New Type Of Bar Codes Is Tool For Quality, Inventory And Warranty Control

The bar coding of finished products is an effective and widespread tool for managing inventory and distribution, expediting work-in-process and simplifying warranty fulfillment.

What has not been practical is the tracing and tracking of individual parts that are internal to finished goods. These are the critical components that determine, after all, whether products perform or fail.

There are several reasons why individual parts have not been marked until recently. Key among them has been the limitation inherent in traditional marking, specifically the inability to withstand common manufacturing processes such as heat treating, mechanical abrasion and chemical baths. But this didn't mean there was not a need for this technology.

Roger Schellhorn, quality coordinator at John Deere (Waterloo, Iowa), was looking for a system that would code individual internal parts. "Our first priority was to achieve individual parts traceability throughout the production line," he explains. "We wanted to put a pedigree on parts, and assign quality data to individual items. We've always been able to correlate quality data with a particular group of parts, but before recently, there had been no way to marry quality data with individual parts."

The company considered numerous systems for achieving individual part traceability, including optical character recognition (OCR). "Our biggest objection," says Mr. Schellhorn, "was the miles—literally miles—of wiring that would have been required. It looked to us like an upkeep nightmare."

Then he found a new marking technology referred to as Bumpy Barcoding (BBC) by its supplier, Mecco Marking Systems, (Ingomar, Pennsylvania). BBC indents a high-integrity 3D mark into metal, plastic and composite materials.

Indented BBC marks are expressed by highs and lows in surface height, rather than variations in black and white. Indented BBC readers use differences in height, rather than contrast, to distinguish the bars and spaces of the code being read. This allows Bumpy Bar Codes to be read where no contrast is available, (for example, when a part is exiting a heat treating cycle and the surface is dark.)

The mark, which is permanent, can be made through indent marking, die stamping, or roll marking on virtually any material of less than Rockwell 45C. Materials do not have to be perfectly flat or smoothmachined; in fact, only highly reflective materials (such as polished stainless steel) are problematic. Marks can also be incorporated easily with most casting, forging or injection molding processes. In all cases, the mark becomes a design feature of the part. BBC marking withstands annealing, heat treating, and abrasive treatments, and is scannable after many coating processes as well. The service life of the mark equals that of the part itself.

John Deere introduced Bumpy Barcoding technology at its Waterloo Engine Works. The company's first application for Mecco's Bumpy Bar Code technology was connecting rods. Each connecting rod is split into two pieces during machining and must be reformed as a matched set. The system allows absolute verification that each rod and rod cap are a matched set.

"Now, if we would develop a problem with connecting rods, we could instantly identify the shift when it was produced, the individual machine involved, the specific quality measurement data generated, and the operator who was on duty," says Mr. Schellhorn. "We can respond quickly and appropriately to any problem, but more importantly, we can respond proactively as well.

The Mecco system purchased by John Deere includes a Mecco SP202 computer controlled marking system and fixed base reader. To accommodate Deere's requirement for a very fast cycle time, the system was engineered with three stations: two marking heads, and one fixed scanner, which was manufactured by Sensis Corp. The first station provides human-readable marking, the second indents the BBC marking; the third station scans and verifies the integrity of the marks. Fixturing, which was designed jointly by Mr. Schellhorn and Mecco engineering vice president Jim Speicher, includes automated parts handling.

The BBC is created by a chisel stylus that strikes the material surface and creates a bar about 1/8 inch in length. The reader is unique in that it reads both Bumpy Bar Codes and traditional black and white printed bar codes, an advantage for users of both technologies. The reader is also distinctive in its use of a proprietary error detection algorithm, which makes misreading a virtual mathematical impossibility.

BBC readers integrate readily with PCs, PLCs, robots and other factory data equipment. They also plug into portable data terminals, which transfer data into a computer by saving it in memory for subsequent downloading, or by transmission via RF link to a base station. In the assembly operation, the connecting rod number is directly linked to an engine serial number. This provides traceability from the machining data to the end customer.

Mr. Schellhorn's goal is to implement BBC parts traceability on key parts, facilitywide, by the end of 2000.