Turning the corner on productivity

Automotive Manufacturing & Production, Nov, 1997 by Colleen A. DeJong

As users demand more "bang for the buck," machine tool builders keep turning out better and better machines. They are faster, more solid, and capable of more throughput. One such machine is the conquest GT27 precision gang tool lathe from Hardinge, Inc. (Elmira, NY). This machine is all about producing parts in minimal time. Interchangeable tool top plates save setup time on repeat jobs. The pre-tooled top plates, each holding up to 10 tools, can be removed and interchanged within 0.0002 in. in under a minute. The machine's gang-tool configuration reduces cycle time since there is no time lost on turret indexing.

All of this saved time does not come at the sacrifice of accuracy. Low-friction/zero-striction linear guideways control movement, and the collet spindle is said to produce faster feeds and higher speeds with good accuracy. Absolute encoders and preset servodrive positioning add to the accuracy of the GT27, and eliminate the homing sequence for the X- and Z-axes. But is it quick? Yes. Rapid traverse rates of 472 ipm in the X-axis and 630 ipm in the Z-axis.

The base is made from the patented Harcrete polymer composite. This lends a stability that is said to provide a 30% longer tool life, since there is less chatter from vibration. Options for the GT27 include a parts removal system, a chip removal system, air blast, and various tooling options.

Hardinge isn't the only one pushing productivity higher. Kaufman Manufacturing Co. (Manitowoc, WI) is building the KAUFMANflex system of multistation rotary transfer machines. They use flexibility and a high degree of automation to produce parts.

Up to seven CNC vertical or horizontal machining units provide as many as eight stations, each with either vertical or horizontal machining units, face gear indexable tables, and an advanced swarf control system. Motorized spindles providing up to 12,000 rpm are also standard. The stations also feature live hydraulic or pneumatic clamping on the pallets, giving pallet rotation time of about one second. There are indexing turret modules and toolchanging modules with six or eight spindles available. Chip-to-chip toolchanger times are around two seconds, and an Indramat MT-CNC control is standard.

The machines can provide up to 35 axes of motion (or more) depending upon configuration. This permits the machining of five-sided prismatic parts in one clamping, as well as the high-speed machining of castings and forgings.

According to Kaufman engineers, ideal applications include machining families of parts, as well as high-volume applications, or those where the part has critical locational tolerances. CNC axis offsets are said to make it easier to control and maintain the tolerances. When three or more stations are used, the KAUFMANflex can replace a like number of stand-alone machining centers. This not only saves floor space, but time as well, since the parts aren't being carted from machine to machine.

Cutting Tool Technology

Just these two examples alone indicate that turning machines are evolving into highly productive, precise machines. And as the machines have developed, so have the cutting tool inserts they use. "Tools have had to be developed that can hold up at higher speeds," says Doug Ewald, manager of lathe products marketing at Kennametal, Inc. (Latrobe, PA). "For most insert makers, this has meant developing new, tougher substrates and tool coatings."

As an example, he cites the KC9010 tool grade. The coated-carbide insert grade is made for high-speed machining on various materials. Steels, ferritic and martensitic stainless steels, and irons can all be machined using this grade. Furthering the insert's toughness is a TiCN/[Al.sub.2][O.sub.3]/TiN coating that provides abrasion resistance and high hardness, even at the higher temperatures that come with higher cutting speeds.

It slices, it dices . . .

Another part of the evolution of turning inserts has been the creation of multiple-function tools. They enable users to perform more than one application without having to change tools. A good example of this is the HeliGrip line of tools from Iscar Metals, Inc. (Arlington, TX). According to Iscar engineers, the tools can perform longitudinal turning, profiting, deep grooving, deep face grooving, and face turning (both toward center and away from center). They can also be used for parting, even on large-diameter workpieces.

These inserts are equipped with a frontal chipformer with a central, positive recess. The side chipformers are a row of small, grooved depressions in each side-cutting edge. They have positive rake angles and reduced contact between the chip and insert rake face.

The HeliGrip inserts are twisted, which makes it possible to machine to depths much larger than the length of the insert itself. As the insert penetrates the workpiece, the slanted rear angle - in relation to its frontal edge - avoids "back side" contact with the side-machined surfaces.

Live demonstrations at a recent Iscar seminar give a pretty good idea of the tool's flexibility. Using a GIPM insert from the HeliGrip line, grooving and turning operations on a crank shaft were performed. Raft Wertheim, head of engineering services at Iscar, explained that the user, in this case, was looking to eliminate a serious problem with chatter and workpiece chipping. It also needed to increase productivity. Not only did the HeliGrip insert output a better finish, but the previous problems of chattering and chipping were all but eliminated. "The user is able to turn out 22 pieces per cutting edge, as opposed to the old insert's record of three pieces per edge," explains Wertheim.