Lost wax casting is known for its ability to produce complex shapes, fine details, and high-quality surface finishes. It is commonly used in industries such as aerospace, automotive, jewelry, and art for creating intricate and precise metal parts and sculptures. Our Sipx Casting offers fine lost casting service for clients all over the world.
What is Lost wax casting?
Lost wax casting is a near-final form process that can produce precision castings. It has a long history in China and is one of the major contributions made by China to the world foundry industry. Since the 1990s, Chinese foundry engineers have fully absorbed new technologies and new processes in lost wax casting from aboard, which has made the application of lost wax casting in industrial production increasingly widespread. In order to help foreign buyers learn more about lost wax casting and better understand our company’s lost wax casting technology, we made this presentation.
We summarized the typical processes of various precision castings, proposed corresponding process design principles and design methods, and listed successful cases of typical precision casting process design.
Starting from the basic technology, we have provided a detailed interpretation of the details in producing lost wax castings, including principle descriptions, process parameter specifications, and application cases in factories. We have also introduced new technologies, materials, and operation guidelines, and we are committed to techniques to improve the quality of precision castings.
This presentation gets strongly support from many senior engineers, and I would like to express our heartfelt thanks
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Lost wax casting manufacturing processes
Step 1: Lost wax mold design
According to the requirements of the casting parts drawing to design mold.
Step2: Manufacturing mold:
According to the mold tooling design drawings to manufacture molds. the mold material normally is iron steel or aluminum.
Step3: Manufacturing the lost wax mold
Using a hydraulic wax injection machine or an air-driven wax press, injecting liquid wax into the press to make a wax mold.
Step4: Wax assembly module
The wax mold is welded or glued to the precast wax stick to form a module
Step5: Degreasing
Immerse the mold in a special degreasing solution to remove the oil and release agent on the surface of the wax mold, so as to increase the adhesion of the wax mold.
Step6:Manufacturing shell
Apply fire-resistant coating(slurry) on the surface of the module, and sprinkle a layer of sand(zircon sand, corundum sand, silica sand, etc.).
Step7: Lost wax casting
Heating the already made mold shell in steam or hot water, melting all the wax molds to obtain a mold shell with internal cavities.
Step8: Shell baking
Placing the shell in a high-temperature oven for high-temperature baking to remove residual wax, various volatile substances and water from the shell.
Step9: Liquid metal casting
Pouring qualified high-temperature metal liquid that has been melted with chemical components into a fully baked hot mold shell
Step10: Deburring and cleaning
deburring with hand tools or virbratory deburring machines, removing sand, cutting the castings after pouring and gating, followed by other cleaning and post-treatment processes.
Step11: Inspection
All lost wax casting parts must be checked then could put into warehouses.
Step12: Packing and transportation
Packed according to client’s needs. Keep safe transportation.
Subsequent processing after casting
Customized Machining Service
For manufacturers in some industries, including but not limited to Medical, Automotive, Aerospace, Elevator, Jewelry, and Optic, their products usually request custom Machining, such as CNC machining, drilling, milling, grinding and lathing even after precision casting. we have great experience and equipment to precisely machine tight-tolerance casting parts and components. We offer customized Machining service with ISO 9001 certified and ITAR registered to exceed rigorous standards and unique demands, all while ensuring rapid production, top-notch quality, and cost efficiency.
Machining Quality & Certifications
- IAF 16949 / ISO 9001:2015 certified
- 99.9% on time delivery and Average 7 days turnaround machining time
- wide range options of machining materials
- Multiple options of machining technology: CNC Machining, Lathing, Drilling, Milling, Grinding and Welding etc.
- Specialized in machining precision casting parts.
