The cutting tool life is a important factor of machining the metal. It is defined as the cutting time required for reaching to life or time elapsed between two consecutive resharpening. The tool server effectively and efficiently during the life period.
Different method of expressing the tool life,
- The volume of metal removal grind
- Number of work machined per Grind
- Unit of time
The factors affecting tool life:
- Cutting speed
- Tool geometry
- Work material and cutting fluid
- Tool material
- Feed and depth of cutting
- Rigidity of work, machine and tool
Cutting speed Definition:
Cutting speed is a greater influence of tool life when the cutting speed increase, the cutting temperature of machining will be increased. So, the crater wear and tool flank wear will be occur. The above conditional of Tool cutting when the tool speed increase, the tool life will be decreased. For getting best result, the tool life will be in increase at low cutting speed. The following relationship between cutting speed and tool Life by Taylor’s formula(Cutting Speed formula);
Cutting Speed Formula
V = Cutting speed of tool (Cutting Speed unit in m/min)
T= tool life in minutes
n= exponent or Index, Which is depends on the tool work.
= 0.1 to 0.5 for high speed Steel tool
= 0.2 to 0.4 for tungsten carbide tool
= 0.4 to 0.6 for ceramic tool
C = Constant
If the tool permit higher cutting speed for same life, tool having better cutting property and more productive. For find out the tool life, there are operated to to failure at different cutting speed and the test result are platted. The relationship between cutting speed and tool life as shown in figure.
Refer about diagram, the parabolic curve decreased in tool life at increase cutting speed obtained. In such relation is plotted as straight lining on Log – Log graph as shown in figure. Run the plot display cutting speed increase at Decrease the tool life. If the cutting tool have low cutting speed when the tool will be lost life.
If the surface finish of tool is improved due to the friction between tool and chip is maintained.The roughness of cutting tool is provide stress concentration, due to cause of surface crack and chip formation. The factor influencing cutting speed permitted by cutting tool as follow,
- Surface finish obtained
- Cutting fluid used
- Tool geometry
- Rate of feed and depth of cut
- Workpiece material
- Machining method
Feed and depth of cut:
The cutting tool life is influenced by the amount of meta removed by per minute. When we are using good Cut feed, then the area of chip pass over the tool face is greater than coarse feed of metal removal volume. In this reason to get more advantages in favour of thick chip, the cutting tool force to providing the thicker chip. It is able to balance two opposing influence to obtained optimum feed rate.
The feed and depth of cutting effected on tool life. The formula is followed by,
V= cutting speed of tool
T= tool life
f= feed in mm per minute
t= depth of cut in mm
The above relationship obtained, when low Carbon Steel material machined by use of cemented carbide Steel tool. Finally, wherever the feed and depth rate increase at life of tool will be increased.
When the tool at large rake angle reduced the cross section. Hence, the tool reduce the sufficient amount of heat absorbing. This is weaken of tool. So, must be used correct rack angle to maintain a long tool life. The tool optimum rake angle for maximum life of tool lie between -5 degree to + 10 degree by machining of austenitic Steel using carbide tool. If tool relief angle have more, the friction will be less of tool on machining. But, it more and more relief angle reduce the life of tool because the strength will be decreased. The optimum rake angle must be in between 12 degree to 15 degree. Similarly, the side cutting edge angle is high to give long life of tool. it side cutting edge angle for optimum level must be 30 degree and 25 degree. Increase in nose radius to improve the life of tool. Since, the stress concentration is lesser under using greater nose radius. The relationship between tool life, cutting speed and nose radius as follows,
By using proper end cutting edge angle to improve the surface finish, rigidity and equivalent cutting speed. The optimum level of end cutting edge in between 4 degree to 10 degree.
By using ideal tool material to remove the maximum volume of material at all cutting speed. The physical and chemical property of cutting tool material will be influence the life of tool. High speed steel cutting tool is more durable of machining than carbon steel tool. But it carbide tools has more life than high speed tool.
The heat produced during the metal cutting process, it heat carried out from the tool and workpiece by means of cutting fluid. When the fluid reduce friction at chip tool interface and increased life of tool. The cutting fluid is directly control by amount of heat at chip tool interfacing. The formula denoted by,
The tool life also depends upon microstructure of work material. Generally, the tool life more than as compared to work piece by means of machining of soft material than hard metal like alloy steel and cast iron.
Rigidity of machine tool and work:
When that tool have supported in strongly, which is rigid the machine will have more life than tool under vibration of machine. Loose work piece will have decrease the life of tool.