing the Shelled Casting
A hammer or another tool is used to remove the shelled casting until all that is left is the original tree. In place of the wax patterns, there will now be the finished workpieces attached to the tree. After the casting has been removed, the workpieces are carefully cut off the tree.
Step 8: Finishing Operations
Each workpiece is inspected for imperfections. If any are found, they are discarded, and the material is recycled. The last step in the investment casting process is to use different finishing methods on the workpieces. They may be sanded, coated, smoothed, machined, etc. to achieve the desired results.

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 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.

Investment Casting Products  Show
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