Do You Know Your SPC?
ISO's SPC guidance will help you implement
ISO 9001:2000-based quality management systems.
by John E. West
For a number of industries, statistical process control is an activity critical to effectively operating a quality
management system and to satisfying customer requirements for product quantity as well as quality. SPC is a well-established quality management tool, and some sectors have had SPC reference
manuals for use in meeting QMS requirements for some time (e.g., the SPC reference manual used with QS-9000 was first issued in 1992). Despite the existence of the ISO 9000 series since 1987, the
International Organization for Standardization hasn't had a good SPC guidance standard to support this critical QMS activity.
This situation should soon be rectified when ISO
11462-1:2001 is published by ISO as a new standard. According to ISO Technical Committee 69, the group responsible for drafting the standard, ISO 11462-1's purpose is to guide an organization in
planning, developing, executing, and/or evaluating a statistical process control system so that an organization can achieve the goals of increasing production efficiency and inherent capability
and reducing interval and cost.
On May 18, balloting on the FDIS version of ISO 11462-1 concluded with a favorable vote by all 14 participating member bodies of TC 69. The
next step is for ISO to formally publish the standard. The Statistics Subcommittee of the American Society for Quality's Z1 Committee has been balloting the adoption of ISO 11462-1 as an American
National Standard during a slightly different but overlapping time period, with an expected U.S. vote of approval on the national level.
ISO 11462-1, Guidelines for
implementation of statistical process control (SPC)--Part 1: Elements of SPC, deals with achieving control of processes to ensure product conformity. Organizations that use this type of control
will be able to improve the economics of achieving conformity and, with the use of data, also improve processes. It's important to understand that ISO 11462-1 has been developed to provide
guidance for all types of organizations.
SPC is most often thought of as being important for organizations that engage in "mass production"--that is, the same
processes, whether related to a product or service, that are repeated frequently and regularly enough to allow the application of statistical techniques. While its application in high-volume
production is most common, SPC can be beneficial in other situations as well. A note to Section 1, Scope, of ISO 11462-1 indicates that SPC "is also applicable to processes producing
services or transactions (for example, those involving data, communications, software, or movement of materials)."
In the past, the use of statistical methods has been a
common weak point in many QMSs. It is expected that parts 1 and 2 of ISO 11462 will be able to help organizations strengthen their systems in this area. (Part 2 of ISO 11462, drafting of which is
expected to be taken up soon by TC 69, will provide a catalog of SPC tools and techniques.)
This has become even more important with the advent of ISO 9001:2000, which moves
away from the manufacturing-
oriented language and approach to quality management and quality control. This new edition of ISO 9001 increases emphasis on the determination and use of
such statistical methods based on the following clauses/subclauses:
Clause 7.1, Planning of product realization, requires planning of the processes for product realization, including the required verification, validation, and inspection and
testing processes specific to a product. This planning needs to include monitoring and measurement of both products and processes.
Clause 8.1, Measurement, analysis and improvement--General, requires planning of
the monitoring, measurement, analysis and improvement processes as well. It also requires that "applicable methods, including statistical techniques…" be determined.
How extensively these methods will be used must also be determined. Clearly the emphasis is not just on identification of the techniques--there is a focus on their use.
Subclauses 8.2.3, Monitoring and measurement of processes, and 8.2.4, Monitoring and measurement of product, require monitoring and measurement of the
characteristics of processes and products to demonstrate the ability of the processes to meet requirements and to demonstrate that product requirements have been met.
ISO 11462-1 has been designed to provide guidance for organizations wanting to use SPC to meet these requirements.
ISO 9001:2000 also requires a planned approach to improvement of the QMS. Planned improvement means that the organization is required to use a number of elements
together to manage the improvement processes. Subclause 8.5.1, Continual improvement, requires use of the quality policy, which must include a commitment to
continual improvement of the QMS's effectiveness; measurable quality objectives; audit results; data analysis; and corrective and preventive action.
