Question

In general, cutting heat in cutting operations mainly affects tool wear, whereas grinding heat in grinding operations has a significant effect on the surface finish of the workpiece. Explain why this is so using a figure. Explain the reason for this with a figure.

I can't read in cursive . Therefore, I would like you to write in block style.

Answer 1

Effect of Heat Generated on Cutting Tool and Workpiece

1 Effect of heat generated on cutting tool
High hardness and heat resistance are major considerations for the choice of cutting tool depending on the type of materials under consideration. However, heat generated during
machining results in tool wear eventually leading to high surface roughness of workpiece . reported that the use of cutting fluid during machining greatly increased tool life
compared to tool life obtained when cutting fluid was not applied under same machining parameters. This was so because hardness value was preserved over a longer period of time
during wet machining hence temperature reduction at cutting zone resulted in a preservation of tool and elongation of tool life. Thermal cracking which is due to the expansion and cracking caused by thermal stresses is
another way the cutting tool can fail . After some time, the cutting tool experiences a reduction in weight due to the wear (flank and crater) at the face.
2 Effect of heat generated on the workpiece
Heat generated during machining could have both positive and adverse effects on the workpiece material. Heat generated during machining could result in the reduction of strength/hardness of
the workpiece material, thereby lowered cutting forces. The reduction of cutting forces more often results a reduction of power consumption and an improvement in machinability of the
workpiece material . However, higher temperature at the cutting zone due to chemical reactivity of workpiece and cutting tool at high temperature, results in adhesion and diffusion
wear . Higher rate of heat is generated at the cutting zone during machining of metals and alloys with low thermal conductivity, this heat cannot be rapidly dispersed into the rapidly moving
chip. Higher temperature generation also affects the micro-structural constituents of the alloys, which may pose danger since the alloy is used for sensitive purposes . One major
effect of heat on workpiece is its influence on surface roughness during metal cutting processes.in the design of machined parts, surface roughness is highly essential and is known to
have considerable influence on properties like wear resistance and fatigue strength. During machining, it can be influenced by a number of factors like cutting parameters, cutting fluid, and
workpiece hardness . Depth of cut, feed rate and cutting speed also have greater influence on the workpiece surface temperature and an increase in workpiece temperature could result in
higher surface roughness . Some other problems heat generation could have on won workpiece include; dimensional inaccuracy in the products as a result of thermal distortion together with expansion-contraction in the process and after machining, surface damage due to oxidation, burning and rapid corrosion . Summarily, when the heat generated affects and
causes deterioration of cutting tool, there is a resultant effect on the workpiece as surface integrity becomes compromised and this has contributed to failure of most fabricated parts

FIG 1 : SOURCES OF HEAT GENERATION IN METAL CUTTING .

What are the consequences of allowing the temperature to rise during grinding? Temperature rise can have major effects in grinding, including: (a) If excessive, it can cause metallurgical burn and heat checking. (b) The workpiece may distort due to thermal gradients. (c) With increasing temperature, the part will expand and hence the actual depth of cut will be greater; thus, upon cooling, the part will contract and the dimensional tolerances will not be within the desired range.

why speeds are much higher in grinding than in machining operations?. Grinding is an operation that typically involves very small chips being removed from the workpiece surface by individual grains along the grinding surface of the wheel Consequently, to remove material at a reasonably high rate for productivity, wheel speeds have to be very high. Note also that high wheel speeds have no particularly adverse effects on the overall grinding operation (unless the wheels cannot withstand the stresses developed). In fact, the trend has been to increase spindle speeds on grinders and develop wheels with higher burst strengths. Recall also that higher removal rates are typically obtained in creep-feed grinding, which is an important industrial process

fig 2 :MECHANICAL AND THERMAL INTERACTIONS IN GRINDING PROCESS

FIG 3 :

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