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The Toyota Production System (TPS) house diagram is often drawn with a triangular roof, a rectangular foundation, and two rectangular columns between the foundation and roof. The space between the columns is filled with one’s choice of the systems, tools, and principles to suit the lean enterprise application. There is some variation on what goes into the foundation, but few disagree that kaizen, standardized work, and heijunka belong there. The columns are just-in-time and built-in quality (aka jidoka).
In essence, the built-in quality pillar is the practice of controlling variables within a process, securing quality at one’s own process, not passing on poor quality, and checking every piece. It is the very opposite of what we often witness in traditional organizations; well-intentioned people passing on questionable quality, performing checks erratically against inadequate or outdated standards, raising alarms and being met in many cases with silencing looks, and in the end spending enormous amounts of time containing the defects that slip through to the customer. With no time to take root cause countermeasures, the cycle continues until a lean transformation or equivalent culture change can implement systems to change these behaviors.
Luckily there is a much better way. The just-in-time pillar of TPS is built on the elements of takt time, one-piece flow, and downstream pull, with many enabling systems, practices, and tools. Likewise the built-in quality wing of the TPS house is structured around four pillars and their enablers.
The first pillar requires that we build quality in at the source. Reliable processes produce reliable results, and processes are the sum of their inputs. The stabilization and control of the inputs or change points such as the 4-M factors (i.e., manpower, material, machine, and method) as well as environmental factors of temperature, humidity, and particle count are necessary. This may take the form of production preparation activities in the new product introduction phase to understand these factors, as well as practical problem solving to address deviations as they are found with more mature processes and products.
Whenever found, deviations from these conditions must be contained in the short term and addressed long-term through root cause countermeasures. The main enablers of quality at the source are a firm understanding of the customer’s quality requirements, cross-functional involvement in the design of products and processes, and the capability and practice of taking root cause countermeasures.
Each process must have the opportunity to find or prevent defects through the second pillar of self checks. This may be a manual check or a sensor built into the equipment to set off an alert when a defect is about to be created. The goal is to find quality defects when they occur, wherever they occur. Enablers include clear and documented quality standards for the product, checks for input conditions from the “at the source” pillar, and standardized work that is followed and frequently updated. The existence and visualization of standardized work allows for the overall process to be audited and for continuous improvement to be made more easily against that standard.
The third pillar builds quality in through successive checks. Each process is responsible for accepting only good quality. When poor quality is found, the previous process is notified immediately so that it does not continue to make defects. In addition to all previous prerequisites, the main enabling systems for successive checks are one-piece flow and process synchronization. When a batch-and-queue production method is used, this makes it difficult if not impossible for the next process downstream to find the first defect and give feedback that allows the producer process to stop making defects.
The lack of one-piece or small-lot synchronization creates the risk that defects are produced in batch and the problem reamins hidden until a later point in time when a successive check can be performed.
The fourth pillar is to build quality in through 100-percent inspection. This is the element of Toyota’s built-in quality system that puzzles most people. We have been taught to believe that inspection is a waste. Does 100-percent inspection mean that there are people in lab coats with white gloves carefully checking every piece of in-process stock and finished product as it rolls through the process? In fact, yes, it does. I have seen the end-of-line inspectors at Toyota under the bright lights with white uniforms and gloves.
At first, everyone has a variation on the reaction of, “Surely those 14 inspectors at the end of the line are a waste? We got rid of our final inspection process years ago. Why does Toyota still have theirs?”
The overall manufacturing quality record of Toyota should be reason enough, the design- and supply chain-related recalls of the past five years notwithstanding. Too much attention is given to these final quality inspectors dressed in white. The important point is that sampling is not enough. When sampling is done at Toyota, it is typically done by group leaders, managers, or quality engineers who are doing redundant checks to audit the process.
Every process must guarantee quality coming in, built in, and passed on. Philosophically, “zero defects” requires “100-percent inspection.” Practically, this means every piece is checked at every process. In fact, a manual check may not be the best method for every process and every piece of work, and Toyota and others do kaizen to find ways to design quality in to the product as well as process at the source, and then use labor-saving sensors to check where it is not safe or economical for people to do so. The main enabler here may have nothing to do with the TPS diagram itself but rather a mindset change, perhaps based on a financial business case, that the 14 line-end inspectors are always cheaper than field failures.
We can’t build pillars, or anything substantial, without a foundation. The four pillars of built-in quality mentioned in this article are a mix of practices, systems, behaviors, and mindsets. Buried in somewhere are tools such as poka-yoke, andon, and so forth. The word “stability” gets thrown around a lot when talking about foundations, lean, and quality.
Stability is certainly essential from the point of view of the “at the source” variables. The other important facet of stability is organizational. Is the organization stable enough to sustain change of the type called for by built-in quality? One of the most difficult shifts required in the minds of people is to go from a quality mindset based on defense to a quality mindset based on offense. This is proactively building in quality by exposing problems, working together, and changing processes every day, not one based on following rules without question, shutting down those who question the existing standards, and containing problems out of view. This requires being comfortable with a certain amount of change, if not instability.
As we become more comfortable with our daily work, as processes become more established, as standards are set and accepted, we are lulled into a feeling of safety, even arrogance. Those many, many checks within the four pillars of a lean system of built-in quality begin to seem like waste. They certainly don’t add value and should be challenged, but not removed without understanding the effect of doing so on the whole system.
It is a delicate balance between maintaining a quality system with many moving parts and not being tricked into thinking that maintaining it is good enough. The just-in-time and built-in quality columns of the TPS house diagram sit on the foundation that includes kaizen—continuous improvement. It is better to experiment with giving one of the four pillars a kick every now and then to see whether the standards, the checks, and the problem-response systems are truly holding up world-class quality. Yesterday’s best will no longer be good enough for our customers tomorrow, so we might as well start building, auditing, and improving our built-in quality system today.