Assembly and Quality Control of Plastic Parts
1. Assembly
At present, the industrial assembly for plastic workpieces is mechanical methods, adhesive methods and friction heat methods. Mechanical methods include snap fits, screws, rivets, and pressure welding. The mechanical method is used to detach workpieces such as car light sets and front and rear skins within their service lives. It can also be used in assembling parts with small batches whose costs exceed the value of the equipment. The adhesive method is a permanent assembly method, and is often used in assembling workpieces whose materials are incompatible with each other. When the plastic workpiece is compatible with the connected part, the friction heat method is used. Parts assembled by this kind of method can be connected permanently. This method cannot be applied to the assembly of consumer goods components, and the method is more cost-effective than the other two methods.
In the assembly process of automobile exterior parts, the plastic parts are mainly installed on the body-in-white. The plastic parts and the sheet metal parts are connected, so the mechanical method and the adhesive method are mainly used. In these two methods, except for the assembly of the outer plate of the top cover and the top cover, adopt buckles and 3M glue, other parts such as fenders, front and rear bumpers and front door skirts all adopt mechanical assemblies such as buckles and screws. The number of buckles and plastic positioning pins is 28, accounting for about half of the total number of mechanical assembly points. It can be seen that the accuracy of the connection between the positioning pins and the buckles on the plastic parts and the body-in-white is directly reflected in the whole vehicle, and whether the final gap level difference meets the standard.
2. Control of the dimensional quality of plastic parts and sheet metal parts
The extensive use of plastic exterior parts has brought new challenges to the control of traditional sheet metal parts and sheet metal parts. The fit between the front door and side panel, door and fender, fender and cover has not been extensively used in the body shop and has been assembled and adjusted to meet the standard requirements. When plastic parts are used for covers, fenders and even door exterior panels, the installation process is transferred to the final assembly workshop. The use of analog blocks to assist assembly has become a necessary means to control the quality of assembly.
The simulation block mainly simulates the edges of parts such as doors and wheel fenders. Through the matching measurement of the sheet metal and the simulation block, judge whether the assembly of the door meets the standard requirements. Generally, the light hole near the door gap is selected as the positioning point of the simulation block, and the edge of the plastic exterior trim is used as the measurement mating surface. When designing the timing sequence of the car door's installation process, it is necessary to add the time to install the simulation block, so that the door's installation can be completed within the design time.
Controlling body sizes in the formal production stage generally uses ABC measurement: measurement A refers to the CMM (three-coordinate) measurement of the body-in-white (excluding door covers and wheel fenders), and the measurement point size of the body is measured by the double cantilever test CMM measuring machine. Data is collected, summarized and sorted to form the SPC report of the body-in-white measuring point. Measurement B refers to the measurement data of the car door cover inspection tool, and the dimensional data of the door is collected through the measuring tool to form the B measurement report. Measurement C refers to the body-in-white (including door covers and wheel fenders) gap and level difference matching measurement. Collect measurement point data through measurement tool to form a C measurement report. By controlling the ABC measurement data within the standard range, the dimensions of the body-in-white are guaranteed to meet the requirements, and the assembly quality of the subsequent final assembly is also guaranteed.
The influence of the extensive use of plastic parts on measurement C is the most obvious. When the measurement C measures the perimeter of the doors and fenders on the body-in-white. The measurement tool cannot be used directly or the measurement accuracy is reduced. The measurement C must use the simulation block to characterize the plastic part assembly effect, and the data of the measurement C is also the data of the measurement of the simulation block rather than those of the body-in-white directly.
The quality control strategy of the whole vehicle also needs to be adjusted accordingly. The output size and quality of the body shop should be based on the characterization data of the simulation block. The assembly of plastic parts in the final assembly needs to be adjusted slightly according to the state of the body to meet the quality requirements of the whole vehicle. The use of analog blocks requires the following two aspects:
(1) Pay attention to the precision protection during the use of the analog block.
(2) The analog block should be calibrated regularly.
