Tool life formula

There are many ways of defining the tool life, and the common way of quantifying the end of a tool life is by a limit on the maximum acceptable flank wear. For example, the amount of wear acceptable on a rough milling insert will be more than that on a finish milling insert.

A typical tool life definition for a roughing insert would be the time period for the flank wear to become 0. For a finishing insert it will be typically a third of this.

Tool wear is not uniform through the life of the tool. The wear is initially rapid, then settles down to a uniform rate, and finally accelerates at a very high rate till catastrophic failure occurs, which is a fracture of the tool.

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But opting out of some of these cookies may affect your browsing experience. For effective planning of the entire production, overall machining or cutting time must be incorporated. Now-a-days the primary goal of industries is to manufacture the product at a faster rate but at minimal cost and that too without sacrificing product quality. As long as conventional machining is utilized, in order to fulfill first requirement faster production rate , the cutting speed and feed rate should have to be increased.

However, this may lead to reduced cutting tool life due to faster wear rate and higher heat generation. Hence, cutting tool is required to change frequently, which will ultimately impose a loss for the industry as a result of idle time for changing tools. Cost of tool is also not negligible. Therefore abrupt increase of cutting speed and feed rate is not a feasible solution; rather, an optimization is necessary.

As the structure becoming more and more perlites, the tool life decreases at any increase in cutting speed, as shown in Fig. The major requirements of cutting tool materials are: Hot hardness, impact toughness, and wear resistance. For better tool life, the material must have the above properties.

It is very clear from the figure; at any cutting speed the tool life is maximum for ceramic tool and lowest for the high speed steel tool. So using ceramic tool maximum volume of material could be removed at any cutting speed for a specific tool life. It means ideal material tool at all cutting speeds, removes maximum volume of work material.

The tool geometry greatly affects the tool life. We will discuss the effect of all the tool parameters on tool life in following pages:. Larger the rake angle smaller will be the cutting angle and larger will be shear angle, this reduces the cutting force and power, and hence less heat generated during cutting, means reduced cutting temperature, results in longer tool life.

But on the other hand, increasing the rake angle results in mechanically weak cutting edge the positive rake tool experiences shear stress and the tip is likely to be sheared-off. Negative rake increases cutting force and power, hence more heat and temperature generated results in smaller tool life. Therefore, there lies an optimum value of the back rake which depends upon tool material and work material. The positive rake tool experiences shear stress and the tip is likely to be sheared off. Whereas tool with negative rake experiences compressive stress.

The carbide and ceramic tools are generally given negative rake because they are weak in shear and good in compression. Therefore, the tool experiences the cutting force gradually and over a larger area.

Hence the tool is safer and tool life is more as compared to the Fig. An increase in clearance angle results in significant reduced flank wear, so increased tool life. But the cutting edge will become weaker as the clearance angle is increased. Therefore an optimum value is required. Larger radius means larger area of contact between the tool and workpiece. Due to which more frictional heat is generated, results in increased cutting force. Due to which the workpiece may starts, vibrating, hence if rigidity is not very high, brittle tools carbides and ceramics will fail due to chipping of cutting edge.

Application of suitable cutting fluid obviously increases tool life or in other words, for the same tool life, allowable cutting speed increases.

The tool life even increases by per cent at some speeds. All types of cutting fluids do not have equal effect, some of them more, some are less. If the cutting is intermittent, the tool bears impact loading, results in chance of its quick failure.

In continuous and steady cutting, the tool life is more. Tool life increases if grain size increases. As if grain size increases, then mean number of grains per square area decreases, and hence hardness decreases, these results in increased tool life.

Higher is the rigidity of system higher will be the tool life. Lower the rigidity of the system, higher is the chance of tool failure, by vibrations of tool or workpiece.