Metal removal process is a machine in which excess

Metal removal process

1. Introduction to Metal cutting Metal removal process is a machining process in which excess amount of material is removed in the form of chips in order to shape the material to the required dimension and size.

2. Orthogonal and oblique cutting The major difference between  orthogonal and oblique cutting  is that in  orthogonal cutting , the  cutting  edge of the tool is  perpendicular  to the direction of motion. In  oblique cutting  the  cutting  edge makes an angle with the direction of motion. S.No Orthogonal Cutting Oblique Cutting 1 The cutting angle of tool make right angle to the direction of motion The cutting angle of tool does not make right angle to the direction of motion 2 The flow of chip is perpendicular to cutting edge. The flow of chip is not perpendicular to cutting edge. 3 The tool has lesser cutting life. The tool has higher cutting life. 4 The shear force per unit area is high which increases the heat per unit area. The shear force per unit area is low which decrease heat per unit area . 5 In this cutting, chip flow over the tool. In this cutting, chip flow along the sideways. 6 In orthogonal cutting, surface fiish is poor. In oblique cutting surface finish is good. 7 Cutting edge is longer than edge of cut. Cutting may or may not be longer than edge of cut. 8 Two mutually perpendicular cutting force act on the workpiece Three mutually perpendicular forces are involved .

3. Classification of cutting tools

4. tool signature for single point cutting tool

5. The Mechanism of Cutting Cutting action involves shear deformation of work material to form a chip. As chip is removed, new surface is exposed Orthogonal Cutting - assumes that the cutting edge of the tool is set in a position that is perpendicular to the direction of relative work or tool motion. This allows us to deal with forces that act only in one plane. (a) A cross‑sectional view of the machining process, (b) tool with negative rake angle; compare with positive rake angle in (a).

6. Mechanics of Orthogonal Cutting Orthogonal Cutting Ideal Orthogonal Cutting is when the cutting edge of the tool is straight and perpendicular to the direction of motion. During machining, the material is removed in form of chips, which are generated by shear deformation along a plane called the shear plane . The surface the chip flows across is called the face or rake face . The surface that forms the other boundary of the wedge is called the flank . The rake angle is the angle between the tool face and a line perpendicular to the cutting point of the work piece surface.

7. The relief or clearance angle is the angle between the tool flank and the newly formed surface of the work piece angle. Mechanics of Orthogonal Cutting

8. Mechanics of Orthogonal Cutting Orthogonal cutting model: t 1 = un deformed chip thickness t 2 = deformed chip thickness (usually t 2 > t 1 ) α = rake angle If we are using a lathe, t 1 is the feed per revolution.

9. The Mechanism of Cutting In turning, w = depth of cut and t 1 = feed

10. The Mechanism of Cutting Cutting forces in a turning operation Cutting force (Fc) is tangential and Thrust force is axial (Ft)

11. Mechanics of Orthogonal Cutting Chip thickness ratio (or) cutting ratio where r = chip thickness ratio or cutting ratio ; t 1 = thickness of the chip prior to chip formation; t 2 = chip thickness after separation Which one is more correct? r ≥ 1 r ≤1 Chip thickness after cut always greater than before, so chip ratio always less than 1.0

12. Mechanics of Orthogonal Cutting Shear Plane Angle Based on the geometric parameters of the orthogonal model, the shear plane angle ө can be determined as: where r = chip thickness ratio or cutting ratio ;  = Rake angle ө = Shear angle

13. Manufacturing Technology Chip formation Mechanics of metal cutting is greatly depend on the shape and size of the chips formed. More realistic view of chip formation, showing shear zone rather than shear plane. Also shown is the secondary shear zone resulting from tool‑chip friction.

14. Manufacturing Technology Four Basic Type of Chips in Machining are Discontinuous chip Continuous chip Continuous chip with Built-up Edge (BUE) Serrated chip

15. Manufacturing Technology Discontinuous chip When brittle materials like cast iron are cut, the deformed material gets fractured very easily and thus the Chip produced is in the form of discontinuous segments Reasons Brittle work materials Low cutting speeds Large feed and depth of cut High tool‑chip friction

16. Manufacturing Technology Continuous chip Continuous chips are normally produced when machining steel or ductile materials at high cutting speeds. The continuous chip which is like a ribbon flows along the rake face. Reasons Ductile work materials High cutting speeds Small feeds and depths Sharp cutting edge Low tool‑chip friction

