Lecture Notes Basic manufacturing Process
Dr P.K.Parida, CET, BBSR 1
Lecturer Notes
Prepared by
Dr Pramod Kumar Parida
Asst. Professor
Department of Mechanical Engineering
College of Engineering & Technology (BPUT)
Bhubaneswar, Odisha
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Lecture Notes on Plastic Deformation of Metals: Metal Forming Processes and Casting, Schemes and Mind Maps of Mechatronics
Lecture notes on plastic deformation of metals, focusing on metal forming processes and casting. Topics include hot and cold working of metals, classification of metal forming processes, preparation of moulds and patterns, advantages of casting, and various types of patterns. The document also covers gating design, pouring, and defects in casting.
What you will learn
- What are the different types of metal forming processes?
- How is the flow stress analysis important in metal forming processes?
- How does gating design affect the casting process?
- What are the different types of patterns used in casting?
- What are the advantages of casting over other manufacturing processes?
Typology: Schemes and Mind Maps
2022/2023
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Download Lecture Notes on Plastic Deformation of Metals: Metal Forming Processes and Casting and more Schemes and Mind Maps Mechatronics in PDF only on Docsity!
Lecturer Notes
Prepared by
Dr Pramod Kumar Parida
Asst. Professor
Department of Mechanical Engineering
College of Engineering & Technology (BPUT)
Bhubaneswar, Odisha
Syllabus
PCME4206 Basic Manufacturing Process Module - I (12 Lectures)
- Foundry : (a) Types of patterns, pattern materials and pattern allowances. (b) Molding Materials - sand molding, metal molding, investment molding, shell molding. (c) Composition of molding sand, Silica sand, Zircon sand, binders, additives, Binders - clay, binders for CO 2 sand, binder for shell molding, binders for core sand. (d) Properties of molding sand and sand testing. (e) Melting furnaces - cupola, resistance furnace, induction and arc furnace. (f) Solidification of castings, design of risers and runners, feeding distance, centre line freezing resistance chills and chaplets. (g) Degasification and inoculation of metals. (h) Casting methods like continuous casting, centrifugal casting, disc casting. (i) Casting defects. Module – II (12 Lectures)
- Welding and cutting: Introduction to gas welding, cutting, Arc welding and equipment’s. TIG (GTAW) and MIG (GMAW) welding, resistance welding and Thermit welding. Weldablity Modern Welding methods like plasma Arc, Laser Beam, Electron Beam, Ultrasonic, Explosive and friction Welding, edge preparation in butt welding. Brazing and soldering, welding defects. Destructive and non-destructive testing of castings and welding.
- Brief introduction to powder metallurgy processes. Module – III (14 Lectures)
- Plastic deformation of metals: Variables in metal forming and their optimization. Dependence of stress strain diagram on Strain rate and temperature. Hot and cold working of metals, classification of metal forming processes.
- Rolling: Pressure and Forces in rolling, types of rolling mills, Rolling defects.
- Forging: Smith Forging, Drop and Press forging, M/c forging, Forging defects.
- Extrusions: Direct, Indirect, Impact and Hydrostatic extrusion and their applications, Extrusion of tubes.
- Wire drawing methods and variables in wire-drawing, Optimum dies shape for extrusion and drawing.
- Brief introduction to sheet metal working: Bending, Forming and Deep drawing, shearing.
- Brief introduction to explosive forming, coating and deposition methods. Text Books
- Manufacturing technology - by P.N.Rao, Tata McGraw Hill publication.
- Welding Technology by R.A. Little, TMH
- Manufacturing Science by A.Ghosh and A K Malick, EWP Reference Books
- Fundamentals of metal casting technology by P.C. Mukherjee, Oxford PIBI.
- Mechanical Metallurgy by Dieter, Mc-Graw Hill
- Processes and Materials of Manufacture by R.A Lindberg, Prentice hall (India)
- A Text Book of Production Engineering by P.C.Sharma, S.Chand
c) Liquid or molten metal is poured into a prepared mould cavity d) allowed to solidify e) product is taken out of the mould cavity, trimmed and made to shape More attention should be given on the following for successful casting operation: (i)Preparation of moulds of patterns (ii)Melting and pouring of the liquefied metal (iii)Solidification and further cooling to room temperature (iv) Defects and inspection Advantages of casting process: Molten material can flow into very small sections so that intricate shapes can be made by this process. As a result, many other operations, such as machining, forging, and welding, can be minimized. Possible to cast both ferrous and non ferrous materials Tools are very simple and expensive Useful for small lot production Weight reduction in design No directional property
- There are certain parts (like turbine blades) made from metals and alloys that can only be processed this way. Turbine blades: Fully casting + last machining.
