Design of assembly and welding platform for the si

2022-08-17
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Design of assembly and welding platform for side wall assembly of car N1

Abstract: the assembly and welding line of side wall assembly is a highly automated assembly and welding line integrating machine, electricity and liquid, which is designed and manufactured by SAIC GM Wuling Automobile Co., Ltd. This paper mainly introduces the design of the assembly and welding stand of the side wall assembly from the aspect of the welding fixture

key words: side wall assembly; Assembly and welding platform; Design

preface

n1 car is a new product designed and developed by SAIC GM Wuling Automobile Co., Ltd. and complies with national safety and environmental protection regulations. In order to make the new product scale on the ground as soon as possible, the company decided to use modern technology to carry out equipment modification 1 An assembly and welding production line with domestic advanced level is designed and manufactured by ourselves for the assembly and welding production of N1 vehicle. The design of N1 vehicle assembly and welding line absorbs foreign advanced assembly and welding line technology, adopts advanced lifting system and horizontal conveyor system structure as the main body of the line, adopts computer control system fieldbus control, and uses automatic up and down line devices to complete the automatic transmission of main component assemblies, assembly positioning and welding, making the line a more advanced welding line in China. Automobile side wall assembly is the key part of automobile body manufacturing, and its manufacturing quality directly affects the appearance and performance of automobile. The following is a detailed introduction to the design and manufacture of the assembly, welding and assembly platform of the side wall assembly

1 overview of the assembly and welding assembly platform

the annual production program of the side wall assembly welding assembly platform is 60000, which is used to weld seven parts, including the side wall outer plate assembly, the A-pillar upper inner plate, the front side upper side beam inner plate, the B-pillar inner plate assembly, the rear side wall upper inner plate assembly, the rear wheel housing outer plate, and the buffer recess, to ensure that the side wall assembly formed after welding meets the dimensional accuracy requirements of the product, so that the side wall assembly has good interchangeability and aesthetics, So as to ensure the appearance quality of the whole vehicle

the side wall assembly welding platform is shown in Figure 1. The platform is 3128m long, 1161m wide and 1137m high. The fixture adopts 31 positioning clamping points in total. The action sequence among the welding fixture, conveying mechanism and lifting system of the side wall assembly welding and splicing platform is as follows: the transmission belt of the conveying mechanism transports the side wall outer plate assembly to the upper part of the splicing platform → the lifting system cylinder shrinks, and the system drops → the side wall outer plate assembly enters the fixture for automatic positioning → the A-pillar upper inner plate, front side upper side beam inner plate, B-pillar inner plate assembly, rear side upper inner plate assembly, rear wheel housing outer plate The buffer concave and other parts are installed in the corresponding positions in turn, and the workpiece is clamped by the manual clamp → the signal is sent after accurate positioning and clamping → the pneumatic clamp is automatically clamped → welding → after welding, the signal is sent to the clamp → the pneumatic clamp is automatically loosened and returned to the original position for material → the manual clamp is opened and returned to the original position for material → the lifting system rises, and the workpiece is lifted → the transmission belt transports the workpiece to the repair welding and splicing platform, Complete a work cycle. The above actions are controlled by the programmable controller (PLC) according to the pre programmed program, forming an automatic cycle of the process. The matching and interlocking of the positioning and clamping, conveying mechanism, lifting system and welding device of the assembly and welding platform depend on electrical, hydraulic and pneumatic control

it is not difficult to see that the assembly, welding and assembly platform integrates machine, electricity and hydraulics, and successfully realizes the automatic loading, automatic positioning and clamping, and automatic control cycle of the workpiece, which is convenient to operate

2 design of welding fixture

the design of welding fixture is difficult. It is not only necessary to achieve accurate positioning, accurate assembly and other functions, but also to consider leaving enough installation space and movement space for the conveying mechanism and lifting system, which cannot interfere with each other, so as to realize the fixture function

