Manufacturing Process Unit-1 (AU2021Reg)

Manufacturing Process Unit-1 (AU2021R)

1. Unit 1 - : l - - - METAL CASTING PROCESSES Sand Casting – Sand Mould – Type of patterns - Pattern Materials – Pattern allowances – Molding sand Properties and testing – Cores –Types and applications – Molding machines – Types and applications–Melting furnaces – Principle of special casting processes- Shell, investment – Ceramic mould – Pressure diecasting – low pressure, gravity- Tilt pouring, high pressure die casting- Centrifugal Casting – CO2 casting –-Defects in Sand casting process-remedies

2. • Casting: process of producing metal components by pouring molten metal into the mould cavity of the required shape and allowing the metal to solidify. The solidified piece is called casting. Casting is done in a foundry. • Sand Casting : a metal casting process characterized by using sand as the mould material. Sand castings are produced in specialized factories called foundrie s. • Most widely used casting • Production of quantities from one to million. • Sand mould is used,

3. SAND MOULD FEATURES

4. Major components of sand molds: Flask - supports the mold Pouring basin - in which molten metal is poured in to Sprue - through which molten metal flows downward Runner system - channels that carry molten metal from the sprue Risers - supply additional metal to the casting during shrinkage Cores - Inserts made of sand Used to make hollow regions Vents - used to carry off gases that are produced and exhaust air from the mold cavity as metal flows in to the mold

5. Sand Moulds 1. Green Sand Moulds 2. Dry Sand Moulds 3. Loam Sand Moulds 4. Cemented -Bonded Moulds 5. CO 2 Moulds 6. Resin - Bonded Sand Moulds 7. Dry Sand Core Moulds 8. Composite Moulds

6. Green Sand Moulds • Mixture of Silica sand, Clay (act as a Binder), water • Green refers to wetness or freshness • Cheapest and reclaimed • Mould is weak in damp condition and cannot be stored for long time • Used to make small and Medium size casting

7. 2. Dry Sand Moulds • 1 to 2% cereal flour and 1 to 2 % pitch additives • Baked in an oven 110 to 260 C for several hours • Additives increases hot strength due to evaporation of water and oxidation and polymerization of the pitch • Used for large castings and better surface finish • Reduces gas holes, porosity • Possibility for tearing 3. Loam Sand Moulds • Fine sand and finely ground refractories clay 50%, graphite and fibrous reinforcements • Used in pit moulding - Large castings (Engine bodies, machine tool beds and frames)

8. 4. Cemented - Bonded Moulds • 10 to 15% cement - binder, Stronger and harder, Pit moulding • Develop strength by air drying, Large steel castings • Poor Collapsability 5. CO 2 Moulds • Sodium Silicate (Na 2 O.xSiO 2 ) used as a binder(2 to 6%) • Sand Mixture hardens due to the following reaction • Na 2 O.xSiO 2 + nH 2 O + CO 2 → Na 2 CO3 + x.Sio 2 .n . n(H 2 O) - Stiff gel 6. Resin - Bonded Sand Moulds • Green sand mixture is mixed with thermosetting resins or linseed oil or soya bean oil • Baking polymerizes and strength increases than dry sand mould • No bake process - Furan resin 7. Dry sand Core moulds • Moulds are made from assemblies of cores • Baked at 175 C to 230 C for 4 to 24 hrs 8. Composite Moulds • Moulds are made of two or more different materials - Shells, plaster, sand with binder and graphite Used in shell moulding - Complex shapes - Turbine impellers, Good surface finish Dimensional accuracy

9. Patterns -Actual replica of the desired casting, used to prepare the cavity into which molten material will be poured during the casting process. Patterns used in sand casting may be made of wood, metal, plastics or other materials. 1. Solid or Single Piece Pattern 2. Split Pattern 3. Loose Piece Pattern 4. Gated Patterns 5. Match Plate Pattern 6. Cope and Drag Pattern 7. Sweep Pattern 8.Skeleton Pattern 9. Segmental Pattern 10. Build up Pattern 11. Shell pattern 12. Box up pattern 13. Lagged up pattern 14.Left and right hand pattern

