PROCESS IMPROVEMENT Combining lean, Six Sigma and theory of constraints Rock creates a process improvement powerhouse . : . : . : . : . .: . .. :. :. L. : . .. .. : . : . : . .. D . : . I . 0 . .. :S . , . : . : . SURFACE MINING AND subsurface mining requires expensive machinery and equipment. A 12-ton In 50 Words front-end loader and 35-ton haul truck, for example, can Or Less • The 6TOC improvement cost $1.2 million and $350,000, respectively. A single site method employs ele- by Todd Creasy ments of Six Sigma, lean can use several pieces of equipment, with additional capi- and the theory of con- straints (TOC) to zero in tal needed for the plant’s fixed machinery, pushing the on process bottlenecks and eliminate waste and variation. up-front investment into the tens of millions of dollars. • A 10-step implemen- tation plan based on Eliyahu Goldratt’s chain project management process and Joseph M. Juran’s management principles can help any industry implement 6TOC. December 2014 • QP 45 PROCESS IMPROVEMENT These capital investments can prevent entry into and the theory of constraints (TOC).2 Its principles and in-house receiving department. Critical process flowchart for the industry and complicate efforts to grow or im- deployment steps are shown in Table 1. In the mining industry, it begins with the stone prove productivity. Because money is the language of Although this approach to process and productivity that has been blasted from the stone face. The pro- mining operation / FIGURE 1 senior management,1 site managers are careful about improvement is presented here in a case study involv- cess continues with the stone traveling to the pri- unnecessary capital expenses, and often try to focus ing a mid-southern U.S. mining organization with more mary crusher, conveyor, secondary crushers and on controlling expenses while improving worker and than 50 sites, 6TOC can apply to a broad spectrum of more conveyors until it reaches stock piles and is equipment productivity. industries.3 loaded onto customer trucks, weighed in tons and The aim to improve operational results while reduc- A hybrid combination, 6TOC has elements of Six ticketed. These tickets produce invoices that are Coarse rock to Conveyed to secondary Loaded on trucks ing inputs or keeping them the same is what led one Sigma, lean and TOC. Six Sigma focuses on quality im- sent to customers. primary crusher crusher and then to then weighed organization to embark on a multiyear quest resulting provement and reducing production variation,4 while After the primary process flow has been un- stockpiles and ticketed in a method called 6TOC (pronounced “six tock”) and lean focuses on eliminating waste in all of its seven derstood, it is separated into three or four seg- Phase I Phase II Phase III results worthy of examination. forms.5 When these two philosophies are combined ments. For each data capture, these segments 6TOC is the unique combination of Six Sigma, lean with TOC6 and its focus on bottlenecks, it makes a often begin and end at logical breaks in the pro- potent combination, particularly if there is manage- cess and generally have measuring systems at the Capabilities8 chart—tons per rial support to improve productivity. Using TOC’s five beginning or end. In the mining industry, the pri- hour / FIGURE 2 Steps to implementing 6TOC / TABLE 1 steps, bottlenecks are exploited and elevated with Six mary process is divided into three sections called 7 Sigma and lean tools. phases related to the processing stage of the rock Step 1 Identify and validate operational metrics. Begin 6TOC by identifying the capstone metric. All correlated with the crushing circuit’s continuous 3,0006 Step 2 Identify capstone metric through correlation analysis. organizations have financial or operational ratios that flow system. Figure 1 illustrates a mine’s stone- 2,500 2,540 predict success or profitability. In this collection of ra- crushing primary process divided into three Step 3 Identify value-creating, primary process flow. 5 5.07 tios or metrics, one has a higher correlation relation- phases. 2,000 Step 4 Divide primary process flow into three or four logical and measureable segments. ship to profitability than all the others. Operational bottlenecks —areas in the prima- 1,500 Cycle time 4 Step 5 Identify bottlenecks or constraints in each segment. As part of 6TOC, teams are charged with improving ry process where demand exceeds capacity—are 1,000 3.55 outcomes that have either a direct or indirect effect on of keen interest to TOC practitioners. Identify- 910 Step 6 Begin with the segment with the most restrictive bottleneck 718 or constraint. the capstone metric. ing and understanding bottlenecks within each 5003 Step 7 Use lean Six Sigma tools to exploit or eliminate bottlenecks in In the mining industry, there are several site-spe- segment comprise the