Theory of Constraints

Theory of Constraints (TOC) is an overall management philosophy introduced by Dr. Eliyahu M. Goldratt in his 1984 book titled The Goal, that is geared to help organizations continually achieve their goal.[1] The title comes from the contention that any manageable system is limited in achieving more of its goal by a very small number of constraints, and that there is always at least one constraint. The TOC process seeks to identify the constraint and restructure the rest of the organization around it, through the use of the Five Focusing Steps.

Key Assumption
The underlying assumption of Theory of Constraints is that organizations can be measured and controlled by variations on three measures: Throughput, Operating Expense, and Inventory. Throughput is money (or goal units) generated through sales. Operating Expense is money that goes into the system to ensure its operation on an ongoing basis. Inventory is money the system invests in order to sell its goods and services.[2]

The five focusing steps

Theory of Constraints is based on the premise that the rate of goal achievement is limited by at least one constraining process. Only by increasing flow through the constraint can overall throughput be increased. [1]
Assuming the goal of the organization has been articulated (e.g., "Make money now and in the future") the steps are:
1. IDENTIFY the constraint (the resource/policy that prevents the organization from obtaining more of the goal)
2. Decide how to EXPLOIT the constraint (make sure the constraint's time is not wasted doing things that it should not do)
3. SUBORDINATE all other processes to above decision (align the whole system/organization to support the decision made above)
4. ELEVATE the constraint (if required/possible, permanently increase capacity of the constraint; "buy more")
5. If, as a result of these steps, the constraint has moved, return to Step 1. Don't let inertia become the constraint.
The five focusing steps aim to ensure ongoing improvement efforts are centered around the organization's constraints. In the TOC literature, this is referred to as the Process of Ongoing Improvement (POOGI).
These focusing steps are the key steps to developing the specific applications mentioned below.

Constraints

A constraint is anything that prevents the system from achieving more of its goal. There are many ways that constraints can show up, but a core principle within TOC is that there are not tens or hundreds of constraints. There is at least one and at most a few in any given system. Constraints can be internal or external to the system. An internal constraint is in evidence when the market demands more from the system than it can deliver. If this is the case, then the focus of the organization should be on discovering that constraint and following the five focusing steps to open it up (and potentially remove it). An external constraint exists when the system can produce more than the market will bear. If this is the case, then the organization should focus on mechanisms to create more demand for its products or services.
Types of (internal) constraints
Equipment: The way equipment is currently used limits the ability of the system to produce more salable goods / services.
People: Lack of skilled people limits the system.
Policy: A written or unwritten policy prevents the system from making more.
The concept of the constraint in Theory of Constraints differs from the constraint that shows up in mathematical optimization. In TOC, the constraint is used as a focusing mechanism for management of the system. In optimization, the constraint is written into the mathematical expressions to limit the scope of the solution (X can be no greater than 5).
Please note: Organizations have many problems with equipment, people, policies, etc. But the constraint is the thing that is preventing the organization from getting more Throughput (typically, sales).

Buffers

Buffers are used throughout Theory of Constraints. They appear as part of the EXPLOIT and SUBORDINATE steps of the five focusing steps. Buffers are placed before the key constraint, thus ensuring that the constraint is never starved. Buffers used in this way protect the constraint and should allow for normal variation of processing time and the occasional upset (Murphy) before the constraint.
Buffers can be a bank of physical objects before a work center, waiting to be processed by that work center. Buffers can also be represented by time, as in the time before work reaches the constraint. There should always be enough (but not excessive) work in the time queue before the constraint.
Buffers are not the small queue of work that sits before every work center in a Kanban system. The assumption in Theory of Constraints is that with one constraint in the system, all other parts of the system have sufficient capacity to keep up with the work at the constraint. In a balanced line, as dictated by Kanban, when one work center goes down, then the entire system must wait until that work center is restored. In a TOC system, the only situation where work is in danger is if the constraint is unable to process (either due to malfunction, sickness or a "hole" in the buffer).

