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Click Here. Skip to content. Get a Quote. What Is Investment Casting? The gates of the patterns are connected to the runner by melting its end on the surface, dipping it in a hot melt adhesive wax, such as the sticky wax, and pressing it to the runner.
As the melted wax cools, it locks to the runner and is welded by a small torch to smooth the connection. Once the casting pattern is assembled and set, the slurry is applied by being dipped in the slurry, which is made up of fine grain silica, water, and some form of binding agent. The combination of these elements creates a ceramic coating that is applied multiple times to achieve the desired thickness.
Following slurry dipping, the pattern assembly is coated with stucco, which was determined during the APQP. The stucco process starts with a thin coating and becomes progressively rougher with each application. The shell coating is an essential part of the process. The strength of the shell has to be sufficient to endure all of the casting procedures.
There are various forms of heating used to remove the wax from the hardened shell. A common modern practice is the use of an autoclave—a steam heating device. The temperature of the autoclave has to be sufficient to melt the wax and preheat the mold for casting. The steam in the autoclave removes any potentially volatile materials. Once the molds are sufficiently cleared and heated, they are ready for the pouring of the metal.
Casting involves pouring molten metal into the preheated mold cavities. At this stage, the key to the quality of the casting rests in time and temperature. After the molten metal has been poured, a vibrating machine gently shakes the ceramic shell for five to seven seconds. The metal from ingots has been melted to a molten state. Once the shell is filled, it is allowed to cool at room temperature.
Once the shell has cooled and the metal has set, the shell material is removed. There are various methods used to remove the shell, including a hammer, high pressure water blasts, a vibratory table, chemicals, or a specially designed knockout machine.
During the knockout process, the shell is tightly clamped and held in position to ensure uniformity of the process. The knockout process can be especially difficult, particularly for parts that have intricate and complex sections. Cut off involves removing the individual parts from the sprue or runner. Once the part has been disconnected from the runner, the remaining portions of the gates are ground away.
There are various methods for removing the parts from the sprue, including the use of a chopping saw, torch, or laser. In highly technical or high production operations, parts may be cut off using a programmable cutting saw. The purpose of heat treatment is enhancement of the mechanical characteristics and properties of the component. The casting process reduces the strength, durability, and toughness of a metal.
Heat treatments eliminate internal stress. The types of heat treatments used for investment casting include vacuum solution annealing, hardening, tempering, and precipitation hardening. The purpose of vacuum solution annealing is to remove precipitative material and change the workpiece to a single phase structure.
After the completion of annealing, the workpiece is soft and ductile, ready to be hardened. At this stage, the workpiece is workable, machinable, weldable, and has dimensional stability. Hardening includes heating the metal until it reaches its austenitic crystal phase. After this, it is cooled very quickly. The process increases the strength and wearability of the workpiece. Tempering heats the workpiece to a temperature just below its critical range, holds it there, then cools it.
The process of tempering reduces brittleness and requires precise control, so it does not affect hardness.
The process includes heating the workpiece, treating it with a solution, cooling, and heating it again before rapidly cooling it. A typical finishing process is grinding that is used to further remove any deformities or remainders of the gate. Though the surface of the part is very smooth, further polishing may be necessary to enhance and perfect it.
The range of surface treatments for investment cast products include rust protection and corrosion resistance enhancing polishing and chemical treatments. The surface of an investment cast part can vary according to the grade of the alloy and product. The types of treatments include:. Though investment casting, or lost wax casting, has been used for thousands of years, there have been innovations that have added to the effectiveness of the process. The variations are designed to enhance the method for developing the pattern and addressing the use of wax.
The overall term used for lost wax casting is evaporative pattern casting since the material used to create the pattern is removed or evaporates. Though these alternate methods create patterns in alternative ways, they have similarities to investment casting and can be considered as offshoots or variations. The main differences in the variations are the materials used to create the pattern or the formation of the pattern. Lost foam casting has gained popularity as a replacement for investment casting due to its ability to fit into mass production and automated processes.
