Lost-wax casting dates back 6,000 years and is one of the oldest metal-forming methods. While its popularity has diminished over the years, it is still used, although very rarely, in various industries, including jewelry, dentistry, art, engineering and product manufacturing. The process is ideal for creating simple or complex objects. While the process may be labor-intensive, we love it for creating stunning custom pieces with intricate detail in the jewelry industry.
You will get efficient and thoughtful service from Cencho.
Also known as investment casting and cire perdue, lost-wax casting is the process of making a metal object from a wax model. A mold is set using wax, which is then melted away, resulting in a cavity. Jewelers can then add the metal to the cavity and create a custom piece. This method is ideal for jewelers as it allows them to capture fine detail in the metal. Lost wax casting is also a highly versatile technique as jewelers can use various metals, including gold, silver, bronze, brass, copper and aluminum, to cast their designs.
Several types of specialty wax may be used for this casting method; however, Microcrystalline wax is often the most suitable option. It is pliable, slightly sticky and easy to work with due to its medium to soft consistency. While paraffin wax may be used to cast molds, it is better suited as an additive to harden existing wax models. Jewelers still need to have some knowledge about other specialty wax, including their melting points, as they can use them for specific purposes such as carving, modeling or patching.
The lost-wax process can vary slightly between industries; however, they generally follow the same steps and create a mold from a wax model. When making a custom ring, experienced jewelers create a wax model and use it to form a mold. Our skilled artisans hand-carve our wax models as it allows us to provide more detail. We can also inspect the wax model for flaws, and clients can adjust their custom design before we make the metal product.
The wax model is attached to a sprue which also serves as the channel for molten metal to enter the mold. The ring model is then surrounded by investment, or high-grade plaster, to create the casting. A vacuum will remove any air bubbles from the plaster to ensure the quality of the cast and produce a perfect mold.
Jewelers then dry the cast before hardening the investment in a kiln and melting the wax. The cast has a ring-shaped cavity ready to hold the molten metal with the wax removed. The metal is poured and set before removing the cast, leaving a perfectly shaped ring attached to the sprue. The sprue is removed, gemstones are set in the ring and then it is finished and polished, making it ready for the client.
Lost-wax casting is used worldwide with the oldest known object, an amulet, created in the Indus Valley over 6,000 years ago. Historians have found discoveries of scepters, furniture and sculptures in many other places, including Nicaragua, Vietnam, Israel and Nigeria, showing how far this casting process spread over the years. By the 18th century, the process of using lost-wax casting to create sculptures and other ornaments was supplemented with piece molding to keep up with the demands of growing industries. While it was never completely forgotten, lost-wax casting went through a decreased popularity cycle and was 'rediscovered' again.
Even to this day with the introduction of modern technology, lost wax casting is one of the most accurate methods of reproducing intricate detail and design in metal jewelry.
Lost-wax casting was first used to produce fine jewelry and, although it is not very common, is still an application used today to create a wide variety of pieces. While technology and 3D printers allow for a smoother workflow, our talented artisans combine this with hand carving to create more intricate and delicate details on custom jewelry designs.
At JPratt Designs, we use state-of-the-art CAD software to develop a concept and then create a lost wax cast model that clients can view and try on before confirming their custom design. We set gemstones in this model to give you an accurate impression of the finished product. This process allows you to express your concerns and for us to make any adjustments to your custom design before setting diamonds and stones in your chosen metal.
Create Custom Jewelry at JPratt Designs Using the Lost-Wax Casting Process
With extensive industry experience and providing our customers with fine jewelry for more than 30 years, you can trust our artisans to create a custom design that you'll love for years to come. Contact us today and schedule your appointment with our team of experts.
In this context, investment refers to the 'putting on of clothes or coverings.' Literally, a sacrificial wax object is reproduced in metal by first investing it with a covering or ceramic and then burning out the wax to leave a perfect cavity in refractory material. Molten metal is then poured into the cavity and allowed to cool and solidify, reproducing the fine details of the original wax pattern.
For more information, please visit customized lost wax investment casting.
Investment (or lost wax) casting is an ancient process. The story of lost wax metalworking is the story of Bronze Age technological innovation. In the modern world, investment casting still has a highly active place in jewelry making. More importantly, the process is used for precision net-shape production of otherwise near-impossible objects like complex and hollow turbine blades. The mass production of such parts is achieved by first CNC machining steel molds into which the wax can be rapidly cast. This enables a degree of repeatability that could not be achieved by individually hand-made masters. This article will further discuss investment casting, how it works, its advantages, and give some examples.
Investment casting is a precision casting process used to create complex and intricate metal parts with high dimensional accuracy and fine surface finishes. This casting method is ideally suited to producing relatively high-quality components with intricate details, delicate features, and tight tolerances.
Investment casting is commonly used in industries such as: aerospace, automotive, jewelry, and medical devices, in which high precision and intricate designs are essential. It also produces castings with very tight tolerances and high dimensional accuracy. Investment castings typically have smooth and fine surface finishes. Investment casting can be used with a variety of materials, including various metals and alloys. It can also produce parts with complex shapes, internal cavities, and thin walls that are challenging for other casting methods.
