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12/18/13

Hareesha N G, DSCE, Bengaluru

1
Unit-1: Introduction to manufacturing process
• Casting Process: Introduction : Concept of Manufacturing process, its
impo...
Classification of manufacturing
process

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Hareesha N G, Asst. Prof, DSCE, BLore

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Classification of manufacturing
process

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Hareesha N G, Asst. Prof, DSCE, BLore

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Types of production systems
• Mass production / continuous flow process
• Batch production
• Job shop production

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Sand casting

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Hareesha N G, Asst. Prof, DSCE, BLore

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Sand casting

molten
metal

polystyrene
pattern

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support
sand

pattern

Hareesha N G, Asst. Prof, DSCE, BLore

p...
Sand casting

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Rolling

Hot-rolling
Cold-rolling

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Extrusion: Schematic, Dies
chamber

die
extruded shape

hydraulic
piston

stock

chamber

Exercise: how can we get hollow ...
Shearing

A large scissors action, cutting the sheet along a straight line

Main use: to cut large sheet into smaller size...
Punching

Cutting tool is a round/rectangular punch,
that goes through a hole, or die of same shape

F ∝ t X edge-length o...
Lathe

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Hareesha N G, Asst. Prof, DSCE, BLore

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Lathe operation ( Turning)

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Drilling operation ( Drilling)

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Hareesha N G, Asst. Prof, DSCE, BLore

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Milling operation ( Drilling)

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Hareesha N G, Asst. Prof, DSCE, BLore

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Grinding operation

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Water jet machining

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Electric discharge machining

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Electro chemical machining

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Plasma arc machining

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Welding operation

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Riveting operation

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Hareesha N G, Asst. Prof, DSCE, BLore

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Soldering operation

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Factors to be considered for selecting a
production process
a) Shape and size to be produced - For products with simple
sh...
Factors to be considered for selecting a
production process
(d) Surface finish and dimensional accuracy - Casting with exp...
CASTING PROCESS

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Terms involved in casting

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Terms involved in casting process
• Mould box (flask) : It is usually a metallic
frame used for making and holding a sand
...
Terms involved in casting process
•

Gate/ingate: It is a short passage way which
carries the molten metal from the runner...
STEPS INVOLVED IN MAKING A CASTING
The basic steps in making a casting are:
(a)
(b)
(c)
(d)
(e)

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Pattern making
...
a) Pattern making
• A pattern is a replica of the object to be cast.
• It is used to prepare a cavity into which the molte...
b) Mould preparation
• Mould preparation involves forming a cavity by packing
sand around a pattern enclosed in a supporti...
c) Core making
• In some cases, a hole or cavity is required in the
casting.
• This is obtained by placing a core in the m...
d) Melting and Pouring
• Metals or alloys of the required composition are
melted in a furnace and poured into the mould
ca...
e) Cleaning and Inspection
• After the molten metal has solidified and cooled, the
rough casting is removed from the mould...
Procedure for making the casting

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Hareesha N G, Asst. Prof, DSCE, BLore

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Hareesha N G, Asst. Prof, DSCE, BLore

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Hareesha N G, Asst. Prof, DSCE, BLore

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Components Produced by
Casting Process
• Casting is the first step and the primary process for
shaping any material.
• All...
Components Produced by Casting Process
• Automotive sector - Nearly 90 % of the parts in automobiles aremanufactured by ca...
Advantages of casting process
• Large hollow and intricate shapes can be easily cast.
• Quick process, and hence suitable ...
Limitations of casting process
• Presence of defects in cast parts is a major disadvantage.
• Casting process is not econo...
INTRODUCTION TO PATTERN MAKING
• A pattern is a mold forming tool in the hands of foundry
men.
• A pattern is a model or t...
Difference between pattern and casting
• The main difference between a pattern and the casting is their dimensions.
• A pa...
Functions of a patterns
• A pattern prepares a mold cavity for the purpose of making a casting.
• A pattern may contain pr...
Pattern materials
Selection of pattern materials
• The following factors assist in selecting proper pattern material:
 Th...
Materials for making patterns
• Patterns may be constructed out of the following
materials.
(a) Wood
(b) Metal
(d) Plastic...
WOOD
•

