Lost wax casting, also known as “investment casting,” is the process by which a single metal object is cast from a wax model. It is a highly versatile process that achieves exceptionally detailed results. This guide will cover how to start lost wax casting and what you can create with the process.
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What is lost wax casting?
Lost wax casting builds a mold around a sacrificial wax model. After the mold investment is set, the wax is melted out and forms a cavity where the metal or glass flows in. Using this method of casting captures fine details in both metal and glass. This ancient method has been used since B.C. to visually capture the stories of ancient cultures and religions throughout history.
What is the lost wax process used for?
Lost wax casting is a 6,000-year-old process still used in both manufacturing and fine art. The precision and accuracy of the process have made it an ideal method for producing objects with thin walls, intricate details, and close tolerances. The process is used to create parts for transportation, agricultural, and medical industries, to name just a few. It can be used to create objects from simple to complex in various metals by casting an original wax model or pattern. The wax model makes an expendable mold that can only be used once in casting. This guide focuses on the lost wax casting process with metallic alloys. You can also use lost wax casting techniques to create cast glass objects. To learn more, head to our glass casting guide.
The lost wax casting process in 8 steps
The basic lost wax casting process involves creating a pattern and a mold, then pouring molten metal into the mold. You will then extract the solid metal casting and finish your piece. This process is customizable for different types of metal casting, along with shapes, sizes, and more. The description below is based on smaller-scale casting processes, often used for jewelry. While essentially the same, in larger castings the mold material is made of Ceramic Shell (colloidal silica and various grades of silica), rather than plaster.
Tools and Materials
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Safety gear: leather gloves and protective glasses
- Wax: microcrystalline, paraffin, or beeswax all work well
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Heat gun and texturing tools
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Casting metal
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Investment
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Gram scale
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Rubber mixing bowl
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Volumetric flask for water
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Vacuum chamber
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Kiln for burnout
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Crucible
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Flux
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Torch
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Bucket with water
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Tongs
Create a model in wax
Create your desired design in wax before building a mold around it. This wax model can only be used once. After that, shape it with texturing tools, a soldering iron, and a heat gun. Many experienced wax sculptors swear by repurposing dental tools to sculpt and carve unique designs in wax effectively. Hollow out your wax model if possible.
When shaping your pattern, make sure you account for any anticipated shrinkage when the metal cools. Patterns may also be gated with sprues to allow the molten metal to flow into the mold. This is especially important if your design contains small intricate elements that may not fill with metal during the casting process.
Make your mold
You can make a mold using a combination of plaster and silica. Use a gram scale to measure each ingredient and mix equal parts by weight of plaster, silica, and water until the investment has the consistency of heavy cream. Plaster gives the mold support and silica has a high refractory, so it can withstand a lot of heat.
❗ When working with dry materials, make sure that your work area is well ventilated, and wear a respirator when working with dry investment.
Remove the wax
The easiest way to melt the wax out of a small mold is in a microwave. First, remove any metal clamps you might have added to your mold, then prop it up on clay supports over a small container underneath to collect the wax. Heat in short bursts in the microwave until all of the wax has dripped into the small container. You can also burn out the wax in a kiln.
Choose the metallic alloy
All metal castings are produced from either ferrous or non-ferrous alloys. Alloys are a mixture of elements that provide the best mechanical properties for the final cast’s use. Ferrous alloys include steel, malleable iron, and gray iron. Non-ferrous alloys most commonly used in casting are aluminum, bronze, and copper. If you are working with precious metals in a jewelry studio, you may work with silver, copper, gold, and platinum. Less common, but especially spectacular, are metal castings with iron, which casts molten iron into a ceramic shell or resin-bonded sand mold.
Melt the alloy
Melting processes vary between alloys because each alloy will have a different melting temperature. Essentially, melting consists of placing the solid alloy in a crucible and heating it over an open flame for smaller projects or inside of a furnace for larger amounts.
Pour into the mold
Pour the molten metal into the mold cavity. If it is a small casting, you may simply pour from the crucible where the metal was heated directly into the mold. However, a larger casting may require a small team to support heating the metal inside a furnace and transferring the metal into a larger crucible or ladle before being poured into the mold.
❗ Make sure to follow all recommended safety guidance when pouring molten metal. Wear protective clothing, including natural fiber clothing, long pants and sleeves, insulated gloves, and safety goggles. Work in a well-ventilated space to avoid any risks from dangerous fumes. Ensure you have a chemical fire extinguisher nearby and keep your walkway between the furnace and the mold clear. Allow the mold to solidify before moving on to the next step.
Release the cast from the mold
When the metal has cooled and solidified, you can remove it from the mold. You will want to quench the plaster in water after the metal has solidified. The water will help break away the mold. If you cast it into a ceramic shell, you can break the mold and chip it away using the necessary equipment.
