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 multi-station 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/Al203/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, profiling, 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. Rafi 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.
While the versatility and precision of the HeliGrip tools makes it a good choice for complex turning applications, it does have limits. "This tool is very efficient for groove/turn applications. You're using one tool instead of two or three," says Alex Bartan from Iscar's technical information department. "But be careful not to use it as a cure all for every application. For regular shoulder turning and longitudinal turning, the HeliGrip may not be worth the cost when regular tools will work just as well."
Made in various widths and grades, the HeliGrip inserts are also available with different coatings, and as custom-designed special tools.
The Systems Approach
Working along this same philosophy is the MDT system from Carboloy, Inc. (Detroit, MI). With this system, each insert/holder combination forms an integrated system that can groove, perform left- and right-hand side turning, profiling, facing, and parting off. According to Carboloy, what makes the tool unique are serrations on the bottom of the insert and the insert pocket in the toolholder. What they do is provide more secure insert retention, enabling deeper cuts and enhanced resistance to high cutting forces.
One company has been using the system to turn piston spools. All OD turning is performed using only two tools. One for roughing, the other for finishing. The first tool faces off the part, then cuts the OD grooves in the plunge roughing cycle. After this, the profile is finished with the second tool. Six or seven completely machined parts are turned out per hour. This almost quadruples the company's previous output, and the need for secondary hand polishing has been eliminated.
The MDT system is available in both inch and metric sizes, and in single- and double-ended versions. The single-ended version provides a reach of five times the insert width, while the double-ended version reaches to three times its width. For stainless steel, cast iron, and high-temperature alloy materials, the CP50 PVD-coated grade is available, as is the TP200 general-purpose grade for most other materials.
Valve Manufacturer Retools for Improved Throughput
As materials go, ductile iron, cast iron, and cast steel can be difficult to machine. For one thing, scale on the castings can tear apart the cutting edge of a tool before it ever gets to cut metal. For another, the hardness and machinability of the core material can vary within the batch, let alone from batch to batch or material to material. This leaves the machinist with the annoyance of resetting the machine often, sometimes from part to part. It's further complicated in structures where all of these materials are being used in part production.
Machinists at Orbit Machining Co. (Franklin Park, IL) faced this problem every day. In particular, was a job machining valve parts that demanded tight tolerances on dimension and finish. Machining the part required various rough and finish turning operations. Between the 0° angle of presentation, and the amount of scale on the casting's exterior, the rough turning tools were damaged often enough that stoppages for edge change were cutting into throughput.
The situation was further complicated by Orbit's machining method. To shorten cycle time, some of the turning is done in the four-axis mode, with two tools working simultaneously, one following the other through a cut. "Four-axis turning has been one of our `little secrets,'" says Orbit's president George Zarytsky. "But it pays off only if you have a dependable edge." If the lead tool went dull or broke (which it often did), the following tool would be overloaded. This caused parts to be out of tolerance, and left the tool with a very short life.
So Zarytsky set out to improve tool life and performance. Tom Williamson from Sandvik Coromant (Fair Lawn, NJ) looked at the situation and concluded that this part, and most of the other valve parts, could be handled with just four insert grades. Before committing to this solution, Orbit ran some test with the new inserts. Running some of the valve's parts at standard speed showed that the Sandvik inserts outlasted the old inserts by about 50%.
Based on these test results, Orbit standardized on four Sandvik inserts for all of the valve turning applications. The GC3015 and GC4015 are used for all cast iron roughing, the GC4025 is used for roughing and finishing cast steel, and the CT 5015 is used for finishing on the ductile iron.
According to Williamson, the GC3015 is an effective tool for finishing and light roughing of low and high-tensile iron, malleable iron, and nodular cast iron. The GC4015 offers smooth and accurate chip flow in axial and radial turning and chamfering applications using cast iron. The GC 40125, with its single-sided positive cutting geometry, also features edge security and low cutting forces. It is recommended for medium roughing and finishing of steel. Lastly, the CT5015 is a wear-resistant grade for finishing abrasive materials. It is especially effective in applications where high surface quality and low cutting forces are required.
With all of the inserts, the carbide substrate is tougher at the core and harder at the edges than previous substrates. Also, their top face geometry creates a positive rake edge presentation which lowers cutting forces.
When the company started full-scale use of the insert package, throughput improved 10%, and the average edge life more than doubled.
Standardizing the tooling for the valve job has led Zarytsky to consider standardizing all tooling with one manufacturer. "It will take training, and some rethinking, but it will be worth it," he concludes.