Plant types

There are four primary types of plants in the TOC lexicon. Draw the flow of material from the bottom of a page to the top, and you get the four types. They specify the general flow of materials through a system, and they provide some hints about where to look for typical problems. The four types can be combined in many ways in larger facilities.
I-Plant: Material flows in a sequence, such as in an assembly line. The primary work is done in a straight sequence of events (one-to-one). The constraint is the slowest operation.
A-Plant: The general flow of material is many-to-one, such as in a plant where many sub-assemblies converge for a final assembly. The primary problem in A-plants is in synchronizing the converging lines so that each supplies the final assembly point at the right time.
V-Plant: The general flow of material is one-to-many, such as a plant that takes one raw material and can make many final products. Classic examples are meat rendering plants or a steel manufacturer. The primary problem in V-plants is "robbing" where one operation (A) immediately after a diverging point "steals" materials meant for the other operation (B). Once the material has been processed by A, it cannot come back and be run through B without significant rework.
T-Plant: The general flow is that of an I-Plant (or has multiple lines), which then splits into many assemblies (many-to-many). Most manufactured parts are used in multiple assemblies and nearly all assemblies use multiple parts. Customized devices, such as computers, are good examples. T-plants suffer from both synchronization problems of A-plants (parts aren't all available for an assembly) and the robbing problems of V-plants (one assembly steals parts that could have been used in another).
For non-material systems, one can draw the flow of work or the flow of processes and arrive at similar basic structures. A project, for example is an A-shaped sequence of work, culminating in a delivered project.

