SPLITTING HAIRS

Ultra-fine shaped wire, frequently one-tenth the thickness of a typical human hair, is the basis of critical components in applications ranging from aerospace and integrated circuits to automotive and, especially, medical instruments.

Minute defects in such wire can crash a supercomputer or lead to life-threatening complications in micro-surgery. With life literally hanging by a thread, this micro-thin wire must meet exact tolerances and specifications. Manufacturers seeking ultra-fine wire, some invisible to the naked eye, frequently find their search ends at the door of California Fine Wire Company (CFW), located in Grover Beach, CA.

CFW has been producing fine wire since 1961 for more than 7,000 customers worldwide. The lion's share of the company's manufacturing is done for medical device OEMs who require micro-thin wire drawn to fine diameters and shapes from hundreds of metals and alloys including stainless steel, aluminum, copper, nickel, nitinol and other precious metals.

Wire manufacturing operations include drawing, plating, straightening, cutting, annealing, enameling, respooling, shaping, cables, stranding, brazing, and soldering alloys, clad and composite wire.

Coatings include Teflon, Formvar, ISO medical polyurethane, polyamide and various plating coatings such as nickel, gold and tin. CFW supplies fine shaped wire in quantities as small as 50 ft and as large as 300,000 ft, but the average order falls between 1,000 and 2,000 ft. The company operates 24-hours-per-day, five days per week.

CFW-produced wire is used in applications such as cochlear hearing implants, heart probes and telemetry devices. Medical OEMs use fine wire to make microsurgical catheters and the tools attached to them. They use ribbon-shaped wire to make the outer shape of the catheter, winding the ribbon on an edge to make it extremely flexible, so it's easier to maneuver inside the human body's cardiovascular system.

Generally speaking, shaped fine wire does not have a round cross-section, the "normal" form in which it is drawn. Shaped fine wire may be square or rectangular with rounded corners, hexagonal or a variety of other geometric possibilities, including ribbon.

The shape specified can relate to a broad range of requirements, such as current carrying capacity, flexibility, corrosion resistance and temperature-related characteristics. Most of these properties also relate to metals and other materials from which the wire is made.

LET'S GET SMALL
While the ultra-fine shaped wire may itself be one-tenth the thickness of a human hair, the dimensional tolerances of its features are measured in millionths of an inch, at the threshold of the nanometer world.

"Our internal standards include tolerances that are within 0.000025 in. Not very many instruments can even make such a measurement," says Mike Greenelsh, the president of CFW.

It's no surprise that quality control is a high priority for this company, both in the inspection of raw materials and the final wire product. California Fine Wire's quality management system is certified to the ISO 9001-2000 standard, conforming to the latest benchmarks for quality systems, management, resources and realization. Although manufacturing at the Six Sigma quality level (fewer than 3.4 defects per million parts) for more than three decades, the company views ISO certification as integral to maintaining and improving its internal quality processes.

"I feel that ISO certification is an important benefit to our customers as well as our company, because it reinforces individual responsibility throughout manufacturing operations," states Greenelsh. "Before QC even looks at a product, it has got to be in perfect condition, meeting the very high standard that we have already set."

When it comes to shaping fine and ultra-fine wire from material with dimensions in thousandths of an inch, producing consistent quality is challenging. Products made from shaped fine wire normally require Five to Six Sigma consistency and ultra close tolerances.

"CHEK-ING" OUT A PROBLEM
"Meeting our customers exacting specifications means measuring tolerances that stretch the capabilities of inspection devices," notes Jorge Jacobs, a quality assurance technician at CFW.

For example, Jacobs describes a job that begins with a bare wire measuring .0003 in. It must be coated with an enamel layer that will result in a coated wire with a diameter that does not exceed .0007 in. That's just a single coating, but sometimes there are as many as three coatings on the wire with three individual coated diameter limitations. In addition, the wire may have to meet NEMA requirements.

The plant uses Starrett (Athol, MA) bench micrometers to check ultra-finished (polished) wire measuring two ten-thousanths (.0002) in diameter with a tolerance of 25-millionths (.000025) of an inch. Inspections occur at critical stages of processing, for example checking incoming wire, at the shaping and coating stages, after manufacturing and final quality checks.

