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CMMs measure aerospace precision.

The ability to perform precise and detailed parts measurement is now considered to be a deciding factor in obtaining aerospace parts manufacturing contracts, according to Richard Short, quality control manager of Multax Inc, Morton, IL.

Multax is a privately owned high-tech jobshop specializing primarily in the manufacture of aircraft components for companies such as General Electric and Pratt & Whitney. Components the shop manufactures range from exotic metal rings, engine seals, fuel-tank parts, and fan blades for jet-fighter engines. The company has 20 CNC machines, supported by a workforce of 29 people.

Multiple applications

Because precision measurement has become an integral part of aerospace manufacturing, Mr Short's company is in the midst of adding a wide range of computer integrated measurement systems to its arsenal of manufacturing data acquisition tools. This began in Dec 1989 with the acquisition of a Xcel Direct Computer Controlled (DCC) CMM manufactured by Brown & Sharpe. The Xcel, capable of capturing data at rates to 60 points-per-minute (ppm), has double or tripled measurement capability throughput over the company's manual CMMs.

Multax is using a variety of Brown & Sharpe software packages for best-fit curve analysis of sculptured parts, to monitor processes, share data shop-wide among CAD/CAM, and develop reverse engineering capabilities. "Our intention," says Mr Short, is to work towards becoming a paperless shop."

Though the Xcel system was warranted to have a volumetric accuracy of 18 microns, Mr Short was pleased to find that when the system was calibrated in his shop, the volumetric accuracy was actually 12 microns. Repeatability was fine-tuned in the shop to within 2 microns over the full travel of the machine.

Beyond the conventional

Initially, Multax has used the system for inspection of parts using the basic geometric dimensioning and tolerancing capabilities of the CMM software. However, rather than use the system to inspect more parts per unit of time, Multax has chosen to do a more thorough inspection in the same amount of time. With rings, the company used to perform eight point checks on diameter. Now it does 16 point checks on five diameters to significantly increase the degree of confidence its customers have in the manufactured part.

While traditional inspection represents the bulk of work currently performed on the Xcel, there are also a number of value-added applications for which the DCC CMM is used. They include:

100% inspection. Of the 30 different jobs currently inspected, five are programmed for 100% inspection. Mr Short said that when the CMM is not being used for something else, these jobs are almost always available--making for near complete utilization of the equipment.

Fan blades. One of the major problems with measuring a contoured surface is actually zeroing in on the portion of the surface that is represented as a curve to be measured on the drawing. Brown & Sharpe's contour measurement software does this with an iterative best-fit analysis of six points that makes it possible to find the appropriate alignment on a free-standing part and compare it to the nominal downloaded from CAD.

Data points are taken every 0.5" over a 12" x 12" area (576 points in all). Using these points, the software creates a contour that can be compared to the drawing specifications. This capability allows Multax to measure contoured parts rapidly and with excellent precision. It has also given Multax an opportunity to perform high-volume contract inspection of jet-engine fan blades.

Special processes. Its CMM has become an integral part of the process for manufacturing a large thin-walled honey-comb seal used in a jet engine. The workpiece is supplied as a 23" near net shape Inconel rolled ring approximately 0.125" thick. When it has been completed, the part is approximately 0.0625" at its thinnest section. The dimensions of features turned on the ring have to be controlled to + or - 0.001".

The challenge is not with holding these tolerances, but with controlling the stretch created by the pressure of the chuck jaws. Multax has developed a process in which the seal is measured when received on the CMM for out-of-roundness and size of five diameters. By using statistical analysis an accurate amount of stretch is calculated and used during the finish operation.

Multax has refined this delicate process so that less than 2% of the parts are out of print. This is considered to be an excellent manufacturing yield for a workpiece that costs $500 before it ever sees a machine tool.

Reducing scrap. In one proprietary manufacturing process, Multax must deal with a single workpiece worth over $100,000. Mr Short said that in order to acquire that kind of work, the customer must have confidence in the shop's ability to control its manufacturing processes. Expertise in using the DCC CMM is an important factor that enters into the decision.

What has the DCC CMM done for Multax's sales? According to Mr Short: When we go after a job, the DCC CMM is part of the capability we present to our customer. It's more than the fact that we own a good one, but that we have acquired considerable expertise in using it."

For more information from Brown & Sharpe, Precision Park, North Kingstown, RI, circle 283.

Intrinsically accurate "L"-bridge CMMs

Helmel Engineering's Microstar Model 850-401 DCC has a measuring range of 50" x 40" and features a dual "L" Bridge construction, all precision mechanical bearing movement, brushless non-contact balanced linear-motor drives, and the company's Geomatic motion-control system with Geomet 300 software.

Said to be unique among large CMMs, the Microstar is constructed with intrinsic mechanical accuracy, and does not require computerized error compensation to operate accurately. Actual performance of the machine shipped is 0.0008" volumetric, with linear bandwidth accuracies of 0.0004", 0.0005", and 0.0002" in X, Y, and Z respectively. The system provides a maximum travel speed of 600"/min in each axis, or 1200"/min on the diagonal.

