Process control

Achieve Process Control by using SPC!

statistical process controlProcess control is about understanding your process, only then can you control it. To understand the process, you must understand variation.

Six Sigma use SPC (Statistical Process Control) to control processes. SPC is a tool to distinguish between normal and special caused variation.

Why should you distinguish between normal and special cause variation? Because special and normal cause variation requires different approach when identifying causes of variation.

If  scrap at a manufacturing company arise from special cause variation, you can identify a specific reason that caused it. If scrap is caused by normal variation, it is more challenging to find the cause. It is not possible to identify a specific reason; the scrap is due to variation caused by the process natural behaviour. Several factors can contribute to the normal variation.

Let me illustrate with an example. A machine has too much normal variation and produce scrap. All machines have normal variation as a result of its design. By adjusting a machine that has undesirably normal variation you can risk making it worse. Adjusting a machine will only help if the problem is accuracy. If the problem is precision (too much normal variation) it will not help to adjust it. You may choose to invest in a machine that is more precise. Another option is to include the expected quality cost in the cost calculation of the product in order to take the right price for the product. I made a video with applications for statistical process control.

When it comes to the quality of the final product, it can be subject to variation from several factors that varies during the production process. If you want to improve product quality, you need to identify the critical factors of your process. Then you can reduce and control the variation of these factors. I was part of the team who implemented online statistical process control - SPC at a production line at Axis-Shield (now Alere). Online SPC was available for all control parameters.

Before implementing SPC, consider the purpose. Here are some examples of applications:

  • Do you want to determine the normal variation of a process in order to determine its robustness? Are the normal variation well within your customer requirements? Otherwise, you should work to make the process more robust, or include the cost of scrap in your calculations.
  • Do you want to determine the normal variation in order to react to special causes?
  • Do you want to connect the process behaviour to maintenance tasks? Wear on equipment will gradually increase normal variation. Alarms related to the standard deviation can alert you when parts need to be replaced.
  • Do you want to assess the effect of a change you have done? If you made an improvement which will reduce the normal variation or change the average of a process, the effect can be determined using SPC. SPC chart before and after the change will show if the change had an effect. 

 

Rate this item
(0 votes)
More in this category: « Variation Overcoming fear »

3 comments

  • Lindsey

    I was just looking at your Process control website and see that your site has the potential to get a lot of visitors. I just want to tell you, In case you didn't already know... There is a website network which already has more than 16 million users, and the majority of the users are interested in websites like yours. By getting your site on this network you have a chance to get your site more popular than you can imagine. It is free to sign up and you can find out more about it here: http://ittsy.com/it/3x - Now, let me ask you... Do you need your site to be successful to maintain your business? Do you need targeted traffic who are interested in the services and products you offer? Are looking for exposure, to increase sales, and to quickly develop awareness for your website? If your answer is YES, you can achieve these things only if you get your site on the service I am talking about. This traffic network advertises you to thousands, while also giving you a chance to test the service before paying anything. All the popular blogs are using this network to boost their readership and ad revenue! Why aren’t you? And what is better than traffic? It’s recurring traffic! That's how running a successful site works... Here's to your success! Read more here: http://bbqr.me/4fj5
    Lindsey http://bbqr.me/4fj5

    Report
    posted by Lindsey Wednesday, 09 September 2015 12:39 Comment Link
  • air conditioning services

    It's laborious to search out knowledgeable individuals on this subject, however you sound like you know what you're speaking about! Thanks

    Report
    posted by air conditioning services Tuesday, 18 August 2015 00:46 Comment Link
  • water ionizers

    I have learn some excellent stuff here. Definitely value bookmarking for revisiting.

    Report
    posted by water ionizers Friday, 14 August 2015 08:43 Comment Link

Leave a comment

back to top