Lost Wax Casting: 2024 Guide to Process & Getting Started

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Lost wax casting, also known as "investment casting", is a traditional technique from ancient China, which has been further improved with the help of modern technology. This guide will introduce you to this wonderful magic from the ancient East in a simple and easy-to-understand way.

 

Lost wax casting, also known as the lost wax method or lost wax investment casting, is a production technique that originated in ancient China. This method involves creating a detailed wax model, which is then encased in a ceramic shell. Once the wax is melted away, molten metal is poured into the mold, resulting in a highly detailed metal object. Despite its ancient origins, this technique remains one of the most effective ways to capture intricate details in metal products today.

 

 

The lost-wax casting process can differ depending on the industry and application, but it generally consists of the following steps. Cast parts can be made from a wax model itself, called the direct method, or from replicas of the original wax model, called the indirect method. The direct method jumps from step one straight to step four.

Step 1: Model-making

The engineer carves a design out of wax. The size and complexity of the wax model is limited to the wax carver&#;s skill, and the capacity of his casting equipment.

Step 2: Creating a mold

A caster then casts this model and polishes the casting to produce a &#;master&#; pattern. The master model is used to make a wax mold out of rubber, which is heated and &#;vulcanized&#; around the master casting to make a flexible wax mold.

Step 3: Producing wax patterns

Molten wax is injected or sometimes poured into the rubber mold. This can be done over and over to make copies of the original design.

Step 4: Assembling the wax pattern

Sprues are added to the wax copies and they&#;re connected to create a tree-like structure, which provides paths for the molten wax to flow out and molten metal to later fill the cavity.

Step 5: Applying investment materials

The wax tree is either dipped into a slurry of silica, or put into a flask and surrounded by the liquid investment plaster.

Step 6: Burnout

After the investment material dries, the flask is placed upside down into a kiln, which melts the wax leaving a negative cavity in the shape of the original model.

Step 7: Pouring

The investment mold is further heated in a kiln to reduce the temperature difference with the molten metal. Metal is melted and then poured, using gravity or vacuum pressure to pull the metal into the cavity.

Step 8: Devesting

Once the molten metal has cooled somewhat, the investment mold is quenched in water to dissolve the refractory plaster and release the rough casting. . The sprues are cut off and recycled, while the casted parts are cleaned up to remove signs of the casting process.

Step 9: Finishing

The casted parts are filed, ground, machined, or sandblasted to achieve final geometry and surface finish. Where necessary, the cast parts are also heat-treated to enhance the mechanical properties of the material.

 

One of the reasons lost wax casting is so popular is that there is no limit to the number of metals that can be applied to the process. We recommend the most common types of metal materials for you.

Stainless steel

The main alloys of stainless steel are chromium, nickel and molybdenum, which determine the grain and mechanical properties of the casting. The way the alloys are combined determines the heat and corrosion resistance of the casting.

Steel

Carbon, low alloy and tool steels are used in the aerospace, agricultural, medical and firearms industries, to name a few. Steel is chosen for lost wax casting because it is economical, available in a variety of grades, and its ductility can be adjusted through heat treatment.

Ductile Iron

Ductile iron castings have excellent surface hardness, modulus of elasticity, corrosion resistance and a strong strength-to-weight ratio. The biggest benefits of ductile iron are that it is cost-effective and offers a wide range of design freedom.

Aluminum

Aluminum is the ideal metal for lost wax casting due to its machinability and corrosion resistance. When it is alloyed with other metals and heat-treated, it develops extraordinary strength that rivals that of mild steel.

Cobalt

Cobalt is naturally resistant to oxidation and has a hard and shiny surface. It prevents oxidation by passivating the oxide film. Cobalt's resistance to corrosion, heat and wear makes it ideal for lost-wax casting and is used to produce parts for the aerospace, automotive industry and military applications.

Brass

Brass is a copper alloy known as red brass or brass, and the lost-wax casting is used for plumbing fixtures and door hardware. The main characteristics of brass are its appearance and quality of finishing and polishing. One disadvantage of using brass is its lead content, which limits its use.

Bronze

The properties and quality of bronze depend on the alloy it is combined with. Added elements to bronze can enhance its performance and quality.

