Unit1
- 3. 1.Mechanics Of Chip Formation, 2.Single Point Cutting Tool, a.Forces In Machining, 3.Types Of Chips 4.Cutting Temperature 5.Cutting Tools – Nomenclature, 6.Orthogonal Metal Cutting 7.Cutting Tool Materials 8.Tool Wear, Tool Life, Surface Finish, 9.Cutting Fluids And Machinability
- 4. Cast, formed and shaped products may need further machining operations to give them the desired final shape, after removal of extra material in the form of chips. Machining processes or Metal cutting process is defined as remove unwanted material from a work piece by 1.CUTTING ( As in case of machine tools like lathe, shaper etc) 2.ABRASIVE ( As in case of a grinding wheel) 3.NON TRADITIONAL ( Processes such as EDM, ECM Etc.) THEORY OF METAL CUTTING
- 5. 1.MECHANICS OF CHIP FORMATION,material to form a chip As chip is removed, new surface is exposed (a) A cross sectional view of the machining process, (b) tool with‑ negative rake angle; compare with positive rake angle in (a).
- 8. 2.SINGLE POINT CUTTING TOOL The single point cutting tool has only one cutting point or edge. These tools used for turning, boring, shaping or planning operations. These tools used on lathe, boring and shaper machines.
- 9. Three most common machining processes: (a) turning, TURNING DRILLING
- 11. force F and Normal force to friction N Shear force Fsand Normal force to shear Fn
- 12. The metal cutting is done by a relative motion between the work piece and the hard edge of a cutting tool. Metal cutting could be done either by a single point cutting tool or a multi point cutting tool. There are two basic types of metal cutting by a single point cutting tool.
- 13. 1.ORTHOGONAL METAL CUTTING, 2.OBLIQUE METAL CUTTING,
- 14. 1.ORTHOGONAL METAL 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.
- 15. 2.OBLIQUE METAL CUTTING, If the cutting face of the tool is inclined at less than 90o to the path of the tool then the cutting action is called as oblique cutting.
- 16. S.N o. ORTHOGONAL METAL CUTTING OBLIQUE METAL CUTTING 1. Cutting edge of the tool is perpendicular to the direction of tool travel. The cutting edge is inclined at an angle less than 90o to the direction of tool travel. 2. The direction of chip flow is perpendicular to the cutting edge. The chip flows on the tool face making an angle. 3. The chip coils in a tight flat spiral The chip flows side ways in a long curl. 4. For same feed and depth of cut the force which shears the metal acts on a smaller areas. So the life of the tool is less. The cutting force acts on larger area and so tool life is more. 5. Produces sharp corners. Produces a chamfer at the end of the cut 6. Smaller length of cutting edge is in contact with the work. For the same depth of cut greater length of cutting edge is in contact with the work. 7. Generally parting off in lathe, broaching and slotting operations are done in this method. This method of cutting is used in almost all machining operations.
- 17. Elements of Metal Cutting 1.Cutting speed : The relative surface speed between the tool & the job. It is the distance traveled by work surface related to the cutting edge of Tool v = πdN / 1000 m / min 2.Feed (s) : The motion of cutting edge of tool with reference to one revolution of work piece. 3.Depth of cut (t) : It is measured perpendicular to axis of work piece and in straight turning in one pass. This can be estimated from the relation t = ( D - d ) / 2 mm 4.Undeformed chip (Fc) : The cross sectional area of chip before it is removed from work piece. it is equal to the product of feed and depth of cut. Fc = s x t mm2 All tools have a major and minor cutting edge. The major cutting edge removes bulk of material. Where as the minor cutting edge gives good surface finish.