2.1 fixture design scheme

in the design scheme, first determine the design basis of the fixture. According to the principle of datum unification, the design datum of the fixture and the assembly datum of the vehicle body should be consistent with the design datum of the vehicle body as much as possible, which is very important to reduce the accumulated error and ensure the assembly and welding quality. Therefore, the design, manufacturing, installation and measurement datum of the fixture of the side wall assembly should be consistent with the design datum of the vehicle body. Secondly, according to the working height, we determine the height of the fixture base plate as 1115bl. Finally, according to the spatial shape, combination relationship, assembly and welding sequence of parts and the layout of welding points, determine the location and approximate structure of the fixture, as shown in Figure 2. The clamping mechanism of each positioning clamping unit is different. B11 and B14 are clamped by manual clamping, B02, B05, B06, B08, B09, B26, B27, B28 and B30 are clamped by manual clamping and pneumatic clamping, and the rest are clamped by pneumatic clamping

2.2 fixture structure design

due to the complex shape, poor rigidity and easy deformation of the automobile body, the assembly and welding fixture of the side wall assembly has the following characteristics in structure:

a, the shape of the fixture positioning surface is complex, the accuracy requirements are high, and the design and manufacture are difficult. Because most of the body stamping parts are spatial curved surfaces, and the working surface of the fixture positioning element must be consistent with the corresponding positioning surface shape of the body. The shape surface positioned in the fixture is the section of each important part of the vehicle body, so the working surface of the fixture positioning element can only be used with profiling or numerical control iso9809_ Part1 equipment processing can make it obtain accurate shape

b. The fixture structure should have the characteristics of convenient operation, easy welding and convenient workpiece loading and unloading; At the same time, it is necessary to prevent interference between adjacent fixtures and between fixtures and workpiece

c. Due to the large overall size of the car body, the positioning element consists of multiple positioning plates to form the spatial shape of the car body surface, and the workload of fixture assembly and adjustment is large

according to the above characteristics and practical experience, the basic structure of the positioning and clamping unit of the side wall assembly fixture is composed of positioning plate connecting plate, positioning block, adjusting gasket, pressing plate, positioning pin, clamping mechanism, etc. The clamping mechanism mainly adopts manual clamping and pneumatic clamping, and its selection is consistent with the scheme. When designing the structure of fixture, we use UG 3D software, which has powerful functions of surface modeling and solid modeling. Next, take the design of fixture positioning and clamping unit B24 as an example to introduce in detail

the function of fixture B24 is to ensure the accurate positioning of the side wall outer plate assembly during welding, so that the side wall outer plate assembly can be positioned and clamped with other parts according to the design requirements. According to its function and structural analysis, fixture B24 is composed of support base, positioning plate, pressing plate, positioning pin, guide part and air cylinder. The support base and guide part are general parts, and the air cylinder is purchased parts. When designing the fixture, only the positioning plate, pressing plate and positioning pin can be designed according to the positioning requirements

2.2.1 design of locating plate

due to the complex shape of body stamping parts, they contact with the locating surface of the locating plate during assembly and welding, which determines that the shape of the locating surface is complex and the dimensional accuracy is required to be high. In order to make the manufacturing, adjustment and maintenance of components convenient, the positioning plate is designed as a separated structure, as shown in Figure 3. The positioning block II is fixed on the positioning block I, and the positioning block I is fixed on the connecting plate. The positions of the positioning block I and the positioning block II are adjusted by adjusting the increase or decrease of the number of shims. The connection mode between the positioning block I and the connecting plate adopts hole pin positioning and bolt connection, and the positioning accuracy of the positioning plate is guaranteed by the position accuracy of the pin (± 0102mm)

since the positioning surface of the positioning block depends on the shape surface of the front side wall outer plate in contact with it, when designing the positioning block, it is necessary to use the u g digital analog of the front side wall outer plate, and link the required shape surface to the UG digital analog diagram of the positioning block with wave geometry linker, so that the relationship between the positioning block and the workpiece is established. According to the shape of the positioning surface, the entity of the positioning block is made with sketch and extracted, and the entity of the positioning block is tangent to the linked surface with trimbody. The positioning surface of the positioning block obtained is completely consistent with the digital simulation of the contact surface. In order to ensure the shape and dimensional accuracy of the positioning surface in the manufacturing process, the positioning surface needs to be processed by numerical control

the function of the connecting plate is to install the positioning block, pressing plate and guide part. According to the shape of the positioning block and the installation position of the support and pressing plate, sketch and extruded are used to make the entity of the connecting plate, and hole is used to drill each characteristic hole to obtain the digital model of the connecting plate

