HIGH-PRESSURE COOLANT TOOLS

Back in the 1950s, when high speed steel was still the mainstay tool material, and a low machining rate was considered adequate for turning titanium and Inconel, the idea of delivering high-pressure coolant (HPC) to the cutting zone probably seemed ahead of its time.

Since then, HPC has proven itself in hundreds of dedicated turning applications on these difficult to machine materials, at removal rates of up to three times more than that of the conventional flood coolant system.

Users report elimination of chip jamming, faster cutting, and much longer edge life in outer and inner diameter turning as well as grooving, parting and holemaking. And, in one high-volume cut-off operation in titanium, HPC turning improved edge life.

Now with the availability of high speed machines offering optional 70-bar coolant systems and through-spindle delivery, HPC technology has grown much more accessible - and proven to be timely. To complete the circle, ISCAR has provided hundreds of specialty HPC turning tools for a multitude of applications. JETHP line solutions have been implemented by customers for more than seven years now.

TARGET COOLANT

What is the magic of HPC turning? The combination of coolant at high pressure (70 bar to 140 bar), and precisely targeting the cutting zone, produce advantages that conventional flood coolant cannot.

The coolant is delivered with enough force to reach the cutting zone as a liquid, not a vapor. In the liquid phase, it actually lubricates the cutting process as it quenches the molten chip, shattering it into smaller, more manageable pieces. And because of its internal flow path, HPC keeps the entire spindle, tool, insert and workpiece cooler, leading to much longer tool and equipment life. In that sense, it works like the cooling system in an automobile engine.

Another benefit is that delivering coolant close to the secondary shear zone improves machinability of the material under high speed conditions. Higher pressure coolant, directed right at the cutting zone, creates smaller, more manageable chips, whether the material is titanium, Inconel or steel. Directing the coolant right to the cutting zone is the key. This is the "laser" approach to coolant deployment, not the "floodlight" approach.

ISCAR's JETHP line of special HPC tools includes CUT-GRIP grooving tools; ISOTURN and HELITURN turning and facing tools; TANG-GRIP parting and grooving tools; and PENTACUT grooving, recessing and parting tools. Turning jobs these tools handle include outer and inner diameter work on titanium and Inconel turbo- machinery discs, titanium airframe parts, miniaturized parts, and a variety of stainless steel components. Coolant pressures have ranged up to 400 bars, but most applications have been in the 70 bar to 100 bar range.

TAKING AIM

In all cases the focus in ISCAR's hydraulic design of HPC cutting systems is two-fold: first, to direct the coolant precisely into the cutting zone; and second, to ensure taking maximum advantage of its cooling properties are used. Here is a look at each point separately.

• Aim - As in real estate and retailing, the key is location, location, location. Not only is pressure or flow rate critical, but the nozzles on the tool must feed the liquid right into that tiny spot where the cutting edge meets the metal and the chip curls off.

• Advantageous coolant properties - At the extreme cutting rates involved with today's HPC turning, high pressure coolant flow is an integral part of the cutting process. Besides avoiding overheating and thermal shock in the cutting zone, the coolant contributes a waterjet cutting-effect to actually enhance cutting action. HPC tools are custom-designed to operate at these extreme pressures and cutting rates.

They deliver an order-of-magnitude higher performance level than their conventional through-tool-cooling counterparts made for lower-pressure service. To use a conventional through-coolant turning tool in an HPC system is as misguided as powering a racecar with a lawnmower engine.

The majority of the HPC experience has been on titanium, at surface speeds up to 500mpm. Typical results have been 20% to 50% shorter cycle time; reduced work hardening, welding and built-up edge; better chip control; and longer tool life.

WHICH INSERTS?

Experience indicates that existing insert geometries, grades and coatings work well in high-speed turning with high-pressure coolants.

There is no need to invent entire new breeds of insert. Rather, the main challenge for tool designers is to cool and lubricate that hard working insert so it breaks up and flushes away the chips. The other job is to create a toolholder husky enough to house a 70 bar conduit, yet compact enough to access the required cut in tight quarters.

OUTLOOK

What is ahead for HPC turning? In the world of metalcutting there are many highpressure tool options, and the enabling equipment is becoming more readily available and affordable. We already have the high speed machines with higher capacity coolant systems available as options on many turning centers. So far, the missing piece of the puzzle has been standard HPCgrade tooling.

In the near future, ISCAR will produce and stock a line of HPC turning tools as standards under the family name JET-HP line (high pressure coolant) tools. They use existing inserts but have the internal pipeline to deliver the coolant exactly where it matters - right into that hot spot known as the cutting zone.

Meanwhile, if you have a dedicated turning operation in a difficult material that is being bottlenecked by chip control problems, look into solutions for high pressure coolant machining today. Why wait?

Iscar Metals Inc.
Arlington, TX
iscarmetals.com