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Inspection Records
Most of our engine valve inspection records are entered
directly into a database by each machine operator using custom software applications specifically
designed for Cal Grinding, Inc. An example of this is our valve stem finish grind inspection
program. As each value is entered, the application compares each with the customer's
specifications that are maintained in the database. If any value is found to be outside
the prescribed limits, the operator is immediately notified so that corrective action is
taken. Otherwise, the data is stored in a database for monthly analysis by our Quality
Control Department.
 This screen shot shows a typical example
of our stem finish grind inspection program. As each sample is entered into the database,
the operator is provided with a graphical history of his/her performance for the current
lot of valves. This allows him/her to immediately make any necessary adjustments to the
machine in order to provide our customers not only with an acceptable product, but with
the best possible product.
For any given valve, we establish our upper and lower
control limits (UL and LL respectively) at 75% of the maximum tolerance allowed by the
customer. This is the range within which our machine operators may perform without any concern. If
they find a sample that has exceeded the UL or LL, all of the parts that have been ground
since their previous sample are inspected to ensure that they are in conformance with the
customer's specifications.
In the example above, you can see that the customer's
specification is 0.23880 in. +/- 0.00025 in. for the finished stem diameter. Our UL and LL
were set at 0.23898 in. and 0.23861 in. respectively. Yet, the operator consistently
produced parts between 0.23875 in. and 0.23885 in. in diameter. This is a deviation of
only (0.23885 - 0.23875) 0.00010 in. in over 900 pieces. The customers maximum allowable
deviation is (+/- 0.00025) 0.0005 in. So, the operator was only using (0.00010/0.0005)
20% of the customers tolerance!
At the same time, this operator maintained stem lobing at
0.00010 in. or less (compared to the customers spec. of 0.0006 in. max.) and kept
the stem surface finish at 13 µin. Ra or less (compared to the customer's spec.
of 18 µin. Ra max.). This is just one example of how our exceptional machine capabilities
and operator experience allow us to provide our customers with a superior product.
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