End Mills with gripping surfaces along the shank can prevent tool slippage and improve rigidity for aggressive roughing passes in aluminum machining.
So many of us have lost parts from tools slipping out of their holders. The reassuring whir of chips being made gives way to a screech and a thud, and we jump into damage assessment, hoping that the part is salvageable and knowing that it likely is not. Tool slippage is becoming more and more common as feed rates that were unthinkable ten years ago become commonplace.
Advanced cutting tools like the RobbJack end mill modeled here are capable of removing material at an incredible rate. However, toolholding also has to be up to the task if the user wishes to avoid tool slippage.
Advanced machining technologies are drastically increasing feed rates for manufacturing, and this is especially prevalent in aluminum machining. The combination of more powerful machine tools and more aggressive machining strategies have pushed the material-removal rates towards levels that would have been unthinkable not long ago. Unfortunately, these high rates of material removal can put an enormous strain on the tooling.
Even light metals such as aluminum can cause problems with tooling when machinists run passes removing so much material. At a certain point, the forces required to remove so much material can pull the cutting tool right out of the toolholder. Losing a tool this way can severely damage a part, and replacing the tool can wipe out the time savings from the aggressive machine passes. Fortunately, some cutting tool companies are addressing this problem.
These models illustrate the tapers for RobbJack’s Anti-Pullout shanks. The shanks have rough textures and tapers designed to keep the tool from pulling out, even during highly strenuous operations.
According to Mike MacArthur, Vice President of Engineering for RobbJack, more and more shops are complaining that tools can slip right out of the holder during aggressive machining operations. “Every job shop wants to remove material as quickly and efficiently as possible, especially in competitive industries like aerospace,” he says. “If a shop wants to make chips at the high rates you can achieve today, then it needs to invest in tooling that can withstand the forces generated by these aggressive passes.” To accommodate high feed rates in aluminum machining, RobbJack has standardized its cutting-tool offerings with features that keep its tools from falling out of place with its anti-pullout shanks.
The first step for improving the tools ability to stay in place was to put a focus on the tolerance of the tool’s shaft. “We made a conscious decision to hold every end mill shaft to h4 tolerance,” MacArthur says. For comparison, shrink-fit tools only achieve h6 tolerance. “The tighter fit provides a tighter grip, minimizing the potential for the end mill to slip.”
Here we can see an example cut made with a RobbJack FMHV series of end mill. The company’s tools can remove as much as 75 pounds of aluminum per minute. See more videos at robbjack.com.
Grinding the cutting tools to such a high tolerance is only the first step, however. According to MacArthur, another major advantage is the gripping surface. “Some tool companies polish their tool shanks to make them as smooth as possible,” MacArthur says. “Instead, we actually grind a rough gripping surface into our shanks for improved holding power.”
The gripping surface provides extra friction that helps keep the cutting tool in place. Together with the high tolerance, this provides excellent grip. According to MacArthur, these techniques have improved the grip of RobbJack tools by 70%. This has enabled some customers to achieve full slotting with a 1" tool, ¾" deep at 33,000 rpm and 1,000 ipm without risking tool slippage.
In addition to preventing tool slippage, the rough surface the company grinds into the shank further improves the performance of RobbJack end mills. The increased grip improves the stability and rigidity of the tools, preventing runout and keeping the cutting edges more uniformly engaged in the material. The uniform pressure this places on the cutting edges increases tool life by avoiding pressure spikes that can damage flutes. Plus, avoiding runout enables the user to consistently hold much tighter tolerances.
According to the company, this also reduces the pains that come with changing out tools because the tight grip helps to eliminate variability in the tools’ performance. Even smaller-diameter tools that do not see aggressive roughing operations can benefit from the reduced runout and improved consistency of of the anti-pullout shanks.
The high-performance FMHV end mill is specifically designed for aluminum machining of aerospace parts. It can remove as much as 76 pounds of material per minute, and the Mirror Edge geometry prevents chatter.
This increased precision and tool life complements other features of RobbJack tools, as you can see in the A1-303 and FM-series end mills for machining aluminum. Specifically designed for aerospace applications, these end mills include the anti-pullout shanks that come standard with RobbJack tools, in addition to the Mirror Edge preparation. This feature is designed to eliminate chatter in aluminum machining, an important benefit for aerospace work. These features together, along with the coating, have extended tool life 500% over similar tools and increased the material removal rate to 76 pounds of aluminum per minute. According to RobbJack, this can save a shop over $400,000 per year.
In order to keep up with the advanced machining strategies available today, shops must invest in tooling capable of supporting these strategies, MacArthur says. “Aerospace and automotive manufacturing are competitive industries, and keeping up with the competition means pursuing aggressive material removal rates. In order to capitalize on these techniques, you need an end mill that will stay in the toolholder and keep the chips flying.”
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