completely, it must be replaced. Any tasks related to replacing tools (including tool tear-down, insert replacement, new tool measurement, offset entry and tool replacement in the machine) are tasks performed for tool maintenance purposes.
The larger the production run, the more tool maintenance that must be done, and the more important it should be to you to minimize, if not eliminate, machine downtime for tool maintenance purposes. A good tool life management system along with some special machine features can help you cut tool maintenance time to the minimum.
Unfortunately, most companies don't think about tool maintenance issues when buying new CNC machine tools. Given the large percentage of machine time that can be taken for tool maintenance, this can be a drastic mistake. Why? Consider that tool maintenance should be considered as part of cycle time. A very realistic definition of CNC cycle time is the total time it takes to complete a production run divided by the number of workpieces produced. And tool maintenance tasks will add to the time it takes to complete production runs.
When attempting to reduce tool maintenance time, your ultimate goal will be to move all tasks related to tool maintenance off-line. That is, your people should be performing all tool maintenance tasks while the machine is in cycle. In reality, this goal can be difficult, but not always impossible, to achieve. How close you can come depends upon several factors.
Can you remove or replace tools while the machine is in cycle? Some machining centers are designed to allow this. They have a kind of standby button that the operator can press to inform the machine that they will be manually activating the automatic toolchanger magazine. If an automatic tool change command is given in the program while the toolchanger is still in this "standby" mode, the machine will halt, waiting for the operator to release manual control of the toolchanger. A similar button is commonly equipped on machining centers with automatic pallet changers to allow the operator to alert the machine when a pallet is completely loaded.
This function will allow the operator to replace dull tools while the machine is in cycle. Of course, the task of tool length and radius offset entry must also be done before the tool is required in the program. Note that tool life management systems make this kind of tool duplication and offset entry very easy.
Unfortunately, not all CNC machines allow tools to be removed and replaced while the machine is in cycle. Some machining center machine tool builders, for example, keep the operator from being able to manipulate the toolchanger magazine while the machine is running. Standard turning centers with turrets present even more problems. If you currently have machines with these tool maintenance limitations, you may be forced to wait until your next machine tool purchase to completely move tool maintenance off-line.
For machining centers, look for machines that have the ability to manipulate the toolchanger magazine during cycle. For turning centers, look for machines that have automatic toolchanger devices with quick-change tooling. Of course, you will also need the ability to manipulate the turning center's toolchanger magazine while the machine is in cycle.
If you cannot completely move tool maintenance tasks off-line, make it as easy as possible for the person performing the work. Anything you can do to minimize on-line tool maintenance time also minimizes the time it takes to complete the production run. Simple suggestions include color coding insert changing wrenches with cutting tools to make it easy for operators to select the right tool, keeping extra insert changing tools near the machine (for times when they're dropped and lost), using Velcro to hold insert changing tools close to the machine for easy access, and ensuring that replacement inserts and cutting tools are close by the machine.
Also, some CNCs offer tool life management systems. These systems can truly streamline your ability to minimize on-line tool maintenance tasks. Next month's Tech Talk will address these very helpful systems.