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Insert simplification?

Insert vendors have tried to bring us a paradise of tool availability. But man users find chaos instead. Why? Progress! Take the case of molded inserts (as opposed to precision-ground types). According to Rick Clark of Rogers Tool Works (RTW) Inc, Rogers, AR, "Until recently, most carbide manufacturers offered molded chipbreaker geometries that would cover a broad application range. Versatility often meant that performance was compromised to permit the tools to function under diverse operating conditions.

"As metalworking machine tools and processes became more sophisticated, the need for chip control, predictability, and optimum performance in specific application ranges became more apparent. Techniques such as unmanned cells with automated robotic parts loading and unloading, touch-probe gaging, and automated chip-removal conveyors mean that the chipbreaking function and predictability of the tool must be flawless."

To meet this challenge, RTW and others now use sophisticated CAD/CAM technology to design, evaluate, and produce high-performance chipbreaking technology. In the last three or four years there has been a veritable explosion of new insert chipbreaker geometries, edge preparations, and carbide grades.

"Today's insert chipbreaker geometries are designed to provide consistent chipbreaking and to reduce cutting forces, heat, and friction at the cutting edge," adds Doba Jackson of GTE Valenite Corp, Troy, MI. "They thereby contribute importantly to effective chip control, longer tool life, and the more reliable and predictable tool performance required for cost-effective use of modern CNC machine tools, automated manufacturing systems, and high-performance engineered materials."

To accommodate operating requirements for light- to heavy-duty turning and boring of a wide variety of steel, GTE Valenite and other cutting-tool manufacturers are developing lines of coordinated chip-groove geometries that can produce acceptable results across a broad range of feed rates in both continuous and interrupted cuts.

"At the same time, these geometries are being combined with new coated-carbide cutting grades, some with surface-enhanced substrates. This adds to the number of choices, but the intent is to create a small core group of engineered carbide cutting materials that can perform such multiple operations as turning, boring, profiling, facing, and back facing, while collectively meeting requirements for a wide range of high to low cutting speeds in light-finishing to heavy-roughing applications-and routine to severe cutting conditions.

"By thus convering 90% or more of all turning and boring applications on steel, this small core group of cutting materials can help users simplify tool selection and reduce insert inventories."

Cermets and diamonds Along with whiskers and other strength boosters, GTE Valenite now has a composite ceramic cutting grade, Quantum 32[TM]. This is a metal-oxide composite that is typically suggested to cut workpieces with hardness ratings between 35 and 70 Rc. It's tough enough for interrupted cuts, and recommended for high-speed roughing and finishing of hardened steels, chilled cast iron, and cast irons with an abrasive scale.

If that isn't performance enough, Norton Co, Northboro, MA, now controls the patent rights to unique forms of plasma-assisted chemical vapor deposition (CVD) processes that allow the economical production of diamond-film products. Under the CVD techniques, methane and hydrogen are converted to a plasma that creates diamond particles at low pressure and low temperature. In other words, they simply "grow" diamond in place ! Practical use? Norton Co is developing a variety of diamond-coated metal-cutting tools. Initial products, released in cooperation with the Swedish company AB Sandvik Coromant, include tool coatings greater than I mm thick (with good adhesion) and diamond-coated surfaces on proprietary ceramic substrates (cutting tools and bearings) up to 2" dia.

"Cutting tools coated with diamond film can operate at higher speeds and with lower cutting force, and will last 10 to 100 times longer than the uncoated cemented-carbide tools currently used for machining nonferrous metals," says Clas Ake Hedstrom, president of Sandvik.

PVD versus CVD Physical vapor deposition (PVD), operating at relatively low temperatures, is coming into its own, for use on carbide substrates, sometimes replacing the higher-temperature CVD process. For example, Fabmet grade UP35N PVD-coated cermet is designed for high-speed turning of steel and cast iron with low to moderate feeds. It's been introduced by Mitsubishi Metal Corp, Garden Grove, CA.

Balzers Tool Coating Inc, North Tonawanda, NY, recently introduced a PVD TiCN coating with a thickness of about 0.0001 ". The coating is harder than TiN coatings, achieving 3000 Vickers.

Balzers points out, however, that coatings won't solve problems stemming from improper tool applications. The firm's Roger Bollier says, "We've found that 30% of the time there's a significant tool-wear problem, the customer is using the wrong tool. Whether the tool is a carbide insert or an HSS twist drill, simply putting a coating on it won't solve a problem of misapplication."

What about milling? Mitsubishi's Fabmet, on one hand, offers a new coated grade F620 for milling various steels in a wide cutting range. Each insert consists of a tough carbide substrate and titanium-compound layer coated by CVD. Its features, compared with uncoated grades and PVD coated grades include high wear resistance, high thermal shock resistance, and superior toughness.