2.2.2 design of pressing plate

the shape of the contact part between the pressing plate and the workpiece is also determined by the shape surface of the workpiece. In the design process, the angle of the open state of the pressing plate should be fully considered, which should facilitate the loading and unloading of weldments and the operation of workers, and should not interfere with adjacent fixtures. Fixture B24 adopts pneumatic clamping mechanism, and the structural design of clamping parts adopts the form of one-piece pin. When designing the pressing plate, use wave geometry linker to link the required digital simulation of the outer plate of the front side wall to the UG digital simulation diagram of the pressing plate, so that the relationship between the pressing plate and the workpiece is established. The solid of the pressing plate is made according to the shape of the positioning surface, and the solid of the pressing plate is tangent to the linked surface. The obtained positioning surface of the pressing plate is completely consistent with the digital simulation of the contact surface, and the digital simulation of the pressing plate can be obtained by punching each characteristic hole with hole, As shown in Figure 4, the working accuracy of the pressing plate is ensured by the position accuracy (± 0.1) and dimensional machining accuracy (.Dh7) of the connecting pin shaft

2.2.3 design of positioning pin

according to the shape of the workpiece and the position of the positioning hole, because the position of the positioning pin is inconsistent with the positioning reference plane, it is necessary to design a fixed support to fix the pin on the positioning plate, and the structure is shown in Figure 5. 8. Experimental speed of the locating pin: 0.001~500mm/min (arbitrarily adjusted) the diameter is slightly smaller than the aperture on the workpiece, its position accuracy is ± 0.1mm, and the dimensional tolerance is 0 ~ -0.1mm. When designing the fixed support, the fixed support entity is made according to the known distance between the positioning plate and the positioning hole, and the digital model of the fixed support can be obtained by punching each characteristic hole with hole. When designing the locating pin, according to the diameter of the known locating hole, the mathematical model of the locating pin can be obtained by using the locating pin entity made by sketch and ex2trued

2.2.4 assembly of parts

when the UG digital model of each part of a set of fixture has been built, it is necessary to assemble it to form a complete fixture. UG software provides rich assembly functions. The assembly conditions of parts can be determined according to the matching relationship between parts, such as align, coplanar (m because plastic extruders serve various industries and develop ate in depth), distance, center, angle, perpendicular, tangent. After assembly, the motion function is used for motion analysis. Figure 6 shows the assembled fixture positioning unit B24

3 conveying mechanism

the conveying mechanism of the assembly and welding line of the side wall assembly adopts synchronous belt transmission, which is mainly composed of reducer motor assembly, universal transmission shaft, synchronous belt, support, synchronous pulley and roller assembly, as shown in Figure 7. The synchronous belt is driven by a reduction motor, and the synchronous belt wheels on both sides are connected by a universal drive shaft to synchronize the movement of the conveyor belts on both sides. At the same time, the workpiece is transported by the synchronous belts on both sides, which can prevent it from sliding. The mechanism has the characteristics of simple and compact structure, stable transmission, accurate transmission ratio, low cost, no lubrication, cushioning and vibration absorption, and can ensure the synchronous transmission of workpieces

4 lifting system

the lifting device of this line adopts the scissor type, as shown in Figure 8, which is composed of two-way cylinder, connecting rod, lifting arm, support and other parts. The connecting rod is pushed by the two-way cylinder to make the cross arm move up and down, which can raise the conveyor by 600

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