Improve CNC Productivity by Addressing Three Production Issues

Production from a CNC machine involves two general tasks: making setups and completing production runs. I define CNC machine setup time as the total time a machine is down between production runs. This includes all machine-readying tasks as well as running the first acceptable workpiece. I define production runtime as the time it takes to complete the balance of workpieces in the lot. By these definitions, CNC machines that have work are either in setup or running production — there is nothing else.

The two most important factors contributing to this balance are lot size and program execution time. Consider the two extremes. At one end of the spectrum, there are one-piece jobs. By my definition, this kind of job will only require setup, since running a passable workpiece is part of setup. At the other end, there are machines dedicated to running one component — day in and day out. Once the setup is made, the machine will remain in production indefinitely. Again, these are the extremes. Most jobs that run on CNC machines fall somewhere in the middle, where both a setup and a production run are required.

As for program execution time, the longer a program takes to execute, the longer the production run will be for a given number of workpieces. To improve a CNC machine’s productivity, prioritize improvements based on this balance. More on why a bit later.

Look for downtime

Each time you walk the shop floor, determine the percentage of CNC machines that are not in cycle. In my experience for the companies I have visited, it is rare to see all CNC machines in cycle.

Do not be too quick to disregard what might seem to be logical or acceptable reasons why machines are down. Again, setup time is the total downtime between production runs and production run time is the total time to run out the job. So, all downtime is part of setup or production runtime.

A machine down for setup may be unattended because the setup person is busy doing something else — possibly attending another machine or gathering components needed for the setup. Or the setup person may be waiting for an inspector in the quality control department to complete a first workpiece inspection.

A machine in production may be idle after completing a cycle while its operator is attending to another machine — possibly loading a part, changing an insert or performing a sampling inspection. Or the operator may have left the machine to collect needed items, like hand tools, inserts or gauges.

While these reasons for downtime may at first glance seem to be acceptable, they all waste time — time that should be targeted for reduction or elimination. In my experience, reducing downtime usually provides the largest potential for CNC machine productivity improvement.

Look for often-repeated tasks

CNC people perform countless tasks during the production cycle. The more a task is repeated, the easier it is to justify improving it, and the bigger its impact on production time. With smaller lot sizes, and especially with shorter program execution times, the most repeated tasks will be setup related. For example, production runtime for a job that takes one hour to set up will be less than 10 minutes for a five-part job having a 60-second program execution time.

If this kind of job is common in your company, things done to improve production running tasks will provide only a small benefit. Concentrate first and foremost on improving setup-related tasks. If jobs are often repeated, consider the entire setup as the repeated task. If not, focus first on those tasks that must be done in every setup.

Conversely, if you determine that the most production time is spent running production (larger lots and/or longer program execution times), focus first on repeated production running tasks.

Once you have identified a task to be improved, there are two ways to improve it; make it easier to perform the task (simple tasks can be performed faster than complex tasks) or provide training to ensure that CNC people can more efficiently perform the more complex task.

Look for confused or under-skilled people

Confused people take excessive time to complete tasks — or worse — they make mistakes. This makes them easy to spot. Duplicated effort, scrapped workpieces and crashed machines are obvious symptoms that indicate your CNC people are not up to the tasks you have assigned them.

While entry-level CNC people are most prone to these issues, even experienced people may get confused when assigned new tasks. Better explanations — possible through improved documentation — may be all that is required for experienced people.

While good documentation is obviously important to newcomers, no amount of information will overcome their basic lack of understanding. Every task you assign entry-level people must be appropriate to their skill level. If skill level is too low, either raise it through training or simplify the task so people with lower skill levels can perform it.