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Laser marks aid micrometer precision.

Laser marks aid micrometer precision

Before being introduced to the laser marking process, Central Tools Inc, Cranston, RI, marked its micrometer products using roll-stamping, manually operated scribing, and an ink-fill-and-wipe process.

Periodically, these methods developed problems such as cracked dies. Valuable manhours were lost on tedious and hazardous ink-filling duties, and separate processes were needed to put all the marks on micrometer barrels, making it difficult to achieve the tight tolerances required.

Barrels are made of 12L15 chrome-plated, cold-rolled, satin-finished steel. Barrel markings consist of ten separate horizontal lines (0.0001" graduations) running along a portion of the unit about 1" long with correlating numerics. In addition, a 1"-long scale of graduations divided into 0.025" increments with corresponding 0.094"-high numerics is required on the same piece.

CTI used a combination of in-house processes to mark the micrometer barrels. First, they roll-stamped all marks except the major line onto the cylindrical barrel pieces. Numerics were not always consistent, and sometimes the dies cracked or wore out after processing only 3000 pieces.

Because roll stamping the major line on the barrel would deform the part, CTI used a manual scribing process. Finally, marks had to be filled with ink--a heavy black lacquer, applied and wiped manually. This messy process was followed by solvent removal of the residue. Both lacquer and solvent are considered hazardous substances.

Laser Marking Services Inc then got into the act, suggesting a Nd:YAG system. Central Tools accepted the idea and asked LMS to help in making the transition to laser marking. CTI gave LMS blueprints with locations and dimensions of the lines and numerics, along with all tolerances (which are in the [+ or -] 0.002" range). Engineers transcribed these data into software language comprised of position points, lines, and arcs.

This digital information was downloaded into a microprocessor that controls two galvanometer mirrors, steering the beam through a focusing lens to the target. CNC movement allows the system to mark around the circumference of workpieces. Tooling here is simply a cylindrical arbor that fits inside the barrel, allowing radial indexing.

The first piece is checked on a toolmaker's microscope. Because all aspects of the process are computer controlled, reject rates usually are less than 1 percent. QC is handled by a 10-percent-through checking method.

The results? CTI gained a number of benefits by sending the micrometer barrels out to LMS for laser marking. They eliminated several manufacturing processes and inconsistent marking. They saved time, money, and manhours, cutting lead times by a matter of weeks. There is less in-house handling, and the barrel marks are always legible for precise reading.
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Publication:Tooling & Production
Date:Mar 1, 1990
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