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SURFACE MINING AND subsurface mining
requires expensive machinery and equipment. A 12-ton
front-end loader and 35-ton haul truck, for example, can
cost $1.2 million and $350,000, respectively. A single site
can use several pieces of equipment, with additional capi-
tal needed for the plant’s fixed machinery, pushing the
up-front investment into the tens of millions of dollars.
In 50 Words Or Less • The 6TOC improvement
method employs ele-ments of Six Sigma, lean and the theory of con-straints (TOC) to zero in on process bottlenecks and eliminate waste and variation.
• 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.
Combining lean, Six Sigma and theory of constraints creates a process improvement powerhouse
by Todd Creasy
December 2014 • QP 45
PROCESS IMPROVEMENT
RockS0LID
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These capital investments can prevent entry into
the industry and complicate efforts to grow or im-
prove productivity. Because money is the language of
senior management,1 site managers are careful about
unnecessary capital expenses, and often try to focus
on controlling expenses while improving worker and
equipment productivity.
The aim to improve operational results while reduc-
ing inputs or keeping them the same is what led one
organization to embark on a multiyear quest resulting
in a method called 6TOC (pronounced “six tock”) and
results worthy of examination.
6TOC is the unique combination of Six Sigma, lean
and the theory of constraints (TOC).2 Its principles and
deployment steps are shown in Table 1.
Although this approach to process and productivity
improvement is presented here in a case study involv-
ing a mid-southern U.S. mining organization with more
than 50 sites, 6TOC can apply to a broad spectrum of
industries.3
A hybrid combination, 6TOC has elements of Six
Sigma, lean and TOC. Six Sigma focuses on quality im-
provement and reducing production variation,4 while
lean focuses on eliminating waste in all of its seven
forms.5 When these two philosophies are combined
with TOC6 and its focus on bottlenecks, it makes a
potent combination, particularly if there is manage-
rial support to improve productivity. Using TOC’s five
steps, bottlenecks are exploited and elevated with Six
Sigma and lean tools.
Begin 6TOC by identifying the capstone metric. All
organizations have financial or operational ratios that
predict success or profitability. In this collection of ra-
tios or metrics, one has a higher correlation relation-
ship to profitability than all the others.
As part of 6TOC, teams are charged with improving
outcomes that have either a direct or indirect effect on
the capstone metric.
In the mining industry, there are several site-spe-
cific and contemporaneous measurements to con-
sider, such as tons produced per hour, total costs
as a percentage of sales, cost per ton and overtime
expense per ton. Table 2 shows examples of site-
specific metrics.
After studying 14 months of operational metrics and
month-end results for more than 50 locations (n = 700),
the metric most positively correlated to profitabil-
ity was determined to be tons per man-hour (TPMH),
which became the capstone metric.
Similar practices have been conducted at large or-
ganizations to determine a single most-important met-
ric. The focus on Southwest Airlines’ gate turnaround
time and Walgreens’ revenue per customer visit,7 for
example, produced positive results for both organiza-
tions.
When demand exceeds capacityThe next step in 6TOC deployment is to determine the
scope of the value-creation process flow or chain. In
some industries, this may begin with overseas com-
ponent manufacturers, raw material suppliers or an
December 2014 • QP 47
in-house receiving department.
In the mining industry, it begins with the stone
that has been blasted from the stone face. The pro-
cess continues with the stone traveling to the pri-
mary crusher, conveyor, secondary crushers and
more conveyors until it reaches stock piles and is
loaded onto customer trucks, weighed in tons and
ticketed. These tickets produce invoices that are
sent to customers.
After the primary process flow has been un-
derstood, it is separated into three or four seg-
ments. For each data capture, these segments
often begin and end at logical breaks in the pro-
cess and generally have measuring systems at the
beginning or end. In the mining industry, the pri-
mary process is divided into three sections called
phases related to the processing stage of the rock
correlated with the crushing circuit’s continuous
flow system. Figure 1 illustrates a mine’s stone-
crushing primary process divided into three
phases.
Operational bottlenecks —areas in the prima-
ry process where demand exceeds capacity—are
of keen interest to TOC practitioners. Identify-
ing and understanding bottlenecks within each
segment comprise the third major step in 6TOC.
Bottlenecks occur when demand exceeds capac-
ity or when actual production in a specified area
is less than its maximum capability for produc-
tion. In this instance, underperformance in one
critical link reduces total production for the en-
tire chain.
Phase one for a common surface mining opera-
tion commences with the loading of coarse rock
(blasted from a stone face) onto a haul truck to
be dumped into a primary crusher, weighed and
stockpiled. This process requires all personnel
and machinery (a large front-end loader, several
haul trucks and a primary crusher) to be used.
