Statistical methods for quality control
The most important source of growth of production efficiency is continuous increase in technological level and quality of products. Rigid functional integration of all elements therefore in them there are no minor elements which can be poor designed and made is characteristic of technical systems. Thus, the modern level of development of the scientific and technical program has considerably toughened requirements to technological level and quality of products in general and their separate elements. System approach allows to choose objectively scales and the directions of quality management, types of production, a form and the methods of production providing the greatest effect of the efforts and means spent for improvement of quality of production. System approach to improvement of quality of products allows to lay the scientific foundation of the industrial enterprises, associations, the planning bodies.
In industries statistical methods are applied to carrying out the analysis of quality of production and process. The analysis of quality is the analysis by means of which by means of data and statistical methods the relation between the exact and replaced qualitative characteristics is defined. The analysis of process is the analysis allowing to understand communication between causal factors and such results as quality, the cost, productivity, etc. Control of process provides identification of the causal factors influencing smooth functioning of production. The quality, cost and productivity are results of process of control. [2]
Statistical methods of quality control of production get the increasing recognition and distribution to the industries now. Scientific methods of statistical quality control of production are used in the following branches: in mechanical engineering, in light industry, in the field of utilities. The main objective of statistical control methods is ensuring production suitable for the use of production and rendering useful services with the smallest expenses.
Statistical methods of quality control of production yield considerable results on the following indicators:
- improvement of quality of the purchased raw materials;
- economy of raw materials and labor;
- improvement of quality of the made production;
- cutting of costs for monitoring procedure;
- decrease in number of marriage;
- improvement of interrelation between production and the consumer;
- simplification of transition of production from one type of production on another.
|
|
|
The main task – it isn't simple to increase quality of production, and to increase quantity of such production which would be suitable for the use. The majority of the tools used to control are based on methods of mathematical statistics. Modern statistical methods and the mathematical apparatus applied in these methods demand from the staff of the organization of good preparation that not each organization can provide. However, without quality control it is impossible to operate quality and the more so to increase quality. From all variety of statistical methods most often use the simplest statistical tools of quality to control. They are called still by seven instruments of quality control. The feature of these tools consists in their simplicity, presentation and availability to understanding of the received results.
Instruments of quality control include:
- Pareto's chart.
- Cause and effect chart (Isikava's chart).
- Temporary ranks.
- Control leaf.
- Histogram.
- Chart of dispersion (dispersion).
- Control card.
Pareto's chart – is a column chart on which intervals are ordered on the descending line. On such chart intervals can represent types of defects, their localization, mistakes and other factors. And height of intervals the frequency of appearance of defects, their percentage ratio, cost, time and other factors.
Isikava's chart or the cause and effect chart (sometimes she is called the chart «fish bone») – is applied for the purpose of graphic display of interrelation between the solved problem and the reasons influencing her emergence. As a rule, this tool of quality is used together with method of «brainstorming» since he allows to sort by key categories of the reason of the problems found by means of «brainstorming» quickly. Isikava's chart gives the chance to reveal the key parameters of processes influencing characteristics of products, to establish the reasons of problems of process or factors influencing emergence of defect in a product. In that case when the group of experts works on a solution, the cause and effect chart helps group to reach the general understanding of a problem.
|
|
|
A time row – is applied when it is required by the easiest way to present the course of change of observed data for a certain period of time. A time row is intended for evident data presentation, is very simple in construction and use. Points are applied on the schedule in that order in what they have been collected. As they designate, change of the characteristic in time, the sequence of data is very essential. The danger in use of a temporary row consists in a tendency to consider important any change of data in time. A time row, as well as other types of the graphic equipment, it is necessary to use to concentrate attention on really essential changes in system. One of the most effective applications of a temporary row consists in identification of essential tendencies or changes of average size.
The control leaf represents – a form for registration and calculation of the data collected as a result of observations or measurements of controlled indicators during the determined time period. The collected data can be both integer, and interval. Basic purpose of a control leaf to present information in the form, convenient for perception. The control leaf allows to categorize data. He shows how often there are these or those events therefore information of a control leaf is more systematized, than usual data collection. In a form, the control leaf is, as a rule, the table which accompanies process or an object, in which data of control register. In the table types of discrepancies which can arise in an object are already defined, and the place for filling of amount of the found discrepancies is provided.
Histogram. It displays distribution of separate measurements of parameters of a product or process. Sometimes it is called frequency distribution as the histogram shows the frequency of emergence of the measured values of parameters of an object. Height of each column indicates the frequency of emergence of values of parameters in the chosen range, and quantity of columns on number of the chosen ranges. Important advantage of the histogram is that it allows to present visually to a tendency of change of the measured parameters of quality of an object and to visually estimate the law of their distribution. Besides, the histogram gives the chance to quickly define the center, dispersion and a form of distribution of a random variable.
|
|
|
The chart of dispersion (dispersion) – is a tool of quality which is intended for identification of dependence between two types of data. These data can belong to characteristics of quality and the factors influencing them, two various characteristics of quality, two factors influencing one characteristic of quality. The chart of dispersion in that case when it is necessary to display that happens to one variable at change another, for determination of the cause of uncontrollable points during multiple statistical control of process, confirmation of the interrelation revealed as a result of application of the cause and effect chart and other factors is applied.
The control card – is the graphical representation of the characteristic of process consisting of the central line, control borders and concrete values of the available statistical data, allowing to estimate degree of statistical controllability of process. There are many different types of control cards depending on the nature of data, a type of statistical data processing and methods of decision-making. Depending on scope of application allocate three main types of control cards:
- control cards of Shukhart and similar him, allowing to estimate whether there is a process in statistically operated state;
- the acceptance control cards intended for determination of criterion of acceptance of process;
- adaptive control cards by means of which regulate process by means of planning of his tendency of change eventually and carrying out anticipatory adjustment on the basis of forecasts.
- Data for control cards divide on quantitative and qualitative.
Quantitative data – are results of the observations made by means of measurement and record of numerical values of this indicator (at the same time the continuous scale of values is used).
Qualitative data – are results of observations of existence of a certain sign. Usually count how many sample units have this sign. Sometimes consider number of such signs which are available in selection of a certain volume. For the analysis and management of processes which indicators of quality are continuous sizes (length, the weight, concentration, temperature, etc.) usually use pair control cards, for example, the card for selective average value and the card of scope: X-card and R-card. Control cards on qualitative sign use when the quality of process is estimated by amount of discrepancies.
It is given developed by me the card of the Shukhart below. As basic data the indicator density of polypropylene yarn is chosen.The Shukharta card developed by me is given below. As a specification the mass fraction of fat of kefir is chosen as indicators.
Дата добавления: 2018-06-27; просмотров: 774; Мы поможем в написании вашей работы! |
Мы поможем в написании ваших работ!