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CMM cuts measurement time by 24:1 ratio.

CMM cuts measurement times by 24:1 ratio

Average inspections of aircraft structural parts now take only a few hours, rather than a few days.

Manual measuring tools such as height gages no longer satisfy Arden Engineering. Specializing in machining of aircraft structural parts, this Orange, CA, job shop now uses a coordinate measuring machine (CMM) to increase production and achieve consistent measurements.

Until a few years ago, the company determined part accuracies primarily by height gages and standard micrometers. Although these traditional, manual tools are accurate, their use consumes a lot of time. Thus they are inefficient for companies making parts in large quantities.

To speed their gaging, Arden investigated ways to improve efficiency through use of up-to-date equipment and methods, primarily CMMs. In looking at them, the company based its evaluation on three criteria:

1. Ability to achieve accurate and repeatable measurements at high rates of throughput.

2. Ease of operation, and

3. Accuracy in measuring small parts as well as large.

After shopping the market, Arden chose a 48" x 80" x 36" Dual Beam CMM and Unimeasure [R] computer system from Numerex Corp, Minneapolis, MN. The equipment and software were installed in 1988.

"With the CMM, we've cut labor costs and boosted production by reducing part inspection time from several days to only a few hours," says Mike Stow, vice-president at Arden. "In fact, part programs for the CMM can be developed in a matter of hours, right off the part's tooling points."

Since the CMM and its computer system were installed, Arden quality-control (QC) personnel have used them every day, for many phases of part inspection. The staff credits the machine with a sizeable increase in throughput and an increased achievement of accurate and repeatable measurements.

Tighter specs

The parts Arden manufactures are designed and machined to customer specs from a variety of materials. These include aluminum, titanium, stainless steel, magnesium, and alloy steels. Specified tolerances range from 0.010" to 0.000 50".

To meet these requirements, strict QC techniques must be maintained throughout the manufacturing process. During the past few years, the margin for error has steadily decreased. As a result, problems associated with accurately measuring and maintaining tight tolerances have grown more acute.

Arden's Dual Beam CMM has graphite components that offer rigidity and stability needed for precise measurement. The machine provides linear accuracy to 0.000 50" in the X axis, 0.000 60" in Y, and 0.000 30" in Z.

Further, the ceramic construction of the Z-axis shaft provides high thermal stability. This makes the shaft virtually immune to changes in temperature and humidity--factors crucial to measurement accuracy.

An advantage

Even though Arden selected a large CMM, recent technical advances allow machines of this size to measure small parts as precisely as much smaller CMMs. Consequently the company can accurately measure all parts it manufactures--small as well as large--on the same machine.

Today, parts made at Arden are inspected on the CMM by QC personnel during first-article, in-process, and final inspections. The CMM's ability to accurately check the same point on every part is a real advantage over variable, manual measurement methods.

Because the CMM is programmed to automatically measure parts according to customer specs, it has reduced the potential for costly manufacturing errors caused by inaccuracies and inconsistencies in manual inspection and data entry. If a part doesn't meet dimensional specs, the CMM allows Arden's engineers to quickly spot the error and correct the process.

Typically, when Arden receives a contract for a part, the first step is process planning. This is supplemented by the QC manager's determination of inspection points, and decisions concerning processes to be performed outside (e.g., heat-treating or finishing).

Also involved in process planning are the company's tooling, CAD/CAM, and NC programming personnel. Programmers enter part dimensions and specs into a CAD file, which offers 3-D part definitions.

After production of hard tooling, prototype parts are machined and inspected on the CMM. QC personnel check all machined points to ensure their measurements match those on the part blueprint.

Eventually, measurement specs gathered on the CMM are analyzed. Any corrections required are incorporated into the NC program to ensure accurate machining. Only after completion of first-article inspection are NC programs released to the shop for production runs.

DCC a plus

CMMs are available as manually operated or direct computer controlled (DCC) systems. Though each version offers benefits of increased quality and reduced inspection time, Arden chose the DCC system for its programming capability.

"The DCC CMM is extremely capable at inspecting locations, sizes of bores, and the like," says Mike Stow. When it comes to inspecting thickness dimensions, only one programmed point need be checked to achieve one reading. Once a part's parameters have been plotted, it's easy to precheck the same part throughout the entire production process."

Using Numerex's Unimeasure software, Arden's QC manager develops a seperate program for in-process inspections on the CMM. This program is based on the customer's part specs.

Independence of the inspection program from the NC machining program is an important check and balance. It makes sure parts are not inspected according to erroneously programmed specs.

Arden's engineers are able to perform true 3-D alignment, geometric tolerancing, and SPC, in addition to both on-line and off-line programming and editing. Inspection programs can be created on-line through a part's tooling points, or off-line by entering X, Y, and Z values manually. Parts also can be measured without use of a program.

According to Stow, developing new programs for the CMM is so easy that company QC personnel often wait to develop inspection programs until the part comes off a machine tool. And, since the CMM has a large-area granite base, several different parts can be set up at one time.

"The CMM is another extension of our ability to offer a good final product," says Stow. "Our customer can be assured we've gone through all the proper QC steps."

PHOTO : An Arden inspector uses a Dual Beam CMM to measure points on a part for a fan reverser, a

PHOTO : component used in jet engines.

PHOTO : Arden's CAD/CAM programmers define parts in 3-D. NC programs generated on the computer

PHOTO : system are downloaded to machine-tool CNCs.

PHOTO : This machine operator works with Arden's QC personnel during the first-article inspection

PHOTO : stage. Data gathered from the CMM are entered into the NC program to ensure correct

PHOTO : machining during production runs.
COPYRIGHT 1990 Nelson Publishing
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Copyright 1990 Gale, Cengage Learning. All rights reserved.

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Title Annotation:coordinate measuring machine
Publication:Tooling & Production
Date:Mar 1, 1990
Previous Article:Maybe you CAM, maybe you CANC: time to get serious about using low-end, low-cost CAM to off-line program your growing army of NC machines.
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