Components Produced by Casting Process Automotive sector Nearly

Components Produced by Casting Process • Automotive sector - Nearly 90 % of the parts in automobiles aremanufactured by castings. A few parts include brake drum, cylinder linings, pistons, engine blocks, universal joints, rocker arm, brackets etc. , • Aircraft - Turbine blades, casing etc. • Marine propeller blades. • Machining - Cutting tools, machine beds, wheels and pulleys, blocks and table for supports etc. • Agriculture and rail road equipments. • Pumps and compressors frame, bushings, rings, pinion etc. • Valves, pipes and fittings for construction work. • Camera frames, parts in washing machine, refrigerators and airconditioners. • Steel utensils and a wide variety of products. Hareesha N G Dept Aero Engg, DSCE, Blore 1

Advantages of casting process • Large hollow and intricate shapes can be easily cast. • Quick process, and hence suitable for mass production. • No limit to size and shape. Parts ranging from few millimeters to meters and few grams to tons can be cast efficiently and economically. • Better dimensional tolerances and surface finish can be obtained by good casting practice. • Castings exhibit uniform properties in all the directions longitudinal, lateral and diagonal. • The casting process is usually the cheapest process. • Unrelieved internal stresses are absent in cast components. • Certain metals and alloys can be manufactured by means of casting only, e. g. , Phosphor-Bronze. Hareesha N G Dept Aero Engg, DSCE, Blore 2

Limitations of casting process • Presence of defects in cast parts is a major disadvantage. • Casting process is not economical for small number of parts. • Properties of cast materials are generally inferior when compared to those made by machining or forging process. • Casting process mostly deals with elevated temperatures. • There are limitations regarding thin sections. • Casting process is not suitable for very small number of components. Hareesha N G Dept Aero Engg, DSCE, Blore 3

INTRODUCTION TO PATTERN MAKING • A pattern is a mold forming tool in the hands of foundry men. • A pattern is a model or the replica of the object to be cast. • Except for the various allowances a pattern exactly resembles the casting to be made. • A pattern is required even if one object has to be cast. • A pattern may be defined as a model or form around which sand is packed to give rise to a cavity known as mold cavity in which when, molten metal is poured, the result is the CAST OBJECT. Hareesha N G Dept Aero Engg, DSCE, Blore 4

Difference between pattern and casting • The main difference between a pattern and the casting is their dimensions. • A pattern is slightly larger in size as compared to the casting, because a pattern, – carries Shrinkage allowance, it may be of the order of 1 to 2 mm/ 100 mm. – is given a Machining allowance to clean and finish the required surfaces. – carries a Draft allowance of the order of 1 and 3 degrees for external and internal surfaces respectively – carries core prints. • A pattern may not have all holes and slots which a casting will have. Such holes and slots unnecessarily complicate a pattern and therefore can be drilled in the casting after it has been made. • A pattern may be in two or three pieces whereas a casting is in one piece. • A pattern and the casting also differ as regards the material out of which they are made. Hareesha N G Dept Aero Engg, DSCE, Blore 5

Functions of a patterns • A pattern prepares a mold cavity for the purpose of making a casting. • A pattern may contain projections known as core prints if the casting requires a core and need to be made hollow. • Runner, gates and risers (used for introducing and feeding molten metal to the mold cavity) may form a part of the pattern. • A pattern may help in establishing locating points on the mold and therefore on the casting with a purpose to check the casting dimensions. • Patterns establish the parting line and parting surfaces in the mold. • A pattern may help position a core (in case a part of mold cavity is made with cores), before the molding sand is rammed. • Patterns that are properly made and having finished and smooth surfaces, reduce casting defects. • Properly constructed patterns minimize overall cost of the castings. Hareesha N G Dept Aero Engg, DSCE, Blore 6

Pattern materials Selection of pattern materials • The following factors assist in selecting proper pattern material: Ø The number of castings to be produced. Metal patterns are preferred when the production quantity is large. Ø The desired dimensional accuracy and surface finish required for the castings. Ø Nature of molding process i. e. , sand casting, permanent mold casting, shell molding, investment casting etc. Ø Method of molding i. e. , hand or machine molding. Ø Shape, complexity and size of the casting. Ø Type of molding materials i. e. , sand etc. Ø The high probability of changing the casting and hence the pattern in near future. Hareesha N G Dept Aero Engg, DSCE, Blore 7

Materials for making patterns • Patterns may be constructed out of the following materials. (a) Wood (b) Metal (d) Plastic (d) Plaster (POP) (e) Wax Hareesha N G Dept Aero Engg, DSCE, Blore 8

