Apply quality to motion control
Six Sigma has achieved dramatic results within companies like General Electric, yielding an annual return of over $100 million in quality improvement savings. But how can you make it work in your application, and where do you start?The first task in applying Six Sigma is to understand its purpose, which is always to optimize quality and throughput.
Six Sigma has achieved dramatic results within companies like General Electric, yielding an annual return of over $100 million in quality improvement savings. But how can you make it work in your application, and where do you start?
The first task in applying Six Sigma is to understand its purpose, which is always to optimize quality and throughput. Six Sigma is a tool that can unveil subtle problems plaguing all processes, silently stealing productivity and quality. Motion-control applications are not immune to production downtime and quality control issues. Slow machine set ups, product-positioning problems, equipment failures, and out-of-spec parts can all contribute to the problem.
Six Sigma projects begin with team building and training. Then, a formal series of steps follows, according to the method's Define, Measure, Analyze, Implement, and Control (DMAIC) roadmap. [See the full September 2001 "web-exclusive" article at www.controleng.com for more details.]
An application in motion control is used to illustrate Six Sigma's power.
Striving for Six Sigma soldering
A rewarding project for motion-control quality at GE Fanuc started in the mid-1990s, shortly after corporate-wide commitment to Six Sigma by parent company GE. The program continues to evolve today.
While evaluating fluxing system options for a Six Sigma wave-soldering project at GE Fanuc's Charlottesville, Va. manufacturing facility, engineers tested and selected an "Opti-Flux I" spray-fluxing system from Ultrasonic System Inc. (USI, Amesbury, Mass.) to resolve flux issues hampering printed wiring board (PWB) production for PLCs.
Control of flux deposition in wave-soldering is essential to the quality soldering of through-hole components on PWBs. Amount of flux applied to the board is critical to the no-clean wave soldering process, as the flux must be completely consumed during soldering, so no residue remains for cleaning.
Earlier, PWB production at GE Fanuc involved dousing the boards with large quantities of water-soluble fluxes followed by cleaning at the end of the line that removed residue and excess flux. Once this process was put under Six Sigma's microscope, Measure and Analyze activities showed the dousing process used excess flux, produced solder-joint defects, caused frequent setup delays, and required additional cleaning after soldering. Thus, the Six Sigma project's main goal was to implement a method for accurately applying just enough flux to ensure solderability of components and eliminate the extra step of cleaning the PWBs.
Opti-Flux I used USI's patented nozzle-free ultrasonic spray technology coupled with a synchronized traversing head that enabled a single, virtually uniform flux coating of the PWB. Effective through-hole penetration was achieved even at low flux volumes. One-step setup let operators quickly enter the recipe for the PWB flux application, resulting in virtually no downtime.
While Opti-Flux I improved fluxing operations, the pneumatically controlled traversing head could induce slight variations in flux depositions across the wiring boards. After GE Fanuc approached USI and discussed the variations inherent in Opti-Flux I, USI joined the Six-Sigma team.
By applying the same Six Sigma DMAIC steps that GE Fanuc followed, USI resolved flux variations of Opti-Flux I by implementing a GE Fanuc servo-motor-based solution. Optimized speed control of the traversing head ensured uniform flux application.
Next-generation Opti-Flux II uses a belt-drive linear actuator with a servo motor to traverse the spray head. This allows independent adjustment of flux flow rate and spray-head traversing speed for precise application and wide flux-position range. It replaces air-actuated cylinder traversing of Opti-Flux I. Operators control the motion by entering deposition specifications into an Operator Control Station in micrograms/in.2, after which the system automatically adjusts flux flow rate and traversing speed of the spray head.
With the motion-control enhancements of Opti-Flux II, each PWB now receives one non-overlapping, uniform coating of flux as it passes over the spray station. This new level of control was attractive not only to GE Fanuc's Six Sigma project, but has also become a competitive advantage for USI, as Opti-Flux II is meeting with great success within the electronics assembly industry.
Since implementing the Opti-Flux II system with servo-motor control, GE Fanuc has realized several benefits. These include improved plated through-hole soldering, resulting in 75% fewer solder defects and 45% reduction in per-board flux usage, as well as lower maintenance costs and set-up time.
While moving closer to the zero defects goal, GE Fanuc's pursuit of Six Sigma continues to evolve and reveal new, surprising variables, as well as helps the company repeatedly "solve for x" at the plant.
Six Sigma methods can be a powerful tool for improving quality and productivity of virtually any process involving motion control.
Kevin Frantz is a Six Sigma leader at GE Fanuc Automation (Charlottesville, Va.). For more information, visit
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