Share

Temperature Control in a Machine Shop

We looked at humidity and the inconsistencies it presents in our last post. Humidity has a close relationship to temperature since relative humidity is calculated based on temperature. Temperature control in a machine shop has its own set of problems. Due to varied rates of thermal expansion for different metals, that control can become quite complex.

Machine Temperature Factors


Motors on a CNC machine generate heat and will increase during the day as motors heat up through extended use. Such motors include the servo motor, lubrication motors, spindle motors, and hydraulic motors.

The most heat, and the most cause for concern, is the point of contact between the cutting tool and the workpiece. Friction, chaff, and thermal energy transfer all contribute to the highest temperature rise in the smallest space. The use of coolants and lubrication is necessary for most high-performance CNC operations.
Cutting tools and spindles are designed with thermal control in mind. Speed of cut and raw material feed is also factored in to provide desired precision with the least temperature variation.

Most material specifications are based on a 68°F (20°C) temperature. Metals expand at a different rate with a temperature rise. Steel expands 6 microinches for every 1°F rise in temperature. Aluminum is 13 microinches in the same temperature difference. With higher demand for tolerances as tight as 0.0005 this expansion can take a part out of tolerance. Further, should the tool, the clamps, and the raw material all be made of different metals, each will expand at a different rate.

Ambient Temperature Factors


Temperature is controlled fairly well to reduce friction, raw material expansion, and sparking/burning of the surface caused by high-speed cutting in the quality CNC machines on the market today. Ambient temperatures around the machine, however, can affect the production outcome as well.
Ambient temperature in many countries, like Canada, changes dramatically throughout the year. Changes in temperature throughout the day should also be addressed to prevent tool warp and raw material expansion. Consider the change inside a shop from a morning temperature of 15°C to 35°C in the afternoon. The tool, itself, may change shape from continued use throughout the day in a high-speed application. Add to that a fluctuation in ambient temperature and even more variability will occur. Quality control is always needed to make adjustments as required. And that may take several measures.

Ambient temperature may also need to be addressed in the micro-climate immediately around your CNC machine. Is there a fan blowing cold air? Is there a window allowing solar heat to hit part of the machine? Or, even a close high-powered lighting fixture? These factors will alter the immediate ambient control around a machine that may need addressing beyond the overall air conditioning or other climate control measures in place for the shop floor.
Cold temperatures, too, can affect performance just as much as high temperatures. Aluminum, for example, will become more rigid in low-temperature environments that will change its reaction to contact with the cutting tool.

Temperature Control


These factors all need to be addressed with one or more approaches to temperature control in a machine shop. General ambient control with a quality HVAC system will provide respite for many potential temperature fluctuations. Unique micro-climates at each machine may also need to be addressed.
CNC machines build up heat in several ways. Consider these factors at each machine.

  1.  Check the specifications of the electric motor with a new CNC machine for heat exchange.
  2.  Consider any additional heat generation to your CNC operation with added hardware, such as a hydraulic arm for loading raw material.
  3.  Consider machine placement proximity to windows or vents.
  4.  The sheer size of the machine and its intended raw material stock will see more variation in heat expansion due to sheer mass.
 

Other factors include tools. Purchase quality tools designed to withstand high temperatures. Design toolpaths with feed and speed considerations to reduce friction and chaff impediment. Also, consider the different thermal expansion factors of the tool and the raw material. Practices like soaking material before it is tooled can facilitate a consistent raw material temperature. Used in conjunction with coolants and smart toolpath design good temperature control can be achieved to prevent warping or expansion.

Further control can take the form of technology like a robotic eye sending immediate feedback to the controller as it watches the toolpath. Adjustments are made to speed, depth of cut, and more based on this accurate feedback. On larger machines, strategically placed temperature sensors can monitor raw material temperature and work within set algorithms to modify cutting paths by feeding data back to the controller. This method currently only measures ambient temperature rise and not peak temperature due to mechanical reactivity.

Regular gauging of equipment and maintenance of fans and filters are important factors in temperature control. Be sure this forms a regular part of your shop routine.

Application
The great number of variables affecting temperature control in a machine shop make each shop, and each machine unique. From geographic location to the size of your CNC machine, and from raw material stock to the amount of direct sunlight bearing down, all affect temperature before you even begin to look at the cutting zone where most effort is concentrated. Adding temperature control in a machine shop to one of your maintenance and design considerations can make a difference in consistent, accurate workmanship.

You may also like

cnc precision machine shop lathe milling