Helmel Engineering Products Inc, Niagara Falls, NY, circle 284.

Z-axis added

Acu-Gage Systems has introduced a Z-axis measurement option for their single-axis and two-axis measuring machines. Large platform, low-profile parts can now be inspected and measured on Acu-Gage CMMs. Full CNC operation of all three axes is available as well as video-based edge detection and SPC. Available in sizes from 12" x 12" to 36" x 48" with 4" Z measuring travel standard.

Acu-Gage Systems, a division of Ocean Industries Inc, Manchester, NH, circle 287.

High throughput CMMs

Brown & Sharpe's UHA Series CMMs (in configurations for the US and European markets) provides an overall improvement in accuracy of about 30% over previous models.

Capable of throughputs to 96 linear measurements per minute, Xcel UHA series machines boast B-89 volumetric accuracy of 8 to 13 microns, depending on machine size. In addition, resolution has been improved from 0.5.micron to 0.1 micron.

The Xcel UHA CMMs feature two advanced compensation systems: Applied Geometric Compensation (AGC) and Geometric Temperature Compensation (GTC). The latter is a firmware-resident program that compensates for changes in various machine structures due to small changes in ambient temperature. With manual GTC, an operator keys in the part temperature, the air temperature, and coefficient of thermal expansion of the part when making a measurement. The system then applies a correction factor for thermal changes in both the machine and part.

Brown & Sharpe Manufacturing Co, North Kingstown, RI, circle 285.

Shop floor CMMs

The Zeiss SMC is a factory hardened, shop-floor CMM with measuring features well suited for automated car body assembly lines and other large manufactured parts. The SMC can replace fixed gages previously used for quality assurance in the automotive industry with the flexibility offered by CMMs.

For protection on the shop floor, all guideways are covered on the new air bearing horizontal-arm CMMs. The machines maintain accuracy over a wide temperature range, due primarily to the use of Coated Aging Resistant Aluminum Technology (CARAT) materials in the column and arm. Measuring uncertainty is approximately 0.05 mm over a measured length of 1.0 m.

Carl Zeiss Inc, IMT Div, Minneapolis, MN, circle 286.

Scanning probes for CMMs

Renishaw Inc says its OP5M laser scanning probes can transform CMMs into speed readers." Designed for high-speed scanning and data acquisition--particularly of profiles and surface geometries--the non-contact probe can take in excess of 2000 readings per second on a suitable CMM. It provides resolution to 2.5 microns, accuracy typically better than 25 microns, and repeatability of 5 microns.

The OP5M's fast scanning capability offers major productivity advantages over touch probing for contoured parts, such as automotive body panels, that involve taking hundreds of data points. Scanning also permits rapid reverse engineering solutions for design studios and model shops in digitizing of models, prototypes, or actual parts where drawings are unavailable.

Renishaw Inc, Schaumburg, IL, circle 288.

Low-cost CMMs

DEA's Swift CMMs are described as low-cost alternatives to the many gages and fixtures they can replace and are available as ready-to-run packages with CNC control, probe, reference sphere, color printer, full measuring software and training.

Its three-axis bench-top machine has a measuring volume of 16" in X, 20" in Y, and 13" in Z-axis. Constructed primarily from aluminum, it has a B-89 volumetric measuring performance of 0.00036".

Each Swift CMM undergoes a total geometric accuracy check of 21 parameters utilizing "AGGIO," a computer-driven inspection and certification program to update its software map for self-calibration of machines covering the full measuring volume of the machine before dispatch.

DEA Company, Livonia, MI, circle 289.

Six-axis CMM design for shop floor

Gidding & Lewis' Pegasus includes an integral environmental enclosure; a dynamic vibration isolation system; automatic temperature compensation; a stress-free, all-aluminum moving structure; and highly stiff porous media air bearings. It can also be configured for off-line part queuing and loading mechanisms, or integration into a flexible manufacturing system or cell.

The Pegasus H-15 has a measuring volume of over 1 m and a measuring range of 1.5 m x 1.0 m x 0.75 m (60" x 40" x 30") with a 915 mm (36") rotary table capable of handling work loads to 4.500 kg (10,000 lb).

Readout resolution of the machine is one micron (optionally one-tenth micron) and 0.5 arc seconds for the rotary table. Accuracies per B-89.1.12M for four-axis machines start at five microns 0.000211) linears and 14 microns 0.000611) for volumetrics. Maximum per-axis velocity for the linear axes is 636 mm/sec (25"/sec) and 36 deg/sec for the rotary table.

Giddings & Lewis Inc, Lac, WI, circle 290.
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Title Annotation:coordinate measuring machines
Publication:Tooling & Production
Date:Jun 1, 1992
Words:1752
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