advanced casting.pdf
- 1. CASTINGS Casting is a manufacturing process in which a liquid material is usually poured into a mould, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a casting, which is ejected or broken out of the mould to complete the process. Casting materials are usually metals or various cold setting materials that cure after mixing two or more components together, examples are epoxy, concrete, plaster and clay. Casting is most often used for making complex shapes that would be otherwise difficult or uneconomical to make by other methods. Casting is a 6000-year-old process. The oldest surviving casting is a copper frog from 3200 BC.
- 2. Die casting Die casting is a widespread non-expendable technique the which metal are forced into the mold cavity under high pressure. Die casting mold that are known as dies can be used repeatedly to produce castings in a variety of sizes, shapes and wall thickness. The mold cavities are designed with intricate designs that enables in producing complex shapes with accuracy, surface finish and attractiveness. Today, the die casting process is constantly getting refined by improving the alloys and the casting process.
- 3. Process: In the die casting process molten metal or other materials are forced, under high pressure into the cavities of the steel mold. Dies are two part molds that are made of alloy tool steel. The fixer die half and the ejector die half. The die or mold is fabricated with the impression of the component that is to cast. The molten metal is injected into the die under high pressure and high speed, which helps in producing a casting that is smooth and precise as the original mold. The pressure is maintained on the mold until the hot metal solidifies. When the metal is hardened, the die is opened to remove the casting
- 4. There are four types of dies: Single cavity to produce one component Multiple cavity to produce a number of identical parts Unit die to produce different parts at one time Combinations die to produce several different parts for an assembly
- 6. Die casting: Advantages: Good dimensional tolerances are possible Excellent part-part dimensional consistency Parts require a minimal post machining Post machining can be totally eliminated A process that can be fully automated Disadvantages: Economical only in very large quantities due to high tool cost Not recommended for hydrostatic pressure applications For Castings where penetrant (die) or radiographic inspection are not required. Difficult to guarantee minimum mechanical properties
- 7. Die casting application Die casting is most suitable for casting medium sized parts with complex details. Die-casting is the largest casting technique that is used to manufacture consumer, commercial and industrial products like automobiles, toys, parts of sink faucet, connector housing, gears, etc. Most die castings are done from non-ferrous metals like aluminum, magnesium, etc.
- 8. Centrifugal casting Centrifugal casting or roto casting is a casting Technique that is typically used to cast thin-walled cyclinders. It is used to cast such materials as metal, glass, and concrete. Its noted for the high quality of the results attainable, particularly for precise control of their metallurgy and crystal structure. It’s chiefly used to manufacture stock materials in standard sizes for further machining, rather than shaped parts tailored to a particular end-use.
- 9. Features This castings can be made in almost any length, thickness, diameter. Different wall thickness can be produced from the same size mold. Resistant to atmospheric corrosion a typical situation with pipes. Mechanical properties of centrifugal castings are excellent because of the grain structure formed due to centrifugal action. Size limits are up to 6m(20ft) Diameter and 15m (49ft) length. Wall thickness range from 2.5 to 125mm Surface finish ranges from 2.5 to 12.5mm
- 10. Diagram
- 11. Applications Typical parts made by this process are Pipes, Fly wheels, cylinder linears and other parts that are axi- symmetric. Its notably used to cast cylinder liners and sleeve valves for piston engines, parts which could not be reliably Manufactured.
- 12. Shell moulding Shell moulding, also known as shell-mould casting It is an expendable mould casting process that uses a resin covered sand to form the mould. As compared to sand casting, this process has better dimensional accuracy, a higher productivity rate, and lower labor requirements. It is used for small to medium parts that require high precision. Shell mould casting is a metal casting process similar to sand casting, in that molten metal is poured into an expendable mould. However, in shell mould casting, the mould is a thin-walled shell created from applying a sand-resin mixture around a pattern. The pattern, a metal piece in the shape of the desired part, is reused to form multiple shell molds. A reusable pattern allows for higher production rates, while the disposable molds enable complex geometries to be cast.
