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METAL CASTING PROCESSES

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Casting of metals and alloys
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METAL CASTING PROCESSES

  1. 1. ME8351 MANUFACTURING TECHNOLOGY 1 UNIT 1 METAL CASTING PROCESS S.BALAMURUGAN ASSISTANT PROFESSOR MECHANICAL ENGINEERING AAA COLLEGE OF ENGINEEERING & TECHNOLOGY
  2. 2. Steps in Casting Process • Melting the metal • Pouring it into a previously made mould which will give the shape for the part • Allowing the molten metal to cool & Solidify in the mould • Removing the solidified component from the mould, cleaning it & subjecting it to further treatment. • The solidified piece of metal, which is taken out of the mould is called Casting. • A plant where the castings are made is called, Foundary. It is a collection of necessary tools, materials & equipment to produce casting. Foundry – Latin word – fundere – Melting & Pouring CASTING PROCESS ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  3. 3. CLASSIFICATION OF CASTING PROCESS CASTING PROCESS Expendable Mould Casting Permanent Pattern, Sand Casting Expendable Pattern, Investment Casting Non Expendable (Permanent) Mould casting Die casting, Centrifugal casting, Continuous casting Permanent Core (Metal Core) Semi-Permanent Core (Sand Core) ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  4. 4. SAND MOULD CASTING• This process accounts 80% of the total output of cast products. • Single cast moulds – completely destroyed for taking out the casting – Knockout. • Moulding material – Sand – To improve the cohesive strength & Mouldability, Small amount of Binder, Additives & Water is added. • To make mould, the moulding material will have to be consolidated & contained around the pattern. The metallic container is called Flask. • One flask design – Pit Moulding process, Full mould process (Evaporative pattern) Types of Sand mould casting process • Bench Moulding – For small work • Floor moulding – Done on the foundary floor – Medium sized casting • Pit Moulding – for Large size casting – Pit will be created in the floor(Drag) – Top flask is placed over the pit – the walls of the pit, Brick lined & Plastered with Loam sand – Bottom of the pit is rammed with a 50-80mm layer of coke to improve permeability – Vent pipes are run from this layer to side surface – Coke is covered with Blacking sand ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  5. 5. GATING SYSTEM ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET Pouring basin: A small funnel shaped cavity at the top of the mold into which the molten metal is poured. Sprue: The passage through which the molten metal, from the pouring basin, reaches the mold cavity. In many cases it controls the flow of metal into the mold. Runner: 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. Also known as “feed head”. Splash core: A ceramic splash core placed at the end of the sprue also reduces the eroding force of the liquid metal stream. Choke: The part having small cross sectional area, to control the rate of metal flow to lower the flow velocity in the runner, to hold back slag & foreign material
  6. 6. ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET Bars & Gaggers: With large cope flasks, added support is normally required to keep the moulding sand from falling out when the cope is raised t remove the pattern. This support is provided by this components. Skim Bob: To prevent heavier and lighter impurities skim bob is used. Skin bob does not allow to impurities to reach mould cavity. Chaplets: Chaplets are used to support the cores inside the mold cavity to take care of its own weight and overcome the metallostatic force. Vent: Small opening in the mold to facilitate escape of air and gases. Chills: Metal plates, with special heat removing devices which are used to remove the heat quickly at places where harder structures are required.
  7. 7. PATTERNS • Element used for making cavities in the mould. • Not an exact replica, Slightly larger than the desired casting, due to the various allowances. • Consists of projections or bosses called core prints.(It is an open space provided in the mould for locating, positioning and supporting the core) REQUIREMENTS • Secure the desired shape & size of casting • Cheap & readily repairable • Having high strength & long life in order to make as many moulds as required. • Surface should be smooth & wear resistant. Light in weight Pattern Materials – Wood, Metal, Plastic. Piece & Short production – Wood, 10 – 500 parts per lot. Mass production – Metal, Mostly Continuos production, 1,00,000 parts per year, Standardized parts – Nuts, Bolts, Washers Batch Production – Plastics, 300 parts per lot, Annual production- 2500 to 1,00,000 parts ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  8. 8. Pattern Materials Wood • It should be dried & seasoned. • It should not contain more than 10% moisture to avoid warping. • It should be straight grained & free from knots. ▪ White pine – Straight grain, soft , easy to work ▪ Mahogany – Harder & more durable than white pine. ▪ Maple, Birch & Cherry – Harder & heavier than white pine, used for small patterns. Advantages • Light in weight, inexpensive, Workability • Holds well vanishes & Paints Disadvantages • Absorbs & gives of moisture, it varies the volume of the part. This drawback can be eliminated by drying, seasoning it & then gives coats of water proof vanishes & paints. • Poor wear & Abrasion resistance • Can’t withstand rough handling ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  9. 