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Insert update - the right tool boosts profits.

Insert update--The right tool boosts profits

Ironically, new cutting-tool materials are so strong that inserts can take the punishment of positive-rake cutting. But some also work at very high temperatures, allowing high-speed cutting of metal in the soft zone, thus reducing stress to the workpiece in negative-rake setups. Either application is good news, because each softens the requirement for rigidity in the machine tool, spindle, fixturing, and work-piece.

Where's the rub? New tools must run according to the instruction book to provide the advertised advantages. If your operators take fast carbides and run them at slow speeds with delicate feeds, they could get worse performance than if they used cheaper inserts.

Fortunately, some new coatings and substrates work well over a wide range of speeds and feeds, even if they don't grant maximum production at the lower speeds. In any event, today's production engineers must know inserts characteristics, and managers must provide training and persuasion to get the good-old boys up to speed.

One toolmaker remarked, "We're glad to see big companies contracting out to small shops, because the smaller outfits are more willing to change--more likely to try new tools and machining methods. Small-shop owners know that a high-priced CNC machining center must be run continuously--three shifts a day--to make it pay for itself."

The bottom line is efficiency. Although long tool life and higher speeds look good on paper, none of it works without operator cooperation. And, consistent life is more important than long life with machining cells, FMS, and those untended third-shift operations.

Positive or negative?

Darrel Smith, manager, milling products, Waukesha Cutting Tools Inc, says, "Positive-cutting-edge geometry permits softer cutting with less horsepower and less stress on the workpiece, the tool, the spindle, and the machining center. That's ideal for today's lighter machine tools with less rigid workpieces and setups, as well as for older machines."

Smith adds, "Positive geometry lets tools remove metal more efficiently. Positive tools actually cut or slice material, rather than bulldozing it off as negative-geometry tools do. Positive setups remove metal with finesse, yet at higher feeds and speeds.

"Sharpness counts, too. Our chemical vapor deposition (CVD) coating process works at low enough temperatures to allow multiple layers for longer wear and maintenance of sharp edges."

Kennametal notes that a sharp edge generates lower cutting forces, especially important for milling thin-wall sections and providing finer finishes and fewer burrs. The firm's KC710 grade for milling steels is coated by a physical vapor deposition (PVD) process that operates at a lower temperature than most CVD systems to save basemetal strength and toughness. As with the Waukesha product, there's less chipping and thermal cracking, so tool life is more predictable.

New geometries

Sandvik Coromant's Darvel Hansen, senior carbide grade specialist, told Tooling & Production, "For the next two years, we'll be revamping the old geometries of the past 15 to 20 years. We're using better chip-breakers, new honing techniques, and improved coating processes. We believe a sharper cutting edge is helpful in cutting some materials, but we need a stronger reinforced edge for others. We use CAD/CAM to design the inserts. Without the computer, it would be impossible to offer all the new style chipbreakers in our program.

"Tool selection is complicated, but we're replacing numbers with letters to ease the pain. Our simplified Q family of chipbreakers, for example has three members: QF, QM, and QR. The letter F signifies finishing, M medium, and R roughing. Supplemental geometry MR is dedicated to medium roughing, working toward the low end of roughing and some semifinishing. This is a big program for us. We've released some 200 insert styles in six different grades in this new geometry. We start with QF, QM, etc, then later will add more letters to fine tune the designations."

One of the problems is lack of an ANSI standard in the US. Number nomenclature is confusing at best, and several firms are asking ANSI for uniform letter identification.

Sandvik is squarely in the positive camp, and tomorrow's geometries will be even more positive. Hansen says, "Whenever possible, for general machining, most users would rather have the freer cutting action of positive geometry than the heavy cutting of negative inserts requiring T-land reinforcement."

Hard edges and tough ceramics

Mr Hansen says, "Today, we're still using tungsten carbide as we have known it for the past 40 years--with only minor improvements in the substrate. But there are major improvements in coating techniques that provide better adherence not possible five years ago. Coatings allow hard, high-speed grades to work at lower speeds and handle interrupted cuts.

