Maps of adjusting variables and attributes

Statistical methods and tools are used in many fields, and the Japanese are considered the most application of these tools, and this is what led to the spread of Japanese products in all markets of the world, and among these tools are the so-called quality control boards.

In this research, quality control based on quality control boards was studied in order to know the types of changes, analyze and study these changes to find out their causes, and solve the problems of these reasons according to specific methods that will be presented later.

These panels are used to track product specifications during the production processes that take place on it, then the reasons leading to defective production can be known, and therefore corrective measures are taken before producing additional quantities.

Thus, the production process can be judged to be stable when changes fluctuate naturally and expectedly, and the causes of change in this case are random causes that cannot be avoided or their causes identified, and their amount is very small and within the permissible limits, and the production process is considered unstable When the changes are large and outside the permissible limits, then we say that the changes are abnormal, hence the importance of this study.

In this research, the descriptive analytical and comparative approach was followed according to the following scheme:

First, an overview of control panels, the importance of their use, and their impact on production processes was given.

Secondly, the most important types and reasons for the changes that occur in the production process were presented, then the control lists were classified into control lists for variables and control panels for properties, with the presentation of the types of each type and the methods of creating those types.

Thirdly, the link between control regulations and the capacity of the production process was explained, and how the capacity of the process is judged through the possibility of analyzing the capacity of the production process through the control panel used.

Fourth, a practical application model was presented that illustrates the method of analyzing the capacity of one of the production processes through control panels.

Chapter one
1-1 Types of changes that occur to products during production processes:

1. A change in the product unit.

2. Changing from one product to another in the same production batch.

3. Changing from one time to another between products at different times of the day.

2-1 The reasons for changes in operations are due to:

1. Conditions of the production process.

2. The quality of employment.

3. The quality of raw materials.

4. Factors such as temperature, humidity, and lighting that affect each of the machines, workers, and test equipment.

5. Factors such as inspection method and measurement method.

3-1 Types of changes according to the way they are measured:

1- Variables: They are the characteristics that can be determined by measuring devices, such as: product dimensions, weights, etc.

2- Attributes: They are the characteristics of the product, which cannot be determined by measurements, but rather by counting and arithmetic, such as: the numbers of defective or valid parts.

4-1 How to use and create dashboards:

First – Determining the control limits of the production process:

1. We take a sample of the product from the production line during each period, so that the size of one sample is not less than five pieces, and the number of samples is not less than twenty-five samples.

2. Carrying out the measurement process on the characteristic to be inspected and recording data, where the focus is on the characteristics or characteristics that affect the performance of the product or the characteristics that result in problems in production or costs, and here the Pareto analytical method can be used to determine those priorities.

3. Calculate the setting limits for the property.

Second: Monitoring the production process:

1. Calculate the range and average for each sample, with calculating the control limits.

2. Draw a rudimentary canvas of the recorded data.

3. Studying the stability of the production process by identifying the points that fall outside the limits of control and determining the reasons for that, as we make sure that there are no intangible reasons for the rest of the points.

4. The point that got out of control and was found to be due to a known cause is replaced

5. The revision board is created from the recorded data without being excluded as the new data is shown on the revision board.

6. Corrective action is taken when some data is out of control.

5-1 Types of Control Panels:

1-5-1- Control Charts for Variables

We use it when we need to:

1. The need to know the ways that lead to quality improvement.

2. The need to determine the efficiency and capabilities of the production process.

3. Giving the necessary information to make decisions related to product specifications that can be achieved according to the capabilities of the production process.

4. Provide sufficient information about the production process as to whether the change occurring in it is normal or if there is some defect in the production process.

5. Giving information about the products of modern production lines.

There are 3 types of these panels:

1. The average control panel to adjust the central tendency of the production process. This map allows studying the change of average values in the production process over production periods.

Here we must know that the specification limits are the permissible limits for the quality characteristic. As for the control limits, they are used to know the change or difference in the quality characteristic between the samples taken and they are linked to the machine used for production.

2. Range control panel to monitor the dispersion of the sample measurement data taken from the product during the production process.

3. Standard deviation control charts to monitor changes of standard deviations of the measurement data of samples taken from the product during the production process, which is a more accurate measure of dispersion used when it is.

How do we choose the sample randomly and how is its size determined?

In general, the samples taken should be homogeneous, that is, their components should be as similar as possible
There are two ways:

1. Taking samples from products that were produced at close times at random, then it is possible to attribute the sample to a specific time, and thus it is easy to identify the causes of deviations, if any.

2. Randomly taking samples from products produced over a period of time

It gives a clearer and more accurate picture of quality.

When determining the sample size, the following should be taken into account:

1- The larger the sample size, the closer the control limits are to the center line, and this leads to an increase in the inspection costs per sample.

2- When using destructive tests, a sample size of 2 to 3 at most should be taken

3- For ease of calculations, a sample of size n = 5 is used in industrial applications

4- It was concluded that the probability distribution of the sample mean is normal for the size of samples n = 4 or more, even if the sample population is not normal.

5- When the sample size exceeds 10, it is recommended to use the standard deviation map instead of the R range map to monitor the dispersion.

Set control limits


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