| |
|
|
| |
Investment Casting | Other Casting Processes |
|
| |
|
|
| |
• Overview |
|
| |
• History |
|
| |
• The Process |
|
| |
• Alloys |
|
| |
• Advantages |
|
|
|
|
| |
Overview |
|
| |
Investment casting is regarded as a precision casting process to fabricate near-net-shaped metal parts from almost any alloy. Although its history lies to a great extent in the production of art, the most common use of investment casting in more recent history has been the production of components requiring complex, often thin-wall castings. Casting is often used for creating one or more copies of an original piece of sculptural (three-dimensional) artwork. It is also used extensively in the automobile manufacture industry, such as the casting of engine blocks or cylinder heads, or vacuum-forming of plastics and in the lost core process.
|
|
|
| The investment casting process is generally considered for the production of small parts in which intricacy of shape or detail as well as high accuracy, dimensional reproducibility are prime considerations. While investment casting are generally more expensive than forged parts or those parts produced by other casting methods, they make up for the higher cost by the reduction of machining which is achieved through the near net shape tight tolerances that can be held. |
|
|
|
|
| |
History |
|
| |
Investment casting is also known as the lost wax process. This process is one of the oldest manufacturing processes. The Egyptians used it in the time of the Pharaohs to make gold jewelry (hence the name Investment) some 5,000 years ago. Intricate shapes can be made with high accuracy. In addition, metals that are hard to machine or fabricate are good candidates for this process. It can be used to make parts that cannot be produced by normal manufacturing techniques, such as turbine blades that have complex shapes, or airplane parts that have to withstand high temperatures. |
|
|
|
|
| |
The Process |
|
| |
The investment casting process begins with fabrication of a sacrificial pattern with the same basic geometrical shape as the finished cast part. Patterns are normally made of investment casting wax that is injected into a metal wax injection die. Fabricating the injection can be expenseive and can require several months of lead time. Once a wax pattern is produced, it is assembled with other wax components to form a metal delivery system, called the gate and runner system. The entire wax assembly is then dipped in a ceramic slurry, covered with a sand stucco, and allowed to dry. The dipping and stuccoing process is repeated until a shell of ~6-8 mm (1/4-3/8 in) is applied.
Once the ceramic has dried, the entire assembly is placed in a steam autoclave to remove most of the wax. After autoclaving, the remaining amount of wax that soaked into the ceramic shell is burned out in a furnace. At this point, all of the residual pattern and gating material is removed, and the ceramic mold remains. The mold is then preheated to a specific temperature and filled with molten metal, creating the metal casting. Once the casting has cooled sufficiently, the mold shell is chipped away from the casting. Next, the gates and runners are cut from the casting, and final postprocessing (sandblasting, machining) is done to finish the casting.
The major impact rapid prototyping processes have had on investment casting is their ability to make high-quality patterns without the cost and lead times associated with fabricating injection mold dies. In addition, a pattern can be fabricated directly from a design engineer's computer-aided design (CAD) solid model. Now it is possible to fabricate a complex pattern in a matter of hours and provide a casting in a matter of days. Investment casting is usually required for fabricating complex shapes where other manufacturing processes are too costly and time-consuming. Another advantage of rapid prototyping casting is the low cost of producing castings in small lot sizes. |
|
|
|
|
| |
Alloys |
|
| |
Nearly all ferrous and non-ferrous alloys may be poured in the investment casting process. On the ferrous side, carbon, tool and alloy steel along with the 300, 400, 15-5PH and 17-4PH stainless steels are the most commonly poured. Most aluminum, copper and other non-ferrous materials can be cast. |
|
|
|
|
| |
Advantages |
|
| |
Design Flexibility |
|
| |
The investment casting process or lost wax process produces near-net-shape configurations. This offers engineers and designers freedom of design in many types of alloys. This process is capable of producing precise detail and dimensional accuracy in parts weighing many pounds to just a few ounces. Precision investment castings are able to reduce costs in many cases due to reduced machining and less materiel waste. |
|
| |
Freedom of Alloy Selection |
|
| |
Any castable alloy can be used, including ones that are impossible to forge or are too difficult to machine. Further, the cost of the alloy is less important in the final price of an investment castingthan in many other metal forming processes; therefore an upgraded alloy can be specified (especially if the part is redesigned to save weight) at little or no increase in price. |
|
| |
Cost Effective |
|
| |
Investment casting can reduce costly machining operations and sometimes even eliminate them.
Investment castings are produced to
close tolerances and near-net size. There is little secondary machining
required, thus offering savings in machining time and material costs. |
|
| |
Production Consistency & Reproducibility |
|
| |
The investment casting process produces a reliable and consistent product. Our process control system yields remarkable consistency from part to part as well as from batch to batch. This reproducibility feature means our customers will save time in both machine set up and assembly. |
|
| |
Wide Range of Application |
|
| |
In addition to comlplex and demanding parts, investment castings also produces many very simple parts competetively. This capability is often made possible by low tooling costs associated with investment castings. Investment castings are competetively produced in sizes ranging from a few grams to more than 300 kg (660 lb) and the upper limits continue to increase. |
|
| |
|
|
| |
 Top of page |
|
| |
|
|
| |
|
|
