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Metal casting processes. Casting is one of the oldest manufacturing process. It is the first step in making most of the products. Steps: - Making mould cavity. - Material is first liquefied by properly heating it in a suitable furnace. - Liquid is poured into a prepared mould cavity. - allowed to solidify.
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- 11.1 Introduction
- 11.2 Introduction to Casting
- Advantages of Casting
- 11.3 Casting Terminology
- Casting Terminology
- 11.4 The Solidification Process
- Nucleation
- Grain Growth
- Molten Metal Problems
- Fluidity and Pouring Temperature
- The Role of the Gating System
- Gating Systems
- 11.5 Patterns
- Pattern Removal
- Parting Line and Drafts
- Casting Designs
- Summary
Products go through a series of processes before they are produced Design Material selection Process selection Manufacture Inspection and evaluation Feedback Materials processing is the science and technology that converts a material into a product of a desired shape in the desired quantitiy
Casting process Material is melted Heated to proper temperature Treated to modify its chemical makeup Molten material is poured into a mold Solidifies Casting can produce a large variety of parts
Complex shapes Parts can have hollow sections or cavities Very large parts Intricate shaping of metals that are difficult to machine Different mold materials can be used Sand, metal, or ceramics Different pouring methods
Pattern- approximate duplicate of the part to be cast Molding material- material that is packed around the pattern to provide the mold cavity Flask- rigid frame that holds the molding aggregate Cope- top half of the pattern Drag- bottom half of the pattern Core- sand or metal shape that is inserted into the mold to create internal features
Mold cavity- combination of the mold material and cores Riser-additional void in the mold that provides additional metal to compensate for shrinkage Gating system- network of channels that delivers the molten metal to the mold Pouring cup- portion of the gating system that controls the delivery of the metal Sprue- vertical portion of the gating sys...
Molten material is allowed to solidify into the final shape Casting defects occur during solidification Gas porosity (solved by adding the vent) Shrinkage (solved by using the riser to add the molten metal) Two stages of solidification Nucleation Growth
Stable particles form from the liquid metal Occurs when there is a net release of energy from the liquid Undercooling is the difference between the melting point and the temperature at which nucleation occurs Each nucleation event produces a grain Nucleation is promoted (more grains) for enhanced material properties Inoculation or grain refinement ...
Occurs as the heat of fusion is extracted from the liquid Direction, rate, and type of growth can be controlled Controlled by the way in which heat is removed Rates of nucleation and growth control the size and shape of the crystals Faster cooling rates generally produce finer grain sizes
Chemical reactions can occur between molten metal and its surroundings Reactions can lead to defects in the final castings Metal oxides may form when molten metal reacts with oxygen Dross or slag is the material that can be carried with the molten metal during pouring and filling of the mold Affects the surface finish, machinability, and mechanical...
Metal should flow into all regions of the mold cavity and then solidify Fluidity is the ability of a metal to flow and fill a mold Affects the minimum section thickness, maximum length of a thin section, fineness of detail, ability to fill mold extremities Dependent on the composition, freezing temperature, freezing range, and surface tension Most ...
Gating system delivers the molten metal to the mold cavity Controls the speed of liquid metal flow and the cooling that occurs during flow Rapid rates of filling can produce erosion of the mold cavity Can result in the entrapment of mold material in the final casting Cross sectional areas of the channels regulate flows
Proper design minimizes turbulence Turbulence promotes absorption of gases, oxidation, and mold erosion Choke- smallest cross-sectional area in the gating system Runner extensions and wells- used to catch and trap the first metal to enter the mold and prevent it from entering the mold cavity Filters- used to trap foreign material
Two basic categories for casting processes Expendable mold processes Permanent mold processes Patterns are made from wood, metal, foam, or plastic Dimensional modification are incorporated into the design (allowances) Shrinkage allowance is the most important Pattern must be slightly larger than the desired part
Parting lines are the preferred method Damage can be done to the casting at corners or parting surfaces if tapers or draft angles are not used in the pattern Factors that influence the needed draft Size and shape of pattern Depth of mold cavity Method used to withdraw pattern Pattern material Mold material Molding procedure
Figure the draft. (Top right) Part with draft unspecified. (Bottom) Various options to produce the top-right part, including a no-draft design.
May be aided by computer simulation Mold filling may be modeled with fluid flow software Heat transfer models can predict solidification
A successful casting requires that every aspect of the process be examined Every aspect from the desired grain structure to the desired finish of the product should be considered during design stages Efforts should be made to minimize cracking and defects There are a variety of processes to improve castings and they should all be considered during ...
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- Sand Casting. It is the most extensively and widely used types of casting process. This is an expendable mold-permanent pattern casting process. The sand casting process involves using a furnace, metal, pattern, and sand mold.
- Investment Casting. n this method, a wax pattern is combined with refractory material and a binding agent to create a disposable ceramic mold, which is then filled with molten metal to create metal castings.
- Permanent Mold Casting. Permanent mold casting is a method of casting metal that makes use of reusable molds, which are frequently made of metal. Permanent mold casting is commonly called gravity die casting because the molten metal is poured into the die rather than forcibly injected.
- Die Casting. Die casting is a very commonly used type of permanent mold casting process. It is used for the production of many components of home appliances like stoves, fans, motors, toys, etc.
1.1 Casting processes. 1.2 Process selection. 1.3 Design of castings. Solidification theory. 2.1 Revision of nucleation theory. 2.2 Solidification mechanisms. 2.3 Solidification of alloys. Microstructure of castings. 3.1 Grain structure. 3.2 Chemical inhomogeneity. 3.3 Porosity. 3.4 Casting alloys.
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Six basic steps of casting. 1. Mold cavity is produced having the desired shape and size of the part. Takes shrinkage into account. Single-use or permanent mold. 2. Melting process. Provides molten material at the proper temperature.
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Definition. Metal casting enables the production of simple to complex parts that meet a variety of needs. The process consists of pouring molten metal into a mold containing a cavity of the desired shape. The most widely used method for small to medium-sized castings is green sand molding.
Dec 1, 2013 · PDF | A new textbook, Metalcasting Principles & Techniques, from the American Foundry Society (AFS) has been published for college-level undergraduate... | Find, read and cite all the research...