10. Pattern Materials Requirements of a good Pattern • Secure the desired shape and size of the casting • Cheap and readily available • Simple in design for ease of manufacture • Light in mass and convenient to handle • High strength and long life in order to make as many moulds • Retain its dimensions and rigidity during the definite service life • Surface should be smooth and wear resistant • Able to withstand rough handling Wood • Properly dried and seasoned • Should not contain moisture more than 10% to avoid warping and distortion Advantages • Light weight, Inexpensive, Good workability, Easy to glue and join, Holds paints • Easy to repair Limitation • Non uniform in structure • Poor wear and abrasion resistance • Cannot withstand rough handling • Absorbs moisture

11. Metal Advantages • More durable and accurate in size than wooden patterns • Smooth surface • Do not deform in storage • Are resistance to wear, abrasion, corrosion and swelling • Can withstand rough handling Limitation • Expensive, Not easily repaired, Heavier than wooden pattern • Ferrous pattern rusted Common metals are C.I., Brass, Aluminium, White metal Plastics • More economical, Highly resistant to corrosion, lighter and stronger than wood • Less sticking, No moisture absorption • Smooth surface, Strong and dimensionally stable

12. Core and core making • A body made of sand used to make a hole or cavity in a casting • Similar to the shape of the cavity in casting

13. Essential qualities • Permeability • Refractoriness • Strength • Collapsibility • Stability

14. Core making materials • Core sand - refractories Si, zircon • Binders - oils, core flour • Additives - wood flour, coal powder, graphite, cow dung. • All are weighed and put in the muller. Dry binders are put. Muller is started and water is added to the dry mixture after a few min. Then oil is added. Total mixing time is 3 to 6 min.

15. Core boxes and core ovens Core box • Half core • Dump or slap • Split core • Strickle • Gang core Core ovens • Batch type • Continuous • Dielectric

16. Core types • According to the state of core • Green sand core • Dry sand core • According to the position of core • Horizontal • Vertical • Balanced • Hanging • Drop core

17. Methods of testing Mould sands • Moisture content test • Clay content test • Grain fineness test • Permeability test • Strength test • Deformation and toughness test • Hot strength test • Refractoriness test • Mould hardness test

18. Moisture content Moisture content = W 1 -W 2

19. Clay content test • Sand sample + distilled water + 1% NaOH • Mixed and stirred for 5 min. The dirty water at the top is removed. Again 1% NaOH and distilled water is added. Dried again till the water become clean. The water is then drained completely and sand is dried completely and weighed. The loss of weight denotes the clay content. • Clay content W 1 -W 2

20. Grain fineness test • Set of known values of graded sieves, one on other. Decreasing order of sieve sizes from top to bottom. Top is the coarsest and bottom most finest. • Sand is put in sieve and shaken for 15 min. then amount in each sieve is measured and the % dist. is obtained. AFS = total products /total sand retained in sieve and pan AFS=(American Foundry men Society)

21. Permeability test • Weighed quantity of moulding sand is taken. • Both clay content and moisture are added and mixed well. • Specimen dimension =50.8x50.8 mm 2 • Permeability Number = VH/APT. • Volume V= 2000 CC • H - height of specimen • A- area of specimen • P- air pressure measured by manometer • T- Time taken by 2000 cc of air to pass through the sand specimen (in min)

22. Strength test • Holding power and bonding power of green or dry sand. • Compressive • Shear • Tensile • Bending Carried out in a UTM Specimen 50.8mmx50.8mm

23. Deformation and toughness • Deformation - testing the plasticity of sand by applying compressive strength. • Toughness - ability of the sand to withstand rough handling.(when pattern is drawn) • Toughness Number = deformation x (green compressive strength

24. Refractoriness test • Cylindrical specimens are made from the mould sand as per dim. • Heated in fire for up to 1550 C for 2 hrs. • Change in shape and appearance is noted. Up to 7% change in dimension indicates good refractoriness.