This combination of elements could be called a "continual improvement loop" for the overall QMS. Many users of ISO 9001:2000 may see definite relationships among the
elements of this loop but may not be able to easily translate their understanding into action. ISO 11462-1 should be a big help in translating this conceptual loop into actions
that can achieve real results for the organization. Understanding what ISO 11462-1 will provide to organizations with an existing ISO 9001:1994, ISO 9002:1994 or ISO
9001:2000-conforming QMS or beginning the ISO 9001:2000 implementation process can make an incredible difference in how they manage their processes.
Aspects of an SPC program
Let's take a look at the aspects of SPC on which ISO 11462-1 provides guidance. These should be useful not only in developing processes to comply with ISO
9001:2000, but also in developing processes for process improvement. Three aspects are discussed below in relation to what ISO 11462-1 provides.
1. Defining the SPC goals. As with many other things, implementing an SPC system starts with the setting of goals. ISO 11462-1 provides guidance on defining the general
and specific goals an organization wants to achieve by implementing SPC. These may include aspects of control, such as:
Reducing variation around target values for product and process characteristics as
well as compensating for process variation to ensure product conformity
Reducing costs while reducing variability thus achieving process optimization
Indicating how the process is likely to behave in the future
Quantifying process capability
Once these more abstract goals are established, ISO 11462-1 recommends the
identification of specific goals that the organiza-tion wants to achieve related to improvement. These may include:
Managing process efficiency to ensure greater consistency and improvement
Using data to identify and eliminate assignable causes of variation
Using data to identify variation or nonconformity so that needed corrections or corrective actions can be defined
Providing information to assist in determining potential root causes of variation or nonconformity
Understanding the relationship between the final product and the process parameters
Meeting financial and other overall organizational objectives
2. Conditions for a successful SPC system. Ongoing benefits of an SPC system are best achieved when the necessary infrastructure is developed and maintained. ISO
11462-1 points out that this can be achieved by establishing the SPC effort as part of a formal QMS, such as that specified in ISO 9001:2000. The needed infrastructure
includes management support, which can be a means to demonstrating the commitment to continual improvement required by ISO 9001.
In other words, to obtain improvement, management must use data to make decisions, support activities (e.g., data recording), react to process disturbances and assign SPC
coordination responsibility. In addition, there should be a link to the management review process required by Clause 5.6 of ISO 9001:2000. For any organization to effectively
identify areas for improvement, there needs to be a periodic top management review of SPC results. Each of these is a job of top management and relates to the requirements
in Section 5, Management Responsibility, of ISO 9001:2000. Programs to ensure the competence of those who will be using the statistical tools are also necessary. Planning
should include these personnel competency needs as well as the activities necessary to address the other elements of an effective SPC system.
3. Elements of an SPC system. The core of ISO 11462-1 is Section 7, Elements of a statistical process control system, which discusses the processes an organization
should implement and the actions it should take to ensure a successful SPC system is in place to support the QMS. ISO 11462-1 covers both the operational and support
activities needed for SPC success.
A look at the core
To help introduce you to this core, let's review the general concept behind each of the 20 elements of an SPC system. While ISO 11462-1 details each element, we'll just be
highlighting the key points of Section 7.
The ultimate point is that Section 7 provides guidance on the operational elements of an
SPC system. These elements can be thought of as roughly paralleling the plan-do-check-act model. Considering these key operational elements as part of an SPC
version of the plan-do-check-act cycle will not only provide consistency with an ISO 9001:2000-conforming QMS but will also make the implementation of SPC easier to conceptualize and execute.
Planning the SPC system encompasses the first three of the 20 clauses in Section 7,
but it's probably the most critical aspect. If you don't plan your system right, you won't be able to control your processes effectively.
