1. CHAPTER (1) General Introduction Dr. Ahmed Abou El-Wafa

2. 2 1.1. Classification of Manufacturing Processes

3. 3 A machine tool (metal cutting machine) is a device in which energy is utilized in deformation of material. The machine tools are generally used for two aims; 1- to produce certain form 2- to finish surfaces. 1.1.1. Objectives of machine tools 1- to hold the workpiece (w.p.) 2- to hold the cutting tool 3- to produce a relative movement necessary to generate the required surface. 1.1.2. Machine tools drive systems 1- Electrical 2- Hydraulic 3- Mechanical 4- Pneumatic

4. 4 1.1.3. Machine tools workpiece holding devices (a) For rotating w.p. 1- Chuck 2- Between centers 3- Faceplate 4- Collet 5- Arbor 6- Mandrel 7- Special attachments (b) For reciprocating w.p. 1- Vise 2- T-slot 3- Magnetic chuck. To perform the machining operation, two motions are required: 1- Cutting motion 2- Feed motion

5. 5 1.1.4. Cutting and feed movements

6. 6 1.2. Materials in Manufacturing 1.2.1. Workpiece materials 1- Metals 2- Ceramics 3- Polymers 4- Composites (non-homogeneous mixtures of the above three types). FIGURE 1.2 W.P. material types Ceramics Metals Metal- polymer composites Metal- ceramic composites Ceramic-polymer composites

7. 7 Metals Metals: - ferrous {e. g. steel (0.02 - 2%C) and cast iron(2 - 4%C)} - non-ferrous {e. g. Al, Cu, Mn, Ag, Ti, etc.} Ceramics Ceramics: is a compound containing metallic (or semi-metallic) and non-metallic elements (O 2, N and C) as an example Al 2 O 3, SiC, WC, TiC and TiN. Polymers Polymers: usually consists of C plus one or more other elements, such as H 2, N, O 2 and Cl. Three types of polymers are exist; thermoplastic: a plastic that repeatedly can be softened by heating and hardened by cooling, e.g. nylon, thermosetting: a class of polymers that, when cured using heat, chemical, or other means, changes into a substantially infusible and insoluble material, e.g. epoxy, and elastomers: exhibit significant elastic behavior, e.g. natural rubber. Composites Composites: consists of particles of one phase (e. g. fiber) mixed in a second phase, called the matrix (e. g. epoxy). A composite is a material consisting of (usually) two phases that are processed separately and then bonded together to achieve properties superior to those of its constituents.

8. 8 1.2.2. Cutting tool materials A cutting tool should have the following properties: 1- Hardness to resist abrasion 2- Red (hot) hardness (the ability to retain this hardness at high temp.) 3- Toughness to withstand shocks 4- Ability to provide a good surface finish to reduce chip/tool friction. Types of tool materials: - Plain high-carbon steel Its use is limited to hand tools. - High-speed steel (HSS) Tungsten (W) is the alloying element responsible for providing the red hardness. HSS is used in medium speed range. The commonest type is 18- 4-2 HSS, being the percentages of W, Cr, and V, respectively, present in steel containing 0.7% C. - Stellite It is a non-ferrous cast alloy of cobalt (50%), chromium (28%) and tungsten (20%) (+ ≈ 2% C), containing iron only as an impurity.

9. 9 1.3. Manufacturing processes They can be divided into two basic types; 1- Processing operations, and 2- Assembly operations. - Cemented carbides WC or BC bonded together by another material (cobalt) and then placed in a mould and heated to a very high temperature in the presence of H 2 since H 2 prevents damage by atmospheric O 2. It can be used as brazed or clamped tips mounted on a tough medium steel shank. - Ceramic tools The most common ceramic cutting tool material is Al 2 O 3. They are used as clamped throwaway-tips only since they cannot be brazed to tool steel shank. They lend themselves to negative rake cutting.

10. 10 1.4. Machinability The machinability of a material is defined as follows: "The most machinable material is the one which permits the removal of material with a satisfactory finish at lowest cost". 1.4.1. Factors affecting the machinability of materials 1- W.p. material 2- Tool material 3- Size and shape of tool 4- Type of machining operation 5- Size, shape and velocity of cut 6- Type and quality of the used machine tool 7- Type of lubricant used during machining operation 8- Coefficient of friction between chip and tool 9- Shearing strength of w.p. material.

11. 11 Web site:http://www.staff.zu.edu.eg/awafa/ downloads – My courses – 1 st mechanical eng – Ch1_Introduction