Question

Q4 The multipoint cutting tools are generally made with the materials having excellent mechanical properties such as red hardness, wear resistance, etc. Though numerous materials are available to meet these properties requirement, some materials are best suited for making the cutting tools in the aspects of tool life and tool cost. (i) Suggest suitable materials and give explanation [2] Page 5 of 6 (ii) Recommend anyone material in the aspects of tool cost [1] (iii) Analyze the crystal structure present in the your recommended material with the following terminology a. The crystal structure present in the material [1] b. Unit cell and effective number of atoms [2] c. Co-ordination number [1] d. Atomic packing factor calculation [3]

Answer 1

cutting tool Multipoint but is nothing it contains 1 than two main mone cutting edges. have excellent Cutting tools should mechanical like red properties hot hardness, wear resistente, ..etc. the c) Different -etc. cutting tool materials i) High Carbon steel ii) High speed steel iii) Cemented Corbides iv) Ceramics v). Diamond vi) (BN (Cubic Boron nitoide), relatively cheap and tough. - Carbon tool hardness Their enough other steels. to machine Corbides are hardes than tool steels less tough cemented than but Carbides. is material. Diamond also → CBN it cannot be osed material haidest steels arre - Cemented are S very hard but The to machine steel. the cost aspect tool steels are (1) Awouding to economical and viable. we mentioned materials are the now in Among analyzing about Diamond of is a) Crystal structure Diamond face centered Letragonal. Diamond Cubic structure

unitiell, 8 are 3 6 are mohe y are unit ceil (b) in a atoms arranged at 3 Conness atoms arranged at Centres of a faces and atoms arranged inside the body diagnols, each body diagnol atom touch with I Connor atom and 3 nearest face center atoms. tach tetrahedral atom located body diagnol with coordinate of lemon) Cornos. Effective No. of atoms = 1 8 x 8 + 1 +6+4 =8 atoms SOS 16 9 a from

(6) Co-ordination Coordination number = 4 (d) Atomic packing factos Calculation CAPF); 8 x APF volume of atoms occupied Volum of unit cell. = 4/35R3 a 3 (!: 2R = 5a = 8 x YAR 3 8R13 ( ) us APF = 0.34