At present, the industrial assembly for plastic workpieces is mechanical methods, adhesive methods and friction heat methods. Mechanical methods include snap fits, screws, rivets, and pressure welding. The mechanical method is used to detach workpieces such as car light sets and front and rear skins within their service lives. It can also be used in assembling parts with small batches whose costs exceed the value of the equipment. The adhesive method is a permanent assembly method, and is often used in assembling workpieces whose materials are incompatible with each other. When the plastic workpiece is compatible with the connected part, the friction heat method is used. Parts assembled by this kind of method can be connected permanently. This method cannot be applied to the assembly of consumer goods components, and the method is more cost-effective than the other two methods.
In the assembly process of automobile exterior parts, the plastic parts are mainly installed on the body-in-white. The plastic parts and the sheet metal parts are connected, so the mechanical method and the adhesive method are mainly used. In these two methods, except for the assembly of the outer plate of the top cover and the top cover, adopt buckles and 3M glue, other parts such as fenders, front and rear bumpers and front door skirts all adopt mechanical assemblies such as buckles and screws. The number of buckles and plastic positioning pins is 28, accounting for about half of the total number of mechanical assembly points. It can be seen that the accuracy of the connection between the positioning pins and the buckles on the plastic parts and the body-in-white is directly reflected in the whole vehicle, and whether the final gap level difference meets the standard.
2. Control of the dimensional quality of plastic parts and sheet metal parts
The extensive use of plastic exterior parts has brought new challenges to the control of traditional sheet metal parts and sheet metal parts. The fit between the front door and side panel, door and fender, fender and cover has not been extensively used in the body shop and has been assembled and adjusted to meet the standard requirements. When plastic parts are used for covers, fenders and even door exterior panels, the installation process is transferred to the final assembly workshop. The use of analog blocks to assist assembly has become a necessary means to control the quality of assembly.
The simulation block mainly simulates the edges of parts such as doors and wheel fenders. Through the matching measurement of the sheet metal and the simulation block, judge whether the assembly of the door meets the standard requirements. Generally, the light hole near the door gap is selected as the positioning point of the simulation block, and the edge of the plastic exterior trim is used as the measurement mating surface. When designing the timing sequence of the car door's installation process, it is necessary to add the time to install the simulation block, so that the door's installation can be completed within the design time.
Controlling body sizes in the formal production stage generally uses ABC measurement: measurement A refers to the CMM (three-coordinate) measurement of the body-in-white (excluding door covers and wheel fenders), and the measurement point size of the body is measured by the double cantilever test CMM measuring machine. Data is collected, summarized and sorted to form the SPC report of the body-in-white measuring point. Measurement B refers to the measurement data of the car door cover inspection tool, and the dimensional data of the door is collected through the measuring tool to form the B measurement report. Measurement C refers to the body-in-white (including door covers and wheel fenders) gap and level difference matching measurement. Collect measurement point data through measurement tool to form a C measurement report. By controlling the ABC measurement data within the standard range, the dimensions of the body-in-white are guaranteed to meet the requirements, and the assembly quality of the subsequent final assembly is also guaranteed.
The influence of the extensive use of plastic parts on measurement C is the most obvious. When the measurement C measures the perimeter of the doors and fenders on the body-in-white. The measurement tool cannot be used directly or the measurement accuracy is reduced. The measurement C must use the simulation block to characterize the plastic part assembly effect, and the data of the measurement C is also the data of the measurement of the simulation block rather than those of the body-in-white directly.
The quality control strategy of the whole vehicle also needs to be adjusted accordingly. The output size and quality of the body shop should be based on the characterization data of the simulation block. The assembly of plastic parts in the final assembly needs to be adjusted slightly according to the state of the body to meet the quality requirements of the whole vehicle. The use of analog blocks requires the following two aspects:
(1) Pay attention to the precision protection during the use of the analog block.
(2) The analog block should be calibrated regularly.
Next: The Stamping Industry
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