Focusing on this phase of the total process,
can you determine which component is the bot-
tleneck targeted for improvement? This approach
is based on Eliyahu Goldratt’s critical chain and
strength of throughput in which the collection
of individual steps and tasks in the process and
their relationships ultimately provide power to
the process.8
Strength arises from recognizing the con-
PROCESS IMPROVEMENT
QP • www.qualityprogress.com46
Step 1 Identify and validate operational metrics.
Step 2 Identify capstone metric through correlation analysis.
Step 3 Identify value-creating, primary process flow.
Step 4 Divide primary process flow into three or four logical and measureable segments.
Step 5 Identify bottlenecks or constraints in each segment.
Step 6 Begin with the segment with the most restrictive bottleneck or constraint.
Step 7 Use lean Six Sigma tools to exploit or eliminate bottlenecks in process.
Step 8 Repeat step 7 working through the next most critical bottleneck.
Step 9 Develop a metrics pyramid for your organization identifying pertinent metrics at each level (corporate, division and location).
Step 10 Develop a communication system using the metrics pyramid for pertinent levels in the organization; consider using scorecards and scoreboards.
Steps to implementing 6TOC / TABLE 1
Production Maintenance Costs Safety
Tons per hour Plant availability Cost per ton Days since last incident
Tons per man-hour Rolling stock availability
Labor cost per ton Number of near misses year to date
Site specific metrics / TABLE 2
Critical process flowchart for mining operation / FIGURE 1
Capabilities chart—tons per hour / FIGURE 2
0
500
1,000
1,500
2,000
2,500
3,000
Loader Haul trucks Crusher
2,540
718 910
Coarse rock to primary crusher
Phase I
Conveyed to secondary crusher and then to
stockpiles
Phase II
Loaded on trucks then weighed and ticketed
Phase III
Truck cycle time actual vs. capable / FIGURE 3
2
3
4
5
6
7
8
Cycle time actual Cycle time capable
Cyc
le t
ime
5.07
3.55
2
3
4
5
6
7
8
Cycle time actual Cycle time capable
Cyc
le t
ime
5.07
3.55
6TOC = A method that combines lean, Six Sigma and theory of constraints.
nections among the individual links and steps. The
strength of the throughput is only as strong as the
weakest link. At this juncture, a capabilities chart is
used (Figure 2, p. 47). With a capabilities chart, each
component is independently tested to determine its
maximum output. Emphasis can be placed on the most
chronic bottleneck slowing the entire process phase to
a suboptimal pace.
The front-end loader was measured to determine
how many tons it could load in one hour. The average
for five trials was 2,540 tons per hour. The haul trucks
also were measured, and their combined average haul
per hour was 718 tons. The primary crusher was tested
in five trials producing an average rate of 910 tons per
hour.
The haul trucks seemed to be the bottleneck. Mea-
sures were taken to improve the weakest link and
hopefully raise the average tons per hour of each haul
truck, including exploiting the bottleneck and raising
the entire phase’s throughput.
Because the team had substantiated the haul truck
theory through Six Sigma-style data capture and anal-
ysis, it avoided erroneous assumptions and rule-of-
thumb management. Until this experiment, manage-
ment had considered purchasing an additional haul
truck or a larger crusher to obtain more throughputs.
Both expenditures would have been premature.
Exploiting and elevating constraintsThe second and fourth steps of Goldratt’s five-step
bottleneck improvement process are exploiting and
elevating. Exploiting a constraint involves trying to
get the most possible out of the constraint. Elevating
a constraint involves major changes that often require
capital expenditures to increase its capacity and re-
moving it as a bottleneck in the system.
Methods of exploiting or elevating a constraint can
be associated with people, process and machinery. The
following questions may help start the processes:
People. Are pertinent people cross trained to al-
leviate problems associated with absences? Are em-
ployees performing a task suboptimally because of
poor training or because that’s the way they’ve always
done it? Do employees consciously slow down the
process to avoid potential unpleasant consequences
such as machine failure? Is the 5S workplace organi-
zation method practiced in the facility and monitored
for compliance?
Process. Does everyone understand the upstream
and downstream process implications of his or her
actions? Does everyone know where the hotspots
(or bottlenecks) in the process are? Is there a formal
way of accomplishing a task and a real way of accom-
plishing a task? Have you considered poka-yoke and
its impact on your process? Has anyone documented
process flow recently?
Machinery. Is current machinery being operated
according to its specifications for throughput? Is it be-
ing calibrated regularly? In terms of facilities layout, is
appropriate machinery located closely together?
