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Flexible gaging for flexible manufacturing.

The four-million sq-ft Saturn plant in Spring Hill, TN, has been described as an everything-under-one-roof plant. It has been purposely designed for maximum efficiency around the concept that the shortest distance between the materials' point of receipt and their use is the most efficient plant floor configuration.

On the plant floor, flexible manufacturing methods allow further efficiencies. For example, both the base single-overhead-cam engine and the high performance double-overhead-cam engine are assembled side-by-side. Also, automatic transmissions are built on the same assembly line as manual transmissions.

This flexibility, engineered into the basic design of the engine and transmission manufacturing plant, is key to Saturn's strategy of producing high-quality cars at competitive prices.

Flexibility is the key

Transmissions are machined and assembled in Saturn's 1.1 million sq-ft Powertrain Building. There, Edmunds postprocess transmission-hub and gear-feedback gages are used in two separate manufacturing applications. One application is the green turning operation; the other is the finish grinding operation.

In the green turning operation, raw forgings for transmission gears and hubs are conveyed by an automatic material-handling system to Mitsubishi TSA and T8A turning centers. After initial turning, the materials-handling system transfers the part to gages, where up to nine critical lengths and diameters are automatically measured on hubs, and up to five checks are made on gears. As real-time data is collected by the gaging system, it is transmitted electronically to the machine telling it to compensate for any deviation from preset control limits.

Heald Centernal and Cenaxis multi-surface grinders are used to grind both the face and the bores of the transmission gears at the same time-- another procedure that improves plant efficiency. After grinding, the material-handling system transfers the gear to the Edmunds gage, where up to five critical ODs, IDs, and lengths are measured. The information is transmitted back to the grinder where necessary changes in the operation, such as infeed rate and compensation for wheel wear, are made automatically through the grinder's computerized control system.

There are three different clutch hubs for automatic transmissions, so Saturn uses a cellular manufacturing approach. Each cell uses a dedicated gaging system, 11 in all.

In the gear area, Saturn uses a combination approach. For green, unhardened gears, a line method is used. In hard gears, the finish grinding operation, each grinder function as a dedicated unit. There are 20 postprocess-feedback gaging systems in the gear area, running in both the line and individual operations. Saturn also uses 11 additional postprocess-feedback gages and 28 off-line audit gages in operation.

Each turning center and grinder in the gear area is set up to run three or four different parts. Modular interchangeable tooling used in the Edmunds gaging system helps make this flexibility possible.

"We're set up to run 32 different parts over 10 different lines, so changeover time and ease of changeover become critical," says Ned Roberts, Saturn manufacturing engineer. "We have a 30-minute changeover window that we have to meet on the machines, and the gage systems meet this requirement very nicely."

Quality and efficiency improved

"Total gage repeatability and reproducibility, when you apply an ANOVA overpackage, has to be less than 30 percent of tolerance for us to achieve the quality levels we want," said Jerry Krull, Saturn quality point person. "The ANOVA package considers stability, accuracy, and linearity along with repeatability and reproductibility. In fact we use it as a selection criterion when picking a gage supplier."

The transmission hub and gear gage communicates with the turning centers and grinders through a computer-aided gaging (CAG) system. CAG is Edmunds own microprocessors-based system designed to report dimensional measurement and data accumulation for real-time instant inspection. The CAG system uses modular structured software and is reprogrammable by the operator to handle dimensional tolerance and size changes.

At Saturn, the gages not only communicate with the production machines, but also, via CAG, with a plantwide computer network called the Manufacturing Planning Management (MPM) system. Data stored in this system is used in quality analysis, such as trending, X-bar, R-charts, and control-chart studies.

"In the hub area, we have a 2500-part buffer in the gages that lets us run approximately three days before the buffer is completely filled," said Mr Roberts. "This stored data is then sent to the MPM system for analysis."

In the gear area, because tooling is changed on a daily basis, inspection data is captured and stored daily on a disk for later analysis.

Analysis is used primarily to make changes in compensation rates, particularly in the turning operation. "The lathe control system is programmed to compensate a specific amount when it receives a signal from the gaging system," said Mr Krull. "The gage may say to compensate 20 microns, for example, but the lathe is set to compensate seven microns. I analyze the date in the MPM system and make changes to machine programming accordingly."

Stored data is also used to adjust the number of parts gaged before the compensation signal is sent to the machine. For example, does the system look at one part, or take an average of three or four? "Sometimes you may not want 100% compensation," Mr Krull said. "You may only want to compensate 80% or 75%, or you might want to compensate 125%. Analyzing date helps us make these decisions. It's how we make changes that constantly improves our process."

Team purchasing

At Saturn Corp, workers aren't called employees, they're called team members. As team members, they're responsible for product quality. They're also responsible for purchasing the equipment that will help them reach their quality goals.

The purchasing team for gages was composed of manufacturing engineers, product engineers, operator technicians, electrical technicians, and executive management.

"We looked at the durability of the gages, whether they could perform in a high-volume production environment with little maintenance. We looked at gage repeatability, accuracy over time, and ease of repair. Also, the gages had to be flexible enough to move from one application to another," said Bill Diamond, senior manufacturing engineer.

Messrs Roberts and Krull were also members of the purchasing team. "I think it's important that operators participate in the purchasing process," Mr Roberts said. "Because of the nature of Saturn Corp, it's a lot easier for the operator, electrical technicians, and mechanical technicians to be involved in the process from the beginning. They learned things during the purchasing process that improved our manufacturing processes."

For more information from Edmunds Gages, Farmington, CT, circle 299.