CNC Machining Materials
| Aluminum | 2024, 5083, 6061, 6063, 7050, 7075, etc. |
| Copper Alloy | brass 360, 101 copper, 110 copper, 932 bronze, zinc, etc. |
| Titanium Alloy | grade 2, grade 5, etc. |
| Stainless Steel | 303, 304, 410, 17-4, 2205 Duplex, 440C, 420, 316, 904L, etc. |
| Superalloy | Kovar,Hastelloy，Inconel,monel,etc |
| Zinc Alloy | 3#,6#,9# etc., |
| Engineering Plastic | POM (Delrin), ABS (Acrylonitrile Butadiene Styrene), HDPE, Nylon, PLA, |
| PC (Polycarbonate), PEEK (Polyether Ether Ketone), PMMA (Polymethyl Methacrylate or Acrylic), | |
| PP (Polypropylene), PTFE (Polytetrafluoroethylene), etc. | |
| Other | Other CNC machining materials: Graphite, VeroClear |
Machining Capabilities
- CNC Lathing and Milling Machine
- CNC Swiss Turn by Tsugami
- High Speed Drilling-Tapping Machine
- MAZAK 5 Axis Turning-Milling Machine
- CNC Milling Turning Centers
- Multi Spindle Cam Automatics
- CNC Swiss Turning Machine
- DMU 5 Axis CNC Machine
Dimension Tests
Chemical & Physical Tests
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Nondestructive Tests
Special Required Tests
Chapter 1
Lost wax casting process has the following advantages and Limitations:
1.1- Advantages
1.1.1-Tolerance
High dimensional accuracy and small surface roughness of lost wax castings. Due to the use of precise and smooth fusible patterns in lost wax casting, it achieves an integral mold shell without parting lines. It also avoids dimensional errors caused by processes like mold release, core removal, and assembly in sand casting. lost wax castings have sharp corners and can achieve dimensional accuracy of CT4~6 grade, with a surface roughness of Rao.8~1.25um. Therefore, castings produced by lost wax casting are closer to the final shape of the parts, reducing the amount of machining required and saving on metal material consumption.
1.1.2-Structure
Lost wax casting, as known as investment casting, is suitable for casting complex and precise structures. It can produce castings that are difficult to produce using other methods, such as various types of turbines, impellers, hollow blades, directionally solidified blades, single crystal blades, etc. It can also cast small components with a wall thickness of 0.5mm, minimum casting hole size of 1mm, weight as small as lg, up to 1000kg, and overall dimensions exceeding 2000mm. Moreover, it allows for the integration of multiple parts into a single casting.
1.1.3-Material
No restrictions on alloy materials. Various alloy materials such as carbon steel, alloy steel, stainless steel, high-temperature alloys, copper alloys, aluminum alloys, magnesium alloys, iron alloys, precious metals, and cast iron can be used in lost wax casting. Especially for alloys that are difficult to machine, lost wax casting is a more suitable process.
1.1.4-Batch Quantity
lost wax casting can be used for both large and small-batch production. Since metal molds are commonly used to produce the lost wax casting patterns, it is suitable for mass production. However, using inexpensive gypsum molds, low melting point alloy molds, or silicone rubber molds (commonly used for art and jewelry casting) can also make it applicable for small batch
1.2-lost wax casting has the following limitations:
It is most suitable for producing medium to small castings with a maximum through-hole diameter of 3-5mm, maximum blind hole diameter of 5mm, minimum casting slot width of 2.5mm, and minimum groove depth of 5mm.
- The production cycle is relatively long.
- The cooling rate of the castings is slow, which can lead to coarse grain structure in the castings and surface decarburization in carbon steel castings.
- Requirements for Mold Materials in Lost wax Casting(1) Melting Point: The melting point and solidification temperature range of the mold material should be moderate, with a melting point generally ranging from 50 to 80° The solidification temperature of the mold material is usually selected between 5 and 10°C to facilitate the preparation of the mold material, mold making, and wax removal processes.
- Thermal Stability: Thermal stability refers to the ability of the mold material to resist softening and deformation as the temperature increases. The thermal stability of wax-based mold materials is often expressed by the softening point. It is the temperature at which the deformation (deflection) of a standard cantilever specimen reaches 2mm after heating and insulation for 2 hours. The softening point of the mold material should generally be at least 10°C higher than the temperature of the mold-making workshop.
- Shrinkage: To ensure that the lost wax casting achieves the required dimensional accuracy, the mold material should have low shrinkage, generally less than 1%. High-quality mold materials can have linear shrinkage rates below 0.5%. A small shrinkage rate corresponds to a small expansion coefficient, which also helps prevent cracking of the shell during wax removal.
- Strength: The mold material should have sufficient strength at room temperature to ensure that the lost wax casting does not deform during the mold-making and shell-making processes.
Chapter 2
Lost Wax Casting Wax Mold
2.1-Requirements of Wax Mold Materials for lost wax Casting
2.1.1-Melting Point:
The melting point and solidification temperature range of the mold material should be moderate, generally ranging from 50 to 80°C for the melting point and 5 to 10°C for the solidification temperature. This facilitates the preparation of the mold material, mold making, and dewaxing process.
2.1.2-Heat Stability:
2.1.3-Shrinkage Rate:
To ensure that the lost wax casting achieves the required dimensional accuracy, the mold material should have a small shrinkage rate, generally less than 1%. High-quality mold materials can have a linear shrinkage rate of below 0.5%. A small shrinkage rate results in a low expansion coefficient and also helps prevent the shell from cracking during dewaxing.
