Companies go to great lengths to account for time, and this means tracking events that occur in the manufacturing environment. This is the only way to determine how well your company is doing: comparing current events to what has happened in the past or comparing these events to a target or goal. And of course, if you intend to implement any improvements, you need a way to gage success once you've done so.
Be careful with the time-accounting system that is applied to your CNC environment. The more elaborate the system, the more likely it is that mistakes will be made, that people will misinterpret the results or that results will be misapplied, adversely affecting your company's output.
I've been in some companies that focus more on time accounting than making the best use of it. I've seen CNC operators spending a large percentage of the day accounting for their time. I've seen 20-minute discussions (arguments) about how time should be logged for a particular task. I've seen machines sit idle while setup people and operators wait for time-accounting log sheets. I've even seen time-accounting systems that are so complicated that new hires must spend hours (or days) in training to learn them. And, if mistakes are made in time accounting, the resulting numbers will be useless. They will be misleading, possibly causing inappropriate reactions. While time accounting is important, it should have a minimal impact on your company's productivity. If your time-accounting system is not completely transparent to productivity, you should re-evaluate it.
While my method may be considered oversimplified, it places productivity first. It is best applied when attempting to gage the productivity of CNC machine tools. With this method, there are only two activities occurring in the CNC environment: Machines are either in setup or they're in production.
Setup includes any task that occurs while the machine is down between production runs, while production includes any task that occurs during a production run. Unless machines are sitting idle because of a lack of work, this accounts for everything that occurs on a CNC machine tool. Tasks that occur during setup include removal of the previous workholding device and cutting tools; mounting/adjusting the new workholding device; assembly; placement; measurement and offset entry for cutting tools; and the loading of the CNC program. Less obvious tasks include gathering components needed for the setup, verifying the CNC program and getting the first workpiece to pass inspection. If a task adds to the length of time a machine is down between production runs, it is a setup-related task.
Tasks that occur during a production run include workpiece loading, cycle activation and workpiece unloading. Less obvious tasks include sizing adjustments completed with offsets to hold size, dull tool replacement and trial machining to ensure replaced tools cut properly. Again, if the task adds to the length of time it takes to complete a production run, it is a production-related task.
Some tasks are physical activities, and the time it takes to complete them is predictable. Removing a vise from a machining center or placing a tool in an ATC magazine are tasks that won't vary much from one time to the next. But other tasks will vary dramatically. It can be difficult to predict, for instance, how long it will take to verify a program or ensure that a workpiece passes inspection.
However, there may be reasons for your time-accounting system other than gaging the productivity of your machines. My oversimplification probably doesn't take into consideration the goals you are trying to achieve. But remember that in value-added terms, your company will only make money when value-added tasks (tasks that further the completion of a workpiece or product) are performed. All other tasks, including any tasks related to time accounting, are necessary-support tasks. While such tasks are important, they do not bring in revenue. Instead, just the opposite is true: Your company has to pay to complete necessary-support tasks.
Unfortunately, many time-accounting tasks (which, again, are necessary-support tasks) must be completed by the people who are responsible for performing value-added tasks-your CNC operators. Many companies don't reach full productivity potential because of the method by which they attempt to measure the current productivity level. The more potential value-added time your people are spending with the time-accounting system, the more likely it is your company is one of them.