The larger the lot size, the more likely it is that tools will dull during a production run. And of course, dull tools must be replaced if the production run is to be completed. As with any task related to production runs, you have three alternatives when it comes to improving.
One: Can you eliminate the task all together? That is, can you increase tool life to the point where tools will last for the entire production run? This is unlikely. Assuming you are using an appropriate process with adequate cutting tools and your cutting conditions are correct, tools are currently lasting as long as possible.
Two: Can you move the task off-line? That is, can your operators replace dull tools while the machine is in cycle? This is the topic of last months CNC Tech Talk related to tool life management systems. While it may be possible to move dull tool replacement off-line, it may not be feasible. The cost and/or effort related to doing so is probably not justifiable.
Three: Can you facilitate the task? That is, can you make this task easier for your operators to perform? Doing so may allow them to replace dull tools more quickly and with less effort. If you can't justify what it takes to eliminate the task or move it off-line, you're left only with facilitating the task.
In our situation, the task we will facilitate is online. That is, dull tool replacement will be done while the machine is down (not in cycle). It adds to the length of time it takes to complete the production run. If we can find a way to shorten the time it takes to replace dull tools, we'll in turn reduce the time it takes to complete the production run. This will, of course, reduce cycle time, making the machine more productive.
As with any task you intend to facilitate, begin by watching the people who are performing the task. In this case, it means watching your CNC operators perform dull tool replacement for the various tools they must replace during a production run.
First look at tools needing to be replaced on the most regular basis (probably roughing tools). You should emphasize those tools that are often replaced and used in many jobs. Facilitating the tasks most often completed allows you to reap the largest gains. Also be on the lookout for tools that give the operator unusual and time-consuming problems. And after the physical task of dull tool replacement is completed, for example, must the operator do anything special (like trial machining) to ensure the new tool cuts properly? Truly, anything that occurs while the machine sits idle will be fair game.
What can you do?
While we offer a few suggestions, remember that the only way to come up with the best alternatives is to watch your own people performing this task. And if you've haven't been paying attention to this task, it's likely you can do a lot to help your operators.
Help with physical tool/insert replacement
- Make it easy to locate the tool to be replaced (this may be more of a consideration when buying a new machine and somewhat beyond your control for current machines). Some turning centers, for example, have a simple multi-position switch and pushbutton to allow quick and easy turret indexing. Others require a more time-consuming manual data input (mdi) command to be given in order to manually index the turret. Some machining centers have large tool storage magazines that can only rotate in one direction. It may take several minutes just to bring a dull tool into an accessible position. When purchasing new machines, look for machines that make it easy to access dull tools.
- Keep all hand tools (Allen wrenches, screwdrivers and so forth) readily available. Don't make operators of two or more machines share. Keep them in a convenient location, possibly using Velcro to stick them right next to where they're needed.
- Paint hand tools a bright color. Some of these tools (like Allen wrenches) are very small. If they fall into the chip pan, you want them to stand out, making it easy for the operator to find them.
- Especially for insert replacement, make it as easy as possible to clean the insert seat. If an air hose is used, keep it close to the machine (and make sure the operator is protected from chips that will be blown from the seat during cleaning).
- Keep an ample supply of replacements close. Be sure that operators have the replacement tools readily available. Don't make them walk to the tool crib to get replacements every time a tool is dull. For tools that require sharpening, stock enough of them to get through the entire production run. Don't make operators sharpen tools while the machine is down.
Eliminate trial machining
- Find a way to replace tools accurately. Remember, if the tool cannot be perfectly replaced, trial machining will be required to ensure the tool will cut properly on the next workpiece to be machined. This is especially important when the tool is machining a close tolerance surface.
- Use a tool touch-off probe with turning centers. Though tool touch-off probes are most commonly used during setup to help assign program zero for each tool, they can also help during dull tool replacement. If a tool must machine a close tolerance surface, the tool touch-off probe may eliminate the need for trial machining.
We cannot overstress the importance of watching your people perform dull tool replacement. This is truly the only way to spot troublesome problems and come up with potential solutions. In doing this, it is likely you'll find some very basic problems that provide a great potential for improvement.