9. Pattern Materials Metal – Prepared using master wood pattern or machining. Advantages • Durable, Accurate in size, Smooth surface • Resistant to wear, abrasion & swelling Disadvantges • Ferrous pattern can get rusted • Expensive, Heavier than wood Materials Cast iron – Heavier, difficult to work, Cheaper, More durable Brass – Easily worked & built up by soldering or brazing – Expensive – Used for small cast parts Aluminium – light in weight, corrosion resistant, easily worked, best pattern material – Shrinkage & wear by abrasive action ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  10. 10. Plastic patterns – Made by • Injection moulding process • Utilizing laminated construction by building successive layers of resin & glass fibre • By pouring glass material into a Plaster mould Advantages • Make it more economical in cost & labour • Mouding sand sticks less to plastc than woood • No moisture absorption • Smooth surface of patterns Finishing of Pattern • Patterns should be finished by sanding, it erases the tool marks & irregularities • Then 2 to 3 coats of shellac, it fills up the pores & gives smooth finish • Good quality enamel paint should be applied on the pattern Pattern Materials ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  11. 11. PATTERN SINGLE PIECE PATTERN • Job is very simple and does not create any withdrawal problems. • Small-scale production or in prototype development. • This type of pattern is expected to be entirely in the drag and one of the surface is expected to be flat which is used as the parting plane. • A gating system is made in the mold by cutting sand with the help of sand tools. • Most inexpensive of all types of patterns. • It is often used for the generation of large castings such as stuffing box of steam engine and for creating simple shapes, flat surfaces like simple rectangular blocks ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  12. 12. TWO PIECE PATTERN It is split along the parting surface, One half of the pattern is molded in drag and the other half in cope. The two halves of the pattern must be aligned properly by making use of the dowel pins, which are fitted, to the cope half of the pattern. These dowel pins match with the precisely made holes in the drag half of the pattern. Widely used type of pattern for intricate castings. It is used in applications where it is very difficult to withdraw casting from the mold. Applications: It is used in AK-47. It is widely used in steam valves. PATTERN ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  13. 13. LOOSE PIECE PATTERN • If solid pattern has projections or backdrafts which lie above or below the parting line, it is impossible to with draw it from the mould. • For this, the projections are made with the help of loose pieces • A loose piece is attached to the main body of the pattern by a pin or with a dovetail slide • First, sand is rammed securely around the loose pieces, then the pins are removed, again sand is packed & rammed around the total pattern. • First, Main pattern drawn, then loose piece drawn from the mould. GATED PATTERN • Used to make multiple components inside the single mold. • It is nothing but the pattern consisting one or more patterns. • For joining different patterns gates are used. These are loose patterns where gates and runners have already attached. • These patterns are very expensive. Due to their high cost they are used for creating small castings. PATTERN ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  14. 14. MULTI PIECE PATTERN • Sometimes castings have very difficult and complicated designs. • In such difficult situations multi piece types of patterns are used. 3 or more patterns are included in multi piece pattern. • Three- piece pattern - Multi piece pattern. • This three- piece pattern consists of top, bottom and middle parts. The bottom part is drag, top part is cope where the middle part is termed as check box. SWEEP PATTERN • It consists of three parts spindle, base and sweep which is wooden board. • This wooden board of proper size is to be rotated about one edge to shape the cavity as circular or rotational symmetry. • Requires less time. • Spindle is directed in vertical direction and base is attached with sand. PATTERN ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  15. 15. MATCH PLATE PATTERN • A split pattern having the cope & drag portion mounted on opposite sides of plate, called the Match plate. • The gate & runners are mounted on the match plate, so very little hand work is required. • Higher productivity • Used for large castings • Several patterns can be mounted on the match plate, if the casting is small. • This will be done in a moulding machine. • Applications – Piston rings if I.C engines PATTERN ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  16. 16. PATTERN COPE & DRAG PATTERN • It is a split pattern. This pattern has cope and drag on separate plate. • Cope and drag pattern has two parts which are separately molded on molding box. • After molding parts, these two separate parts are combined to form the entire cavity. Cope and drag pattern is almost like two- piece pattern. • Used in production of large castings where the molds are very heavy and unhandy for a user. ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  17. 17. PATTERN Follow Board Pattern • In casting process some portions are structurally weak. It is not supported properly and may be break under the force of ramming. In this stage the special pattern to allow the mold may be such as wooden material. Shell pattern • It is specially used for obtaining hollow shaped structure. Along the center the parting process is done. The resultant halves produced after parting are both doweled. Segmental pattern • It is used to prepare the mold of larger circular casting to avoid the use of solid pattern of exact size • The sweep pattern is give a continuous revolve motion to generate the part, but the segmental pattern itself and mold is prepared. • In this segmental pattern construction should be save the material for pattern make and easy carried. ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  18. 