If John Winter of toolmaker Sandvik Coromant (Fair Lawn, NJ) were to start his own machine shop, all of his machines would be equipped for through-spindle coolant (TSC).
“Carbide drills and taps are starting to see more coolant through the spindle and the same with end mills, solid-diameter end mills, and carbide end mills,” said Winter, who is Sandvik Coromant’s product manager for the eastern US. “So, from that point of view, through-spindle coolant is going further than flood coolant.”
The advantages of high-pressure coolant applied through the spindle vs. flood coolant drive Winter’s opinion: longer, more predictable tool life, better surface finish on the workpiece, the ability to flush chips from deep holes, and higher productivity.
Winter and others knowledgeable about metalworking fluids who were interviewed for this article estimate that 70–80+% of machines in shops today are equipped for TSC, also called through-tool coolant.
“It’s four to five times higher than 10 years ago,” said Randy Hudgins, national product manager for turning and threading for toolmaker Iscar Metals (Arlington, TX). “It’s become very popular because there’s so many benefits to it.
“If you can direct it better, you’ll get better lubrication, which will give better surface finish, which in turn gives you longer, more predictable tool life,” he said. “Then you can have redundant tooling [using a second tool for the same operation when the first one is worn].”
Kyle Walker, product application and technical services manager for fluid technologies provider Milacron (Cincinnati), said customers are purchasing machine tools with the add-on benefit of TSC, and while they may not use it now, they buy it with an eye toward future use.
“It’s pretty easy to purchase a machine tool that’s manufactured with the option of through-spindle coolant and later add a system from ChipBlaster [Meadville, PA] or someone of that nature,” Walker said.
When Hudgins was a shop foreman, workers would come to him for advice when their tools started to break. “One of the things I would do is say, ‘Check the concentration of your coolant’ because historically when somebody gets low on coolant, they want to add a bucket of water,” Hudgins said. “And before you know it, your coolant is watered down.”
And as soon as the coolant got watered down, it became less effective and the workers would start breaking tools. To prevent that from happening, Hudgins recommends using an inexpensive refractometer to check the concentration of coolant in water.
Some materials demand through-spindle coolant and the lubricity it provides due to the heat they create during turning applications: aerospace and medical materials such as titanium, high-nickel alloys like Inconel and Hastelloy, superalloy steels and stainless steels. Some operators find they need to double the concentration of coolant mixed with water for these materials.
“Ideally, these materials would like to be machined using straight oil as the preferred coolant,” said Luke Pollock, product manager for toolmaker Walter USA LLC (Waukesha, WI). “This provides the most lubrication for the cutting operation.”
There are also applications that through-spindle coolant excels at where chip evacuation is critical. Machining methods such as drilling (particularly deep-hole drilling), deep grooving and pocket milling need help flushing out the chips due to the restrictive cavities they create.“If the chips cannot be easily moved away from the cutting edge, the cutting tool edge can be destroyed,” said Pollock.
The disadvantages of TSC relate to price—of the tools themselves and the coolant.
“There’s no downside to through-the-spindle coolant as far as doing its job,” said Ed Jones, chief operating officer and technical director at metalworking fluids provider Hangsterfer’s Laboratories Inc. (Mantua, NJ). “There surely is a premium to pay, but that’s price vs. value. For the most part, if you pay a higher price for lubricant, you’re getting a higher value, or a higher quality, and you’ll get a return on the cost.”
TSC generally has features that add to its price: additives to lower the formation of foam while maintaining lubricity and elevated flashpoints (if it’s a cutting oil). These coolants require more synthetics, and like synthetic motor oil, tend to be higher in price.
Engineered through-spindle coolants contain about 20 ingredients vs. the five to 10 additives that make up flood coolant, Jones said.
“They’re much more complex mixtures and contain more complex additives that are necessary,” said Jones. “With proper formulating techniques, one of the design features is to make the product very long lasting and able to withstand cutting forces, centrifugal forces, heat and bacteria. As long as the customer has modern equipment to filter out contaminants, maintains it well and has good water quality, the longevity is very good.”
When choosing a coolant, Jones’ first advice is to make sure your choice complies with the latest regulations. There are a lot of regulatory changes happening due to environmental concerns, worker safety or industry rules. For example, the aerospace industry is putting restrictions on boric acid, a common component in lubricants, chlorine, sulfur and extreme pressure additives. In the medical industry, there are tight restrictions on animal derivatives, typically bovine ones, because of concerns over transmission of Creutzfeldt-Jakob Disease, a fatal neurological malady.
“It’s also important to let your metalworking fluid supplier know if you’re shifting materials,” said Milacron’s Walker. “It’s nothing to see shops increase their titanium use by about 30% these days over aluminums.”
For example, 6AL4V titanium, which is about as light as aluminum, is hard to cut, hardens when heated, is abrasive, and is not a good heat conductor, so tools wear out faster, Walker said. Milacron has fluids that are far more efficient cutting titanium vs. aluminum. That’s because heat activates extreme-pressure lubricants. Shops use different ones depending on the application because they activate at different temperatures.
Filtering and maintenance of the coolant become more important as the coolant is used longer through recycling. The small coolant passages in many tools are susceptible to clogging from large particles, so having proper filtering and maintaining additives to keep the coolant performing at a high level are critical.
