Research on the application of lean production man

2022-08-24
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Research on the application of "fixture flow" lean production management

Abstract: as the processing carrier of products, fixtures shoulder the important task of assisting in the realization of product processing technology. With the help of "fixture flow", mobile fixtures participate in the coordination of resources in all links of the workshop. Therefore. As a form of value stream, fixture flow has research value of lean production management. Fixture input ratio. And cycle times reflect the current production management level of the workshop. Reducing the production input of the flow fixture and improving its turnover cycle times can not only reduce the production input cost, but also improve the lean production management level of the workshop. Therefore, the research of "fixture flow" lean production is not only an important content of workshop production management research. It is also to enhance the product competitiveness of enterprises. An effective way to improve the economic benefits of enterprises

1 production and application of fixture

tooling fixture plays an important role in the processing of products and is an indispensable material guarantee in the processing of products. It has a direct impact on the processing quality, processing cost and production efficiency of products. Strictly controlling the production management, logistics timeliness and other requirements of tooling fixtures can not only coordinate resources through the production and circulation process of fixtures, but also create the "flow value" of fixtures and improve the workshop management. The structure of the fixture and its assembly and disassembly mode should meet the requirements of fast and automatic clamping, so as to reduce the auxiliary operation time, improve the processing utilization rate of the equipment, reduce the labor intensity, and realize the batch production cooperation mode of reliable clamping and rapid and timely positioning. The production application of fixture not only makes general processing equipment (such as CNC) more flexible, but also helps to promote the realization of flexibility and automation of manufacturing system. For example, the "Gripper Fixture" of the robot in the "one pulling eight" flexible machining system, and the pneumatic fixture in the automatic material taking and placing system of forging are all the processes of automatic clamping through the pneumatic/electric control fixture

2 the application of fixture in CNC production and processing process

at present, there are some problems in the production management of the workshop, such as unclear and unreasonable division of labor, insufficient JIT awareness of personnel, weak overall concept, backward maintenance and management level, and poor coordination between processes. These problems are the important factors that lead to the backward level of workshop management. The processing quality, cost and delivery time of products are the key to market competition, and they are the comprehensive embodiment of many influencing factors. Therefore, to improve the product competitiveness of enterprises, we should first improve the production management level of the workshop, and the application of fixtures is like a "barometer" reflecting the management level of the workshop. Through the investigation and analysis of the fixture in the workshop production process, it is helpful to understand the management status of the workshop

during the CNC processing of a product in the workshop, after the fixture is clamped in place at one time, it has gone through the processing processes of logistics, processing, inspection, marking, cleaning and so on, and completed the processing and assembly means required for the whole process from blank to finished product. In this process, the fixture carries out transfer flow processing with products between different processes, and the resulting process cycle flow is called "fixture flow", which is called flow fixture (follow-up fixture). Through "fixture flow", the product completes the progressive processing between different processes in the machining section. "Fixture flow" is actually a kind of value flow. Through analysis, the whole production flow process of products in the workshop is presented, so as to better understand the value flow of fixtures, find waste links in "fixture flow", and put forward technical management improvement plans

the CNC machining process of products has the characteristics of large cutting volume, many machining parts, many types and quantities of cutting tools, high requirements for product size and appearance accuracy, large production batches and so on. Therefore, the CNC machining process of products is divided into several main processes, and a reasonable CNC load distribution plan is formulated in different processes to meet the processing quality and capacity requirements of products

Figure 1 shows the circulation process of flow fixture in CNC production and processing. After the product is clamped in place at one time through the fixture, the logistics transmission is carried out between different CNC processes and auxiliary processing links to realize "fixture flow". Finally, the fixture flows back to the disassembly and assembly section, disassembles the processed products, clamps the shell products of home appliances to be processed, and re inputs into the "fixture flow" to enter the processing cycle of the next product

Figure 1 the circular processing process of the flow fixture in each process of CNC

as the processing carrier of the product in each process, the flow fixture has carried out the repeated assembly and disassembly processing process in the production, effectively ensuring the consistency of the processing benchmark between the products in each process, meeting the quality requirements such as the processing accuracy of the products, realizing the rapid clamping in the machine, reducing the processing auxiliary time, and improving the processing efficiency

3 factors affecting the production investment proportion of mobile fixtures

the production investment capital of mobile fixtures can be fully included in the processing cost of products through "fixture flow", but the production investment of mobile fixtures and their cycle times are the key factors affecting the processing cost of products

the CNC machining process effectively ensures the accuracy and consistency of CT time for product processing. Therefore, in a certain workshop production environment (layout, logistics mode, process flow), in the lean production process, the investment ratio (ratio) of flow fixture and processing equipment is certain, and the flow cycle frequency is basically determined. The ratio of input quantity of flow fixture and processing equipment, referred to as fixture input ratio for short, and the cycle times of flow fixture, can not only measure the input quantity of fixture, but also reflect the status of processing technology and the current production management level of workshop

the production input of mobile fixtures in the workshop is affected by many factors, such as workshop layout, process flow, number of processes, number of equipment, number of logistics personnel, logistics volume, capacity balance, abnormal production, degree of automation application, production management mode, etc. Among them, the nonstandard, disorderly and blindness of workshop production management will have a great impact on the input of fixtures, production management and product processing quality, making the actual input of fixtures fluctuate greatly. After the input ratio of the flow fixture exceeds the rated (lean) input ratio, the greater the ratio, the less the number of production cycles. The slower the "fixture flow" flows, the lower the effective utilization rate of fixtures, the higher the input cost, and the stronger the inert impact on production workers

