What is SPC

What is SPC

SPC stands for Statistical Process Control. SPC mainly refers to the application of statistical analysis technology to monitor the production process in real time, scientifically distinguish between random fluctuations and abnormal fluctuations in product quality during the production process, and thus issue early warnings for abnormal trends in the production process, so that production managers can take timely measures to eliminate abnormalities and restore process stability, thereby achieving the purpose of improving and controlling quality.

In the production process, the fluctuation of the processing size of the product is inevitable. It is caused by the fluctuation of basic factors such as people, machines, materials, methods and environment. There are two types of fluctuations: normal fluctuations and abnormal fluctuations. Normal fluctuations are caused by accidental reasons (inevitable factors). It has little impact on product quality, is difficult to eliminate technically, and is not worth eliminating economically. Abnormal fluctuations are caused by system reasons (abnormal factors). It has a great impact on product quality, but measures can be taken to avoid and eliminate it. The purpose of process control is to eliminate and avoid abnormal fluctuations and keep the process in a normal fluctuation state.

SPC Technology Principle

Statistical process control (SPC) is a process control tool that uses mathematical statistics. It analyzes and evaluates the production process, promptly discovers signs of systematic factors based on feedback information, and takes measures to eliminate their influence, so that the process is maintained in a controlled state affected only by random factors, in order to achieve the purpose of controlling quality. When the process is only affected by random factors, the process is in a state of statistical control (referred to as the controlled state); when there are systematic factors in the process, the process is in a state of statistical out-of-control (referred to as the out-of-control state). Since process fluctuations have statistical regularity, when the process is controlled, the process characteristics generally obey a stable random distribution; when out of control, the process distribution will change. SPC uses the statistical regularity of process fluctuations to analyze and control the process. Therefore, it emphasizes that the process operates in a controlled and capable state, so that products and services can stably meet customer requirements.

Benefits of SPC for your business

....SPC emphasizes full-process monitoring, full-system participation, and the use of scientific methods (mainly statistical techniques) to ensure full-process prevention. SPC is not only applicable to quality control, but can also be applied to all management processes (such as product design, market analysis, etc.). It is precisely because of this idea of ​​full participation in quality management that the implementation of SPC can help companies truly achieve "pre-emptive" prevention and control in quality control. SPC can:

· Make reliable assessments of the process;

· Determine the statistical control limits of the process to determine whether the process is out of control and whether the process is capable;

Provide an early warning system for the process, monitor the process status in time to prevent the occurrence of waste;

Reduced reliance on routine inspections, regular observations and systematic measurement methods replace a large amount of testing and verification work;

With the above prevention and control measures, our company can certainly:

Reduce costs

Reduce defective rate, rework and waste

Improve labor productivity

Provide core competitiveness

· Win a wide range of customers

Better understanding and implementation of quality systems

Commonly used statistical analysis methods in quality management

....The following tools and methods are very practical and simple, and are widely used in many countries, regions and industries:

Control chart: used to monitor, measure, diagnose and improve process status.

Histogram: A statistical graph that uses a set of unintervaldable bars to show the frequency distribution characteristics, which can intuitively display the distribution of data.

Arrangement chart: Also known as Pareto chart, it is a tool to arrange the impact of each project from the most important to the least important. It can be used to distinguish the main, minor and general problems that affect product quality, find out the main factors that affect product quality, and identify opportunities for quality improvement.

Scatter plot: It reflects the correlation between variables through the distribution of points. It is a graphical tool used to discover and display the type and degree of correlation between two sets of data, or to confirm their expected relationship.

Process Capability Index (CPK): Analyzes the degree to which process capability meets quality standards and process specifications.

Frequency analysis: forms a table of the distribution of different levels of the observed variables.

Descriptive statistics analysis: such as mean, maximum, minimum, range, variance, etc., to understand some overall characteristics of the process.

Correlation analysis: studies the closeness of the relationship between variables, and assumes that the variables change randomly, regardless of priority, and are in an equal position.

Regression analysis: Analyzing the relationship between variables.

Two Phases of SPC Implementation

The implementation of SPC is divided into two stages: the analysis stage and the monitoring stage. The control charts used in these two stages are called analysis control charts and control control charts.

The main objectives of the analysis phase are to:

First, make the process in a statistical steady state.

2. Make the process capability sufficient.

The first thing to do in the analysis phase is production preparation, that is, to prepare the raw materials, labor, equipment, measurement system, etc. required for the production process in accordance with standard requirements. After the production preparation is completed, it can be carried out. Be careful to ensure that the production is carried out without abnormalities in the factors affecting production; then the data collected during the production process can be used to calculate the control limits, make analysis control charts, histograms, or conduct process capability analysis to check whether the production process is in a statistical steady state and whether the process capability is sufficient. If any of them cannot be met, the cause must be found, improvements must be made, and production and analysis must be prepared again. Until the two goals of the analysis phase are achieved, the analysis phase can be declared over and the SPC monitoring phase can be entered.

The main work of the monitoring stage is to use the control chart for monitoring. At this time, the control limits of the control chart have been determined based on the results of the analysis stage. The data of the production process is timely drawn to the control, and the control chart is closely observed. The fluctuation of the points in the control chart can show whether the process is controlled or out of control. If out of control is found, the cause must be found and its impact must be eliminated as soon as possible. Monitoring can fully reflect the role of SPC preventive control.

In actual factory applications, each control project must go through the above two stages, and the process from analysis to monitoring will be repeated when necessary.

Latest Developments in SPC

After nearly 70 years of practice around the world, SPC theory has been developed to a very complete level. Its integration with computer technology has become increasingly close, and its application scope and degree in enterprises have become very extensive and in-depth. In general, the development of SPC presents the following characteristics:

(1) Powerful analysis function and obvious decision-making support. Based on the practice of many enterprises, a variety of statistical methods and analysis tools have been developed. These methods and tools can be used to conduct in-depth research and analysis of data from different angles according to different purposes. In this process, the decision-making support function of SPC has been increasingly strengthened;

(2) Reflecting the idea of ​​total quality management. With the popularization of the idea of ​​total quality management, the application of SPC in enterprise product quality management has gradually expanded from quality control of the manufacturing process to quality control of each link such as product design, auxiliary production process, after-sales service and product use, emphasizing prevention and control of the whole process;

(3) Close integration with computer network technology Modern enterprise quality management requires that more factors inside and outside the enterprise be included in the scope of inspection and monitoring, and the management functions of different departments within the enterprise are characterized by increasingly detailed division of labor and increasingly close cooperation. This requires that data from different sources can be processed quickly and resources can be shared to the greatest extent. To meet this need, SPC is increasingly integrated with computer technology, especially network technology.

(4) The degree of system automation is constantly increasing. In traditional SPC systems, raw data is manually transcribed, then manually calculated, dotted and traced, or manually input into a computer, and then statistically analyzed using a computer. With the improvement of productivity, in manufacturing companies with high-speed, large-scale, and repetitive production, SPC systems have increasingly adopted the method of automatically collecting data using data acquisition equipment and transmitting it to the quality control center in real time for analysis.

(5) The requirements for system scalability and flexibility are getting higher and higher. The development and change speed of the external and internal environment of enterprises is showing an accelerating trend. The successful application of the system must not only meet the current needs, but also meet the requirements of future development. It puts forward higher and higher requirements in terms of the diversity of system platforms, the advancement of software technology, functional adaptability and flexibility, and system openness.