Statistical Process Control Assigment
Task1: Describe two basic types of inspection used in sampling for process control and explain two processes at your company that could benefits from each type of inspection. In you answer gives the example of variation expected from that process. Answer 1- There are two types of data inspection which are below: 1. Variable or continuous scale 2. Attribute or discrete scale 1. Variable or continuous data inspection: The variable data inspection is the type of inspection which varies time to time and it is the scale of measurement for any process used in different industrial process as well as in our daily life.
In variable data inspection there is not breakup between the process. Which means the variable data scale always vary with the time. Examples: Temperature, distance, Analogue signal, Acceleration, Velocity, Weight etc. Explanation: 1- As we know that the analogue signal always varies the values from zero to its maximum values with the different periods of time. Analogue signal start from zero value and its goes to high peak and then after that its values become low which goes to minimum to zero. This example shows that this type of inspection is always continuous with time.
But we should be remembering that in variable data inspection the value always was remaining continues. 2- In another example suppose a cooking oil company selling the different type of oil drums into market. Then we differentiate all these drums in local shop by checking their size , weight, volume, shapes, capacity. 2. Attribute data inspection: In is scale of measurement in any process which should not be vary or continue. The attribute data inspection scale is measured by checking their quality. For example pour quality, bad , accept, and good , yes or not.
Examples: 1- For example we want to buy a motorbike in showroom. So then we do not need to look its engine power or its speed and other features. Just we will be choosing that looks good for us. But in case of attribute data inspection we need to see its all features. For example its model or its engine power capacity which make motorbike different from other models. Also by looking its more characteristics. 2- Suppose a company producing different type of product like a pen etc. Then in attribute data inspection scale we just look and select any of them.
But we will consider its quality, and their writing life time. The above both scale of measurement are necessary in industrial but often time we give the priority to variable data scale because it is important that to get more success in our products quality. And checks the product everything by using the attribute data scale. For example today a lots company producing the electronics components which are used in printed circuit board for electronics industry design. But to make safe working operation of any electronics devices we must check the components life time, materials quality, its temperature.
Which make the circuit operation more effective and increased the circuit finally stability. So thus why by using the attribute data inspection our product will work more efficient. Which also keep the customer happy and satisfy? But we used the other type of inspection at this stage then we have more change that our business or product goes in loss and it’s reduce the customer unhappy and keep down market value over all. Task 2: Describe clearly the significance of natural and assignable causes of variation. Answer: There are two type of variation which is below. – Natural or common cause of variation: Explanation: This type of variation is actually happened in system by automatically or naturally. But the effects of this variation in process is low than other variation. All these variation automatically generated and effect the process because nature of system. For example in electronics field we can see that are too many natural variation which normally involves in the system and change the system output overall. The rays of sun, industrial noise etc which often affect the transistors and change its current.
All these variation is inheriting the process. But a main thing is how we keep our process our process away from this natural variation. According to my own point of view this is only required to modify the system which can decrease effect of natural variation in process. This can be done when we select a good team and team management skills. 2-Assignable variation or special cause of variation: The special or assignable variation is the type of variation which occurred in process by different method for example the change of the environment, lack of attention of operator or problems in machine.
So assignable variation is not generated automatically in process but all these variation cause when you see some problems in machine or the lack of attention of the operator who do not have extra skill to properly handle it or used it. So we need to check the environment as well because the change of environment suddenly can also affect our result. By making some good decision and applying some strategies we can eliminate the assignable variation in process. It is easy to avoid the special cause of variation in system comparatively naturally variation. Task 3:
Explain the purpose of modified control limits for variable data inspection: A control limits is very important for any process to run in right direction. By controlling limits narrow our project will be look more effective and perfect. The wider control limit is the signe which show the project is going to be fail. Which means there are lots of variations in project which can effect our product as well. It does not matter that how much project is big or large, but main thing is in project that how we can handle the limits by the using good technical skill or scientific method.
So by controlling the limits of variation in our process our project will be run more smooth and can keep satisfy of our customer and increase products quality through production methodology. Figure -1 Control limit diagram The above figure -1 is basic diagram of a control limit chart of any process. Where we can see tow lines. The upper line is called upper control and lower line is called lower control limit line and between them there is one more line which is called average line or centre line.
If for example if we increased the distance of upper and lower control limit lines then its much difficult to us to find the error in our process, because the variation in our process is very high. So we have maximum chance that our project will be damage at any stage. If we see less distance between upper and lower limit lines then we can say our process is under control or project is stable. Which means there is nothing wrong in our system which damages our project to its success? If the data is fall down out size these two control lines then we should be know that some things is wrong in our process which take us to the damage.
In the process is in control and process statistic is normal, 99. 7300% of all the points will fall between the control limits. Any observation outside the limits, or systematic pattern within, suggest the introduction of a new and like unanticipated source of variation, known as special cause variation. Since increased variation means increased the quality costs, a control chart (signalling) the presence of a special – cause requires immediate investigation. This makes the control limits very important decision aids.
