First, the basic concept of group technology
In the field of modern machinery manufacturing, due to the rapid development of new technologies and new technologies, diversification of social needs, and the ever-shortening of the product update cycle, a large number of enterprises of multi-species and small-batch production have increased. The single-piece, low-volume production has low productivity, high cost, long manufacturing cycle, backward technology, and complicated management. The effective way to change the backwardness of multi-species and small-batch production enterprises, increase productivity, and make full use of equipment to reduce product costs is to use group technology.
Group technology is to classify multiple products, components or parts of a company according to certain similarity criteria, and group and group, and organize production and all links to achieve product design, manufacture and management of multiple varieties and small batch production. Rationalization. This overcomes the shortcomings of traditional small-batch production methods, enabling small-batch production to achieve technical and economical results close to mass production.
For part design, many parts have similar shapes, and those similar parts can be merged into a design family. A new part can be formed by modifying an existing part of the same family. Applying this concept, composite parts can be identified. Composite parts are parts that contain all the features of a design family. It consists of a combination of all the geometric elements of the part in the design family. An example of an integrated part is shown in Figure 10-9.
For mechanical manufacturing processes, the application of group technology appears to be more important than the part design. Not only can components with similar structural features be grouped together, parts with different structures may still have similar manufacturing processes. For example, most box parts have different shapes and functions, but they all require boring, milling, drilling, and the like. Therefore, it can be concluded that they are all similar. In this way, parts with similar processing characteristics can also be grouped together. From this point of departure, the process design work can be simplified. Since similar parts require a similar process, a machining unit can be created to manufacture the same part. For each processing unit, it is only necessary to consider the processing of parts with similar processing characteristics, so that the level of production planning, process preparation, production organization, and management work can be improved.
In addition, with the application and development of computer technology and numerical control technology, group technology has also become the basis of computer-aided process design, flexible manufacturing systems, and computer integrated manufacturing systems.
Second, the part technology in the group technology
(A) The basic principle of part classification and coding
Classification is the process of dividing things into different groups based on the presence or absence of feature attributes. Encoding can be used for classification, it is to give different codes for different groups of things. The coding of the group technology is to give different codes to various features of the mechanical parts. These features include: the structural shape of the parts, the types and configuration of the various composition surfaces, geometric dimensions, parts materials and heat treatment requirements, a variety of dimensional accuracy, shape accuracy, position accuracy and surface roughness and other requirements. To abstract these features and format them, we need to express them with certain code (symbols). The code used can be Arabic numerals, Latin letters, or even Chinese characters, and combinations thereof. The most convenient, the most common is the digital code.
For process design, it is hoped that the code will uniquely distinguish product family members. When designing or determining a coding scheme, there are two properties that must be guaranteed, ie the code must be: 1 unambiguous; 2 complete. This requires a clear stipulation and explanation of the meaning represented by the code. This provision and description is called the coding law, also known as the coding system. The various features of the part are coded and the parts are actually categorized. So the part coding system is also called a classification coding system.
There are three different types of code structures in the currently used group technology coding system: hierarchical, chain (matrix), and hybrid.
Hierarchical is also referred to as a unit code. The meaning of each code is limited by the previous code. Its advantage is that it can represent a large amount of information with few code bits; the disadvantage is that the coding system is very complicated. So difficult to develop.
The chain type, also known as the multi-code, each code on the code bit represents some kind of information, has nothing to do with the previous code bit. With the same number of code bits, the chain structure has less capacity than the hierarchy, but the coding system is relatively simple.
Hybrid is a mixture of hierarchical and chained. Most encoding systems use hybrids.
At present, there are more than 100 group coding technology systems used in industrial production. The JLBM-1 classification coding system is a group technology coding system developed and approved by the Ministry of Machinery Industry of China.
(b) Introduction to the JLBM-1 Classification System
The system uses a mixed structure of main code and sub-code segmentation and consists of 15 code bits. Its structure is shown in Table 10-2.