On the other hand, Kennametal Inc uses some PVD to coat carbide inserts. Dennis Quinto, director of new materials technology at the firm's Greensburg, PA, facility, is glad to discuss the merits of both: "There are intrinsic differences in the microstructure and residual stress state of CVD and PVD hard coatings. High compressive residual stress and finer grain size in PVD relative to CVD coatings contribute to increased microhardness and microfracture toughness.

"Because PVD processing preserves the toughness of the carbide substrate, in contrast to the tendency of high-temperature CVD to degrade it, PVD coatings can serve on sharp-edge tools and tools that handle interrupted cuts for threading, grooving, and milling. For turning, however, CVD coatings are still the most effective."

Book simplification

Carboloy Inc, Detroit, MI, conducted a survey that revealed the need for simplified tool-selection procedures. Almost 65% of the people queried said they had problems selecting and optimizing turning inserts, and nearly 80% said they would make use of a simplification system made available to them.

For turning applications, the firm offers the new Secolor product line, which includes a selection system based on a nine-block grid. Rows are color coded according to ISO standards for basic ferrous materials. For instance, blue symbolizes steel, yellow is for stainless steel, and red for cast iron.

Tint-coded columns symbolize the type of cut to be taken. Left is lightest, for fine machining; right is darkest for roughing; and the middle is for medium machining. Knowing just workpiece material and type of cut, users can turn directly to one page in Carboloy's new Guide to Turning Inserts. Each page lists all first-choice inserts for these two machining variables. The only thing left is to select insert size and shape-to match toolholders. A series of further, equally simple steps, leads to an optimized selection. Once the operator makes his first choice, and observes the tool in operation, the guide helps him adjust groove and grade selection to fine tune the performance. That's the rub. Fine tuning may get you back to research and soul searching. But even here, the guide can help you.

Pamphlet approach

Kennametal says most manufacturers offer at least three basic geometries: narrow groove, wide groove, and land angle (dropped floor). Each may feature a modified geometry at the insert nose radius to cover shallow depths of cut, and they may also be superimposed with a variety of bumps, waves, or dimples. The firm admits that the growing multiplicity of chipbreaker designs breeds confusion, and says there are two basic solutions:

1. Simplicity above all-with exceptions. This approach suggests that three geometries are sufficient for all needs: finishing (F); general-purpose (G); and roughing (R). But some firms believe you need five; so they add F/G and G/R. And one adds heavy roughing and ultra-fine finishing for a total of seven! Thus simplicity quickly falls victim to progress.

2. More choices-with application advice. To help customers apply tools efficiently, many companies now offer application recommendations in compact form such as the Carboloy system already mentioned. Kennametal has 11 different geometries, and believes that users really want this variety to get increased productivity. So the firm's engineers have published a series of Application Advisors in the form of individual guides for each of ten workpiece materials.

In the second phase of this advisory approach, the publications rank available geometries in sequential order from ultra-fine finishing to heavy roughing. Users can systematically modify, in discreet increments, the performance of cutting tools. For example, if you are using a given geometry and want to improve chip control, then select the next geometry in the finishing direction. Of, if chips are breaking satisfactorily and you want to increase feedrate, then select the next geometry in the roughing direction.

Computer vs salesman

Kennametal puts it all on computer, too. Tool-advice data are all available in PC software entitled Grade Application Advisor. It's part of the ToolPro family of software products, and it recommends inserts grades and cutting parameters for turning. Working on a personal computer, it also keeps track of your tool selections and establishes a historical record of your machining processes.

Or, you may want to try a very basic approach suggested by Ingersoll Cutting Tools Co, Rockford, IL. Manager Rod Drummond wants the end user to take advantage of the tool manufacturer's experience in applying products.

For example, Ingersoll sells direct and has a large field sales force. Mr Drummond says, "Our sales engineers are tooling experts, trained in the application of our products. These individuals can recommend tools for specific applications and will help users fine tune speeds and feeds."

High-performance carbides, ceramics, and superabrasives are stronger than ever before, and many are easier to use in a wide variety of applications. You may get excellent performance without fine tuning them at all. But specialty niche tools require careful application, and modern, high-speed machine tools don't forgive misapplications. So don't be afraid to ask for advice.
COPYRIGHT 1991 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1991 Gale, Cengage Learning. All rights reserved.

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Title Annotation:what's new in geometries, materials, multilayer coatings and tool-selection guides
Author:Miller, Paul C.; Mlachak, Nicholas N.
Publication:Tooling & Production
Date:Jan 1, 1991
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