WOOD • The most common materials for making patterns for sand casting is the wood. Advantages – Inexpensive. – Easily available in large quantities. – Easy to machine and to shape to different configurations and forms – Easy to join to acquire complex and large pattern shapes – Light in weight – Easy to obtain good surface finish – Wooden patterns can be preserved for quite long times with the help of suitable wood preservatives. Limitations – Wooden patterns are susceptible to shrinkage and swelling. – They possess poor wear resistance. – They are abraded easily by sand action. – They absorb moisture, consequently get deformed and change shape and size. – They cannot withstand rough handling. – They are weak as compared metal Hareesha Nto G Dept Aero patterns. Engg, DSCE, Blore 9

Metal • Metal patterns are employed where large number of castings have to be produced from the same patterns. • Metal patterns are cast from wooden patterns. • The different metals and alloys used for making patterns are, – – – Aluminium and Aluminium alloys Steel Cast Iron Brass White Metal Hareesha N G Dept Aero Engg, DSCE, Blore 10

Advantages of Metal Patterns – Unlike wooden patterns, they do not absorb moisture. They retain their shape. – They are more stronger and accurate as compared to wooden patterns. – They possess life much longer than wooden patterns. – They can withstand rough handling. – They do not distort – They possess greater resistance to abrasion. They have accurate dimensional tolerances. They are far stable under different environments. – It is easy to obtain smooth surface finish. – They possess excellent wear resistance and strength to weight ratio. Limitations of Metal Patterns – – – Expensive as compared to wood patterns. Are not easily repaired e. g. (Aluminium patterns). Ferrous patterns get rusted. They (ferrous patterns) are heavier than wooden patterns, They cannot be machined so easily as wooden ones. Hareesha N G Dept Aero Engg, DSCE, Blore 11

Plastic • Advantages – – – – Durable Provides a smooth surface. Moisture resistant. A plastic pattern does not involve any appreciable change in its size or shape. Lightweight. Wear and corrosion resistant. Provides good surface finish. It possesses low solid shrinkage. • Limitations – Plastic patterns are fragile and thus light sections may need metal reinforcements. – Plastic patterns may not work well when subject to conditions of severe shock as in machine moulding. Hareesha N G Dept Aero Engg, DSCE, Blore 12

PLASTER • Advantages – can be easily worked by using wood working tools. – Intricate shapes can be cast without any difficulty. – It has high compressive strength (up to 285 kg/cm 2) • Disadvantages – Can be used for small castings only • Plaster Patterns Material: Plaster patterns may be made out of Plaster of Paris or Gypsum cement. • Applications: Plaster is used for making (i) Small and intricate patterns, and (ii) Core boxes. Hareesha N G Dept Aero Engg, DSCE, Blore 13

WAX • Advantages ØWax patterns provide very good surface finish ØThey impart high accuracy to the castings. ØAfter being molded, the wax pattern is not taken out of the mold like other patterns; rather the mold is inverted and heated; the molten wax comes out and/or is evaporated. Thus there is no chance of the mold cavity getting damaged while removing the pattern. • Applications • Wax patterns find applications in Investment casting process. Hareesha N G Dept Aero Engg, DSCE, Blore 14

PATTERN ALLOWANCES • A pattern is always larger in size as compared to the final casting, because it carries certain allowances. • The various pattern allowances are below (a) (b) (c) (d) (e) Shrinkage or contraction allowance. Machining or Finish allowance. Draft or Taper allowance. Distortion or camber allowance. Shake or rapping allowance. Hareesha N G Dept Aero Engg, DSCE, Blore 15

Shrinkage Allowance • Almost all cast metals shrink or contract volumetrically after solidification and therefore to obtain a particular sized casting, the pattern is made oversize by an amount equal to that of shrinkage or contraction. • Different metals shrink at different rates because shrinkage is the property of the cast metal or alloy. • The metal shrinkage depends upon • The cast metal or alloy. • Pouring temperature of the metal or alloy. • Casting dimensions (size). • Casting design aspects. • Molding conditions (i. e. , mold materials and molding methods employed). • Cast iron poured at higher temperatures will shrink more than that poured at lower temperature. • Wood patterns used to make metallic patterns are given double allowance; one for the shrinkage of the metal of the pattern and the other for that of metal 16 to Hareesha N G Dept Aero Engg, DSCE, Blore be cast.