third major step in 6TOC. 0 process. cific and contemporaneous measurements to con- Bottlenecks occur when demand exceeds capac- 2 Loader Haul trucks Crusher Step 8 Repeat step 7 working through the next most critical sider, such as tons produced per hour, total costs ity or when actual production in a specified area Cycle time actual Cycle time capable bottleneck. as a percentage of sales, cost per ton and overtime is less than its maximum capability for produc- Step 9 Develop a metrics pyramid for your organization identifying expense per ton. Table 2 shows examples of site- tion. In this instance, underperformance in one pertinent metrics at each level (corporate, division and Truck cycle time location). specific metrics. critical link reduces total production for the en- After studying 14 months of operational metrics and tire chain. actual vs. capable / FIGURE 3 Step 10 Develop a communication system using the metrics pyramid for pertinent levels in the organization; consider using month-end results for more than 50 locations (n = 700), Phase one for a common surface mining opera- 8 scorecards and scoreboards. the metric most positively correlated to profitabil- tion commences with the loading of coarse rock 6TOC = A method that combines lean, Six Sigma and theory of constraints. ity was determined to be tons per man-hour (TPMH), (blasted from a stone face) onto a haul truck to 7 which became the capstone metric. be dumped into a primary crusher, weighed and Similar practices have been conducted at large or- stockpiled. This process requires all personnel 6 ganizations to determine a single most-important met- and machinery (a large front-end loader, several / TABLE 2 ric. The focus on Southwest Airlines’ gate turnaround haul trucks and a primary crusher) to be used. Site specific metrics 5 5.07 time and Walgreens’ revenue per customer visit,7 for Focusing on this phase of the total process, Production Maintenance Costs Safety example, produced positive results for both organiza- can you determine which component is the bot- tions. tleneck targeted for improvement? This approach Cycle time 4 Tons per hour Plant availability Cost per ton Days 3.55 since last is based on Eliyahu Goldratt’s critical chain and incident When demand exceeds capacity strength of throughput in which the collection 3 Tons per man-hour Rolling stock Labor cost per ton Number The next step in 6TOC deployment is to determine the of individual steps and tasks in the process and availability of near scope of the value-creation process flow or chain. In their relationships ultimately provide power to 2 misses 8 year to some industries, this may begin with overseas com- the process. date ponent manufacturers, raw material suppliers or an Strength arises from recognizing the con- Cycle time actual Cycle time capable 46 QP • www.qualityprogress.com December 2014 • QP 47 PROCESS IMPROVEMENT Cycle time comparison by per hour was 718 tons. The primary crusher was tested in five trials producing an average rate of 910 tons per Methods of exploiting or elevating a driver / FIGURE 4 hour. 12 The haul trucks seemed to be the bottleneck. Mea- constraint can be associated with people, sures were taken to improve the weakest link and 10 hopefully raise the average tons per hour of each haul 8 Dan process and machinery. truck, including exploiting the bottleneck and raising 6 Bill the entire phase’s throughput. Time 4 Kyle Because the team had substantiated the haul truck 2 theory through Six Sigma-style data capture and anal- In the mining case study, attempts were made to People. The haul truck operators were not aggres- 0 ysis, it avoided erroneous assumptions and rule-of- exploit the haul truck bottleneck by getting as much sively driving their trucks to achieve maximum produc- 1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 Cycles thumb management. Until this experiment, manage- out of the constraint as possible. We began using lean tion. They took their time. The drivers were not posi- ment had considered purchasing an additional haul to determine how much time would elapse during a tioning their haul trucks correctly near the loader prior truck or a larger crusher to obtain more throughputs. typical haul truck cycle. It begins with the truck be- to being loaded. The loader operator was not loading nections among the individual links and steps. The Both expenditures would have been premature. ing loaded with coarse rock, it travels to the primary the truck efficiently, using techniques that consumed strength of the throughput is only as strong as the crusher, it dumps the rock into the crusher and it trav- more time. weakest link. At this juncture, a capabilities chart is Exploiting and elevating constraints els back for another load. The distance from rock load- Cycle times were not communicated to drivers so used (Figure 2, p.