Finish your piece
File and polish your solid metal cast! Finishing techniques include scrubbing away excess mold material in water, breaking off the casting gates with clippers for small objects, or even an angle grinder for large pieces. You can also choose to polish or patina your metalwork to give it color and dimension.
How to learn lost wax casting
At The Crucible, you can learn to cast metals for small or large projects in different types of metallic alloys. The Crucible offers a wide variety of classes teaching lost wax casting and metalworking techniques. So whether you want to learn the fundamentals of casting or something more advanced, The Crucible has you covered.
In our Jewelry Department, you can cast small-scale silver and bronze objects from wax and organic objects. Our Foundry Department guides you in casting larger projects in bronze and aluminum using ceramic shell molds. Lost wax casting doesn’t stop at casting metals—you can even learn to cast glass into molds in our Glass Casting and Coldworking Department.
Lost wax casting classes at The Crucible
Casting Wax to Silver
Learn the ancient process of lost wax casting sculptural jewelry. Experimenting with different types of wax, you will carve, cast, and finish at least one small fetish, pendant, or ring in silver or bronze. Students are encouraged to bring in personal sketches and ideas.
Foundry I: Ceramic Shell Process
Ceramic shell is a mold material used in the lost wax casting method. Learn basic wax-working techniques and explore basic metal finishing in this fascinating course. You will create a wax sculpture and build ceramic shell molds, transforming your original wax piece into bronze or aluminum.
Foundry II: Ceramic Shell Process
This class is for people with metal casting experience who have completed waxes to cast. We can also accommodate 3-D printed PLA (best unpigmented). Students will prepare their patterns, gate them, build the ceramic shell mold, cast in either bronze or aluminum, destroy the mold, and remove the gates.
Bell Casting
Bell Casting introduces participants to bell design and the lost wax foundry technique. In this class, you can design, cast, and finish a bell approximately six inches in diameter. This entry-level class provides a foundation for further exploration in this versatile foundry approach.
Iron Casting
In Iron Casting, you will explore mold construction and preparation while building a sand mold with resin-bonded sand to cast your own iron sculpture. Learn the steps required to prepare the cupola for an iron pour. At the spectacular iron pour event, students prepare iron and coke charges, operate the cupola, and pour molten iron into their new mold.
Design and Make Your Own Waffle Iron
In our Foundry, you can make your own stovetop waffle iron with a waffle pattern of your own design. We will make sand molds and use a cupola furnace to melt the iron. At the spectacular iron pour event, students prepare iron and coke charges, operate the cupola, and pour molten iron into their new mold.
Kiln Casting Glass Sculpture I
In our Glass Casting & Coldworking Department, you can create a glass sculpture using the ancient technique of lost wax. In this class, you will learn wax sculpting techniques to create wax positives that are invested in a refractory material to create a mold. The mold is de-waxed to create a void that is filled with glass melted in a kiln. When cooled the refractory is divested and the wax positive is now glass.
Lost wax casting FAQs
Can I lost wax cast at home?
It is best to start lost wax casting in an established casting studio with a professional instructor. Lost wax casting can involve more advanced equipment that can be costly to set up. The safest and least expensive way to start lost wax casting is in a public class. Once you have experience and a strong understanding of the process and tools involved, you may explore setting up a lost wax casting studio at home.
What metals can you use for lost wax casting?
Lost-wax casting is a highly versatile technique and can be used to cast objects in gold, silver, brass, copper, bronze, and aluminum.
What are the differences between lost wax casting and die casting?
The most significant difference between the die and lost wax casting process is the mold material. Die casting uses a metal mold, which is a nonexpendable mold. Lost wax casting uses a mold made out of plaster or ceramic shell, an expendable mold. In the die casting process, molten metal is forced into a mold cavity with high pressure.
What kind of wax is used for lost wax casting?
Microcrystalline wax is best for modeling because it is pliable and slightly sticky. In addition, it’s medium-soft consistency makes it easy to work with. Paraffin wax can also be used for lost wax casting, but it is not ideal for modeling. Paraffin wax is best used as an additive to harden an already existing wax model. Different kinds of specialty wax can also be used. Each type of specialty wax has a specific purpose, such as carving, modeling, or patching, and requires knowledge of their different melting points.
With an increase in industrial demands and applications, there has been a parallel increase in the demand for complex and high-quality products. Fortunately, there are different types of casting processes that can manufacture complex and precise products for various applications and user needs.
In order to select the right method of casting for your manufacturing requirements, it is beneficial to realize the advantages and disadvantages of these methods. This article provides a brief overview of various types of casting processes and their pros and cons.
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Overview of Casting Process
The casting process is a manufacturing method that produces desired-shape metal parts by pouring molten metal into a mold and solidifying and cooling it to the room temperature. It’s capable of producing complex and intricate parts, irrespective of their sizes.
