Six Sigma, Lean And T O C ( A S Q ComparacióN TeoríAs)


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Breve y conciso comparativo de estas teorías que han evolucionaron hasta reconocerse como filosofías y hasta metodologías de diseño y administración de sistemas completos.

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Six Sigma, Lean And T O C ( A S Q ComparacióN TeoríAs)

  1. 1. P R O C E S S I M P R O V E M E N T How To Compare Six Sigma, Lean and the Theory of Constraints A framework for choosing what’s best for your organization by Dave NaveW ITHIN THE AMERICAN business Six Sigma community a multitude of process Six Sigma claims that focusing on reduction of improvement champions are variation will solve process and business problems. vying for leadership attention. By using a set of statistical tools to understand the Each champion advocates the fluctuation of a process, management can begin to adoption of his or her improve- predict the expected outcome of that process. If thement methodology in your organization. Almost allplead that if you adopt their specific tools or follow outcome is not satisfactory, associated tools can bea specific way of thinking, all your business prob- used to further understand the elements influenc-lems will be solved. ing that process. After listening to multiple champions advocate Through a rigid and structured investigationtheir special methodology, how do you choose methodology, the process elements are more com-what will be best for your situation? What method- pletely understood. The assumption is the outcomeology fits the culture of your organization? of the entire process will be improved by reducing Many process improvement methodologies the variation of multiple elements.appear to conflict with each other or at least down- Six Sigma includes five steps: define, measure,play the contribution of othermethodologies. This montage of TABLE 1 Improvement Programstools and philosophies creates theillusion of conflicting strategies. Program Six Sigma Lean thinking Theory of constraints In this article, I will discuss the Theory Reduce variation Remove waste Manage constraintsbasics of the three improvement Application 1. Define. 1. Identify value. 1. Identify constraint.methodologies and present a model guidelines 2. Measure. 2. Identify value stream. 2. Exploit help you understand their con- 3. Analyze. 3. Flow. 3. Subordinate processes. 4. Improve. 4. Pull. 4. Elevate constraint.cepts and effects and similarities 5. Control. 5. Perfection. 5. Repeat cycle.and differences. Table 1 describes Focus Problem focused Flow focused Systems constraintsthe essence of each methodology. QU A L I T Y P R O G R E S S I M A R C H 2 0 0 2 I 73
  2. 2. H O W T O C O M PA R E S I X S I G M A , L E A N A N D T H E T H E O RY O F C O N S T R A I N T Sanalyze, improve and control zation can respond to cus-(commonly known as DMAIC): tomer needs more quickly.• Define. Practitioners begin by Six Sigma is founded on defining the process. They ask two main assumptions. who the customers are and First, people in an organi- what their problems are. They identify the key characteristics Six Sigma The assumption is the outcome zation understand and appreciate the fact that important to the customer numbers can represent along with the processes that features and characteris- support those key characteris- tics of a process. They tics. They then identify exist- of the entire process will be appreciate that a deeper ing output conditions along understanding of data and with the process elements. data analysis can be used• Measure. Next the focus is on measuring the process. Key improved by reducing the to produce improvements, and graphical representa- characteristics are categorized, tions of data can provide new and different per- measurement systems are veri- fied and data are collected. variation of multiple elements. spectives of the process.• Analyze. Once data are col- Analytical types, such as lected, it is analyzed. The engineers and scientists, intent is to convert the raw generally respect this data into information that pro- approach. vides insights into the process. Another assumption is These insights include identi- that through the reduction fying the fundamental and most important causes of variation of all the processes, the overall perfor- of the defects or problems. mance of the organization will be improved. But while• Improve. The fourth step is to improve the process. it is hard to argue against improvement, the economic Solutions to the problem are developed, and reality of business is we want the most improvement changes are made to the process. Results of process for the least investment. Improving all of an organiza- changes are seen in the measurements. In this step, tion’s individual processes could actually have a detri- the company can judge whether the changes are mental effect on the company’s ability to satisfy the beneficial, or