What is Dwell Time?
If you’ve seen our recent demos of the API XD Laser and SwivelCheck for Machine Tool Calibration (MTC) on YouTube, then you’ve probably heard us mention dwell time in both of those videos. Dwell Time is a very popular search term because it is actually used in several different fields, including mass transportation, information retrieval, military deployments, and radar technology. But for CNC machine tools, dwell time has a very specific and important definition. So, we’re a deeper look at dwell time for machine tools. What is it? Why is it important? And how is it used for MTC?
Basically, Dwell Time is a G04 command on your CNC. And it is used to specify a number of seconds that a machine’s axis will pause (or dwell) at a given point, while the other functions of the machine (spindles, bores, coolant, etc.) continue to function. Given that any moment of inaction on a tool is lost productivity, most machine shops try to reduce dwell time to the smallest number of seconds possible.
What is the importance of Dwell Time?
Dwell Time can have several uses for a machining process. Hole drilling or counter boring might use a few seconds of dwell time to ensure all of the material that was drilled out has been cleared out of the
newly formed hole. This can actually speed up production later, as less time needs to be spent cleaning or touching up the part before it goes to an assembly. Some operators will also add in a few seconds of dwell time to relieve tool pressure at the bottom of a pocket or to ensure a long, straight cut finishes smoothly.
It’s very important to note that Dwell Time should not be used to compensate for other features of the tool that are falling behind or losing capacity. If you’re having to program in extra Dwell Time to allow for your coolant to fire full blast or for an aging spindle to accelerate to velocity, you’re not just slowing down your production times, you’re flirting with disaster. These kinds of problems only get worse over time and can eventually lead to complete collapse of the tool’s performance. It’s best to repair any issues like this as soon as they appear, instead of trying to program around them.
How is Dwell Time Used in MTC?
The software for most MTC equipment will allow you to quickly and easily program in a few seconds of dwell time at each interval of the machine’s movement throughout your calibration measurement. You can also set the window for how long before the stop point the equipment will start calculating dwell and how much of the time will be used for Auto-Sampling data. And this Dwell Time benefits both the machine and the calibration equipment. The calibration equipment is able to see how accurately and completely the machine settles into its dwell and is able to detect any movements during the stationary period.
This pause also allows the calibration equipment’s internal level and encoders to settle in and take a sampling of the data to ensure the equipment is consistent throughout the starts and stops of these measurements. And it also gives the software an extra beat to record this data before the machine moves onto the next point.
To recap, Dwell Time is a pre-programmed pause of a machine tool’s axis that can help the tool finish clearing out a drilled hole. But it is also used by MTC equipment to verify the absolute accuracy of both the machine tool and the measurement equipment. API’s MTC equipment incorporates Dwell Time into its software programs, and our XD Laser is the only machine calibration laser that can capture all 21 error parameters on a 3-axis tool in one setup. To learn more about XD, SwivelCheck, and Ballbar, or to contract a calibration with our Globally-Local Services team, please visit apimetrology.com and contact us to speak to a Real Metrologist today.
Sources:
https://www.mmsonline.com/columns/are-you-dwelling-to-overcome-machine-problems https://www.cnccookbook.com/g04-gcode-pause-dwell/
http://cnc-programming-by-gord.blogspot.com/2012/07/dwell-g04.html