- Size and weight of the product is not a limitation for the casting process. Limitations:- Accuracy and surface finish are not very good for final application Difficult to remove defects due to presence of moisture Metal casting is a labour intensive process Automation: a question
Application:- Cylindrical bocks, wheels, housings, pipes, bells, pistons, piston rings, machine tool beds etc. Typical sand mould Mould Section and casting nomenclature
Facing sand : The small amount of carbonaceous material sprinkled on the inner surface of the mould cavity to give a better surface finish to the castings. Bottom board – Board used to start mould making (wood) Backing sand – used and burnt sand Core : A separate part of the mould, made of sand and generally baked, which is used to create openings and various shaped cavities in the castings. Pouring basin : A small funnel shaped cavity at the top of the mould into which the molten metal is poured. Sprue: The passage through which the molten metal, from the pouring basin, reaches the mould cavity. In many cases it controls the flow of metal into the mould. 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 mould cavity. Chaplets: Chaplets are used to support the cores inside the mould cavity to take care of its own weight and overcome the metallostatic force. Riser: A column of molten metal placed in the mould to feed the castings as it shrinks and solidifies. Also known as “feed head”. Vent: Small opening in the mould to facilitate escape of air and gases.
Steps in making sand castings:
The basic steps in making sand castings are, (i) Pattern making, (ii) Core making, (iii) Moulding, (iv) Melting and pouring, (v) Cleaning
Pattern making – Pattern is the replica of the part to be cast and is used to prepare the mould cavity. It is the physical model of the casting used to make the mould. Made of either wood or metal.
- The mould is made by packing some readily formed aggregate material, such as moulding sand, surrounding the pattern. When the pattern is withdrawn, its imprint provides the mould cavity. This cavity is filled with metal to become the casting. If the casting is to be hollow, additional patterns called ‘cores’, are used to form these cavities. Pattern Materials:- In genral materials – wood, metals & plastics Wood- Adv:- Easy availability, Low weight, Easily shaped, Cheap, Care to be taken Disadv:- Moisture absorption, Distortion, Dimensional change, seasoning Example – Pine, Teak, Deodar Others – plywood boards and particle boards Reason – Availability in various thicknesses Higher strength No need for seasoning Use – Used for flat type and no three dimensional contour shapes Large scale casting Choice of pattern materials depends on Size of casting No. of castings to be made from pattern Dimensional accuracy required A pattern is always made larger than the final part to be made. The excess dimension is known as Pattern allowance. Pattern allowance => shrinkage allowance, machining allowance Shrinkage allowance : It will take care of contractions of a casting which occurs as the metal cools to room temperature.
Machining allowance : It will take care of the extra material that will be removed to obtain a finished product. In this the rough surface in the cast product will be removed. The machining allowance depends on the size of the casting, material properties, material distortion, finishing accuracy and machining method. Machining allowances of various metals Metal Dimension (inch) Allowance (inch) Cast iron Up to 12 12 to 20 20 to 40
Cast steel Up to 6 6 to 20 20 to 40
Non ferrous Up to 8 8 to 12 12 to 40
16 Draft – Vertical faces of the pattern are to be made tapered to reduce the chances of damage to the mould cavity. It varies with the complexity of the job. Inner details require more allowance than outer. This allowance is more for hand moulding than machine moulding.
Typical Draft Allowances
Pattern
material
Height of the
given surface
(inch)
Draft angle
(External
surface)
Draft angle
(Internal
surface)
Wood 1
1 to 2
2 to 4
4 to 8
8 to 32
Metal and
plastic
1 to 2
2 to 4
4 to 8
8 to 32
Pattern having draft allowance on vertical surfaces
Shake allowance – This is a negative allowance. Applied to those dimensions which are parallel to parting plane. Distortion allowance – Metals just solidified are very weak, which may be distorted. This allowance is given to the weaker sections like long flat portion, U & V sections, complicated casing, thin & long sections connected to thick sections. The distortion in casting may occur due to internal stresses. These internal stresses are caused on account of unequal cooling of different sections of the casting and hindered contraction.
Used where depth of job is too high Aligned with dowel pins fitted to cope (c) Gated pattern – Gating and runner system are integrated with the pattern Improves productivity (d) Cope and drag pattern - Similar to split pattern For cope and drag, separately attached gating system to metal plate Heavy and inconvenient for handling Useful for Continuous production (e) Match plate pattern – Similar to cope and drag patterns with gating and risering system mounted on a single matching plate Pattern and match plate are made up of metal (Al) Useful for small casting with high dimensional accuracy Suitable for large scale production Gating system is attached to the match plate Expensive (f) Loose piece pattern – Withdrawing of the pattern from the mould is difficult,Useful for highly skilled job, Expensive (g) Follow board pattern – Used for structurally weak portions Bottom board is modified as follow board (h) Sweep pattern – Useful for axi-symmetrical and prismatic shape Suitable for large scale production (i) Skeleton pattern – Stripes of wood are used for building final pattern Suitable for large casting Core making Cores are placed into a mould cavity to form the interior surfaces of castings. Thus the void space is filled with molten metal and eventually becomes the casting.
