A Waste of Time
Here are five productivity killers to look for the next time you walk through your manufacturing shop.
Any time I am invited to tour a manufacturing facility, I go on high alert. I look for areas of the shop’s operation that could use some help, and I can usually spot a few. Surprisingly, I often find that many different companies seem to be hampered by some of the same issues related to wasted productivity.
Here are five common productivity killers you should look for the next time you walk through your shop:
1. People squaring vises and other workholding devices. Although any workholding device used on a machining center must be squared with the machine’s table, there are ways to keep a setup person from having to tediously perform this task every time a device is mounted on the table. Look into pinning or keying devices right to the table, or consider using a subplate to which workholding devices can be mounted repeatedly and accurately. In similar fashion, if a qualified workholding device is repeatedly removed and replaced, be sure to include program zero assignment values (fixture offsets) in G10 commands.
2. Turning center spindles repeatedly accelerating and decelerating. When you walk by a turning center, stop and listen for a cycle or two. Do you hear the spindle slowing down as the turret retracts for a tool change? Does it speed up again when the next tool approaches?
Such repeated acceleration and deceleration of the spindle at turret indexes should be taken as a signal that constant surface speed is not being efficiently programmed. The programmer is leaving the machine in constant surface speed mode (G96) during turret indexes. This results in wasted time, because it usually takes longer for the spindle to change speeds than it does
to rapid to or from the turret index position. It also results in wasted electricity, because
electricity is expended even during spindle slowdowns, as well as undue wear and tear on the spindle drive system.
Have your programmer change the program so that during each tool’s retraction to the toolchange position, the machine switches to rpm mode (G97) and the speed needed at the next tool’s approach position is programmed.
3. Idle machines. How many CNC machines to do you see sitting idle when you walk through your shop? While some idleness—possibly during setup—may be acceptable, specifically look for times when there’s no one around. In many shops I visit, setup people and operators are kept so busy that they cannot keep up with the machines they run. In extreme cases, half the machines regularly sit idle. (In these cases, I often wonder if the company could actually get by with just half the machines it owns.)
At the very least, determine the reasons why machines are sitting idle and question the acceptability of having them do so. Consider focusing more on machine utilization than personnel utilization.
4. People working hard but not necessarily working smart. Here’s an example of this that I came across during a lengthy production run: The cycle ends. The operator opens the door and removes the completed workpiece. He brings it to the bench, cleans it, deburs it, measures it, reports the measured finding to the SPC system and makes a sizing adjustment. He then picks up the next piece of raw material. It’s grimy. He cleans it and removes a burr that will affect workpiece loading. He then places it in the workholding device, closes the door, and starts the next cycle.
What’s wrong with this picture? There are many things, of course, that the operator could be doing while the machine is in-cycle in order to get ready for the next cycle and to minimize the number of things that must be done while the machine is down between cycles. I’ve heard this referred to as staging. Figure out what can be staged for upcoming work, and be sure operators know as well. Similarly, figure out what the operator (or someone else) could be doing to get ready for an upcoming job.
5. People are not where they are supposed to be. As you walk the shop, look for people who are not where they belong, meaning they are not operating the machines they are supposed to be operating. It’s likely that they’ve had to walk away from their machines in order to get something—a hand tool, a gage, an insert. While certain items obviously will have to be gathered before a setup can be made or a production run completed, be sure that shop workers are consolidating their trips to minimize the number of times they must leave a machine. Your goal should be to keep setup people at their machines for the entire setup and operators for the entire production run. If all items needed to complete a setup or production run can be gathered once (and before the job comes up) you can eliminate a lot of downtime in your shop.
Identifying wasted productivity can be as easy as taking a stroll through the manufacturing facility and observing what the people and machines in it are doing—or not doing. If you look for common productivity killers such as those described here, you can come up with solutions for eliminating the waste.
Take a closer look at these reference position commands.
Any time saved by skipping preparation for programming can be easily lost when the program makes it to the machine. Follow these steps to ensure success.
Many people determine cycle time by measuring cycle start to cycle start time. As the operator presses the cycle start button, he or she starts the stopwatch.