Nickel

Nickel, containing nickel, chromium and molybdenum, has exceptional strength and resistance to heat, wear and corrosion. It was chosen as the cast metal because it is easy to weld and fabricate, and it is resistant to cracking and corrosion.

 

 

Automotive Parts

Lost wax casting is extensively used in the automotive industry to produce a wide range of precision parts. Components such as engine blocks, transmission cases, and intricate brackets are often made using this method due to its ability to create complex shapes with high accuracy. The process ensures that parts are durable, resistant to wear, and able to withstand the demanding conditions of automotive applications.

Construction Hardware Casting

In the construction industry, lost wax casting is employed to manufacture various hardware components, including hinges, locks, and structural connectors. The method allows for the production of parts with fine details and strong mechanical properties, which are essential for the safety and integrity of construction projects. The flexibility of lost wax casting also enables the creation of custom-designed parts tailored to specific architectural needs.

Bathroom Hardware Casting

Bathroom fixtures and hardware, such as faucets, showerheads, and towel racks, are often produced using lost wax casting. This process allows manufacturers to create products with intricate designs and smooth finishes, which are not only aesthetically pleasing but also highly functional. The corrosion resistance and durability of the casted materials make them ideal for use in the moist environment of bathrooms.

Agricultural Equipment Casting

Bathroom fixtures and hardware, such as faucets, showerheads, and towel racks, are often produced using lost wax casting. This process allows manufacturers to create products with intricate designs and smooth finishes, which are not only aesthetically pleasing but also highly functional. The corrosion resistance and durability of the casted materials make them ideal for use in the moist environment of bathrooms.

Hydraulic Equipment Casting

Hydraulic systems rely on precise, robust components to function effectively, and lost wax casting is a preferred method for producing these parts. Items such as valves, pumps, and cylinder heads are commonly cast using this technique, ensuring they meet the strict tolerances required for hydraulic applications. The process allows for the production of high-quality parts that can withstand the high pressures and stresses typical of hydraulic systems.

 

We will use tables to outline some of the content to compare these two different metal processes.

Comparison Dimension Lost wax Forging Definition Casting is a metal-working process where the metal is first heated till it melts, then poured into a mould and made to cool to obtain the shape. Forging involves the use of localized compressive forces on the solid material in order to create desired shapes. Strength Casted material is low in strength as they are poured into a cavity which lets the material take its shape freely. Forged material are stronger as they possess a definite grain structure which is pressed with force, increasing their mechanical strength. Suitability for Hollow Shapes Casting is often preferred for the production of material containing hollows spaces or cavities. Forging excludes cavities and porosity from their compositions. Uniformity The casted material is not always uniform Forged material can be made to a uniform structure preserving consistency in shape. Size Restrictions Casting doesn&#;t have any size or shape limitations as all material will be melted before putting them into shape. Materials weighing up to 50kgs can be forged yet higher power is required if material to be forged is heavier than 50kgs. In this case, casting would be the alternative. Level of Complexity Casting is able to produce complex patterns and shapes. Forging is more focused in producing uniform and simple material. Cost Casting uses relatively inexpensive equipment. Machines used for forging such as heavy duty industrial dies are more expensive.

 

1. Precision and Complexity

One of the most significant advantages of lost wax casting is its ability to produce highly complex and detailed parts with excellent precision. This process allows for intricate geometries and fine details that would be difficult or impossible to achieve with other casting methods. The wax model can capture every nuance of the design, resulting in a finished product that closely matches the original specifications.

2. Versatility in Material Choices

Lost wax casting can be used with a wide variety of metals and alloys, including steel, aluminum, bronze, and titanium. This versatility allows manufacturers to select the best material for the application, whether it requires high strength, corrosion resistance, or a specific aesthetic finish.

3. Minimal Waste

The process of lost wax casting is highly efficient, with minimal material waste. The wax models can be reused, and any excess metal from the casting process can often be recycled. This efficiency not only reduces costs but also makes lost wax casting an environmentally friendly option compared to other manufacturing methods.