18. REASONS FOR PROVIDING COLOURS • To quickly identify the main pattern body & different pattern parts • To identify the loose piece, core prints • To visualize machined surface RED – Cast surface to be machined BLACK – Surface to be left unmachined YELLOW – Core prints seats RED STRIPS ON YELLOW BASE – Loose Piece & Seating CLEAR OR NO COLOUR – Parting Surface YELLOW STRIPS ON BLACK BACKGROUND – Core Prints for Machined Castings SUPPORTS – Black Strips on Yellow Base PATTERN COLOURS ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  19. 19. PATTERN ALLOWANCES • The difference in the dimension of pattern & final product of casting is known as Pattern Allowance. • Factors – Composition of Alloy, Mold Material, Mold design, Complexity of pattern, component size Shrinkage Allowance • Metal shrinks on solidification & contracts further on cooling to room temperature. • To compensate this problem, linear dimensions of the patterns are increased. Cast Iron, malleable iron = 10 mm/m, Steel = 20 mm/m Aluminium, Copper, Brass = 15 mm/m • Liquid Shrinkage – Reduction in volume of metal, when it transforms from liquid to solid • Phase transformation Shrinkage – During Phase Transition • Solid shrinkage – Reduction in volume as the solid metal cool down • Liquid Shrinkage, Phase transformation Shrinkage are compensated by feeding molten metal from the riser till metal solidified. ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  20. 20. DRAFT / TAPER ALLOWANCE It is hard to remove casted object from pattern if it has vertical faces as shown in fig. Vertical faces causes a continuous contact or friction when object is removing from the pattern. The leading edge may break off during removal of cast, To avoid this, vertical faces of the pattern are tapered in small known as draft angle. Outer surface – 1 to 3 degree, Inner surface – 5 to 8 degree Draft allowance, Hand moulding > Machine Moulding Smaller vertical surfaces, needs more draft angle. PATTERN ALLOWANCES ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  21. 21. Machining Allowance • Dimensional accuracy obtained by a casting product are poor. • The ferrous material would have scales on the skin when it solidifies. • To get dimensional accurate, a subsequent finishing operation is required. • It depends on the material, complexity of surface details, type of moulding & required surface finish. • To reduce machining allowance, entire cast inside the drag flask such that reducing defect due to parting line. Shake Allowance - Rapping Allowance • The pattern when withdrawn from the mould it distort the sides and shape of the cavity. • To avoid this, the pattern is shaked to create a small void or gap between the mould and pattern surface for easy removal. • This increases the size of cavity and hence to compensate this, the size of the pattern is slightly smaller than castings. Shake allowance is considered as negative allowance PATTERN ALLOWANCES ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  22. 22. Distortion Allowances Castings get distorted during solidification, due to their shape. U,V or L shape, it will tend to contract at the closed end causing the vertical legs to look slightly inclined. This can be prevented by making the legs of the shaped pattern converge slightly, so that distortion will have its sides vertical. It may occur due to internal stresses, this stresses are due to unequal cooling of different sections of the casting. To prevent this • Modification of casting design • Providing sufficient machining allowance to cover the distortion affect • Providing suitable allowance on the pattern, called camber or distortion allowance (inverse reflection) PATTERN ALLOWANCES ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  23. 23. ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  24. 24. MOULDING MATERIALS Basic Moulding Material – Silica Sand, various Binders Auxiliary Group – Additives Constituents of Moulding Sand Silica sand Cheap, Thermal Stability, Highly Refractory, Easily Moulded, Reusable Binder (Clay) • Combined with water act as a bonding agent, coating with moist clay, the strength of the sand mix in increased. • It imparts cohesiveness & Plasticity to the moulding sand in the moist state & increases the strength after drying. Additives It imparts strength, thermal stability, permeability, refractiveness, thermal expansion to the moulding sand Water Proper amount of water added to give a high strength with sufficient plasticity after tempering the mould. ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  25. 25. PROPERTIES OF MOULDING SAND PERMEABILITY • Permeability or Porosity of the moulding sand is the measure of its ability to permit air to flow through it. STRENGTH OR COHESIVENESS • It is defined as the property of holding together of sand grains. Moulding sand should have ample strength so that the mould does not collapse. REFRACTIVENESS • It is the ability of the moulding sand mixture to withstand the heat of melt without showing any sign of softening or fusion PLASTICITY or FLOWABILITY • It is the measure of moulding sand to flow around & over a pattern during ramming & to uniformly fill the flask. COLLAPSIBILITY • It permits the Moulding sand & Core to collapse easily during shake out. • Lack of collapsibility leads to formation of cracks in the casting. It depends on the amount of binder. ADHESIVENESS • It is the property of sand mixture to adhere to another body (Moulding flask). The mould does not fall when the flask are lifted or turned over CO-EFFICIENT OF EXPANSION • Sand should have low coefficient of expansion • How the size of an object changes with change in temp. ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  26. 