Removing fines is also important to maintain machinery. The pumps that generate the high pressure for TSC can’t operate with stray metal contaminants and can seize up.
When it comes to products with low oil or no oil, they usually have properties that will reject all if not most contaminants like tramp oils, hydraulics and oils that get into a machining system during operation. They pop those to the top where they can be easily removed.
“Through-spindle coolant allows you to break the vapor barrier of heat and ‘get the medicine where the pain is’ because fluids do two things: lubricate and cool,” said Walker. “And that alone will extend your tool life exponentially.”
Hudgins of Iscar Metals agreed, and went a step further by quantifying tool life improvement at 50% or more.
As far as workpiece quality, with traditional flood coolant the liquid doesn’t get to all the necessary surfaces of the tool/workpiece interface—the cutting edge and various parts of the tool—to optimize the lubricant’s ability to do its job, said Jones of Hangsterfer’s.
“As a result, if contact occurs without coolant, you have adhesion, and adhesion increases wear and decreases quality,” he said.
When it comes to productivity, TSC is the best method where operators are monitoring more than one machine and it’s the only way to go with lights-out operations, Hudgins said.
“Productivity’s where you’re going to get a return on your investment,” he said. “You’re getting your jobs out quicker, which leads to more jobs. The return is sometimes not exactly immediately seen on paper, but it allows companies to bring more work into their facilities.”
And as far as speed, “What we’ve learned is that the coatings on inserts like a higher temperature than the carbide substrate that’s underneath the coating,” said Sandvik Coromant’s Winter. “So, if you keep the substrate cool with the coolant underneath, you can run at higher cutting speeds and be more productive.”
Chip control is where TSC’s advantages really come into focus.
“Because the coolant is coming from the tool, the exit ducts are typically very close to the cutting edge and precisely aimed at the cutting edge,” said Pollock of Walter USA. “This provides better chip flushing and cooling of the cutting edge. Not all applications benefit from using coolant, but if they do, internal coolant is the most effective delivery method.”
One of the advantages of TSC is that it overcomes problems from flood coolant splashing on top. The splashing can cause long, stringy chips because it cools the material before it can curl enough to break.
Which direction you use the coolant can also be advantageous.
“You need to have it in the proper zone so it’s coming beneath the chip, between the cutting insert and the material, so it helps break the chip,” Winter said. “We found that you want coolant on the underside of the tool, coming up beneath the cutting zone. What that does is keep the cutting zone cooler.
“Some materials can be gummy and soft and it’s hard to break a chip, and with our tool you can plug off the top coolant and just have under coolant because you want more heat in the material to get it to break,” Winter continued. “And then you can keep the substrate cool.”
TSC also eliminates the need for copper lines and coolant nozzles used in flood coolant applications. Chips can wrap around these lines and nozzles and cause problems.
The higher cost of TSC is only one factor that adds to a shops’ cost. The high-pressure pump is a cost factor, as are the filtration systems required to screen out fine metal shavings in order to recycle the fluid.
Hudgins said TSC tools cost at least 50% more to make due to additional machining to create threaded holes for fittings, nozzles, manifolds, and in some cases numerous ports for the coolant because customers may want them at different places.
Then there’s the effect of applying high pressure to a liquid, which induces foam.
“Foam is not a very good lubricant because it’s not effectively getting coolant to the cut zone,” said Bruce Koehler, senior product manager at Milacron. “So, you have to formulate with raw materials that are low-foaming in nature or reduce foam with the use of defoamers.”
Also, machine tool builders are using smaller sumps to deal with the lower volumes of liquid, Koehler said. The reduced sumpage puts stress on the fluid because there’s less time for the foam to settle.
“So, all these factors—higher pressure, lower sumpage and filtration—put a lot of stress on fluids,” Koehler said. “Defoaming agents reduce foam through suppression. They are large molecules and can be removed by filtration, so knowing the micron size of the filter media is critical. Formulating products with low foaming additives helps remove potential problems, but the downside is the loss of detergency, which could result in unsightly residue issues. Formulating metalworking fluids is a delicate balancing act.”
One of the upsides to flood coolant is its cost. Not only is the fluid itself cheaper, so are the tools. Also, machines don’t require sophisticated equipment to supply flood coolant.
And even with the advantages that come with TSC, there are some machines that work better with flood coolant.
“Open machines may be better for flood coolant: engine lathes, turret lathes, some of your machining centers that are open,” Hudgins said. “Or for high-speed tooling, not carbide.”
Milacron’s Walker agreed.
“In the past, most people used high-speed steel tools [i.e. drills] because they’re a lot cheaper,” Walker said. “Then you need boundary lubrication, and the best way to get it is with a high-oil product delivered with the flood method.”
The problem with what Walker described is that chips aren’t evacuated. The solution is to do peck drilling, he said.
“Go in and then back out,” he said. “And let things cool down and evacuate the chips out of the hole and away from the cut zone,” he said.
In addition to open machines and high-speed tools, flood coolant helps to keep dust down while machining iron and cast iron, and those materials usually break chips pretty easily, Winter said.
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