Table 10-6 
The system's first and second digits indicate the name category of the part. It uses the function and name of the part as a marker to facilitate design department search, as shown in Table 10-3. The three to nine-digit codes are the shape and the processing code, which represent the external shape, internal shape, plane, hole, and the types of machining and auxiliary machining of the rotary and non-revolved parts, as shown in Table 10-4.
Ten to fifteen yards are auxiliary codes (subcodes) indicating the material, blank, heat treatment, major dimensions, and accuracy characteristics of the part. The size code defines large-, medium-, and small-size three-dimension groups, which are used for three types of enterprise parameters such as instrumentation machinery, general machinery, and heavy machinery. The precision code specifies four levels of low precision, medium precision, high precision, and ultra high precision. Between the two grades of medium accuracy and high precision, subdivided into several types according to the combination of different processing surfaces with precise requirements, and represented by different characteristics, as shown in Table 10-5 and Table 10-6.
Table 10-7 shows an example of classifying and encoding rotary parts according to JLBM-1.
(III) Parts coding method
There are two kinds of coding methods: manual coding and computer-assisted coding. Manual coding is the encoding principle of the coding system based on the classification coding system, and the codes of the code bits are coded one by one with the manual parts. Manual coding is inefficient and labor-intensive. Codes compiled by different coders are often inconsistent. Computer-assisted coding is conducted in a human-machine dialogue. There are two types of dialogues, one is question and answer. According to questions from the computer's umbilical panel, the keyboard is used to answer one by one. Generally, if the answer is “y†or “Nâ€, the code of the part can be automatically coded. The other is a selection type, also called a menu type. According to the menu displayed on the computer screen, the number of the corresponding item (usually a number between 0 and 9) is selected by the keyboard, and the coding of the parts can be realized. The computer-assisted editing efficiency is high, the error rate is low, and the labor intensity of the coder is reduced, and the coding error caused by the understanding or judgment error during manual coding can be avoided.
Third, parts classification method
At present, the classification of parts into groups includes the following methods: visual inspection, production process analysis and coding classification.
1. The visual inspection method is based on the parts drawing or the actual parts and their manufacturing process by an experienced craftsman, intuitively judging the similarity of parts by experience, and classifying the parts into groups. This method is simple and effective as a rough classification. For example, parts are divided into rotary bodies, box bodies, rods, etc., but detailed classification is more difficult. Therefore, the application is less.
2. The production process analysis method is a method classified according to similarity of process characteristics. First, according to the routing card for each part, the routing table shown in Table 10-8 is listed. The “ˇ†symbol in the table indicates that the part is to be machined on the machine tool, and then the table 10-8 can be converted into the form shown in Table 10-9 by analyzing, summarizing, and sorting the production process. It can be clearly seen from Table 10-9 that the 20 kinds of parts given can be grouped into three groups, and each group has a similar process route. Production process analysis is a very common method.
Table 10-9 Routing 
3. Coding classification
Parts have been coded and they have been finely classified. However, if only the parts with exactly the same coding are grouped together, the number of parts in each group is often very small, which can not reach the goal of expanding the batch size of the process. In fact, parts that are not exactly the same code often have similar processes and can belong to the same group. For this reason, the coded parts can also be grouped in two ways: signature-based method and code-domain method.
(1) Signature method
From the part code, select the part of the code that reflects the part's process characteristics as the basis for grouping, and then you can get a set of part families with similar process features. These several code bits are called feature code bits. As shown in Table 10-10, the parts with the same code points of 1, 2, 6, and 7 are divided into one group. It can be seen that the characteristics of this set of parts are shaft parts L/d>3, outer cylindrical surfaces with bidirectional steps, diameter d>20~5Omm, and the material is high quality steel. So this set of parts can be processed on the same machine using the same clamping method. Although the part 4 code is 6 instead of 4, the first bit code has only one more function slot than the three parts above, so it can also be combined in this category.