The control limits tell you about process behaviour and have not intrinsic relationship to any specification targets or engineering tolerance. In practice , the process mean (and hence the centre line) may not coincide with the specified value or target of the quality characteristic because the process’ design’ simply cannot deliver the process characteristic at the desired level. The purpose of control charts is to allow simple detection of events that are indicative of the actual process change. This simple decision can be difficult where process characteristic is continuously varying.
The control chart provides statistically objective criteria of change when change is detected and considered good it is cause should be identified and possibly become the new way of working, where the change is bad then its cause should be identified and eliminated. Task no 6: p3. 1, p3. 3, 4. 2: According to my experiment in class the data collected by taking the length and diameter measurement. In all of the 25 readings I draw a distribution chart and according to that chart most of the values of length of dowels are in between 29. 81mm to 30. 00mm and then the 2nd most common values are in 30. 1mm to 30. 20mm while the rest of values are in between 29. 00mm to 29. 80mm. As shown in below figure 1. 1 As showing in this SPC chart 1. 1 where the data is moving away from the mean line which mean there is something happening wrong in the process but it is still in control so we need to check it out properly in order to get bet product of dowel from process. SPC chart 1. 1 Similarly I draw some control chart relating to dowels diameter and no of dowels in which I can see that most of the data existing near to the mean value but there is two point which is point A and point B as shown in the SPC 1. where the data is moving away from the mean line which mean there is something happening wrong in the process but it is still in control so we need to check it out. SPC 1. 2 In figure 1. 2 the data shown in the chart tells us that the most of the data is below the mean line but is in control but if the process going in the same direction then after some time we can see that all those points which are near to mean line moving away from it and it cross the lower limits and it become uncontrollable. SPC 1. 3 In figure 1. the chart for the diameter of the dowels shows that the most of the diameter of the dowels are between 7. 81mm to 8. 00mm then the 2nd most common value of diameter is existing between8. 01mm to 8. 20mm, while the remaining values are in between 8. 21mm to 8. 40mm , 7. 60mm to 7. 80mm and 8. 61mm to 8. 90mm. Task: 7 P2. 5; p3. 3 Recommendations to the manufacturing manger on how to control the dowel production process. This could be in the form of a control program. Answer: The manufacture manger is person who is responsible to control the all kind of variation in dowel production in process system.
Because without knowing variation which can effect the dowel performance cannot be improve the process of dowels. First of all the manger should be know that what kind of variations can effect system of dowel during their measurement or during the process of dowels. As i mentioned in beging that there are two kinds of variations which can involved in system and it can damage the system of dowel. These two variation are very common , and production manger need to control them by using some wise step. These two variations are given below. * Common cause of variation Special cause of variation The first kind of variation in dowel production can be effect by the nature of system. Because all these kinds of variation is actually generated automatically. So the manger should be making a list in which he need to write all kinds of common cause variation. Here are some given some example of common cause variation * Inappropriate procedures. * Poor design. * Poor maintenance of machines. * Lack of clearly defined standard operating procedures. * Poor working conditions. e. g. lighting, noise, dirt, temperature, ventilation. * Machines not suited to the job. Substandard raw materials. * Measurement error. If the above variation happens in production of dowel then the manufacturing manger should be control by applying different strategies. For example they need to use some new and good error less equipment which can show proper measurement of dowel. Also he needs to check the raw materials in the production of dowel. Always try to use the good materials and should be provide safe working environment to their employees. According to my own opinion the work environment can play an important role in dowel production plant.
If the manger implement some role in plant then they can improve both quality and workers performance in order to get best performance of their production. Because a happy work place or environment is productive office or place weather all employees put their efforts to improving the quality. Often time the engineers / works enhance their ability when their management provide them safe and secure atmosphere. The assignable variation cannot affect the system by automatically but these all variation effect the process of dowel by unusually. Here are some examples of assignable variations * Operator absent. Poor adjustment of equipment. * Operator falls asleep. * Faulty controllers. * Machine malfunction. If all above the variation is control by the manger during the dowel production then they have very less chance to be fail of their product. This process is called the statistical process control, if system is in under control then in SPC chart show the how line is close to mean lines. But any of above variation affects the system and which is not control then the process is called out of control. Which show that there are some problems which may be lack of attention of operator or used by faulty equipments.
Always he should be draw some SPC charts in which he can judge all kinds of variations by putting their values as we I given the example in above SPC charts. The production manger needs to use these tools and techniques in order to improve quality of dowels. The tools and techniques most commonly used in process improvement are: • Problem solving methodology, such as DRIVE • Process mapping • Process flowcharting • Force field analysis • Cause & effect diagrams • CEDAC • Brainstorming • Pareto analysis • Statistical process control (SPC) • Control charts • Check sheets • Bar charts • Scatter diagrams Matrix analysis • Dot plot or tally chart • Histograms All above tools and technique help the manger to improve the dowels quality in process system. Below diagram 1. 5 most power full tools or techniques which enable to manger that he needs to look all of them to improve the process. Regulators Error less equipment or Machine Human Skills and experience Knowledge Output Controls Input Process Of dowel Physical Site Mechanical Service Product Internal Data Supplies External Raw materials Capacity Resources Standard References: http://www. businessballs. com/dtiresources/TQM_process_improvement_tools. pdf