The most common materials for making patterns for sand casting is the wood.
Advantages
– Inexpensive.
– Easily ava...
Metal
• Metal patterns are employed where large number of
castings have to be produced from the same patterns.
• Metal pat...
Advantages of Metal Patterns
– Unlike wooden patterns, they do not absorb moisture. They retain their
shape.
– They are mo...
Plastic
• Advantages
–
–
–
–
–
–
–
–

Durable
Provides a smooth surface.
Moisture resistant.
A plastic pattern does not in...
PLASTER
• Advantages
– can be easily worked by using wood working tools.
– Intricate shapes can be cast without any diffic...
WAX
• Advantages
Wax patterns provide very good surface finish
They impart high accuracy to the castings.
After being m...
PATTERN ALLOWANCES
• A pattern is always larger in size as compared to
the final casting, because it carries certain
allow...
Shrinkage Allowance
•

•
•

•
•

Almost all cast metals shrink or contract volumetrically after solidification and
therefo...
•

Machining Allowance

A casting is given an allowance for machining, because

– Castings get oxidized in the mold and du...
Draft or Taper Allowance
• It is given to all surfaces perpendicular to the parting
line.
• Draft allowance is given so th...
Fig. shows two patterns — one with taper allowance and the
other without it. It can be visualized that it is easy to draw ...
Distortion Allowance

• A Casting will distort or warp if:

– it is of irregular shape,
– all its parts do not shrink unif...
Shake Allowance
• A pattern is shaken by striking the same with a wooden
piece from side to side. This is done so that the...
TYPES OF PATTERNS

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• For selecting a particular kind of pattern for making a casting,
one may consider the following points:
– Quantity of ca...
• The different types of patterns commonly used
are:
– One piece(Solid) pattern
– Split pattern
– Loose piece pattern
– Ma...
One Piece (solid) Pattern

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One Piece (solid) Pattern
• It is the simplest type of pattern.
• As the name suggests the pattern is
made from one piece ...
Split Pattern

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Split Pattern

• Patterns of intricate (shaped) castings cannot be made in one piece
because of the inherent difficulties ...
Loose Piece Pattern

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Loose Piece Pattern
• Certain patterns cannot be withdrawn once they are
embedded in the molding sand. Such patterns are
u...
Match Plate Pattern

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Match Plate Pattern
• A match plate pattern consists of a match plate, on
either side of which each half of (a number of) ...
Match Plate Pattern
• Cope and drag are then assembled and this completes
the mold.
• Patterns, match plate, runner and ga...
Sweep Pattern

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Sweep Pattern

• A sweep pattern is just a form made on a wooden board
which sweeps the shape of the casting into the sand...
Gated Pattern

castings

Gating system

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Gated Pattern
• Gated patterns are usually made of metal which
increases their strength and reduces the tendency to
warp.
...
Skeleton Patten

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Skeleton Patten
• A skeleton pattern is the skeleton of a desired shape. The skeleton
frame is mounted on a metal base.
• ...
Follow Board Pattern

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Follow Board Pattern
• A follow board is a wooden board and is used for
supporting a pattern which is very thin and fragil...
MOLDING SAND BINDERS
• Binders produce cohesion between the molding sand grains in the
green or dry state (or condition).
...
MOLDING SAND BINDERS
• Clay binders are most commonly used for bonding molding sands.
• Clay binders can be classified as:...
MOLDING SAND BINDERS
• Fire Clay:
– Fire clay is a refractory clay usually found in the coal measures.
– Fire clay particl...
WATER
•
•
•
•
•
•
•
•
•
•
•
•

The amount of water may vary from 1.5 to 8%.
water is responsible for the bonding action of...
ADDITIVES
• The basic constituents of molding sand mixture are;
– Sand
– binder and
– water

• Materials other than the ba...
• Facing materials:
– Facing materials tend to obtain smoother and cleaner surfaces of castings
and help easy peeling of s...
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Introduction to manufacturing process

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This Presentation gives the information of Manufacturing process-1 of Mechanical Engineering course as per VTU Syllabus. Please write to me at: HAREESHANG@GMAIL.COM for suggestions and criticisms or visit : hareeshang.wikifoundry.com for more info.

