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Marking system change eliminates downtime on high-speed production line. (ID Marking).

More consistent, legible marking and a reduction of routine maintenance time from hours to minutes convinced this automotive parts manufacturer to switch marking machines.

The TRW Automotive facility (Greenville, NC) makes steering components; specifically inner and outer tie rod ends, pinions, and torsion bars for rack and pinion steering assemblies. The approximately 100,000 sq.ft. plant employs 250 - 300 people. The production line is organized in cells, and one particular cell produces about 14,000 finished inner tie rod ends each day. Starting with cold-headed, e-coated 1018 steel stock, the cell produces 16" - 18" rod ends, composed of the inner tie rod end, the socket assembly, and the upper and lower bearing, at the rate of two assemblies every 12 seconds. The cell runs three shifts each day and usually involves three operators per shift.

The cell consists of two machining centers operated by one person for the inner tie rod, and the socket is made on another machining center run by another operator. The machine that assembles these components is run by a third operator. This particular line has been in operation for nearly 10 years, during which time it has been made slightly more compact as a part of a multi-piece flow system. Each part is marked with seven human-readable characters, approximately 3/16" by 1/8" -- the Julian date, and machine and shift identification numbers -- to provide full part traceability.

The assembly machine has two sides, with a marking station on each side. The marking process, which takes 3-4 seconds for each part, does not cause any production delay during assembly. Only completed assemblies are marked after they have been tested to verify key characteristics; rejected parts are not marked. If for some reason, years later, a part failure or some other event would require it, the assembly history can be traced via the identification mark. The operators also maintain paperwork that includes shift reports and SPC (statistical process control) charts. These same procedures are used in other parts of the plant and have been in use throughout the plant's 20-year history.

The SPC database can be accessed at various times, including at the end of the shift, to verify information, track cell performance, and log rejected parts and the reason for rejection. A dock audit of the assemblies provides a final check of marking identification for missing digits, or parts that lack proper legibility and are not easily readable, before transfer to the company's internal customer or the automotive end-user, for which TRW Automotive is a Tier-1 supplier.

This particular tie rod cell had experienced ongoing problems with the original marking system, which consisted of two marking heads being controlled by one CPU (central processing unit) at each station. In this situation, if one print head failed, then the marking station went down, and the entire assembly machine shut down. Another problem involved print head maintenance and replacement component availability. Since the parts were uniquely designed for that particular marker, replacement component delivery could take from two weeks to two months.

Because of the, tie rod shape, and since the imprinting occurs on a cylindrical surface, there was always a compromise as far as depth penetration. The relative shift in the centering of the machine impacted on this significantly, so that there was always a minimal depth penetration. Consequently, problems would occur if the part were not centered properly for marking. Often, with the original marking system, one of the key numbers would be lost during marking, caused by sticking pins or dirt in the marking head. The reliability of the marking process is critical; and, it is up to the operator to maintain marking legibility and durability on all parts.

Throw Away That Magnifying Glass

The manufacturing engineer responsible for this particular operation is Vince Mancuso, who has been with TRW for nearly nine years. He recalls, "I was not happy with the original marking situation. Every time that we ordered things from the supplier there were changes made in the marking machine, and we did not have any adaptability to interchange components, different print heads, and such. Controls were constantly changing, and the replacement part situation was rather bad. Then, when we started having some component problems with the machine, the supplier started giving us extreme lead times for making repairs. This was about a year ago.

"So, I promoted the switch to Pannier," Mancuso explains. "My first contact was with a Pannier sales representative that stopped in to talk. I gave him some of our parts to mark, and he took them back to Pannier. After he returned them to me, I looked at the marking and decided that, if they were able to do this, then they were worth considering."

The Pannier machine that Mancuso ultimately chose is the MK3-T8 (originally called the MSG 1000). According to Bob McHugh, director of Pannier Corporation's Engineered Marking Systems division, "We have been carrying the MK3 for nearly eight years; the machine has been produced by Sitel (who manufacture it as their model T8) for nearly 15 years." The MK3 was integrated on this one particular cell in TRW's manufacturing operation, which is currently about twice as fast as any of the other 12 cells in the plant that make similar products.

"The actual marking structure remained the same after the changeover," says Mancuso. "We didn't push for a more enunciated mark, but Pannier was able to provide a more readable mark over the curvature of the part. Before, you would have to look at the mark under a magnifying lens to read it. Now, after marking, you can readily read the part number and the rest of the marking even standing away from the machine, outside the safety barriers. With the Pannier mark, you don't have to use a magnifying glass.

"Also, the pins on the earlier system were very sensitive to any kind of dirt or miniscule particles," Mancuso reports. "Cleaning the pins on the earlier system was very meticulous and required tools to take the heads apart to clean them. This involved a lot of time, and it was a try-and-see thing. After the operator would take it apart, clean everything, and put it back together, it would have to be run to see if it would work properly. Sometimes, we would have to take it apart again, and try this and try that to get it to run correctly. This would usually take more than one hour.

"On the MK3," he continues, "the operator is required to perform an occasional cleaning of the print heads, which takes around 10 minutes. Everything is readily interchangeable, and this includes the CPUs. And, there are no tools required. Unscrewing a knurled knob is all that is needed to remove the housing. Visual inspection of the machine is quick and easy. There is a world of difference between the two machines."

Flawless Operation: Four Months and Counting

According to Mancuso, the operators have not had any problems with pins hanging up with the MK3. Cleaning the machines is routinely done about once each week, and each operator's shift report includes a verification of marking legibility. Generally, when there was a stamping issue with the original marking machines, it was a significant downtime problem, often losing as much as a shift or a shift-and-a-half of production. "Now, with the plug-and-play situation for the MK3, and having the backups for all the necessary components, our downtime is generally less than an hour as a worst-case scenario," he notes. "And, we have not had a situation like that in the past four months.

"Showing the operators what to do, as far as maintenance and whatever, didn't take long at all," says Mancuso. "It was simply a matter of disassembling a machine, showing the operators what to look for, and putting it back together. Pannier was here with us every step of the way. We had 24-hour turnaround-on any components, and they supplied loaners. Where there were questions, they supplied the research and engineering assistance for the integration, including having the manufacturer of the machine's components coming to our facility." Engineered Marking Systems, Division of Pannier Corporation

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Article Details
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Author:Olson, Larry
Publication:Modern Applications News
Date:Mar 1, 2002
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