Automotive half shafts are prone to spiral deformation on the radial shaft sealing surface during machining, which is called twisted angle, and the twisted angle can easily lead to leakage of the mating surface. This article describes how to implement relevant measurement methods with precision instruments, and the methods suitable for manufacturing enterprises to detect and evaluate the twisted angle of rotating sealing surfaces.
The sealing surface of the automotive half shaft adopts the grinding process, and the vibration of the machine tool-workpiece-grinding wheel system is mainly formed on the surface of the parts in the process of grinding process, which is called the surface texture. The writhing structure in the surface texture (also known as the "writhing angle") affects the flow characteristics of the fluid, and the slewing sealing surface on the half shaft is in contact with the sealing gasket, which plays a significant role in the sealing effect of the part. How to detect the presence of twisted structures in machined parts during the half-axis machining process has become a key quality control tool.
Overview of twisted corners
The twist angle refers to the surface phenomenon observed on the entire circumference of the axisymmetric surface of the rotary sealing surface. The twisted angle shows continuous or intermittent threads in the area around the circumferential direction, which includes a zero degree angle, a few arc minutes, and has a large number of threads for the structure, even a large angle. According to different types of twisted angles, they are divided into macroscopic writhing angles and microscopic writhing angles, and the specific classification criteria are shown in Table 1. Usually, the macroscopic torsion angle is controlled and detected during the grinding of the rotary sealing surface.
Table 1 Types and characteristics of writhing angles
Torsion angle detection method
1. Existing torsion angle detection methods
A sufficient amount of measurement data is required on the defined circumference and axis area of the seal surface to be inspected for the evaluation of macroscopic torsion angles. In order to reliably determine the machining structure, the lateral resolution of the axial direction must be higher than the resolution in the circumferential direction.
The standard measurement method for macroscopic torsional angles is the contour method with axial measurement of the feed direction. The test specimens are clamped and positioned in a circumferential direction (e.g. geometric measuring instruments, rotary feeds).
The parallelism deviation of the rotating feed to the component axis must be limited to prevent swing errors from having a significant impact on the measurement results. The measurement strategy and measurement conditions of the standard measurement method are specified in Figure 1. Usually, a high-precision roughness meter is used to detect the micromorphology of the rotary sealing surface of the workpiece with full coverage to verify the presence of the writhing angle. Performing this inspection requires a precision servo turntable to provide precise rotational speeds. The probe moves in a straight line along the axis, and the measurement length and sampling density are set in advance. When a test is completed, the workpiece is driven by a certain angle, and the returned probe begins the next measurement. The specific test conditions are shown in Table 2.
Figure 1 Schematic diagram of the detection of torsion angles using a high-precision roughness meter
Table 2 Detection Conditions
2. Improved detection method
Although the above method is very precise and the evaluation according to the characteristics of the twisted angle structure is also very standardized, it often takes 2 hours to complete a measurement, and the application in the mass production process is too limited, so there must be a simpler and faster method for detection. Through a large number of practices and experiments, a rapid and practical detection method is proposed.
This can be done with a shaft measuring instrument capable of rotating the workpiece, plus a mount weight of a specific weight (Fig. 2). The specific test conditions are as follows:
Fig. 2 Rapid detection method and illustration of twisted angle
1) Use a lathe or test equipment that can be rotated clockwise and counterclockwise, and load the shaft into its central axis for measurement.
2) Flatten the shaft with the help of a mechanical level.
3) Wash the surface of the rotary sealing surface with an oily solvent and a lint-free cloth.
4) Dry the surface of the rotary sealing surface with a dry lint-free cloth.
5) Place the coil with a weighted weight on the surface of the part to be evaluated: the coil is 3 strands of 100% cotton reinforced sewing thread, with a diameter of 0.23mm, must be cylindrical, soft and smooth and uncoated; the thread must be cut rather than torn; the cotton thread should be long enough, and the resulting bow shape should be in contact with the measurement surface of the shaft at 220° to 240°; after each step of measurement, the new thread should be replaced (such as new cotton thread after each shaft has completed step 6, and new cotton thread after each shaft has completed step 7).
6) Low-speed, uniform rotation of the shaft, 10 ~ 60r / min rotation 8 turns, can be driven by the motor: if the cotton line in the axis forward rotation reversal is not along the direction of the shaft rod, then the identification of no torsion angle; if the cotton line only appears when the axial rotation in one direction, then perhaps the shaft rod is not placed horizontally, or the shaft is tapered; if the cotton line is forward along the shaft, reverse the shaft with the same speed, if the cotton line moves again at the same rate, it means that there is a torsion angle in the detection site; if there is a twist angle, The angle of the twist can be determined by the number of rotational turns corresponding to the moving displacement of the cotton line, and this data can calculate the spiral angle.
7) Apply a WD40 oil film to the entire slewing sealing surface, repeat step 6), the oil film must cover the entire slewing sealing surface surface, but should not drip from the surface.
8) If the twisted angle is confirmed in step 6) or step 7), it is described as "left-handed" or "right-handed" according to its orientation. When the shaft rod rotates clockwise (from the air end of the rotary sealing surface), the suspension cotton thread moves to the right or moves to the air end of the sealing gear, the twisted angle is called right-handed, and the right-handed rotation causes the oil to be pumped out to the air end; when the shaft rotates clockwise (from the air end of the rotary sealing surface), the overhang cotton line moves to the left or moves to the oil seal file, the torsion angle is called left-handed, and the left-handed will cause air to pump into the oil seal end.
summary
The torsion angle on the slewing seal surface of shaft parts is a microscopic texture phenomenon generated after grinding and cannot be reflected in the usual roughness test results. Therefore, although the roundness and roughness of the rotary sealing surface processed according to the drawings and process requirements are qualified, due to the existence of the twist angle, there is a risk of spillage of grease in the sealing area of the parts during movement. How to establish a simple and fast detection method helps to improve the quality control ability of production and processing units in the mass manufacturing process and eliminate the quality hazards of products.
Source: AI "Automotive Manufacturing"
Author: Chen Xiaomin Xia Zhefan
Work unit: Wanxiang Qianchao Co., Ltd. constant speed drive shaft factory
【Important Statement】This article is an original article and may not be reproduced without permission
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