26. Sand • Natural sand – from Natural Deposits, Clay content is higher than desired • Synthetic Sand – Prepared by mixing a relatively clay free with specified type of binder, water & Additives. Based on metal to be cast, sand grains selected. • Chemically coated sand – Clean silica sand coated with hydrocarbon resin, which act as a binder, clay also added. Excellent refractiveness – Clean surface can obtained Binders Inorganic Binder – Clay – Formed by the weathering & decomposition of rocks. Fire-Clay, Kaolinite, Bentonite, Portland cement, Sodium Silicate Organic Binder – Used for Core Making Obtained from Wheat, Corn & Resins (Drying oils, linseed oil, Soyabean oil, Pitch & Molasses) Additives To enhance the existing Properties – Better Surface finish - To eliminate defects. Cereals(Corn), Saw dust, Wood Flour, Silica flour, Iron oxide Facing Materials To obtain the smooth surface – Easy peeling of sand from casting – Asphalt, Graphite, Pitch(distilled from soft coal) Cushion Materials While pouring the molten metal, mould will expand. For getting this kind space, Wood flour, Cereals & Cellulose added. MOULDING MATERIALS ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  27. 27. SAND PREPARATION & CONDITIONING • Hand Mulling – Natural Sand • Remove all the impurities • Mixing of sand ingredients in dry state by Muller • Temper the moulding sand ingredients & continue mulling action till the uniform distribution of the ingredients • Aeration process – Power operated screening, beating the sand or by passing the sand stream over toothed belt. • This process separates sand grains into individual particles • To avoid difficulties in mould making, sand is cooled below 37°C • Wheel is either rest on sand or 5-10mm above the base • Plows stir the sand & bring it under the wheels, Wheels mix the sand with a squeezing action. ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  28. 28. TESTING OF MOULDING SAND ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET Moisture Content Test • Test sample is weighed 50 gm of moulding sand. Heated for 2 hours at 110°C • Allowed to cool to room temperature. Then reweighing the sample. Moisture Content= 𝑰𝒏𝒊𝒕𝒊𝒂𝒍 𝒘𝒆𝒊𝒈𝒉𝒕 −𝒇𝒊𝒏𝒂𝒍 𝒘𝒆𝒊𝒈𝒉𝒕 𝑰𝒏𝒊𝒕𝒊𝒂𝒍 𝒘𝒆𝒊𝒈𝒉𝒕 × 100 Clay Content Test • Take the standard dried sand sample (50 gm) • Mixed with distilled water & 1% NaOH solution, stirring for 5 minutes, then allowed to settle down 10 minutes. • This step repeated until, the water above the sand is clean. Now the sand is dried & weighed. The loss of weight gives the clay content. Clay Content= 𝑰𝒏𝒊𝒕𝒊𝒂𝒍 𝒘𝒆𝒊𝒈𝒉𝒕 −𝒇𝒊𝒏𝒂𝒍 𝒘𝒆𝒊𝒈𝒉𝒕 𝑰𝒏𝒊𝒕𝒊𝒂𝒍 𝒘𝒆𝒊𝒈𝒉𝒕 × 100 Strength Test • UTM machine. Compressive, Shear, Tensile & Bending Strength • Test Specimen – 5.08cm dia × 5.08 long
  29. 29. TESTING OF MOULDING SAND Permeability Test • Ability to permit air to flow through it. • Test Specimen – 5.08cm dia × 5.08 long(h) , Volume of air(V) – 2000cm3, A – Area • Air pressure(p) – 10gm/cm2, t - Time • Permeability Number = 𝑽× 𝒉 𝒑 ×𝑨× 𝒕 Fineness Test • With the help of sieve with different size, the size of the grains will be determined. Completely dry & Clay free sand. 15 minutes by electric motor. • Top – Coarse sieve, Bottom – Finest Sieve Hardness Test • To check the ramming density of the sand, prepared mould surface is tested. • 40 – Lightly Rammed Sand, 50 – Medium, 70 – Hard Rammed Sand. ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  30. 30. Moulding is the process of making a cavity similar to the product required in sand. • Selection of a mould is governed by the type of metal to be cast, size of casting, accuracy & the surface finish of the casting. MOULDING PROCESS GREEN SAND MOULD • Green sand contains Silica sand, Clay, Water & Additives. • 10 - 15% Clay, 4 - 6% Water & remaining Silica sand. • Small & Medium Sized Castings • Non ferrous metals & Alloys ADVANTAGES • Less time(No drying) & cost DISADVANTAGES • Less surface finish, Low mould strength • Blow hole defect ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  31. 31. DRY SAND MOULD • Green sand mould is dried after making the mould. • Mixture of silica sand, coal dust, clay & molasses DRYING • Large size moulds – Oxy acetylene flame • Small moulds – Oven ADVANTAGES – Stronger than green sand mould, Long life, Permeability more DISADVANTAGES – Time consuming, Cost high, Subjected to Hot Tear LOAM MOULDING • Very large castings – moulding box & Pattern can not be used due to cost • Loam sand is a mixture of Silica sand, Graphite powder & more amount of clay. • Initially rough frame work made by Bricks. Then loam sand is applied over the brickwork. Plates & Bars used to reinforce the brick. • A sweep pattern is used to get the required shape ADVANTAGES - Large casting with less cost, good surface finish DISADVANTAGES – Time consuming, Skilled labours MOULDING PROCESS ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  32. 32. BENCH MOULDING – For small work FLOOR MOULDING – Done on the foundary floor – Medium sized casting PIT MOULDING – For Large size casting – Pit will be created in the floor(Drag) – Top flask is placed over the pit – the walls of the pit, Brick lined & Plastered with Loam sand – Bottom of the pit is rammed with a 50-80mm layer of coke to improve permeability – Vent pipes are run from this layer to side surface – Coke is covered with Blacking sand. SWEEP MOULDING • Part is symmetrical about vertical axis • Used for large & medium sized casting • Drag on the floor, A sweep board having a shape required MOULDING METHODS ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  33. 33. MOULDING MACHINE JOLTING MACHINE SAND SLINGER Mass production – Reduce labors, increase the quality of the mould OPERATION – 1) Ramming the moulding sand 2) Shake the pattern for easy removal 3) Removing the pattern from the sand • Pattern is placed in the flask • Filling of sand • Raising the table with mouding box to 80mm & sudden drop • Operated by pneumatic or Hydraulic • Used for ramming horizontal surfaces on the mould • Noisy operation • Pattern is placed in the flask • Slinger is operated • Slinger has an impeller which can be rotated with different speeds. • Due to rotation, impeller throws a stream of sand at greater velocity into the flask. • The density of sand is controlled by the speed of the impeller. ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  34. 34. MOULDING MACHINE The moulding sand in the flask is squeezed between the machine table & a squeezer head • Mould is clamped on the table • The flask is placed on the mouding board • Placing of pattern in the flask • Filling of sand in the flask • The table is raised by the table lift mechanism against squeezer head. • The plate enter the sand frame & packs the sand. • Then the table comes down to starting point • Pattern is placed on the mound table • Mound table is clamped on the Ram • The flask is placed on the frame & filled with sand • The table with pattern is raised up against the squeezer head • The flask with pattern is squeezed between squeezer head & table • Then the table returns to starting point ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  35. 35. CORES It is used to provide internal cavities, recesses, or projections in the casting. It is usually positioned into a mould after the removal of the pattern. It is a body of refractory material (Sand or Metal) It is subjected to severe thermal & mechanical effects than mould, they surrounded all side except end. Requirements • Strength – Based on the sand & Binder • High Refractiveness – Increased by Thin coating of Graphite to the surface. • Good permeability – Based on grain size & distribution of grains in the core sand mix. • Collapsibility – Enhanced by Oil Binders ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  36. 36. TYPES OF CORE BASED ON THE STATE OF CORE GREEN SAND CORE • It is formed by the pattern itself when it is rammed. • It is made up of same sand as the moulding sand. • Cores are weak, for Light Castings DRY SAND CORE • This core made sepeartely & then positioned in the mould, after the pattern is taken out & before the mould is closed. BASED ON THE POSITION OF THE CORE HORIZONTAL CORE • Placed horizontally in the mould, positioned along the parting line of the mould. • The ends of the core rest in the seats provided by the core prints on the pattern VERTICAL CORE • Positioned vertically, the two ends of the core rest on core seats in the Cope & Drag. • Maximum position of the core supported in drag. ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  37. 37. BALANCED CORE • Used for blind holes along the horizontal axis. • Core supported at one end, this support should be sufficient length to prevent its falling into the mould. HANGING CORE • This will be used, When a cored casting is to be completely moulded in the drag, with the help of a single piece solid pattern. • Core is supported above & hangs into the mould DROP CORE • A hole which is not in line with the parting surface is to be produced at a lower level. KISSING CORE • Used when a number of holes of less dimensional accuracy is required. No core prints are provided, No seat is available for the core. • The core is held in position approximately between the cope and drag and hence referred as kiss core. TYPES OF CORE ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  38. 38. MELTING FURNACE • To pour the metal into the mould, the metal to be in liquid state. • Furnace is used to melt the metal. • Heat source – Fuel combustion, Electric Arc, Electric Resistance • It contains a high temperature zone surrounded by a refractory wall structure which withstands high temperature. • Blast furnace – Basic Melting operation • Electric Arc Furnace, Foundary Furnace – Remelting operation SELECTION OF FURNACE • Initial furnace cost • Type of metal melted • Melting & Pouring Temperature required • Quantity & Quality of metal to be melted According to the melting method: Furnace for Batch Melting – Crucible Furnace, Electric Furnace, Air Furnace Operated by Coal, Coke, Oil, Gas or Electricity Furnace for Continuous Melting – Cupola Furnace ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  39. 39. CRUCIBLE FURNACE • Simplest of all furnaces, used in small foundries. • Melting is not continuous & Large variety of metals can be melted in small quantities. • Melting of metal takes place inside a melting pot, called Crucible • Crucible is made up of Clay & Graphite ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  40. 40. COKE FIRED FURNACES OIL FIRED FURNACES • Installed in Pit form, Pit Furnaces • Used for melting small quantity of ferrous & Non-Ferrous metals • It consists of Refractory lining inside & Chimney at the top • Fuel – Coke • Natural & Artificial draught used • Metal pieces are placed inside the crucible. • Crucible is placed on the coke bed, Coke is placed around the crucible • Crucible is placed on a pad • Fuel – Oil or Gas • A mixture of Oil & Air or Gas & Air is fed into the furnace, which burns inside to produce the required temperature • While burning, the mixture enters tangentially & encircles the crucible • To prevent heat loss, a cover is provided at the top Applications – Cast iron & Non- Ferrous Alloys in small quantity Applications – Cast iron & Non- Ferrous Alloys in small quantity
  41. 41. ELECTRIC FURNACE APPLICATIONS – High quality Carbon steels & Alloy steels • First, the furnace is preheated • Charging of Steel scraps • The electrodes are lowered down & a gap between the electrode & metal charge is maintained by Automatic control. • Electrode are consumable APPLICATIONS – To melt cast iron, steel, copper & its alloys. HEAT SOURCE Heat radiation from arc Hot Refractory walls of the furnace Conduction from the hot linings when the furnace rocks ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET • Used for High quality castings – Oxidation loss eliminated, Alloying elements can be added without loss, Composition & its temperature can be controlled accurately.
