Manufacturing
→ Involves making products from raw materials by various processes, machinery and operations, following
a well-organized plan for each activity required
→ A manufactured item has undergone a number of changes in which a piece of raw material has become
a useful product, it has value defined as monetary worth or marketable price
→ Thus manufacturing has the important function of adding value
Manufacturing activities must be responsive to several demands and trends:
→ a product must fully meet design requirements and specifications
→ a product must be manufactured by the most economical methods in order to minimize costs
→ Quality must be built into the product at each stage
→ Production methods must be sufficiently flexible so as to respond to ever-changing market demands
→ New developments in materials, production methods and computer integration of both technological
and managerial activities in a manufacturing organization must be constantly evaluated with a view to
their timely and economic implementation
→ Manufacturing activities must be viewed as a large system. Such systems can be modelled in order to
study the effect of factors such as changes in market demands
→ The manufacturing organization must constantly strive for higher productivity, defined as the optimum
use of all its resources. Output per employee per hour in all phases must be maximized
Examples of manufactured products: → paper clips, transistors, incandescent light bulbs, jet engines
The Design Process:
SCAN TABLE
Shapes and Common methods of Production
Shape
Production Method
Flat surfaces
Rolling, planning, broaching, milling, shaping, grinding
Parts with cavities
End milling, electrical-discharge machining, electrochemical machining,
ultrasonic machining, cast-in cavity
Parts with sharp
Permanent-mould casting, machining, grinding, fabricating
features
Thin hollow shapes
Slush casting, electroforming, fabricating
Tubular shapes
Extrusion, drawing, roll forming, spinning, centrifugal casting
Shaping of tubular
Rubber forming, expanding with hydraulic pressure, explosive forming,
parts
spinning
Curvature on thin
Stretch forming, peen forming, fabricating
sheets
Openings in thin sheets Blanking, chemical blanking, photochemical blanking
Reducing cross-sections Drawing, extruding, shaving, turning, centerless grinding
Producing square
Fine blanking, machining, shaving, belt grinding
edges
Producing small holes
Laser, electrical-discharge machining, electrochemical machining
Producing surface
Knurling, wire brushing, grinding, belt grinding, shot blasting, etching
textures
Detailed surface
features
Threaded parts
Very large parts
Very small parts
Coining, investment casting, permanent-mould casting
Thread cutting, thread rolling, thread grinding, chasing
Casting, forging, fabricating
Investment casting, machining
Overdesign: → products are too bulky, made of materials of too high quality, made with unwarranted
precision and quality for the intended uses
→ may result from uncertainties in design calculations or the concern of the designer and
manufacturer over product safety
Selecting materials:→Irons and steels (carbon, alloy, stainless, tool and die steels)
→ Nonferrous metals and alloys (aluminium, magnesium, copper, nickel, titanium, super
alloys, refractory metals, beryllium, zirconium, low-melting alloys, precious metals)
→ Plastics (thermoplastics, thermosets, elastomers)
→ Ceramics (glass ceramics, glasses, graphite, diamond)
→ Composite Materials (reinforced plastics, metal-matrix and ceramic-matrix
composites, honeycomb structures)
Properties of materials:→ Mechanical properties (strength, toughness, ductility, hardness, elasticity,
fatigue, creep)
→ strength-to-weight and stiffness-to-weight ratios (important for aerospace and
automotive applications)
→ Physical properties (density, specific heat, thermal expansion and conductivity,
melting point, electrical and magnetic properties)
→ Chemical properties (oxidation, corrosion, general degradation of properties,
toxicity, flammability)
→ Manufacturing properties (whether materials can be cast formed, machined,
welded, heat treated)
Availability and cost:→ if availability of raw, processed materials and manufactured components in desired
