Using at a certain velocity. The workpiece steel

Using the thermal modal it is possible
to plot lines to determine at what critical specific energy burn occurs at
different workpiece speeds. When experimental critical specific data is added
it is then possible to determine the maximum temperature of the grinding wheel
at a certain velocity. The workpiece steel used in this model is thermally
damaged at 523.15K this model is however estimating what is actually occurring
as we see that the third workpiece burns at a temperature below 523.15K. This
seems to be a problem but could be quickly rectified, through further testing
and fine-tuning the model could be used after ascertaining the exact
temperature that burn occurs within the thermal model. This would allow the
model to be used but caution should still be practised while using any model,
to use it in an industry setting lots of experimental testing and modifications
should be made to guarantee that no thermal damage occurs.

This data was recorded by a highly
reliable source (Andy Pettit) having written many academic papers on grinding
Andy has lots of knowledge recording data from grinding experiments. A reliable
source however does not prevent systematic or random errors in data. Systematic
errors for example could be equipment not being calibrated properly, the
distance between the edge of the grind wheel and the centre of the headstock.
This would be a continual error that would only be exaggerated through
calculations resulting with in correct final outcomes. Quantitative errors can
also not be overlooked, temperatures while operating machinery could affect the
accuracy of recording apparatus causing incorrect readings running the machine
for a long time would increase the likelihood of these temperatures. Random
error could be from the dynamometer not keeping up with the constant
fluctuations in power change. This would lead to an incorrect max power reading
as it is not a liner constant recording, but instead lags behind jumping making
it hard to get an accurate reading.

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Grinding is a very accurate machining
process capable of achieving very fine cuts in materials. Grinding tolerances
for surface finish for example are typically between 0.20µm and 0.81µm giving very clean precise surfaces. Grinding
is also very good at cylindrical or roundness achieving an accuracy of up to
1.3µm for diameter and an incredible 0.25µm for roundness an accuracy which
many other processes cannot achieve. Hard turning however is intended to
replace or limit traditional grinding operations achieving a roundness accuracy
of 0.5µm to 12µm however and a surface finish of 0.8µm to 7µm which although
still incredibly accurate isn’t quite accurate enough to compete with grinding
on a surface finish level it is however a feasible procedure for other less accurate
parts including gears, pump components and hydraulic components. It does
however have other uses such as facing and grooving processes which are not
used with grinding machines making it a more versatile process making it very
suitable alternative depending on the level of accuracy required. 
Using the model in its current state it is difficult to say where the optimum
and safe machining parameters are as the third workpiece burnt below the
supposed burn temperature of 523.13K. In order to accurately outline these
parameters changes would have to be made to the model or further testing
carried out. We can see that from the first and last values within the
experiment the grinding wheels was dressed this has clearly effected the
critical specific energy needed to grind especially when comparing it to the
same workpiece velocity when not recently dressed. With sharper grains and
unclogged pores the grinding wheel is much more efficient however no change is
made within the programing to account for this causing the grind wheel to cut
through the workpiece too quickly causing thermal damage. The thermal model
also doesn’t take into account the partition of thermal energy into each heat
sync, coolant was used and sparks created but none of this is accounted for
within calculations. Simple calculations could account for 5% to both energy
accumulating in swarf and energy entering the coolant and between 10 and 20%
entering the grinding wheel leaving an estimated 70% of the total energy going
into the workpiece. However to guarantee that thermal damage is avoided an
adaptive control system could be incorporated using thermal models to prevent
thermal damage while also speeding up and making the process more efficient.
This could be programed directly into a CNC machine, this could then be linked
to a dynamometer measuring power at set intervals which could in turn be fed
through equations to constantly calculate critical specific energy if these
calculations get too close to the thermal model the grinding parameters could
be altered to lower the power consumed allowing for optimal conditions
guaranteeing the workpiece isn’t burned.  

The most appropriate type of grinding
wheel is dependent on many factors such as what product the grinding wheel is
being used for along with the scale of the company for example if the grinding
wheel is being used to create many of the same part for example within a
factory machining cylindrical workpieces then a high quality diamond grinding
wheel would suit as the wheel does not need to be dressed as often as others
and if hard wearing meaning that the process isn’t slowed by swapping out or
re-dressing worn wheels making the process more efficient. This however
wouldn’t be appropriate if different jobs where being performed as the wheel
would have to be swapped out for a different grade or quality each time. This
is the case for large scale companies to a diamond wheel is perfect as it
doesn’t need swapping out or dressing as frequently as other types meaning a
more efficient production however the diamond wheels cost a lot more than
perhaps a silicon carbide wheel making it less of a viable option for small
scale companies due to the high price. Small scale companies are better using
cheaper wheels such as silicon carbide as they are cheaper and therefore more
affordable for a small scale company they do however wear faster but smaller
companies should not need as high levels of wear as a larger company due to
lower production output. Using the current model however the grinding wheel can
consist of any material as long as it meets the calculation requirements of
thermal diffusivity and thermal conductivity using a different wheel with
different characteristics will change how the grinding performs resulting in a
different model being required.


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