Programmed measurement

Brown & Sharpe Mfg Co's Digi-Hite Plus electronic height gage features programmed routines to speed up and simplify complex measuring functions. The height gage has an accuracy, repeatability, and resolution to 0.0001" (0.002 mm) over its full 24" range.

The gage automatically calculates measurement dimensions to save time and ensure accuracy. The tool determines the gage-head constant to minimize setup times. Programmed routines can be engaged by simply pressing a button, thus eliminating time-consuming manual operations.

The gage automatically calculates center-to-center distances from grooves, holes, studs, and other given features on a work piece. A floating-zero program establishes zero at any point, with all future measurements automatically calculated from the zero reference. The Indirect Reference Program enables numerical values to be entered for reference planes that cannot be directly contacted by the probe. Digi-Hite Plus can then measure distances from the indirect reference to any surface of the workpiece.

An interactive LC display shows numerical values, selected program, and signals the measurement function being performed. The display also alerts the user to errors, low batter power, and whether the tool is in memory mode.

The gage operates for up to 25 hours of continuous use with an rechargeable battery pack. RS-232 output sends measurement data directly to computers and printers for analysis and documentation. The universal gage can be used as a height gage, transfer gage, or scriber for the quality assurance lab, inspection department, or at the machine.

Brown & Sharpe Mfg Co, North Kingston, RI, circle 300.

Economy priced digital gage

The L S Starrett Co's 752 Digital Electronic Height Gage series is designed to provide versatile, economical solutions for most standard height measurement applications. The series includes three models with maximum measuring ranges of 12", 18", and 24" (300 mm, 450 mm, and 600 mm).

The gages offer two separate reading modes: a large, easy-to-read LCD display with a readabout resolution of 0.0005" (0.005 mm), and a graduated scale 0.05" (1 mm) increments on the gage column for fast readings when less precision is required. The gage features a battery life of more than one year and is equipped with an automatic shutoff.

All models within the series feature an interface port for SPC analysis, data collection, and hard-copy documentation. Also, all models can be easily linked to other Starrett peripherals, such as data-collection systems, multiplexers, SPC processors, and printers.

L S Starrett Co. Athol, MA, circle 301.

Laser speeds gage block measurement

A new laser-based height gage from Federal Products is now available for direct measurement of gage blocks. Eliminating the need to compare each block to a master, the system greatly improves speed and accuracy of gage block measurements.

A high accuracy, long-range measurement system, the Laser Interferometer Height Gage allows measurement of gage blocks and master balls with resolutions of 0.1"/0.002 [Mu]m over a 5" working range. By generating a beam of an exactly known wavelength, the laser-based system provides its own measurement standard. This eliminates the need to maintain master standards for each block size, as well as eliminating the related costs of calibration and documentation.

The system consists of a heavy cast base for mechanical and thermal stability, a laser source and interferometer for measurement, a carriage for transporting the upper measuring contact, a lower contact for establishing the true point-to-point dimension of a gage block, and staging for the parts.

A desktop computer acts as both controller and display, incorporating three modes of operation: absolute mode, which reads the absolute measure of the block rather than its deviation from a nominal value; set points mode, which shows absolute measure of the block as compensated by using two gage blocks as limits settings; and comparative mode, which duplicates present gage-block measurement.

Federal Products Co, Providence, RI, circle 302.

Remote measurement

A precision height-measurement gage that floats on an air cushion and features resolution up to 0.1 micron has been introduced by Mauser. The new V5 includes such features as an infrared connection to the control system, a motorized and inductive probe, nine measurement functions, a teach function, complete statistical analysis, and storage of up to 22,600 measurements.

The gage is described as an independent unit with its own set of interchangeable accumulators and a unique infrared connection system. This eliminates the need for cabling, which leaves the area around the gage free from entanglements. The operator can issue commands and program instructions within a 6.5 ft radius.

The gage's air cushion, which uses an air pump built into the base, allows easy movement over the surface plate. A motorized probe provides constant and precise positioning, while an inductive probe automatically checks perpendicularity and uses this information for two axes calculations.

Depending upon the model, the V5 series gages have a maximum height capacity from 23" to 63". The operator selects from four resolution levels, including 0.1 micron, 0.5 micron, 1.0 micron, and 5.0 micron.

Fully programmable, the V5 can handle up to 50 programs, with a storage capacity of 100 steps each, and 22,600 measurements can be stored in association with these programs. In an off program mode, the last 100 measurements on each axis are stored.

French Technology Press Office, Chicago, IL, circle 303.

Measuring circular geometry

Expanding upon the capabilities of the Formscan circular geometry gage, the Model 3300 also measures cylindricity, vertical straightness, parallelism, and cylindrical co-axiality.

The system features touch-screen controls and color graphics. Formscan 3300 consists of a rugged instrumentation console that houses a precision air-bearing rotary table imbedded in a granite surface plate for increased stability. Computer-aided tilt/centering also helps reduce setup time and increase accuracy.

Part positioning is aided by the unit's air-bearing precision vertical slide, motorized on both the vertical and horizontal axes to provide smooth motion for increased accuracy and repeatability. When the stand is moved information is instantly updated by the system computer.

The gages have multiple measurement capabilities for roundness and related geometry analysis, including measurement of out-of-roundness, concentricity, circular waviness, squareness and axial runout, and circular parallelism of the top and bottom flange faces, delta radius/delta angle and slope analysis, as well as harmonic analysis.

Federal Products Co, Providence, RI, circle 307.
COPYRIGHT 1992 Nelson Publishing
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Copyright 1992 Gale, Cengage Learning. All rights reserved.

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Title Annotation:Quality Solutions
Publication:Tooling & Production
Date:Sep 1, 1992
Words:2112
Previous Article:Flexible systems go with the flow.
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