Machining Allowance • A casting is given an allowance for machining, because – Castings get oxidized in the mold and during heat treatment; scales etc. , thus formed need to be removed. – It is intended to remove surface roughness and other imperfections from the castings. – It is required to achieve exact casting dimensions. • How much extra metal or how much Machining allowance should be provided, depends upon: • Nature of metal i. e. , ferrous or non-ferrous. Ferrous metals get scaled whereas non-ferrous ones do not. • Size and shape of the casting. Longer castings tend to warp and need more material (i. e. , allowance) to be added to ensure that after machining the casting will be alright. • The type of machining operation (i. e. , grinding, turning, milling, boring etc. ) to be employed for cleaning the' castings. Grinding removes much lesser metal as compared to turning. • Casting conditions i. e. , whether casting conditions result in a rough casting or a semi-finished one. Casting conditions include the characteristics of mold-materials etc. • Molding process employed. Die casting produces parts which need little machining (allowance) whereas sand-casting, require more machining allowance. • Number of cuts to be taken. Machining allowance is directly proportional to the number of cuts required for finishing the casting. • The degree of surface finish. Hareesha desired on the cast part. N G Dept Aero Engg, DSCE, Blore 17

Draft or Taper Allowance • It is given to all surfaces perpendicular to the parting line. • Draft allowance is given so that the pattern can be easily removed from the molding material tightly packed around it without damaging the mold cavity. • The amount of Taper depends upon – Shape and size (length) of the pattern in the depth direction in contact with the mold cavity. – Molding method. – Mold materials. • Draft allowance is imparted on internal as well as external surfaces; of course it is more on internal surfaces. Hareesha N G Dept Aero Engg, DSCE, Blore 18

Fig. shows two patterns — one with taper allowance and the other without it. It can be visualized that it is easy to draw the pattern having taper allowance, out of the mold without damaging mold walls or edges. Taper on external surfaces = 10 to 25 mm/metre. Taper on internal surfaces = 40 to 65 mm/metre, Hareesha N G Dept Aero Engg, DSCE, Blore 19

Distortion Allowance • A Casting will distort or warp if: – it is of irregular shape, – all its parts do not shrink uniformly i. e. , some parts shrink while others are restricted from doing so, – it is U or V-shaped, – it has long, rangy arms as those of the propeller strut for the ship, – it is a long flat casting, – the arms possess unequal thickness, – one portion of the casting cools at a faster rate as compared to the other, etc. • Distortion can be practically eliminated by providing an allowance and constructing the pattern initially distorted i. e. , outsize in the opposite direction so that the casting after cooling neutralizes the initial distortion given on the pattern and acquires the correct shape. • The amount of distortion allowance may vary from 2 to 20 mm depending upon the size, shape and material of the casting. Hareesha N G Dept Aero Engg, DSCE, Blore 20

Shake Allowance • A pattern is shaken by striking the same with a wooden piece from side to side. This is done so that the pattern is loosened a little in the mold cavity and can be easily removed. • In turn, therefore, shaking enlarges the mold cavity which results in a bigger sized casting. • Shake allowance is normally provided only to large castings because it is negligible in case of small castings and is thus ignored. • The magnitude of shake allowance can be reduced by increasing the taper. Hareesha N G Dept Aero Engg, DSCE, Blore 21

TYPES OF PATTERNS Hareesha N G Dept Aero Engg, DSCE, Blore 22

• For selecting a particular kind of pattern for making a casting, one may consider the following points: – Quantity of castings to be produced. – The size and the complexity of the shape of the casting to be produced. – Type of molding method to be used (i. e. , hand or machine molding). – Problems associated with the molding operation such as withdrawing the pattern from the mold etc. – Other difficulties resulting from poor casting design or pattern design. Hareesha N G Dept Aero Engg, DSCE, Blore 23

• The different types of patterns commonly used are: – One piece(Solid) pattern – Split pattern – Loose piece pattern – Match plate pattern – Cope and Drag pattern – Sweep pattern – Gated pattern – Skeleton pattern – Follow board pattern. Hareesha N G Dept Aero Engg, DSCE, Blore 24

One Piece (solid) Pattern Hareesha N G Dept Aero Engg, DSCE, Blore 25

One Piece (solid) Pattern • It is the simplest type of pattern. • As the name suggests the pattern is made from one piece and does not contain loose pieces or joints. • It is inexpensive. • It is used for making a few large size simple castings • One piece pattern is usually made up of wood or metal depending upon the quantity of castings to be produced. • For making the mold, one piece pattern is accommodated either in the cope or in the drag. Hareesha N G Dept Aero Engg, DSCE, Blore 26