25. Mould hardness • Specimen is made and indentation is made on it. Dimension of specimen and indentation is noted. •Indicates the ramming density of molding sand Mould hardness number = P ------------------------------ D-√ D 2 - d 2

26. Moulding Machines • Used for mass production • Reduces labour and increases mould quality. • Operations involved - Ramming the sand - rapping the pattern for easy removal - removing pattern from sand • Types - Jolting machines - Squeezing machines - Sand slingers

27. Jolting machines • Pattern placed in a flask on table. • Mold sand is filled. • The flask is then raised to 80 mm and dropped suddenly. This makes even distribution of sand in the flask. • Table is operated hydraulically/ pneumatically. • Operation is noisy.

28. Squeezing machine • Top squeezing • Bottom squeezing Moulding sand squeezed between m/c table and squeezer head. Top squeezing • Mould board on table. Flask on mould board. Pattern in flask. Sand filled in flask. Table raised against squeezer mechanism. Sand is packed tightly. Table is set to original position after packing is done. • Sand at top is rammed more densely than the bottom

29. Bottom squeezing • Pattern on table • Table is clamped on ram. Flask is placed on a frame and is filled with sand. • Table with pattern is raised against squeezer head, thus flask is with pattern is squeezed b/w sq. head and table. Table then returns to original position.

30. Squeezing machines

31. Sand slingers • Here the pattern is placed on a board. • Flask is placed over it. Slinger contains an impeller which can be rotated at different speeds. When impeller rotates it throws a stream of sand at high velocity into the flask, by which the sand gets packed well. • The slinger can be moved to pack the sand uniformly. Density of sand is controlled by speed of impeller. • Appropriate for medium and large sized molds. • Ramming is uniform with good strength.

32. Sand slinger

33. Cupola Furnace Used to melt cast iron due to its cost of construction, installation and operation Principle: • Metallic charge - Pig iron and scrap is melted • Coke and oxygen in air as fuel • Lime stone works as flux to separate impurities in the form of slag from liquid metal • Charging of material is Continuous Description: • Long cylindrical shell made of mild steel - lined with fire clay refractory bricks • Door for charging and a spark arrester to prevent sparks and unburnt fuel particles from flowing into the atmosphere. • Bottom has a circular door hinges for emptying the contents of the furnace • Air is supplied by blower through a wind box for uniform pressure and number of rectangular openings - tuyers • Metal tap hole and slag hole is kept above the tap hole Operation: • Should be thoroughly dried before firing • Layer of sand 150mm ht is placed over the doors and sloped towards tap hole • Wood is kindled with fire and coke is added slightly above the tuyers • Lime stone - 2 to 4% by weight of metal charge • Coke - 8 to 12% of the metal charge

34. Various zones of cupola: 1. Well or crucible 2. Tuyer zone 3. Combustion Zone 4. Reducing Zone 5. Melting Zone 6. Preheating Zone Advantages • Low cost, continuous operation, easy to operate Drawbacks • Difficult to control temp. and composition

35. Blast furnace • A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally iron , but also others such as lead or copper . • In a blast furnace, fuel, ore, and flux (limestone) are continuously supplied through the top of the furnace , while a hot blast of air (sometimes with oxygen enrichment) is blown into the lower section of the furnace through a series of pipes called tuyers, so that the chemical reactions take place throughout the furnace as the material moves downward. The end products are usually molten metal and slag phases tapped from the bottom, and flue gases exiting from the top of the furnace. The downward flow of the ore and flux in contact with an upflow of hot, carbon monoxide- rich combustion gases is a countercurrent exchange process.

