Discussion on the new method of assembling and
At present, domestic and foreign auto companies basically adopt new technologies and new processes such as laser welding, multi-head automatic welding machines, welding robots, online measurement and hybrid automatic assembly lines for car body assembly assembly, while ensuring product quality and simple manufacturing process , The car body assembly welding line itself has low investment cost and short production cycle.
New welding technology for assembly of car body assembly
The parts of the car body that need to be assembled and welded are mainly divided into four door and two cover assembly welding, left and right side enclosure assembly welding, body floor engine compartment assembly welding, and body assembly assembly welding.
1. Welding process of four doors and two covers assembly
The four-door and two-cover assembly is very independent and special. It is both a safety part and a sports part, or a car decoration. In order to improve production efficiency and make the appearance beautiful and product safe, foreign automobile companies adopt the clinch connection method in the door cover area, through the gas-liquid booster cylinder stamping equipment and connecting mold, after stamping processing, according to the coldness of the material of the plate itself Squeeze and deform to connect two layers of plates with different materials and different thicknesses.
The traditional spot welding connection easily destroys the plating on the surface of the board, and also causes thermal deformation of the board, and the connection quality cannot be detected without damage. The new process has no requirements on the surface of the board, the original coating and lacquer layer on the connection surface are not damaged, the degree of automation of the connection process is high, and the damage-free connection strength can be detected. Because there is no tear damage and stress concentration at the connection point, clinch can eliminate the dimensional error caused by the inconsistent reference transmission; before the fixture is officially used, the deformation error of the fixture positioning structure is fully resolved to reduce the size of the product The influence of precision, to achieve the coordination between parts and parts assembly, and appearance quality and assembly speed of the vehicle, etc., to achieve extremely high dynamic connection strength.
2. Welding process of left and right side wall assembly
Due to the complicated design structure of the left and right side car assembly, foreign automobile companies used to use manual welding guns for manual welding. However, in order to improve production efficiency, foreign automobile companies have made design improvements to mobile spot welding guns to reduce the total number of welding to achieve automatic welding; at the same time, the welding lines of the left and right side assembly assemblies were modified, and the carousel conveyor and The welding fixtures on the left and right sides can be alternately operated to realize automatic clamping on one side and automatic welding on the other side, while the parts are transported on the mechanical conveyor belt according to the prescribed production cycle. All automatic welding machines used for assembly are equipped with electronic eyes to prevent accidental operation of the automatic welding machine.
The internal and external assembly is done through two manipulations at the same station. First build the body frame at the internal assembly station, and then cover the outside enclosure to complete the external assembly. This is like putting a coat on the car. When designing a new model, you only need to change the outer wall and other outer covers.
This processing method can not only improve production efficiency, but also effectively reduce the dimensional error caused by two positioning welding and workpiece transfer. In the welding process, since the same body of the car body is welded twice, it will reduce or avoid the appearance of multi-layer board welding points, improve the stability of the welding points, and also help to reduce the volume of the welding gun cylinder, thereby improving the flexibility of the robot. This design method will greatly improve the flexible production capacity of vehicles in the design and manufacture of new models, reduce the investment cost of new models, and greatly shorten the manufacturing cycle of new models.
3. Welding procedure for the engine compartment assembly of the underbody
The underbody engine compartment assembly is a key component of the car body assembly. The welding and transportation system of the underbody engine compartment assembly of the foreign automobile company adopts a transmission line type, and the workroom is transported, lifted and lowered along the squeeze channel with hooks.
Its welding assembly is completed on a mobile assembly table with five stations, which are connected to each other by rails. The parts to be welded are automatically positioned and clamped on the mobile conveyor belt, and then sent to the conveyor belt by power. Station. The first and third stations are mainly used to position and clamp the parts through hydraulic fixtures. The second and fourth stations use laser welding to complete the welding of the bottom plate and the engine compartment respectively through multiple automatic welding robots; Through multiple automatic welding robots, the welded bottom plate and engine compartment are closed and laser welded, and then the assembly is sent to the body assembly assembly welding line through the power drive conveyor belt.
