Figure 8.1. Engineering drawing of the “steer support”, a critical component of the Xootr scooter. The “height” of the steer support is specified by the dimensions (shown in the lower center portion of the drawing) as falling between and mm.

Figure 8.2. Steer support within Xootr scooter assembly. The height of the steer support must closely match the opening in the lower handle.

Figure 8.3: Examples for variation types

Time periods Process Parameter Upper Control Limit (UCL) Lower Control Limit (LCL) Center Line Figure 8.4: A generic control chart

Figure 8.5: X-bar chart and R-chart

Figure 8.7: Comparison of three sigma and six sigma process capability 33 Upper Specification Limit (USL) Lower Specification Limit (LSL) X-3  A X-2  A X-1  A X X+1  A X+2  X+3  A X-6  B X X+6  B Process A (with st. dev  A ) Process B (with st. dev  B )

Browser error Number of defects Figure 8.8: Order entry mistakes at Xootr Order number out off sequence Product shipped, but credit card not billed Order entry mistake Product shipped to billing address Wrong model shipped Cumulative percents of defects

Step 1Test 1Step 2Test 2Step 3Test 3 Rework Step 1Test 1Step 2Test 2Step 3Test 3 Figure 8.9: Two processes with rework

Step 1Step 2Step 3 Final Test Step 1Test 1Step 2Test 2Step 3Test 3 Figure 8.10: Process with scrap

Process Step Bottleneck Based on labor and material cost Market End of Process Defect detected Defect occurred Defect detected Cost of defect $ $ $ Based on sales price (incl. Margin) Recall, reputation, warranty costs Defect detected Figure 8.11.: Cost of a defect as a function of its detection location assuming a capacity constrained process

Figure 8.12.: Information turnaround time and its relationship with buffer size ITAT=7*1 minute ITAT=2*1 minute Good unit Defective unit

Kanban Direction of production flow upstreamdownstream Kanban Authorize production of next unit Figure 8.13.: Simplified mechanics of a Kanban system

Inventory in process Buffer argument: “Increase inventory” Toyota argument: “Decrease inventory” Figure 8.14.: More or less inventory? A simple metaphor

Figure 8.15.: Tension between flow rate and inventory levels / ITAT Flow Rate Inventory High Low High Inventory (Long ITAT) Low Inventory (short ITAT) Now Frontier reflecting current process Reduce inventory (blocking or starving become more likely) Increase inventory (smooth flow) New frontier Path advocated by Toyota production system