(2) Code Domain Method
The code domain method specifies several allowable data for each code bit feature of a part code, and uses it as a basis for grouping to relax the range of similar features of corresponding code bits. In the part family feature matrix shown in Table 10-11a, the horizontal digits represent the code bits, and the vertical digits represent the codes on each code bit. The “x†in the figure denotes the range called the code domain. Table 10-11a is a feature similarity feature matrix developed based on a large number of statistical data and production experience. The code on each part of the part falls within the code domain, which is classified as the same part group. The three parts shown in Table 10-11b are a group, or a family of parts.
Fourth, group process design
After the parts are grouped into groups, a processing group is formed. The next step is to develop a group process that is suitable for each part in the group for different processing groups. There are two ways to prepare a group process: the composite part method and the composite route method.
(a) composite parts method
The method of designing the process specification according to the composite parts in the parts group is called a composite part method or a sample method. A composite part is one part of all the surface features to be machined that have the same set of parts. It can be a specific part actually existing in the part group, or it can be a hypothetical part. Since it contains all the surface elements to be machined that are included in other parts of the group, the grouping process of the composite part design is as long as To remove some of the steps or steps used for a part, it can be used for all parts of the group to form the processing technology for each part.
Figure 10-10 shows an example of a group of parts that are designed as a group by their composite parts. This part group consists of four parts. The first is its composite part, which contains the five processing surface elements that four parts have. Based on this composite part, a group process was designed. On the basis of the group process, the process contents unnecessary for each part were deleted, and the specific processes of each part in the group were obtained. See Table 10-12.
(B) Compound Route Method
For non-revolving parts, because of its irregular shape, it is often difficult to find a composite part for a part group. Therefore, the above composite part method is generally suitable only for a rotary part. Instead of rotating parts, the compound route method is often used.
The composite route method is based on the classification of parts into groups, comparing the process routes of the same group of parts, based on the process route of the most complex parts within the group, and then comparing this route with the process routes of other parts within the group. Any process that is not required in the process route represented by other parts in the group is added one by one to form a group process that can meet the requirements of the entire group of parts. Table 10-13 is an example of a composite route design grouping process.
V. Group production organization
According to the actual application of the group processing, the group processing system has the following three basic forms: grouped single machine; grouped production unit; group production line. These three types of equipment are arranged between the fleet type and the flow type. The cluster type is suitable for traditional single-piece low-volume production, while the assembly line is suitable for traditional mass production. Which form is adopted for group production depends mainly on the batch size of the same family part after the part is formed into a family.
1 group single machine
The group single machine is developed on the basis of the cluster type arrangement. It is to group parts families with the same or similar processes on one machine tool. Its characteristics are mainly for workpieces that can be completed on the same type of equipment from the blank to the finished product, and can also be used to complete only a few processes.
This form of organization is the initial form of group technology. Due to the centralized processing of similar parts and the increase of batch size, the adjustment time of the machine tool is reduced and a certain economic effect is obtained. For more complex parts processing, when machining on multiple machines, the effect is not significant. However, with the application of numerical control machine tools and Machining Center machine tools, especially the development of flexible transport systems, the organizational form of the single machine group processing has become important again.
2. Group production unit
A group production unit refers to the entire process of one or more sets of similar parts in the process and is completed by a corresponding group of machine tools, which constitute a closed production unit of the workshop. Figure 10-16 shows the layout of a production unit. It is composed of four machine tools and can complete the production unit of all the six components.
The main feature of the group production unit is that a closed production system is composed of several types of machine tools and the entire process of one or more similar parts is completed. It has a certain degree of independence, has clear responsibilities, improves equipment utilization, shortens the production cycle, and simplifies production management. It is widely used by various companies.
3. Group production line
Group production lines are higher-level organizational forms of group technology. The main difference between it and the general assembly line is that it is not a kind of part that flows on the production line, but a variety of similar parts. The rhythm of each process on the assembly line is basically the same, and its work process is continuous and rhythmic. However, for each kind of part, it does not necessarily go through every machine tool on the assembly line, so it can process many workpieces and the scope of application of the process is large.Sawing Machine,Cut To Length Line Machines,Metal Sawing Machine,Jai Band Saw Machine
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