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Advanced Product Quality Planning (APQP) - Control Plan

03 September 2020
APQP is gaining momentum within the aerospace sector and more businesses are adopting the approach to minimise the risk and impact of production issues. 

Although the tool can seem too much for smaller organisations, there are still some useful elements that can be extracted and adopted to any sized business, it just makes good business sense.

One of the key tools that are required for APQP and also of benefit as a stand-alone element for any business is the Control Plan. To use the words from AS9145 (The APQP Standard for the aerospace sector); “a control plan is a documented description linking manufacturing process steps to key inspection and control activities.  The intent of a control plan is to control the design characteristics and the process variables to ensure product quality”.

Control plans, whether being used for APQP or not, are an excellent tool for monitoring product and process key characteristics and critical items to reduce process variation and as a result, reduces the number of errors and failures.  

There is a misconception that control plans need to be complex and lengthy and include all identified risks to the process, in reality, if implemented correctly, they are easy to generate and you only need to focus on the key risks identified within your process.  

Control plans should be used when you are implementing a new process, after risks have been identified and mitigated within the process, following process changes and when problems have been identified as a result of non-conformances. They should be a live document, not set and forgotten, especially as a result of any process or product changes.

Benefits of a Control Plan

As highlighted above, the control plan can be used for any manufacturing organisation, not just one who is aiming towards APQP.

Improves Product Quality

  • Improves ability to prevent nonconforming products

  • Identifies and manages sources of variation (input variables), and reduces variation in product characteristics (output variables)

  • Reduces scrap and rework

Improves Efficiency/Cost

  • Reduces waste in a process, improving throughput/manufacturing efficiency

  • Reduces costs without sacrificing quality

Improves Customer Satisfaction

  • Focuses resources on the product/process characteristics most important to the customer and the organisation

  • Prevents nonconforming product from reaching the customer

Improves Process Management

  • Establishes a plan for responding to changing process conditions

  • Communicates changes in product/process characteristics, control method, and measurement methodology

  • Monitors processes and assures that process improvements are maintained over the life cycle of the product

  • Employ prevention rather than detection (e.g. use of error-proofing instead of operator dependant work or inspection)

Creating the Control Plan

Control Plan Inputs

In order to gain the most of out your control plan you need to have done some background work beforehand. If you are following the APQP Process then you would have naturally performed the necessary steps. The Control Plan is generated in phases 3 and 4 of the APQP 5 Phase process, phases 1 and 2 would have given you all of the necessary inputs.

If you are not following the full APQP process and would like to generate a control plan you need to identify the inputs to the control plan and in order to do that, you need to have completed some preparatory documents. If you have AS9100 already in place then a lot of these would naturally have been completed.  

The inputs include (depending on your type of organisation):

  • Process Flow Diagram (FPD, flowcharts, swimlanes, SIPOC, Turtles etc)

  • Process Failure Mode and Effects Analysis (PFMEA)

  • Design Reviews (If you are the design authority)

  • Product Key Characteristics (From Design Failure Mode and Effects Analysis or could already be identified on the drawing if you are manufacturing only).

  • Process Key Characteristics

  • Measurement System Analysis (MSA)

  • Special Characteristics Matrix

  • Lessons learned from similar parts

  • Cross-functional team knowledge about the process

  • Field or Warranty Issues

The intent of the control plan is to align the plan with your process flow diagram and focus the attention on the high-risk process points as identified in your PFMEA. Is it advised to start the process as early on as possible during the initial stages of development, you should identify what controls you need to put in place to further reduce the risks within the processes.

Prevention is always better than cure so the control plan should focus on using tools such as error-proofing instead of operator dependant work or inspection.

Three Key Elements of a Control Plan

There are three distinct parts to a control plan; the processes, the characteristics and the control methods. Each part has a number of features which need to be identified as applicable.

Within the Supply Chain Management Handbook (IAQG Website) you can download a template for the control plan for free. Please see an example here.

1 - Operation / Process Number: List process step, usually listed in the process flow being charted
2 - Process Function/Operation Description: The CRITICAL steps in the production of the part (not every process step or risk from the PFMEA). Remember, you don’t need to enter all PFMEA risks, focus on the higher risk points. The steps can be identified from the Process Flow Diagram
3 - Machine, Device, Jigs and Tools: This is where you would list any specific tools and machinery that are required to control the process, this could be specific gauges, tanks, machine IDs, jigs.
4 - Characteristics: The distinguishing feature, dimension, or property of a process or product on which variable or attributable data can be collected. Use visual aids where applicable
5 - Product/Process Characteristic ID: Either a sequential tracking number or a cross-reference number from other applicable documents such as the Process Flow DIagram or PFMEA.
6 - Product Characteristics: List Product Characteristics that are important. The features or properties of the part, component or assembly that are listed on engineering drawings. The team should identify the product characteristics by referring: Engineering drawings, customer critical characteristics, key/critical characteristics that affect the product. There may be several for each operation-can be dimensional, performance or visual criteria
7 - Process Characteristics: List Process Characteristics that are important. A Process Characteristic (parameters) is a setting made within a process that affects the variation within the operation. The team should identify process characteristics for which variation must be controlled to minimise product variation. There could be one or more process characteristics listed for each product characteristic. Examples include temperature, pressure, speed, feed, torque, flow rate.
8 - Characteristic Classification:
     a. Key Characteristics: An attribute or feature whose variation has a significant influence on product fit, performance, service life, or productibility; that requires specific action for the purpose of controlling variation;    
     b. Critical Items: Those items (e.g., functions, parts, software, characteristics, processes) having a significant effect on the product realisation and use of the product; including safety, performance, form, fit, unction, producibility, service life, etc.; that require specific actions to ensure they are adequately managed. 

Examples include safety CIs, fracture CIs, mission CIs Key Characteristics (KCs), and maintenance tasks critical for safety.

The engineering drawing will typically indicate key/critical characteristics.  However, the user may identify additional characteristics that are critical to quality

9 - Methods: The procedures, instructions and tools to control the process.
10 - Product/Process Specification/Tolerance: Specifications and tolerances are obtained from engineering specifications or a key process characteristic.
11 - Evaluation Measurement Technique: Identifies how the characteristic is going to be measured.  Examples include calipers, attribute gauges (Go/No go), fixtures, test equipment, or visual.
12 - Sample Size & Frequency: This column defines how many parts will be measured and how often.  Examples include: final testing, visual criteria, 100% inspection, SPC, audit, sample size and frequency
13 - Control Method: This column contains a brief description of how the characteristic will be controlled. 

Examples include:

  • X-bar/R-chart

  • Np chart

  • Pre-control chart

  • Checklist

  • Log sheet

  • Mistake proofing

  • 1st piece inspection

  • Lab report

14 - Reaction Plan: The reaction plan specifies what happens when the characteristic or parameter is found to be out of control.

The Reaction Plan must include:

  • Segregation of nonconforming product

  • Correction Method

  • Contact Supervisor

The Reaction Plan may include:

  • Sorting

  • Rework/Repair

  • Customer Notification

The actions should normally be the responsibility of the people closest to the process, the operator or supervisor.

AS13006 Process Control Methods includes a table that helps with completing the method part of a control plan.

Authored: Michael Venner, NQA Aerospace and Automotive Director

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