A control plan is a document describing the critical to quality characteristics, the critical Xs or Ys, of the part or process. Through this system of monitoring and control, customer requirements will be met and the product or process variation will be reduced. However, the control plan should not be a replacement for detailed operator instructions in the form of work instructions or standard operating procedures. Each part or process must have a control plan. A group of common parts using a common process can be covered by a single control plan.
Types of Control Plans:
For the automotive sector, lSO/TS 16949:2002 and the Advanced Product Quality Planning APQP (2000). Thethree control plan phases are:
A prototype control plan is used in the early development stages when the part or process is being deﬁned or conﬁgured. This control plan will list the controls for the necessary dimensional measurements, types of materials, and required performance tests. A pre-launch control plan is used after the prototype phase is completed and before full production is approved. lt lists the controls for the necessary dimensional measurements, types of materials, and performance tests. This plan will have more frequent inspections, more in-process and final check points, some statistical data collection and analysis, and more audits. This stage will be discontinued once the pre-launch part or process has been validated and approved for production. A production control plan is used for the full production of a part. It contains all of the line items for a full control plan part or product characteristics, process controls, tests, measurement system analysis, and reaction plans.
The control phase is forgotten C in DMAIC. The project control phase is necessary in order to sustain the project gains. The control plan must be a living document for it to remain an effective mechanism to monitor and control the process. A responsible person must be placed in charge of the control plan. This ensures successful monitoring and updating. A black belt may or may not be a suitable person for the role, as he/she may be replaced or transferred to a different position. A better selection would be the process owner. The current process owner can be listed on the control plan, but in reality it is a functional role that is to be passed on to the next individual in that same organizational position. If the control plan is not maintained, the benefits of the project could slowly be lost. The frequent changing of process owners, combined with large numbers of process projects, can easily result in neglected or lost control plans.
Some considerations in the closing phase of the project include:
Identify the process owner
Involve the team in the control plan
Create new or updated work instructions and procedures
Notify and train the affected personnel
Ensure that the control plan training is effective
Place the control plan in the proper quality system document
Attain agreement between the team members and process owner
A number of inputs or sources contribute to understanding, manufacturing, and controlling the part or process. Many of the following are included:
Process flow diagrams
System FMEAs, DFMEAs, and PFMEAs
Special customer characteristics
Team process knowledge
Quality function deployment
Customer requirements may dictate the exact form of the control plan. Often, there is some ﬂexibility in the construction of the forms
Provide a title for the control plan. The control plan is often placed into another document, such as an operating instruction or six sigma database. If necessary, indicate if this is a prototype, pre-launch, or production plan.
Provide a reference number. This number may be supplied by the responsible department.
If a cross functional team is involved, provide the members names.
This could be the black belt in charge of the project, however, the name and function of the process owner are more important.
Provide page numbers if the control plan exceeds one page. Control plans may run up to 20 pages.
indicate the original date of issue of the control plan.
Provide the latest revision date of the control plan.
List the part number or the process flow being charted.
Key input variable (X):
Note the key input variable, when appropriate. On any line item, only the X or Y variable is filled out, not both. This is to clearly indicate which item is being monitored and controlled.
Key output variable (Y):
Note the key output variable, when appropriate.
Special characteristic note:
Indicate if a special characteristic is to be monitored and controlled.
For manufacturing applications, the engineering specifications for the part should be monitored and controlled. For other applications, one would provide upper and lower speciﬁcation limits, as well as the target value
Measurement gage technique:
The gage or measurement technique should be described. The gage, tool, fixture, or test device used for data collection must be in conformance with the needed measurement system analysis (MSA) requirements. When necessary, this would include:
This can be more difficult when attribute data is of concern. The AIAG MSA manual is a good guide.
Provide the current capability of the measurement system.
The AlAG MSA manual lists:
Under 10% error as acceptable
10% to 30% error may be acceptable, depending on the cost and the situation
Over 30% error is not acceptable
Measurement devices may need uncertainty determinations
Provide the Sample frequency, List how often the inspection or monitoring of the part or process is required.
This provides an indication of process capability.
Person responsible for measurement:
Indicate who will make and record the measurement.
Note how this X or Y variable will be controlled. Examples include
Describe what will happen if the variable goes out of control. How should the responsible person respond to the situation?
Control plan construction is often led by the black belt incharge of the six sigma project. The team is usually cross functional with individuals from different areas, including the process owner. The team will ensure that the control plan contains the critical variables, the Xs and the Ys, of the product or process. The control plan must show compliance and control before project closure. A successful control plan should remain a living document to ensure that the beneﬁts of the project are fully realized.
Elements of Response Plan
An effective control system is characterized by formal documents. These documents provide directions to the employees on how to accomplish a task, who is responsible for performing the task, or how the company systems work.
There are various names for these documents including:
Manuals (including the quality manual)
Standard operating procedures
Many companies organize the documentation into a hierarchy
The manual is the highest level document in the system
Procedures are at the second level and describe the responsibilities of various personnel and the administrative system is used to accomplish the tasks. The manual details what is to be done and procedures describe who will do it. The third level is the work instructions that describe how to do the tasks. The work instructions detail the speciﬁc steps to accomplish the goals defined in the manual and the procedures. Some organizations include the standard operating procedures (SOPs) at this level, and some include them as part of the procedures level. Records include the data collected on the products and processes.
The basic content of any good procedure or instruction should include:
Purpose of the document
Basis of the document
Scope of the document
Documentation is necessary for the continued success of a company. Formal procedures or instructions have the following benefits and characteristics. Procedures or instructions are a means for management to describe, in writing, and in a readily accessible manner, their required modes of operations. Procedures or instructions are not static, they must be continuously adjusted in a controlled manner to meet changing times and conditions. Procedures or instructions are a reasonably simple vehicle for defining and standardizing proven methods. Operational procedures define how policy requirements are to be implemented in terms explicit enough to be easily understood. Procedures or instructions are a means of establishing continuity of operations when personnel changes occur and as training for new employees. Procedures or instructions prevent undesirable changes. Procedures or instructions provide a written standard to which operations may be audited. A good documentation system can add value to a company. Company documents must be meaningful, and developed with specific detail so the operations can be improved. Documented procedures allow the improvement of processes (both administrative and technical) by first establishing a baseline. The baseline is established by defining the steps of the process. This deﬁnition of the process steps then can be used for subsequent improvements.
Following are the general guidelines for documentation:
Keep the documentation simple
Keep the documentation clear and inviting
Include options and instructions for “emergencies”
Keep the documentation brief
Keep the documentation handy
Have a process for updates and revisions
Documentation must be written to the level that is understood by the users.
It should also reflect the current processes and methods.
After completion of a process improvement, the documentation should correspond to the new methods, and the users should be trained on the new documentation. It may also be necessary to revise the procedures used to detect and eliminate potential problems. The corrective action procedure itself should be revised when needed.
Effective project or process improvement activities should ultimately lead to the advancement of company operations. However, this is not automatic. Continuous improvement takes the concentrated and continuing efforts of everyone. In addition to changes resulting from improvements, there should be a balanced mix of measurements to monitor overall process performance.
Changes in customer requirements
Process capability measurements
The above results are often reported in management reports. In almost all situations, graphs and charts are preferable to texts and columns of numbers. The organization should have an oversight or executive committee to respond to both problems and opportunities. Many of the approaches discussed earlier in gap, root cause, and risk analysis are effective tools for the ongoing evaluation of the improvement process.