The specific influencing factors and analysis process of fixture investment ratio are as follows:

(1) in the production process, the number of logistics personnel participating in the flow of fixtures, their enthusiasm for operation and timeliness of logistics not only have a great impact on the production capacity, but also have a great impact on the fixture investment. Due to the untimely logistics operation, the phenomenon of "stacking" is easy to occur in some processing links, so the input of fixtures has to be increased. Therefore, effectively controlling the amount of fixture investment in the production cycle can not only better control the production cost investment, but also help to improve the enthusiasm of operators, but also improve the level of lean production management in the workshop

(2) under different production modes, the amount of fixture input will also be different, such as the amount of fixture required for "one pulling eight" robot flexible processing, two station group processing, manual operation and single station processing

(3) the more intermediate links in the processing process, the greater the number of fixtures required

(4) the layout of the workshop and the way of organization and management will affect the timeliness of logistics, as well as the production input of fixtures

(5) the number of people invested in the flow fixture affects the smoothness of the "fixture flow", and directly affects the continuity and stability of the production system. Once the production is interrupted (shutdown, rest), the flow of the fixture must take a period of time to return to normal. The more complex the product process, the slower the recovery of the production management system

(6) the occurrence of abnormal production causes the processing equipment to have to stop, the overall production capacity will be affected, the continuity of "fixture flow" will also be affected, and the demand for fixtures will increase

therefore, the production input of fixtures should be combined with the actual production process and organization and management status of the workshop. Under the condition of meeting the minimum demand of "fixture flow", the occurrence of "fixture flow" interruption should be minimized, and the actual input quantity of fixtures should be determined according to the frequency of abnormal occurrence and time consumption

4 "fixture flow" lean production process analysis

lean fixture input ratio and turnover times can not only effectively ensure the processing utilization of equipment, ensure production capacity, reduce production input costs, but also improve the lean production management level of the workshop. The faster the flow speed of "fixture flow", the higher the frequency of fixture use, the more significant the economic benefits of output.

through the CNC processing process of a product The whole process of "fixture flow" is tracked and investigated, and the stagnation time of the flow fixture due to processing, waiting, exceptions and other factors in the clamping, processing, inspection and other links of the process flow is measured and analyzed, so as to understand the effective utilization of the flow fixture in the actual production process

the number of CNC in a workshop is 240, the input of mobile fixtures is 2400, the fixture input ratio is 10:1, and the production capacity of each shift is about 6130 sets of products. The average cycle frequency of the single shift theory of mobile fixtures is 6130/2400 = 2.6 times/shift, which indicates that the production utilization rate of fixtures is low, and the flow timeliness of "fixture flow" is poor. The average cycle time of the flow fixture is 8300s (2.3h), of which the CNC standard pure processing time is 1200s, the time occupied by other stations (inspection, marking, etc.) is 900s, and the logistics time is 1000s. Therefore, in actual production, the whole process of necessary processing (including logistics) takes a total of 3100s, and the dead time (abnormal, waiting) accounts for about 5200s, accounting for 63% of the total time of "fixture flow", while the pure processing time (CNC + auxiliary process) is 2100S, accounting for about 25% of the total time of "fixture flow", and the logistics time accounts for about 12% of the total time of "fixture flow". Therefore, 75% of the time consumed by "fixture flow" in the whole process of product processing is invalid operation time (logistics + waiting)

the analysis of the flow fixture in the actual production process shows that the time for the products to be processed to really be in the processing and inspection links only accounts for 20% - 25% of the production cycle, while 75% - 80% of the time is in the logistics handling, or the "fixture flow" stagnates due to various factors that cannot record the impact process. Through "fixture flow", we know that there is a large room for improvement in workshop production management

optimize "fixture flow" to reduce fixture production input and improve its utilization. The specific measures are as follows:

(1) reduce the abnormal rate of CNC and other processing equipment to reduce the stagnation and disconnection of "fixture flow"

(2) reduce the in-process quantity of fixtures in each link, especially the in-process quantity of fixtures to be processed next to CNC, so as to reduce the waste of flowing fixtures waiting in line for processing

(3) reduce the single material flow, increase the logistics cycle times of logistics personnel, reduce the waiting of logistics personnel, and enhance the logistics JIT (timeliness) awareness of logistics personnel

after optimization and improvement, the number of fixtures required to actually meet the smooth flow of "fixture flow" is only 1500, accounting for only 63% of the original fixture investment, saving 900 fixtures. Fixture input

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