Albion Devices, Inc.
Case study: Temperature compensation of engine cylinder bores
• Automobile engine block production rate increased: By over 50%
• Cylinder bore dimensional accuracy increased: 1 micron repeatability and accuracy held
Critical internal dimension inspection measurements on cylinder bores were being rendered inaccurate by thermal influences on a production line in one of the world’s biggest automobile engine plants. Aluminum blocks were being bored prior to the insertion of steel cylinder liners. The inability to hold accurate size could lead to liners subsequently cracking during engine operation. Albion Devices, Inc., was asked to solve the problem.
Ambient conditions in the plant, air flow from the air gage onto the workpiece and the boring machine process prior to block inspection were each influencing variations from the reference temperature, 68 degrees F / 20 degrees C (the International Reference Temperature, ISO 1). Resulting temperature gradients in the engine block and the gage head led to significant fluctuations in process control data.
At Albion’s recommendation a gage head was designed to include a temperature probe imbedded in the gage head. The probe used Albion’s proven, durable temperature sensing technology in a package that would sense the temperature of the gage head and the inner wall of the cylinder, without surface wear or scratching. It monitored temperatures within the cylinder bore while the air gage took dimensional measurements in x and y orientations. The data obtained was used in one of Albion’s compensating controllers to calculate the necessary correction and transmit it to the host gage computer to be added or subtracted to the measured dimension.
The automotive company engineer responsible for retaining Albion for this job reported that tests of the completed, temperature compensated gaging system gave “outstanding results”. They were better than any he had seen previously from an air gage. Measurements were repeatable to within 1 micron. Gage Repeatability and Reproducibility (R&R) studies produced greatly improved results. Reliable, accurate and repeatable process control information could now be obtained for the operation.
However, most importantly in this case, the engineer was able to accelerate the production line. Previously the boring machine had operated at 2,000 rpm, limiting cycle time to 44 seconds. Any faster operation caused excessive heat build-up in the cylinder block and resulting increases in measurement errors. With the temperature compensation system installed the bore speed was raised to 3,000 rpm without any deterioration in dimensional control. This was possible because the gaging system, in a feed-back loop to the machining process, continued to report dimensions, after applying automatic correction, as if temperatures were being held steady at reference temperature: 68 degrees F / 20 degrees C. Production output increased by 20 cylinder blocks per hour (an increase of approx. 25%) and cycle time dropped to 36 seconds. Further tests at maximum boring machine speed of 4,000 rpm, which reduces cycle time to 29 seconds, were equally successful, with the result that a total of over 50% production time improvement became achievable.
