Cycle time reduction during tool change
By GV Dasarathi
CNC
Reduce cycle time by controlling what the spindle does at tool change
On a CNC lathe, what you do with the spindle during tool change can make a difference to the cycle time. The spindle takes some time to accelerate to the programmed speed. The larger the lathe, the more time it takes, because of the higher size and inertia of the spindle. A typical machine would take 1 sec. for every 1000 RPM. E.g., 3 secs. to reach 3000 RPM.
You can do one of 3 things:
1. Stop the spindle before moving to the tool change position. Restart it after the tool change.
Result: When the tool approaches the next operation, the machine will wait at the destination position for the spindle to accelerate to its programmed speed. To save time you can program the spindle start during the approach to the operation from the tool change position, but even then the rapid motion will take less time than the spindle acceleration, and the machine will wait. E.g., if you are turning a 50 dia. part at 300 m/min, the spindle accelerates to 1900 RPM each time, taking approx. 2 seconds – for 5 tool changes that’s 10 seconds.
During spindle acceleration the power consumption is momentarily very high (you can see the power meter going beyond 120 %). This increases the power bill, reduces the motor and spindle life.
2. Keep the spindle running in CSS (Constant surface speed) mode, with the same surface speed
Result: The spindle slows down to a very low speed as the tool moves to the tool change position (because the diameter at the tool change position is very large), then speeds up again to a high RPM when the tool approaches the operation area. Almost the same effect as option 1, but slightly better – the spindle starts from some speed instead of from zero. Taking the same example, if the tool change position is at 200 dia., the spindle decelerates to 475 RPM each time and then accelerates to 1900 RPM, taking approx. 1.5 secs.
3. Keep the spindle running with CSS OFF before tool change, switch back to CSS ON after tool change. Change only the mode, not the surface speed.
Result: The spindle is running at the same RPM as when cutting was going on, does not decelerate or accelerate during the motion to and from the tool change position. There is no time lost.
Action point
Option 3 is the best option: Switch to Constant spindle speed mode before tool change, back to CSS mode after tool change
Etc.
Fauja Singh – ‘Turbaned Tornado’
Here’s someone I find very inspiring.
Fauja Singh, born in 1911, migrated from Jalandhar to England about 25 years ago. His first marathon (a 42 km. road run) was in 2000 in London. This was at the age of 89, when he started running to ovecome the death of his wife and son. He stopped running in 2013, at the age of 101, after completing a Hong Kong 10 km. run in 1 hour 32 minutes.
He’s run the marathon 8 times so far. His latest was the Toronto marathon last year, at the age of 100. He took 8 hrs. 25 minutes, and came in last. Kenneth Mungara of Kenya came in first, at just over 2 hrs. – but then he’s 62 years younger than Fauja Singh.
At the age of 100, Fauja Singh broke eight world records for the 100+age group in one day in Toronto, Canada : 100 m., 200m., 400 m., 800 m., 1500 m., 3000 m., 5000 m., 1 mile.
He ran the 100 metres in 23.14 seconds (the average person in his twenties would do it in 12).
In each one he improved upon the previous record in that age division (some events had no previous record holder, as nobody over age 100 had ever attempted to run the distance).
He’s a vegetarian, and the oldest person to be featured in a PETA (People for Ethical Treatment of Animals) campaign. Check out the slogan ‘Sikhs and the city’ on his T-shirt in the pic above. A take off on ‘Sex and the City’, a TV series later made into a movie.
About the marathon, Fauja Singh: “The first 20 miles are not difficult. As for last six miles, I run while talking to God.”
As for me, I say : “The first 3 miles I run with some difficulty. As for last 23 miles, I leave them for God to run”. For some strange reason, I can cycle quite long distances at a stretch, but can’t run even short distances. Must be a different bunch of muscles used in each activity.