Workshop Practices: Casting Methods

Workshop Practices CASTING Dr Siddharth Jain Associate Professor Mechanical Cluster UPES  Casting Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired...

Workshop Practices CASTING Dr Siddharth Jain Associate Professor Mechanical Cluster UPES  Casting Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process. Casting materials are usually metals or various time setting materials that cure after mixing two or more components together; examples are epoxy, concrete, plaster and clay. Casting Process in which molten metal flows by gravity or other force into a mold where it solidifies in the shape of the mold cavity The term casting also applies to the part made in the process Casting is most often used for making complex shapes that would be otherwise difficult or uneconomical to make by other methods. Heavy equipment like machine tool beds, ships' propellers, etc. can be cast easily in the required size, rather than fabricating by joining several small pieces. Casting Sand Casting Production Sequence A successful casting process needs Preparation of moulds and patterns Melting and pouring of liquefied metal Solidification and further cooling to room temperature Defects and inspection Capabilities and Advantages of Casting Can create complex part geometries that can not be made by any other process Can create both external and internal shapes Some casting processes are net shape; others are near net shape Can produce very large parts (with weight more than 100 tons), like m/c bed Casting can be applied to shape any metal that can melt Some casting methods are suited to mass production Disadvantages of Casting Different disadvantages for different casting processes: Limitations on mechanical properties Poor dimensional accuracy and surface finish for some processes; e.g., sand casting Safety hazards to workers due to hot molten metals Environmental problems Parts Made by Casting Big parts Engine blocks and heads for automotive vehicles, , machine frames, railway wheels, pipes, bells, pump housings, mill rolls Small parts Dental crowns, jewelry, small statues, frying pans All varieties of metals can be cast - ferrous and nonferrous  Casting is usually performed in a foundry Overview of Foundry = factory equipped for Casting making molds Technology melting and handling molten metal performing the casting process cleaning the finished casting Workers who perform casting are called foundrymen  Different Types of Casting Process 1. Sand Casting Process Sand casting is a versatile casting process that can be used to cast any metal alloy, ferrous or non-ferrous. It is widely used for mass production in industrial units, such as automotive metal casting parts, like engine blocks, cylinder heads, crankshafts, etc.  1. Sand Casting Process Advantages Disadvantages Relatively inexpensive in terms of production costs, Lower degree of accuracy as compared to alternate especially in low-volume production methods Difficult to use this method for products with pre- Fabrication of large components determined size and weight specifications The process yields products with a rough surface Casting both ferrous and non ferrous alloys finish Recycling ability Processing of metals with high melting temperatures, such as, steel and titanium 2. Gravity Die Casting Gravity die casting, also typically known as permanent mold casting, uses reusable molds made of metal, like steel, graphite etc. to fabricate metal and metal alloys. This type of metal casting can manufacture various parts like gears, gear housing, pipe fittings, wheels, engine pistons, etc. In this process, the direct pouring of molten metal into the mold cavity takes place under the effect of gravity. For better coverage, the die can be tilted to control the filling. The molten metal is then allowed to cool and solidifies within the mold to form products. As a result, this process makes casting of materials like lead, zinc, aluminum, and magnesium alloys, certain bronzes, and cast iron more common. 2. Gravity Die Casting Advantages Disadvantages Provides better surface quality of products due to Casting complex objects is difficult rapid solidification Casting products have high precision and tight Manufacturing costs of molds are higher tolerance Reusable molds save time and increase productivity At times, the ejection mechanism to remove the which reduces production costs casting from the mold forms a dent in the product The products possess better mechanical properties Production of thin walled products 3. Pressure Die Casting There are two types of pressure die casting depending on the pressure. Namely, the low- pressure die casting and the high-pressure die casting. High pressure die casting is more popular for mass production of complex geometries that require high precision. Whereas, for large and simple parts production, low- pressure die casting is a preferable casting process. In this type of metal casting, non-ferrous metals and alloys such as zinc, tin, copper and aluminum are injected into a reusable mold coated with a lubricant at high pressure. Thus, high pressure is maintained throughout the rapid injection process to avoid metal hardening. Finally, after completion of the process, extraction of casting and finishing takes place to remove any excess material. 3. Pressure Die Casting Advantages Disadvantages High precision and dimensional tolerance Relatively high tool costs Difficult to ensure the mechanical properties of High efficiency and good product quality products, therefore, it is not used for structural parts Reduced need for post-casting machining Complete setup requires a large capital investment Rapid cooling of molten metal pertaining to faster production rates The process can run for longer hours without the need to replace the die 4. Investment Casting Investment casting, also known as lost-wax casting, is a process that invests wax pattern with refractory material and a binding agent to shape a disposable ceramic mold, and then molten metal is poured into the mold to make metal castings. Investment casting is an expensive and labor-intensive process and can be used for mass production or in complex castings to produce metal casting products ranging from gears, bicycle trunks, moto discs, and spare parts in blasting machines.