A control plan is an example of a quality control (QC) strategy. Put one in place after you create a new process or change an existing one. It helps you to ensure that staff monitor new and modified processes correctly.
Typically, you’ll have one plan per process. Alternatively, one per product or service that you offer. What’s the difference? Some products and services will involve more than one process. In this situation, you’ll usually perform QC per process.
Product Control Plans
A plan for a product – or service – typically contains:
- The name of the item.
- Its important characteristics. For example, length, width, color, strength.
- How to measure those characteristics. For example, the tool you need to use.
- The acceptable range for each characteristic. Commonly called the tolerance range.
- Testing frequency. This might be a time period (once an hour) or amount (1 per 1000).
- How to plot measurements. This will usually be a type of chart.
- Who is responsible for quality control on the item.
It might also include:
- Contingency measures to take for certain scenarios.
- When and how to review the plan.
7-Point Process Control Plans
A plan for a process typically contains:
- Specifications and measuring guidance. This includes measurements, how to make them, and the tolerance allowable.
- Inputs and outputs. What should go into the process (materials)? What should come out?
- Performance criteria for the process. How do you know when the process is working well? This might include QA figures or a production rate.
- Sampling and reporting frequency. How often will you perform quality control checks? Then, how often will you create QC reports for the process?
- How to record information about the plan. What sort of charts should you use?
- Contingency measures. What should you do if X goes wrong?
- The owner of the process. Who is responsible for reporting and oversight?
Why Use One?
The plan helps to limit variation. It does this by making the QC requirements clear and easy to find. This allows staff to test new items quickly and easily, and also makes it simpler to onboard new people.
Importantly, the plan also helps you to make sure that your improvements ‘stick’. This is one of the biggest issues most companies face in making process changes. When you make an change, entropy tends to erode it back to the old process. Of course, that’s if you do nothing to keep it in place. A control plan fights the entropy by helping people to remember the changes and use them.
Control Plans and DMAIC
Guidelines for Creating a Control Plan
A control plan must be:
- Clearly and concisely presented: users familiar with the QC procedure can skim it for a quick reminder.
- Easy to follow: new users can follow it without having to redo steps because they misunderstood.
- Comprehensive: doesn’t rely on assumed knowledge, like which gauge to use.
- Repeatable and reproducible: two people following the plan using the same items will get the same results.
Example Control Plan
A company that makes fixings for the building industry has developed a new line of screws made from a tougher blend of steel. Now that it has the products, it needs a control plan to maintain quality control.