Casting can produce isotropic metal parts in bulk quantities, as a result, making it suitable for mass production. Furthermore, to meet specific user requirements, there are different types of casting that differ by the material and mold used.
Different Types of Casting Process
There are different types of casting processes, and each process has its own advantages and disadvantages as per the user requirement.
1. Sand Casting Process
Sand casting is a versatile casting process that can be used to cast any metal alloy, ferrous or non-ferrous. It is widely used for mass production in industrial units, such as automotive metal casting parts, like engine blocks, cylinder heads, crankshafts, etc.
The process uses a mold that’s made of silica-based materials, such as naturally-bonded or synthetic sand form the smooth mold surface. The mold surface has 2 parts, cope (the upper half) and drag (the lower half). Molten metal is poured into the pattern using a pouring cup and left to solidify to take the final shape. Finally, trimming off extra metal is done for the finishing of the final metal casting product.
Sand casting has its advantages and disadvantages.
2. Gravity Die Casting
Gravity die casting, also typically known as permanent mold casting, uses reusable molds made of metal, like steel, graphite etc. to fabricate metal and metal alloys. This type of metal casting can manufacture various parts like gears, gear housing, pipe fittings, wheels, engine pistons, etc.
In this process, the direct pouring of molten metal into the mold cavity takes place under the effect of gravity. For better coverage, the die can be tilted to control the filling. The molten metal is then allowed to cool and solidifies within the mold to form products. As a result, this process makes casting of materials like lead, zinc, aluminum, and magnesium alloys, certain bronzes, and cast iron more common.
This casting process works on the bottom-up approach to fill the mold, in contrast, to other pressure casting processes. Although, the process has a higher casting rate than sand casting. But, it is relatively higher in cost due to expensive metal molds. Check its advantages and disadvantages below.
3. Pressure Die Casting
There are two types of pressure die casting depending on the pressure. Namely, the low-pressure die casting and the high-pressure die casting. High pressure die casting is more popular for mass production of complex geometries that require high precision. Whereas, for large and simple parts production, low-pressure die casting is a preferable casting process.
In this type of metal casting, non-ferrous metals and alloys such as zinc, tin, copper and aluminum are injected into a reusable mold coated with a lubricant at high pressure. Thus, high pressure is maintained throughout the rapid injection process to avoid metal hardening. Finally, after completion of the process, extraction of casting and finishing takes place to remove any excess material.
Pressure die casting differs from gravity die casting in the process of filling up the mold. Where pressure die casting uses high-pressure injection of molten metal into the metal mold. The molten metal is then solidified rapidly to produce the required product.
Its advantages and disadvantages are summarized below.
More: Choose A Righ Process Between Die Casting vs Sand Casting for Your Applications.
4. Investment Casting
Investment casting, also known as lost-wax casting, is a process that invests wax pattern with refractory material and a binding agent to shape a disposable ceramic mold, and then molten metal is poured into the mold to make metal castings. Investment casting is an expensive and labor-intensive process and can be used for mass production or in complex castings to produce metal casting products ranging from gears, bicycle trunks, moto discs, and spare parts in blasting machines.
Below summarizes its advantages and disadvantages.
5. Plaster Casting
The plaster casting process is similar to sand casting, except that the mold is made of a mixture called ‘Plaster of Paris’. Due to the low thermal conductivity and heat capacity of plaster, it cools the metal more slowly as compared to sand, which helps in attaining high accuracy, especially for thin cross-section parts. However, it is not suitable for high-temperature ferrous materials.
Particularly, small castings of 30 grams, as well as large castings of 45 kilograms, can be manufactured through the plaster mold casting process. For example, the image below shows a cast component of a section thickness of 1 mm made by this process.
Learn more about its advantages and disadvantages.
6. Centrifugal Casting
Centrifugal casting, also known as roto casting, is a process for industrially manufacturing cylindrical parts with centrifugal forces. This type of metal casting uses a preheated spinning die in which the molten metal is poured. The centrifugal forces help to distribute the molten metal within the die at high pressure.
Three variations of centrifugal casting exist; true centrifugal casting process, semi centrifugal casting process, and vertical centrifugal casting process. Semi centrifugal casting, unlike true centrifugal casting, has the mold completely filled using a sprue. However, in true centrifugal casting, molten metal sticks to the sides due to continuous rotation. On the contrary, vertical centrifugal casting, as the name suggests, uses directional molding following the same process as true centrifugal casting.
Typically, centrifugal casting produces rotational shapes like cylinders. In particular, parts like bush bearings, clutch plates, piston rings, and cylinder liners, etc. Also, the pouring of metal in the center of the mold helps in reducing defects such as blow holes, shrinkage, and gas pockets. However, it is not suitable for all kinds of metal alloys.
