Minimizing Tool Maintenance Time

One time-consuming task that often goes overlooked is tool maintenance. Tool maintenance is any task that involves upkeep on cutting tools used in the machining cycle. Insert changes, tool replacements, trial machining after tool replacement, and offset adjustments for tool wear during a tool's life are among the many tasks related to tool maintenance. The larger your lot sizes, the more negative impact tool maintenance can have on your production run, and the more you should seek ways to minimize tool maintenance time.

The ultimate goal would be to move all tool maintenance off-line, meaning the machine is in cycle during every tool maintenance task. But this may not be feasible for all companies. Whether or not your equipment has some of the following features has a major bearing on how close you can come to achieving this goal.

• Tool life management—This feature allows the CNC user to double up on those tools that are most prone to breakdown. So as one tool gets dull, the machine will automatically select a fresh, identical tool and alert the operator.
• In-cycle tool replacement—More and more machines (especially machining centers) are allowing a user to replace cutting tools in the machine's magazine during automatic operation. The machine need not stop for tool replacement.
• Automatic toolchangers on turning centers—Since most turning centers are pitifully short on tool stations, this feature allows the user to double up on cutting tools that are most prone to wear or failure.
• Quick-change tooling on turning centers—This feature minimizes the time it takes to get tools in and out of the turret. While it may not allow all tool maintenance to be done off-line, online maintenance can be dramatically reduced.
• Automatic tool tip probing on turning centers—This device will automatically determine the position of cutting tools. While this is commonly thought of as a setup-related task, tool touch-off probes will also eliminate the tool maintenance time normally required for trial machining.

Unfortunately, completely moving all tool maintenance time off-line may not be feasible, especially for existing CNC machines. However, if you study the amount of time your operators devote to tool maintenance, you may find it easy to justify the purchase of features like those just mentioned.

Even if you cannot move all tool maintenance off-line, there are still things you can do to minimize the amount of online time your operators spend performing tool maintenance. Truly, anything you can do to help them is a step in the right direction. Consider these ideas:

• Make replacement cutting tools and inserts accessible. Be sure your operators have easy access to replacement tools. And if possible, be sure that they gather replacement tools while the machine is in cycle.
• Be sure each machine has its own set of cutting tool replacement hand tools. And place these tools right by each machine for easy access. You might even consider using Velcro to hold each hand tool (Allen wrench, nut driver, and so on) right in the machine, close to the tool for which it's required. It's not a bad idea to color-code hand tools with the station numbers for which they're needed. Be sure to use bright colors so that they're easily spotted when dropped into the chip pan!
• Specify when tool maintenance is required. Though this may not always be possible, too many shops leave it completely to the operator to determine when tools must be replaced. This leads to a great deal of inconsistency. Also, it is not uncommon for operators to simply replace all tools at the beginning of their shifts if they're not sure about the remaining life on the tools. This is one of the best benefits of tool life management systems. These systems take the guesswork out of tool replacement intervals.
• Make it easy for the operator to determine which offset controls each workpiece attribute. Most companies will make the offset number for a tool the same as the tool station number. While this is a good rule of thumb, operators still have to determine which tool has machined each surface before they can adjust the associated offset to deal with tool wear. One excellent method of documenting offset use is to color-code a working copy of the workpiece drawing. Use a different color pen to mark up those surfaces being machined in the cycle. Each color can correspond to the offset number being used to control the tool that is machining the surface.