In a typical floor resistance spot welding application, the robot carries a welding gun to weld from different locations of the part. In order to reach the welding point of the arched area in the middle of the bottom plate, the throat depth and throat width of the welding gun must have enough space to avoid the interference of the parts, and the welding in this area is completed. Therefore, the traditional torch in the area of ??the bottom plate will be very large and heavy, and the robot will be very clumsy and inconvenient when moving.
The programmable base plate resistance spot welding method can increase the number of weldable solder points by 30% in the same time, and can also significantly reduce the floor space of the workshop site, reduce the maintenance cost of the welding gun, reduce the number of welding equipment, and shorten the establishment of the system. And debugging cycle. At the same time, the resistance spot welding of the bottom plate uses two robots to separate the upper and lower electrode arms of the welding gun, one of which is the master and the other is the slave. Robot control can ensure the alignment of the electrodes. The bottom plate resistance spot welding method has low cost and good flexibility. Two sets of floor resistance spot welding equipment can meet the welding of more complicated spot welding on the body channel.
4. Assembly and welding process of body assembly
The welding and conveying system of the car body assembly of foreign automobile companies also adopts the transmission line type. The hooks are used to transport, lift and descend along the squeeze channel in the workshop. The positioning error between the sub-packaging groups is also about 1 mm. The assembly of the body assembly uses an automatic line, which can automatically position, automatically clamp, and automatically load and unload.
The body assembly is assembled on the mobile body assembly assembly table. This equipment has a total of 8 stations. Due to the use of high-horsepower mechanical conveyors, the mobile conveyor belt can complete automatic positioning within 8 seconds, so that The body assembly assembly table can be correctly positioned and clamped in the prescribed work station. When the positioning and clamping of these general assemblies are completed, the key parts of the body assembly body are welded according to the specified welding requirements.
In order to ensure that the body assembly has sufficient rigidity and body structure size with sufficient accuracy, more than 90% of the 1600 welds of the body are welded by more than 70 automatic welding robots, of which more than 40 are five-axis automatic welding robots. Each automatic welding robot can weld 2,000 welds per hour. The welding method is laser welding. The laser beam welds the edge of the roof and the side panel to form a continuous weld of up to 1600mm on one side, thus ensuring Weld quality.
Moreover, laser welding can improve the welding strength while satisfying the production process, and the weld seam is smooth and smooth, which is extremely beautiful. Before each welding, the robot needs to know the start and end points of the weld by measuring; during the welding process, the robot also needs to track the position of the roof edge in real time to ensure that the position of the weld is exactly on the edge and side of the roof Around the junction.
Laser welding represents the advanced technology of car body manufacturing, and laser edge welding is one of the most advanced technologies in laser welding. The assembly speed on the assembly line is 100 units per hour, which is 50% higher than the average speed of other automobile assembly lines. After the welding of the positioning welds specified in the body structure size is completed, these accompanying fixtures will automatically move to, the body assembly leaves the mobile body assembly assembly line and enters the special conveyor system.
There are multiple automatic welding machines on both sides of the special conveyor system to complete the welding of the remaining welds of the body assembly. Each automatic welding machine correctly repeats a series of prescribed action instructions according to the prescribed procedure. The welding method is also laser welding. Wan Yucheng After the welding instruction, the body assembly automatically assembles the door and other components, and then enters the paint shop.
Quality control of assembly welding of car body assembly
The quality control methods of assembly welding of the main parts of the car body are as follows.
1. Welding strength inspection
Regarding the welding strength of solder joints, methods such as non-destructive inspection of welding, destructive inspection of welding and ultrasonic inspection are generally adopted, and these evaluations are controlled and analyzed by the destructive laboratory.
① Non-destructive inspection of welding
According to the frequency, method and judging criteria required by the chiseling drawings, the quality of the solder joints is evaluated. The inspection is generally completed by the operator.
For these assembly weldments every day, according to the prescribed frequency, first clean the number of solder joints and whether the appearance quality meets the requirements, and then insert a special chisel into the solder joints 3-10mm of the prescribed inspection. Move the chisel to check whether the welding spot is loose, then pull out the chisel and restore the part with a 0.5-1 pound hammer. If the welding spot is loose, fill in the defect record that describes the defect location and type for the defective welding spot.