Split Pattern Hareesha N G Dept Aero Engg, DSCE, Blore 27

Split Pattern • Patterns of intricate (shaped) castings cannot be made in one piece because of the inherent difficulties associated with the molding operations (e. g. withdrawing the pattern from the mold etc. ) , such patterns are, then, made as split or two piece patterns. • The upper and the lower parts of the split pattern are accommodated in the cope and drag portions of the mold respectively. • Dowel pins are used for keeping the alignment between the two parts of the pattern. • The parting (surface or) line of the pattern forms the parting (surface or) line of the mold. • Patterns for still more intricate castings are made in more than two pieces for facilitating their molding and withdrawing. • A pattern having three pieces will require a three piece flask for the molding purposes Hareesha N G Dept Aero Engg, DSCE, Blore 28

Loose Piece Pattern Hareesha N G Dept Aero Engg, DSCE, Blore 29

Loose Piece Pattern • Certain patterns cannot be withdrawn once they are embedded in the molding sand. Such patterns are usually made with one or more loose pieces • Pieces for facilitating their removal from the molding box and are known as loose piece patterns. • Loose parts or pieces remain attached with the main body of the pattern, with the help of dowel pins. • The main body of the pattern is drawn first from the molding box and thereafter the loose parts are removed, the result is the mold cavity. • Loose piece patterns involve more labour and consume more time in the molding operation. Hareesha N G Dept Aero Engg, DSCE, Blore 30

Match Plate Pattern Hareesha N G Dept Aero Engg, DSCE, Blore 31

Match Plate Pattern • A match plate pattern consists of a match plate, on either side of which each half of (a number of) split patterns is fastened. • A number of different sized and shaped patterns may be mounted on one match plate. • The match plate with the help of locator holes can be clamped with the drag. • The match plate has runner and gates also attached with it. • After the cope and drag have been rammed with the molding sand, the match plate pattern is removed from in between the two (i. e. , cope and drag. ) Hareesha N G Dept Aero Engg, DSCE, Blore 32

Match Plate Pattern • Cope and drag are then assembled and this completes the mold. • Patterns, match plate, runner and gates — all may be made up of aluminium, because it is light and relatively inexpensive. • Match plate patterns are normally used in machine molding. • Match plate patterns are preferred for producing small castings on mass scale. • They produce accurate castings and at faster rates. • Piston rings of I. C. engines are produced with the help of match plate patterns. Hareesha N G Dept Aero Engg, DSCE, Blore 33

Sweep Pattern Hareesha N G Dept Aero Engg, DSCE, Blore 34

Sweep Pattern • A sweep pattern is just a form made on a wooden board which sweeps the shape of the casting into the sand all around the circumference. The sweep pattern rotates about the post. • Once the mold is ready, sweep pattern and the post can be removed • Sweep pattern avoids the necessity of making a full, large circular and costly three dimensional pattern. • Making sweep pattern saves a lot of time and labour as compared to making a full pattern. • A sweep preferred for producing large castings of circular sections and symmetrical shapes. • The manufacture of large kettles of cast iron requires a sweep pattern. Hareesha N G Dept Aero Engg, DSCE, Blore 35

Gated Pattern castings Gating system Hareesha N G Dept Aero Engg, DSCE, Blore 36

Gated Pattern • Gated patterns are usually made of metal which increases their strength and reduces the tendency to warp. • The sections connecting different patterns serve as runner and gates. This facilitates filling of the mold with molten metal in a better manner at the same time eliminates the time and labour otherwise consumed in cutting runners and gates. • A gated pattern can manufacture many castings at one time and thus it is used in mass production systems. • Gated patterns are employed for producing small castings. Hareesha N G Dept Aero Engg, DSCE, Blore 37

Skeleton Patten Hareesha N G Dept Aero Engg, DSCE, Blore 38

Skeleton Patten • A skeleton pattern is the skeleton of a desired shape. The skeleton frame is mounted on a metal base. • The skeleton is made from wooden strips and is thus a wooden framework. • The skeleton pattern is filled with sand is rammed. • A strickle (board) assists in giving the desired shape to the sand removes extra sand. • If the object is symmetrical like a pipe, the two halves (of the pipe) can be molded by using the same pattern and then the two molds can be assembled before pouring the molten metal. • Skeleton patterns are employed for producing a few large castings. • A skeleton pattern is very economical as compared to a solid pattern, because it involves less material costs. • Castings for turbine castings, water pipes, channels, etc. , are N G Dept Aero Engg, DSCE, Blore 39 made with the help of. Hareesha skeleton patterns.

