As machining has evolved, toolholders have advanced to include rigid, secure systems with anti-pullout protection. These advanced systems are needed to take on difficult-to-machine materials, such as titanium and heat-resistant superalloys (HRSA), and accommodate ambitious removal rates and long tool overhangs. Think of them as insurance against tool pullout and breakage—a situation nobody wants.
When taking a holistic view of the manufacturing process, the material machined is just one small variable, according to Steve Boss, product manager for Horn USA Inc. (Franklin, TN). “You can machine an aerospace part made of titanium and not experience the pressures that will cause the tool to pull out, but everyone wants to make parts faster, so it is the manufacturing process that has changed and [required] toolholders with better security and higher clamping forces,” he said.
As cutting tools have advanced, machine speeds have increased and toolpath strategies have become more aggressive, so using the same amount of gripping torque to secure a tool in place is no longer enough to keep it from moving in certain environments, according to Drew Strauchen, vice president of business development and marketing for Haimer USA LLC (Villa Park, IL).
Every toolholder, brand or system does not necessarily offer an anti-pullout solution. “Gripping torque is often the de facto standard for how toolholder manufacturers quantify tool security,” said Strauchen. “It has been proven that having just friction-fit by itself doesn’t guarantee that pullout will not occur. The way to guarantee pullout will not occur is with a system that utilizes a friction clamping system and a form fit.”
In modern machining environments, toolholders must provide strong gripping force, high precision and vibration control. “In most instances, toolholder systems that function using heat or hydraulics are used, but even these systems run the risk of cutting tools pulling out of the holders,” said David McHenry, engineering and technical manager for Rego-Fix Tool Corp. (Whitestown, IN). “While mechanical toolholding systems provide incredible holding power, tooling manufacturers continue to develop systems that offer even more security against cutter pullout.”
According to Boss, there are four quadrants of machining: the machine tool and/or controller speed; the software that creates the toolpath; the toolholder itself; and the cutting tool. These quadrants work together to make machining better, however, one quadrant is always advancing faster than the others.
“The machine tools are getting better and faster and the controllers can keep up with higher feed rates and more lines, allowing for some of these programs to be lengthy,” added Boss. “The controller needs to be fast enough and look ahead to process these points without disruption of feed rates. This has created a new term called ‘high-dynamic machining,’ a high-feed scenario where a solid end mill and full flute length of the tool are utilized.
“With high-dynamic machining, large depths of cut are made with a small radial cut using a high helix end mill,” explained Horn USA’s Boss. “The long length of cut with a high helix is pulling the tool into the workpiece and out of the holder—the forces are extreme, which is why we at Horn USA think a mechanical toolholding system is the direction the industry needs to go in.”
Anti-pullout holders are very common in aerospace applications. “Aluminum and titanium HRSAs are machined with high cutting speeds and forces,” said Boss. “We are at a point where we have to ensure the cutting tool is secure and cannot be pulled or slip out of the holder and at the same time provide dampening characteristics. With shrink systems, the cutting forces and frequencies will be taken out on the cutting tool, which is why a mechanical toolholding system is optimal [naturally dampening properties]. Due to aerospace requirements, there are no fixes [possible] on the part if a tool breaks.”
Anti-pullout toolholders are often utilized in die and mold applications, where Monoblock machining is often performed. “If you are a die/mold builder and your end mill pulls out, the path changes, or the tool crashes, you can repair or rework the die. Repairing or reworking the die adds additional costs and long term it isn’t the correct approach, but it can be saved, unlike an aerospace part,” said Boss.
According to Dino Fracassi, channel sales manager for Arch Global Precision (Livonia, MI), a consolidated precision cutting tool company, custom toolholders are often used in aerospace and automotive applications, and by high-volume manufacturers, such as OEMs and Tier 1 Companies, where custom tools and toolholders are highly valued. Arch Global Precision’s engineering solutions group specializes in custom toolholders and workholding.
“Many metalworking applications on the high production side are using volume tools, so it justifies making a specific custom tool with specific geometries for these types of applications,” said Fracassi. “We do this by looking at all the fundamentals of the application, including toolholders. Often, custom toolholders and cutting tools reduce scrap rates, increase throughput and improve quality.
“Historically a mechanical system has been the best avenue to keep the tool from coming out,” Fracassi continued. “The evolving technology to better hold an end mill in a shrink-fit application with a mechanical connection will start to take over a portion of the market.”
Typically, anti-pullout toolholders are more expensive than standard toolholders, but if a standard toolholder is used and a tool pulls out of it and breaks, the cost of scrapping a part must be considered.
“If a tool breaks in a roughing application, it can destroy the part it is machining,” said Strauchen. “For example, take an aerospace application where a block of titanium is being machined, and it can cost $10,000–$100,000. An average toolholder may be $250, and an anti-pullout toolholder may be $300, so the $50 cost is negligible. Customers often look at a toolholder as a consumable, but it really is not—the toolholder should be viewed as a long-term capital investment.”
