Printer Friendly

Small but fast tools get new machine.

Developments in materials technology for cutting tools including coated carbides, PCD (polycrystalline diamond), and CBN (cubic boron nitride) materials have sparked interest in machining with small diameter tools, primarily end mills made from these materials.

Typically, though, development of the cutting tools has run ahead of developments in the machine tools to handle them. That's changing as Tree Machine Tool, Racine, WI, working with one of its customers, Key Cutting Tools Inc, Milwaukee, WI, developed a high-speed milling machine, the Journeyman 325 HSS ultra speed mill, for machining such materials as composites, plastics, graphite, aluminum, stainless steel, and superalloys.

Demand for high performance CNC mills has grown due to the proliferation of applications brought about by the growth in die-casting, injection-molding, and vacuum-forming industries. The technology in these processes has progressed to a point where it allows casting or molding very tiny and intricate features into components. These features must be first machined into the dies and molds needed to produce them.

A second force driving this demand involves the growing, widespread use of materials that have high strength-to-weight ratios. Materials such as plastics, fiber-reinforced composites, super alloys, and a variety of aluminum alloys require machining at higher tool surface speeds to produce required surface finishes, dimensional specifications, and provide affordable tool life economics.

"Obviously, the need for cutting at higher surface speeds translates into higher machine spindle rpms, often as high as 50,000 rpm," explains Jeff Dei of Key Cutting Tools. "Typically, the CNC mills available in the past had a top spindle speed of 6000 rpm. When this limitation is imposed on these machining operations, the results are disastrous."

The crux of the problem has to do with heat build-up that occurs when machining takes place at surface speeds below the recommended levels, he says. "In these situations, the heat that is generated during the cut is mostly retained in the cutter and the workpiece. This results in poor surface finish and extremely short tool life. When the cutting speed can be increased to acceptable levels, most of the heat is transferred to or retained in the chip, which, when properly evacuated, reduces the temperature in the cutting zone considerably."

But spindle speed is only one of the issues to be addressed. The other is feedrate. As spindle speed is increased, in order to maintain an acceptable chip thickness, the feedrate increases proportionately. Thus a fivefold increase in spindle speed results in a corresponding fivefold increase in feedrate. Frequently, these feedrates reach 150 ipm, which even exceeds the rapid traverse of many CNC mills. This, in turn, requires a machine control response rate that exceeds that of machines that are most suitable for these operations.

Tree machine's answer was to build and field test prototype machines that led to the eventual introduction of the Journeyman 325 HSS Ultraspeed mill which features two spindle choices: a 15,000 to 50,000 rpm spindle that employs an air/oil mist bearing lube system; or, for machining materials such as graphite that require a dry lube system, a grease-packed bearing spindle that has a 10,000 to 40,000 rpm range.

Spindle accuracy is 0.0001" TIR at the spindle nose. The machine's three-axis CNC control allows feedrates up to 150 ipm. Positioning accuracy is [+ or -]0.0005", and repeatability is [+ r -]0.00015". Machine travels are X,Y,Z of 27", 14", and 6" quill travel plus 11" knee travel.
COPYRIGHT 1993 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1993 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Title Annotation:High speed milling
Publication:Tooling & Production
Date:Aug 1, 1993
Previous Article:High-speed machining from solid stock.
Next Article:PC-based DNC takes off at Convair.

Related Articles
Fewer setups for smaller lots.
It takes more than a fast spindle.
High speed cutting finishes the job.
Lightning-fast mill zaps mold shop's backlog.
High speed milling.
High speed cutting ride the fast lane.
Toolholder solves distortion problem.
A spindle set-up: high-speed strategy tested by moldmaker. (Technology Update).

Terms of use | Copyright © 2016 Farlex, Inc. | Feedback | For webmasters