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Lost wax casting, now called investment casting or precision casting, is a precision casting process with little or no cutting. It is an excellent process technology in the precision casting industry and is widely used. It is not only suitable for precision casting of various types and alloys, but also produces castings with higher dimensional accuracy and surface quality than other casting methods. Even complex, high-temperature-resistant, and difficult-to-process castings that are difficult to cast with other precision casting methods can be cast using lost wax precision casting.
Lost wax casting (also called investment casting or precision casting) is an ancient casting technology that can be traced back to early civilizations such as ancient Egypt and ancient China, and is still widely used in many industries such as jewelry manufacturing, sculpture, and precision machinery parts manufacturing.
The lost wax casting process has been around for thousands of years, and the earliest known examples of the lost wax casting process are thought to date back to 3700 BC after carbon-14 dating tests. They were found in the Treasure Cave in southern Israel. Other early examples of the investment casting process also exist in many different countries and regions.
In the historic Mesopotamia region, lost wax casting was widely used for small and large castings; in Pakistan in South Asia, people have found 6,000-year-old copper amulets made with this process. Objects cast with this technology have been found in Egypt, Greece, East Asia, Africa, Europe...all over the world.
Lost wax casting is used to produce fine, complex metal parts, which are then used in a variety of industries and occasions. This technology may have originated thousands of years ago, but it still plays a very important role in casting today.
The initial step in the lost wax casting process begins with the creation of a 3 dimensional CAD rendering of the part to be produced, which will be used to create the aluminum die.
The die is created using the design from the CAD rendering. It is a negative relief of the part to be cast.
Wax, in a semi-liquid state, is poured into the die to form the wax pattern, which is adjusted to allow for shrinkage. This process can be repeated as many times as necessary depending on the number of parts to be cast.
The wax patterns are connected along a runner to form the sprue, which may be connected to other pattern groups to form a cluster. The sprue, runner, and wax patterns are referred to as a tree.
To build the shell, the pattern is dipped in ceramic slurry, which coats the pattern to form a hard exterior shell around the pattern. One end of the wax tree is left exposed for removal of the wax.
The hardened ceramic shell will be where the molten metal will be added to form the final part. To accomplish this, the wax on the interior of the ceramic shell has to be removed, which is done by placing the ceramic shell in an autoclave or oven. As the ceramic shell is heated, the wax melts and runs out of the shell. It is this part of the process that gives lost wax casting the name "lost wax".
Though the mold has undergone the dewaxing process, there still may be residual wax and moisture in it. To remove these extraneous materials, the mold is subjected to a burnout process, which heats it to over 1037° C or 1900° F. Also, this step helps to solidify and harden the ceramic mold to prepare it to receive the molten metal.
The ceramic mold is placed with the open side up to have the molten metal poured in. This process can be completed by simply allowing gravity to distribute the metal in the ceramic mold or have it forced in by a form of pressure. The method that is chosen depends on the size of the mold and the type of molten metal.
Regardless of the descriptor, the ceramic material that forms the mold has to be removed. This can be accomplished using a variety of methods, which can include simply hammering the ceramic, blasting, high pressure water, or the use of some form of chemical that may include liquid nitrogen.
The finished part has to be separated from the gates and runners once the ceramic mold has been removed. This is normally performed with a grinder and the waste material is collected for reuse.
Though the part is fully molded, it will need to be sandblasted to remove scales and residual ceramic to enhance its finish. This can be completed in a variety of ways that include shot, small metal balls, or sand blasting.
There are certain parts that require extra protection from rust, corrosion, and weather damage. This added coating is applied by dipping the part in anti-rust solution or oil. Other surface treatments include painting and galvanizing.
1) High precision and good surface finish
The dimensional accuracy is good and can reach 5% of the nominal size, and the roughness level is Ra0.8-3.2μm, which reduces the workload of subsequent machining. In the case of near-net shape or even net shape, machining is almost completely eliminated.
2) The mechanical properties of the casting are superior and the molding cost is low
Due to the superiority and stability of the process itself, the mechanical properties of the casting can be maintained at a relatively high level. Lost wax casting is particularly suitable for situations with complex structural shapes. A reasonably designed single casting can sometimes replace equipment for multiple parts, which may include ordinary casting, machining, stamping, forging, injection molding, sheet metal, etc. At the same time, given the flexibility of the process, molding is easy, and the weight of the parts can be significantly reduced, thereby reducing the processing cost. In addition, it is also very conducive to saving and environmental protection.
3) Wide material adaptability
Silica sol lost wax casting is suitable for most casting alloys, including various cast irons, carbon steel, low alloy steel, tool steel, stainless steel, heat-resistant steel, nickel alloy, cobalt alloy, chrysene alloy, bronze, brass, aluminum alloy, etc. And its overall processing effect is relatively stable, especially suitable for materials that are difficult to forge, weld, and machine.
4) Excellent production flexibility
It is very suitable for large batches, small batches, and even single-piece production, and sometimes there is no difference in production costs. There is no need for very complex mechanical equipment, and the mold processing scheme is also flexible and diverse. In addition, my country's casting companies and other research units have also developed some new investment casting processes and technologies. For example: multi-channel casting process equipment molds and fusible alloy mold technology for casting.
