HISTORY OF CUTTING TOOL MATERIALS
• Cutting tool used during the industrial revolution in 1800 A.D
• First cutting tool was cast using crucible method (1740) and slight hardened by H.T.
• 1868: R. Mushet found by adding Tungsten we can increase hardness and tool life ( Air Quenching)
• F.W.Taylor in Pennsylvania did the most basic research in metal cutting between 1880-1905
• Invented high speed steel (better H.T. process)
• Better alloy
• Tungsten Carbide was first synthesized in 1890.
• Took 3 decades before we got Cemented carbide.
• First used in Germany.
• Sintering technology was invented.
Cutting Tool Geometry
• Top Rake: Evacuates chip…rolls chip out
• Heel or Clearance Angle: This is the clearance between the cutter and the surface that has just been cut. Insures that the cutting edge (and not the back side or heel of the cutter) contacts the work piece first
• Lead Angle: This is formed by the leading edge of the cutter and a plane perpendicular to the cutter feed motion
• End relief angle: The clearance below the end of the tool
• Side Relief Angle: The clearance below the cutting edge
• Back Rake: This is a shear angle that also evacuates the chip or rolls the chip out
• Nose Radius: The nose radius stretches the cutting edge. It increases the amount of cutting edge in contact with the work
Heel Angle (Positive):
A small positive heel angle provides a stronger cutting edge and minimizes tool chatter.
Heel Angle (Negative): A zero or negative heel angle will cause the tool to drag on the work piece material and prevents the tool from entering.
Heel Angle (large positive) : A larger positive heel angle provides a keener cutting edge that will penetrate the work piece more readily, but gives the tool a fragile cutting edge. A larger positive heel angle also increase the potential for tool chatter.
CUTTING TOOLS- AN INTRODUCTION
Metal cutting tools are subjected to extremely arduous conditions, high surface loads, and high surface temperatures arise because the chip slides at high speed along the tool rake face while exerting very high normal pressures (and friction force) on this face. The forces may be fluctuating - due to the presence of hard particles in the component micro-structure, or more extremely, when interrupted cutting is being carried out. Hence cutting tools need:
• strength at elevated temperatures
• high toughness
• high wear resistance
• high hardness
During the past 100 years there has been extensive research and development which has provided continuous improvement in the capability of cutting tool. A key factor in the wear rate of virtually all tool materials is the temperature reached during operation, unfortunately it is difficult to establish the values of the parameters needed for such calculations, however experimental measurements have provided the basis for empirical approaches. It is common to assume that all the energy used in cutting is converted to heat (a reasonable assumption) and that 80% of this is carried away in the chip (this will vary and depend upon several factors - particularly the cutting speed). This leaves about 20% of the heat generated going into the cutting tool. Even when cutting mild steel tool temperatures can exceed 550oC, the maximum temperature high speed steel (HSS) can withstand without losing some hardness. Cutting hard steels with cubic boron nitride tools will result in tool and chip temperatures in excess of 1000oC.
CUTTING TOOL MATERIALS:
1 Carbon Steels
2 High Speed Steel (HSS)
3 Cast Cobalt Alloys
7 Ceramics - Alumina
8 Cubic Boron Nitride (cBN)
10 Other Materials
1 Carbon Steels...
Please join StudyMode to read the full document