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Development of an established product
The manufacturing process
The clinch nuts are made from continuous lengths of aluminium alloy bar
(round in cross section). These bars are stacked in the end of computer
controlled lathes
(G)
and are automatically fed into the machine as the previous bar runs out.
Several functions are carried out on the one machine: turning
(G)
the outline profile of the nut; drilling through the centre and tapping
the thread in this hole. This automated process runs all day overseen
by skilled supervisors in two shifts. If demand is high enough, it also
continues part way through the night with no one in attendance.
The machines are left running when everyone goes home and continue until
sensors detect a problem. They are then automatically shut down and await
attention in the morning. This increases production without increasing
labour costs in the factory. The company staff refer to it as 'two-and-a-half
shift production'.
By automating the processes in this way the unit
cost (G)of the nuts can be kept as low as possible.
Testing the performance of a design continues throughout the development
process as new prototypes are produced. Once the design is finalised the
concern shifts to maintaining the quality of every product that comes
off the production line. Each one must match the manufacturing specifications
set out by the final (production) prototype.
TR were very familiar with this problem but for the BMW bumper nut their
customer insisted that they should not be supplied with a single defective
part. If you think about the thousands being made and how cutting tools
gradually get less sharp (just as one example) you can see how difficult
this might be.
The traditional approach would have been to check the nuts as they came
off the production line by having a Quality Control inspector carefully
measure say one in every 100 or every 50 to see that quality was being
maintained. However, this would allow occasional bad parts (that did not
meet the specification) to get through.
To ensure that this did not happen, for the BMW nut TR had a special automated
camera inspection system developed. With this, before packing every single
nut is checked by three separate digital cameras connected to a computer.
This checks the profile of the nut to verify the form of the screw thread,
the core diameter and nine external dimensions. Any nut not meeting these
quality controls is rejected before packing. As a result, the customer
can rely on TR to know that each nut is to specification.
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