quantities, shapes and dimensions then product cost is increased
→ Reliability of supply, and demand, affects cost
Selecting Manufacturing Processes: → casting (expendable mould, permanent mould)
→ forming and shaping (rolling, forging, extrusion, drawing, sheet
forming, powder metallurgy, moulding)
→ machining (turning; boring; drilling; milling; planing; shaping;
broaching; grinding; ultrasonic, chemical, electrical, electrochemical
and high-energy beam machining)
→ joining (welding, brazing, soldering, diffusion bonding, adhesive
bonding, mechanical joining)
→ Finishing operations (honing, lapping, polishing, burnishing,
deburring, surface treating, coating, plating)
→ Selection of a particular manufacturing process depends on the
shape to be produced, the type of material and its properties
→ Manufacturing processes usually alter the properties of materials
Consequences of improper selection of materials and processes:
→ it stops functioning
→ it doesn’t function properly
→ it becomes unreliable or unsafe for further use
Assembly:→ after individual parts have been manufactured, they are assembled into a product
→ Important phase of the overall manufacturing operation
→ requires consideration of the ease, speed and cost of assembling parts
→ many products are designed to be taken apart for maintenance
→ assembling requires joining (welding, brazing, soldering, diffusion bonding, adhesive bonding,
mechanical joining)
→ parts may be assembled by manual labour or by automated equipment
Design for assembly involves following basic considerations:
→ design of the product to permit assembly with ease (the easier  the faster  the lower production
cost)
→ possibility of designing multipurpose parts so that they can be used in different lines of products 
reducing number of parts to be made
→ capabilities and limitations of each manufacturing process (the greater the variations in these
characteristics  the more difficult proper assembly becomes)
→ methods by which individual parts are brought together for assembly (conveyors, feeders, transfer
equipment, programmable industrial robots)
Metal Casting processes: → Is divided into two categories according to type of mould (expendable,
permanent)
→ Sand casting
→ Shell moulding
→ Vacuum moulding
→ Expanded polystyrene process
→ Investment casting
→ Plaster mould and ceramic mould casting
→ Basic permanent mould process
→ Variations of permanent mould casting
→ Die casting
→ Centrifugal casting
→ Foundry practice
→ Casting quality
→ Metals for casting
→ Product design considerations
Sand casting:→ by far the most widely used casting process
→ can be used for metals with high melting temperatures
→ permits castings of parts from very small to very large
→ pouring molten metal into a sand mould, allowing the metal to solidify and then breaking
up the mould to remove the casting
→ casting is then cleaned and inspected and heat treated sometimes to improve metallurgical
properties
→ sand mould is formed by packing sand around an approximate duplicate of the part to be
cast and then removing the pattern by separating the mould into two halves
→ mould contains the gating and riser system
→ if casting is to have internal surfaces (hollow parts or holes) a core must be included in the
mould
→ since the mould is sacrificed to remove the casting a new mould must be made for each
part that is produced
Patterns and Cores:→ A pattern is a full-sized model of the part enlarged to account for shrinkage and
machining allowances in the final casting
→ materials used to make patterns include wood, plastics and metals
→ types of patterns include solid patterns, split patterns, match-plate pattern, copeand-drag pattern
→ for complex part geometries split patterns are used
→ for higher production quantities match-plate or cope-and-drag patterns are used
→ Core is required when the casting is to have internal surfaces
→ a core is a full scale model of the interior surfaces of the part
→ the core is usually made of sand compacted into a desired shape
→ the actual size of the core should include allowances for shrinkage and machining
→ chaplets are the supports which hold core in position in the pattern
