Polymer chip manufacturing is a multi-step, large-volume process that makes hundreds of millions of pounds of products annually at a typical plant. Unlike fiber extrusion, which requires the use of multiple units of specialized equipment, chip manufacturing involves fewer machines operated in either continuous or batch modes. Chip manufacturing is often driven by operator decisions, such as when to cut a batch, when to clean equipment, when to pack out and when to downgrade material. These operators typically exhibit a range of competencies as they gain experience.
The following case study outlines an improvement project aimed at reducing variability in a polymer chip manufacturing process. The lessons learned in the project may apply to a number of processes that involve operator decision making.
A major nylon manufacturing plant was experiencing lower-than-expected polymer yields in their multi-product, batch-process operation. They formed a Black Belt-led Six Sigma team to address the opportunity and charged them with three goals:
- Identify the sources of waste by product, shift and product transition.
- Estimate the capacity gain that could be achieved by optimizing the multiple-product scheduling.
- Increase “A” grade (top-quality product) yields by 1 percent (which translates into millions of dollars worth of savings).
This team realized success in a short time, as many teams do when a manufacturing area becomes focused on a problem. Figure 1 quantifies the polymer waste improvement experienced in a matter of months after the team was formed. Off-grade waste created at all three stages of the process fell dramatically as the team increased the area’s focus on quality and waste elimination. While this type of improvement frequently happens as personnel focus on opportunities for improvement in a process – especially after upper management has highlighted the need – this particular improvement was achieved mainly by improving operator performance.
The team undertook two specific actions to improve operator performance: 1) a panel of three experienced area supervisors interviewed each operator extensively in one-hour sessions (in some cases longer) and 2) a troubleshooting manual was created.
Table 1 depicts a matrix that captures a portion of the operator interview results. In this partial matrix (the full matrix has 30 columns grouped into specific areas of the process), each row captures a particular operator’s rating. Starting with the third column from the left, each column tracks competency in a specific component of the process. Note that major process components are grouped and color-coded.
Over a four-day period, each operator went before this panel of three process experts to be quizzed about all areas of the process in which the operators were expected to be proficient. When these experts felt that the operators had the necessary understanding for a particular area, they were given an “X” (color-coded green). If the operators did not demonstrate the requisite knowledge, they were given an “O” (color-coded yellow).
The review panel assessment was then followed up with training. If more than half of the operators were judged deficient in an area, a class was scheduled on that subject. In the case of fewer deficient operators, individual sessions were conducted by the operator’s supervisor during a regular production shift.
Table 1: Operator Certification
|Operator||Assess-ment Date||Polymer Cut Quality||Cast-ing Mach-ine Water||Hydro-mation||Sock Filters||Heat Exchan-gers||Water Filters||Casting Machine Inter-locks and Alarms||Cutter and Feed Roller||Sifting Screens||Tag and Lock-out Proce-dures||Area Safety Rules and PPE|
|5||New and untested|
|7||New and untested|
In any process that is manned by operators covering a wide range of experience levels, certain individuals who have the experience and know the tricks will rise to the occasion and keep the process humming along. There also will be those with less experience who are constantly being challenged. The team’s goal was to pass the knowledge along quickly from the first group to the second, and later to any new operators that might join the process in the future. The team chose to identify as many of the operational challenges as they could think of and collate the area’s experiences into a document that could then be used as a training tool.
Over a few short weeks, a process supervisor created a 25-page troubleshooting manual, a page of which is shown in Table 2. This supervisor interviewed everyone experienced in the process, including some who had moved on to other areas of operation. Then, after the group reached a consensus, the supervisor detailed specific sets of actions to be taken when encountering one of 66 specific problems. These problems, too, were grouped by process area. As one might imagine, this manual continues to be a tremendous training aid for new operators joining the area.
Table 2: Casting Floor Troubleshooting Guide
|Original issue: Sept. 27, 2007 (25 pages, 66 issues grouped by process area)|
|1. Machine cuts “tails” in the polymer chips||a. Cutter blades and/or bed knife are dull. Contact the shift mechanic to check them. The shift mechanic can change the feed roller, but a “day” mechanic will be needed to change the cutter blades.b. Check the water sprays and water temperature. A simple flow adjustment may be all that’s required.|
c. Check polymer flake size.
|2. Machine cuts “sticks” in the polymer chips||a. Check the water flows on the machine, especially the conditioning water and overflow water. Both can cause unwanted movement of the polymer strands, turning them sideways on entering the cutter.b. Check conditioning water sprayers for pluggage.|
c. Check flake and strand size, as you may be running too light.
d. Check for strands and “angel hair” wrapped on the feed roller.
e. Look at the strands as they exit the die plate. Any breaks, which cause the curled up strands of nylon you see occasionally, can be caused by a poorly cleaned die plate, and a die plate change may be needed.
Any time an operator’s decision-making can add variability to a process, experience and competency can become a major issue. Panel assessment, followed by training and the production of process-specific troubleshooting manuals, are two approaches to improving competency (a method to rapidly transfer experience). Both are truly “low-hanging fruit.”