- 18. Elements of Metal Cutting
- 19. 3.SINGLE POINT CUTTING TOOLS Nomenclature,
- 20. Part Description Shank It is the body of the tool which is ungrounded. Face It is the surface over which the chip slides. Base It is the bottom surface of the shank. Flank It is the surface of the tool facing the work piece. There are two flanks namely end flank and side flank. Cutting edge It is the junction of the face end the flanks. There are two cutting edges namely side cutting edge and end cutting edge. Nose It is the junction of side and end cutting edges. PARTS OF A SINGLE POINT CUTTING TOOL
- 22. IMPORTANT ANGLES OF A SINGLE POINT CUTTING TOOL 1.Relief or clearance angle •Side relief •End relief 2.Rake angle •Back Rake angle •Side Rake angle 3.Cutting edge angle •Side Cutting edge angle •End Cutting edge angle 4.Nose Radius
- 23. Relief or Clearance angle: Ground on the end and side faces of a tool to prevent it from rubbing on the work piece. To enable only the cutting edge to touch the work piece. Side Relief angle: • Angle ground directly below the cutting edge on the flank of the tool End Relief angle: • Angle ground from the nose of the tool
- 24. Cutting edge angle • Ground on a tool so that it can be mounted in the correct position for various machining operations. Side Cutting edge angle • Allows flank of the tool to approach the work piece first • Spreads the material over a greater distance on the cutting edge, thereby thinning out the chip. • Approximately 150 End Cutting edge angle • Allows the cutting tool to machine close to the work piece during turning operations • Usually 20 – 300
- 25. TOOL ANGLE APPLICATION Factors to consider for tool angles •The hardness of the metal •Type of cutting operation •Material and shape of the cutting tool •The strength of the cutting edge
- 26. TYPES OF CHIPS Chips are separated from the Workpiece to impart the required size and shape to the Workpiece. The type of chips edge formed is basically a function of the work material and cutting conditions. The chips that are formed during metal cutting operations can be classified into four types: 1.Discontinuous or segmental chips 2. Continuous chips 3. Continuous chips with built-up edge. 4. Non homogenous chips
- 27. 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: •Ductile work materials •High cutting speeds •Small feeds and depths •Sharp cutting edge •Low tool-chip friction 1.DISCONTINUOUS OR SEGMENTAL CHIPS
- 28. 2.CONTINUOUS CHIPS 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: •Brittle work materials • Low cutting speeds • Large feed and depth of cut • High tool-chip friction
- 29. 3. Continuous chips with built-up edge. 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 Reasons: •Ductile materials •Low-to-medium cutting speeds •Tool-chip friction •BUE forms, then breaks off, cyclically
- 30. Cutting Tool Properties 1.Hardness Cutting tool material must be 1 1/2 times harder than the material it is being used to machine. hardness and strength at high temperatures. Capable of maintaining a red hardness during machining operation Red hardness: ability of cutting tool to maintain sharp cutting edge at elevated temp. It is also sometimes referred to as hot hardness or hot strength 2.Wear Resistance Able to maintain sharpened edge throughout the cutting operation Same as abrasive resistance 3.Shock Resistance Able to take the cutting loads and forces 4.Shape and Configuration Must be available for use in different sizes and shapes.
- 31. CUTTING TOOL MATERIALS A cutting tool is any tool that is used to remove metal from the work piece by means of shear deformation. It is one of most important components in machining process It must be made of a material harder than the material which is to be cut, and the tool must be able to withstand the heat generated in the metal cutting process. Two basic types •Single point •Multiple point
- 32. SINGLE POINT CUTTING TOOL
- 33. MULTI POINT CUTTING TOOL
- 34. Cutting tool bits generally made 1. Carbon tool steel 2. High-speed steel 3. Cast alloys 4. Cemented carbides 5. Ceramics 6. Cermets 7. Cubic Boron Nitride 8. Polycrystalline Diamond
- 35. Cutting tool bits generally made 1. Carbon tool steel compositions Carbon-0.8% to 1.3% Silicon-0.1% to 0.4% Manganese-0.1% to 0.4% *it is suitable for low cutting speed below 200o C *It is cheap ,easy to forge
- 36. Cutting tool bits generally made 2.High-speed steel (HSS) May contain combinations of tungsten, chromium, vanadium, molybdenum, cobalt can take heavy cuts, withstand shock and maintain sharp cutting edge under red heat. The cutting speeds can be 2 to 3 times higher than carbon steels. This tool steel hardness maintain even upto 900o C Generally three types (general purpose) 1.18-4-1 HSS 2.Molybdenum hss 3.Cobalt hss Cobalt added if more red hardness desired
- 37. 1.18-4-1High-speed steel May contains 18% tungsten,4%chromium,1%vanadium.It has about 0.75% CARBON. The cutting speeds can be 2 to 3 times higher than carbon steels. This tool steel hardness maintain even upto 600o C 2.MOLYBDENUM HIGH-SPEED STEEL It has composition of molybdenum =6%;Tungsten -5%;chrominm=4% and Vanadium=2% rest steel It has high toughness and cutting speed 3.COBALT HIGH-SPEED STEEL It has composition of COBALT=12%,tungsten=20% ;chrominm=4% and Vanadium=2% rest steel It is also known as super HSS
- 38. 3.Cast alloys 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