Quality management has a complete system, which is gradually produced and perfected with the development of production and science and technology. Its management content includes determination of quality policies, objectives and responsibilities, and all activities to achieve them through quality planning, control, assurance and improvement in the quality system. We often talk about quality management, but we seldom introduce it from the perspective of methodology. This article will focus on the means of quality management, namely tools and methods.
01 Five major tools
1) Statistical Process Control (SPC, Statistical Process Control)
Apply statistical analysis technology to monitor the production process in a timely manner, and scientifically distinguish random fluctuations and abnormal fluctuations in product quality during the production process, so as to provide early warnings for abnormal trends in the production process, so that production managers can take timely measures to eliminate abnormalities and restore the process. Stable so as to achieve the purpose of improving and controlling quality.
2) Measurement System Analysis (MSA, Measure System Analysis)
Use mathematical statistics and charts to analyze the error of the measurement system output to evaluate whether the measurement system is suitable for the measured parameters and determine the main components of the measurement system error. The commonly used methods are quantitative analysis (range method, mean range method, etc.), count analysis (crossover method), destructive analysis (nested method), etc.
3) Failure Mode & Effect Analysis (FMEA, Failure Mode & Effect Analysis)
In the planning and design phase of products/processes/services, etc., analyze the subsystems and components that make up the product, and the procedures that make up the process and service one by one, find out potential failure modes, analyze their possible consequences, and evaluate their consequences. Risks, so as to take measures in advance, reduce the serious procedures of failure modes, reduce the probability of their possible occurrence, effectively improve the quality and reliability, and ensure the systematic activities of customer satisfaction.
4) Advanced Product Quality Planning (APQP, Advanced Product Quality Planning)
A structured method for identifying and formulating the steps required to ensure that a product satisfies customers. The goal of Product Quality Planning is to facilitate contact with everyone involved to ensure that the required steps are completed on time. Effective product quality planning depends on the commitment of the company's top management to the goal of striving to achieve customer satisfaction. The benefits of its implementation are to direct resources to satisfy customers, facilitate early identification of required changes, avoid late changes, and provide quality products in a timely manner at the lowest cost.
5) Production Part Approval Process (PPAP, Production Part Approval Process)
Specifies the general requirements for production part approval including production material and bulk material. The purpose of PPAP is to determine whether the supplier has correctly understood all requirements of the customer's engineering design records and specifications, and whether its production process has the potential capability to meet the customer's requirements according to the specified production cycle in the actual production process. It is a practical technology used to verify that the products manufactured by the production tooling and process meet the technical requirements through the product approval and recognition procedures before the first batch of products are shipped.
02 Seven methods
1) Checklist
The checklist is a method of listing the contents or items that need to be checked one by one, and then checking them one by one on a regular or irregular basis, and recording the problem points, sometimes called a checklist or a spot checklist. For example: inspection form, diagnosis form, work improvement checklist, satisfaction survey form, assessment form, audit form, 5S activity checklist, engineering anomaly analysis form, etc.
Implementation steps:
① Determine the inspection object;
② Develop a checklist;
③ Check and record according to the checklist items;
④ Require the responsible unit to improve the problems found in the inspection in a timely manner;
⑤ The inspectors confirm the improvement effect within the specified time;
⑥ Regular summary and continuous improvement.
2) Layer method
The classification method is to classify a large number of viewpoints, opinions or ideas on a specific topic into groups, and to group a large amount of collected data or materials according to their mutual relationship, and to classify them. The stratification method is generally used in combination with other seven methods such as Plato and histogram, and can also be used alone. For example: sampling statistics table, bad category statistics table, ranking list, etc.
Implementation steps:
① Determine the subject of the research;
② Making forms and collecting data;
③ Group the collected data into groups;
④ Comparative analysis, analyze the data, find out the internal reasons, and determine the improvement items.
3) Plato
The use of Plato is based on the premise of the stratification method, and the items determined by the stratification method are arranged in descending order, and the graph of the cumulative value is added. It can help us identify key issues, grasp the important minority and the useful majority, and is suitable for counting value statistics. Some people call it an ABC chart, and because Plato's sorting is from large to small, it is also called a permutation chart.
