CUTTING TOOL GEOMETRIE
1. RAKE ANGLE
Rake angle is a cutting edge angle that has large effects on cutting resistance, chip disposal, cutting temperature and tool life. Increasing rake angle in positive direction improves sharpness of the cutting edge and the cutting force decreases but at the same time it lowers the strength. To increase the cutting resistance the rake angle must be increased in negative direction.
Small rake angle - Machining of fragile and hard materials.
Big rake angle - Machining of plastic materials and soft materials
2. RELIEF ANGLE
Flank angle prevents friction between flank face and work piece resulting in smooth feed. Increasing flank angle decreases the cutting force and surface roughness becomes better but on the other hand this lowers the cutting edge strength and decrease the flank wear occurrence.
Small flank angle - Machining of hard and demure materials. For roughing operation with stable cutting edge.
Big flank angle - Precision machining with low cutting force Work pieces suffer from work hardening easily.
3. INCLINATION ANGLE
The positive and negative edge inclined angle decides the discharging direction of chips. In heavy cutting, the cutting edge receives extremely large shock at the beginning of cutting. Cutting edge inclination keeps the cutting edge from receiving this shock and prevents fracturing. On the other hand the back force increases and occurs vibration. A finishing operation a positive angle is more suitable.
When the edge inclined angle is negative, i.e. the cutting edge is located at the lowest point relative to the bottom plane of the tool holder, the chips flow to the machined surface of work piece.
When the edge inclined angle is positive, i.e. the cutting edge is located at the highest point relative to the bottom plane of the tool holder, the chips flow to the un-machined surface of work piece.
4. ENTERING ANGLE (APPROACH ANGLE)
Reducing the lead angle increases the strength of the cutting edge. Heat dispersion is good and roughness of machining surface is small. Because lead angel is small, the cutting width is long, the force on the unit cutting edge length is small. At the same time, reducing the lead angle can increase the tool life. Normally, when turn thin long shaft and ladder shaft, the lead angle adapts 90°. The lead angle is increased, radial force is reduced, cutting is stable, cutting thickness is increased and chip breaking performance is good.
Small entering angle - material with high tensile strenght, high hardness or hardened layer on surface.
Big entering angle - For machine with low rigidity
5. MINOR ANGLE
The minor cutting edge angle is the main angle on influence surface roughness; its size is also influence strength of cutter. When the minor cutting edge angle is too small, the cutting force increases and results in chattering and vibration. The selection principle for the minor cutting edge angle is, under the condition of rough machining, or un-influencing friction and producing vibration, the smaller angle should be chosen; the bigger angle can be used for precision machining.
6. CORNER RADIUS
The corner radius effects the cutting edge strength and the finished surface. By increasing the corner radius the surface finish becomes better and the cutting edge strength improves. Flank and rake wear decreases. If the radius becomes to big cutting force increases and causes vibration. Also chip control becomes worth.
Small corner radius - Finishing with small cutting depth Machining thin long shafts. Rigidity of machine is insufficient
Big corner radius - Rough machining, high cutting edge strength is required. Rigidity of machine is good. Machining harden materials and interrupted cut