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

Introduction Statistical Process Control (SPC) is not really about statistics or control, it is about competitiveness. Organisations, whatever their nature compete on three issues – quality, price and delivery. The reputation of an organisation depends upon the quality of its products and services

So which is the quality car?

So What is Quality? Meeting the requirements of the customer – the question really, is how do you know what the requirements of the customer are? Fitness for purpose (Juran) Right first time (Crosby) The total composite product and service characteristics of marketing, engineering, manufacture and maintenance through which the product and service in use will meet the expectation by the customer (Feigenbaum)

So What is Quality? There is a belief with some companies that to achieve quality we must check, test, inspect or measure – the ritual ‘pouring’ on of quality at the end of a process – and that quality therefore is seen as an additional cost.

So What is Quality? To reduce the total cost of quality, control must be at the point of manufacture or operation – quality cannot be inspected into an item or service after its has been produced!

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 that transforms a set of inputs into a desired output 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!)

Process Analysis – SIPOC

Process - Analysis The output from a process is that which is transferred to somewhere or someone – the customer. Clearly to produce an output which meets the requirements of the customer, it is necessary to define, monitor and control the inputs to the process, which in turn may have been supplied as an output from an earlier stage. At every supplier-customer interface there resides a transformation process and every single task throughout an organisation must be reviewed as a process in this way.

Process - Analysis Thus to begin monitoring and analysing any process, it is first necessary to identify what the process is and what the inputs and outputs are. The goal in any operation of a process is the total avoidance of failure. The key to success is to align the employees, their roles and responsibilities with the organisation and its processes.

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? https://www.youtube.com/watch?v=GHvnIm9UEoQ&index=2&list=PLFF3iDLW3ARBV3MRiGdDUvfauXJO22Rvn&spfreload=10 https://www.youtube.com/watch?v=3pmQGTJQ_nc&list=PLFF3iDLW3ARBV3MRiGdDUvfauXJO22Rvn&index=18&spfreload=10 https://www.youtube.com/watch?v=578gaOpT6PU&index=21&list=PLFF3iDLW3ARBV3MRiGdDUvfauXJO22Rvn&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 5 10 15 20 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

Information on performance Detection System PROCESS Method People Material OUTPUT Environment Equipment 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 do companies waste their time inspecting things?

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, a company must therefore… …continually strive to reduce costs. So why does a company that pursues the traditional approach to quality put up with the additional cost of inspection? 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 of errors!

Information on performance 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.

Prevention System Has implications for the suppliers which spills over to regarding the process upstream as your internal supplier and you becoming an internal customer of the process downstream.