The tool is sharp shape object of hard material. It is usually made from H.S.Steel. Rather than H.S.S. machine tool is also made from High Carbon Steel, Satellite, Diamond, Ceramics, Abrasive, etc. The main required condition of tool material is hardness. It must be very hard enough to resist cutting forces applied to the work piece. Hot hardness, wear resistance, coefficient of friction, Toughness, Thermal conductivity, & specific heat, are other requirement of tool material. All these properties should be high enough.
Classification of cutting tools
According to number of cutting edge
- Single point cutting tool
It is simplest type of cutting tool & it have only single cutting edge.
Examples – shear tools, lathe tools, planer tools, boring tolls etc.
2.Multi point cutting tool
In this more than one single point cutting tools arranged together as a unit. The rate of machining is more & surface finish will be better in this case.
Example– drills, milling cutter, brooches, grinding wheels, abrasive sticks etc.
According to motion
- Linear motion tools – lathe tools, brooches
- Linear & rotary motion tools ,drills, taps, etc.
- Rotary motion tools – milling cutters, grinding wheels
Single point cutting tool geometry
The single point cutting tool mainly consist of cutting part and tool shank called point. The point of cutting tool is covered by cutting face, end flank, side or main flank, & base. The chip slide along the face.The side or main cutting edge ‘ab’ is formed by intersecting of face & side / main flankThe end cutting edge ‘ac’ is formed by the interconnection of end flank & base.The point ‘a’ which the intersection of side cutting edge and end cutting edge is called nose. Mainly the chip cuts the material by side cutting edge.
Terminology of single point cutting tool
- Shank– It is main body of tool. The shank used to trap inside the tool holder.
- Flank– The surface or surface below the area of the cutting edge is called flank of the tool.
- Face– It is top or upper most surface of the tool along which the chips slides.
- Base– It is a bearing surface of the tool when it is situated in tool holder or directly clamped in a tool post.
- Heel– It is the intersection of the base and flank of the tool. It is a curved portion at the bottom of the tool.
- Nose– It is the point where side cutting edge & base cutting edge intersect.
- Cutting edge– It is the edge on face of the tool which clear the material from work piece. The cutting edges are major cutting edge & minor cutting edge
- Tool angles-Tool angles have great importance. The tool with accurate angle, reduce breaking of tool, cut metal more efficiently, generate less heat.
- Noise radius–It provide long life & good surface finish sharp point on nose is highly stressed, & leaves grooves in the path of the cut.Long nose radius produce chatter.
After use of tool for longer period of time tool is subjected to wear.
Cause of tool wear—
- Interaction between chip and tool.
- Cutting forces.
- increase in Temperature during cutting.
Effect of tool wear
Tool wear changes tool shape, decrease efficiency. Tool wear reduces the dimensional accuracy, loss of surface finish. It increases power consumption during operation.
Classification of tool wear
- Crater wear on tool face
- Loss of hardness at high temperature
It occurs on the flank. It is due to friction between newly machined contact area of flank and wokpiece surface . The worn region at flank is called ’wear land’.
The width of the wear land (hf) is account as a measure of wear & it is determined by tool maker microscope.
- Feed of brittle material is less than 0.15 mm/rev.
- Abrasion by hard particles & inclusions in workpiece.
- Abrasion by fragment of built up edge.
- Shearing of micro welds between tool & work.
- Crater wear
The small cavity or hole is crated on the face of the tool. This small cavity is called ‘crater’ which is formed at some distance from cutting edge.
- Pressure of chips when it is slide over face of tool.
- High temperature at tool- chip interface. Some times it creates the melting temperature.
- Crater wear is more in case of continuous chips of ductile material.
- Lack of lubrication.
- Feed is less than 0.15 mm/rev.
- Low cutting speed.