Implementation steps:
① Collect data, classify by stratification method, and calculate the percentage of each stratum item in the overall project;
② Summarize the classified data, arrange them from more to less, and calculate the cumulative percentage;
③ Draw horizontal and vertical axis scales;
④ Draw a histogram;
⑤ Draw the cumulative curve;
⑥ Record necessary items
⑦ Analyzing Plato
⑧Key points:
A Plato has two ordinates, the left ordinate generally indicates quantity or amount, and the right ordinate generally indicates the cumulative percentage of quantity or amount; B Plato’s abscissa generally indicates inspection items, according to the degree of influence, from left to right Arranged in order; C When drawing Plato, according to the frequency of each item or amount of money, draw a rectangle corresponding to the left ordinate, draw the cumulative frequency of each item, corresponding to the right ordinate to draw the points, and put these points in order Connected into lines.
4) Causal Diagram
The cause-and-effect diagram, also known as the characteristic factor diagram, is mainly used to analyze the causal relationship between the quality characteristics and the possible causes that affect the quality characteristics. It promotes the solution of problems by grasping the status quo, analyzing the reasons, and finding measures. It is a method for analyzing quality characteristics. A tool that relates (results) to factors (causes) that may affect a characteristic. Also known as fishbone diagram.
Implementation steps:
① Set up a cause-and-effect diagram analysis team, preferably with 3 to 6 people, preferably representatives of various departments;
② Determine the problem point;
③ Draw the main bone, middle bone, and small bone of the main line and determine the major reasons (generally find out the reasons from six aspects of 5M1E, namely Man, Machine, Material, Method, Measure, and Environment);
④ Participants discussed enthusiastically, analyzed according to major reasons, found medium or minor reasons, and drew them on the cause-and-effect diagram;
⑤ The cause-and-effect diagram group should form a consensus, and mark the items that are most likely to be the source of the problem with a red pen or a special mark;
⑥ Enter the necessary items.
5) Scatter plot
The data corresponding to the causal relationship is depicted on the XY axis coordinate system to grasp whether the two variables are correlated and the degree of correlation. This kind of graphics is called "scatter diagram", also known as "correlation diagram".
Implementation steps:
① Determine the two variables to be investigated and collect the latest relevant data, at least 30 groups;
② Find the maximum and minimum values of the two variables, and draw the two variables on the X-axis and Y-axis;
③ Mark the corresponding two variables on the coordinate system in the form of points;
④ Items such as picture title, creator, and production time are included;
⑤ Interpret the correlation and degree of correlation of the scatter diagram.
6) Histogram
The histogram is aimed at the characteristic value of a certain product or process, using the principle of normal distribution (also called normal distribution), to group more than 50 data, and calculate the number of occurrences of each group, and then use similar histograms to depict them in the on the horizontal axis.
Implementation steps:
① Collect the same type of data;
② Calculate the range (full range) R=Xmax-Xmin;
③ Set the number of groups K: K=1+3.23logN
④ Determine the minimum unit of measurement, that is, when the number of decimal places is n, the minimum unit is 10-n;
⑤ Calculate group distance h, group distance h=range R/number of groups K;
⑥ Find the upper and lower limits of each group. The first group lower limit = X min - the smallest measurement unit 10-n/27 The second group lower limit (the first group upper limit) = the first group lower limit + group distance h;
⑦ Calculate the center value of each group, group center value = (group lower limit + group upper limit)/2;
⑧ Make a frequency table; ⑨ Draw a histogram according to the frequency table.
7) Control chart
The control chart method is such a quality control method that focuses on prevention. It uses the quality characteristic values collected on site to draw a control chart, and judges the quality status of the product's production process by observing the graphics. Control charts can provide a lot of useful information and are one of the important methods of quality management.
Implementation steps:
Creating a control chart generally involves the following steps:
A draw samples according to the specified sampling interval and sample size;
B Measure the quality characteristic value of the sample and calculate its statistical value;
C draw points on the control chart;
D Determine whether there is parallelism in the production process.