December 2014 • QP 49
PROCESS IMPROVEMENT
QP • www.qualityprogress.com48
In the mining case study, attempts were made to
exploit the haul truck bottleneck by getting as much
out of the constraint as possible. We began using lean
to determine how much time would elapse during a
typical haul truck cycle. It begins with the truck be-
ing loaded with coarse rock, it travels to the primary
crusher, it dumps the rock into the crusher and it trav-
els back for another load. The distance from rock load-
ing to rock dumping can range from several hundred
feet to two miles.
The time lapse between each load of rock being
dumped into the primary crusher was measured using
a proximity switch attached to each haul truck. The
proximity switch fed information to an on-board GPS
unit linked to a mobile phone and uploaded daily cycle
times into the cloud and database.
We tested each haul truck to see what its cycle time
capability was compared to its actual production time.
Several trials were conducted. Example results are
shown in Figure 3, p. 47. A lower cycle time equates
to greater production levels, thus exploiting the bottle-
neck.
People, process and machinery The capability time was one minute and 30 seconds
faster than the actual. It may not seem significant, but
it was. If each truck carries 35 tons of material, and
the site uses three trucks, the difference is significant.
With a five-minute cycle time, each truck will deliver
96 loads a day (12 loads an hour x eight hours). With a
three minute and 30 second cycle time, each haul truck
will deliver 136 loads a day (17 loads an hour x eight
hours).
These theoretical additional 40 loads x 35 tons x
three trucks equate to 4,200 tons a day in improved pro-
duction with the same equipment, the same equipment
operating hours and no additional overtime.
Let’s explore the people, process and machinery fac-
tors that led to this constraint exploitation.
People. The haul truck operators were not aggres-
sively driving their trucks to achieve maximum produc-
tion. They took their time. The drivers were not posi-
tioning their haul trucks correctly near the loader prior
to being loaded. The loader operator was not loading
the truck efficiently, using techniques that consumed
more time.
Cycle times were not communicated to drivers so
they did not know how they were performing. This
failure to adhere to Joseph M. Juran’s principle of
“placing employees in a state of control”9 was recti-
fied, resulting in a healthy competition between driv-
ers for the lowest cycle time. Times were posted daily
reflecting the previous day’s results. See Figure 4 for
an example.
Process. Other vehicles on the route often would
clog the passageway, slowing the cycle time. The haul
roads were not wide enough in some areas for two
trucks to safely oppose one another in their transport.
Cycle time comparison by driver / FIGURE 4
0
2
4
6
8
10
12
1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49
Tim
e
Cycles
Dan
Bill
Kyle
Metrics pyramid for the mining industry / FIGURE 5
Senior level metrics (organization)
• Tons per man-hour (capstone metric)• Cost per ton• Labor cost per ton
Middle metrics (division)
• Tons per man-hour • Tons per hour• Plant availability • Total tons
produced• Average selling price
Foundational metrics (location)
• Haul truck cycle time • Overtime hours• Plant availability • Downtime
hours• Total tons produced
These metrics should provide a line of sight to the capstone metric.
Ultimate lagging metrics
Leading and lagging metrics
Leadingmetrics
6TOC communication system / FIGURE 6
scoreboardand foremen
Each level of metrics needs a real-time communication system.
Audience Form and frequency
Capstonemetric
Middlemetrics
Foundationalmetrics
Daily Seen by site managers
Seen by senior management
Seen by divisional or regional management
Monthly financials
Weekly scorecard
Methods of exploiting or elevating a constraint can be associated with people, process and machinery.
6TOC = A method that combines lean, Six Sigma and theory of constraints.
December 2014 • QP 51
PROCESS IMPROVEMENT
TODD CREASY is an associate professor at Western Carolina University in Cullowhee, NC, and a consultant at Bridgepoint LLC in Asheville, NC. He holds a doctorate in Management from Case Western Reserve University in Cleveland. An ASQ member, Creasy is an ASQ-certified Six Sigma Black Belt.
One truck would have to stop and wait for the other
to pass, causing cycle delays.
Machinery. The roads on the haul route were not
smooth. The rough rides caused bodily discomfort dur-
ing transport and slowed cycle times. Different brands
and models of trucks with different maximum operat-
ing speeds being used complicated team synergy and
produced lower cycle times. Preventive maintenance
was not being performed as required, which slowed
production during downtime events.
Communication strategy The process of exploiting or elevating bottlenecks oc-
curred throughout the site’s entire production flow
process. These findings were replicated to other sites.
