Statistical Process Tools

Middlesex provides automated test and manufacturing equipment used for the Statistical Process Control of the manufacturing process.  Our equipment is used in a variety of industry applications such as thermal controls, pressure transducers, bi-metal forming, and environment controlled test and treatment chambers. 

Statistical Process Control of Bimetal Disk Manufacturing

Middlesex SDC (Statistical Disk Control) and DFOC (Disk Forming Offset Controller) equipment is used to measure and control the manufacturing process for bimetal snap action disks used by the thermal controls industry.  The SDC machine is designed for in-process control of bimetal forming equipment.  It accepts a 30 piece sample of formed disks, and measures the top and bottom snap temperature of each disk in order to predict lot yield and compute statistics that may be used to maintain control of forming presses.  With the DFOC option, the SDC results are applied to a mathematical model of the forming process, to directly compute the needed changes to press parameters in order to return the forming press to the desired nominal setting.  Optional stepper motors may be employed to fully automate this feedback.





100% sorting of Bimetal Disks

The Middlesex 100DC line is used to 100% sort formed bimetal disks.  An automated chain carries disks through a sequence of temperature controlled baths (four to seven baths, depending on the model), where each disk is optically scanned for snap orientation, so they may be automatically sorted into one of several baskets at the end of the machine.  Depending on temperature range, models are available using either air or a variety of heat transfer fluids.





Thermal switch testing

Once bimetal disks are assembled into thermostat switches, they may be electrically tested in a variety of temperature controlled environments.  Air baths may be employed to ramp up and down in temperature, recording a snap temperature for each device.  Lot statistics are computed to predict lot yield, or individual devices may be sorted based on acceptance criteria.  A creep option is also available to measure the quality of the switch opening and closing, under high voltage, in order to sort out devices whose contacts may be creeping or bouncing on open or close.  Acceptable creep timers may be programmed according to device specifications.
If exact transition temperatures for each device are not needed, a sorting system may be used instead where a chain advances the devices through a sequence of temperature controlled fluid or air baths.  Devices are then sorted according to temperatures into a number of categories depending on user requirements.




Thermal Switch Calibration

Thermostat switches needing calibration may be calibrated with the Middlesex temperature controlled calibrators.  Devices are soaked in a temperature controlled bath (air or fluid, depending on requirement), where they are calibrated with a computer controlled motor driving a screwdriver or other calibration tool.  Devices are quickly cooled to snap them back, and then final inspected in a sequence of sorting baths, similar to the thermal switch sorting equipment.  Devices may be sorted into one of several categories depending on user requirements.