by Jim Barnes
Toolholder options for through-coolant delivery
Through-tool and through-spindle coolant delivery is getting more attention thanks to its potential for extending tool life and improving quality and productivity. Choice of toolholder is key in making this happen efficiently.
When coolant is delivered consistently to the cutting edge of the tool, benefits in quality, productivity, chip breaking and tool life follow.
Feeds, speeds and depth of cut can be ramped up as the coolant is applied more effectively. Most tools need to run within a certain speed range for optimum performance, notes Steve Geisel, senior product manager, Iscar Tools Inc., Oakville, ON. Too slow is as bad as too fast. Heat lost to more efficient cooling often has to be made up with more aggressive cutting.
There are basically three levels of coolant pressure you’ll see on standard machines, notes Alan Miller, engineering manager, product manager, BIG Kaiser Precision Tooling Inc., Hoffman Estates, IL. There’s the 150 psi range for flood coolant pumps; about 300 psi, the low range of a coolant-through spindle; and the 500 to 750 psi range you get with higher performance pumps. “Beyond that, it’s generally an additional piece of equipment on the floor for high pressure in the thousand-plus psi range,” he says.
New machines are more readily adapted to high-pressure coolant, says Chad Miller, product manager -Turning and Advanced Materials, Seco Tools Inc., Troy, MI. Nevertheless, he adds, “a lot of customers with older machines don’t think the systems will be of benefit to them. We see benefits to through-tool cooling, even at low pressure.”
You need to assess your filtration capabilities when looking at high-pressure through-coolant systems.
“The nozzles we use for high-pressure coolant systems are quite small. A standard coolant line could have a quarter inch diameter hole in it. When you’re talking about through-tool, you might be talking about a one millimeter hole,” says Geisel.
“On the older machines, we like to have a minimum of 20 µ filtration. On the newer machines–the thousand psi-plus type machines–they’re getting down to 5 µ,” says Chad Miller.
Water-based coolants pose less of a challenge to toolholders and tooling in terms of filtration, notes Brendt Holden, president, Haimer USA, Villa Park, Ill. With heavy oil coolants, viscosity might become an issue.
Maintenance is another concern. Like any toolholder, these units must be checked periodically for wear.
There isn’t much difference in maintenance between a high-pressure toolholder and a conventional toolholder, says Seco’s Chad Miller. “There’s some hosing and tubes that need to be connected, but once it’s in the machine, it’s like any other toolholder.”
Nothing lasts forever. “These are perishable items. People forget sometimes that whether it’s a high-pressure toolholder are a conventional toolholder, there is a shelf life,” says Seco’s Chad Miller.
BIG Kaiser’s Alan Miller recommends toolholders be disassembled if they are not to be used for a while. “Most coolants have some kind of rust preventative in them. That’s fine if it is sitting in the tank and in the machine. However, if you put it in the rack and come back a couple of months later, that coolant will often have evaporated and left a residue. The toolholder may rust and accuracies will suffer because of it.”
Making a choice
The choice of toolholder, as always, will depend on the application–the workpiece material and the machining operation. If you have a large tool inventory, through-spindle coolant might help you maximize your ROI. If you already have through-tool tooling, the choice is simpler.
For drilling operations, through-tool cooling is an effective solution thanks to its ability to flush chips back up, says Haimer’s Brendt Holden. “With milling, you’re putting a side load on the end mill. You don’t want a hole in it. That tends to weaken the structure and there’s a potential for breakage. Also, the price is higher. With the coolant flush system, the coolant system is built into the toolholder itself, so you can use the tools you were using before the toolholder takes care of the coolant,” says Holden. “Ultimately, I think we will wean them off through-tool coolant, except for drills. End mills with the coolant hole are probably 30 per cent more expensive than the exact same geometry without the coolant hole. That’s a consumable product. The toolholder stays there forever.”
For Rego-Fix Tool Corp. of Indianapolis, IN, the main question is the seal,” says David McHenry, senior product engineer. Some machines have coolant through the strength of the taper. Other machines have the coolant through the flange. “The customer has to figure out what kind of design he has, and 98 per cent of the time it’s through the taper. That makes it easier on our side. Then it’s just a question of picking which system of coolant sealing is best for them,” says McHenry. SMT
Jim Barnes is a contributing editor. [email protected]