With a good application and when properly applied, a tool life management system can dramatically increase the output from a CNC machine tool. But I’ve seen quite a bit of misapplication and confusion when it comes to how and where to use these tools. Although it is a short explanation, this column should help you assess the appropriateness of applying a tool life management system to your applications and get you off on the right foot.
When considering whether this system is right for your applications, remember that the ultimate goal of any tool life management system is to keep all tool maintenance offline. Tool maintenance includes any task done to keep tools cutting on size (measuring workpieces and sizing tools) as well as any task performed when tools get dull (tool/insert replacement, remeasuring program zero, trial machining, and more). By doing tool maintenance offline, I mean the task must be done in conjunction with the production run, while the machine is in cycle.
If this can be achieved, tool maintenance being done during a production run will have no effect on cycle time. We define cycle time as the total time it takes to complete a production run divided by the number of usable parts that have been produced. Think about it: In most applications, tool maintenance can add a lot of time to a production run. Many CNCs (especially turning centers) must be down while dull cutting tools are replaced. If you can keep tool maintenance from affecting production run time, jobs will be completed faster and cycle times will be reduced.
How close you can come to achieving this goal depends on many factors. Unless the tool life management system can be applied to several consecutive jobs, the production run must be long enough to require dull tool replacement. For most companies that have small lots to run, this system may not be advantageous.
Also, to move machine maintenance offline, the machine must be designed in such a way that tools can be safely removed and replaced during tool maintenance while the machine is running. If they cannot, you may only be postponing the inevitable.
Consider, for example, a typical CNC turning center that has a 12-station turret. Perhaps a long-running job requires four tools, so there is ample space in the turret to duplicate the tools that wear out the quickest (such as roughing tools). So you double tool the roughing tools in the turret and program the tool life management system to switch to the new roughing tool when the first one gets dull. All you’re really doing is prolonging the time between tool maintenance. Eventually all tools will be dull, and the machine will have to be down during tool maintenance. Though your operator can probably replace all of the tools at one time more quickly than replacing them one at a time, you’re not moving tool maintenance offline.
When the tool life management system detects one or more dull tools, it will alert the operator. The operator will check to see which tools are dull and will note their related station numbers. At the toolchanger magazine, there will be a special switch. When the switch is placed on “manual,” the machine will not allow a tool change, and it will keep track of the current magazine status. The operator can manually rotate the magazine to remove or replace tools. When finished, the operator will place the switch back to “auto,” and the magazine will rotate to its original position.
As you may have guessed, you probably won’t be able to achieve the goal of moving all tool maintenance offline with your existing equipment. Machine functions that contribute to tool life management may have to be factory installed. However, I’m amazed at the number of companies that have perfect applications for a tool life management system but do not even consider one during the purchase of a new machine. Indeed, incorporating the benefits of moving tool maintenance offline in a machine’s justification may make the difference when it comes to being able to justify a new machine purchase.
Also, machine tool builders are getting very good at helping users move tool maintenance offline. Take advantage of this expertise when you purchase your next machine. At the very least, let the builder help you determine whether or not you have an appropriate application for a tool life management system.