For high melting temperature metals, if a small number of specialized castings with high tolerances required investment solutions suitable. investment casting produces bioengineering components, and some are used in the aerospace industry. The technique provides us with good dimensional accuracy and the small end surface finishing operations are needed. Light allay materials used. Because of the properties should produce products in time and to be at the correct value. Death will be used over and over. lost wax casting method of investment: the first is prepared for wax injection. After injection of wax is (30 sec) death opened, then the wax pattern insertion HCI very dilute acid. This process is to dissolve the soluble core. Then, the tree is the small patterns (Core dissolved in 12 hours) to hold in isopropanol and tridoroethene, then into pure isopropanol and drying compressed air.
Then give us the pattern ceramic coating; This will eventually form the mold foal. (By dipping it in zircon, refractory powder coated enemy; now it is known as mold). We dry the mold by passing it through ammonia vapor. Then dewaxing process, comes could ruin any wax left side expensive solutions. The process is 900 ° C oven gas used fire. We then left the work to be cooled down on shelves. Now it is extremely heavy and brittle. Models heated again for four hours, now the model is ready for casting. This is very economical because you have many form one projection from the furnace melt. Each must be steel in the furnace at the same temperature (1650 C). When the furnace temperature was ideal, a small amount of silicon is added to help run more easily in the mold metal. Check temperature again. Mold is placed upside down on the furnace. Then the whole lot is tipped over. When the metal flowed into a mold, it is allowed to cool, powder is added to ensure the uniform cooling throughout the model. 20 minutes later the mold is taken for further cooling.
The best way (effective and safe) removing the ceramic coating by hammering, although it is dusty and noisy. Lastly the castings through a number of vigorous tests, such as X-rays, Ultraviolet light test. Then dimensional accuracy is also tested. Investment casting method is ideal for metals that can not be machined successfully as Tungsten and Cobalt such. Production method is profitable; and you have the opportunity to make both large and small castings.
Housing figure for a rotary engine developed by Engineering Norton for motorcycles and both thick (15 mm) and thin (2 mm outer shroud) sections. This is sand casting, but filled by gravity, showing that systems can fill simple to work well for many castings and system is not filling up the hill always necessary (although it would almost always produce good solutions). In Figure We now set three sand castings used by the aerospace industry. This is a lightweight space frame for a pilot ejector seat. Figure shows the air intake for the engine Rolls Royce Gem powers of the Lynx helicopter, and more complex air intake figure for aerospace engine produced in France.
I would now like to turn to yet another completely different area of foundry technology: investment casting. This is of course, widely known as lost wax casting, because the use of stock wax coated with refractory (ie the stock to invest in layers alternate slurry and stucco), the stock wax melted out later to leave a hollow shell into which the metal is cast. The elegant die from Deritend Precision Castings, Droitwich, United Kingdom makes the impeller in wax patterns. The center made of steel, bronze used for the sliding inserts. Figure is a series of wax patterns together into a system running commonly called tree and hand dipped into a ceramic slurry.
The coated pattern is removed, coated in stucco refractory and allowed to dry. The dipping process is repeated many times until you have enough thickness shell of built up, usually a minimum of ~ 7 mm. Until recently, the amount of investment castings is limited by the amount of shell could be manhandled. The overall picture is a modern facility for making ceramic shells shown in Fig. A series of slurry tank and the stucco fluidized beds arranged around a robot. The increased transport weight capacity available by registering revolutionized the investment casting industry, because it is now possible to make castings with overall dimensions of a meter or more.
A research team at the Georgia Institute of Technology has developed a new way to perform investment casting. The basic process dates back thousands of years: Molten metal is poured into an expendable ceramic mold to form a part. The mold is made by creating a wax replica of the part to be cast. The replica gets surrounded or “invested” with a ceramic which dries and hardens to form the mold. The wax is then melted out — or lost — to form a mold cavity into which metal is poured and solidified to produce the casting. However, creating the mold currently involves a sequence of six major operations needing expensive, precision-machined dies and hundreds of tooling pieces.
In contrast, the Georgia Tech approach involves a device that builds ceramic molds from CAD data, completing the task quickly and producing few bad parts. The new technique, dubbed large area maskless photopolymerization (Lamp), builds molds layer by layer (each 100-microns thick) by projecting bitmaps of UV light onto a mixture of photosensitive resin and ceramic particles, then selectively curing the mixture to a solid.
After the mold forms, the cured resin is burned away and the remaining ceramic is sintered in a furnace. The result is a ceramic structure into which molten metal — such as nickel-based superalloys or titanium-based alloys — can be poured, producing highly accurate castings.
“We have developed a proofof- concept system which is turning out complex metal parts. It fundamentally transforms the way high-value castings are made,” says Suman Das, director of the Direct Digital Manufacturing Laboratory in the Manufacturing Research Center. “We’re confident our approach can lower costs by at least 25% and reduce the number of waste parts by more than 90%, while eliminating 100% of the tooling.”
A prototype Lamp machine currently builds six typical turbine-engine airfoil molds in 6 hr. Das predicts that a larger machine — currently being built at Georgia Tech and scheduled for installation at a PCC Airfoils facility in Ohio in 2012 — will create 100 molds at a time in about 24 hr.
Although the current work focuses on turbine-engine airfoils, Das believes the Lamp technique will be effective for making many types of intricate metal parts. He envisions companies sending out designs to “digital foundries” and receiving test castings a short time later, much as integrated-circuit designers send CAD plans to chip foundries today.
The so-called investment casting process , it is simply said that use fusible material fusible model covered with several layers of special refractory coating in the model surface, after drying and hardening to form a whole body shell, then steam or hot water from type shell model melt away , and then placed in the shell sand box , after filling the dry sand molding around it , and finally it is cast into the roaster in the high-temperature roasting, mold or shell after roasting, in which pouring molten metal and casting finally obtained.
The biggest advantage of investment casting is that due to the investment casting with high dimensional accuracy and surface finish, so it can reduce mechanical processing work, just in the component parts of the high demand for a little machining allowance, and even some castings only grinding, polishing allowance, don’t need to machining can be used. Using investment casting method, therefore, can save a lot of machine tool equipment and processing time, and greatly save metal materials. Another advantage of the method of investment casting is that it may be cast complex castings of various alloys, particularly may be cast super alloy castings. Such as jet engine blades, with the machining process its sleek outline and cooling cavity is almost impossible to form. Investment casting process to produce not only mass production can be done to ensure the consistency of the casting, and avoid stress concentration of residual knife pattern after machining.
The available investment casting production of alloy types include carbon steel, alloy steel, heat-resistant alloy, stainless steel, precision alloy, permanent magnet alloy, bearing alloy, copper alloy, aluminum alloy, titanium alloy and nodular cast iron etc.. investment casting process is complicated, and not easy to control, use and consumption of material is expensive, so it is suitable for production of complex shape, high precision, or difficult to other processing of small parts, such as turbine engine.