if another set of changes is necessary. customer’s needs and provide product and services at• Control. If the process is performing at a desired the right time at the lowest cost. The realized savings and predictable level, it is put under control. This to the system might be less than the cost of all the last step is the sustaining portion of the Six Sigma improvements. methodology. The process is monitored to assure no So, an organization that improves things just unexpected changes occur. because it can may be improving the wrong things for Focusing on the primary area of variation reduction the business.produces other secondary effects, too. Quality isimproved. Process investigation produces the re-eval- Lean thinkinguation of the value added status of many elements. Lean thinking is sometimes called lean manufactur-Some elements are modified, while others are discon- ing, the Toyota production system or other names.tinued. Elements are refined and improved. Mistakes Lean focuses on the removal of waste, which isand opportunities for mistakes are reduced. defined as anything not necessary to produce the Some elements discovered during the Six Sigma product or service.investigation constrain the flow of products or ser- One common measure is touch time—the amountvices through the system. Flow is defined as the time of time the product is actually being worked on, orfrom the input of raw material to the output of a sal- touched, by the worker. Frequently, lean’s focus isable item. Improvement of a process that was restrict- manifested in an emphasis on flow results in reduced variation, better quality There are five essential steps in lean:and improvement in the volume of the process out- 1. Identify which features create value.put. Thus the organization has less money tied up in 2. Identify the sequence of activities called the valuein-process inventory. The time from paying for input stream.material to seeing a profit is reduced, and the organi- 3. Make the activities flow.74 I M A R C H 2 0 0 2 I W W W . A S Q . O R G
  3. 3. 4. Let the customer pull product or service through stant attempt to remove nonvalue activity, improve the process. flow and satisfy customer delivery needs.5. Perfect the process. While lean focuses on removing waste and improv- Identify value. The determination of which features ing flow, it too has some secondary effects. Quality iscreate value in the product is made from the internal improved. The product spends less time in process,and external customer standpoints. Value is expressed reducing the chances of damage or terms of how the specific product meets the cus- Simplification of processes results in reduction of vari-tomer’s needs, at a specific price, at a specific time. ation. As the company looks at all the activities in theSpecific products or services are evaluated on which value stream, the system constraint is removed, andfeatures add value. The value determination can be performance is improved.from the perspective of the ultimate customer or a The lean methodology also makes some assump-subsequent process. tions: Identify the value stream. Once value is identified, • People value the visual effect of flow.activities that contribute value are identified. The • Waste is the main restriction to profitability.entire sequence of activities is called the value stream. • Many small improvements in rapid succession areThen a determination is made as to whether activities more beneficial than analytical study.that do not contribute value to the product or service • Process interaction effects will be resolved throughare necessary. Necessary operations are defined as value stream refinement.being a prerequisite to other value added activities or People in operations appreciate this approach.being an essential part of the business. An example of Lean involves many people in the value stream.a nonvalue added but necessary process is payroll. Transitioning to flow thinking causes vast changes inAfter all, people need to be paid. Finally the impact how people perceive their roles in the organizationnecessary, nonvalue added activities have on the and their relationships to the product.process is reduced to a minimum. All other nonvalueadded activities are transitioned out of the process. Theory of constraints (TOC) Improve flow. Once value added activities and nec- TOC focuses on system improvement. A system isessary nonvalue activities are identified, improvement defined as a series of interdependent processes. Anefforts are directed toward mak- analogy for a system is theing the activities flow. Flow is chain: a group of interdepen-the uninterrupted movement of dent links working togetherproduct or service through the toward the overall goal. Thesystem to the customer. constraint is a weak link. Major inhibitors of flow arework in queue, batch processingand transportation. These Lean the Lean focuses on The performance of the entire chain is limited by the strength of the weakest link. Inbuffers slow the time from prod- manufacturing processes, TOCuct or service initiation to deliv-ery. Buffers also tie up money removal of waste, which concentrates on the process that slows the speed of prod-that can be used elsewhere in uct through the system.the organization and cover up TOC consists of five steps:the effects of system restraints is defined as anything 1. Identify the constraint.and other wasted activities. 