4. Excellent Surface Finish

Lost wax casting produces parts with a smooth surface finish, often requiring little to no additional machining or finishing. The molds used in this process can capture fine details and create surfaces that are free from defects, reducing the need for further processing and improving the overall quality of the final product.

5. Design Flexibility

Lost wax casting offers considerable flexibility in design, allowing for the production of parts that may combine multiple components into a single piece. This capability can reduce assembly times and costs, as well as improve the structural integrity of the final product by eliminating the need for welds or joints.

6. Dimensional Accuracy

The precision of lost wax casting results in parts with tight tolerances and consistent dimensions. This accuracy is crucial for applications where exact measurements are necessary, such as in aerospace, automotive, and medical industries. The ability to maintain dimensional accuracy across large production runs ensures that each part meets the required specifications.

7. Cost-Effective for Small to Medium Runs

While lost wax casting may have higher initial setup costs compared to some other casting methods, it becomes cost-effective for small to medium production runs. The ability to produce high-quality, detailed parts with minimal post-processing requirements can offset the initial costs, especially when producing parts with complex geometries or specific material properties.

 

When Is It Appropriate to Use Lost Wax Casting

Complex Geometries: Lost wax casting is capable of producing extremely complex and detailed parts that may contain intricate cavities, thin walls, complex contours, or small decorative features. The process faithfully replicates complex designs without the limitations of traditional casting methods through the use of wax patterns and ceramic shells. It is particularly suitable for fields such as aerospace engine blades, complex mechanical components, and high-precision medical devices.

High Dimensional Accuracy: The lost wax casting process provides excellent dimensional accuracy and tolerance control. Castings typically achieve tolerances of ±0.1mm or finer, which reduces or completely eliminates the need for subsequent machining. Due to this high accuracy, lost wax casting is especially suitable for applications requiring strict dimensional and shape control, such as precision mechanical parts, automotive engine components, and high-performance valves.

Excellent Surface Quality: The process is capable of producing castings with smooth surfaces and rich details, usually without the need for additional surface treatment. This surface finish makes lost wax castings ideal for manufacturing parts with high requirements for surface appearance and feel, such as decorative parts, precision instruments, and medical device components. The smooth surface not only enhances the product's appearance quality but also improves its corrosion resistance and performance.

Medium to Large Batch Production: Despite the high initial mold and tool investment, lost wax casting is cost-effective in medium to large batch production. For orders with production quantities of more than 25 pieces, the reduced post-processing time and labor costs often significantly reduce the overall production cost. The process provides consistent high quality and stability in mass production, making it suitable for fields such as automotive, aerospace, military, and industrial equipment that require high precision and consistency.

 

Let's take a look at some of the cost drivers associated with lost wax casting.

Design Complexity of Castings

Part design is a major factor affecting the cost of lost wax casting. Simple part designs with no internal passages, holes or features help reduce costs for customers.

Material selection

The metal of choice is another cost driver for lost wax casting. There are different grades of common metals and alloys. So even with the same metal, a higher purity alloy will cost more than a lower grade alloy.

Quantity of shell-building layers

As the shapes of investment castings are always different, there will exist differences in shell-building layers. For more complex structures, more shell-building layers will be needed, which will cost more.

 

Q1. How much shrinkage in lost-wax casting?

Shrinkage in lost-wax casting typically ranges from 1% to 2%, depending on factors like the type of metal, part complexity, and mold material. Metals like steel tend to shrink more than aluminum or bronze, and intricate designs with varying wall thicknesses can lead to differential shrinkage. Careful consideration of these factors during the design and casting process is essential to minimize dimensional changes and ensure accuracy in the final product.

Q2. What is the maximum size and weight of parts that can be produced using lost wax casting?

The size and weight of parts produced via lost wax casting are limited by the capacity of the casting equipment and the feasibility of creating large wax patterns. Generally, lost wax casting is used for parts ranging from a few grams to several kilograms, but advancements in technology have allowed for larger components to be produced, especially in industries like aerospace and automotive.

Q3. What are the limitations of lost wax casting when it comes to complexity and design?

While lost wax casting excels in producing complex and detailed parts, it does have limitations. Extremely thin sections (below 1mm) or parts with intricate internal channels might be challenging due to the fragility of the wax patterns and the risk of defects during the investment and burnout stages.