36. • The tuyers are used to implement a hot blast, which is used to increase the efficiency of the blast furnace. The hot blast is directed into the furnace through water- cooled copper nozzles called tuyers near the base. • The hot blast temperature can be from 900 °C to 1300 °C (1600 °F to 2300 °F) depending on the stove design and condition. The temperatures they deal with may be 2000 °C to 2300 °C (3600 °F to 4200 °F). • Blast furnaces operate on the principle of chemical reduction whereby carbon monoxide reduces the iron to its elemental form

37. Blast furnace 4 3 2 1 1. Melting zone ( bosh ) 2. Reduction zone of ferrous oxide ( barrel ) 3. Reduction zone of ferric oxide ( stack ) 4. Pre-heating zone ( throat )

38. Crucible furnace - crucible placed underground

39. Coke fired stationary furnace Above ground level. Steel shell lined with firebricks.

40. Oil fired tilting furnace

41. Direct Arc Electric Furnace Principle : • Heat is generated when resistance is offered to the flow electricity. • Furnace electrode carries 25000 A, 3 Graphite or Carbon electrodes • 750 mm Diameter electrode, 1.5 to 2.5m in length. • Length can be adjusted depends on amount of charge & wear of electrodes • 3 phase supply, 600 to 850KWh of electric energy to produce 1 tonne of steel. • Temp 1925 C, Can melt Chromium, Tungsten, Molybdenum Indirect Arc Electric Furnace • Arc is struck between two electrodes • To melt copper base alloys • 2 Carbon or graphite electrodes • Capacity 1000Kg Advantages • High thermal efficiency • Most alloying elements Cr, Tungsten, Nickel can be recovered from scrap • Quicker readiness for use, longer hearth life and ease of repair Disadvantages • High power consumption

42. Induction Furnace (alloy steels) • All the heat is generated in the charge itself instead of arc • Furnace contains a refractory lined crucible surrounded by a water cooled Cu coil • Works on the principle of transformer. Water cooled coil is Primary and secondary is • The charge. When a .c is passed through the Cu tubing, a magnetic field is set up. • The magnetic field induces eddy current in the crucible charge which melts metal Charge: Steel : 40 to 60% Pig Iron: 4 to 7% Capacity : 50 kg to 10 tonnes 1. Core -less or high frequency Induction furnace Water cooled Cu coil completely surrounds the crucible. High frequency current (10,000 cps to 5,00,000 cps) is passed through the coil Heavier current is induced in the charge 2. Core or Channel furnace or Low frequency induction furnace Coil surrounds only a small portion of the crucible and low freq. (50 to 60 cps) Melt Steel, iron, bronze, brass and Al base alloys Advantages • Readily started or stopped, High rate of melting and deliver at regular intervals • Very high temp, Automatic stirring due to strong electromagnetic forces •Uniform composition

43. Special casting process • Shell casting (expendable moulds) • Investment or lost wax method (expendable moulds) • Ceramic casting • Pressure die casting • Centrifugal casting • CO2 casting • Stir casting

44. Shell Mold 1. Heated metal pattern ready for shell formation from resin-binded sand. 2. Box inversion for shell formation. 3. Partial cured shell layer hardened; box re- inverted to allow the loose sand particles to be separated.

45. 4. Sand shell is heated to complete the curing. 5. Sand shell removed from the pattern 6. Two halves of the sand shell are assembled and ready for pouring. 7. Finished shell casting with sprue removed.

46. Shell Mold Pros: - Smoother surface finish than sans casting. - Surface finish of 2.5  m can be obtained. - Good dimensional accuracy  0.25 mm on small to medium size parts. - No further machining is needed. - Capability for automation lowers the cost for larger quantities. Cons: - More expensive metal pattern, especially for small batch.

47. Investment Casting 1. Wax Pattern made. 2. Patterns attached to wax sprue. 3. Pattern tree coated with thin layer of refractory material. 4. Pattern tree coated with sufficient refractory material.