2. Exploit the constraint. Allow customer pull. After 3. Subordinate other processeswaste is removed and flowestablished, efforts turn to let- not necessary to produce to the constraint. 4. Elevate the constraint.ting the customer pull product 5. Repeat the cycle.or service through the process.The company must make the the product or service. Identify. The constraint is identified through variousprocess responsive to providing methods. The amount of workthe product or service only in queue ahead of a processwhen the customer needs it— operation is a classic indicator.not before, not after. Another example is where Work toward perfection. This products are processed ineffort is the repeated and con- batches. QU A L I T Y P R O G R E S S I M A R C H 2 0 0 2 I 75
  4. 4. H O W T O C O M PA R E S I X S I G M A , L E A N A N D T H E T H E O RY O F C O N S T R A I N T S Exploit. Once the constraint is identified, the improvement programs: that many programs use aprocess is improved or otherwise supported to mass, one size fits all approach to improvement. Withachieve its utmost capacity without major expensive the mass approach, a company hopes that by refiningupgrades or changes. In other words, the constraint is and improving each process individually and inde-exploited. pendently to maximum output, Subordinate. When the con- the entire system output willstraining process is working at improve.maximum capacity, the speeds TOC methodology operates TOCof other subordinate processes on several assumptions:are paced to the speed or • As in the case of lean, thecapacity of the constraint. Someprocesses will sacrifice individ- The performance of the organization places a value on the speed at which itsual productivity for the benefit product or service travelsof the entire system. through the system. Speed Subordinate processes are entire chain is limited by and volume are the mainusually found ahead of the con- determinants of success.straint in the value stream. • Current processes are essen-Processes after the constraint tial to produce the desiredare not a major concern—they the strength of the output.are probably already producing • The product or service designunder capacity because they is stable.have to wait on the constrain-ing process. weakest link. Value added workers do not need to have an in-depth Elevate. If the output of the understanding of this improve-overall system is not satisfac- ment methodology. Suggestionstory, further improvement by the workforce are not con-is required. The company sidered vital for successfulmay now contemplate major implementation of the theory ofchanges to the constraint. constraints. Organizations withChanges can involve capital hierarchical structure and cen-improvement, reorganization tralized knowledge value thisor other major expenditures of approach.time or money. This is called elevating the constraintor taking whatever action is necessary to eliminate it. Comparing the three methods Repeat. Once the first constraint is broken, another There are some commonalities and general criti-part of the system or process chain becomes the new cisms of all improvement models. In addition, allconstraint. Now is the time to repeat the cycle of process improvement theories and methodologiesimprovement. The performance of the entire system make a few of the same assumptions. The main pointsis re-evaluated by searching for the new constraint of each methodology are summarized in Table 2.process, exploiting the process, subordinating and Improvement methodologies begin by taking theelevating. product or service configuration at face value and By focusing on constraints, this methodology pro- improving the processes or system. They assume theduces positive effects on the flow time of the product following:or service through the system. Reduction of waste in • The design of product or service is essentially cor-the constraint increases throughput and improves rect.throughput time. When the constraint is improved, • The design of the product or service is the most eco-variation is reduced, and quality is improved. nomical. Constraint focus does not require intimate knowl- • Customer needs are satisfied with that design.edge of data analysis or that a large number of people • The current product configuration fulfills the func-understand the elements of the system. Understanding tional requirements of the market and a few people with the power to change things is all • The management structure supports and nourishesthat is necessary. The effort can be localized with mini- change.mum involvement of the workforce. These assumptions may not be valid and require TOC overcomes one criticism of most process exploration.76 I M A R C H 2 0 0 2 I W W W . A S Q . O R G
