metal cutting

• Metal cutting


  Cutting away excess metal with a chisel
• Work piece to be chipped

  • Held in a vice
• Chisel


  • Held firmly but at the same time lightly to ease the shock of the hammer blows
  • Hammer handle is gripped near the end and struck with a force suited to the metal been chipped

  
• Cutting angle for chisels

  • Aluminium: 30°
  • Copper: 45°
  • Brass: 50°
  • Low Carbon Steel: 55°
  • Cast Iron: 60° to 65°
  • High Carbon Steel: 65°

  
• Tang chisels


  There is a tang on the end of the blade which fits inside the handle
• Socket chisels

  Handle fitted in a socket which is part of the blade
• Types of chisels

  • Flat Chisels
  • Cross cut (Cape Chisel)
  • Diamond point Chisels
  • Round nose Chisels
• Flat Chisels


  • Conventionally used for chipping, cutting thin sheet metal, removing the rivet heads, etc.
  • Cutting angle approximately 60°
  • Width of the cutting edge varies from 20 to 25 mm
  • Length 10 -250mm

  
• Cross cut (Cape Chisel)


  • Used to cut keyways, grooves and slots
  • Have a narrow cutting edge, 6 to 10mm wide
• Diamond point Chisels


  • Used to cut into corners of slots, internal angles, etc.
  • The cutting edge of this chisel is shaped like a diamond

  
• Round nose Chisels


  • Used to cut grooves
  • The cutting edge of such chisels is semi circular

  
• Care of chisels and chipping

  • Use safety goggles
  • Check the head of the chisel and the handle of the hammer
  • Chip away from your body
  • Place the chisel against the work piece and strike with hammer
  • If the surface to be chipped is too long, cut grooves along the whole surface by cross cut chisel and then chip away the metal
  • For chipping large volume of metal, lubricate the cutting edge of the chisel for its longer life and quicker cutting action
• Classification of files by effective length

  • 100mm to 150mm for fine work
  • 250mm to 450mm for general and large sized work
• Types of file cuts

  • Single cut
  • Double cut

  
• Single cut file


  • Has teeth slanting only in one direction, from left to right toward the point, or end of the file
  • Used with light pressure, produces a fine, smooth finish on metal surfaces or a sharp edge on such cutting tools as scissors, knives, and saw teeth
• Double cut file


  • Has two sets of teeth
  • Greater pressure is used, metal is removed faster, and the finish is not so smooth
  • Good for filing hard materials
• Grades of file cuts

  • Smooth cut
  • Second cut
  • Bastard cut

  
• Selecting the file


  • Depends on the type of metal, the shape of the piece, the shape it is to be filed, and the degree of accuracy required
  • Begin with a bastard-cut file for filing brass, bronze, or cast iron and finish with a second-cut file, or smooth-cut file
  • Use a file of proper length for the work
• Methods of filing


  • Cross filling (Rough Filing)
  • Draw filling
• Taps


  • Cutting tools used to cut internal threads
  • Made from high quality tool steel, hardened and ground
  • Have 2, 3 or 4 flutes cut lengthwise to provide room for the chips and admit cutting fluid to lubricate the tap
  • The end of the shank is square so that a tap wrench can be used
• Types of taps


  • Taper tap
  • Plug tap
  • Bottoming tap
• Metric tap


  M - Metric tap

  4 - Nominal dia of the thread in mm

  0.7 - The pitch of the thread in mm
• Pitch


  Distance between one thread and the next
• Lead


  Distance a screw thread advances axially in one revolution
• Tap drill size


  • Tap drill size = Major Diameter - Pitch
• Machining


  All material removal process
• Metal cutting


  The process in which a thin layer of excess metal (chip) is removed by a wedge-shaped single-point or multipoint cutting tool with defined geometry from a work piece, through a process of extensive plastic deformation
• Rake face


  • The surface along with the chip moves
• Tool flank


  • The other surface in a wedge shaped cutting tool
• Rake angle


  The angle between the rake face and a line perpendicular to the work surface
• Clearance angle


  The angle between the tool flank and a line perpendicular to the work surface
• Orthogonal cutting


  • Cutting edge is perpendicular to the motion direction of the tool
  • Chip slides directly in the orthogonal plane (directly up the tool surface)
• Oblique cutting


  Cutting edge is not perpendicular to the motion direction of the tool
• Factors influencing the cutting process

  • Cutting tool material
  • Cutting tool shape and sharpness
  • Work piece material
  • Work piece condition (e.g. temperature)
  • Cutting parameters (e.g. Speed, feed, depth of cut)
  • Cutting fluids
• Cutting tool materials


  • Carbon and medium-alloy steels
  • High-speed steels (HSS)
  • Cast-cobalt alloys
  • Carbides
  • Coated tools
  • Ceramics
  • Cubic boron nitride (CBN)
  • Silicon nitride
  • Diamond

  
• Rake angle and clearance angle for different tool materials


  • Brass/cast iron: Rake 0°-5°, Clearance 10°

  Steel: Rake 15°-30°, Clearance 10°

  HSS tool: Rake 0°-5°, Clearance 10°

  Carbide tool: Rake 0°-5°, Clearance 10°
• Single point cutting tools


  Consists of a rectangular section called 'tool shank' on one end of which are ground the tool faces and tool flanks, which intersect to form the cutting edge
• Single point cutting tools with inserts


  The cutting edge is formed by a replaceable insert
• Twist drill


  • The body has two spiral flutes which usually have a 30° helical angle
  • Act as a passageway for chip extraction and for coolant to enter the hole
  • The point is in the shape of a cone and the point angle is typically 118°