Under Pressure

Author Derek Phillips
Published
January 01,2000 - 11:00am

What to consider when buying a high-pressure coolant delivery system.

It’s the ultimate goal of machining: Maximize speeds and feeds while improving the finish of the cut. Many a good tool has perished in this quest and many a shop manager has lost sleep because of the pressure.

But some say that the best way to achieve the goal is with pressure specifically, high-pressure through-coolant (HPTC) systems. They deliver a constant stream of coolant to the cutting edge at pressures of 1,000 psi and higher.

Users of HPTC systems can generally expect at least a 25 percent increase in productivity and tool life, according to Frank Simonetti, West Coast vice president of sales at High Pressure Systems Co., a division of the Daniluk Corp., Oklahoma City. Simonetti added that often the productivity gains are even more impressive.

"I had one customer in Texas who actually reduced his cycle time by 60 percent [after installing a 1,000-psi HPTC system]," he said. The customer was drilling 2"-dia., 5"-deep holes in 4140 steel.

B&B Manufacturing improved the productivity of one of its drilling operations by more than 25 percent after retrofitting a 1,500-psi, variable-pressure pump to one of its machine tools. The unit replaced the 1,000-psi, mechanical-bypass, diaphragm-type pump that was originally installed on the machine.

Additionally, the company’s vice president of operations, Jeff Lage, said that since replacing the smaller pump, he has noticed a significant reduction in tool failure.

B&B, a Valencia, Calif., manufacturer serving the aerospace industry, found that the high-pressure pump also helped it keep a customer happy. "We couldn’t meet the volume of parts required by our customer," Lage explained. "It was a matter of reducing our cycle time or implementing additional machine sources." He said that the 1,500-psi pump let B&B reduce the cycle time enough to meet its customer’s demands.

"It was such a dramatic change," said Lage. "We were looking for a 25 percent improvement in our drilling cycles, and we far exceeded those expectations."

What Is High Pressure?
Except for the machine tool with the 1,500-psi pump, B&B’s other machines are equipped with factory-installed, 1,000-psi systems. Lage said that they work fine, but he doesn’t really consider them to be high-pressure systems.

As might be expected, not everyone agrees on what constitutes "high pressure." Some machine tool builders consider the 300- and 400-psi systems that come with their equipment to be high pressure. Aftermarket suppliers of HPTC systems disagree.

"High pressure is anywhere from 1,000 to 5,000 psi," said Simonetti.

Jeremy Elder, director of marketing at ChipBlaster Inc., Meadville, Pa., said that at least 1,000 psi is necessary to break the vapor barrier that forms around tools, especially when they’re in a hole. The barrier is created when the spinning of the tool and the heat generated by the friction of the cutting action combine to form steam.

One thousand psi is needed to break the vapor barrier that surrounds a tool especially when it's in a hole.The steam and spinning motion, in effect, create a mini-atmosphere around the tool that acts as a barrier, preventing coolant from reaching the point of cut.

Simonetti added that it is the combination of pressure and volume that effectively breaks the vapor barrier. "Gallons and pressure equal force, and that’s what you need to eject chips," he said.

The force needed varies from user to user. But many metalcutting companies find that 1,000-psi, 8-gpm systems fill their needs.

According to Simonetti, that is the pressure and coolant-delivery rate of High Pressure’s most popular system. It comes with a variable-drive pump, two filters and a tank, and it costs $11,495.

ChipBlaster’s most popular systems run from $7,900 for a 1,000-psi, 8-gpm pump to $16,000 for a 2,000-psi, 13-gpm pump.

As for installation costs, Elder said that if a machine tool is properly prepped, ChipBlaster can usually retrofit it with an HPTC system in a day. "Our flat installation fee for prepped machines is $1,680," said Elder. "But if we have to machine a new block and install all the coolant lines, it can get pretty pricey—up to $4,500."

Elder and Simonetti said that most of today’s machines are built to accept an HPTC system. Simonetti tells his customers that if they’re buying a machine that’s not prepped for high-pressure coolant, they’re probably buying outdated equipment.