Q4. How does lost wax casting handle high-performance alloys, and what are the challenges involved?

Lost wax casting is well-suited for high-performance alloys, including those that are difficult to machine or form by other methods. However, casting high-temperature alloys like superalloys can pose challenges, such as increased mold material costs, higher burnout temperatures, and the need for specialized equipment to handle the molten metal.

Q5. What is the typical lead time for producing parts via lost wax casting?

Lead time for lost wax casting can vary depending on the complexity of the part, the production run size, and the foundry's capabilities. Generally, the lead time ranges from a few weeks to several months, factoring in mold creation, casting, and any necessary finishing processes.

Q6. How does the lost wax casting process accommodate high-production volumes?

TLost wax casting is more suited for low to medium production volumes due to the labor-intensive process of creating wax patterns and molds. However, for high-production volumes, multi-cavity molds and automated pattern-making techniques can be employed to increase efficiency and reduce costs per part.

 

Besser Casting is a leading investment casting company in China. We have more than 20 years of experience in the field of lost wax casting. We have a professional engineering team that oversees and handles the whole process to ensure smooth operation.

In addition, we confirm that all products meet the tolerances specified by ISO standards.

This strict adherence ensures that all of our castings are to exact dimensions.

Our sole purpose is to provide you with quality lost wax casting products at an affordable price.

If you place an order, our professionals will discuss with you the finer details of what you would like to be fulfilled.

 

Lost wax casting, or investment casting, is a casting process that uses a wax pattern to create the initial design for a part to be produced in a ceramic mold.

Lost wax casting can produce a variety of complex and intricate parts with excellent tolerances.

Lost wax casting is used to produce parts that require tight tolerances with thinner walls and exceptional surface finishes that require very little after process finishing.

With competitive price and timely delivery, Yitai sincerely hope to be your supplier and partner.

The casting process for lost wax casting involves multiple steps that begin with the creation of the pattern, or master, which is made from wax.

Lost wax casting uses a wide assortment of metals to create parts with exceptional accuracy and tolerances.

Lost wax casting is a highly technical process, and with more than 20 years of manufacturing experience, we are able to provide you with lost wax investment casting services. So feel free to inquire about our services and one of our team members will discuss your project needs with you.

 

Lost-wax investment casting process is a process in which one-off, precision, one-piece ceramic shell molds are used to produce a casting, made from one-off patterns using liquid sands. Before pouring the melt, the model is removed from the ceramic mold by melting, burning, dissolving, or evaporation. To remove the remnants of the model and harden the form, it is heated to high temperatures. 

By calcining the ceramic mold before pouring, the almost complete exclusion of its gas content is achieved, and the fallibility of the mold with the melt improves. 

 A model or a link of model 2 is made in a detachable mold 1, the working cavity of which has the configuration and dimensions of an investment wax pattern with allowances for shrinkage of the model composition and casting material, as well as cutting. 

The model is made from materials that either have a low melting point (wax, stearin, paraffin) or are able to dissolve (carbamide) or burn without the formation of solid residues (polystyrene).

Finished Model Molten metal Wax pattern

Finished models or links of models are assembled into block 3, which has models of the elements of the gating system from the same material as the investment wax pattern model. The block of models consists of links, the central part of which forms models of feeders and a riser. 

Models of the bowl and the lower part of the riser are made separately and installed in the block during its assembly.

Wax Patterns with Metal Casting

To obtain shell molds, the resulting block of models is immersed in a container with liquid molding sand &#; a suspension consisting of dust-like refractory material, for example, powder-like quartz or electrocorundum, and a binder. As a result, a layer of suspension 4 with a thickness of less than 1 mm is formed on the surface of the model. 

To strengthen this layer and increase its thickness, layers of refractory granular material 5 (fine quartz sand, electrocorundum, granular fireclay) are applied to it. The operations of applying the suspension and sprinkling are repeated until the shell of the required thickness is obtained on the model (3&#;10 layers). In this case, each coating layer is dried in air or in ammonia vapor 6, which depends on the binder.

After drying the shell form, the model is removed from it by melting, dissolving, burning or evaporation. 