All casting methods use a heat-resistant cavity that is the shape of the desired part as a volume to be filled with liquid metal, which is removed once solidified. The means by which the cavity is formed is the primary differentiator of casting methodologies. Die casting uses a two-part (or more) hardened-steel cavity tool that is expensively and precisely machined from billet material. Sand casting forms a cavity by packing sand with a binding agent around a reusable pattern or master of the part. Investment casting forms the cavity by drying and then kiln baking a skin of refractory material over a pattern or master that is sacrificial.
Precision and extent of detail differ greatly between casting methods. Die casting is high precision, although gravity (poured) die casting is less precise than the various forms of pressure die casting. Pressure die casting facilitates compensation for shrinkage, which retains/reflects the shape and dimensions of the cavity more faithfully in the cast part. Pressure die-cast parts can maintain very high levels of detail, so long as that detail can be extracted from the tool features. Sand casting is of moderate precision because the process does not lend itself to forming very accurate and repeatable cavities. It can maintain only relatively thick sections and coarse details. Investment casting is renowned for its combination of precision and fine detail while avoiding the major up-front costs of die casting.
To learn more, see our guide on Casting Methods.
Investment casting is most used in industries in which precision, complexity, and fine details are crucial, and volumes are insufficient to justify the cost of die casting. The aerospace industry uses investment casting for the manufacture of high-complexity gas turbine components for gas flow such as turbine blades and fuel components. In automotive applications, it is used to manufacture components for low-volume and race vehicles, heavy goods/construction equipment, tractors, and agricultural machinery. In the medical sector, it is used to produce parts for MRI machines, wheelchairs, hospital beds, operating room equipment, and surgical tools.
Investment casting works by pre-applying coatings to the pattern'before investment casting mold creation, or to the mold'once it is fired. This serves several important purposes. Refractory coatings are applied to the interior surface of the mold to provide a barrier between the mold material and the molten metal. This reduces oxidation, contamination, and marking. An internal stucco layer in the mold can improve the release and texture of the surface to improve cosmetics by concealing slight flaws. Parting compounds applied to the mold surfaces ease the release of the casting at breakout.
Thermal barrier coatings applied selectively to the pattern can control the cooling rate and prevent rapid solidification. Anti-penetration coatings applied to the pattern can reduce the penetration of melt into the refractory material, to improve the quality of the surface finish.
Listed and discussed below is the step-by-step process of investment casting:
There are three basic routes to delivering the precision wax patterns that are the starting point for investment casting. For decorative items and one-off products such as jewelry or technical items for which precision is a lower priority, it is common to hand carve the wax master to the desired dimensions/shape. This starts with either assembling preformed wax shapes to form the part or extracting the part from a solid block by cutting or melting locally. For mass-produced items that will be investment cast in relatively large volumes, it is generally preferred to build a steel tool that forms a wax casting cavity. A more recent development has been the ability to 3D print (rapid prototype) relatively small wax parts, to allow volume production without the cost of a wax casting tool. This is particularly useful in iterative development, allowing multiple generations of small changes to be trailed without huge cost.
Attach a feeder structure consisting of a sprue and channel to the part to allow the fill to be successful. Attach the part and feeder structure to a casting board that forms the structure to allow the flask (the completed cast tool) to stand securely. Any areas that are liable to vent poorly require air passage features to be added. Where multiple parts are to be cast in one pour, these structures are best established as individual cavities/galleries. Feed them from a single sprue/pour point. Care and experience are required to enable effective fill when the gallery structure or part geometry is more complex.
A first immersion in the correctly formulated slurry will coat the surfaces of the pattern/sprue/support structure. Once the assembly is coated, it can be withdrawn and allowed to drip. Once drained, apply a layer of stucco'dry powder sprinkled all over to stabilize the first layer. Repeat the dip/drain/stucco steps until sufficient thickness is developed all over. The rest/drying time between layers can be several hours, to allow sufficient drying and stabilization for each layer. Set aside to completely dry, giving this enough time for the coating to become firm and rigid.
Bake the completed and dried flask to remove the wax and fully integrate the refractory coating. The supplier-recommended temperatures and durations for this stage are dependent on the type of material such as: water glass, clay, and silica. At the end of this baking process, the mold or flask will be fully fused into a single, strong body. The wax will have been fully volatilized or burned off. The cavity or cavities, sprue, and galleries will be clear and open. The support structure of investment and braces will be able to support the structure, ready to fill.
Lift the crucible with tongs and pour the contents into the upper opening to the sprue. Fill/charging should continue until the entire structure is full. This is usually confirmed by the visible presence of molten metal in the upper vents, showing good flow through.
When the cast has cooled, break away the refractory material without distorting the newly cast metal. In some cases, such as for simple and robust castings in stainless steel and bronze, this can be a vigorous and rapid process. Where more delicate features and softer metals such as gold and silver are present, much greater care must be taken.
The removal of cast material from sprue, vents, and supports will damage the desired casting. Any cosmetic damage can be repaired using die grinding, sawing, and clipping followed by surface restoration by sanding and polishing as required.
The company is the world’s best customized stainless steel investment casting supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.