7. Lost-Foam Casting
Lost-foam casting method is similar to investment casting with the difference that it uses foam for the pattern instead of wax. Once the pattern is formed, coating with a refractory ceramic takes place by dipping, coating, spraying, or brushing. Then, the molten metal is poured into the mold to form the desired product.
This technique can be used for various materials like alloy steel, carbon steel, alloy cast iron, ferrous alloy, etc. In particular, products like pump housing, fire hydrants, valves, and fittings are made through the lost-foam casting process.
Lost foam casting possesses numerous advantages which include high precision and high accuracy production. However, there are a few limitations of this process that makes it unsuitable for low-volume applications.
8. Vacuum Casting
Vacuum casting, as the name suggests, is the type of casting where production occurs under vacuum pressure of 100 bar or less to exhaust gas from the mold cavity. In this process, molten metal is poured into the mold cavity inside a vacuum chamber in order to eliminate bubbles and air pockets. The vacuum evacuation of the die cavity reduces the entrapment of gases within the cavity during the metal injection process. Finally, the metal is cured in a heating chamber and removed from the mold.
The vacuum die casting process is popular in various industries including automobiles, aerospace, electronics, marine, telecommunication, etc. As a result, some components fabricated by this manufacturing process include structural chassis components and automotive body parts.
9. Squeezing Casting
Liquid forging or squeeze casting is a hybrid metal forming process that merges permanent mold casting and die forging in a single step. In this process, a specific amount of molten metal alloy is injected into a die, and pressure is applied to shape it. Then, the metal part is heated over melting temperature and extracted from the die.
Particularly, squeezing die casting is a potential casting process for safety-critical parts in automotive systems. For example, space frame joints, aluminum front steering knuckles, chassis frames, brackets, or nodes.
This type of metal casting combines the benefits of casting and forging processes. For example, the high pressure applied during solidification helps prevent shrinkage and porosities. However, due to specific tooling requirements, it is not as popular as other casting processes for mass production.
10. Continuous Casting
As the name suggests, it allows consistent mass production of metal profiles with a constant cross-section. This type of casting is popular in the production of steel bars. Also, the vertical cast creates semi-continuous casting like billets, ingots, bars, etc.
In this process, molten metal is poured at a calculated rate in a water-cooled, open-ended mold that allows a surface of solid metal to form on the liquid metal in the center. Metal solidification, thus, happens from the outside in. After this process finishes, strands of metal can be continuously extracted from the mold. Predetermined lengths of products can be cut off by mechanical shears or traveling oxyacetylene torches.
Generally, the products created using continuous casting are homogeneous, consistent, and dense. However, it also limits its use to such applications. Some other advantages and disadvantages are:
11. Shell Molding
Shell molding is an expendable mold casting process. It is similar to the sand casting process except for that the hardened shell of sand forms the mold cavity instead of a flask of sand. The sand used is finer than that utilized in sand casting and it is mixed with a resin so that it can be heat treated and hardened into the shell around the pattern.
Shell molding makes industrial products, for example, gearbox housing, connecting rod, small-size boats, truck hoods, cylindrical heads, camshafts, valve bodies, etc.
The casting products possess a good surface finish and dimensional accuracy. However, the limitation of this kind of casting includes the size and weight limitation of the parts. Some other advantages and disadvantages are:
Basic Steps of Different Casting Production
Mostly, casting processes follow some basic steps like pattern making, mold making, selection and pouring of metal alloys and finally, finishing of the casted part.
To create a pattern, it is important to determine the shape of the mold. For this, the materials used are wax, sand, plastic or even wood.
Following on, there is a requirement to create different types of molds for casting. Single-use mold can be made out of sand, plaster, or ceramic shell. Each of them has a different production method. Also, patterns made from foam or wax are burnt in a kiln.
Metal castings are produced from ferrous or non-ferrous alloys. Alloys are a chemical mixture of elements with mechanical properties which are best for the final cast applications. Where, ferrous alloys include steel, malleable iron and gray iron. While non-ferrous metals include aluminum alloys, bronze and copper.
After the selection of the metal alloys, the next step is the pouring of metal into the mold. The process involves placing a solid metal over a crucible and heating it with an open flame or inside the furnace until it melts. For small casting, pouring the molten metal directly from the crucible is possible. However, larger castings may require the transferring of metal into a larger ladle before pouring into the mold.
After solidification, the casting product is removed and metal surface finishing is done on it. Furthermore, the process of finishing can include the removal of excess material by scrubbing or machining for larger waste material.
Outsource Your Casting Needs to RapidDirect
It is important to choose the right type of casting process and expertise for your products. At RapidDirect, we provide you access to a team of professional engineers with a vast experience in different casting services, like die casting services, vacuum casting, etc. The expertise of our working team puts us in a better place to advise you and answer any queries that you may have.
Contact us to discuss your requirements of Expendables Refractory. Our experienced sales team can help you identify the options that best suit your needs.
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