  42. 42. CUPOLA FURNACE – CONTINUOUS MELTING • Used for Grey Cast iron, Nodular Cast Iron, Copper based alloys & Pig Iron products • Fuel – Low suplhur coke, Anthratic coal, Carbon Briquettes • Cylindrical shell, Boiler Plate, 6-10mm thick, Cast Iron Legs • Tuyeres are the opening through which pressurized air is forced into cupola • Air from blower, comes through Blast pipe & enters a chamber called Wind Box ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  43. 43. PREPARATION OF CUPOLA • The bottom door is dropped to open, to remove the slag, coke & iron, which is left in the previous melting operation. • Repairing the damaged fire bricks, Refractory lining with refractory patching mixture. • Then bottom door is closed, tempered sand bottom of 10cm thick slope will created to the Tap hole. LIGHTING THE FIRE • To start the cupola, dry & soft wooden pieces are placed on the rammed sand • Coke is placed over the wooden pieces & the wooden pieces are ignited • Air required for combustion of coke enters from the tuyeres • After the well burning of initial coke, additional coke is added to the desired height CUPOLA FURNACE – CONTINUOUS MELTING ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  44. 44. CHARGING OF CUPOLA • After igniting the coke bed properly, the cupola is charged from the charging door, by using alternate layers of limestone, iron & Coke upto the level of charging door • Ratio of Metal to Fuel – 4 : 1 to 12 : 1 By weight • Metal Charge – Pig Iron 30%, Cast iron Scrap 30%, 10% Steel Scrap & 30% Returns(Sprue, Gates, Risers) • Charging should be completed 45 minutes to 1 hour, before the air blast is turned on. MELTING • The charge is heated up with natural draft for 20-50 min • Soaking period, Blowers are not started • At the end soaking period, the blast is turned on & the coke becomes fairly hot to melt the metal charge • 10 minutes after the start of blast, Melting will start. • By using the moulding sand bolt, the tap & slag holes are closed • 5 minutes for collecting the molten metal CUPOLA FURNACE – CONTINUOUS MELTING ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  45. 45. SLAGGING & METAL TAPPING • After the collection of Molten metal, slag hole is opened & it is removed • The bolt inserted in the Tap hole is Knocked out & molten metal is taken out • Air blast still continues, melting progresses & the molten iron is tapped • The Tap hole is sealed with conical clay plug when the slag appears in the tap hole. • Repeating the Slagging & Tapping till metal is tapped • Then heating finished, charging stopped & Blast is off. • Bottom door are dropped, allow all the materials from the cupola to floor COMBUSTION ZONE – LOT OF HEAT IS LIBERATED C + O2 CO2 + Heat, 2Mn + O2 2MnO2 + Heat, Si + O2 SiO2+Heat REDUCTION ZONE – REDUCES THE HEAT UPTO 1200°C Protects the metal from oxidation, CO2 + C 2CO – Heat MELTING ZONE - 1600°C – First Layer of Coke Bed 3Fe + 2CO Fe3C + CO2 PREHEATING ZONE – Gases CO2, CO & N2 rising upwards, 1150°C CUPOLA FURNACE – CONTINUOUS MELTING ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  46. 46. SPECIAL CASTING PROCESS SHELL MOULDING CASTING Pattern creation - A two-piece metal pattern is created in the shape of the desired part, Pattern material - Copper Alloys, Aluminum Alloy(Low Volume) or graphite for casting reactive materials. Mold creation - First, each pattern half is heated to 175-370°C and coated with a lubricant to facilitate removal. Next, the heated pattern is clamped to a dump box, which contains a mixture of sand and a resin binder. The dump box is inverted, allowing this sand-resin mixture to coat the pattern. The heated pattern partially cures the mixture, which now forms a shell around the pattern. Each pattern half and surrounding shell is cured to completion in an oven and then the shell is ejected from the pattern. ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  47. 47. SPECIAL CASTING PROCESS SHELL MOULDING CASTING Mold assembly - The two shell halves are joined together and securely clamped to form the complete shell mold. If any cores are required, they are inserted prior to closing the mold. The shell mold is then placed into a flask and supported by a backing material. Pouring - The mold is securely clamped together while the molten metal is poured from a ladle into the gating system and fills the mold cavity. Cooling - After the mold has been filled, the molten metal is allowed to cool and solidify into the shape of the final casting. Casting removal - After the molten metal has cooled, the mold can be broken and the casting removed. Trimming and cleaning processes are required to remove any excess metal from the feed system and any sand from the mold. ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  48. 48. SHELL MOULDING CASTING • CASTING MATERIALS - Alloy Steel, Carbon Steel, Cast Iron, Stainless Steel, Aluminum, Copper, Nickel ADVANTAGES • Can form complex shapes and fine details • Very good surface finish • High production rate • Low labor cost, Low tooling cost, Little scrap generated DISADVANTAGES • High equipment cost APPLICATIONS • Cylinder heads, connecting rods ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  49. 49. INVESTMENT CASTING or LOST WAX PROCESS Pattern creation - The wax patterns are typically injection molded into a metal die and are formed as one piece. Cores may be used to form any internal features on the pattern. Several of these patterns are attached to a central wax gating system (sprue, runners, and risers), to form a tree-like assembly. The gating system forms the channels through which the molten metal will flow to the mold cavity. Mold creation - This "pattern tree" is dipped into a slurry of fine ceramic particles, coated with more coarse particles, and then dried to form a ceramic shell around the patterns and gating system. This process is repeated until the shell is thick enough to withstand the molten metal it will encounter. The shell is then placed into an oven and the wax is melted out leaving a hollow ceramic shell that acts as a one-piece mold, hence the name "lost wax" casting.
  50. 50. INVESTMENT CASTING or LOST WAX PROCESS Pouring - The mold is preheated in a furnace to approximately 1000°C and the molten metal is poured from a ladle into the gating system of the mold, filling the mold cavity. Cooling - After the mold has been filled, the molten metal is allowed to cool and solidify into the shape of the final casting. Casting removal - After the molten metal has cooled, the mold can be broken and the casting removed. The ceramic mold is typically broken using water jets, Once removed, the parts are separated from the gating system by either sawing or cold breaking (using liquid nitrogen). Finishing - Often times, finishing operations such as grinding or sandblasting are used to smooth the part at the gates. Heat treatment is also sometimes used to harden the final part. ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  51. 51. ADVANTAGES • Can form complex shapes and fine details • Many material options • High strength parts • Very good surface finish and accuracy • Little need for secondary machining DISADVANTAGES • Time-consuming process • High labor cost • High tooling cost • Long lead time possible APPLICATION - Turbine blades, armament parts, pipe fittings, lock parts, jewelry INVESTMENT CASTING or LOST WAX PROCESS ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  52. 52. PRESSURE DIE CASTING Die casting is a manufacturing process that can produce geometrically complex metal parts through the use of reusable molds, called dies. HOT CHAMBER DIE CASTING – LOW MELTING TEMP. – ZINC, TIN, LEAD COLD CHAMBER DIE CASTING – HIGH MELTING TEMP. - ALUMINUM TOTAL CYCLE TIME 2 SEC TO 1 MIN CLAMPING • Time required for close & clamp the die depends upon the machine • Lubrication in die halves – after 3 cycles INJECTION •Injection time depends on materials, wall thickness of casting •Injection pressure 68 bar to 1350 bar •This pressure holds the molten metal in the die during solidification COOLING • High wall thickness requires long cooling time • Complex geometry also requires long time – additional resistance to the flow of heat EJECTION - During cooling, the part shrinks & adheres to the die TRIMMING - During cooling, the material in the channels of the die will solidify attached to the casting. This excess material, along with any flash that has occurred, must be trimmed from the casting.
