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CIM data banishes rejects.

For DJ Inc., a custom injection molder with two plants in Kentucky and a third in Texas, CIM began as a way to turn some money-losing jobs into winners. The company launched its CIM program early in 1996, when it adopted the "decoupled molding" technique from RJG Technologies, Traverse City, Mich., on 22 jobs that weren't turning a profit but were essential for the sake of customer relations. "Some of those jobs were losing a little money. Some were losing a lot of money," recalls Brian Guinn, DJ's manager of new technology. "All those numbers have since turned around." Decoupled molding, which controls the molding process through a computer analysis of cavity-pressure signals, worked so well that the 22 jobs quickly evolved into a process-control network that links all three of DJ's plants.

Says Guinn, decoupled molding and DJ's related CIM efforts immediately helped the firm meet or exceed the already stringent quality standards of its appliance, automotive, and consumer-electronics customers. CIM also engendered productivity improvements that helped DJ realize a return on its initial CIM investment in less than a year.

DJ's CIM system now embraces 65% of the company's 240 injection machines of 55 to 700 tons and about 500 of its molds. That figure includes all the machines and molds at the company's Louisville and Hazard, Ky., plants, while the El Paso, Texas, facility currently has about 20% of its machines on line.


DJ's CIM system starts with RIG data-collection boxes on each machine, which collect process data from cavity-pressure sensors and other instrumentation. RJG's DartNet networking product links these boxes to Windows 95 PC terminals. Since DJ is organized as a collection of "plants within a plant," each "internal" plant has its own terminal. "That's about one for every 12 machines, says Guinn. More of these Windows terminals can be found on the desks of supervisors and process engineers.

A Novell local-area network connects all the internal plants within the Louisville facility. This network also links the other two locations via a high-speed telephone connection. This arrangement gives DJ supervisors in the Louisville headquarters plant a real-time view of both process and production data throughout the company. "We can watch what's happening inside any cavity from anywhere in our organization," says Guinn. That ability to "get inside the cavity" from remote locations has made diagnostics a breeze. For example, tough molding problems at the Hazard plant are routinely solved by process engineers in Louisville.

For production reporting, scheduling, and back-office computing, DJ runs an MRP II system on an IBM AS/400 mid-range computer. Production schedules are fed from Louisville to the Hazard plant, though El Paso does its own scheduling. Although the MRP II system is not yet tied into the process-control network, daily production reports for the plant managers do include quality-related information on the consistency of cavity-pressure control on each job running.


Although production reporting plays an important role in DJ's operations, the emphasis of its CIM installation has been squarely on process data. "We don't just monitor our cavity pressure; we control with it," says Guinn, who notes that all the computerization efforts support DJ's "three-sigma" quality program.

The results have been impressive: Before decoupled molding, DJ typically measured cavity pressure of [+ or -]600 psi (one standard deviation equaled 200 psi). Nowadays, the company controls to better than [+ or -]60 psi, and one sigma has shrunk to less than 20 psi. 'That's on all of our instrumented tools," Guinn reports. He attributes much of this control improvement to the ability to accommodate inevitable material viscosity variations. "We've taken that source of variation out of play," says Guinn.


Unlike many CIM converts, DJ has hard numbers to document how computer integration has helped its bottom line. Today, with a year and a half and $1.3 million invested in its expanding CIM project, DJ is well on its way to recouping its entire investment. Guinn notes that the dollars spent include not just monitoring and communications hardware and software but also automation equipment such as robots and conveyors.

Most of the return on CIM comes from cycle-time reductions. On the original 22 jobs, for example, the payback on the initial $200,000 CIM investment came in less than a year. "Every one of the original 22 molds has saved cycle time," Guinn says. The time savings added up to $330,000 in the first year. "That savings doesn't include efficiency improvements and the reduced cost of quality," he adds.

With quality improvements thrown in, payback gets even better. "The cost of poor quality went away," Guinn says. For instance, a tough-to-mold spring cover for a seatbelt accounted for 63% of DJ's internal rejects in the days before decoupled molding and CIM came on line. Guinn explains that the problem was rooted in a snap-fit design that would fill properly only within a very narrow processing window. "When we hooked up our system, the reject rate on that part went down to zero for six months straight," says Guinn. He notes that some parts still don't fill properly on every shot, but DJ has added reversible conveyors on this and other machines to catch any rejects before they head downstream.

On a set of jobs for an automotive customer (8 million parts so far), rejects went from 180 ppm down to 55 ppm in one year as some of the tools were fitted with cavity-pressure sensors. This year, with all tools instrumented, rejects on this part fell to just 5 ppm - and 80% of those resulted from post-mold operations.


This year, DJ plans to finish implementing CIM and decoupled molding by hooking up the remaining machines in El Paso. After that project is complete, DJ has an ambitious plan to move to what Guinn calls "process certification on the fly." The first step will he integration of a third-party statistics package that will create SPC charts as the parts are made.

Guinn says DJ's process control today is good enough that the company could, in theory, do away with many after-the-fact quality checks. "Our correlations show that if we stay within our alarm limits, we'll never produce a part that's out of dimension," he says.
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Copyright 1997, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

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Title Annotation:custom injection molding
Publication:Plastics Technology
Date:Dec 1, 1997
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