The method of lost foam casting is a recent addition to evaporation casting. It was developed by H. Shroyer in as a process that uses polystyrene foam placed in casting sand.
Like in investment casting, an aluminum die is used to create the pattern. Polystyrene beads are placed in the mold or die and are steam heated; this causes the beads to melt and take the shape of the mold. As the beads are heated, they expand and assume the contours and dimensions of the die.
The individual patterns are attached to a sprue or runner and sprayed with a refractory coating of ceramic material. The coated mold is placed in a vented container, which is packed with sand to hold it in position. As molten metal is poured into the container, the polystyrene evaporates, making room for the molten metal. In some cases, patterns do not have to be shaped in a die but can be hand carved. Using a machine or shape tool, polystyrene can be cut, formed, and configured to the desired dimensions of the workpiece.
This type of pattern making is used for one-off parts or prototypes. Lost foam casting is a manufacturing process used to create ornate, decorative, and complex metal configurations, shapes, and designs and can be used by engineers to create three dimensional renderings of their conceptualizations. Direct investment casting differs from traditional investment casting, which is referred to as indirect investment casting, by how the pattern is created.
With indirect casting, the pattern is formed in a die to create a wax representation. Several wax duplicates are attached to a sprue or runner, dipped in a ceramic solution, dipped in stucco, and dewaxed for the pattern to be filled with molten metal to form several versions of the component.
Direct casting varies in the way the pattern is formed and preformed using a variety of techniques. The first of these techniques is carving the pattern by hand or machine to create a one up version that is processed using the lost wax method.
This process is used for producing a prototype, assessing dimensions, or for short runs of finished parts. Compared to machining apart, investment casting can economically offer undercuts, high definition, complex detail and a smooth surface finish.
Frequently Asked Questions What kind of parts are typically made through investment casting? Investment castings are used in a wide range of industries, including firearms, food service, gas and oil, as well as the energy industry.
While these are some of the industries served through investment casting, they are not the only ones served by Milwaukee Precision Casting. Investment castings can be used for almost anything where steel, aluminum, brass, and many other materials are required. To download the complete casting process guide, please click here.
Learn more about investment casting vs. Effective part configuration is the critical element in achieving strict tolerances for investment casting parts. By injecting wax into a permanent-molding die to form wax patterns, investment casting are the solution for many complex parts that are required in large quantities. We produce investment castings in lost wax patterns from a few grams up to 40 pounds, and can economically produce low quantities with manual tooling, or high volumes utilizing multi-cavity automatic molding tools.
Works were created from hand sculptured wax patterns with delicate detail. During the post — WWII period, this process evolved and expanded into virtually every industry and marketplace, as seen today.
Robotic Technology Our robotic technology allows for efficient shell dipping with less drying time between dips, less breakage and patching, and less ceramic inclusions resulting in high-quality castings with a smooth surface finish for our customers.
Milwaukee Precision Casting, Inc. Our services include quality assurance testing, heat treatments, and non-destructive testing to provide custom investment casting parts that fit your specifications.
Our lead times are among the shortest in the industry. All of our parts are made in the USA allowing for quick turnaround times for projects located throughout the country.
Go to Navigation Go to Content. What Is an Investment Casting? What kind of parts are typically made through investment casting? What secondary operations can be done with Investment Castings?
Milwaukee Precision Casting has close relationships with many local vendors to allow for the best possible part at the lowest possible price. The difference in strength between castings and other methods of metal working, while there, are negligible. As with most materials and design decisions, a discussion with a metals expert can help drive the best decision.
To learn more about this process or to determine if it is a fit for your application, please contact us. November 23, Investment Casting Lost Wax Casting Factors such as design requirements, cost, and feasibility to manufacture dictate which casting process is most suitable to manufacture a product.
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