When we have completed Steps 13 and 14, we can start to develop the required control plans.
What Is a Process Control System?
A process control system is a strategy for maintaining the improved process performance over time. It outlines the specific actions and tools required for sustaining process
improvements or gains. There are several ways to develop a control system:
• Risk management
• Poka-yoke—mistake-proofing devices
• Statistical process control (SPC)
• Data collection plans
• Ongoing measurements
• Audit plans
• Process documentation
• Process ownership
A process control system is critical for all projects because it helps to:
• Define the actions, resources, and responsibilities required to make sure that the problem remains corrected and that the benefits from the solution continue to be realized.
• Provide the methods and tools needed to maintain the process improvement, independent of the current team.
• Ensure that the improvements made have been documented (this is often necessary to meet regulatory requirements).
• Ease full-scale implementation by promoting a common understanding of the process and planned improvements.
While there are several ways to develop a process control system, we will discuss the three most common methods (see Figure 5.2).
Figure 5.2 Three Categories of Control Mechanisms
What Is a Quality Plan?
A quality plan is a documented plan whose purpose is to ensure that each product or service characteristic or process requirement stays in conformance. Examples of these documented plans include the final state process map, checklists, or the newly documented standard operating procedures. Ideally, a quality plan should include:
1. Process standards, such as procedures to follow, specifications, or operating tolerances.
2. A description of the process flow and documentation of roles and responsibilities—a flowchart is very useful.
3. A description of the new standard operating procedures (SOPs). SOPs have to be very specific, telling the employees precisely what actions to take and when and where to take them. The descriptions need to be at a level such that the job can be performed well by a person who is not fully trained. And finally, they need to describe how to prevent process variation.
4. Process controls, that is, items to be monitored or audited, and the corresponding response planning if the process should deviate.
What Is Mistake-Proofing?
Mistake-proofing, also known as the Lean tool poka-yoke, is a technique for eliminating errors by making it impossible for mistakes to occur. When you are applying the concept of mistake-proofing in developing a control plan, it is important to remember its guiding
principles:
• Respect the intelligence of employees (mistakes are the fault of processes, not people).
• Eliminate high-volume repetitive tasks or actions that require employees to constantly be alert.
• Free employees’ time and mind to pursue more creative and value-adding activities.
• It is not acceptable to produce even a small number of defects or defective products.
• The objective is zero defects.
If we understand the root cause of errors, we can better define solutions. Generally the main drivers of errors are:
• Incorrect procedures or operational definitions
• Excessive variation in the process or its inputs
• Inaccurate measuring devices
• Human error
Examples of things in our everyday lives that have been mistake-proofed include:
• Irons that shut off automatically
• ATM stations that accept debit cards only if they are inserted correctly
• Cars that stop automatically if a seatbelt is not worn
How Is Mistake-Proofing Different from Traditional Inspection Processes?
Many organizations have dedicated people or use portions of people’s time to review other employees’ work or to audit the end product or service for quality control on a regular basis.
In these organizations, errors are caught after human labor and cost have been applied to develop and deliver the product or service. More important, this mode of inspection relies on humans to catch errors, and this is not 100 percent effective. The key reason why firms rely on inspection instead of mistake-proofing has to do with the traditional view of errors rather than the Lean Six Sigma view of errors.
• The traditional view of errors is that they are inevitable, because:
People are only human.
There is variation in everything.
Lack of standard operating procedures results in each person having his own way of doing things.
Inspection is necessary.
• The Lean Six Sigma view on errors is that they can be eliminated.
Not all errors can be eliminated, but many can, and others can be reduced.
The more errors we can eliminate, the better our quality.
The need for inspection can be reduced or eliminated.
Figure 5.3 helps to outline the difference between traditional quality control plans that rely on inspection and a mistake-proofed process.
Figure 5.3 Feedback
The key differences between traditional inspection and mistake-proofing are given in Table 5.1.
Table 5.1 Key Differences Between Traditional Inspection and Mistake-Proofing In the end, you cannot inspect quality into a process; you have to build it in.
Steps in Mistake-Proofing
The steps required for mistake-proofing are rather simple, but they do rely on the expertise of the process, product, or service subject-matter experts. The steps are shown in Figure 5.4.
Figure 5.4 Poka-yoke
The advantages of mistake-proofing are that:
• No formal training is required to get the team started.
• It can help to eliminate many inspection points.
• It relieves employees from repetitive tasks, which helps them focus on value-adding activities.
• It results in defect-free work.
• It provides immediate action when problems arise.
When you are applying the mistake-proofing principle with your team, just remember:
• Your goal is to build quality into your process(es).
• All inadvertent errors and defects can be eliminated or reduced significantly if everyone works together to identify the true causes of these errors and defects.
• Employees can stop doing things wrong and start doing them right.
• Avoid getting caught up in excuses; the team needs to think about how work can be performed error-free.
• You may not be able to eliminate an error completely, but even a 70 percent chance of success is good enough—this is all about continuous improvement.
• Seek out the true cause of an error, using fishbone, brainstorming, five whys, FMEA, and other tools.
Statistical Process Control
The third technique for developing a process control system is statistical process control (SPC).
What Is an SPC Chart?
An SPC chart is nothing more than a time-ordered plot of your process data (see Figure 5.5).
When these data are graphed using statistical software, the resulting plot outlines the
expected range of variation of the data. Since the expected range is known, anything outside of that is considered a special occurrence that needs investigation and correction.
Figure 5.5 SPC Chart
What Is the Purpose of an SPC Chart?
SPC charts can be used to monitor either your process Xs or your process Y (inputs or output), or both. When process data are readily available, these charts can help the process owner quickly identify:
• When a process is working the way it is intended to—experiencing variation, but nothing unusual or unexpected
• When the process has changed and action needs to be taken
Ultimately, SPC charts can help reduce rejects and rework, improving productivity.
Types of SPC Charts
In general, there are two categories of SPC charts: variable and attribute. Variable charts require continuous data (length, dimension, cycle time, and other such measures), and attribute charts use discrete data (good/bad, pass/fail, and other such measures). There are four types of attribute charts: NP, P, C, and U. For variable charts, there are two types:
individuals and moving range, and X-bar and range.
So how does one know which chart in each category to use? The answer will depend on several variables: whether you have lots of data or a little, and whether the data set is
consistent in size or variable. These factors affect the type of graph you should use. The flow chart in Figure 5.6 helps outline the selection process.
Figure 5.6 Which SPC Chart to Use
Based on your process data, you can determine what chart can be generated. Once you have collected the data, you can use statistical software to produce the appropriate chart(s) and provide continuous monitoring of the process. Table 5.2 and Figure 5.7 provide an example of an SPC C chart for a process that is monitoring the number of missing data in incoming applications. Each application has 20 critical customer data. For 20 days, 25
random applications are collected and the total number of missing data points is monitored.
A chart of the data is then produced (see Figure 5.7).
Table 5.2 Data Table for SPC Chart
Figure 5.7 SPC Chart Example
How Do You Read an SPC Chart?
When you develop an SPC chart for process Xs and/or Ys, you are monitoring the process for two types of variation:
• Common-cause variation. Natural and random variations, such as natural volatility in the incoming volume of requests or processing time.
• Special-cause variation. Unusual, unexpected, or sporadic variation, such as that caused by a financial market meltdown or equipment failure.
If a process is experiencing only common-cause variation, meaning that it is in control and stable, but is not meeting customer expectations, then fundamental process changes have to be implemented. If, on the other hand, the process is experiencing special-cause variation, it is out of control and unstable, and the root cause has to be investigated immediately. Quick action has to be taken in order to avoid recurrence.