The End of an Era

The End of an Era

When General Motors filed for bankruptcy yesterday it marked the end of an era. The first truly modern, manage-by-the-numbers corporation, created by Alfred Sloan in the 1920s, was laid to rest as a viable concept. But what comes next?
This is not just a question for GM or large enterprises more generally. Yesterday also marked an end of the lean narrative that has been unfolding for thirty years, ever since GM first began to decline in the recession of 1979. David (in fact a team of Davids) finally felled Goliath just as Goliath was finally paying attention to the lean message. So we need to consider what happens next for the Lean Community as well.
What's Next For GM?
At the beginning of 2009, GM had three major weaknesses. It had too much legacy debt – bondholders and retirees. It had compensation costs for current employees that were too high to compete with transplant operations in North America. And the money it received for its products in most segments of the market was far below average, partly as a legacy of decades of defective products and partly due to losing the pulse of the public on what the company and its products should mean for customers.
Ironically, GM also had considerable strengths. It had competitive factories in terms of productivity and quality and a competitive product development process when it could focus its energies. (E.g., the new Chevy Malibu.) After failing for 15 years to learn lessons from NUMMI (its California joint venture with Toyota), GM had in recent years developed a competitive and consistent global manufacturing system and rationalized its global product development organization. It had even taken impressive steps to lean its internal business processes. But -- as in the case of its cast-off parts supplier Delphi -- lean came too late.
The bankruptcy re-sets the trip odometer. The legacy debt has been written down to a manageable level and compensation costs for current employees will now be much more competitive. In addition, the company is dramatically retrenching toward a reasonable portfolio of brands with production capacity appropriate to its realistic share of likely market volumes.
So what is the problem? Simply that GM has now explained what it is not. It is not Saturn or Saab or Pontiac or Hummer. (Or Opel or Vauxhall either, although surely the new Opel will be a supplier of fully-engineered cars for GM for a long time to come.) And GM is not a significant manufacturer in the U.S. outside of the Midwest. And GM is not, from a profitability standpoint, mainly a finance company. And GM will not have a dealer net blanketing every area of every city across the continent.
But what a company is not is of no interest to consumers. If General Motors is no longer "your father's GM" (to paraphrase its advertising line in the last years of Oldsmobile) or "the company that let you down" (as CEO Fritz Henderson phrased it at yesterday's news conference), then what is it? Why should any new customers care to shop GM products, much less pay the top-of-the-segment prices GM needs to flourish? And who can define what the new, appealing GM is?
Sloan's great genius in re-creating General Motors in the 1920s (after its second trip through reorganization – yesterday marked the third in 100 years) was to provide a compelling explanation of how GM fit into every American's life. He presented a complete range of vehicles from a used Chevrolet as a first car for the low income buyer to a fully-equipped Cadillac for those who had succeeded financially. And GM products were carefully arrayed in a status hierarchy with brilliant attention to the look and feel of each product in relation to American tastes. Indeed, as it gained massive size, GM was often the arbiter of American tastes.
So far the only message about what GM is is the Volt, its extended-range hybrid. Perhaps this is a start, although with enormous risks given the flux in technologies and in political and public perceptions about climate change and energy dependency. But even if it is a start, it is a very small start. Who can comprehensively define "your son's GM", "the GM that never lets you down"? And what freedom will they have to do so?
It is easy to blame GM's recent management for its troubles. But the senior GM managers I have known – almost all of whom had strong finance backgrounds --were remarkably competent at running the company in the financially oriented, manage-by-results way that had produced success for generations. So the problem is not the individual competence of mangers but GM's irrelevant conception of what management needs to do. In simplest terms, where is the new Sloan, the leader able to rethink GM's management and purpose and make it relevant to Americans again?
And supposing the new Sloan (or Sloans) can be found. What freedom will this person or team have to run the company in a way that restores its former glory? This is truly a central question because the U.S. government, as the new owner, is sure to be enormously conflicted:
Should the company be immediately and completely "right-sized" for its new place in the world? (This would be the best way to boost share prices so the government can sell the stock to recoup its massive investment. And it would be the best way to help Ford and Chrysler as well, by eliminating excess capacity.) Or should GM stimulate employment in a deep recession and placate the union by minimizing cutbacks? It can't do both.
Should GM focus in the next few years on the big pick-ups and SUVs that account for all of its profits? (This would be another excellent way to boost share prices so the government can recoup its investment.) Or should GM take a dramatic turn toward highly fuel-efficient products, which won't sell and certainly not at high margins unless energy pricing is also dramatically adjusted upward toward world levels? (e.g., $5 versus $2 per gallon.) It can't do both.
Clearly the hard part comes now, after bankruptcy, and we will all watch what happens. But let me make an exception for those readers – and there are many – who work at GM and who can take an active role in making it happen. I truly wish you the best.
What's Next for Lean?
For 30 years now the Lean Community has benefited from a strong trailing wind. GM steadily declined as Toyota steadily advanced. All we needed to do was standby and cheer! But this narrative is over.
GM and almost all large manufacturers have now accepted lean as a management theory, although the actual practice is always a struggle. As I noted above, GM was becoming a vastly leaner enterprise just as it collapsed and I have confidence that it will continue to embrace lean principles and methods in the years immediately ahead.
At the same time Toyota has turned out to have flaws of its own in the current financial crisis. It barged ahead with capacity expansion across the world that outran its ability to create lean managers and defied reasonable expectations for long-term market demand. (As I have mentioned in previous e-letters, in the mid-1990s Toyota redefined its purpose from being the best organization at solving customer problems to being the largest, an objective of no interest to any customer.) This has been a real setback for the lean movement.
We in the Lean Community therefore find ourselves in the odd position of winning a battle of ideas without actually getting most believers to fully practice their new convictions. And we have as our ideal organization a company that is experiencing significant management and revenue challenges despite "winning" the great contest between modern management and lean management.
Even as this drama plays out within manufacturing, lean ideas are spreading rapidly to new fields, from the beleaguered financial industry to healthcare to government services. Yet we have not fully defined what lean means in these areas, much less how to implement and sustain it. So the dramatic events of recent weeks are not a time for self-congratulation. Instead, they are a time for modesty and self-reflection – hansei, if you will – as we all struggle with the economic crisis while trying to re-define our own purpose as a Lean Community for the new era ahead.