Making the Right Choice
Simonetti has a simple rule for selecting an HPTC system: Coolant should be delivered at the rate of 1 gpm for every 0.1" of the cutting tool’s diameter.

"The rule is to size your coolant-delivery system based on your drills," he said. "If you’re drilling with 1"-dia. drills, you need about 10 gpm at 1,000 psi."

Another factor to consider is the material to be machined. According to Simonetti, titanium, for example, likes to workharden, so a minimum of 1,500 psi is required to machine it.

Elder agreed that material is an important factor when selecting a system, and he said that ChipBlaster will often test-cut materials for its customers. The tests help ChipBlaster make recommendations about speeds and feeds and determine the optimal pressure for breaking chips.

The ability of an HPTC system to break chips when machining materials like titanium and Inconel impresses David Fischer, project coordinator at machine tool builder Okuma America Corp., Charlotte, N.C.

"You don’t get long, stringy chips," he said. "[The HPTC system] breaks them up and flushes them out."

He added that the ability to control pressure is an important consideration when deciding on an HPTC system. "You may not always need high pressure," Fischer said. "You might have some fragile materials where high pressure could damage the part."

Other situations in which high pressure would be inappropriate are when parts can’t be clamped down tightly and when tools are so small that they could be damaged.

Besides a variable-pressure capability, Fischer also recommends that users buy an HPTC system with an automatic shutoff control, an auto-mixer and a thermostatic control.

An auto-shutoff guards against the tool running without coolant and ensures that the HPTC system will not overflow the machining center’s tanks.

An auto-mixer combines the proper ratio of coolant to water, which helps maintain consistency of lubrication and, therefore, improves tool life.

A thermostatic control helps maintain the proper coolant temperature. This is especially important when machining materials that produce long, stringy chips, which can wind around a tool and cause it to break. Coolant that is at the correct temperature causes chips to thermally fracture into tiny pieces that are easier to eject from the point of cut.

Extending Tool Life
The primary way that an HPTC system extends tool life is by effectively breaking chips that form at the tool/workpiece interface. Simonetti said that these systems also give tools hydrodynamic strength, an effect he compared to a garden hose that stiffens after the water is turned on. The pressure and volume of coolant makes tools more rigid, especially solid-carbide through-coolant drills.

However, CJT KoolCarb Inc.’s vice president of sales, Tom Trost, cautions against using extremely high pressures with these drills.

"The coolant has to twist back up through the helix of the drill, causing turbulence, which vibrates the drill," said Trost, whose Carol Stream, Ill., company manufactures a variety of through-coolant tools.

Trost recommends limiting the pressure for drills used on CNC machines. He said that a 3mm-dia. drill, for example, should be run at no higher than 1,500 psi.

Coolant Considerations
An important element of any HPTC system is the coolant itself.

Andy Nelson, product manager at Master Chemical Corp., a coolant manufacturer in Perrysburg, Ohio, recommends the use of nonfoaming coolant.

"Foam is partially made up of air, making it less effective than straight liquid," he said. "It neither cools nor lubricates, effectively shortening the life of the tool."

Nonfoaming coolant initially costs a little more than standard coolant, but Nelson pointed out that higher upfront costs can lead to savings down the road. "Nonfoaming coolant is designed for heavy-duty machining, therefore it’s built to last," he said.

Ensuring proper coolant filtration is also critical to the successful operation of an HPTC system.

The systems from both High Pressure Systems and ChipBlaster filter pArticles as small as 5µm. Elder said that ChipBlaster also makes recommendations based on the material a customer is machining.

"Cast iron, for example, produces a lot of soot," said Elder. "So we’ll recommend a dual-filter system and a magnetic separator."

Better filtration, Elder said, ensures that the coolant will last longer. Bacteria and tramp oil are removed, leaving cleaner coolant that has higher lubricity, which extends tool life.

Nelson added, "The better the filtration, the longer the coolant life and the better the surface finish." And that, obviously, means a better operation overall.

 

Putting Pressure to the Test

LeFiell Manufacturing Corp. recently installed a high-pressure through-coolant system on its turning center and took it for a test ride. The Santa Fe Springs, Calif., machine shop wanted to see if the HPTC system would, as promised, reduce cycle times and increase tool life.