  53. 53. PRESSURE DIE CASTING - HOT CHAMBER DIE CASTING • Low melting temperatures, such as zinc, tin, and lead. • High temperature would damage the pump, which is in direct contact with the molten metal. • The molten metal then flows into a shot chamber through an inlet and a plunger, powered by hydraulic pressure, forces the molten metal through a gooseneck channel and into the die. • Typical injection pressures for a hot chamber die casting machine are between 68 and 340 bar. • After the molten metal has been injected into the die cavity, the plunger remains down, holding the pressure while the casting solidifies. • After solidification, the hydraulic system retracts the plunger and the part can be ejected by the clamping unit.
  54. 54. PRESSURE DIE CASTING – COLD CHAMBER DIE CASTING • Used for alloys with high melting temperatures. Aluminum, Brass, Magnesium • Melting of metal takes place in open holding pot. Using ladles, molten metal poured in the pouring hole. this holding pot is kept separate from the die casting machine • The metal is poured from the ladle into the shot chamber through a pouring hole. Injection is usually oriented horizontally and does not include a gooseneck channel. • A plunger, powered by hydraulic pressure, forces the molten metal through the shot chamber and into the injection sleeve in the die. Injection pressure between 135 and 1350 bar. • After the molten metal has been injected into the die cavity, the plunger remains forward, holding the pressure while the casting solidifies. • After solidification, the hydraulic system retracts the plunger and the part can be ejected by the clamping unit. ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  55. 55. GRAVITY CASTING• Permanent Mould Casting – Nonferrous metals Zinc, Copper, Aluminum, Lead, Magnesium, Tin Alloys • APPLICATION – Carburetor bodies, Oil pump bodies, Pistons • Used for large number of casting • Permanent mould is made up of heat resisting Cast Iron, Alloy Steel, Graphite. • Pouring cup, Sprue, Riser are made in this molud itself • First, the mould is preheated • Refractory coating By Spraying or Brushing – Protects from Erosion & Sticking • Molten metal is fed into the mould by Gravitational force
  56. 56. CONTINUOUS CASTING • Long vertical mould, made of copper, Brass or Graphite • Water cooled mould – molten immediately solidified • Saw or Oxy-Acetylene flame is used to cut the casting of required length • X-Ray unit controls the pouring rate of molten metal from ladle • Lubricating oil is applied between casting & mould wall to reduce friction • Argon gas applied on the top of the mould to prevent the atmospheric reaction • The guide rolls at the bottom keep on pulling the casting to match with the cooling rate. • By controlling the cooling rate, the grain size & structure of metal can be regulated. Application – Rods, Pipes, Slabs, Bars
  57. 57. CARBON DIOXIDE CO2 PROCESS • In this process the sand molding mixture is hardened by blowing gas over over the mould. • Carbon di oxide molding deliver great accuracy in production. • Suitable proportions of Silica sand & Sodium silicate binder(3-5%) are mixed • Addition of additives (Aluminum oxide, Molasses) • Placing of pattern in the drag box, Parting sand sprinkled on the pattern surface • Filling the sand mixture & Ramming, Placing Sprue, Riser pin • Passing the CO2 gas through vent holes • Sodium silicate reacts with carbon dioxide gas to form silica gel that binds the sand particles together. • Removal of Sprue, Riser & the Pattern Na2SiO3 + CO2 Na2CO3 + SiO2 ADVANTAGES • Good Surface Finish • High Production runs DISADVANTAGES • Poor collapsibility • Over gassing affect the property of sand ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  58. 58. CENTRIFUGAL CASTING • Centrifugal casting, sometimes called rotocasting, is a metal casting process that uses centrifugal force to form cylindrical parts. • This differs from most metal casting processes, which use gravity or pressure to fill the mold. • In centrifugal casting, a permanent mold made from steel, cast iron, or graphite is typically used. Use of expendable sand molds is also possible. ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  59. 59. CENTRIFUGAL CASTING 1.Mold preparation - The walls of a cylindrical mold are first coated with a refractory ceramic coating, which involves a few steps (application, rotation, drying, and baking). Once prepared and secured, the mold is rotated about its axis at high speeds (300-3000 RPM), typically around 1000 RPM. 2.Pouring - Molten metal is poured directly into the rotating mold, without the use of runners or a gating system. The centrifugal force drives the material towards the mold walls as the mold fills. 3.Cooling - With all of the molten metal in the mold, the mold remains spinning as the metal cools. Cooling begins quickly at the mold walls and proceeds inwards. 4.Casting removal - After the casting has cooled and solidified, the rotation is stopped and the casting can be removed. 5.Finishing - While the centrifugal force drives the dense metal to the mold walls, any less dense impurities or bubbles flow to the inner surface of the casting. As a result, secondary processes such as machining, grinding, or sand-blasting, are required to clean and smooth the inner diameter of the part.