  5. 5. After extensive refinement of the exist-ing processes or systems, many improve- TABLE 2 Comparison of Improvement Programsment methodologies begin to look at theproduct or service design. However, Program Six Sigma Lean thinking Theory of constraintseach views the design through its theory Theory Reduce variation Remove waste Manage constraintsand tools. Application 1. Define. 1. Identify value. 1. Identify constraint. Quality function deployment and guidelines 2. Measure. 2. Identify value stream. 2. Exploit constraint.value management are two techniques 3. Analyze. 3. Flow. 3. Subordinate processes.used to help connect the product or ser- 4. Improve. 4. Pull. 4. Elevate constraint.vice design to customer needs. Both 5. Control. 5. Perfection. 5. Repeat cycle.bring marketing, finance, operations, Focus Problem focused Flow focused System constraintsdesign, customer and suppliers together Assumptions A problem exists. Waste removal will Emphasis on speedto systematically explore how the prod- Figures and numbers improve business and volume.uct performs the function the customer are valued. performance. Uses existing systems. System output improves Many small improvements Process interdependence.needs. if variation in all are better than An interesting part of this investiga- processes is reduced. systems analysis.tion is that cost can be associated with Primary effect Uniform process output Reduced flow time Fast throughputfunction. When marketing and cus- Secondary Less waste. Less variation. Less inventory/waste.tomers know the cost of specific features, effects Fast throughput. Uniform output. Throughput costthey make informed choices about the Less inventory. Less inventory. accounting.configuration of the product or services. Fluctuation—performance New accounting system. Throughput—performance measures for managers. Flow—performance measurement system.Major obstacles to improvement Improved quality. measure for managers. Improved quality. Improved quality. There are major obstacles to the Criticisms System interaction Statistical or system Minimal worker input.improvement methodologies: not considered. analysis not valued. Data analysis not valued.• They address management theory as a Processes improved secondary or tertiary issue. independently.• They don’t address policies, either for- mal or informal.• They don’t address how managers are measured Beneath a theory of management is a system of and rewarded for process improvements. organizational values. Is the purpose of the organiza-• They don’t address the general theory of manage- tion solely to increase the wealth of the stockholders? ment used by the organization. Or is the existence of the organization to benefit soci-• They don’t address the organization’s values. ety, the nation or some other group? Do not get caught In any organization many activities are driven by in the trap of thinking an organization’s only purposepolicies whose purpose has been lost in time. All is to make money. Money, or profit, is the result ofchange programs challenge the existing ways of doing good management toward satisfying a societal need.things. This necessitates asking what purpose a specif- Also, consider that some organizations are created notic policy serves and whether that purpose is still valid to make a today’s environment. The issues of theory of management and organiza- One technique for assessing an organization’s man- tional ethics and values are beyond the scope of thisagement theory is to search for the underlying article but have been raised to point to other areasassumptions supporting each policy. A challenge of needing consideration when looking at process or sys-assumptions provides a starting point for determining tem improvement programs.whether the current policy is still supporting some- Champions of each of these methods say they canthing of value today. overcome these drawbacks because implementation of The management theories of W. Edwards Deming their particular methodology and focus on their tools,may help organizations challenge current manage- methods and theories will allow an improved theoryment practices and assumptions—not by suggesting of management and business strategy to emerge.incremental improvements but by pointing to a newway of managing. Through this line of study, leaders How to chooseachieve a greater understanding of the way they can To help work through the apparent conflicts of dif-influence the social and economic well-being of their ferent improvement programs, use a model that iden-organization. tifies a hierarchy of cause and effect relationships. QU A L I T Y P R O G R E S S I M A R C H 2 0 0 2 I 77