48. Investment Casting 5. Invert tree and melt wax by heat. 6. Preheat mold to high temperature to induce flow and remove contaminants. 7. Mold broken and parts remove.

49. Investment Casting Pros: - Capability to cast parts with great complexity and intricacy. - Close dimensional control (  0.076  m tolerance). - Good surface finish. - Wax can be recovered and reuse. - Additional machining normally not required. Cons: - Normally cater for smaller parts. - Relatively expensive.

50. CO 2 casting • Used to make good quality castings in large numbers. • Pure dry Si sand with Sodium silicate liquid is used as binder. • Moisture 3% , additives sawdust 1.5 % , asbestos powder 5% makes the core more deformable and collapsible. • Sand mix is filled in core box and rammed. CO 2 gas is passed for 30 sec. at Pr. 140 KN/m 2. • CO 2 reacts with Sodium silicate and forms sodium carbonate and silica gel. The Silica gel binds the sand tightly and provides strength and hardness to the core.

51. Permanent Mold Casting - Die Casting Molten metal is injected at high pressure (7 to 350 MPa) into the mold cavity. Pressure is maintained at solidification and part is removed after mold opening.

52. Permanent Mold Casting - Die Casting Hot-chamber die casting : Metal furnace is an integral part of the mould. Typical injection pressures are 7 to 35 MPa. The piston is made to force the molten metal into the die. Finished parts are ejected out after solidification. The process is often used for low melting point metals such as zinc, tin, lead or magnesium alloys.

53. Permanent Mold Casting - Die Casting Hot chamber casting

54. Cold-chamber die casting Molten metal is poured into an unheated chamber from an external furnace . Typical injection pressures are 14 to 140 MPa. Often used for high melting point metal such as aluminum, brass, and magnesium alloys

55. Permanent Mold Casting - Die Casting Cold chamber casting

56. Permanent Mold Casting - Die Casting • Mold made of tool steel. • Mold opening mechanism to be synchronized with ejector pins. • Venting is needed for air and gas typically at the parting surface. • Flash formation is common.

57. Permanent Mold Casting - Die Casting Pros: - High production rates are possible. - Economical for large quantities. - Close tolerances are possible (  0.076 mm). - Good surface finish. - Thin sections are possible (down to 0.5 mm). - Rapid cooling, fine grain, high strength. Cons: - melting point of metals. - shape restriction.

58. Permanent Mold Casting - Centrifugal Casting Used for making hollow castings like tubes,drums, gun barrels. Molten metal is poured into a rotating tube to generate a tubular part. High density part produced. Shrinkage compensated by centrifugal force. Impurities on the outer wall only.

59. LIST OF DEFECTS 01. Shrinkage 02. Cold Shut 03. Mismatch 04. Blow holes 05. Pin Holes 06. Fin 07. Drop 08. Swell 09. Metal Penetration 10. Hot Tears 11. Porosity 12. Scabs 13. Hard Spots 14. Buckles\Rat Tails 15. Misrun

60. Shrinkage

61. Cold shut When two streams of molten metal approach each other in the mould cavity from opposite directions but fail to fuse properly, with the result of discontinuity between them, it is called a cold shut

62. Mismatch • It is a shift /misalignment between two mating surfaces or the top and bottom parts of the casting at the mould joint .

63. Blow holes • Balloon-shaped gas cavities caused by release of mould gases during pouring are known as blow holes.

64. Pin holes • Pin holes are tiny blow holes appearing just below the casting surface.

65. Fins • Fins are excessive amounts of metal created by solidification into the parting line of the mold

66. Drop • Drop is an irregularly-shaped projection on the cope surface caused by dropping of sand.

67. Swell • Swells are excessive amounts of metal in the vicinity of gates or beneath the sprue

68. Penetration • Penetration occurs when the molten metal flows between the sand particles in the mould. These defects are due to inadequate strength of the mold and high temperature of the molten me