Keep The Machine Doors Closed

Everyone agrees that the job market is crazy. Keeping skilled people in front of machines is the biggest challenge faced by modern machine shops. As a result, shops are increasingly turning to automation to offset the demand for skilled craftsmen.

Automation can be simple like a bar feeder on a lathe or complex like a fully integrated robot. In other cases, it might be a high-capacity magazine coupled to a horizontal machining center with multiple pallets. In all cases the goal is to keep the machine producing parts with minimal human intervention. Or as we say where I work, “keep the doors closed longer.” Because open machine tool doors let the money out.

When a machine is running unattended a broken or damaged cutting tool can be catastrophic. So, one of the key components to successfully automating a machining operation is implementing tool management. A world class tool management regime not only safeguards the process from broken tools, it also recognizes worn tools and has the ability substitute tools when necessary.

Tool monitoring can take a few forms. Some methods of monitoring are straightforward and cost-effective while others can be very complex and expensive.

For a shop on a budget the simplest way to protect an automated process from broken tools is to use tool life management software that is included in the machine’s control. Modern CNC controls come with onboard tool life management that allows the user to monitor and limit tool cutting times. Users can measure total cut time or, more commonly, the number of parts, and when a limit is reached the machine ceases to use the old tool. Controls also allow the user to designate alternates to be used so that machining operations continue uninterrupted after a tool has reached end of life.

At a previous employer we had machining centers combined in a cell with robotic loaders. Obviously with robotic loading there should be very little human intervention. In this case things did not go well because we had tooling issues, setup issues and quality problems. The machines were set up with one roughing tool and one finish tool and they were only good for 100 parts before they needed to be changed.

Because of the numerous issues. tool changes could cost us four to eight hours of production. Our first step in solving the issues was to load the machine up with eight roughing tools and eight finish tools and utilize the onboard tool management software. Once we reached 100 parts the machine would cease using the current tools and start to use the next set of tools without interruption. We were not only more productive, we bought ourselves time to work on the other problems.

Tool management software is effective, but it will not detect broken tools. In the scenario above there was almost zero chance of breaking a tool so we only used the onboard software. In other cases where there is high risk of tools breaking it is necessary to monitor tools for breakage.

There are a few types of contact devices available for broken tool detection. Whisker sensors are a simple option. These devices have a small wire that is rotated into the tool and the position indicates if the tool is present. Obviously if the tool is broken, the rotating wire travels too far and the machine is signaled. These can be used outside of the machining envelope, so they do not interrupt production and they are often found on the tool changer.

Whisker sensors can easily miss a broken tool if the break is below the point where the whisker sensor contacts the tool. When processes are less stable, and tool breakage is more likely, a different monitoring tool may be needed.

Tool probes or tool setters are the next option. Although they were developed for onboard tool measurement, they are also ideal for monitoring cutting tool condition. These devices are typically found inside the machining envelope and used for measuring and recording tool lengths. Cutting tools are fed into the setter in a controlled manner and the setter triggers the machine to stop. Once stopped the machine will read and record the position of the tool so it can be used later.