The Quality Influence and Overlapping Points of Car Exterior Covering Parts

The quality of the exterior covering parts of a sedan directly affects the appearance of the entire vehicle, such as whether the gaps are consistent, whether the body styling lines are smooth, whether the overlap between various parts is continuous, and whether the overlap with exterior parts (such as headlights, front bumpers, etc.) is uniform. All of these require auxiliary tools such as single product inspection tools, assembly inspection tools, welding inspection tools, fixtures, etc. to test and overlap the debugging stamping parts in the mold production process, in order to further optimize the product, stamping process, and control the quality of automotive body in white. The exterior components of a sedan mainly consist of a left front door, a left rear door, an engine hood, a luggage compartment, a left side panel, a top cover, and a left fender.

1 lap joint

In the first round of mold debugging, press out a round of body stamping parts. Measure the data of the first round of stamped parts that have been debugged on the single product inspection tool, analyze the rationality of the status of the single product stamped parts and the product, and then overlap the riveted components of the stamped parts to visually observe and detect the overlap size and tolerance zone requirements, thereby correcting and optimizing the stamped parts product, and providing theoretical basis for mold debugging. Below, taking the front door as the object, describe in detail the one-time overlapping process of its components and assemblies. The main components of the left front door assembly include the left front door inner panel, left front door outer panel, left front door inner panel reinforcement plate, left front door outer panel reinforcement plate, etc.

1.1 Laser cutting

Generally, the date for providing the first batch of parts is earlier, 2 months before the official tooling. At this time, the manufacturing and debugging of the entire process mold had not yet been completed. The first round of stamping parts only produced stretching process parts and forming, flanging and other process parts. To meet the overlap requirements, laser cutting can be used to achieve the desired size of the edges and holes.

1.2 Testing

Place the manually trimmed stamped parts on the fixture for positioning and clamping, and then perform single item inspection on the stamped parts based on the parts and key points provided in the inspection report. The reasonable setting of inspection points is of great significance for the rectification of parts and the improvement of qualification rate. To investigate the stability and comparability of dimensions such as contour and profile of stamped parts, a minimum of 3 units of each type of stamped part should be tested.

1.3 Analysis and Feedback

Based on the inspection data of the stamped parts, an overall data analysis was conducted on the overlapped stamped parts, and the theoretical data of the product numerical model was compared with the actual stamped part data to discover product defects and errors. On the basis of not affecting the assembly of the whole vehicle, for the parts that are difficult to achieve in the drawing and stamping process, a reasonable adjustment of the product should be made, and a product design change should be applied for. The welding workshop should provide a feedback letter for the one-time overlap correction of the product to provide theoretical basis for mold debugging.

For example, there is a gap in the overlap between the outer panel of the left side panel and the rear connecting panel of the left side panel, which leads to poor sealing of the left and right rear light ports and leakage. For the quality of the vehicle's installation, it has been decided to adopt a design change by appropriately reducing the process cut at the rear light mouth of the side panel outer panel on the basis of the existing size.

1.4 Remediation measures

Based on a feedback report on overlap correction, DL design personnel and mold debugging personnel jointly analyzed and provided technical support for mold debugging through process supplementation, modification, and adjustment of process content. Detailed rectification plans were proposed to achieve qualified dimensions for stamping products and optimize the product during the overlap process.

2 secondary overlaps

By correcting product defects, mold defects, and fixture defects in a single lap, single piece and sub assembly lap joints are carried out on stamped parts produced by wheel pressing. This time, the assembly overlap is basically done in the form of riveting. As the provided stamped parts are all stamped by molds, theoretically, the overlap accuracy is higher than that of a single overlap.

2.1 Testing

In addition to single item inspection and sub assembly inspection, secondary overlap also requires inspection of the facial and paint quality of the outer panel. Taking the front door as an example, the following inspections are conducted.

1) Single item inspection and sub assembly inspection

In addition to testing the secondary lap joints according to the quality standard book, targeted re inspection and testing should also be conducted on the problem points of the primary lap joints. The main focus is on detecting key areas such as the compression overlap surface and adhesive coating surface of the inner lining board. The minimum number of inspections for each type of stamped part is still 3 vehicles.

2) Surface and paint quality inspection

The inspection of surface quality and paint quality mainly focuses on the surface quality of exterior components. Noodle quality inspection is the process of polishing the secondary overlapped stamped parts of the outer surface product with an oilstone, and determining the surface quality of the stamped parts through visual inspection and tactile sensation. Paint quality inspection is the process of spraying paint onto the secondary overlapped stamping parts of the outer surface product to make them closer to real car components, and also using visual and tactile judgment to assess the surface quality of stamping parts with topcoat.

2.2 Analysis Feedback

In the second lap joint, from the results of the qualification rate, the average qualification rate of the single product of the left front door outer panel in the first lap joint is 61%, while the qualification rate of the second lap joint is 51.8%, which is lower than that of the first lap joint. The main reasons are as follows.

a. The single lap stamping product is only formed by mold pressing in the drawing process, and other processes (trimming, punching) are manually trimmed.

b. The first lap joint and the second lap joint are in an alternating transition period, and the stamped parts are damaged or deformed during storage or transportation.

c. Inappropriate testing standards or methods result in inaccurate data.

d. Based on the correction information provided by a lap joint, the mold was debugged, and the original defects were corrected, resulting in the emergence of new defects. In addition to analyzing and providing feedback on the detection accuracy of stamping parts and sub assemblies, secondary overlap also requires overall analysis and feedback on surface products (oil stone polishing parts) and painted parts.