Effective management of the hottest welding fixtur

Effective management of welding jigs

in the process of automobile body manufacturing, nearly 100 sets of small assembly welding jigs, sub assembly welding jigs and body assembly welding jigs are usually required, and 3000 ~ 5000 welding points are punched on these jigs

compared with other fixtures, the positioning and clamping components of automotive welding fixtures have complex surfaces, high accuracy requirements and great difficulty in design and manufacturing. In addition, due to the large size of auto parts and thin sheet metal, the positioning components cannot be made into an integral structure. Generally, independent positioning blocks and positioning pins are used and installed on the integral base board. In daily work, if the position of the fixture positioning element is offset, the positioning element is worn, and the clamping force of the clamp is not enough, it will lead to the distortion of the parts, cause the positioning deviation, and cause the change of the gap position of the parts. Finally, it will lead to the increase of the assembly dimensional error and the deterioration of the stress state of the components, which will directly affect the accuracy, quality and safety of the BIW. Experimental fixture friction coefficient experimental fixture compression experimental fixture deformation experimental fixture elongation experimental fixture zigzag strength experimental fixture elastic modulus experimental fixture peel strength experimental fixture puncture experimental fixture rupture experimental fixture shear strength experimental fixture... Tensile testing machine fixture is an indispensable part of electronic tensile testing machine

to ensure the accuracy of welding fixture in the process of use, It is one of the most concerned problems of manufacturers in ensuring the accuracy of car bodies. Only the effective management of fixtures can ensure the accuracy of fixtures, reduce the deviation of body in white shape and size, and improve the accuracy of car body manufacturing

our company's management policy in the use of welding fixtures is: daily maintenance + regular maintenance, find out the causes, take measures to eliminate them, prevent them, and incorporate them into the system (see Figure 1)

Figure 1 management ideas in the use of welding fixtures

this paper only starts with daily maintenance and regular maintenance, and verifies and manages the effect of welding fixtures by means of body in white precision detection, and can timely feed back relevant information to promote the effective management of welding fixtures

daily maintenance

the daily maintenance of our company's welding fixture is divided into fixture 5S, fixture status and pre shift spot inspection (see Figure 2)

Figure 2 daily maintenance of welding fixture

1. Fixture 5s

the role of enterprises in implementing 5S: improving effective working time, reducing waste, ensuring quality, ensuring safety, improving efficiency, enhancing enterprise competitiveness and enhancing enterprise image. The main items of 5S management of welding fixture include: area division, positioning and placement, removal of welding slag, sorting out messy gas pipes, and ensuring the integrity and cleanness of the contact surface

2. Pre shift spot inspection

the inspection items before the fixture starts work are mainly to check whether the power device (such as air source pressure, air pipe, cylinder and start switch) and the fixture working state (such as positioning pin, positioning block, fastening screw and lubrication condition, etc.) are normal. Before each fixture starts work, it must be checked to prevent omission, and it is necessary to fill in the fixture start work inspection record form and establish files, Collect shape wear data about positioning elements

3. fixture status confirmation

at present, automobile manufacturers are mostly flexible production lines. For mixed line production or a set of fixtures that produce multiple products by switching, the status should be confirmed before production. Do not misuse the fixture or positioning elements, and ensure that the working state of the fixture (such as positioning pins, positioning blocks and fastening screws, etc.) is in the best state before switching, so as to prevent product errors caused by human factors

regular maintenance

the regular maintenance of our company's welding fixture is divided into fixture preventive maintenance, predictive maintenance and body accuracy measurement

1. fixture preventive maintenance

preventive maintenance refers to the measures planned to eliminate the causes of equipment failure and unplanned interruption of production. As an output of manufacturing process design, the main content is regular inspection and maintenance. Its purpose is to find hidden function faults of products, ensure the specified performance of fixtures, and prevent multiple faults of fixtures. Fixture regular inspection and maintenance is based on the pre work inspection of fixtures, that is, pre shift spot inspection. It is mainly aimed at the inspection and maintenance of fixture function. If defects are found, it should be repaired in time to prevent major defects of fixtures caused by accumulated defects, which will affect the accuracy of vehicle body and interrupt the production process. Such as air circuit triplet, air pipe, cylinder, start switch, lubrication condition, copper sleeve, clamp and limit element, etc