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Transcript of "Introduction to manufacturing process"

  1. 1. 12/18/13 Hareesha N G, DSCE, Bengaluru 1
  2. 2. Unit-1: Introduction to manufacturing process • Casting Process: Introduction : Concept of Manufacturing process, its importance. • Classification of Manufacturing processes. Introduction to Casting process & steps involved. • Varieties of components produced by casting process. Advantages & Limitations of casting process. • Patterns: Definition, functions, Materials used for pattern, various pattern allowances and their importance. Classification of patterns. • Binder: Definition, Types of binder used in moulding sand. • Additives: Need, Types of additives used. 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 2
  3. 3. Classification of manufacturing process 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 3
  4. 4. Classification of manufacturing process 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 4
  5. 5. Types of production systems • Mass production / continuous flow process • Batch production • Job shop production 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 5
  6. 6. Sand casting 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 6
  7. 7. Sand casting molten metal polystyrene pattern 12/18/13 support sand pattern Hareesha N G, Asst. Prof, DSCE, BLore polystyrene burns; gas escapes 7
  8. 8. Sand casting 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 8
  9. 9. Rolling Hot-rolling Cold-rolling 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 9
  10. 10. Extrusion: Schematic, Dies chamber die extruded shape hydraulic piston stock chamber Exercise: how can we get hollow parts? 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 10
  11. 11. Shearing A large scissors action, cutting the sheet along a straight line Main use: to cut large sheet into smaller sizes for making parts. 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 11
  12. 12. Punching Cutting tool is a round/rectangular punch, that goes through a hole, or die of same shape F ∝ t X edge-length of punch X shear strength crack (failure in shear) t Punch piece cut away, or slug sheet die die clearance 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 12
  13. 13. Lathe 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 13
  14. 14. Lathe operation ( Turning) 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 14
  15. 15. Drilling operation ( Drilling) 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 15
  16. 16. Milling operation ( Drilling) 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 16
  17. 17. Grinding operation 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 17
  18. 18. Water jet machining 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 18
  19. 19. Electric discharge machining 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 19
  20. 20. Electro chemical machining 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 20
  21. 21. Plasma arc machining 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 21
  22. 22. Welding operation 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 22
  23. 23. Riveting operation 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 23
  24. 24. Soldering operation 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 24
  25. 25. Factors to be considered for selecting a production process a) Shape and size to be produced - For products with simple shape, machining is best suited. But for complex and intricate shapes, casting is preferred. The size of the product is also an important factor. For example, 'long' products such as rails or 'thin' products such as car-body panels can be best made by forming process compared to others. (b) Quantity to be produced - Both machining and casting can be used for producing large quantity products, but are not suitable for small quantity products, as they are not economical. (c) Type of material - Materials possess various properties like ductility, hardness, toughness, brittleness etc. Hard materials cannot be machined easily. Brittle materials cannot be mechanically worked (Forming process). In such cases, casting is preferred. 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 25
  26. 26. Factors to be considered for selecting a production process (d) Surface finish and dimensional accuracy - Casting with expendable moulds does not yield good surface finish. However," if casting process is selected, it should be followed by machining process to obtain the desired surface finish and dimensional tolerance. (e) Quality and property requirements - A defect-free product with specific properties serve its purpose for long life. Properties of cast material are generally less when compared to that of mechanically worked materials. Also, casting gives a lot of defects. Hence, a process that gives better properties and quality should be selected. (f) Cost of the product - Customers often demand for products with more features and performance at reduced prices. Hence, a low cost production process should be selected, but at the same time, see that no compromise is made in terms of quality. 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 26
  27. 27. CASTING PROCESS 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 27
  28. 28. Terms involved in casting 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 28
  29. 29. Terms involved in casting process • Mould box (flask) : It is usually a metallic frame used for making and holding a sand mould. The mould box has two parts: the upper part called 'cope', and the lower part called 'drag'. • Parting line/parting surface: It is the zone of separation between cope and drag portions of the mould in sand casting. • Sprue: It is vertical passage through which the molten metal will enter the gate. • Pouring basin: The enlarged portion of the sprue at its top into which the molten metal is poured. 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 29
