Through-coolant toolholders: efficient, economical

Imagine that this nightmare machining scenario has just hit: Your tool life suddenly shrinks from 100 parts to 10 parts, the surface finish of your workpiece rapidly degenerates and—worst of all—an endmill breaks in the toolholder.

Quick: What do you check first?

According to Drew Strauchen, vice president of marketing and business development for Haimer USA LLC, Villa Park, Ill., machinists often run down five or six rabbit holes and spend a lot of time and money investigating the cause of the problem before they think, ” ‘Wait—how are we delivering coolant here?’ “

“It’s usually one of the last things they check,” he said.

Applying coolant while machining is important for two related reasons: It keeps the cutting tool edge cool and clears chips from the cutting zone.

According to Chelsea, Mich.-based Advanced Industries Inc.’s Chris Beckington, whose company makes KoolBlast toolholders, coolant is especially important when machining with carbide tools. “The thermal stress of heat caused by friction in the cutting zone can wear out the carbide,” he said. “This alternate heating and cooling causes weakness in the tool, so we try to [constantly] keep … coolant on the tool to eliminate the effects of thermal shock.”

There are three basic ways to apply coolant during machining. The most common way is with external nozzles—a process called flood cooling. However, problems often occur with this type of system. For example, copper flood coolant lines are fixed to the machining head so they don’t move. But when machining parts with features such as a shoulder or a ledge, the tool can dip down below that ledge to work at the bottom of a surface, blocking coolant from reaching the cutting zone.

Similarly, flood coolant systems incorporating flexible plastic nozzles often aren’t positioned properly, “because the operator assumed positioning does not matter,” Strauchen said, “or, more likely, something happened during a machining process or a tool change where the nozzles got bumped and are no longer directing coolant anywhere near where they’re supposed to.”

A second method of applying coolant is to run it through the tool itself. This is the most accurate way to direct coolant to the cutting zone, but tools with through-coolant capability are mostly limited to drills, Strauchen said.

“In the majority of cases for endmills, the coolant’s either being fed externally with nozzles or it’s coming through the toolholder,” he said.

Through-coolant toolholders—the third method of coolant delivery—have one or more internal coolant passages. Coolant runs through the spindle, all the way up to the nose of the holder, where it exits two or more ports located close to the shaft of the tool. The toolholders, which are typically modified standards, come with a range of port styles, from simple holes bored with an EDM to elaborate angled passageways running through the chuck.

The KoolBlast Thermalfit through-coolant toolholder from Advanced Industries features D-shaped orifices and the company’s PressureMax design, which together minimize turbulence as coolant contacts the cutting tool. Image courtesy Advanced Industries.

Because through-coolant toolholders eliminate the variances often experienced with external cooling nozzles, the additional cost of such holders, which is sometimes zero, can be easily justified through the reduction of cycle times and improvement of tool life and part quality.

“Any time there is an unplanned stoppage due to tool breakage or additional rework added to a job to fix bad parts, a huge cost is incurred,” Strauchen said. “We try to convey to people that a through-coolant toolholder is a
capital expenditure and should be implemented as a best practice. You’re going to benefit for the next several years from it.”

Types of Toolholders

Haimer offers Cool Jet and Cool Flash systems for its shrink-fit chucks. Cool Jet, which comes standard with nearly all Haimer shrink-fit holders, features angled internal bores in the walls of the holder that facilitate coolant exiting the nose of the chuck. Cool Flash is an upgradable option that has a series of T-slots around the ID of the chuck to apply coolant directly to the shank of a cutting tool. This option is particularly beneficial at higher speeds, where greater pressure is inherently needed.

BIG KAISER Precision Tooling Inc., Hoffman Estates, Ill., offers a line of through-coolant hydraulic chucks with two small holes on the face of the chuck angled to direct coolant down the endmill shank.

Pioneer through-coolant toolholders come with two orifices standard. The company will EDM additional holes for a charge. Image courtesy Pioneer.

It’s rare to see through-coolant in a hydraulic chuck because it has a lot of internal features, making it difficult to get coolant around them and out, said Alan Miller, engineering manager at BIG KAISER. “We really only recommend hydraulic chucks for finishing endmills—it’s typically going to be a ballnose endmill, probably in a 5-axis environment, to really get the benefit.”

BIG KAISER also offers through-coolant features on several different series of collet chucks. “That gives you the versatility of a collet chuck program—to grab any tool size—whereas hydraulic chucks are more or less dedicated to one specific size,” Miller said.

Advanced Industries makes two types of KoolBlast through-coolant toolholders: one series with a standard Weldon setscrew and a series of Thermalfit holders. Both use the same unique internal coolant distribution design, according to Beckington.

Pioneer N.A. does things a little differently. It will EDM through-coolant holes into any of the toolholders it inventories.

“We put in two holes standard, but we charge $20 per additional hole, so if a customer has enough coolant volume coming through the machine to support it, we can put in more,” said Lee Flick of Pioneer, Elk Grove Village, Ill. “We’ve done as many as 12 holes in a holder for one of our customers.”

Pressure Situations

Flick said the amount of coolant pressure available will dictate how fast a tool can run and yield effective results, based on how fast the coolant evacuates chips. “If you have enough pressure to support it, the more holes you have, the faster you’re going to be able to cut, and the longer your cutting tools are going to last,” he said.

Flick noted that a lot of older machines have 50-psi coolant pumps while many newer machines are equipped with 1,000-psi systems. “Most of these higher-pressure machines can run at 20,000 rpm because they have enough coolant pressure, while the older machines are probably running 3,000 or 4,000 rpm.”