  6. 6. H O W T O C O M PA R E S I X S I G M A , L E A N A N D T H E T H E O RY O F C O N S T R A I N T S First, identify the primary theory. What is the core use, the main issue left to explore is the speed at whichemphasis of the program or methodology? This core a method will be accepted into an organization:emphasis is usually a few words or a short phrase: Six • If your organization values analytical studies andSigma’s is variation reduction, lean’s is waste reduc- the relationships of data, charts and analysis, Sixtion and TOC’s is constraint reduction. Sigma is a perfect program for you to start with. Then identify the relationship between the primary • If your organization values visual change and righttheory and the primary focus of the tools and method- now time, then lean thinking might be the way toology. This relationship indicates how the primary the- go.ory manifests itself in tangible results—what I call the • If your organization values a systems approachprimary effect. This is an if/then type of relationship: where total participation is not desired and if it val-• For Six Sigma: “If we focus on reducing variation, ues the separation between worker and manage- then we will have more uniform process output.” ment, then TOC might be a good way to start.• For lean: “If we focus on waste removal, then flow More and more organizations are trying to deter- time will improve.” mine what improvement method will work best and• For TOC: “If we focus on constraints, then through- fit best with their culture. When you are working put volume will improve.” through the apparent conflicting claims of perfor- The next to last level of the model in Table 2 (p. 77) mance improvement programs, my advice is to con-identifies secondary effects. Secondary effects can be centrate on the primary and secondary effects of theirdescribed by using an if/theory and primary philosophies. Once the values of a specific improve-effect/results type statement. While the primary theo- ment program are identified, the comparison of thosery to primary effect relationship is usually one-to-one, values with the values of the organization can makethe secondary effects are several-to-many, including: the method of selection easier, if not obvious.• For Six Sigma, focus on reducing variation and Never stop learning. Each improvement methodol- achieving uniform process results in less waste, less ogy contributes valuable concepts, ideas and tech- throughput time and less inventory. niques to your organization. Your challenge is to use• For lean thinking, focus on waste and flow time whatever strengths the methodology possesses to help results in less variation, uniform output and less your organization improve. inventory.• For TOC, focus on constraints and increased BIBLIOGRAPHY throughput results in less inventory and a different Deming, W. Edwards, The New Economics for Industry, accounting system. Government, Education, second edition (Cambridge, MA: Each improvement methodology appears to be dri- Massachusetts Institute of Technology, 1994).ving toward common tools and concepts. However, Dettmer, William H., Goldratt’s Theory of Constraints: A Systemsdifferent methodologies begin the journey from differ- Approach to Continuous Improvement (Milwaukee: ASQent perspectives. At the secondary effects level of the Quality Press, 1997).model, the results from each methodology start to Goldratt, Eliyahu M., The Goal: A Process of Ongoinglook similar. Many of the secondary effects of one Improvement, second edition (Great Barrington, MA: Northmethodology look similar to the primary effect or River Press, 1994).focus of another methodology. Goldratt, Eliyahu M., It’s Not Luck (Great Barrington, MA: Extending the fundamental philosophy through each North River Press, 1994).methodology’s primary, secondary and tertiary effects, Womack, James P., and Daniel T. Jones, Lean Thinking: Banishyou might conclude each method strives to achieve Waste and Create Wealth in Your Corporation (New York:similar results. Even along the journey, each methodol- Simon & Schuster, 1996).ogy incorporates the primary effects of other improve-ment programs. Can we infer that after extensive timeand effort implementing a single methodology, the end DAVE NAVE works on assignment to Boeing Commercialresult will be similar no matter which path we take? Airplanes for Comforce Technical Services. He holds a master’s Where does that leave us? As a manager, how do degree in management systems from the Deming Scholarsyou select an improvement methodology or program Program at Fordham University in New York. Nave is a memberto overcome your obstacles? of ASQ. QP Selection of a process improvement methodology isdependent on the culture of your organization. If manypopular programs appear to end up in the same placeaddressing the same issues after a number of years of © 2002 American Society for Quality. Reprinted with permission.78 I M A R C H 2 0 0 2 I W W W . A S Q . O R G