- 13. shell mold casting requires the use of a metal pattern, oven, sand- resin mixture, dump box, and molten metal. shell mold casting allows the use of both ferrous and non- ferrous metals, most commonly using cast iron, carbon steel, alloy steel, stainless steel, aluminum alloys, and copper alloys. Typical parts are small-to-medium in size and require high accuracy, such as gear housings, cylinder heads, connecting rods, and lever arms. The shell mold casting process consists of the following steps: pattern creation - a two-piece metal pattern is created in the shape of the desired part, typically from iron or steel. other materials are sometimes used, such as aluminum for low volume production or graphite for casting reactive materials.
- 14. mold creation - first, each pattern half is heated to 175-370 °c (350-700 °f) 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.
- 15. 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. Examples of shell molded items, Include gear housings, cylinder heads and connecting rods. it is also used to make high-precision molding cores.
- 16. Shell moulding
- 17. ADVANTAGES: (I) Shell molding can be completely automated for mass production. (ii) The high productivity, low labor costs, good surface finishes, and precision of the process can more than pay for itself if it reduces machining costs. (iii) Complex shapes and fine details can be formed with very good surface finish, high production rate, low labor cost (if automated). (iv) Low tooling cost, little scrap generated. (v) Very large parts and complex shapes can be produced. (vi) Many material options. (vii) Low tooling and equipment cost. (viii) Scrap can be recycled. (ix) Short lead time possible.
- 18. DISADVANTAGES: The gating system must be part of the pattern because the entire mold is formed from the pattern, which can be expensive. The resin for the sand is expensive, although not much is required because only a shell is being formed. high equipment cost. poor material strength. high porosity possible. secondary machining often required. high labor cost if done manually. the advantages ok but there also so many mistakes they are creating.
- 19. Application: Cylinder heads, connecting rods, Engine blocks and manifolds, machine bases
- 20. Continuous castings Continuous casting is the process whereby molten metals solidifies into continuous forms of strips and billets that can be further worked upon in the finishing mills. These "semi finished" billet, bloom, or slab are casted by using open ended mold and water spray technique. The continuous casting process was developed only in 1950, before that steel was poured into a stationary mold to form 'ingots'.
- 21. Continuous Casting Process: In continuous casting, molten metal is poured into an open-ended mold that can be made of graphite or copper. Graphite molds are widely used both in vertical and horizontal continuous casting. Most molds are made from iso statically pressed graphite. However, extruded graphite molds can also be used for vertical casting of large ingots. The metal is first melted in a furnace and poured into a ladle. From the ladle the hot metal is transferred into the tundish. The hot metal is poured into the continuous casting machine from the tundish. The mold is water cooled. When the hot metal is poured into the furnace, the metal near the walls cool first forming a skin like thin strip. While the meal to the inside is still molten.
- 22. The thin shell like solidified metal withdraws from the mold and pass through a straightening roller. In the chamber the strand is water sprayed which prevents porosity. The thin strip, now called a strand, rolls on a rotating roller. After solidification, predetermined lengths of strands are cut into pieces using mechanical shears or travelling oxyacetylene torches. The cast size are are called strips, billets, slabs etc. Continuous casting can be better controlled by making the process automated. The two common types of continuous casting are horizontal and vertical continuous casting. Long shapes of simple cross section like round, square and hexagonal rods can be done in a short, bottomless, water cooled metal mold.
- 23. Advantages of Continuous Casting: Cost effective, time saving, casting process A highly productive process that can be fully automated High quality castings can be done
- 24. Application A great tonnage of continuous casting is done using cast steel. Other metals that are continuous casting are copper, aluminum, grey cast irons, white cast irons, aluminum bronzes, oxygen-free copper, etc. Metals are cast as ingot for rolling, extrusion, or forging, and long shapes of simple cross section are cast as round, square, hexagonal rods, etc.
