As the hardness increases, the permissible velocity decreases for a given tool life. For example, the tool life is 50 minutes for cutting less hard material, now if say harder material is to be cut then to maintain the tool life as 50 minutes, the cutting velocity should be reduced proportionate.

Every device or tool has its functional life. At the expiry of which it may function, but not efficiently. So it is also true with a cutting tool. During use, the tool losses its material, i.e., it gets worn out. As the wear increases, the tool losses its efficiency. So its life has to be defined and on expiry of its life, it should be reground for fresh use.

Tool lifemonitoring sheet in Excel

On carbide and ceramic tools where crater wear is almost absent. Tool life is taken as corresponding to 0.038 or 0.076 mm of wear land on the flank surface for finishing respectively.

The roughness of the surface is measured continuously along its length. When the roughness reaches the specified value, the cutting is discontinued. For example, this maximum specified value of surface roughness may be occurs on the 10th workpiece, so the 11th and next workpieces won’t be machined with the same tool, without regrinding.

According to this criterion, the cutting with the tool is continued till it is able to cut. So when the tool fails to cut, then only it should be reground. This criterion is not used in practice because of its obvious disadvantages.

Before her diagnosis, Kerry was enjoying life like most girls in their early 20s. Adored by her friends and family, in a happy relationship with her boyfriend and looking forward to her future, which like many other young women included dreams of getting married and having children eventually. She was also training to be a paramedic while working as an admin assistant in a hospital.

According to the Taylor’s tool life equation, tool life decreases when feed rate increases. Also, the same case for depth of cut.

Fig. 9.29 shows two different arrangements of principal cutting edge angles. Fig. 9.29 (a), the contact is gradually starting from a point quite away from the tip. 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. 9.29 (b) in which the principal cutting edge angle is 90°.

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. The best compromise is 5° (with carbide tools) to 8° (with H.S.S. tools) for common work materials.

iii. 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.

Tool lifecriteria

This is what Kerry Harvey said in August 2013.  Just five months before she had been diagnosed with inoperable pancreatic cancer.  Like most patients, she had never heard of pancreatic cancer before diagnosis.

iii. Decrease of tool life with increased speed is twice as great (exponentially) as the decrease of life with increased feed.

As the structure becoming more and more perlites, the tool life decreases at any increase in cutting speed, as shown in Fig. 9.27.

According to this criterion, when the surface roughness reaches a specified high value, the cutting with the tool is stopped and grinding is done. Say at a particular cutting condition the surface roughness, comes to be 0.7 microns. As in process of cutting the flank wear develops so the cutting edge becomes rough and irregular so the surface roughness gradually increases, as shown in Fig. 9.24. Say 1.3 microns, for example, are kept as a criterion.

Tool lifemonitoring in FANUC

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. Fig. 9.26 shows tool life variation against cutting speeds for different tool materials. 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.

Also, it is important to note that, the flank wear is not uniform along the active cutting edge, therefore, it is necessary to specify the locations and the degree of wear, when deciding tool life criterion, before regrinding.

Fig. 9.28 shows cutting process using positive and negative rake tools. 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.

So, the constant C can be interpreted physically as the cutting speed for which the tool life is equal to one min. The tool life equation can be represented on log-log paper; it becomes straight line as shown in Fig. 9.26.

Today Kerry Harvey should have been celebrating her 27th birthday!  Sadly, after her diagnosis of pancreatic cancer in April 2013, she died in February 2014  aged just 24.  In just ten months, she did all she could to raise awareness of the signs and the symptoms of pancreatic cancer to ensure that at least one person was diagnosed in time for surgery – currently the only cure!

After reading this article you will learn about:- 1. Meaning of Tool Life 2. Methods for Tool Life Measurements 3. Expectancy 4. Plots 5. Criteria 6. Factors Affecting.

iv. The greatest variation of tools life is with the cutting speed and tool temperature which is closely related to cutting speed.

An ideal tool material will have n = 1 (Taylor’s tool life index). It means ideal material tool at all cutting speeds, removes maximum volume of work material.

Tool lifecalculator

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.

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.

Due to wear on the flank, the actual depth of cut decreases from AC to BC as shown in Fig. 9.23. The workpiece becomes taper if cutting continued. This is the most usual criterion followed in practice. The flank wear is measured with a tool maker’s microscope.

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.