2.1.4-Strength:
The mold material should have sufficient strength at room temperature to ensure that the mold does not break or fracture during the production processes of mold making and shell building. For small castings, the tensile strength of the mold material should be greater than 1.4MPa (14kgf/cm2), and for large castings, it should not be less than 2.5MPa. If the mold material is tested for flexural strength, it should be greater than 2.0MPa, preferably between 5.0 and 8.0MPa.
2.1.5- Hardness:
The mold material surface should have a certain hardness to prevent damage or abrasion during the production process. The hardness of the mold material is usually indicated by the penetration degree (penetration degree: 1 degree = 1/10mm). The surface hardness of high-quality mold materials can reach 4 to 6 degrees. However, excessively high hardness can lead to poor machinability and brittleness.
2.1.6-Flowability:
The mold material should have good flowability to facilitate filling the mold cavity under pressure, achieving sharp edges, accurate dimensions, and a smooth and polished surface of the lost wax casting. It also facilitates the flow of the mold material out of the shell during dewaxing.
2.1.7- Wetting Property:
The mold material should wet the refractory material well and form a uniform covering layer. The wetting property of the mold material can be measured by the wetting angle between the lost wax casting and the binder.
2.1.8- Ash Content:
The residue after burning the mold material is called ash content. After the shell is calcined, the residual mold ash in the cavity should be minimal, generally less than 0.05% (mass fraction), to avoid affecting the surface quality of the casting.
2.1.9-Weldability:
Most lost wax casting assemblies are welded, so the mold material should have good weldability to prevent fractures at the welding points during transportation and shell building processes.
2.2-Wax Mold Materials
2.2.1-Wax-based Mold Material
Wax-based mold material is actually a mixture of paraffin wax and stearic acid. The commonly used formula is 50% paraffin wax and 50% stearic acid. The requirements for the ingredients are that the paraffin wax (CnH2n+2) should have a melting point of around 58°C and should be refined or semi-refined from paraffin wax. The stearic acid (C17H35COOH) should be of grade one (block form).
Paraffin wax is the main component of the mold material. The addition of stearic acid is because stearic acid molecules are polar, and they have good wetting properties in coatings. They can improve the coating ability of the mold material and enhance its thermal stability. Liquid paraffin wax and stearic acid have good miscibility. This type of mold material has a low melting point, making it easy to prepare, mold, and dewax. It has a high wax recovery rate and good reusability.
Changing the ratio of paraffin wax and stearic acid will affect the performance of the mold material. Increasing the paraffin wax content by 10% can increase the strength of the mold material. However, when the paraffin wax content exceeds 80%, the surface of the mold material is prone to foaming, and the surface quality of the molded pattern is poor. It also reduces the coating ability and flowability of the mold material. Increasing the stearic acid content by 10% improves the coating ability, flowability, and thermal stability of the mold material. However, when the stearic acid content exceeds 80%, the strength and toughness of the mold material decrease significantly, so it should not be used.
The strength and thermal stability of paraffin wax stearic acid mold material are not high (softening point is 31°C). Moreover, during use, stearic acid is prone to displacement reactions with active metals, as well as neutralization reactions with alkalis or alkaline oxides, forming water-insoluble soap (stearic acid salts), which causes the mold material to deteriorate. Additionally, the sticky soap residue on the cavity surface can affect the surface quality of the castings. Since the saponification reaction consumes some stearic acid in the mold material, adding new stearic acid when reusing the mold material is beneficial for stabilizing the performance of the mold material.
The performance of paraffin wax stearic acid mold material is not only related to the ratio of the ingredients but also influenced by the melting point of the paraffin wax. If paraffin wax with a melting point above 60°C is used instead of the 58°C paraffin wax, the strength and thermal stability of the mold material are significantly improved, and the shrinkage rate is reduced. Therefore, the performance of the mold material can be enhanced.
Although the paraffin wax stearic acid mold material has advantages such as convenient preparation, easy molding and demolding, and good reusability, it also has the disadvantages of low thermal stability and susceptibility to deformation, especially prone to saponification and deterioration during production. This type of mold material needs to undergo recycling treatment before it can be reused. The residual acid solution in the recycling process is prone to environmental pollution. Therefore, in recent years, various wax-based mold materials without stearic acid have been introduced.
2.2.2-Paraffin Low Molecular Weight Polyethylene Mold Material
The composition of the paraffin low molecular weight polyethylene mold material is 95% paraffin and 5% low molecular weight polyethylene. This type of mold material has a melting point of 66 °C and a softening point of approximately 34 °C. The molecular weight of the low molecular weight polyethylene is about 2000-5000. It has good compatibility with paraffin. Using low molecular weight polyethylene instead of stearic acid-based wax material has advantages such as high strength, good toughness, smooth mold surface, stable chemical properties, no saponification after use, and convenient material recovery. This type of mold material has a higher viscosity, so it is necessary to appropriately increase the temperature of the paste-like material and the wax injection pressure during molding.
