GE 102Manufacturing Technology

Workshop TechnologyW. A. Chapman Workshop Processes and MaterialsBruce J. Black Materials and Processes in ManufacturingE. Paul DeGarmo

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TABLE OF CONTENTSPage Title Chapter

1 Health and Safety Chapter 1

11 Engineering Materials Chapter 2

27 Casting Processes Chapter 3

43 Sheet-Metal Operations Chapter 4

53 Measuring Equipment's Chapter 5

71 Machining Processes Chapter 6

103 Plastic Forming Processes Chapter 7

117 Joining of Metals Chapter 8

133 Carpentry Chapter 9

Workshop Training

Title Workshop

Turning 1

Welding 2

Casting 3

Sheet-Metal 4

Carpentry 5

Engineering Materials

2-1 IntroductionEngineering materials are those the engineer uses in his work. Nearly all materials existing on and under the ground are used in engineering. Some of these materials are used directly as water, sand, etc., others need more or less treatment as iron ore, petroleum. Moreover, some materials are used alone in industry as wood, leather, etc., others are mixed together to produce other materials having specific properties as adding chromium to steel to improve its corrosion resistance.

2.3. Properties of Materials2.3.1 Classification of propertiesa) Physical properties: As the shape, dimensions, porosity, etc. b) Chemical properties: As the chemical composition, acidity, etc. c) Thermal properties: As the expansion, thermal conductivity, specific heat, etc. d) Electrical and Magnetic properties: As the electrical resistivity and conductivity, magnetic permeability, etc. e) Optical properties: As the color, light reflection and absorption etc. f) Acoustical properties: As the acoustic reflection and absorption, etc. g) Mechanical properties: They are the properties, which determine the behavior of the material under loads.

2.3.2 Main Mechanical properties of Materials 1-Elasticity: Is the ability of the material to restore its original shape or volume at once when the load is released.2- Plasticity: Is the ability of the material to change its shape and dimensions under load and to keep the new shape and dimensions after the load is released. 3- Ductility: Is the ability of the material to deform (elongate) in static tension without failure. 4- Malleability: Is the ability of the material to change its shape under pressure (compressive load) without failure. 5- Brittleness: Is the ability of the material to fail without a noticeable in its dimensions. 6- Hardness: Is the resistance of the material to penetration of another harder body?

7- Stiffness: Is the resistance of the material to any change of shape, it is measured by Young’s modulus. 8-Strength:Is the measure of the ability of materials to resist stresses (tensile, compressive, bending, shearing or torsion) under different conditions of loading (static and dynamic) and different temperatures. It is measured by the stress units ( = force/area) 9- Toughness:Is the ability of the material to resist the dynamic load (i.e., to resist shocks)

2.4 Main Mechanical Tests of Metals 2.4.1 Tensile TestTensile test is of a static type, it is the easiest mechanical test to perform. It is carried out to determine the strength and plasticity of materials. Moreover, the result of the tensile test gives a clear idea about the other mechanical properties of the material under test, mainly its ductility. For the tensile test to be carried out, we use a test specimen and a tensile test machine. Test specimen: It is either round or flat shape cross-section. It ha s a standard shape and dimensions to be able to compare the obtained results. Fig 2.1 shows test specimens. The mechanical properties in tensions are determined on the gauge length lo of the specimen.

Fig. 2.1 Tensile test specimens

A tensile test machine

Fig. 2.3 a tensile test diagram for mild steel

The elastic load Pe:Is the maximum load that causes elastic deformation only, i.e.,

deformation that disappears when the load is removed. The corresponding stress is the elastic limit e

e = Po/Fo Pa or MPa.where Fo: Initial cross-sectional area of the specimen Here is a line relation in the region of elastic deformation between stress and strain for metals and alloys. It confirms to the low of proportionality (Hook’s low):

= E . Pa or MPa . E = / = tan Where (strain) = l/lo

= (l1-lo)/lo

The coefficient of proportionality E, called the nodules of elasticity or Young’s modulus, characterizes the rigidity of a material, i.e., its resistance to elastic deformation in tension.

Examples:

1- When testing a steel specimen of diameter D=10 mm., the maximum load Pu is 28400 N. Calculate the ultimate strength u.Solution:

Fo = D2/4 = .102/4 = 78.5 mm2 = 78.5 x 10-6 m2

u = Pu/Fo = 28400/78.5 x 10-6 = 361.8 MPa.

2- Determine the elongation of steel, if the specimen gauge lengths before and after teat lo and l1 are: 50 and 58 mm. respectively. Solution: = (l1 – lo)/lo x 100 = (58-50)/50 x 100 = 16%

2.4.2Hardness Test Hardness test is of a static type. It has found extensive applications in all branches of industry due to its rapidity, simplicity and its non-destructive character.Because the hardness of the metal is its resistance to penetration to another harder body, thus hardness test is applied by pressing a body in the metal under test, then evaluating its influence.There exist several hardness testing methods having the same principles but differ in the shape of the penetrating body. A brief idea about those most widely used is given in table 2.1

Method Symbol Penetrating body

Parameter of hardness

evaluationBrinell HB Steel ball Applied force

and area of indentation

Rockwell HRBHRC

Steel ball or Conical-shaped

diamond

Difference in depth of

indentation made by additional and preliminary loads*

Vickers HV Square-based

diamond pyramid

Applied force and mean value of

diagonals’ lengths

2.4.3 Impact Test Impact test is of a dynamic type. It indicates the resistance of metals to fracture when it is subjected to impacts. Fig 2.4 shows a pendulum type impact machine.The notched specimen is placed on its support so that the blow of the striker will be opposite to the notch. The pendulum of weight G is raised to a constant height h1 from where it is released to fracture the specimen and rises again to the height h2.

The work done to fracture the specimen is:

A= G (h1 – h2) joule.The heights of the pendulum

before and after the blow are expressed by the angles through which it is raised. Thus

A= G.l (cos1 - cos2) joule.The angle 1 is constant, while

the angle of swing of the pendulum after fracturing the specimen 2 is measured on a circular scale on the machine. The resistance of metal to impact is given by:

ak = G(h1 – h2)/Fo = G.l/Fo (cos1 - cos2) joule/m2

Where Fo… is the cross-sectional area in m2 of the specimen at the place of fracture.

2.4.4 Fatigue Test.

The failure of a metal under repeated reversing stresses is called fatigue. The resistance of a metal to fatigue failure is characterized by its fatigue limit, which is the maximum stress the specimen can withstand without failure when this stress is repeated for a specified number of cycles (5x106 cycles for steels and 20x106 cycles for non-ferrous metals).

The fatigue limit is usually determined by subjecting rotating specimen to repeated reversing stresses. At least six specimens must be tested to determine the fatigue limit. The first specimen is tested at a stress 1 and the number of cycles N1 at which failure is determined. The stresses 2, 3 etc., for the second and subsequent specimens are increased or reduced, depending on the number of cycles which caused the failure of the first specimen. The corresponding number of cycles N2, N3, etc., at which failure of such specimens occurs are determined too. The obtained results are plotted on a diagram Fig. 2.5. The horizontal section is a straight line and it is the maximum stress at which failure will not take place after an infinite number of loading cycles.