 In order to strengthen the mold before pouring, it is placed in a metal container and covered with refractory material 8.

Wax Pattern and Invest Material

To remove the remnants of models from the mold and strengthen the binder, the container with the shell mold is placed in oven 9 for calcination. The calcination of the mold is carried out at a temperature of 900 &#; ° C, then the calcined mold 10 is removed from the furnace and poured with a melt.

 After the investment wax pattern has solidified and cooled to a predetermined temperature, the mold is knocked out, the castings are cleaned of ceramic residues, and sprues are cut off from them. In many cases, shells are calcined in a furnace until they are filled with refractory material, and then they are filled with preheated refractory material to strengthen them.

 This makes it possible to reduce the duration of mold annealing before pouring and reduce energy consumption. So, for example, a technological process was organized on automatic lines for the mass production of investment wax patterns.

Dimensional Accuracy in Lost Wax Process

The low surface roughness of the mold with a sufficiently high refractoriness and chemical inertness of the material makes it possible to obtain an investment wax pattern with a high-quality surface. After cleaning from the remains of the shell mold, the surface roughness of the castings ranges from Rz = 20 µm to Ra &#; 1.25 µm.

The absence of a mold split, the use of materials for the manufacture of models that make it possible not to disassemble the mold for their removal, the high fire resistance of the mold materials, as well as heating it to high temperatures before pouring, help to improve fallibility.

The ceramic shell and sand casting make it possible to obtain investment wax patterns of the most complex configuration, as close as possible or corresponding to the configuration of the finished part, from almost all known alloys. 

Produce Wax Patterns and its manufacturing process

The achievable coefficient of the accuracy of the investment casting process by weight (KTM = 0.85 &#; 0.95) contributes to a sharp reduction in the volume of cutting and metal waste into chips. 

The accuracy of the investment casting process can correspond to accuracy classes 2, machining allowances for castings up to 50 mm in size usually do not exceed 1 mm, and for investment casting process up to 500 mm in size &#; about 3 mm.

Features of the formation of the investment casting process and their quality

 Obtaining castings in a shell mold is associated with some features, in particular, before molten metal is poured; the mold cavity is heated to relatively high temperatures. This determines the following technological moments.

Small thermal conductivity, heat capacity, the density of shell-shaped materials, and elevated mold temperature reduce the rate of heat removal from the melt, which helps to improve the fallibility of the mold.

Ceramic Slurry with Wax Patterns

 Due to this, it is possible to obtain a complex steel investment casting process with a wall thickness of 0.8 &#; 2 mm with a significant surface area. Improving the fallibility of the mold is also facilitated by the low roughness of its walls, the possibility of using external influences on the melt, such as the field of centrifugal or electromagnetic forces, pouring using a vacuum, etc.

The low intensity of melt cooling in a heated shell mold leads to a decrease in the rate of solidification of castings, an enlargement of the crystalline structure, the possibility of the appearance of massive nodes and thick (6&#;8 mm) walls of shrinkage defects in the central part &#; shells and porosity. Thin walls (1.5 &#; 3 mm) harden rather quickly, and axial porosity does not form in them. 

Multiple Wax Patterns

To reduce shrinkage defects, it is necessary to create conditions for directional solidification and feeding of the investment casting process. Heat treatment is used to improve the crystal structure of castings.

The increased temperature of the mold during pouring contributes to the development of physical and chemical processes on the surface of contact between the investment casting process and the mold.

This can result in both a desirable change in the structure of the surface layer of the investment casting process and an undesirable one, i.e., leading to the appearance of surface defects.

Liquid Investment Material

For example, on carbon steel castings, a characteristic defect is an oxidized and decarburized surface layer up to 0.5 mm deep. The reason for the oxidation and decarburization of the investment casting process is the interaction of atmospheric oxygen with the metal of the investment wax pattern during its solidification and cooling. 

The main factors influencing the decarburization process are the composition of the gaseous medium surrounding the investment casting process, the temperature of the casting and mold, and the carbon content in the investment casting process.

Also, this technology is used in the casting of heat-resistant hard-to-cut alloys (turbine blades), corrosion-resistant steels, and carbon steels in mass production (automotive industry).