In the wax-based acid-free mold material, materials such as polyethylene, EVA, lignite wax, montan wax, and rosin are added. Low-density polyethylene has a low solubility in paraffin, generally not exceeding 10%. However, the smaller the molecular weight of polyethylene, the greater its solubility in wax material. Therefore, low molecular weight polyethylene and EVA with a molecular weight of 2000-5000 are more soluble than low-density polyethylene. Moreover, the molecular structure of polyethylene is similar to that of paraffin, so adding it to wax-based mold material can act as a crystallization nucleus, refine the crystals of paraffin, and improve the mechanical properties of the mold material.
Therefore, adding low molecular weight polyethylene to paraffin-based mold material can enhance the strength and heat resistance of the mold material. However, excessive addition may result in increased shrinkage without significant improvement in performance. Similar effects can be achieved by adding EVA. Practical application has shown that polyethylene exhibits aging characteristics over long-term use, which deteriorates the performance of the mold material. Adding lignite wax can improve the thermal stability of the mold material, but it also increases the melting point and injection temperature of the mold material.
Polyethylene and other polymers have both crystalline and amorphous structures. In other words, they have a unique structure in which crystalline and amorphous regions coexist. Within the polyethylene spherulites, the polymer chains are interconnected, with each polymer chain passing through several crystalline and amorphous regions. Due to the presence of these interconnecting chains, the strength of polyethylene is much higher than that of wax materials.
In addition to polyethylene and ethylene-vinyl acetate copolymer (EVA), polystyrene can also be added to wax materials. Polystyrene has a high melting point, is less sensitive to temperature changes, has lower thermal deformation than wax materials, higher strength and hardness, lower shrinkage, and higher transparency. Adding polystyrene to the mold material can improve its strength and softening temperature. However, due to reasons such as high viscosity and poor demolding properties, its application is limited.
What is lost wax casting and how is it different from other casting methods?
Lost wax casting is a manufacturing process that involves creating a mold, pouring molten metal into the mold, and then removing mold to reveal the finished part. It is different from other casting methods in that it allows for the production of highly complex and intricate parts high precision and accuracy.
What industries use lost wax casting?
A wide range material can be used in lost wax casting, including stainless steel, aluminum, copper, brass, and various alloys-performance materials such as titanium and Inconel can also be used.
What industries use lost wax casting?
Lost wax casting is used in various industries including aerospace, automotive, medical, military, and jewelry.
What should I look for in a lost wax casting manufacturer?
When choosing a lost wax casting manufacturer, it is important to consider factors such as quality of products, experience and expertise, production capacity, customer service and support, price competitiveness.
How can I get a quote from a lost wax casting manufacturer?
To get a quote from a lost wax casting manufacturer, you typically need to provide them with the part design, material requirements and expected production volume.
What is the typical lead time for lost wax casting?
The typical lead time for lost wax casting varies depending on the part complexity and production volume, but can range from a few weeks to several months.
How can I ensure the quality of my investment cast parts?
To ensure the quality of investment cast parts, is important to work with a reputable manufacturer that uses quality control processes and has a track record of producing high-quality.
What are some common defects that can occur in lost wax casting?
Common defects in lost wax casting include porosity, shrinkage, cracks, and surface irregularities.
What is the cost of lost wax casting compared to other manufacturing methods?
Lost wax casting is generally a more expensive manufacturing method compared to casting methods, but it offers benefits such as the ability to produce complex parts with precision and accuracy.
What is the minimum order quantity for lost wax casting?
The minimum order quantity for lost wax casting varies depending on manufacturer and part complexity.
What post-casting services do lost wax casting manufacturers offer?
Lost wax casting manufacturers typically offer post-casting services such as machining, surface finishing, and assembly.
What is the typical tooling cost for lost wax casting?
The typical tooling cost for lost wax casting depends on the part complexity and production volume, but can range from a few thousand to tens of thousands of dollars.
What is the maximum wall thickness for lost wax casting?
The maximum wall thickness for lost wax casting depends on the material and part geometry but is typically around 1 inch.
What is the maximum weight limit for lost wax casting?
The maximum weight limit for investment also depends on the material and part geometry, but can range from a few ounces to several hundred pounds.
Can lost wax casting be used to produce parts with internal cavities?
Lost wax casting can be used produce parts with internal cavities using ceramic cores.
What is the typical surface finish for investment cast parts?
The typical surface finish for investment cast parts is around -250 RMS (root mean square) but can be improved additional surface finishing processes.