Figure 3 regular maintenance of welding fixture

2. Predictive maintenance of fixture

predictive maintenance refers to the activity of avoiding maintenance problems by predicting possible failure modes based on process data. Experience tells us that mechanical, electromechanical and electronic components with potential fault characteristics or loss mechanism and components with hidden fault form are the starting point for considering predictive maintenance objects. Our predictive maintenance points for fixtures mainly consider the accuracy of positioning elements (positioning pins, positioning surfaces), which is carried out on the basis of preventive maintenance of fixtures. The positioning element is the most important component in the fixture, which ensures the position of the assembled parts in the fixture, thus ensuring the technical requirements of the mutual position of all the assembled parts, and sometimes directly determines the shape of the welding structure. The accuracy of the positioning element directly affects the accuracy of the workpiece. Therefore, it is of great significance to ensure the accuracy of the positioning element. In daily work, the method to ensure the accuracy of fixture positioning elements is mainly to detect the shape accuracy of positioning elements and the position accuracy of positioning elements. At the same time, regression analysis is used to replace or adjust them regularly

(1) shape accuracy detection of positioning elements

during the use of fixtures, the positioning elements will inevitably wear, but if the wear exceeds a certain amount, the positioning elements will fail. As many as 1700 ~ 2500 positioning elements are installed in nearly 100 sets of invalid sub jigs on the car body, the wear of positioning elements needs to be tested periodically after a certain time or a certain production volume is specified according to the actual production situation. The detection method is to use vernier caliper and micrometer to measure the positioning element, and then subtract the theoretical value (design value) of the positioning element from the actual measured value to obtain the wear amount of the positioning element. Then compare the actual wear amount with the maximum wear amount (the setting is based on the material of the positioning element, no heat treatment and wear failure theory combined with the actual production) to determine whether the positioning element can continue to be used or needs to be replaced

carry out mathematical statistical analysis on all measured data in production, and use regression analysis to grasp the wear law. Replace or adjust the positioning element before failure. Generally, it is analyzed based on the data determined by the phenomenon of blocking the relative movement on the contact surface measured by the wear state of the fixture, and then the maintenance is carried out. Compared with the predictive maintenance based on time, it requires higher maintenance technology and corresponding detection instruments. Therefore, generally, we recommend the predictive maintenance based on time

(2) positioning element position accuracy detection

during the use of the fixture, because the body welding fixture is designed with an independent positioning plate, in addition to wear, the positioning element will also shift. Fruits, pork, vegetables, dairy products, paper products and daily chemical products in many places of automobile welding are on sale. The position accuracy requirements of fixture positioning elements are very high. The position accuracy changes of positioning elements are difficult to detect with the naked eye and ordinary measuring tools. It must be detected with the help of three coordinate measuring instruments. At the same time, it is necessary to establish the position accuracy management archives of fixture positioning elements, In conclusion, the medium and long-term energy science and technology development strategy and development plan to 2020 are formulated, such as statistical process analysis (SPC), and the failed positioning elements are adjusted according to the analysis report. Because it takes a lot of manpower, material resources and time to use the three coordinate measuring fixture, we strongly recommend using the experimental design tool (DOE) to design the offset, and using regression analysis to determine the cycle, so as to achieve the purpose of reducing costs

3. Vehicle body accuracy detection

with the development of laser measurement technology and its successful application in the welding production line, a station installation detection system can be set at the end of the welding production line to hit the laser beam on the vehicle body, use the optical sensor to recover the signal, calculate the actual coordinates of the measurement points through the computer, and compare and analyze them with the theoretical coordinates. When it is out of tolerance, it can alarm to realize 100% control of the vehicle body quality management point

the above is only for the inspection and maintenance of a single welding fixture, but in the actual manufacturing process, measuring the position accuracy of nearly 100 sets of welding fixture positioning elements requires a long cycle, and the role of the fixture is very important. The position failure of the positioning element will occur at any time without predictive maintenance or before it is implemented. In order to prevent the failure caused by the positioning element of the fixture, To avoid the deterioration of the accuracy of a large number of vehicle bodies, regular vehicle inspection is required. According to the data analysis of the detected body accuracy, in turn, the accuracy of the fixture is managed. When the production line starts production, the cycle of vehicle inspection is shorter, but when all fixtures have established predictive maintenance, the cycle of vehicle inspection can be increased or stopped

conclusion

in order to implement the 2mm project, Chinese automobile enterprises need to take control measures in the following three aspects - the design quality of the body, the design and manufacturing quality of the body welding fixture, and the deformation of the body during matching welding. Since the latter two items are guaranteed by the accuracy of the welding fixture, the accuracy of the welding fixture has a great impact on the dimensional error of the vehicle body. In the actual production process, the effective management of welding fixture is one of the keys to ensure the manufacturing accuracy of car body