Ultra-fine shaped wire, frequently one-tenth the thickness of a human hair, is the basis of critical components in applications ranging from aerospace and integrated circuits to automotive and medical instruments. Minute defects in such wire can crash a supercomputer or lead to life-threatening complications in microsurgery. Therefore, this micro-thin wire, measured in millionths of an inch, must meet exact tolerances and specifications. Manufacturers seeking ultra-fine wire frequently find their search ends at the door of California Fine Wire Co. (CFW, Grover Beach, CA).
Generally speaking, shaped fine wire does not have a round cross-section, the normal form in which it is drawn. The 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.
Checking Out a Problem“Meeting our customers’ exacting specifications means measuring tolerances that stretch the capabilities of inspection devices,” explains Jorge Jacobs, quality assurance technician at CFW.
For example, Jacobs describes a job that begins with a bare wire measuring 0.0003 inch. It must be coated with an enamel layer that will result in a wire with a diameter that does not exceed 0.0007 inch. That is 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 National Electrical Manufacturers Association (NEMA) requirements.
CFW uses Starrett (Athol, MA) bench micrometers to check ultra-finished (polished) wire measuring 2 ten-thousandths in diameter with a tolerance of 25 millionths 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 at CFW are accustomed to routine inspections to confirm that wire is within tolerance. However, CFW’s 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,” Jacobs recalls. “The last digit was rounding up so we knew we needed a 6-digit readout.”
While the 11 Starrett bench micrometers on the CFW shop floor are fully capable of accurately measuring the fine wire, the old gage amplifiers could not consistently resolve at the tightest tolerances. CFW began a search for the correct solution.
Jacobs says, “We looked into various methods to solve the problem. 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 the Starrett Gage-Chek 776 amplifier, which allows a resolution of 0.000001 inch when measuring to 5 millionths accuracy.”
Starrett and Metronics (Bedford, NH), a developer of metrology software, provided an application program formula for the Gage-Chek that counted revolutions of the Starrett bench micrometer to achieve the six-digit resolution. Inspectors at CFW found the Starrett Gage-Chek 776 amplifier was the answer to the “case of rounding at five digits,” and key to restoring confidence in their QC inspections.
At CFW, Starrett 776 Series LVDT (linear variable differential transducers) probes are attached to the bench micrometers. The micrometer contacts the wire and measures the variance from acceptable wire. Operators orient the wire in the micrometer, contact the work and view the value on the Gage-Chek. If required, operators can press a print button to record the inspection. The Starrett Gage-Chek 776 has a three-color, microprocessor-based display, allowing even inexperienced inspectors to make quick decisions on part quality.
Inspectors require a finely tuned touch to hold the wire taut, place it in the micrometer and then 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,” says Jacobs.
The Starrett Gage-Chek 776 is an amplifier 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 eight 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 be created for total indicator runout (TIR), volume and angles between features. The unit also interfaces with PCs and other devices for data collection, reports and other forms of documentation. Statistical process control (SPC) functions are integrated in the Gage-Chek, so operators are able to ensure a process is corrected before out-of-tolerance work is manufactured or shipped.
Thin Wire FlowingPresently, six Starrett Gage-Chek amplifiers are on the job at CFW, but future plans call for five more to accommodate all bench micrometers on the production floor and set the stage for implementing a 100% SPC program. “Now material is flowing smoothly throughout the shop,” says Jacobs. “And we are not wasting time running down conflicting readouts.
“Upgrading to the Starrett Gage-Chek amplifiers has increased our productivity by 30%,” states Jacobs. “They have helped us reduce our rework 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. When you add the lost production costs of our previous method to the value of scrapped material, we conservatively calculate our annual savings at more than $50,000.”
- The L.S. Starrett Co.