17. Manufacturing Technology Continuous chip with Built-up Edge (BUE) When the friction between tool and chip is high while machining ductile materials, some particles of chip adhere to the tool rake face near the tool tip. When such sizeable material piles upon the rake face, it acts as a cutting edge in place of the actual cutting edge is termed as built up edge (BUE). By virtue of work hardening, BUE is harder than the parent work material Reasons Ductile materials Low‑to‑medium cutting speeds Tool-chip friction causes portions of chip to adhere to rake face BUE forms, then breaks off, cyclically

18. Manufacturing Technology Serrated chip Semi Continuous ( saw tooth appearance) chips produced when machining tool steels or Harden materials at high cutting speeds. Reasons Ductile materials Low‑to‑medium cutting speeds Tool-chip friction causes portions of chip to adhere to rake face BUE forms, then breaks off, cyclically Merchant circle diagram

19. Merchant circle diagram

20. Cutting tool materials and applications. Cutting tool materials -Selection of cutting tool materials is very important -What properties should cutting tools have -Hardness at elevated temperatures -Toughness so that impact forces on the tool can be taken -Wear resistance -Chemical stability

21. 26 Cutting-Tool Materials Tool bits generally made of seven materials High-speed steel Cast alloys (such as stellite ) Cemented carbides Ceramics Cermets Cubic Boron Nitride Polycrystalline Diamond

22. 27 Cutting Tool Properties Hardness Cutting tool material must be 1 1/2 times harder than the material it is being used to machine. Capable of maintaining a red hardness during machining operation Red hardness: ability of cutting tool to maintain sharp cutting edge Also referred to as hot hardness or hot strength

23. 28 Cutting Tool Properties Wear Resistance Able to maintain sharpened edge throughout the cutting operation Same as abrasive resistance Shock Resistance Able to take the cutting loads and forces

24. 29 Cutting Tool Properties Shape and Configuration Must be available for use in different sizes and shapes.

25. 30 High-Speed Steel May contain combinations of tungsten, chromium, vanadium, molybdenum, cobalt Can take heavy cuts, withstand shock and maintain sharp cutting edge under red heat Generally two types (general purpose) Molybdenum-base (Group M) Tungsten-base (Group T) Cobalt added if more red hardness desired

26. 31 Cast Alloy Usually contain 25% to 35% chromium, 4% to 25% tungsten and 1% to 3% carbon Remainder cobalt Qualities High hardness High resistance to wear Excellent red-hardness Operate 2 ½ times speed of high-speed steel Weaker and more brittle than high-speed steel

27. 32 Carbide Cutting Tools First used in Germany during WW II as substitute for diamonds Various types of cemented (sintered) carbides developed to suit different materials and machining operations Good wear resistance Operate at speeds ranging 150 to 1200 sf/min Can machine metals at speeds that cause cutting edge to become red hot without loosing harness

28. Introduction to basic metal cutting machine tools: The lathe is a machine tool which holds the work piece between two rigid and strong supports called centers or in a chuck or face plate which revolves. The cutting tool is rigidly held and supported in a tool post which is fed against the revolving work. The normal cutting operations are performed with the cutting tool fed either parallel or at right angles to the axis of the work. The cutting tool may also be fed at an angle relative to the axis of work for machining tapers and angles.

29. LATHE

30. 46- 36 Lathe Accessories Divided into two categories Work-holding, -supporting, and –driving devices Lathe centers, chucks, faceplates Mandrels, steady and follower rests Lathe dogs, drive plates Cutting-tool-holding devices Straight and offset toolholders Threading toolholders, boring bars Turret-type toolposts

31. various operations carried out on lathe

32. Kinematics of lathe

33. Capstan Lathe Turret Lathe It is a light-duty machine. It is a heavy-duty machine. The turret head is mounted on the ram and the ram is mounted on the saddle. The turret head is directly mounted on the saddle and the saddle slides over the bed ways. The saddle will not be moved during machining. The saddle will not be moved during machining. The lengthwise movement of the turret is less. The lengthwise movement of the turret is more. Short workpieces only can be machined. Long workpieces can be machined. It is easy to move the turret head as it slides over the ram. It is difficult to move the turret head along with the saddle. The turret head cannot be moved crosswise. The turret head cannot be moved crosswise. As the construction of lathe is not rigid, a heavy cut cannot be given. As the construction of lathe is rigid, a heavy cut can be given. It is used for machining workpieces up to 60mm diameter. It is used for machining workpieces up to 200mm diameter. Collet is used to holding the workpiece . Jaw chuck is used to hold the workpiece . Comparison Chart