  30. 30. Terms involved in casting process • Gate/ingate: It is a short passage way which carries the molten metal from the runner/ sprue into the mould cavity. • Riser: A riser or feed-head is a vertical passage that stores the molten metal and supplies (feed) the same to the casting as it solidifies. • Gate/ingate: It is a short passage way which carries the molten metal from the runner/ sprue into the mould cavity. • Riser: A riser or feed-head is a vertical passage that stores the molten metal and supplies (feed) the same to the casting as it solidifies. • Mould cavity: The space in a mould that is filled with molten metal to form the casting upon solidification. • Core: A core is a pre-formed (shaped) mass of sand placed in the mould cavity to form hollow cavities in castings. • Core print: It is a projection attached to the pattern to help for support and correct location of core in the mould Asst. Prof, DSCE, BLore cavity. 12/18/13 30 Hareesha N G,
  31. 31. STEPS INVOLVED IN MAKING A CASTING The basic steps in making a casting are: (a) (b) (c) (d) (e) 12/18/13 Pattern making Mould preparation (including gating and risering) Core making Melting and Pouring Cleaning and Inspection Hareesha N G, Asst. Prof, DSCE, BLore 31
  32. 32. a) Pattern making • A pattern is a replica of the object to be cast. • It is used to prepare a cavity into which the molten metal is poured. • A skilled pattern maker prepares the pattern using wood, metal, plastic or other materials with the help of machines and special tools. • Many factors viz., durability, allowance for shrinkage and machining etc., are considered while making a pattern. 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 32
  33. 33. b) Mould preparation • Mould preparation involves forming a cavity by packing sand around a pattern enclosed in a supporting metallic frame called 'flask' (mould box). • When the pattern is removed from the mould, an exact shaped cavity remains into which the molten metal is poured. • Gating and risering are provided at suitable locations in the mould. – Gating - Passage through which molten metal flows and enter the mould cavity. – Risering - A reservoir of molten metal connected to the mould cavity to supply additional metal so as to compensate for losses due to shrinkage, as the metal solidifies. 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 33
  34. 34. c) Core making • In some cases, a hole or cavity is required in the casting. • This is obtained by placing a core in the mould cavity. • The shape of the core corresponds to the shape of the hole required. 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 34
  35. 35. d) Melting and Pouring • Metals or alloys of the required composition are melted in a furnace and poured into the mould cavity. • Many factors viz., temperature of molten metal, pouring time, turbulence etc., should be considered while melting and pouring. 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 35
  36. 36. e) Cleaning and Inspection • After the molten metal has solidified and cooled, the rough casting is removed from the mould, cleaned and dressed. • This involves removing cores, adhered sand particles, gating and risering systems, fins, blisters etc., from the casting surface. • then sent for inspection to check for dimensions or any defects like blow holes, cracks etc. 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 36
  37. 37. Procedure for making the casting 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 37
  38. 38. 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 38
  39. 39. 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 39
  40. 40. 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 40
  41. 41. Components Produced by Casting Process • Casting is the first step and the primary process for shaping any material. • All materials have to be cast before it is put to use. • The ingots produced by casting process are used as raw material for secondary processes like machining, forging, rolling etc. • More than 90 % of all manufactured goods and capital equipment use castings for their manufacture. • To list the components produced by casting is an endless process. A few major components produced by casting are given below. 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 41
  42. 42. Components Produced by Casting Process • Automotive sector - Nearly 90 % of the parts in automobiles aremanufactured by castings. A few parts include brake drum, cylinder, 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. 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 42
  43. 43. 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. BLore 12/18/13 43 Hareesha N G, Asst. Prof, DSCE,
  44. 44. 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. 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 44
  45. 45. 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. 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 45
  46. 46. 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 12/18/13 are made. 46 Hareesha N G, Asst. Prof, DSCE, BLore they
  47. 47. 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. 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 47
  48. 48. Pattern materials Selection of pattern materials • The following factors assist in selecting proper pattern material:  The number of castings to be produced. Metal patterns are preferred when the production quantity is large.  The desired dimensional accuracy and surface finish required for the castings.  Nature of molding process i.e., sand casting, permanent mold casting, shell molding, investment casting etc.  Method of molding i.e., hand or machine molding.  Shape, complexity and size of the casting.  Type of molding materials i.e., sand etc.  The high probability of changing the casting and hence the pattern in near future. N G, Asst. Prof, DSCE, BLore 12/18/13 48 Hareesha
