Stop employing these four common CNC shop practices to make better use of employee and machining time.
While visiting CNC-using companies, I often witness practices that negatively impact productivity. I find it troubling that these practices are so common, despite the fact that they are simple to identify, diagnose and correct. Here are four of the most common issues:
Making CNC operators share needed items. One company that I recently visited has a machining department that consists of six CNC machining centers spaced about 30 feet apart from each other. The machines use magnetic tables to clamp workpieces. It is imperative that these tables, and anything clamped on them, be perfectly flat and free of burrs. To this end, CNC operators use a relatively inexpensive circular sharpening stone to remove any burrs and ensure that the clamping surfaces (both on the workpieces and the magnetic tables) are flat.
The sharpening stone is required every time a workpiece is loaded on a machine, yet the operators were sharing a single stone among all six machines. This meant that before an operator could load a workpiece, he had to find the stone and retrieve it. Each operator usually waited until he needed the stone to find it, and his machine sat idle until the stone was found.
This is but one example of how sharing items can reduce productivity. Others examples of items that workers routinely are required to share include vise handles and other hand tools,
perishable tooling (like inserts), gages, and workholding components. Obviously, productivity suffers if machines sit idle while workers locate needed items. The simple and often inexpensive solution is to purchase multiples of these items and keep them at the machines/locations where they are needed.
Allowing CNC people to wait until they need an item before they retrieve it. Though there are exceptions, CNC people usually have some downtime during which they are not immediately required to do something. A setup person may have all the machines set up and running production. A CNC operator may be running a job that has a lengthy machining cycle; once the workpiece is loaded and the cycle is activated, there is a long period of time during which that operator is not required to do anything.
There are usually many things that could be done during this time to prepare for upcoming jobs, however, such as gathering tooling components, preparing gages, assembling cutting tools and even loading programs using a feature called “background edit.” Do not allow CNC people to wait until it is time to begin a particular operation before performing the related preparation tasks, especially if this means that machines will sit idle while this preparation is being completed.
Making CNC people figure things out for themselves. Many CNC setup people and operators are left on their own to determine how to run their CNCs. While they may have come up with workable methods, and their ingenuity is sometimes admirable, they may not be using your machines as appropriately as is possible. This is especially true if several operators are involved in running a machine, each performing a given task in a different manner.
Use setup and production run documentation to outline general tasks that must be performed. Then, provide more specific documentation (and the related training) to ensure that every worker performs each task in the manner in which you want. This detailed documentation can be kept in a binder close by the machine at which related tasks must be performed.
This means, of course, that you must first know the method(s) that best suit your needs. If you are in doubt, solicit help from machine builders, tooling manufacturers and other related companies. Or bring your CNC people together to discuss and decide which method works best for any given task.
Assuming that parameters set by the machine builder are appropriate for your needs. Parameters control countless CNC functions, and many of them affect the way CNC cycles are run in general. Machine builders tend to set certain parameters assuming worst-case scenarios, but your applications may not fall into this category.
Consider parameters that are related to canned cycles. The FANUC high-speed peck-drilling cycle G73 (used for breaking chips as a hole is machined), for example, uses a parameter to determine how far the drill will retract between pecks. Usually, a value of 0.1 mm or 0.005 inch, depending on your measurement system choice, is appropriate. Yet some machine builders set this parameter to an excessive value, possibly as much as 2.0 mm or 0.1 inch. If the peck depth is set to 0.1 inch (Q word in the canned cycle) and the retract amount is set to 0.1 inch (in the parameter), it will take the machine almost twice as long to drill each hole as it should.
Other examples of parameters that machine builders sometimes set to worst-case values include the clearance amount for a G83 deep-hole peck-drilling cycle, and the retract amount for G71 and G72 rough-turning in multiple repetitive cycles on a turning center. Truly, any time you see a noticeable pause or excessive non-cutting time, take it as a signal that a parameter may be inappropriately set.
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