Investment Castings

About Investment Castings and Investment Casting Manufacturers Including: Investment Casting Process, Lost Wax Casting, Precision Casting & Steel Castings.

Investment casting is the production of industrial parts through the metallic replication of wax models. In the first step of this process, investment casting manufacturers inject wax into an aluminum die to create an injection-molded wax pattern that is in turn used to form a model of the proposed finished product. The resulting wax pattern is used to form a ceramic mold, which can be created using the ceramic mold process or the solid mold process. Ceramic shell molds are created by dipping the wax pattern into ceramic material, called slurry, and allowing the ceramic material to harden. Solid molds are formed by placing a wax pattern into a flask and filling the flask with plaster, which hardens into a mold. Once the slurry or plaster hardens, the wax pattern is melted out of the mold, and the molds are heated to remove leftover wax and to prepare the mold for casting. The mold is then filled with molten metal, which will harden into the final product. Once the metal has cooled, the mold is broken away.
 
The investment castings are then subjected to other treatments, as necessary, which include additional heating, polishing and refinishing. The bulk of the investment can be removed by sandblasting. Gating stubs are ground flush and flashing is removed when needed. Major sections of the investment cast pieces are welded together and the seams are ground down. Other casting defects are fixed. Finally, investment casting manufacturers sand the part down once again sanded and then texturize and finish it.
 
Investment casting materials are quite plentiful. Typically, all ferrous and non-ferrous materials can be used. Carbon, tool and alloy steels and many grades of stainless steel are some of the ferrous materials commonly investment cast. Non-ferrous materials include most aluminum and copper-based substances, among others. Heat-resistant alloys can be investment cast for high-temperature applications. The investment cast process allows the switching back and forth between metals (ferrous or non-ferrous) within the ceramic shell molds. Selecting the right combination of alloys will provide the highest corrosion resistance.
 
Industrial manufacturers often choose the investment casting process when complex parts or large quantities of parts are needed during production. Investment casting manufacturers can create an assortment of parts in all sizes, shapes and weights, such as dental braces, automotive engine parts and medical equipment. Although the weight of parts ranges from one ounce to one ton, the majority of investment castings are less than 20 pounds. Because of the wide application of manufactured metal parts, investment castings are found within almost every industry, including the automotive, military, dental, mining, music, food processing, sports and telecommunication industries. Although, the initial cost may be higher than that of other casting procedures, investment casting provides greater design flexibility, greater detail, near net shape (which lowers material usage) and greater alloy selection to enhance part performance.

Investment Castings and Investment Casting Manufacturers Images Provided by Ferralloy Inc.

Types of Investment Castings

• Aluminum investment castings can be cast into complex geometric shapes and are commonly used in the aerospace industry. Aluminum investment castings are also used in aviation, electronics, hydraulics and military applications.
  
• Ferrous investment castings are cast out of metals that contain iron, including 300- and 400-series stainless steels, carbon and alloy steels and cobalt and tool steels.
  
• Investment casting process is the method through which industrial parts are produced through the metallic replication of wax models.
  
• Lost wax casting consisted of creating and plastering a wax model, replacing the wax with molten metal and removing the plaster after the metal cooled.
  
• Non-ferrous investment castings are formed from metals that do not contain iron, including aluminum and copper-based alloys.
  
• Precision casting is the process of creating metal shapes with wax molds.
  
• Steel castings shapes liquid steel into molds and dies.
  
• Titanium investment castings are used for lightweight, complex structural applications. Titanium investment castings are also used by engineers to create one-piece and near-net-shape pieces, which require a minimum of machining and assembly time.

Investment Casting Terms

Alloy – A compound consisting of either more than one metal or a metal and a nonmetal blended together.
 
“As Cast” Condition – Casting that is not heat treated after being removed from the mold.
 
Burnout – The process whereby excess water and wax is removed from a molding.
 
Casting – Forming and shaping a material substance, such as an industrial piece of equipment, by pouring liquid into a mold and allowing it to harden.
 
