Production Technology Casting Technology PDF

Mechanical Engineering Dept. Production Technology Casting Technology Associate Prof. Mohamed A. Bhlol  Topics Casting process definition Classifications and types of casting processes Casting advantages, and disadvantages. Sand Casting...

Mechanical Engineering Dept. Production Technology Casting Technology Associate Prof. Mohamed A. Bhlol  Topics Casting process definition Classifications and types of casting processes Casting advantages, and disadvantages. Sand Casting process Casting Defects  Casting process definition Casting is a manufacturing process in which a liquid material is poured into a mold, which contains a hollow cavity of the desired shape, 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 process definition Casting Products  Classifications and types of casting processes Casting is mainly categorized into two types, based on nature of mold. Expendable mold which must be destroyed to remove casting. Mold materials: sand, wax, plaster, and similar materials, plus binders Permanent mold which can be used to produce many castings Made of metal (or, less commonly, a ceramic refractory material)  Classifications and types of casting processes Many types of casting are known and applied in industry, some of these types are: Die casting Investment casting Centrifugal casting Sand casting  Classifications and types of casting processes Die casting Die casting is a metal casting process that is characterized by forcing molten metal under high pressure into a mold cavity. The mold cavity is created using two hardened tool steel dies. Die casting is used for mass production of high-accuracy and good finished parts.  Classifications and types of casting processes Die casting  Classifications and types of casting processes Investment casting Investment casting is one of the oldest manufacturing processes in which molten metal is poured into an expendable ceramic mold. The mold is formed by a wax pattern using ceramic slurry that hardens into the mold. Investment casting also called "lost-wax casting".  Classifications and types of casting processes Investment casting  Classifications and types of casting processes Centrifugal casting In the centrifugal casting, molten metal is poured into permanent molds while they are rotating. The metal falling into the centre of the mold at the axis of rotation is thrown out by the centrifugal force under sufficient pressure towards the periphery where it solidifies after cooling.  Classifications and types of casting processes Centrifugal casting  Classifications and types of casting processes Sand casting Sand casting, also known as sand molded casting, is a metal casting process characterized by using sand as the mold material. Sand casting is simply melting the metal and pouring it into a preformed cavity, called mold, allowing the metal to solidify and then breaking up the mold to remove casting. Classifications and types of casting processes  Advantages and disadvantages of casting process Advantages of the Casting Process: 1. It is possible to cast any material (ferrous or non-ferrous). 2. Extremely large and heavy parts can be cast when they would be difficult or impossible to be produced otherwise. 3. Highly adaptable to mass production. 4. It is economical, with very little wastage: the extra metal in each casting is re-melted and re-used. 5. Cast metal is isotropic. It has the same physical and mechanical properties along any direction.  Advantages and disadvantages of casting process Disadvantages of the Casting Process: 1. Poor dimensional accuracy and surface finish for some processes; e.g., sand casting. 2. The metal casting process is a labor intensive process 3. Safety hazards to workers due to hot molten metals. 4. Environmental problems.  Sand casting process Sand Casting Terminology Flask A metal or wooden frame in which the mold is formed Flask consists of two halves: Cope = upper half of mold Drag = bottom half of mold Mold = flask + sand + gating system  Sand casting process Sand Casting Terminology Gating System Channels used to deliver metal into the mold cavity, it consists: -Pouring Cup: The part of the gating system that receives poured metal. -Sprue: The passage through which the molten metal from the pouring cup, reaches the mold cavity. - Runners: The channel through which the molten metal is carried from the sprue to the gate. -Gate: A channel through which the molten metal enters the mold cavity - Riser : A column of molten metal placed in the mold to feed the castings as it shrinks and solidifies.  Sand casting process Sand Casting Terminology Vent: Small opening in the mold to facilitate escape of air and gases. Core: A separate part of the mold, made of sand which is used to create openings and various shaped cavities in the castings. Mold Cavity: Hollow mold area in which metal solidifies Pattern: It is the replica of the final object to be made.  