  49. 49. Materials for making patterns • Patterns may be constructed out of the following materials. (a) Wood (b) Metal (d) Plastic (d) Plaster (POP) (e) Wax 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 49
  50. 50. 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. – 12/18/13 They are weak as compared to G, Asst. Prof, DSCE, BLore 50 Hareesha N metal patterns.
  51. 51. 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, – – – – – 12/18/13 Aluminium and Aluminium alloys Steel Cast Iron Brass White Metal Hareesha N G, Asst. Prof, DSCE, BLore 51
  52. 52. 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. 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 52
  53. 53. 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 Hareesha N shock as in machine moulding.G, Asst. Prof, DSCE, BLore 12/18/13 53
  54. 54. 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/cm2) • 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. 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 54
  55. 55. WAX • Advantages Wax patterns provide very good surface finish They impart high accuracy to the castings. After 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. 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 55
  56. 56. 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) 12/18/13 Shrinkage or contraction allowance. Machining or Finish allowance. Draft or Taper allowance. Distortion or camber allowance. Shake or rapping allowance. Hareesha N G, Asst. Prof, DSCE, BLore 56
  57. 57. 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 ofNthe pattern and the other for that of metal to 12/18/13 57 Hareesha G, Asst. Prof, DSCE, BLore be cast.
  58. 58. • 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 desired on the cast part. 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 58
  59. 59. 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 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore surfaces. 59
  60. 60. 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, 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 60
  61. 61. 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. 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 61
  62. 62. 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. 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 62
  63. 63. TYPES OF PATTERNS 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 63
  64. 64. • 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. 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 64
  65. 65. • 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. 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 65
  66. 66. One Piece (solid) Pattern 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 66
  67. 67. 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 • It is inexpensive. contain loose pieces or joints. • 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. 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 67
  68. 68. Split Pattern 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 68
  69. 69. 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 12/18/13 69 Hareesha N G, Asst. Prof, DSCE, BLore molding purposes
  70. 70. Loose Piece Pattern 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 70
  71. 71. 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. 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 71
  72. 72. Match Plate Pattern 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 72
  73. 73. 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 twoHareesha N G, Asst. Prof, and drag.) (i.e., cope DSCE, BLore 12/18/13 73
  74. 74. 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.G, Asst. Prof, DSCE, BLore 12/18/13 74 Hareesha N
  75. 75. Sweep Pattern 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 75
  76. 76. 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. 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 76
  77. 77. Gated Pattern castings Gating system 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 77
  78. 78. 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. 12/18/13 78 Hareesha N G, Asst. Prof, DSCE, BLore
  79. 79. Skeleton Patten 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 79
  80. 80. 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 and is rammed. • A strickle (board) assists in giving the desired shape to the sand and 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. Hareesha N Asst. Prof, • 12/18/13 Castings for turbine castings,G,waterDSCE, BLore channels, etc., are 80 pipes,
  81. 81. Follow Board Pattern 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 81
  82. 82. 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 12/18/13 82 Hareesha drag are assembled. N G, Asst. Prof, DSCE, BLore
  83. 83. 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. 12/18/13 83 Hareesha N G, Asst. Prof, DSCE, BLore
  84. 84. 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. 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 84
  85. 85. 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. 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 85
  86. 86. 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 and 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 toNdevelop DSCE, BLore the optimum properties can be 86 12/18/13 Hareesha G, Asst. Prof, found out experimentally.
  87. 87. 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. 12/18/13 Hareesha N G, Asst. Prof, DSCE, BLore 87
  88. 88. • 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 12/18/13 • Other special Additives: Hareesha N G, Asst. Prof, DSCE, BLore – Finely ground corn floor, Iron oxide, Boric acid, diethylene glycol 88
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