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Optimum size selection
The simplest example of an optimised size selection is the
choice of a round bar that is closer in cross-sectional diameter
to the final component (see diagram opposite).
Two through-cost savings are
made: there is less machining required on the bar so machining
through-costs (operator time and tool wear etc) are lower and
the scrap though-costs are lower because less scrap is produced.
The closer the raw material is in
diameter to the finished component, the greater the cost saving
and it may even by possible to purchase a bar that is exactly
the size required for the finished component. Bars can be
produced to very close tolerances in the first place and if this
is possible the total cost of the machining operation will be
saved. If you’re using large amounts of the raw material it may
even make economic sense to have a very specific diameter and/or
tolerance produced at the production mill.
A second example of optimised
size selection is the choice of bar length. Bars will often be
supplied in full, standard, lengths but this may not be ideal
for your application (see diagram right). By choosing a bar
length that is an exact multiple of the length of your finished
component, it may be possible to make a significant through-cost
saving on scrap.
Optimum shape selection
It may seem very obvious but many people overlook the
possibility of buying raw materials in shapes that more closely
match their requirements. Round bar is very popular and indeed
sometimes cheaper to purchase but machining it down to other
shapes (e.g. hexagons) is often a false economy.
One example that is often
overlooked is the use of hollows. Rather then purchasing a round
bar only to machine away its centre, a hollow can be purchased
in the first place and the machining and scrap through-costs
eliminated.
Optimum grade selection
Optimising the grade (alloy) of material you purchase is perhaps
more difficult than optimising the size and/or shape but it can
have a major impact on through-costs.
Production costs can be increased
dramatically if an incorrect grade of materials is selected. For
example, if a particular grade that is selected is difficult to
machine, the machining times and associated costs will be
higher. However that particular grade may have been chosen
because it was necessary to achieve the required finished
component performance.
In optimising grade selection a
balance must be struck. Component performance criteria must be
matched against the possible through-cost savings that can be
made by improving the efficiency of manufacturing processes.
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