Clause 7.1, Process documentation and control plan, outlines a planning step related to the ISO 9001:2000 clause of the same number on planning of product realization
processes. Implementing organizations must fully understand the process and develop a plan of control to ensure the process will meet requirements. This includes use of
techniques to understand process inputs, outputs, flows, measurement points and boundaries. Understanding these aspects of each process can help identify which
process parameters affect product conformity. It is then that you should determine the process parameters that can be monitored and measured to ensure conformity of
product. Clause 7.1 also recommends that organizations plan the actions to be taken when out-of-control signals are detected.
Clause 7.2, Definition of process targets and limits, provides guidance on developing the target values and limits for each parameter, beyond which an organization would
consider a process unacceptable or unfeasible. ISO 11462-1 indicates that the target setting process should be dynamic so that targets and limits are properly set and
updated as conditions change.
The final clause that provides guidelines on the planning process is 7.3, Measurement
system evaluation and control. Because the measurement system needs to be evaluated to ensure that its uncertainty is known--which will help prevent false alerts that a
process is out-of-control or the output of nonconforming product--the standard gives some simple guidelines for accomplishing this.
Measurement, monitoring and controls also involve three of the 20 clauses in Section
7, but they relate to the application of the SPC system to the QMS. They are also spread out within Section 7. These clauses involve the actual role of SPC in supporting
day-to-day operations and the functioning of the QMS.
First, Clause 7.6, Process data recording and collection, discusses the need to design a
data collection system usable in an organization's actual operational environment. The data collection system should be carefully designed so that it will yield the needed data.
The organization implementing an SPC system using ISO 11462-1 will need to answer such questions as what will be measured, what the sample size is, where in the process
the measurement is to be taken and who is responsible for the sampling.
Clause 7.6 introduces a number of other considerations for an organization, including
the need to provide proper measurement equipment as well as any training needed for the equipment's use.
Clause 7.12, Process output monitoring system, then states that an organization should track the outputs of its processes and collect the data so that the processes can be
analyzed. The monitoring system should include a mechanism to initiate a reaction to problems and to identify and take advantage of opportunities for standardization on best practices.
Finally, Clause 7.13, Process control system, involves controlling the process that creates the product. The standard provides several options for such process control
systems, each of which addresses the need to monitor and measure process parameters to ensure that they meet process requirements. If a parameter is outside its limits or
undesirable patterns are detected, correction and/or corrective action is needed to bring the process back into control. As its title indicates, ISO 9001:2000's Subclause 8.2.3,
Monitoring and measurement of processes, also requires these Clause 7.13 processes, so the guidance provided in ISO 11462-1 may be helpful in meeting Subclause 8.2.3's requirements.
Assessment of variability and communication of analysis results is perhaps most
important to the SPC system's effectiveness because the information an organization obtains as a result of planning and doing and on which it will act leads to improvement
of the SPC system and also of the QMS. Three clauses focus on checking activities:
7.14, Short-term variability assessment, recommends activities that should be considered in developing a process for assessing process changes that occur during a
short period of time and typically involving a limited number of factors.
7.15, Long-term variability assessment, provides guidelines for assessing long-term process capability once assignable causes have been eliminated and the process is in a
state of statistical control. Long-term assessments are viewed as building on the changes taken or identified as needed because of the findings of the short-term efforts.
7.16, Communicating the results of process analyses, covers communication of process analysis results to those who design and operate the processes as well as to
leaders and others as necessary to achieve the SPC system goals. Communication of process analysis results is one of the things organizations should consider when
addressing Subclause 5.5.3, Internal communication of ISO 9001:2000.
Using the analysis results is the focus of the guidance in Clause 7.20, Process improvement, optimization and troubleshooting, which by itself is the action clause. All
the data collection and analysis is just wasted activity if it's not used to achieve results, thus completing the continual improvement loop successfully. Once long-term process
variability has been studied, it's possible to prioritize processes to be optimized and improved. Clause 7.20 suggests several types of approaches for taking actions to
correct, control and improve the processes.
