Ensuring product quality with the Control Plan

High product quality ensures the functionality of your products and increases customer satisfaction. This is why you should not neglect the topic of quality planning. One common method is Advanced Product Quality Planning (APQP). The APQP method describes a holistic procedure for ensuring product quality during production and is primarily used to structure a product development project. The Control Plan is a tool of the APQP method, but can also be used independently and provides you with valuable insights for existing products. We will show you how you can use the control plan for your production and what you need to bear in mind.

Where is the Control Plan used?

The APQP method comes from the automotive industry and is the predominant standard here. It was defined by the AIAG (Automotive Industry Action Group). In aviation, a slightly modified version has been established by the IAQG (International Aerospace Quality Group), which takes into account the special features of this industry. The method is also used in other sectors, for example in metalworking or electrical engineering, although it is not as widespread here. APQP is useful wherever complex production processes meet high quality requirements. The method defines 5 phases with different activities, with the creation of the control plan being one such activity.

The control plan or process control plan is a central document in advance quality planning. It contains all product parameters and process parameters that affect product quality and defines, among other things, how the corresponding parameters are checked and the procedure in the event of a deviation. The benefit lies in incorporating these findings into production planning and optimizing the production processes in terms of subsequent product quality.

APQP requires a lot of resources and presupposes certain organizational structures. This is why the method is mainly used by large OEMs and their suppliers. However, it is also possible to use the control plan independently. This makes sense if you manufacture products with complex production processes. This allows you to optimize existing production processes with little effort and plan future ones better. I will show you how and with what you can create your first control plans and what advantages this will bring you.

Creation of the control plan

The control plan is a cross-departmental document, which is why a multifunctional team (MFT) should be involved in its development. The following composition has proven itself: Work preparation, quality planning, design and inspectors. The experience of the people involved is particularly important here.

The primary input for the control plan comes from the following sources:

• Construction document: This contains the characteristic values and tolerances that the finished component must fulfill. As part of APQP, the relevant characteristic values are already taken into account during the design and creation of the construction document and marked as Key Characteristics (KC).
• PFMEA: A process failure mode analysis in which the risks of the manufacturing process are considered and mitigated by appropriate countermeasures. Such a countermeasure can be an active control within production and is included in the control plan.
• Process flow: The control plan follows the structure of the production process.
• MFT decisions: Further content may result from discussions within the team if someone considers a certain measure to be useful based on their experience with comparable products. This content is then included in the control plan by MFT decision.

Follow this procedure to create your first control plans quickly and efficiently:

1. Determine the members of the MFT. The quality planning representative is usually the person responsible for the control plan and is responsible for creating the document.
2. The person responsible for Control Pan creates an initial draft based on the construction document and the PFMEA. If a PFMEA has not been carried out, you can decide for yourself whether you still want to carry it out or whether it is not necessary for the product under consideration.
3. The MFT sits down and discusses the first draft. Changes can be made and content can be added. The response plans should also be defined here, more on this later.
4. The person responsible for the control plan implements the changes discussed.
5. The finished document is validated by the MFT managers and, if applicable, department heads. This confirms that all areas involved agree with the elaborations.

Tools and templates for the control plan

There are several options for creating the control plan. The simplest option is to use an Excel template. You can use a control plan template and adapt it to your own requirements if necessary.

There are also special software solutions that specialize in the creation and management of control plans. These are often found as a module within a CAQ (computer-aided quality) program, e.g. in solutions from Babtec, PLATO or Relyence.

If you work with SAP, there is also a corresponding module that allows you to manage control plans. Above all, you benefit from the direct integration with the ERP system and have everything from a single source.

Which solution makes the most sense for you depends on how deeply you want to get to grips with the topic of APQP. Due to the investment and resources required for implementation, the software solutions in particular only make sense if you want to align your entire production with the process. The Excel templates, on the other hand, are easy to use and are ideal for trying out the concept or only applying it to individual products where quality plays a decisive role.

In the following, I will show you how to work with the Excel template and what insights you can draw from it.

How to design a control plan

The control plan is structured in a table. One process step is shown per row, whereby only the process steps with an impact on quality are relevant, while the columns contain the contents of the control plan.

The required columns are:

• the process step number and the process description including the tools and machines used
• the respective product or process parameters with their specifications or limit values
• the measuring and testing equipment used
• the scope and frequency of testing
• the response plans

A detailed explanation of the individual columns can be found in the template. Additional columns can be added as required, including reference documents, required inspector qualifications or the type of inspector registration.

The control plan should reflect the product structure, so you need individual control plans for all individual parts as well as for the assembly orders. The structure of the individual control plans should be based on the structure of the production order. Ideally, you should use the same process step numbers that you use in your production orders within your ERP system.

The main function of the control plan is to provide an overview of all the quality specifications for a product. In the case of a new product launch, the control plan is created before the start of production and provides the input for setting up the production order. However, it can also be useful to create control plans retrospectively for existing products.

Benefits of the Control Plan

The first control plans are created quickly, but what benefits do they bring you? The primary benefit of the control plan is that it encourages the departments involved to communicate with each other at an early stage and to plan the production process in advance. This prevents potential errors before they can even occur. The document itself serves primarily as proof of the decisions made and as a reference source for possible queries.

However, the definition of reaction plans within the control plan provides a decisive benefit. A reaction plan describes which activities are to be carried out if the product or process parameter under investigation does not meet its specifications. These are particularly useful for intermediate checks during production, as it is still possible to actively intervene in the process here.

Here is an example: Imagine you have to drill holes in a component that are relevant for assembly. Have the worker check the holes immediately afterwards. If the hole is too small, the reaction plan would be to drill out the hole and inspect and possibly replace the drill bit, as the tool may be worn. If the hole is too large, the component would be removed directly from the process. This procedure saves you an enormous amount of time and money compared to the case where the fault is only discovered during assembly. It also defines the worker’s authority for possible intervention, within which he can decide freely. This creates a systematic approach, especially in the case of recurring faults.

With this in mind, it can also make sense to apply control plans to existing products, especially if the same quality defects are repeatedly identified. In this way, you can incorporate simple countermeasures into the existing process to counteract the problems.

Analyses with the Control Plan

To optimize your existing production processes with the help of the Control Plan, proceed as follows:

1. Find the products you want to analyze. It makes little sense to create control plans retrospectively for products where there are no problems. Concentrate on products with a high proportion of rework or high costs for quality services. You may need to carry out further analyses for these.
2. Fill in the control plan template with the process structure from your ERP system. Take a look at the inspection processes and identify the production steps that are responsible for generating the inspection parameters.
3. Do you have many inspection processes after production? Are you considering which of these you can replace with a worker self-inspection in the corresponding production step? This saves time and costs compared to a subsequent inspection.
4. Do you have a high proportion of rework? Find the inspection parameters that are mainly responsible for the rework and build in controls at the relevant production steps to counteract this.
5. Discuss the results in the MFT. Be sure to invite the workers to do so, as they in particular can provide valuable insights into the causes of the error-prone production steps.
6. Agree on the actions to be taken and don’t forget to define response plans where applicable.
7. In the interests of continuous improvement, you should repeat this MFT meeting regularly to discuss the effect of the measures until you are satisfied with the result.

Summary

Control plans are an effective tool for advance quality planning that help you to plan and optimize your production processes. With the explanations and tips presented here and our template, you can start improving the quality of your products immediately and save time and money in the long term!