Inspectors were accustomed to routine inspections to confirm the wire is within tolerance. However, the shop's previous amplifiers were giving conflicting readouts. This necessitated a sometimes lengthy process of elimination to discover the reason for the variations. Finally quality inspectors pinpointed the problem. "Some of the gage amplifiers were producing different readouts due to the resolution limitations of the amplifiers," recalls Jacobs. "The last digit was rounding up, so we knew we needed a 6-digit readout."

While the 11 bench micrometers on the shop floor are fully capable of accurately measuring the fine wire, the old gage amplifiers could not consistently resolve at the tightest tolerances, so the company started a search for the necessary resolution.

"We looked into various methods to solve the problem," says Jacobs. "For example, we tried laser micrometers, but found the fine, airborne dust from the environment interfered with the laser beams. Besides, the problem wasn't really the bench mics which our inspectors preferred, but getting the resolution we needed out of our amplifiers. That's when we tried a Starrett Gage-Chek 776? amplifier, which allows a resolution of .000001 in when measuring to 5 millionths (.000005) accuracy."

Starrett and Metronics (Bedford, NH) provided an application program formula for this amplifier that counted revolutions of the bench micrometer to achieve the 6-digit resolution. Inspectors in the plant found that this amplifier was the answer to the "case of rounding at five digits," and key to restoring confidence in their QC inspections.

In the plant, 776 Series LVDT probes (linear variable differential transducers) are attached to the bench micrometers. The micrometer contacts the wire and measures the variance from acceptable wire. Users orient the wire in the micrometer, contact the work and view the value on the amplifier. If required, users can press a print button to record the inspection. The Gage-Chek uses a three-color, microprocessor-based display that allows even the most inexperienced inspector to visually make quick, easy decisions on part quality.

Inspectors require a finely-tuned touch to hold the wire taut, place it in the micrometer and then with their little finger, depress the spring-loaded lever to release the spindle for contacting the wire. "It takes a precise micrometer, a real knack, and patience to attain the right feel to sense the wire in your fingers while making successful contact," adds Jacobs.

The amplifier is a versatile unit that combines the simplicity of go/no-go gaging with the power of a microprocessor. Although CFW uses one probe sensor, the 776 accepts up to 8 direct probe outputs. The probe readings can be algebraically and mathematically combined for dimensions such as thickness, flatness, angles, length and heights with the choice of a numerical or graphic display. The readings can be archived for process studies such as simple X-Bar and Range charts.

Trigonometric formulas can convert linear measurements into angular measurements. Other formulas can also be created for TIR (total indicator runout), volume, angles between features and more. The unit also interfaces with PCs and/or other devices for data collection, reports, and other forms of documentation. SPC functions are integrated into the amplifier, so operators are able to ensure a process is corrected before out-of-tolerance work is manufactured or shipped.

THIN WIRE FLOWING
The amplifiers are doing their part to boost productivity and reduce waste at CFW. Presently, six amplifiers are on the job, but future plans call for five more to accommodate all of the bench micrometers on the production floor and set the stage for implementing a 100 percent SPC program.

"Now material is flowing smoothly throughout the shop" notes Jacobs. "And we are not wasting time running down conflicting readouts. Upgrading to these new amplifiers has increased our productivity by thirty percent and helped us reduce our re-work of bare wire and minimize the amount of insulated wire that must be scrapped."

Scrapping micro-thin wire and ribbons, especially when they are made from precious metals like gold and platinum, is a significant expense. Add in the lost production costs of the previous method to the value of scrapped material, and the plant conservatively calculates their annual savings to be more than $50,000.

At California Fine Wire Company, there is an appreciation for all things small. With a footprint smaller than a piece of copier paper, the amplifier may indeed be small, but it has helped save time and money in the ongoing quest for flawless medical manufacturing, the fastest growing segment of the company's business.

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California Fine Wire Company, 338 South Fourth Street, Grover Beach, CA 93433-0199, 805-489-5144, Fax: 805-489- 5352, www.calfinewire.com.

Metronics Incorporated, 30 Harvey Road, Bedford, NH 03110, 603-622-0212, Fax: 603-623-5623, www.metronics.com.