Inspection methods for stamped parts
Inspection methods for defects in stamped parts
1. Inspection methods for appearance defects in stamped parts
There are five commonly used methods for the appearance quality inspection of stamped parts in the industry: visual inspection, touch inspection, oilstone grinding inspection, flexible sand screen grinding inspection and oiling inspection. Different car companies choose appropriate inspection methods according to their technical level and production plan. Common inspection methods are visual inspection, touch inspection and oilstone grinding inspection.
(1) Visual inspection
Visual inspection is to directly find the location and type of defects through human eyes. This inspection method is simple and quick, but requires rich experience. The commonly used method of visual inspection is to use sufficient light and take a certain angle to carefully observe each part of the stamped part. Since the photosensitivity of stamped parts is poor before painting, it is difficult to find general defects such as pits and bulges by visual inspection. Only defects such as necking, cracking and obvious pits and bulges are suitable for this inspection method.
(2) Touch inspection
Touch inspection is a major inspection method for surface defect detection of stamped parts. Due to the poor sensitivity before painting, some pits and convexities after painting are difficult to detect visually. These defects can be found by touching with the palm of the hand. The disadvantage is that the touch inspection method is difficult to master and requires long-term work experience and continuous practice. The specific method of touch inspection is: put the palm flat, put the four fingers together, put the hand on the part to be inspected, fit the palm to the surface of the stamping part, and touch the fitting surface repeatedly with appropriate force. The defects on the surface of the stamping part are detected by the sensory cells on the surface of the palm. When the concave and convex parts are touched, there will be a strange feeling.
(3) Oilstone grinding inspection
The oilstone grinding inspection can accurately check the defect location and size of the pits and convexities on the stamping parts, as well as the changes in the defects during the repair process. There are many specifications of oilstones, and the commonly used specifications are rectangular oilstones with a length of 20 cm, a width of 2.5 cm, and a height of 2.5 cm. Since the oilstone is relatively fragile and is prone to breakage when it falls to the ground or collides with other hard objects, a protective cover is usually installed on the oilstone to prevent it from breaking. The quality of the stamping part surface can be judged by the marks produced by the oilstone when it passes over the surface of the stamping part. The prominent bright spots formed by the oilstone marks on the surface of the part are convex hulls, and the intermittent parts of the oilstone marks on the part are pits, as shown in Figure 6.
(4) Flexible sand net grinding inspection
When using the sand net for inspection, first wipe the surface of the outer cover with a clean gauze, and then use the flexible sand net to close the surface of the part and grind it longitudinally to the entire surface. Any pits and indentations can be easily found after grinding. The disadvantage is that it is difficult to find defects such as larger waves and flat ponds with flexible sand net grinding.
(5) Oiling inspection
Before oiling, wipe the outer surface of the part with a clean gauze, then use a clean brush to evenly apply the oil to the entire surface of the part in the same direction. Place the part under a bright light for inspection. This method can easily find tiny defects such as pitting, dents and waves on the part.
2. Functional dimension inspection
(1) Gauge measurement
Using measuring instruments such as gauges, steel rulers, feeler gauges and flush gauges, the profile dimensions, material edge dimensions, hole diameters and hole positions of stamped parts can be measured. At the same time, combined with the product's digital model, the dimensional condition of the stamped parts can be confirmed, as shown in Figure 7. Since the inspection is carried out by manual measurement, the clamping order, measurement techniques and reading methods of the inspector have a certain impact on the measurement results.
(2) Three-coordinate measurement
Three-coordinate measurement is the use of a three-coordinate machine to accurately measure the hole position and profile dimensions of parts. Different from the measurement of the inspection fixture, the three-coordinate measurement is to place the measured object in the measurement space of the three-coordinate measuring machine, and use the contact or non-contact detection system to obtain the coordinate position of each measuring point on the measured object. According to the spatial coordinate values of these points, the software performs mathematical operations to obtain the geometric size, shape and position to be measured. Therefore, the three-coordinate measuring machine has the characteristics of high precision and high efficiency, and is an ideal solution for completing the geometric measurement and quality control of various automotive parts. The disadvantage is that the equipment cost is relatively high, and the parts and software are all imported, and it costs a lot to replace the parts due to wear.