Circuits Assembly - June 2008 - (Page 27)

Cover Story ! "! $! %! &! ! #! #! #! (! '! ! 9;! &! #! 1! #! 6! #! 7! 9! 8! "! #! $! 9! %! :! &! #! '! %;! &! "! ! 1! "! 6! "! 7! #9! 8! "! ;! $! #! %! ;! &! #! '! ! '! *! &! '!()*+, /)0!! #! '!12334*!,/54!! "! +! #! *! $! ,! %! *>! '! .! "! ! .! #! -! $! +! %! Figure 4. The best patterns in terms of reduction of average buffer levels, five and eight station lines with average buffer capacities of two and six. Table 1. IT Change vs. Balanced Equal Buffer Size +>! '! *! "! *! #! *! $! +! %! +! )! ,! (! ,! &! Line Length Pattern 1 12.30 Saving/increase (%) 5 2 -16.14 3 19.83 8 4 1.75 ?>! '! *! "! *! #! *! $! +! %! +! )! ,! (! ,! &! /! 0!12345676829!! ,! 0!":;;<3!58=<!! Table 2. Best Pattern’s ABL vs. Equal Buffer Capacity Line N Pattern Saving (%) 5 -48.60 5 6 -56.13 7 -47.11 8 8 -45.52 Figure 3. The best patterns in terms of reduction of idle time, five and eight station lines with average buffer size of two and six (not to scale). The patterns can be described in five general policies: Ascending order: Buffer capacity concentrated at end of line. Descending order: Buffer capacity concentrated at beginning of line. Inverted bowl shape: Buffer capacity concentrated in middle of line. Bowl shape: Buffer capacity lowest in middle of line. General: Buffer capacity not concentrated at one area of the line. It can be either no particular pattern, or zigzag, in which buffer capacity alternates between high and low. Following the simulations, we were able to see that none of these five general policies was noticeably better or worse than any of the others in broad terms, but particular patterns within the five general policies showed substantial improvements of performance, either in IT or ABL, when compared to the balanced-buffer line. In each policy, we found that the less extreme the buffer capacity allocation – i.e., the more evenly spread it was – the better the results insofar as IT was concerned. The two best patterns obtained from the simulations fell into the “general” policy and are illustrated below. Pattern 2 (Figure 3) shows a reduction in idle time (-16.14%) compared to the balanced-buffer line. The other lines were all worse than a line with equal buffer sizes would be, and showed an increase in IT (Table 1). In terms of ABL, the best two patterns had their buffer capacities concentrated toward the end of the line (ascending order policy) (Figure 4). We can see from Table 2 that the savings obtained are considerable. All four patterns consistently show great improvements in ABL over the balanced-buffer line. It seems to be well worth unbalancing the buffers to improve stockholding performance. · · · · · Conclusions One of the main conclusions is that how to allocate different sized buffers between workstations will depend on the particular conditions of the production facility. It may be important to keep as few units of partly completed products in storage as possible; for example, we could imagine fresh produce where hygiene and safety issues are foremost. In this case, it might be advantageous to opt for reductions in ABLs; i.e., placing more buffer capacity toward the end of the line. This is especially the case where just-in-time and Lean buffering strategies are in place. On the other hand, if we are considering a sector where labor costs are high – automotive, for example – it may be better to move toward reductions in IT, and distributing buffer capacity evenly along the line. We should remember, however, these patterns are specific patterns among numerous possibilities, and imbalance directed in the wrong way could lead to the opposite effect: increases in ABL or IT. Finally, the sheer size of the potential savings in IT (16%) and ABL (56%), multiplied over the lifespan of a production line, means purposely unbalancing the buffer sizes the right way may be a policy worth pursuing. n Dr. Sabry Shaaban and Dr. Sarah Hudson are at the Rennes International Business School (schoolbusiness.com); sabry.shaaban@esc-rennes.fr. circuitsassembly.com Circuits Assembly JUNE 2008 27 http://www.school-business.com http://www.school-business.com http://circuitsassembly.com

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Circuits Assembly - June 2008 Contents Letters Caveat Lector Industry News Market Watch Talking Heads Screen Printing Better Manufacturing China Goes ‘Upmarket’ Out of the Garage Improving Production Line Performance Manufacturing Steps Onto the Enterprise IT Stage Measuring and Controlling Wave Height and Dwell Time Wave Soldering Tech Tips Test and Inspection Process Doctor Pb-Free Lessons Learned Getting Lean Eastern Advances Semicon West Product Preview Product Spotlight Ad Index Assembly Insider Technical Abstracts

Circuits Assembly - June 2008

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