Improved Temperature Profile Control Increases Productivity

Introduction:

Due to continually increasing competition and price pressure in the industrial manufacturing arena, Continuous Operational Improvement (COI) efforts are at an all time high. The desire for speed and quality in processes that require heat often result in requirements for better temperature uniformity and improved control to increase process through-put without increasing scrap. In addition, the need to reduce equipment floor space in order to increase productivity is also key- the less required the better!

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Customer Challenge:

During a manufacturing Kaizen event, the Operations manager was informed that a new piece of equipment was needed to address a bottleneck in the production cell. The team had evaluated the process "takt" time and knew that they could never improve productivity with the old machine. They needed a machine that could ramp up and cool down faster to increase production throughput as well as reduce the amount of scrap due to inadequate temperature uniformity. They needed an improved temperature uniformity across the surface of the equipment, however they could not determine what they were currently getting because they could not locate any type of sensor in the process without disrupting the process. The result was a "best guess" uniformity requirement of +/5 deg. F, based on experience with the materials. The large size (24" x 72") of the old equipment promoted "batching" in the work cell and increased Work In Process (WIP) as well as scrap. The new desired dimension for the equipment footprint was 24" x 36" overall. Another major concern for the Operations manager was safety. The old equipment presented an operator risk of exposure to high temperatures.

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Single Iteration Solution:

To meet the temperature uniformity specification requires a complete understanding of the system including mechanical design, environmental conditions and measurement/validation techniques employed.

Due to the perceived importance of the temperature uniformity requirement of +/- 5 deg. F, Single Iteration first constructed a thermal model to establish the actual temperature range required to achieve the desired part temperatures based on material properties. This model revealed a uniformity of +/- 10 deg. F to be the correct process value. This uniformity, the large surface area and the desire to accomplish one-piece flow instead of batching resulted in the selection of a multi-zone control approach as the best cost solution. Analysis determined a 6-zone control would provide optimal flexibility along with the capability for automatic verification of part quality and preventative maintenance. On each process cycle, key parameters from each zone could be compared against a known good profile. Deviations were locally indicated to the operator for immediate attention. In addition, through up-load transfer of parametric process data from each zone to a remote computer, statistical process variation over time could be monitored such that trend deviations could be identified and corrected before bad parts began to be produced. This interface also allowed trouble reports to be automatically issued to service personnel such that the equipment could be serviced as scheduled maintenance rather than waiting for the operator to detect bad parts. Once the temperature uniformity was addressed and effective statistical process control limits

were established, reduction of the throughput time was addressed. This was achieved through the addition of active cooling which reduced the cycle time from 30 minutes to 15.

Safety was addressed early and throughout the equipment improvement process. Dramatic reduction in operator risk of injury was realized through the addition of temperature-based interlocks that prevented access to working surfaces until temperatures were within touch-safe limits.