Core and core print: - Cores are used to make holes, recesses etc. in castings
- So where coring is required, provision should be made to support the core inside the mould cavity. Core prints are used to serve this purpose. The core print is an added projection on the pattern and it forms a seat in the mould on which the sand core rests during pouring of the mould.
- The core print must be of adequate size and shape so that it can support the weight of the core during the casting operation.
MOULDING MATERIALS
Different types of moulding materials are
- moulding sand
- system sand (backing sand )
- rebonded sand
- facing sand
- parting sand
- core sand Choice of moulding materials depends on processing properties. Properties_-
- Refractoriness- Ability to withstand high temperature of molten metal so that it does not cause fusion Refractory materials - silica, zirconia, alumina
- Green strength- Moulding sand containing moisture is known as green sand. The strength of the green sand is known as green strength.
- Dry strength- When moisture is completely expelled from the moulding sand, it is known as dry sand and the strength of the sand is the dry strength.
- Hot strength- After moisture elimination, the sand is exposed to higher temperature of molten material. Strength of sand to hold the shape of mould cavity at this higher temperature is known as hot strength.
- Permeability – Moulding sand is porous, so it escapes gases through it. This gas evolution capability of moulding sand is known as permeability. Other properties include collapsibility, reusable, good thermal conductivity etc. MOULDING SAND COMPOSITION- Main ingredients of moulding sand are silica grain (SiO2), Clay (binder) and moisture (to activate clay and provide plasticity) (a) Silica sand - this is the major portion of the moulding sand. About 96% of this sand is silica grain. Rests are oxides (Al2O3), sodium (Na2O +K2O) and magnesium oxide (MgO +CaO). Main source of silica sand is river sand (with /without washing). Fusion point of sand is 14500C for cast iron and 15500C for steels. Grain size varies from micrometer to millimetre. The shape of the grains may be round, angular, sub angular or very angular. (b) Zircon sand - The main composition is zirconium silicate (ZrSiO2). Composition- ZrO2- 66.25% SiO2-30.96% Al2O3-1.92% Fe2O3-0.74% Other - oxides It is very expensive. In India, it is available at quilon beach, kerela. The fusion point of the sand is 2400oC. Advantage - High thermal conductivity
When it mixes with sand, the volume increases 10 to 20 times. High dry strength, so lower risk of erosion Better tolerance of variation in water content Low green strength High resistance to burn out Southern Bentonite - It is rich with calcium ion It has low dry strength and high green strength Its properties can be improved by treating it with soda ash (sodium carbonate) Water:- Used to activate the clay Generally 2 to 8% of water is required Other materials added:- Cereal binder – (2%) – to increase the strength Pitch (by product of coke) – (3%) – to improve hot strength Saw dust (2% ) – To increase permeability Testing sand properties:- Sample preparation can be done by mixing various ingredients like sand, clay and moisture. During mixing, the lump present in sand should be broken up properly. The clay should be uniformly enveloped and the moisture should be uniformly distributed. The equipment used for preparation of moulding sand is known as Mueller. This is of two types. (i) Batch Mueller- Consists of one/two wheels and equal no. of blades connected to a single driving source. The wheels are large and heavy. (ii) Continuous Mueller- In this type, there are two bowls with wheel and ploughs. The mixture is fed through hopper in one bowl. After muelled, it is moved to another bowl. This type of Mueller is suitable for large scale production.
Moisture content:- 1 st method - 50g of moulding sand sample is dried at 1050C to 1100C for 2hrs. The sample is then weighed. Wt. diff * 2= % of moisture content 2nd method - Moisture teller can be used for measuring moisture content. The Sand is dried suspending sample on fine metallic screen allowing hot air to flow through sample. This method takes less time in comparison to the previous one. 3rd method - A measured amount of calcium carbide along with moulding sand in a separate cap is kept in the moisture teller. Both should not come in contact with each other. Apparatus should be shaken vigorously such that the following reaction takes place. CaC2 + 2H2O – C2H2 + Ca(OH) The acetylene coming out will be collected in space above the sand raising the pressure. A pressure gauge connected to the apparatus would give directly the amount of acetylene generated, which is proportional to the moisture present. Clay content:- A 50g of sand sample is dried at 1050C to 1100C and is taken in a 1lt. glass flask. 475ml distilled water and 25ml of a 1% solution of caustic soda (NaOH 25g/l) is added to it. The sample is thoroughly stirred (5 mins). The sample is then diluted with fresh water upto 150 mm mark and then left undisturbed for 10mins to settle. The sand settles at bottom and the clay floats. 125mm of this water is siphoned off and again topped to the same level. The process is repeated till water above the sand becomes clear. Then the sand is removed and dried by heating. The difference in weight multiplied by 2 will give the clay % of sand.