After establishing priorities, an organization can use ISO 11462-1's guidance to
improve or optimize the priority processes. SPC and business goals should be considered during the improvement activities. These concepts related to process
improvement and optimization may help organizations develop effective mechanisms to meet the requirement of ISO 9001:2000 Subclause 8.5.1, Continual improvement.
While the operational elements are very important, ISO 11462-1 also points out and explores a number of other elements important to a successful SPC system. The
following may be viewed as supporting processes or support elements:
Clause 7.4, Documented work instructions--Work instructions are a key support element of an SPC system. ISO 11462-1 gives guidance on the creation of work
instructions that are appropriate to the SPC environment.
Clause 7.7, Traceability and production sequence identification--ISO 11462-1 includes guidance related to a variety of traceability concepts, including the use of
traceability to improve the ability to analyze processes. Whether the traceability requirements of ISO 9001 apply, organizations should consider Clause 7.7's guidance on this subject.
Clause 7.9, Process input sequencing--This concept is linked to the notion of traceability. Under some conditions, process sequence is critical to production and, if
inputs to the process are used in the order in which they were produced, there will be less process variability or at least the variability should be easier to analyze. Such
sequencing can have great advantages, but extensive work is needed in many organizations to reach the point where it is fully implemented.
Clause 7.10, Process logs--In most cases, a systematic process is needed for
logging process disturbances, process adjustments and operational changes.
Consistent and useful logging can yield information for after-the-fact analysis to
identify patterns over time. ISO 11462-1 lists the types of information that should be recorded and how to use the data.
Clause 7.5, Employee training and involvement in process data--The proper
addressing of personnel issues is critical to success when an organization introduces an SPC system. Organizations frequently fail to achieve the desired results from their SPC
activities even though the technical activities are accomplished, generally because the human elements of SPC have not been adequately addressed. Because employee
involvement in the proper data-related activities is critical to success, the missing link is often detailed training in the use of data for those involved. The SPC guidelines
standard points out that it's necessary to instruct employees on how to plan for data collection, design control systems using the proper techniques, identify measurements
requirements and assess measurement capabilities. Perhaps most important, the right employees must be able to use the proper techniques to ensure data integrity as well as
conduct proper data analysis and interpretation. This means there must be people in the organization with sufficient education to be able to understand what tools to use and how to use them.
Clause 7.19, SPC projects and teams--ISO 11462-1 recognizes the project-by-project nature of improvement by recommending that organizations maintain
projects to reduce variation and improve processes. It also recognizes that, where appropriate, these projects should be conducted by cross-functional teams from the
functions involved in or affected by the process being considered. Teams might be especially important to ensuring that projects improve or optimize processes.
There are several other systematic activities examined in the clauses of Section 7 that ISO 11462-1 recommends should be included in an organization's SPC system.
Organizations should consider:
Subcontractor performance evaluation--This involves establishing a system for obtaining information about variation of parameters in incoming product from suppliers and/or subcontractors.
Process reliability--This addresses the maintenance of process equipment.
Customer information system--Consideration should be given to implementing a system to provide customer feedback on the suitability of the organization's product.
Internal SPC audits--There should be a supporting audit program to periodically determine how effectively the organization has been in implementing SPC.
When it becomes available in the near future, organizations will find ISO 11462-1 useful in developing their QMSs for both compliance with ISO 9001 and for achieving improvements.
About the author
John E. West is chair of the U.S. Technical Advisory Group to ISO/TC 176, the technical committee responsible for the ISO 9000 series of quality management
standards, and serves as the lead U.S. delegate to TC 176. West is co-author of ISO 9001:2000 Explained (ASQ, 2001). E-mail him at email@example.com .
This article was first published, in a slightly different form, in the March 2001 (vol. 6,
no. 3) issue of "The Informed Outlook," a newsletter co-published by the American Society for Quality and INFORM ( www.informintl.com