Automatic Process Control of Investment Casting
It is easy to describe automatic process control of investment casting. Charge the furnace, heat the charge uniformly to the desired temperature, then cast. The resulting casting cycle time would be minimized, which would maximize productivity; temperatures would always be the same, which would maximize quality.
Unfortunately, the second step – heat the charge uniformly to the desired temperature – presents serious problems. The problems are different but no less serious depending on the technique chosen for temperature measurement. Immersion thermocouples can only make a very limited number of measurements per melt cycle. Conventional pyrometers are inaccurate and have poor reproducibility. Consequently, neither thermocouples nor conventional pyrometers are suited for control. Fortunately, third-generation pyrometers – Spectropyrometers – can make thousands of fast, accurate temperature measurements during the entire cycle, and many foundries use them successfully to automate the investment casting process.