Sand casting process Steps of Sand Casting The basic steps in making sand castings: ❑ Patternmaking ❑Core making ❑Molding ❑Melting and pouring ❑Cleaning and fettling ❑ Inspection and tests  Sand casting process 1. Pattern making A pattern is a model or the replica of the object to be casted. The common materials used for making patterns are wood, metal, plastic, or wax. Common types of patterns: Solid or single piece pattern Split pattern Cope and drag pattern Match plate pattern  Sand casting process 1. Pattern making Split pattern single piece pattern Cope and drag pattern Match plate pattern  Sand casting process 1. Pattern making Pattern allowances Allowance are the extra dimensional compensation give to the pattern in order to attain the correct shape and size of the final solidified metal casting. Types of allowances are: 1. Shrinkage or contraction allowance. 2. Draft or taper allowance. 3. Machining or finish allowance. 4. Distortion or camber allowance.  Sand casting process Pattern allowances Shrinkage or contraction allowance. As metal solidifies and cools, it shrinks and contracts in size. To compensate for this, a pattern is made larger than the finished casting by means of a shrinkage allowance or contraction allowance  Sand casting process Pattern allowances Draft or taper allowance. Draft is the taper allowed on vertical faces of a pattern to permit its removal from the sand without tearing the mold cavity surfaces.  Sand casting process Pattern allowances Machining or finish allowance. Rough surface of castings that have to be machined are made to dimensions somewhat over those indicated on the finished working drawings. The extra amount of metal provided on the surfaces to be machined is called machine finish allowance.  Sand casting process Pattern allowances Distortion or camber allowance. Sometimes castings, because of their size, shape and type of metal, tend to warp or distort during the cooling period depending on the cooling speed. It is called camber. For example, a U-shaped casting will be distorted during cooling with the legs diverging, instead of parallel For compensating this warpage.  Sand casting process 2. Molding Molding consists of all operations necessary to prepare a mold for receiving molten metal. Molding usually involves: - placing a molding aggregate around a pattern - held with a supporting frame, - withdrawing the pattern to leave the mold cavity, - setting the cores in the mold cavity and - finishing and closing the mold.  Sand casting process 2. Molding Molding sand: The principle material used in making a mold is sand. A good molding sand contains the following ingredients:- 1. Silica sand: 80.80% 2. Alumina: 14.9% 3. Iron oxide: 1.3% 4. Combined water: 2.5% 5. Other inert materials: 1.5%  Sand casting process 2. Molding Molding sand: A molding sand must fulfil the following requirements: a) It must be sufficiently refractory to withstand the temperature of the molten metal. b) It must contain sufficient bonding materials to retain the shape of the mold c) It must be sufficiently permeable to allow gases escape.  Sand casting process 3. Melting and pouring The preparation of molten metal for casting is referred to simply as melting. Melting is usually done in a specifically designated area of the foundry, and the molten metal is transferred to the pouring area where the molds are filled. Furnaces are used in industry for melting purposes.  Sand casting process Steps of Sand Casting  Sand casting process 4. Cleaning and fettling Cleaning refers to all operations necessary to the removal of sand, scale, and excess metal from the casting. The operations of cutting off the unwanted parts, cleaning and finishing the casting are known as fettling.  Casting Defects Blow holes: A relatively large cavity produced by gases that prevent the molten metal from filling the mold completely. Shifts: This is an external defect in a casting. Due to core misplaced or mismatching of top and bottom parts of the casting usually at a parting line. Misalignment of flasks is another likely cause of shift.  Casting Defects Inclusion: Contamination of the casting by external materials such as slag or chips broken off from the ladle. Misrun: Is created when the molten metal does not completely fill the mold either due to high viscosity or absence of a riser.  Casting Defects Shrinkage cavity: Shrinkage cavity is a void or depression in the casting surface which means that the molten metal cannot fill the spaces after contraction on cooling. Hot Tears: Hot tears are internal or external cracks, which are formed by contraction stresses in a casting, just as solidification is complete, and the metal is still relatively weak (little strength).  Casting Defects Swell: enlargement of the mold cavity by metal pressures, results – localized or overall enlargement of castings. Caused due to insufficient ramming of the sand. Also due to rapid pouring of molten metal. Thank you