Application of suitable cutting fluid obviously increases tool life or in other words, for the same tool life, allowable cutting speed increases. Fig. 9.30 shows the effect of cutting fluid on tool life for different tool materials. The tool life even increases by 150 per cent at some speeds. All types of cutting fluids do not have equal effect, some of them more, some are less.

A tool fails when it no longer performs its function properly. This may have different meaning under different circumstances. In a roughing operation, where, surface finish and dimensional accuracy are of little importance, a tool failure can mean an excessive rise in cutting forces and power requirements.

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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.

Define tool lifepdf

According to this criterion, a tool will be considered to have failed, if the amount of cutting force increases by certain specified amount. This is due to flank wear. Flank wear increases the area of contact between the workpiece and the tool, resulting into increase in the cutting force. Fig. 9.25. shows that an increase in cutting force with development to flank wear.

According to this criterion, a tool will be considered to have failed if there is a deviation in the size of a produced finished component from its specified value.

Define tool lifein machining

C = Machining constant, found by experimentation or published data-book. It depends on properties of tool material, workpiece and feed rate.

Impurities and hard constituents in the workpiece material (such as rust, slag, scale, etc.) are also cause of abrasive action which reduces tool life.

The tool geometry greatly affects the tool life. We will discuss the effect of all the tool parameters on tool life in following pages:

Factors affectingtool life

Negative rake increases cutting force and power, hence more heat and temperature generated results in smaller tool life.

Just ten days before she died, when she was incredibly ill, she even appeared on ITV’s This Morning : https://www.youtube.com/watch?v=lomNCfQ27mY

We remember a very special lady, who along with the late Andy Luck and Penny Lown, helped over 20 million people in the UK become more aware of pancreatic cancer.  Happy Birthday Kerry!

Tool life curves are generally plotted on log-log graph paper. These curves are used to determine the value of exponent ‘n’. The exponent ‘n’ can indeed become negative at low cutting speeds. Fig. 9.22 (a) shows the tool life plot between tool life and cutting speed for various workpiece materials having different hardness. It shows that, as the cutting speed increases, the tool life decreases rapidly. If cutting speed Versus tool life, curves are plotted on a log-log graph paper, straight lines are obtained as shown in Fig. 9.22. (b).

Due to wear on the tool, the cutting force increases and surface finish deteriorates. Therefore, when should we say that a tool has failed and it should be reground. In other words, certain criterion is required for judging the tool failure.

Therefore, there lies an optimum value of the back rake which depends upon tool material and work material. It ranges from -5° to +15°. An optimum value of rake angle is about 14° which gives maximum tool life.

It is clear that the cutting speed has the highest effect on tool life followed by feed and depth of cut, respectively. As cutting speed increases, the cutting temperature increases, and tool life decreases.

What istool lifeequation

Sadly her life ended far too early when she died of pancreatic cancer on 22nd February 2014, aged just 24.  In the weeks leading up to her death, her beautiful face was seen in newspapers, magazines and social media across the world.  This was as a result of her participation in our hard-hitting advertising campaign.  She did this to raise awareness and ultimately save lives by encouraging people to go to the doctor if they suspected they had symptoms.

In 1907, F. W. Taylor developed relation between tool life and cutting speed, temperature, by keeping feed as constant. The Taylor’s Equation for Tool Life Expectancy provides a good approximation.

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In a finishing operation, where, surface finish and dimensional accuracy are prime important, a tool failure will mean that the specified conditions of surface finish and dimensional accuracy can no longer be achieved. All of these failures are basically related to the wear on the clearance face of the tool.

F.W. Taylor has conducted numerous experiments in the field of metal cutting. In 1907, he gave the following relationship between tool life and cutting speed, which is known as Taylor’s Tool Life Equation.

This criterion becomes specially important when close fitting objects are machined. Due to rough and uneven surfaces, the proper fitting may not be done.

Tool life curves are plotted between tool life and various process parameters (such as cutting speed, feed, depth of cut, tool material, tool geometry, workpiece hardness, and cutting fluids, etc.). To draw these curves, experimental data obtained by conducting cutting tests on various materials under different conditions and with varying process parameters.

According to this criterion, when the wear on the flank reaches a certain height the cutting with the tool is discontinued and grinding is done. Say when the flank wear height h equals to 0.3 mm, for example, the tool is said to have failed. Some common recommended values of wear land are given in Table 9.11. (a, b).

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. Rigidity is the prime requirement in case of intermittent cutting specially when brittle tools are used.