Avoiding excessive cutting tool wear

The pressure to decrease costs and drive up profitability means getting every ounce of efficiency from machine tools and cutting tools. To this end, shops constantly strive to reduce cycle times and extend tool life. However, while pursuing these goals, it is easy to push tools past their useful life, allowing excessive wear and its corresponding problems to occur.

Obviously, the goal is to apply a tool as many times as possible before discarding, which means resharpening it as many times as possible. When tool wear is excessive, the tool grinder must remove a large amount of material to renew the cutting edge. This shortens overall tool life and increases the reconditioning cost by increasing the time needed to renew the cutting edge.

Courtesy of All images: C. Tate

Josh Yeo, a master tool grinder at toolmaker G.W. Schultz Tool, understands that a machine shop’s goal is to apply a tool as many times as possible before discarding, which means resharpening it as many times as possible

Excessive wear also adversely affects tool performance, changing the machining conditions and dynamics. I encountered a situation where machinists were told to change tools only after a specific number of parts had been run. As tools wore, they would have to shift the work coordinates to keep the parts in spec.

Once a machinist produced the required number of parts, he inserted a new tool into the machine. However, the first part machined with the new tool was always bad. This is because a dull tool exerts more pressure on the part than a sharp tool. Therefore, the cutting pressure decreased after a tool change so the part did not push away as it did with the dull tool. Less push off, combined with shifted work coordinates, caused the part to be cut undersize.

Excessive wear can also cause catastrophic tool failure, leading to scrapped parts, rework and machine tool damage.

Tool wear is a general term that has numerous classifications. These include flank wear, adhesive wear, abrasive wear, diffusion, fatigue, delamination, microchipping, notching, gross fracture, plastic deformation, cratering and built-up edge. Each classification is a wear mechanism that can act on the tool in various ways and areas.

Determining the correct time to change a tool is a challenge. If you asked older shop guys, they would tell you to rely on sights and sounds to indicate when a tool is starting to wear. I was curious what an expert would say, so I called my friend Tomas Roman at carbide tool manufacturer G.W. Schultz Tool Inc., Tavares, Fla. He agreed that machining condition is probably the single best indicator of tool wear.