Lost-wax investment casting process 

Lost-wax investment casting process is the process of obtaining castings from molten metal in molds, the working cavity of which is formed due to the removal (outflow) of low-melting material of the model during its preheating.

Investment Casting Advantages:
The lost wax investment casting process provides accurate and complex castings from various alloys weighing from 0.02 to 15 kg with a wall thickness of 0.5 to 5 mm.

Technological process of investment casting process:

Investment models are made in metal molds from model compositions, including paraffin, wax, stearin, and fatty acids. The composition fills the cavity of the mold well, and gives a clear imprint. After the model composition has hardened, the ceramic mold opens and the model is pushed into cold water.

Then the models are assembled into model blocks with a common gating system by soldering, gluing, or mechanical fastening. From 2 to 100 models are combined into one block.

The model block is immersed in a special liquid refractory mixture, followed by sprinkling with quartz sand. Then the model blocks are dried in air or in ammonia. Usually, 3&#;5 layers of refractory coating are applied, followed by drying of each layer.

Investment material Is Removed

Patterns are removed from molds by immersing the mold in hot water or using heated steam. After removal of the model composition, thin-walled investment casting process molds are placed in a flask, covered with quartz sand, and then calcined in a furnace for 6&#;8 hours at a temperature of 850&#; C to remove residual model composition, water evaporation.

Poured into the Mold

Pouring of ceramic molds according to investment models is carried out immediately after calcination in a heated state. Filling can be free, under the action of centrifugal forces, in a vacuum, etc.

After solidification of the poured metal and cooling of the investment casting process, the ceramic mold is destroyed, the castings are separated from the sprues by mechanical methods, sent for chemical cleaning, washed, and subjected to heat treatment.

Production efficiency and scope

 Based on production experience, the following advantages of the investment casting process method can be distinguished:

1. the ability to manufacture castings of complex configuration from almost any alloy, thin-walled, with low surface roughness, high accuracy by weight, minimal allowances for machining, with a sharp reduction in metal waste into chips;
2. the ability to create complex structures that combine several parts into one unit, which simplifies the technology of manufacturing machines and devices;
3. the possibility of cost-effective implementation of the process in single (pilot) and mass production, which is important when creating new machines and devices;
4. reducing the consumption of molding materials for the manufacture of the investment casting process, reducing the material consumption of production;
5. improving working conditions and reducing the harmful effects of the foundry process on the environment.

Along with the advantages, this method has the following disadvantages:

1. the ceramic mold manufacturing process is multi-operational, labor-intensive and lengthy;
2. a large number of technological factors affecting the quality of the ceramic mold and investment casting process, and, accordingly, the complexity of their quality control associated with this;
3. a large range of materials used to obtain a form (materials for models, suspensions, block sprinkling, support materials);
4. the complexity of manipulatory operations for the manufacture of models and forms, the complexity of automating these operations;
5. increased metal consumption for sprues and therefore low technological yield (TVG).

These advantages and disadvantages determine the effective scope of investment casting into shell molds, namely:

Production of investment casting processes that are as close as possible in configuration to the finished part, to reduce the laboriousness of machining hard-to-cut metals and alloys by cutting, reduce the use of pressure treatment of hard-to-deform metals and alloys, replace labor-intensive welding or soldering operations to increase rigidity, tightness, and reliability of parts and assemblies structures;

production of thin-walled large-sized investment casting process of increased accuracy to reduce the weight of the structure while increasing its strength, tightness, and other operational properties;

Production of the high-precision investment casting process from alloys with special properties and structure.

Precision Casting with Complex Shapes

The production of investment castings is widely used in various branches of mechanical engineering and in instrument making. The use of casting in shell molds to obtain blanks for machine parts instead of making them from forged blanks or rolled products leads to an average reduction in metal waste into chips by 34&#;90%. 

At the same time, the labor intensity of machining is reduced by 25 &#; 85% and the cost of manufacturing parts &#; by 20 &#; 80%. However, it should be taken into account that the economic efficiency significantly depends on the choice of the nomenclature of castings produced by this method.

 Only with the right choice of the nomenclature of parts, the high economic efficiency of this production is achieved.