High Pressure Systems Co. manufactured and installed LeFiell's new 1,500-psi, 13-gpm HPTC system.

The test part was a titanium brace for an aircraft. LeFiell contour-turns the part from an 8"-dia. titanium billet. The company's manager of continuous improvement, John King, said that machinists normally turn the part at a 0.300" DOC.

Running at a spindle speed of 100 rpm and a feed rate of 11 ipm, the operation takes about three hours to complete using the turning center's factory-installed, 80-psi coolant-delivery system. Also, tool life is short because of heat.

"We generate so much heat that regular carbide inserts just wear right out," said King. He added that the whole idea behind high-pressure coolant delivery is to keep the chip and the tool cool, which, in turn, should extend tool life and increase productivity.

After a week of testing speeds and feeds with the new HPTC system, King reported that machinists were making a 0.250" DOC and running at 222 rpm and 12 ipm for the first four passes. A 0.030"-deep finishing pass was revved up to 300 rpm and 15 ipm. Overall, the HPTC system shaved more than an hour off the run time.

LeFiell anticipates that productivity will increase even more after it makes several tool changes suggested by High Pressure Systems. "We're going to put in a different insert holder and use a coated insert that will be directed at about a 40° angle," King said.

He also said that he's eager to try the new coolant-delivery system with other applications. "We'll be able to utilize it for machining aluminum parts and, depending on what insert we use, we may be able to speed up those operations immensely."

-D. Phillips

Related Glossary Terms

  • computer numerical control ( CNC)

    computer numerical control ( CNC)

    Microprocessor-based controller dedicated to a machine tool that permits the creation or modification of parts. Programmed numerical control activates the machine’s servos and spindle drives and controls the various machining operations. See DNC, direct numerical control; NC, numerical control.

  • coolant

    coolant

    Fluid that reduces temperature buildup at the tool/workpiece interface during machining. Normally takes the form of a liquid such as soluble or chemical mixtures (semisynthetic, synthetic) but can be pressurized air or other gas. Because of water’s ability to absorb great quantities of heat, it is widely used as a coolant and vehicle for various cutting compounds, with the water-to-compound ratio varying with the machining task. See cutting fluid; semisynthetic cutting fluid; soluble-oil cutting fluid; synthetic cutting fluid.

  • feed

    feed

    Rate of change of position of the tool as a whole, relative to the workpiece while cutting.

  • flat ( screw flat)

    flat ( screw flat)

    Flat surface machined into the shank of a cutting tool for enhanced holding of the tool.

  • inches per minute ( ipm)

    inches per minute ( ipm)

    Value that refers to how far the workpiece or cutter advances linearly in 1 minute, defined as: ipm = ipt 5 number of effective teeth 5 rpm. Also known as the table feed or machine feed.

  • lubricity

    lubricity

    Measure of the relative efficiency with which a cutting fluid or lubricant reduces friction between surfaces.

  • metalcutting ( material cutting)

    metalcutting ( material cutting)

    Any machining process used to part metal or other material or give a workpiece a new configuration. Conventionally applies to machining operations in which a cutting tool mechanically removes material in the form of chips; applies to any process in which metal or material is removed to create new shapes. See metalforming.

  • tramp oil

    tramp oil

    Oil that is present in a metalworking fluid mix that is not from the product concentrate. The usual sources are machine tool lubrication system leaks.

  • turning

    turning

    Workpiece is held in a chuck, mounted on a face plate or secured between centers and rotated while a cutting tool, normally a single-point tool, is fed into it along its periphery or across its end or face. Takes the form of straight turning (cutting along the periphery of the workpiece); taper turning (creating a taper); step turning (turning different-size diameters on the same work); chamfering (beveling an edge or shoulder); facing (cutting on an end); turning threads (usually external but can be internal); roughing (high-volume metal removal); and finishing (final light cuts). Performed on lathes, turning centers, chucking machines, automatic screw machines and similar machines.

Author

Derek Phillips is assistant editor of Cutting Tool Engineering.