With the capstone metric firmly established, each level
of the organization (corporate, strategic business units
and site locations) had metrics that were directly or in-
directly tied to the capstone metric. The establishment
of these associated metrics enabled the organization
to align toward a common direction.
Figure 5 on p. 48 is an example of the metrics pyra-
mid. This pyramid has three sections. The top portion
represents the metrics of primary interest to senior
management, which includes the capstone metric.
The second tier represents middle metrics and is of
primary interest to divisional management. The third
section has foundational metrics used by location-
specific personnel.
The last stage of implementing 6TOC is the manage-
ment and employee communication system. To keep
employees in a state of control, Juran said they must
understand the goal, understand their performance
and have the autonomy to meet the goal if perfor-
mance lags.10
Using lean, a series of communication systems was
established based on the metrics identified as impor-
tant for each level of the organization. Senior manage-
ment received communication monthly through stan-
dard financial reviews and reports on the capstone
metric and other pertinent metric values.
Regional or divisional management received perfor-
mance information weekly that compared locations.
Location-level managers and personnel often required
information that is posted daily and populated with
data from the previous day’s activities. See Figure 6 on
p. 49 for a schematic of 6TOC’s communication system
and Figure 7 for the communication system’s example
of a scorecard and scoreboard.
Doing more with less6TOC enabled the mining organization to go against
the operating paradigms and traditional thinking prev-
alent in the industry. This hybrid of Six Sigma, lean
and TOC proved you can do more with less and don’t
need to reach for the checkbook to improve produc-
tivity.
Because production goals were generally met
before an eight-hour shift was completed, preven-
tive maintenance activities, which were normally
conducted during overtime hours, were conducted
during normal shift hours. Also, because of the ag-
gressive preventive maintenance schedules, plant
and equipment availability climbed into the mid-90%
range from the upper 70 to mid-80% level.
In most locations, little capital was expended to
achieve these results. Most long-time employees previ-
ously believed new equipment or refurbished machin-
ery would have to be purchased to improve equipment
availability and productivity.
Equipment expenses dropped because the desired
tonnage was being produced in fewer hours. Inven-
tory accuracy improved because of the increase in
measurements along the throughput process, which
prevented financial surprises at the end of an account-
ing period.
For a comparison of mean tons per hour, month-
over-month production comparisons by location (rep-
resented in box plots), refer to Figure 8.
Practitioners of continuous improvement con-
stantly search for tools to help lead teams and orga-
nizations toward successful outcomes. The marriage
of lean and Six Sigma illustrates the complementary
strengths each method offers for delivering on organi-
zational or project needs.
The addition of TOC creates a potent combination
for quickly finding root causes and producing solu-
tions with a direct bottom-line impact. Regardless of
industry, 6TOC can save time, effort and money when
dealing with process constraints and productivity im-
provement goals, and enable organizations to better
serve all stakeholders, including customers, suppliers,
team members and managers. QP
REFERENCES1. Joseph M. Juran, The Quality Handbook, McGraw-Hill, 1999.2. Todd Creasy, “Pyramid Power,” Quality Progress, June 2009, pp. 40-45.3. Todd Creasy and Sarah Ramey, “Don’t Lose Patients,” Quality Progress,
February 2012, pp. 42-49.4. Louis Johnson and Kirk McNeilly, “Results May Not Vary,” Quality Progress,
May 2011, pp. 42-48.5. Greg Kruger, “The Power of Prediction,” Quality Progress, June 2013, pp.
26-32.6. Eliyahu Goldratt, Critical Chain, North River Press, 1997.7. Jim Collins, Good to Great, Harper Collins, 2001.8. Goldratt, Critical Chain, see reference 6.9. Juran, The Quality Handbook, see reference 1.10. Ibid.
Scorecard of divisional or regional metrics
Site location
Margin per ton compared to
group average
Cost per ton compared to
group average
Plant availability compared to
group average
A
B
C
D
E
F
G
= good = bad
Scoreboard of site or location-level metrics
Communication system / FIGURE 7
Monthly performance / FIGURE 8
Location A tons per hour
700
650
600
550
500
450
400
March April May June July Sep.Aug. Oct. Nov.
Baseline = 475 tons
36%improvement
463
484
527
583
606
621
577
649
631
Dat
a
Location B tons per hour
June July Aug. Sep. Nov.Oct. Dec.
Dat
a
725
700
675
650
625
600
575
550
10%improvement
613617
647
608
651
673677
Baseline = 625 tons
Location C tons per hour
April May June July Sep.Aug. Oct. Nov.
Dat
a
650
600
550
500
450
23%improvement
Baseline = 500 tons497
517
536526
560 556
602 613
QP • www.qualityprogress.com50