→ chaplets are made of metal of higher melting point than casting metal
Moulds and Mould Making:→ Foundry sands are silica (SiO2) or silica mixed with other minerals
→ sand should possess good refractory properties, the capacity to stand up
under high temperatures without melting or degrading
→ grain size and shape play a role:  small grain size results in better surface
finish
 large grain size results in higher
permeability (gases escape easier during
pouring)
 irregular grain shape results in stronger
moulds but restricts permeability
→ Mixture of sand is 90% sand, 7% clay, 3% water
→ quality of sand mould is determined by its strength, permeability, thermal
stability, collapsibility, reusability
→ sand moulds classified as greensand, dry-sand, or skin-dried moulds
→ greensand are made of sand, clay and water (green refers to presence of
moisture at time of pouring) and are most widely used
The Casting Operation: → after the core is positioned (if one is used) and the two halves are clamped
together, casting is performed
→ casting consists of pouring, solidification, and cooling of the cast part
→ the gating and riser system in the mould must be designed to deliver liquid
metal into the cavity and provide for a sufficient reservoir of molten metal
during solidification and shrinkage
→ Air and gases must e allowed to escape
→ One hazard during pouring is that the buoyancy of the molten metal may
displace the core
→ 𝐹𝑏 = 𝑊𝑚 − 𝑊𝑐
→ Fb is the buoyancy force (N), Wm is the weight of the molten metal displaced
(N), Wc is the weight of the core (N)
Shell Moulding: → casting process in which the mould is a thin shell made of sand held together by a
thermosetting resin binder
→ surface of the shell mould cavity is smoother than a greensand mould
→ produces better surface finish and dimensional accuracy
→ Parts made using this method include  gears
 valve bodies
 bushings
 camshafts
Vacuum Moulding: → also called the V-process uses a sand mould held together by vacuum pressure
rather than a chemical binder
→ Recovery of the sand is an advantage of vacuum moulding since no binders are used
and no water is mixed with the sand so moisture-related defects are absent from
the product
→ it is slow and not readily adaptable to mechanisation
Expanded polystyrene process: → uses a mould of sand packed around a polystyrene foam pattern that
vaporizes when the molten metal is poured into the mould
→ includes the sprue, risers and gating system and internal cores if needed
→ the mould does not need to be opened into cope and drag sections
(advantage)
→ the pattern does not need to be removed from the mould (advantage)
→ a new pattern is required for every casting (disadvantage)
Investment casting: → a pattern made of wax is coated with a refractory material to make the mould, after
which the wax is melted away prior to pouring the molten metal
→ process is also known as the lost wax process
→ capability to cast parts of great complexity (advantage)
→ close dimensional control (advantage)
→ good surface finish (advantage)
→ recovery of wax (advantage)
→ additional machining is not required (advantage)
→ Parts made using this method include  machinery parts
 components of turbine engines
 jewellery
 dental fixtures
Plaster mould casting: → similar to sand casting except mould is made of plaster of Paris (2CaSO4 • H20)
→ talc and silica flour are added to control contraction and setting time, reduce
cracking and increase strength
→ to make mould the plaster mixture combined with water is poured over a plastic
or metal pattern in a flask and allowed to set
→ good dimensional accuracy (advantage)
→ capability to make thin cross-sections in casting (advantage)
→ good surface finish (advantage)
→ curing the plaster mould in high production (disadvantage)
→ not permeable (disadvantage)
→ Antioch process  using 50% sand mixed with plaster, heating mould in
autoclave, then drying
→ plaster moulds are limited to the casting of lower melting point alloys such as
aluminium, magnesium, some copper-based alloys
→ Applications: metal moulds for plastic and rubber moulding, pump and turbine
propellers
Ceramic mould casting:→ similar to plaster mould casting except that the mould I made of refractory