②Destructive inspection of welding
According to the items, frequency and requirements of the welding destructive operation instructions, the quality of these assembly solder joints is judged, usually by a specially trained inspector.
The inspection method is to use hydraulic tension pliers or pneumatic chisels to tear all the welding points of these products, check the tear holes and weld nuggets left on the base material, check whether the tear holes are burned through, and whether there are unacceptable welding cracks. Such defects; butt weld nugget is to use vernier calipers to check its size, if it meets the requirements of the standard, then this weld is qualified, otherwise it is a divergent grid, then fill in the defect weld to describe the defect location and type of defect records.
② Ultrasonic technical inspection
Foreign automotive companies have recently widely used ultrasonic technology to check the quality of solder joints. Such inspections should be completed by specially trained inspectors. This method is that the technical staff first design different inspection plans according to the plate configurations of various assemblies. As long as the inspection staff puts the ultrasonic tester into the tested assembly according to the requirements of the inspection plan according to the different assemblies, it can be checked out The solder joint quality of the tested assembly. It must be noted that when the ultrasonic detector starts to operate, it must first check whether the detection procedure is correct, and then check whether the external equipment of the detector is normal before the operation can be carried out.
2. Welding size inspection
Regarding the welding size, the general inspection standard sample rack, flexible inspection tool, laser measuring instrument and cantilever three-coordinate measuring instrument are generally used for inspection, and the three-coordinate test room controls these inspections and analyzes these inspection data.
① Standard sample rack
Whether the welding dimensions of the four-door and two-cover assembly meet the requirements, a standard sample rack is generally used for sampling inspection. The standard sample rack is designed and manufactured according to the external dimensions and assembly requirements of the four-door and two-cover assembly of the car. Moreover, the measurement points of the standard sample racks of these assemblies should be regularly verified, and the measurement points should be corrected every day with standard sample pieces. The relevant staff shall test the results of the assembly size, the verification results of the measurement points of the sample racks and the measurement of the sample racks. The correction results of points shall be recorded and analyzed according to regulations.
② Flexible inspection tool
The underbody engine compartment assembly and the left and right side enclosure assemblies have complex shapes, making it difficult to manufacture and use standard sample racks. Foreign automotive companies generally use flexible inspection tools to detect the welding dimensions of these assemblies. Before the flexible inspection tool is used, a special computer software engineer compiles the operation program. The inspection staff must strictly follow the operation program. The engineering technicians modify the program according to the collected data, complete the best program for use, and periodically analyze the collected data.
③ Laser measuring instrument and cantilever three coordinate measuring instrument
Domestic car manufacturers mostly use cantilever three-coordinate measuring instruments to detect the welding size of car body assembly. Because the number of car body assemblies to be measured occupies about 3,000, and the measurement period is long, it is difficult to improve the measurement frequency, and it is impossible to effectively control the change in product welding size.
At present, foreign car companies have widely used laser measuring instruments to perform 100% online measurement of the body-in-white. The laser probe and camera installed on the robot are used to sample and measure the face, hole and groove on the body-in-white. This is a big improvement over the three-level measurement and random inspection of body-in-white body quality. It also has the advantages of short measurement time, 100% measurement, instant deviation detection, and instant alarm.
By complementing the advantages of the online measurement system and the three-coordinate measurement, the size status of the body-in-white can be better grasped, and the quality of the body-in-white is improved. Before the online measurement system is used, a special computer software engineer must prepare the operation program. The inspection staff must strictly implement the operation program. The engineering technicians modify the program according to the collected data, complete the best program for use, and periodically analyze the collection data.
It must be noted that the data collected for the detection of various types of assembly of each batch of cars should be completed under the same production process conditions, and the production batch number of each type of assembly of each batch of cars should be maintained. All types of assemblies that have passed the inspection shall be issued according to the batch number to prepare for retrospective inspection. Where any defective product of various assemblies is found during inspection, inspection records and summary analysis must be made according to the production lot number, and corrective measures and quality improvements should be formulated by relevant parts.
It can be seen that the assembly process of the body assembly is a continuously updated and developing technical field. With the continuous deepening of the research on the assembly process of the car by domestic and foreign auto companies, the cause analysis and the corresponding quality improvement measures are formulated for the problem of product quality. The level of technology is bound to continue to improve.