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High-precision tools cut secondary operations.

High-precision tools cut secondary operations Combined reaming and fineboring tools perform finish machining in one pass, relying on symbiosis between the interaction of machine tools and cutting tools.

Depending on the scope of machinery involved, cutting tools comprise only 3 to 5 percent of initial capital expenditure for a new machine-tool setup. But this small investment influences 95 to 97 percent of the success of the capital outlay. To paraphrase one of Henry Ford's chief engineers: "The benefit of all manufacturing is at the cutting edge."

True precision-finish machining takes place within millionths of an inch, leaving little tolerance margin. Cutting blades and toolholders must use only a fraction of the available tolerance, so some is left for tool wear to provide extended life between sharpenings and adjustments.

Looking at precision from another angle, it is of paramount importance to provide an optimum combination of machine tool and cutting tools to run sophisticated machines untended for prolonged periods of time. In the final analysis, it is the cutting edge that determines productivity, efficiency, performance, and return on investment.

Antivibration tools Vibration has often been a problem in machining. A conventional multiflute reamer built to provide steady performance. In this early attempt at antivibration design, the cutting edges have a dual function, namely, cutting and guiding. They don't have a clearance angle, which means they don't cut material but more or less press their way through the bore. As a result, they run at limited cutting speeds from 60 to 70 sfm.

Multiflute reamers require costly, time-consuming grinding. Their performance is unpredictable, and they don't produce uniform machining. Most workpieces processed with these tools require secondary operations such as honing or roller burnishing.

For these reasons, Mapal developed the single-indexable-blade reamer, with guiding and cutting functions separated. Here, peripherally arranged guide pads provide proper guiding of the tool, while the cutting blade does what it's supposed to do exclusively--cutting.

Fineboring development

Although reamers can offset the centerline deviation between spindle and workpiece, they must be mounted in floating toolholders. This setup in itself limits machining parameters, and sets a maximum tool-rotation speed of about 1000 rpm.

Thus, Mapal engineers set out to devise a tool that could be applied at much higher speeds and feeds. They employed a single-point design following the lines of the conventional boring bar, but with improvements.

In traditional design, the cutting force transfers to the machine spindle, tending to bend the bar and cause vibration. To reduce deflection forces, users had to keep cutter radii small, resulting in low feedrates per revolution. Unfortunately, boring bars must operate at high feed rates to be efficient, forcing blades to take long cuts at the cost of substantially reduced tool life.

Now, if we design a tool that is meant to cut as a boring bar, but is built as a Mapal reamer, we obtain a fineboring tool offering stable cutting geometry and good vibration absorption, resulting in high machining data and high-precision cutting.

Deflecting cutting forces are absorbed by the guide pads, eliminating vibration, and the configuration can include a stable secondary cutting edge. The new geometry ensures better cutting consistency, longer tool life, and much higher speeds and feedrates.

One pass

The new tool allows more complete machining. It can fine cut and finish machine several diameters, surfaces, bore transitions, and chamfers in one pass. And it can take advantage of today's CNC machines that run at speeds well over 3000 to 5000 rpm. It maximizes performance in new materials capable of machining at higher speeds then even before. It also handles the wide variety of materials now chosen for specific machining tasks.

For example, the lead photograph depects critical machining of crankshaft bores. The free-standing tool shown has a length-to-diameter ratio of 10:1, operating without bushing support. It employs several guide pads on the periphery, and its body is "heavy metal" with high tungsten content.

An ABS shank and locking system holds the tool in the spindle, and an adapter provides radial adjustment between machine spindle and tool to compensate for spindle runout. Surface finish is 60 rms, and straightness is held to 12 micrometers.

The fineboring tool is part of an overall tooling system. A shorter tool premachines a chamfer on the first journal before entry of the long bar to eliminate tool deflection at the beginning of the cut. And, after the operation shown, a third fineboring tool finish-machines all journals in one pass. In case of a six-cylinder engine, there are seven journals being machined from one side. Camshaft bores are being machined equally well with this method.

Complete machining of parallel multistep bores in one pass is performed by the tool. It handles bore transitions and outer facing operations, with emphasis on producing large quantities of pump housings of consistent quality.

The disk-type tool body has several smaller built-in tool bodies in a planetary configuration to provide several different machining jobs in one sequence. A polycrystalline diamond cutting blade consistently produces 5000 parts of the same quality and 8 rms surface finish. Stock removed is 1 mm on the diameter, and cutting speed ranges between 300 and 1000 sfm.

In summary, fineboring tools work well with new machine-tool spindles that run faster than ever before, cutting new materials more economically. The high-precision tools are designed to solve problems for specific manufacturing processes and machining tasks. They cut machining time, reduce the number of tools needed for each job, increase productivity, enhance quality, and often eliminate secondary machining operations. For automation, they offer predictable tool life and consistent performance.

PHOTO : In crankshaft-bore operation, the tool rotates at 1000 rpm to cut cast iron at 644-sfm,

PHOTO : 0.0079 ipr. Bores are 69.85 mm dia, plus or minus 0.01 mm.

PHOTO : This tool performs complete machining of multistep parallel bores in one pass, coping with

PHOTO : bore transitions and outer facing operations.
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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Title Annotation:reaming and fineboring tools
Author:Erdel, Bert P.
Publication:Tooling & Production
Date:Jul 1, 1989
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