Cavity – The empty space within the mold into which the molten metal will be poured.
 
Centrifugal Casting – The process of filling a permanent mold cavity with molten material while rotating the mold. Centrifugal casting is often used during the investment casting process to increase the amount of pressure exerted upon the metal in order to reproduce mold details, such as lettering and holes.
 
Ceramic Mold Process – The process by which an investment mold is created from a pattern in order to be cast. Ceramic molds consist of solid molds and ceramic shells.
 
Ceramic Shell Process – The method of creating a ceramic mold through the immersion of a pattern into a slurry of liquid and covering the coated pattern with sand. The pattern is usually immersed and coated nine to ten times before the shell is completed.
 
Cocoon Process – The method of applying protective plastic to metal.
 
Cold Shut – Lines on the surface of a casting that are the by-product of the incomplete fusion of metal streams.
 
Concentricity – The sharing of a common point or axis of two or more surfaces of shapes, such as cylinders, cones, spheres and hexagons.
 
Core – A form inserted into a mold to create internal mold features.
 
Dirty Casting – A surplus of nonmetal substances within a casting.
 
Ferrous – Pertaining to or containing iron.
 
Forging – The method of reshaping metal through the application of heat and compression.
 
Gates – The openings in the gating system that transfer the molten metal from the runners into the mold cavity.
 
Gating System – The structure that transfers the molten metal into the mold. Gating systems are designed to uniformly transfer the metal into the mold cavity to create an even mold.
 
Inclusions – Small pieces of refractory materials, sand, slag or deoxidation products that have been trapped within the casting while it was solidifying.
 
Injection Molding – The injection of a molten substance, usually metal, under substantial pressure into a mold.
 
Lost Wax Process – An ancient process related to investment casting that consisted of creating and plastering a wax model, replacing the wax with molten metal and removing the plaster after the metal cooled.
 
Misrun – An incomplete casting.
 
Mold – A hollow container from which liquid substances can be formed into solid shapes.
 
Molten – A solid that has been converted into a liquid through the application of heat.
 
Non-ferrous – Not pertaining to or containing iron. Examples of non-ferrous metals include aluminum- and copper-based substances.
 
Pattern – A casting model created by injecting metal dye with wax. When the wax solidifies, it forms the pattern, which is then molded and cast.
 
Pattern Oversize Factor – A term that refers to the extent to which the pattern size must be increased to allow for metal shrinkage.
 
Plaster Mold Casting – The process in which a wax pattern is sprayed with plaster slurry to create a mold.
 
Permanent Mold Casting – The process of using metal, often iron, to create the mold. Permanent molds are cheaper than sand molds when a large quantity of parts is produced, as they can be used more than once.
 
Pouring Cup – The part of the gating system that pushes the molten metal into a mold.
 
Riser – An open space in a mold into which extra molten metal is trapped.
 
Runners – Horizontal mechanisms connected to the sprue that transfer the molten metal from the sprue to the mold.
 
Sand Casting – The process of pouring molten metal into a natural or an artificial sand mold to form large parts, often made of iron.
 
Shell Casting – The process in which sand and plastic are poured over a hot metal pattern, whose heat causes the sand and plastic to mold to the pattern. The mold is removed from the metal, filled with molten metal and broken once the metal hardens, forming a cast.
 
Shrinkage – The contraction of metal during the cooling process.

Shrinkage Allowance – The degree to which a pattern is enlarged to allow for the contraction of the metal during the cooling process.
 
Slurry – The thick, insoluble liquid made of substances like plaster and silica from which a mold is created by repeatedly covering the patterned wax with the liquid.
 
Solid Mold Process – The method in which a wax pattern is placed within a steel container called a flask. The flask is then filled with a liquid plaster, which hardens into a mold of the pattern.
 
Sprue – Vertical mechanism connected to the pouring cup that transfers the molten metal to the runners.
 
Straightness – A term that refers to the deviation of the cast axis from the true axis.
 
Vents – Small holes in the gating system through which air is pushed out of the mold as molten metal is poured into the mold.