- 25. Co2 moulding
- 26. CO2 Moulding A sand molding technique and uses sand grain in which is mixed a solution of sodium silicate that acts to bind the sand particles. CO2 gas is used to harden the sand after the mould has been prepared. H2O+Na2SiO3+ CO2 →Na2CO3+SiO2
- 27. The Mold for Co2 Casting is made of a mixture of sand and liquid silicate binder which is hardened by passing Co2 gas over the mold. The equipment of the molding process include Co2 cylinder, regulator, hoses and hand held applicator gun or nozzle. Carbon di oxide molding deliver great accuracy in production. Any existing pattern can be used for the molding purpose which can be placed in the mold before the mold is hardened. This method helps in producing strong mold and cores that can be used for high end applications. If the process is carefully executed then casting can be as precise as produced by the shell casting method.
- 28. Carbon di oxide casting is favored both by the commercial foundry men and hobbyist for a number of reasons. In commercial operations, foundry men can assure customers of affordable castings which require less machining. The molding process which can be fully automated is generally used for casting process that require speed, high production runs and flexibility. In home foundries this is one of the simplest process that improves the casting quality.
- 29. Advantages: Compared to other casting methods cores and molds are strong Reduces fuel cost since gas is used instead of to other costly heating generating elements Reduces large requirement for number of mold boxes and core dryers Provides great dimensional tolerance and accuracy in production Moisture is completely eliminated from the molding sand This process can be fully automated.
- 30. Application Co2 casting process is ideal where speed and flexibility is the prime requirement. molds and cores of a varied sizes and shapes can be molded by this process.
- 31. INVESTMENT CASTING • Investment casting is also called lost-wax process or precision Investment Casting • metals that are hard to machine or fabricate are good candidates for this process. • The mold is made by making a pattern using wax or some other material that can be melted away. • Term investment derives from the fact that the pattern is invested with the refractory material
- 32. INVESTMENT CASTING • This wax pattern is dipped in refractory slurry, which coats the wax pattern and forms a skin. • Slurry – Fine silica sand + water/ethyl silicate or Gypsum solution • This is dried and the process of dipping in the slurry and drying is repeated until a robust thickness is achieved. • After this, the entire pattern is placed in an oven and the wax is melted away. • This leads to a mold that can be filled with the molten metal. • Because the mold is formed around a one-piece pattern, (which does not have to be pulled out from the mold as in a traditional sand casting process), very intricate parts and undercuts can be made
- 33. Step by step procedure • Make a master pattern of the part to be cast (metal easily machined such as brass, Aluminum alloy, alloy of tin lead bismuth) • Making a master dies
- 34. Schematic illustration of investment casting 1. WAX INJECTION : Wax replicas of the desired castings are produced by injection molding. These replicas are called patterns. 2. ASSEMBLY : The patterns are attached to a central wax stick, called a sprue, to form a casting cluster or assembly. 3. SHELL BUILDING : The shell is built by immersing the assembly in a liquid ceramic slurry and then into a bed of extremely fine sand. Up to eight layers may be applied in this manner. 4. DEWAX : Once the ceramic is dry, the wax is melted out, creating a negative impression of the assembly within the shell.
- 35. • 5. CONVENTIONAL CASTING In the conventional process, the shell is filled with molten metal by gravity pouring. As the metal cools, the parts and gates, sprue and pouring cup become one solid casting. • 6. KNOCKOUT When the metal has cooled and solidified, the ceramic shell is broken off by vibration or water blasting. • 7. CUT OFF The parts are cut away from the central sprue using a high speed friction saw. • 8. FINISHED CASTINGS After minor finishing operations, the metal castings-- identical to the original wax patterns--are ready for shipment to the customer.
- 36. Casting with expendable mould: Investment Casting
- 37. Advantages and Limitations • Parts of greater complexity and intricacy can be cast • Close dimensional control 0.075mm • Superior surface finish • Un machinable Alloys can be cast • The lost wax can be reused • Additional machining is not required in normal course • Preferred for casting weight less than 5 kg,( weighing 1g – 35Kg) • Maximum dimension less than 300 mm, Thickness is usually restricted to 15mm • High-melting point alloys • Al, Cu, Ni, Carbon and alloy steels, tool steels etc. are the common materials • Not a cheap process