Higher National Certificate in Engineering Unit 36 Lesson 1 - Statistical Process Control

Statistical Process Control Learning Outcomes –LO 1 – Understand the basic types, variations and characteristics of statistical techniques used in process control –LO 2 – Be able to select data, construct process control charts and initiate a control programme for a specified application –LO 3 – Be able to evaluate process capability against a given product or component quality requirement using modified control chart limits –LO 4 – Be able to analyse types of variation within a process and record information on that variation

Learning Outcome 1 LO 1 – Understand the basic types, variations and characteristics of statistical techniques used in process control. –1.1 evaluate the two basic types of inspection used in sampling for process control –1.2 describe the significance of natural and assignable causes of variation –1.3 use selected data to construct frequency distribution and calculate mean, range and standard deviation –1.4 relate the characteristics of the normal curve to the distribution of the means of small groups

Learning Outcome 1.1 LO 1.1: evaluate the two basic types of inspection used in sampling for process control

So What is SPC? Statistical: the collection, representation and interpretation of data. –Statistics provide a means of assessing risks and predicting results –SPC actually involves the handling of data and understanding a basic chart. Process: any activity is a process –An activity (and hence a process) is a combination of method, people, materials, environment and equipment Control: controlling the activity

So What does Control look like? Processes (activities) are initially brought under control and then improved by reducing the variability about the nominal or, if appropriate, reducing the level of rejects to zero. Control means avoiding fire-fighting: the instantaneous reaction to problems as and when they occur Control means planning and prediction. It should be recognised that when a process is brought into control it is then the job of management to continue to improve that process! (IMPROVEMENT SHOULD NEVER STOP!)

Some History Fischer - agriculture Dr Walter Shewhart – Bell telephone labs –Application during WW 2 Dr W. Edwards Deming –Re-building of Japan

So What does Control look like? &index=2&list=PLFF3iDLW3ARBV3MRiGdDUvfa uXJO22Rvn&spfreload=10https:// &index=2&list=PLFF3iDLW3ARBV3MRiGdDUvfa uXJO22Rvn&spfreload=10 &list=PLFF3iDLW3ARBV3MRiGdDUvfauXJO22R vn&index=18&spfreload=10https:// &list=PLFF3iDLW3ARBV3MRiGdDUvfauXJO22R vn&index=18&spfreload=10 ndex=21&list=PLFF3iDLW3ARBV3MRiGdDUvfau XJO22Rvn&spfreload=10https:// ndex=21&list=PLFF3iDLW3ARBV3MRiGdDUvfau XJO22Rvn&spfreload=10

Why introduce SPC? External Pressure –Demand by customers Internal Benefits – see next slide Survival –Perceived competitive advantage Quality Costs

Why introduce SPC? Quality costs as a percentage of sales Prevention Appraisal Internal Failure External Failure

Benefits of SPC Less downtime Improved performance Fewer defectives Fewer production interruptions Fewer complaints Increased capacity Less scrap More involvement from operatives Less trouble at next operation Savings in time

Detection System Method People Material Environment Equipment OUTPUT PROCESS Information on performance Action on output

Detection System Traditional based on inspection 100% inspection is only about 80% efficient Repeated inspection see this figure actually reduce! Inspection based systems are expensive Inspection based systems can be demotivating Focus is on scrap, rework, recycling, warranty claims and concessions

But how ‘good’ is inspection? If Alfred Fields had though of it first, few of them would have listened and, of those, fewer would have cared because that’s the effect Alfred has on all of us.

But how ‘good’ is inspection? If Alfred Fields had though of it first, few of them would have listened and, of those, fewer would have cared because that’s the effect Alfred has on all of us.

See if your Inspection has improved with feedback! First of all she followed all the rules of the game (as suggested by her friend). But if her friend had offered to find the fundamental principle before she began, her understanding of what was expected of her would have been greatly enhanced before the off.

Did you achieve 100% !! First of all she followed all the rules of the game (as suggested by her friend). But if her friend had offered to find the fundamental principle before she began, her understanding of what was expected of her would have been greatly enhanced before the off.

So how good is Inspection as a tool to ensure your Quality? Statistics show that 100% quality inspection is only, at best, about 95% effective. So why not inspect things twice! Would you identify 100% of the defects if you inspected things twice? Statistics show that inspecting things twice the chance of finding all the defects fall to 88%. Why do you think this is?

Quality Inspection The key point therefore is that you cannot depend upon inspection to identify all your quality defects! Why therefore are you wasting your time?

The Traditional Approach to Quality Inspection Detection of Defects Rejection Rectification or Scrap This approach tolerates poor quality – it does nothing to avoid it!

To remain viable, we must therefore… …continually strive to reduce costs. So what does traditional approach to quality cost? –To gain an understanding of what quality costs in your company, try answering the following questions…

The Cost of Administering Traditional Quality How many Inspectors do you have? How much does its cost for their services? What is the cost of rework? What is the cost of scrap? What is the cost associated with your workforce reworking / scrapping defects? What are your warranty costs? Why are companies adding all this expense to control ensure quality. In effect you are throwing away money?

Statistical Process Control (SPC) Fortunately there is an alternative to the traditional approach to quality, that based on Statistical Process Control. The basis of this approach is.. –Collect information –Record –Analyse –Act SPC is an approach based upon prevention rather than detection!

Prevention System Method People Material Environment Equipment OUTPUT PROCESS Information on performance Action on output Information on process Action on process

Prevention System Requires operatives to be given ‘tools’ to interpret the process Requires operatives to become more involved in finding solutions to problems which has serious implications for the way companies so business. Has implications for the suppliers which spills over to regarding the process upstream as you internal supplier and you becoming an internal customer of the process downstream.