5) Complex shapes
Lost wax casting can produce castings with complex shapes without the need for parting lines or complex mold structures, which is difficult to achieve with traditional casting methods.
6) Precision parts
Particularly suitable for manufacturing parts with complex shapes and fine details, such as jet engine blades in aerospace.
7) Economical and efficient
For parts that require high precision and complex shapes, lost wax casting is more cost-effective than other casting methods.
8) Batch adaptability
It is suitable for both small and large batch production.
Lost wax casting (also known as investment casting or the lost wax process) is a very flexible casting method that can be used with many different types of metals. Because this method is able to produce castings with high precision and complex shapes, it is suitable for a wide range of metals and alloys. Here are some commonly used metals and alloys:
Copper alloys: Copper-based alloys have excellent thermal and electrical conductivity, low wear rates, and good ductility. They are commonly used in the marine, plumbing, and electrical industries. Copper-containing alloys include bronze for bearings and ship propellers, brass for musical instruments, pipes, and explosives, and copper-nickel alloys that are commonly used to make castings for the marine industry.
Aluminum alloys: Aluminum alloy lost wax castings are popular for their ease of processing and corrosion resistance. Due to its fluidity, aluminum alloys can have thin walls, and when combined with other metals or heat treated, the metal develops excellent strength. Aluminum is one of the most abundant of all metals, as it makes up 8% of the Earth's crust. It is a lightweight metal that is commonly used in the aerospace, military, automotive, packaging, food processing, and electrical industries. In addition to aluminum lost wax casting, Dean Group also offers aluminum die casting services.
Zinc alloys: Used to produce some low-cost small parts.
Carbon steel: Widely chosen for its low cost, economy, and ferromagnetic properties, carbon steel is available in a variety of grades and has a flexible ductility after heat treatment. Carbon steel alloys are often used in the aerospace, agricultural, medical, and firearms industries.
Stainless steel: Stainless steel offers a variety of options for castings and is widely used in many industries. This material is made from a mixture of chromium, nickel, and molybdenum. The grain and properties of the alloy produced when using stainless steel will be determined by the content of each metal. Since chromium always accounts for 10% of the metal used, these alloys will have corrosion and oxidation resistance.
Inconel: Used in applications with high temperatures and corrosive environments.
Hastelloy: Also suitable for high temperatures and corrosive conditions.
Used in aerospace, medical equipment and high-end sports equipment.
Such as niobium alloy, molybdenum alloy, etc.
(1) Influence of casting structure: a. The thicker the casting wall, the greater the shrinkage rate; the thinner the casting wall, the smaller the shrinkage rate. b. The free shrinkage rate is large, and the hindered shrinkage rate is small.
(2) Influence of casting material: a. The higher the carbon content in the material, the smaller the linear shrinkage rate; the lower the carbon content, the greater the linear shrinkage rate. b. The casting shrinkage rate of common materials is as follows: casting shrinkage rate K=(LM-LJ)/LJ×100%, LM is the cavity size, and LJ is the casting size. K is affected by the following factors: wax mold K1, casting structure K2, alloy type K3, pouring temperature K4.
(3) Influence of mold making on casting linear shrinkage rate: a. The influence of wax injection temperature, wax injection pressure, and holding time on the size of the investment mold is most obvious in wax injection temperature, followed by wax injection pressure. The holding time has little effect on the final size of the investment mold after the investment mold is formed. b. The linear shrinkage rate of wax (mold) material is about 0.9-1.1%. c. When the mold is stored, it will further shrink, and its shrinkage value is about 10% of the total shrinkage. However, after 12 hours of storage, the size of the mold is basically stable. d. The radial shrinkage of the wax mold is only 30-40% of the longitudinal shrinkage. The effect of the wax injection temperature on the free shrinkage is much greater than that on the hindered shrinkage (the optimal wax injection temperature is 57-59℃, and the higher the temperature, the greater the shrinkage).
(4) The influence of shell materials: zircon sand, zircon powder, Shangdian sand, and Shangdian powder are used. Because of their small expansion coefficient of only 4.6×10-6/℃, they can be ignored.
(5) The influence of shell baking: Due to the small expansion coefficient of the shell, when the shell temperature is 1150℃, it is only 0.053%, so it can also be ignored.
(6) The influence of casting temperature: The higher the casting temperature, the greater the shrinkage, and the lower the casting temperature, the smaller the shrinkage, so the casting temperature should be appropriate.
There are many different applications for lost wax casting in many different industries. For a very long time, this technique has been used to cast jewellery and small parts, as well as sculptures.
However,investment casting now forms part of most industry’s supply chains and includes the medical industry (knee and hip implants), the automotive, rail and mining industries, the aerospace industry And virtually every other manufacturing method that needs precise metal components.
Lost wax casting is a highly technical process, which requires extensive knowledge and skill at each stage of the process so that the resulting components have high integrity and quality. A high degree of process control is also essential in order to maintain quality standards. DEZE has extensive experience in lost wax casting, so don’t hesitate toenquireabout our services and a team member will discuss your project needs with you.
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