ceramic materials that can withstand higher temperatures
→ good dimensional accuracy (advantage)
→ good surface finish (advantage)
Permanent Mould casting processes:
→ the economic disadvantage of any of the expendable mould processes is that a new mould is required
for every casting
→ in permanent mould casting processes the mould is reused many times
→ permanent mould casting, die casting, centrifugal casting
Permanent mould casting:→ uses a metal mould constructed of two sections that are designed for easy,
precise opening and closing
→ Moulds are commonly made of steel or cast iron
→ cavity with gating system included is machined into two halves to provide
accurate dimensions and good surface finish (advantages0
→ cores can be used if they are removable from the casting or they must be
mechanically collapsible
→ mould is preheated and cavity is sprayed with several layers of coating for
easier separation of mould from casting
→ more rapid solidification and stronger castings (advantages)
→ process is limited to metals of lower melting point (disadvantage)
→ Parts made using this method include  automotive pistons
 pump bodies
 certain castings for aircraft and
missiles
Slush Casting: → permanent mould process in which a hollow casting is formed by inverting the mould
after partial freezing at the surface to drain out the liquid metal in the centre
→ exterior appearance is important
→ things made using this method include  statues
 lamp pedestals
 toys out of low melting point metals (zinc, tin,
lead)
Low Pressure Casting:→ the liquid metal is forced into the mould cavity under low pressure from beneath
→ clean(not exposed to air) molten metal is introduced into the cavity
→ gas porosity and oxidation defects are minimized and mechanical properties are
improved (advantage)
Vacuum Permanent mould casting: → variation of low-pressure casting in which a vacuum is used to draw
the molten metal into the cavity
→ reduced air pressure in the cavity due to the vacuum forces the
molten metal into the cavity
→ same advantages as in low pressure casting
Die casting: → Permanent mould casting process in which molten metal is injected into the mould cavity
under high pressure
→ the pressure is maintained during solidification after which the mould is opened and the cast
removed
→ moulds in the casting process are called dies
→ two main types of die casting machines  hot-chamber machines
 cold-chamber machines
→ Advantages high production rates
 economical for large production quantities
 close tolerances
 good surface finish
 thin section are possible
 rapid cooling → small grain size → good strength
Centrifugal Casting: → refers to several casting methods in which the mould is rotated at high speeds so
that a centrifugal force distributes the molten metal to the outer regions of the die
cavity
→ Types  true centrifugal casting
 semi-centrifugal casting
 centrifuge casting
True centrifugal casting: → molten metal is poured into the rotating mould to produce tubular parts
→ exterior shape takes the exact shape of the mould cavity whereas the interior
shape is perfectly round due to equal radially symmetric forces
→ Centrifugal force: 𝐹 =
𝑚𝑣 2
𝑅
F = force (N), m = mass (kg), v = velocity (m/s), R = interior radius of mould
𝐹
→ G-factor is the force of gravity on the mould: 𝐺𝐹 = 𝑊 =
𝑚𝑣 2
=
𝑅𝑚𝑔
𝑣2
𝑅𝑔
→ v can be replaced by 2πRN/60 = πRN/30, where N = rotational speed, rev/min
𝐺𝐹 =
R(
𝜋𝑁 2
)
30
𝑔
→ Rearrange for N and using diameter D rather than radius:
Rotational speed for horizontal centrifugal casting
→ Rotational speed for vertical centrifugal casting:
𝑁=
𝑁=
30
𝜋
30
𝜋
2𝑔𝐺𝐹
√
𝐷
2𝑔𝐿
√𝑅2 −𝑅2
𝑡
𝑏
Where L is the vertical length in m, Rt and Rb are the inner radii at the top and
bottom respectively
Semi Centrifugal casting:→ in this method centrifugal force is used to produce solid castings
→ the rotational speed is set so that GF is around 15
→ density of metal in the final casting is greater in the outer sections compared to
the centre of rotation
→ expendable moulds are often used in this process
ingot
Centrifuge casting:→
Formulae:
Buoyancy Force : 𝐹𝑏 = 𝑊𝑚 − 𝑊𝑐
Rotational speed for horizontal centrifugal casting 𝑁 =
Rotational speed for vertical centrifugal casting:
𝑁=
30
𝜋
30
𝜋
2𝑔𝐺𝐹
√
𝐷
2𝑔𝐿
√𝑅2 −𝑅2
𝑡
𝑏