Printer Friendly

Gaging internal geometries.

Gaging internal geometries

Combining the strengths of old and new--proven inspection methods and modern microprocessor techniques--was the key to implementing advanced manufacturing strategies at OMC Corp's new gearcase plant in Andrews, NC. The plant produces gearcases for high-performance outboard engines. Historically, dedicated gages had offered special advantages for inspecting internal geometries of precise gearcase bores, and OMC's quality engineers wanted to stay with dedicated gaging. Yet, they wanted to strengthen their competitiveness by increasing manufacturing efficiencies and flexibility.

The solution came in building dedicated gaging systems around new microprocessor-based electronic and air/electronic columns from Sheffield Measurement, Dayton, OH. Microprocessors greatly expand the flexibility and range of functions possible with dedicated gaging systems, while making them faster, easier to operate, and more accurate, says Frank Musich, OMC quality engineer.

Andrews-plant dedicated gaging systems were custom engineered by Sheffield to new gearcase designs and installed in March, 1988 and mid '89. Each system included electronic columns, transducers, plug gages, masters, fixtures and components, and a rolling stand. This mobility allows the gaging system to be easily relocated when production shifts from one machining center to another.

Why dedicated gages?

The people at Andrews recognize that the trend in industry is to flexible inspection systems, but they felt that by combining microprocessor capabilities with dedicated and functional gaging systems they could achieve these objectives: * Higher throughput and production efficiency. Lower costs and inprocess inventories. These are achieved by enabling machine-tool operators to inspect their own work and eliminate the need and cost for a separate, post-process inspection function. * Defect prevention through direct, timely process feedback. The gaging system allows difficult, critical, internal gearcase dimensions to be taken quickly and accurately by the operator. A gearcase can be inspected in four minutes--less than the its machining time. This maximizes productivity, while providing for earliest process feedback and correction--before bad parts can be produced. * Ease of operation and training. This is a vital step toward making operators responsible for inspection as well as machining, notes Musich. Because, as a greenfield operation, they started with a workforce new to precision machining, they needed inspection routines that were simple, fast, and accurate.

For example, a special function keyboard makes the Sheffield microprocessor-based electronic columns easier to use than traditional, float-type air gages, says Donnie Griggs, machine operator and setup technician. Automatic mastering of min, max, and offset values allows 30- to 50-percent faster mastering than with column air gages. "You just put the plug into the master ring and hit the master key," explains Griggs. "You can check calibration more often and not cost yourself any time."

Make inspection fit the process

Design of an inspection system should be based on the processes used, the parts being produced, and the people performing the operations, says Musich. Whereas flexible inspection--like CMMs--work best at measuring prismatic surfaces and checking hole position, Musich's plant prefers dedicated gages for inspecting bore sizes and internal geometry, because "these features are far more likely to change in machining a gearcase than is hole position."

Dedicated gages can report actual dimensions, unlike some inspection systems that average dimensions, he notes. "In gearcases, where cylindricity is critical, averaging systems could show a part in spec and miss a bore taper or out-of-roundness condition. In the past, our hardest dimensions to check have been taper in the bore and most minimum diameter. These new gages make them a snap to check." The gage columns provide a TIR (total indicator reading) function for out-of-round detection as a standard feature.

People factors

Because most of the plant's 400 employees were new to precision machining practices and brought varying levels of skill and expertise, strong consideration was given to people factors in deciding on functional gages. To get both production and quality up to target as fast as possible, inspection needed to be quick and accurate.

This thinking led to the use of plug gages as the first test of gearcase conformity. Machined to key bore diameters, these go/no-go gages immediately signal a problem with diameter size, out-of-roundness, taper, or concentricity if the plug fails to slip into the bore. One plug gage has four diameters for testing machined accuracy and alignment of four concentric bores at one time. These bores comprise the housings for the forward and reverse gears and prop-shaft bearings.

After the fit test with plug gages, the operator uses transducer spindle gages and electronic columns to determine dimensions and tolerances for gearcase features. Management likes the way that the columns prioritize feedback information for operators, Musich stresses.

Traffic-signal type limit lights show green when dimensions are within tolerance limits, yellow if drifting beyond, and red if exceeding spec. For operator ease and recording accuracy, these colors match the plant's control charts. A 101-LED (1-percent resolution) bar graph provides analog display of a part dimension against the ideal and max/min limit pointers. This display is easier to read than floats on air columns that require operator interpolation and allow opportunity for error, and it offers two modes of readout--thermometer style or single discrete light.

A seven-digit LCD display gives a choice between actual dimensions or deviation from the ideal, in either English or metric units. Musich appreciates this feature for its ease of data collection when doing process studies. An enhanced version of the column provides storage of up to 2880 readings and real-time clock storage of first and last readings, as well as RS-232 communications port that allows application of automated SPC and part-documentation functions.

The plant people recognize the dangers of the data trap--too much data or the wrong format so that it's not usable by those who need it most. With dedicated gaging, operators get what they need quickly and directly, says Musich, and having a separate gage column for each characteristic helps isolate any process change for proper correction.

The microprocessor capabilities of the system allow simple conversion of electronic gages and columns to engineering changes. "It takes about 15 minutes to configure and set up the gages," notes Musich. "Our dedicated systems aren't fixed. They give us the essential flexibility and fast response we need to changes, while retaining ease-of-use, simplicity, and direct readout."

PHOTO : Integrated shop-floor gaging system, on a mobile 4 X 8 ft table, inspects complex internal

PHOTO : machined geometrics of outboard-engine gearcases. Four-minute inspections provide

PHOTO : immediate feedback while the next part is being machined.
COPYRIGHT 1990 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1990 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Publication:Tooling & Production
Date:Mar 1, 1990
Previous Article:Flexible cell doubles Boeing wing output.
Next Article:Turning to Deming.

Related Articles
EDM today and tomorrow.
Gaging systems take command.
Column gages - holding their own.
Measuring & inspection equipment.
Sizing up in-process gaging.
Microfinishing hard-turned parts.
Modular gaging and quality manufacturing.
In-process probing: growing in popularity, it's a powerful tool for quality control in metalworking.

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