"There are some new materials, ceramics for one, and sialon. Our silicon-nitride offering for cast-iron machining will come in two grades--one for turning, and one for milling. We believe it takes two grades to optimize both operations."

Rogers Tool Works Inc (RTW) offers high-performance coated carbide said to balance toughness and wear resistance. Grade 925 combines a tough substrate with a multiphase aluminum-oxide coating for thermal stability. The tools are positive rake.

NTK Cutting Tools says cermets (bondded mixtures of ceramic and carbide) are ready! Its newest product is all-purpose grade T35 for roughing and finishing carbon steel and alloy tool steel at speeds from 250 to 650 sfm, feeds, from 0.004 to 0.008 inch/tooth, and depths of cut to 0.200".

The firm believes T35 inserts deliver longer tool life than other grades of cermet, while producing better surface finish than either coated or uncoated carbide.

The inserts have high resistance to thermal shock, and transverse-rupture strength is equivalent to C6 carbide. In NTK's wear-resistance tests, T35 outlast carbide by nearly 10 times when milling 4140 alloy steel. In mechanical-breakage tests, the inserts resist five times as many impacts before breaking than C7 carbide inserts, and 10 times as many as titamium carbide (TiC).

Greenleaf Corp recently announced a ceramic cutting-tool material for both ferrous and nonferrous alloys. Designated WG-70, this patented material is engineered to stand up to high-velocity machining of alloy steels. It adds to the 3-yr-old whiskered WG-300 inserts now used for cutting nickel-based alloys.

WG-70 has a broad range of applications, working at speeds from 80 to 3000 sfm in turning, boring, and milling of almost everything from soft steel and iron to highchrome materials. It survives mechanical shocks and temperatures up to 1200 C. It's chemically inert.

For 1989, Komet has introduced Cerkomet cermet inserts composed of titanium nitride, titanium-carbide, and a metallic binder. The positive-rake inserts suffer less edge buildup, while providing good flank wear, cratering resistnce, and higher cutting speeds. These are solid substrates with no coatings.

The two grades handle semifinish, finish, and minor roughing in nearly all workpiece materials including stainless steel. They are precision ground, with corner-to-corner reindexability of 0.0008". The tools are not for serious roughing. Rather, they play to the concept of buying quality castings and eliminating secondary operations. They take 0.001" to 0.002" off net-sized castings and provide good finish without grinding.

Tooling systems

Inserts do not work alone. They must be clamped to holders quickly and precisely. That took a lot of skill and patience with older designs employing special screws, plates, shims, washes, and other gadgets. Today's tooling is simpler and easier to assemble in a hurry.

For example, Komet offers System 01 tool management for internal boring and external turning. The system features one insert size (inscribed circle or IC), one wrench, and one screw that lets the user combine 66 different tools. Qualified holders provide up to five different lead angles.

Boring bars in the system have through-the-tool coolant, with coolant hitting the cutting edge of the insert, granting better chip evacuation, better heat transfer, and extended tool life.

A central clamping mechanism applies equal pressure when attaching two components, using a receiving screw and floating pin. A taper holder grips tools with just a slight tightening, and the tools don't move off center in the process. Thus, preset tool stay on course.

Finally, for efficient presetting, Teledyne Firth Sterling offers the Firth Set digital presetter. It can be manual, with soft touch probe; visual, with camera-enhanced vision system; or computer enhanced, with special optics and software to create, store, and retrieve graphic colored tool overlays. The vision provides high-resolution video imaging of tool points and surfaces, with a B&W monitor and camera.
COPYRIGHT 1989 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1989 Gale, Cengage Learning. All rights reserved.

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Author:Miller, Paul C.
Publication:Tooling & Production
Date:Feb 1, 1989
Words:1392
Previous Article:Getting into DNC.
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