According to Boss, when looking at the history of toolholders, the chuck and holder are a standard product and the ultra-perishable product is the cutting tool. With some of our competitor’s anti-pullout solutions, they require something to been ground onto the cutting tool shank which requires additional cost to the cutting tool. “Horn USA’s Centro| P WD Anti-Pullout System is an annual purchase to make versus adding approximately $40 per end mill every time a tool must be replaced—and some customers buy thousands of end mills.”
Productivity also helps justify the cost of anti-pullout toolholders. “When an end mill breaks during machining, the customer often blames the cutting tool,” said Strauchen. “They don’t know the end mill moved a millimeter—and if the end mill breaks, it is unlikely they will notice pullout after the fact.”
In this scenario, a shop may change the end mill or they will slow the cutter down, which sacrifices productivity. Also, a shop may decide to use a sidelock holder, which incorporates a flat in the side of the tool. The tool goes into a holder and a pin holds it in place.
“The problem with the sidelock holder is it does not guarantee pullout will not occur,” said Strauchen. “Sidelock holders are generally not very accurate and have poor accuracy and balance properties, so the customer must slow the tool down in this holder as well.”
According to Strauchen, this is how Haimer’s SafeLock came about. “Haimer had a large aircraft customer that was using a sidelock holder due to pullout issues. They knew they were sacrificing metal removal rates, but could not find another solution to guarantee tool security. So, they asked us to come up with a solution and SafeLock was developed.” SafeLock provides the pull-out protection of sidelock chucks, without sacrificing runout accuracy or balance. The result is greater machining efficiency and longer tool life, according to Strauchen.
Many cutting tool manufacturers offer tools with advanced substrates, geometries and coatings, but despite these technologies, at the end of the day, customers are still putting 100-year-old technology on the non-cutting end of their tools, he said.
“Putting the SafeLock configuration on the back of their tools really increases cutting tool performance,” said Strauchen. “This is where we see SafeLock going in the next 10 years—it will not just be a solution for aerospace companies, but will become an upgrade to the old Weldon side lock.”
SafeLock technology is being integrated into more toolholders from Haimer’s licensed partners. “The range of toolholder types that SafeLock can be utilized in—shrink-fit, collet and hydraulics—is growing,” said Strauchen.
Utilizing the Weldon flat system is another alternative, according to Boss. He noted that Horn USA partnered with Fahrion (Kaisersbach, Germany) to distribute Fahrion toolholders in the US. Fahrion’s Centro|P.WD wedge collet is a high accuracy ER collet-based toolholding system. WD refers to the collet with anti-pullout feature, which uses a Weldon flat on the shank of the cutting tool.
“This system is guaranteed at 5 microns—a very accurate system when compared to a side lock system, which could have as much as 1 or 2 thousandths of runout,” said Boss. “This system started out a few years ago, and we have gone through minor adjustments. In a mechanical situation it’s about how accurate can you be at the point of cut with your tool at a certain reach. With this system, we are achieving the [required] accuracies while providing anti-pull out and dampening effects.”
Another improvement to the Weldon flat is Rego-Fix’s secuRgrip system, which uses a threaded insert or key that eliminates the need to alter cutters. “The simple and effective design is part of our well-established powRgrip mechanical toolholding system and one that allows the use of any off-the-shelf tool as long as it has a standard Weldon flat on its shank,” said McHenry. “The secuRgrip further enhances the holding capability of powRgrip systems.”
The secuRgrip holders accommodate cutter diameters from 0.472″ up to 1.000″ (12 mm up to 25.4 mm). And with holder body tensile strengths higher than those of the cutting tools being held, the secuRgrip holders will withstand cutting forces that could break the cutters before ever damaging the toolholder itself.
“As machine tool spindle speeds and feed rates continue to increase, the more critical a toolholder’s vibration dampening capabilities become,” said McHenry. “The better a toolholder controls or even eliminates vibration, the tighter its TIR. The tighter a holder’s TIR, the more it helps increase tool life as well as improve part accuracies and surface finishes.”
There are no tricks when using anti-pullout toolholders, according to Strauchen, but one important tip for shops experiencing pullout is to define where it occurs.
“When looking at customer buying patterns, you can see they still use side lock holders, which is a good indicator that they are roughing and at some point were likely experiencing tool pullout,” said Strauchen. “What they don’t know is they are sacrificing productivity and accuracy when they are using these types of holders. Some people think that when roughing accuracy is not needed, but the accuracy doesn’t only affect the part—having better run out accuracy improves tool life as well.”
Another tip for customers is to contact the toolholder manufacturer if they are having problems with the toolholder. “It’s important to follow the manufacturer’s suggestions,” said Boss. “If you have challenges go back to manufacturer and ask them for a recommendation.”
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