Follow Board Pattern Hareesha N G Dept Aero Engg, DSCE, Blore 40

Follow Board Pattern • A follow board is a wooden board and is used for supporting a pattern which is very thin and fragile and which may collapse under the pressure when the sand above the pattern is being rammed. • With the follow board support under the weak pattern, the drag is rammed, and then the follow board is withdrawn. • The rammed drag is inverted, cope is mounted on it and rammed. During this operation pattern remains over the inverted drag and gets support from the rammed sand of the drag under it. • Ultimately, the pattern is removed and the cope and Hareesha N G Dept Aero Engg, DSCE, Blore 41 drag are assembled.

MOLDING SAND BINDERS • Binders produce cohesion between the molding sand grains in the green or dry state (or condition). • Binders give strength to the molding sand so that it can retain its shape as mold cavity. • Binders (to the molding sands) should be added as optimal minimum. • Increasing binder content reduces permeability of molding sand. • Increasing binder content, increases green compression strength up to a limit; after which green compression strength remains practically unchanged with further increase in binder content. • Clay binders are most commonly used for bonding molding sands. • The best clay is one which imparts the optimum combination of bonding properties, moisture, life and cost of producing the required casting. Hareesha N G Dept Aero Engg, DSCE, Blore 42

MOLDING SAND BINDERS • Clay binders are most commonly used for bonding molding sands. • Clay binders can be classified as: – Fire clay – Bentonite • Sodium montmorillonite • Calcium montmorillonite – Illite – Kaolinite • Bentonite: – The most commonly used clay binders are Bentonites as they produce strongest bonds in foundry molding sands. – Bentonite deposits are available in India in Rajasthan and Bihar – Bentonites are the weathered product of volcanic ash and are soft creamy white powders. Hareesha N G Dept Aero Engg, DSCE, Blore 43

MOLDING SAND BINDERS • Fire Clay: – Fire clay is a refractory clay usually found in the coal measures. – Fire clay particles are about 400 times as large as compared to those of Bentonite ; hence the same percentages of fire clay produce lower strengths. • Illite – – – Illite is the decomposition product of micaceous materials due to weathering. Illite is found in natural molding sands. Illite has softening point of about 2500°F. Illite does not swell in the same way as bentonite but gives reasonable strength. Illite particles have thickness and width of 20 and 100 -250 milli-microns respectively. • Kaolinite – – Kaolinite is the residue of weathered granite and basalt. Kaolinite binder has its composition 60% kaolinite, 30% illite and 10% quartz, Kaolinite gets Very low swelling due to water and is non-gel forming. Kaolinite particles possess thickness and width of 20 and 100 -250 milli-microns respectively. Hareesha N G Dept Aero Engg, DSCE, Blore 44

WATER • The amount of water may vary from 1. 5 to 8%. • water is responsible for the bonding action of clays. • Water activates the clay in the sand the clay-sand mixture develops strength and plasticity. • Water added to the sand mixture, partly gets adsorbed by clay and partly remains free and is known as Free Water. • The absorbed water is responsible for developing proper bond and the green strength. • The free water acts as a lubricant, • It increases plasticity • It improves moldability, but It reduces strength of the sand mixture. • For a given type of clay and its amount, there is an optimum required water content. • Too little water will not develop proper strength and plasticity. • Too much water will result in excessive plasticity and dry strength. • The amount of water required to develop the optimum properties can be Hareesha N G Dept Aero Engg, DSCE, Blore 45 found out experimentally.

ADDITIVES • The basic constituents of molding sand mixture are; – Sand – binder and – water • Materials other than the basic ingredients are also added to molding sand mixtures, of course in small quantities, in order to – enhance the existing properties. – To develop certain other properties. – to give special qualities like resistance to sand expansion, defects etc. • Some of the additive materials along are given below. Hareesha N G Dept Aero Engg, DSCE, Blore 46

• Facing materials: – Facing materials tend to obtain smoother and cleaner surfaces of castings and help easy peeling of sand from the casting surface during shake out. – A few facing materials are • • Sea coal Graphite Coke Silica floor • Cushion materials: – Cushion materials burn when the molten metal is poured and thus give rise to space for accommodating the expansion of silica sand at the surfaces of mold cavity. – In the absence of cushion materials, large flat surfaces of castings may buckle due to thermal expansion of silica sand grains. – A few cushion materials are: • Wood floor • Cellulose • Other special Additives: Hareesha N G Dept Aero Engg, DSCE, Blore – Finely ground corn floor, Iron oxide, Boric acid, diethylene glycol 47