  60. 60. Due to the high centrifugal forces, these parts have a very fine grain on the outer surface and possess mechanical properties approximately 30% greater than parts formed with static casting methods ADVANTAGES • Can form very large parts • Good mechanical properties • Good surface finish and accuracy • Low equipment cost • Low labor cost • Little scrap generated DISADVANTAGES • Limited to cylindrical parts • Secondary machining is often required for inner diameter • Long lead time possible APPLICATIONS - Pipes, wheels, pulleys, nozzles CENTRIFUGAL CASTING ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  61. 61. STIR CASTING • It is a liquid state method of composite materials fabrication in which a dispersed phase(ceramic, particles, short fibers) is mixed with a molten matrix metal by means of mechanical stirring. • Metal Matrix Composite (MMC) • First matrix material is melted • Next reinforcement material added to the melt. • Finally we obtain the MMC mixture (suitable dispersion) through stirring. • Pouring of molten metal into the desire cavity ADVANTAGES • Low cost, simple & flexible operation • High productivity • Very large size parts can be made ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  62. 62. DIFFICULTIES INVOLVED IN CASTING STEELS OVER CAST IRON • Steel contains 2% carbon –forge by hammering without breaking • Cast iron 2.4 – 4% carbon – more brittle – difficult to forge by hammering • Steel • High Melting point • Greater shrinkage rate – Require Proper mould design – More capacity of Risers required • Thinner areas will cool quicker than Thicker areas leads to internal stress points – Fracture • Molten steel is less fluid than molten iron – Pouring & filling of mould is difficult • Molten steel can react with moulding sand – Unpredictable results ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  63. 63. CASTING DEFECTS BLOW HOLES – Appears as cavities in Casting – Due to gases & Steam formed • Excess moisture in the mouding sand • Core are not sufficiently Baked, Rust & Moisture on Chills, Chaplets • Moulds are not adequately vented POROSITY – Occurs in casting in the form of pinhole porosity • High temperature of pouring • Gas dissolved in metal charge • Less amount of flux, Slow solidification SHRINKAGE – Volumetric Shrinkage – Depression on the casting surface • Faulty gating & riser system, Improper Chilling ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  64. 64. CASTING DEFECTS HOT TEARS or HOT CRACKS – It is the crack in the casting by high residual stress. An oxidized surface showing an irregular & Ragged Appearance on the Fracture • Lack of Mould, Core collapsability • Faulty mould design • Hard Ramming of Mould MIS RUN or COLD SHUTS - • Lack of fluidity in molten metal (Proper Pouring Temperature) • Faulty Design & Gating HARD SPOTS • In iron casting, this spots developed in casting surface, Rich in Silicon Content, due to local chilling of those spots in Moulding sand. • Faulty Metal Composition, Faulty Design of Casting ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  65. 65. CASTING DEFECTS SCABS (CUT & WASHES) - The Cavities formed on the Mould & Core surfaces due to erosion are filled by molten metal • Low strength of Mould & Core, Faulty Gating • Lack of Binders in Facing & Core sand MISMATCH & CORE SHIFT – Misalignment between two mating surfaces & Changing their location • Worn out or Bent clamping pins, Faulty core boxes • Misalignment of two halves of pattern • Improper location & support of core SCAR - Due to improper permeability or venting. • Scars are shallow blows that appear on a flat surface • Blisters are scars covered with a thin layer of metal. ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  66. 66. CASTING DEFECTS METAL PENETRATION Metal penetration occurs when liquid metal penetrates gaps in the molding sand. The penetration is visible to the naked eye as a rough and uneven surface finish of the casting. • Use of sand with low strength and high permeability • Use of large or coarse sand grain: the coarser the sand grains, the more severe the metal penetration • Lack of mold wash • Soft ramming of sand SWELLS - Swells are an enlargement of the casting. Swells typically take on the shape of a slight, smooth bulge on the vertical face of castings. • Soft ramming of the mold • Low strength mold. https://www.intouch-quality.com/blog/21-casting-defects-and-how-to-prevent-them-in- your-products ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  67. 67. DESIGN CONSIDERATION OF CASTNG PROCESS Designs showing the importance of maintaining uniform cross-sections in castings to avoid hot spots and shrinkage cavities. ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  68. 68. The use of metal padding (chills) to increase the rate of cooling in thick regions in a casting to avoid shrinkage cavities design modifications to avoid shrinkage cavities in castings. DESIGN CONSIDERATION OF CASTNG PROCESS ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  69. 69. Redesign of a casting by making the parting line straight to avoid defects DESIGN CONSIDERATION OF CASTNG PROCESS PLACEMENT OF PARTING LINE SHOULD BE EVEN ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  70. 70. DESIGN CONSIDERATION OF CASTNG PROCESS USE OF GOOD RIBS DESIGN TO OBTAIN IMPROVED STIFFNESS & REDUCE WEIGHT OF CASTING ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET
  71. 71. Sharp corners, edges and rapid changes in cross section should be avoided in cast parts. Fillets should be added to sharp corners and edges. Uniform Wall Thickness Wall thickness should be kept uniform as it helps to create high quality cast parts. Sudden variations and geometry changes and in wall thickness affects metal flow, resulting in air enclosures and poor surface finish of parts. Draft is the taper given to core and cavity for easy removal of casting (or pattern). Adding proper drafts on the cast parts improves cycle time and quality of surfaces. The sidewalls of the castings and other features perpendicular to the parting line must be drafted as much as possible. DESIGN CONSIDERATION OF CASTNG PROCESS ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET

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