Tool inspection is not just for checking a cutter or holder before you machine with it. Companies are discovering that thorough tool inspection by scanning helps them prevent scrap by avoiding use of inaccurate tools.
Every company has trouble with tool accuracy--they just may not be aware of it. Every company using something other than a cheap end mill is affected by tool inaccuracy, and is losing money because of it. You cannot assume that the toolholders you use are always accurate. And you cannot expect a machine tool to compensate for tooling deficiencies.
Larger companies may consider dedicating an inspection machine to inspect incoming tools before they are put into the tool crib. Smaller companies using tools with a critical geometry can preset them and inspect critical dimensions to make sure the tool fits their criteria: such as runout, diameter, radii, angles, chamfer, and--if required--the whole geometry.
In many cases, an optical comparator will not be able to tell the whole story, because comparators are 2-D devices and tools are 3-D objects. But if you can scan the complete tool assembly (cutting tool and holder), and provide a digital overlay of the inspected tool, deviations from the tolerance become clear. Even inspection for runout alone can yield better quality and longer tool life. If a tool has excessive runout, check tool and holder individually, and also as an assembly, to determine whether the holder or the tool is bad.
Is this too much attention to a tool? Not at all. Ensuring that the tool meets tolerances before accepting it from a vendor saves time, and prevents the tool's use in a machine where it would produce only unacceptable parts. Scanning tools is a process that requires only a few minutes, but yields information that directly and immediately impacts production quality.
Checking parts after you machine them may prevent the delivery of bad parts to your customers, but you have already spent time to manufacture those unacceptable parts. Some features on a part may not even be reachable with a gage after machining. Tool inspection can help prevent this loss of production, and the more complex the tool, the more vital is inspection to manufacturing success.
With the right equipment you should be able to perform automatic, user-independent cutting tool inspection. Contour, step length, diameters, radii, ball noses, should be compared to your tolerance requirements. In an automatic cycle, the machine can tell you if the tool you have meets each of those requirements--from ball-nose end mills to spark plug tools in an automatic application. In a cycle requiring from less than 1 min to 3 1/2 min, you can inspect features you may not even have considered inspecting previously.
There is a major difference between a basic tool presetter and vision-based cutting tool inspection machines that inspect each feature on a cutting tool, then compare the results to your intended tolerances. A vision system automatically measures the tool, and the camera focuses on the cutting tool angles, chamfer lengths, critical intersection points, diameter, step lengths, and other features as the tool rotates. The output is in nominal values, tolerance values, actual measurements, and more. A vision system will allow you to actually see the contour that will produce the part, and compare that to your tool-tolerance values. It can also tell you if the profile of the tool you are inspecting will deliver the results you expect.
As tools become increasingly complex--some having different flute geometries within the same tool--and as cutting tools are designed to accomplish more in a single pass, thorough inspection of those tools becomes an even more valuable tool for assuring production quality.
This article was first published in the March 2005 edition of Manufacturing Engineering magazine.