01
Stroke adjustment riveting process
At present, knurled round rivet nuts are widely used in aluminum alloy body, and the stroke adjustment pneumatic rivet gun is installed on the prefabricated bottom hole to provide threads for subsequent assembly.
During installation, according to the specifications of the rivet nut and the plate thickness of the position to be installed, set the appropriate compression stroke S (that is, the stroke of the core shaft of the rivet gun) on the rivet gun, screw the rivet nut into the core shaft, insert the installation hole, and the contraction of the spool shaft will squeeze the thin wall deformation area of the rivet nut, making it plastic deformation and convex outward. Clamp the workpiece between the bump and the nut to complete the riveting.
The installation of the riveting nut is mainly achieved by adjusting the stroke of the riveting gun mandrel, so it is called the stroke adjustment riveting process. The parameters of M6 knurled round riveting nuts commonly used on aluminum alloy car bodies (see Table 1) are suitable for workpieces with plate thickness of 3 ~ 4.5mm. If it is riveted to a plate thickness of 4mm on the workpiece, the required riveting stroke S=6.3-e=6.3-4=2.3mm.
Table 1M6x21.4 Round rivet nut parameters? For the extruded aluminum profile used in the aluminum alloy body, due to the extrusion process, mold manufacturing accuracy and long-term wear of the mold, the actual plate thickness may not be equal to the theoretical plate thickness, and even the plate thickness of different batches of aluminum profiles is different.
When the actual plate thickness is lower than the theoretical thickness, the S-riveting value calculated according to the theoretical plate thickness cannot compress all deformation areas of the riveted nut. In the later application, under the action of the bolt preload, the riveted nut will be further compressed along the axial direction after a long period of vibration and impact load, resulting in a decrease in the bolt preload, a decrease in torque, and even loosening, affecting the reliability of the product.
In order to avoid this risk, it is necessary to accurately measure the thickness of the workpiece plate at each riveted nut position before installation and calculate the riveting stroke S to ensure the final rivet quality.
Taking the round riveting nut as an example, if the actual plate thickness of the measured workpiece is 3.5mm, the actual riveting stroke should be set as S=6.3-3.5=2.8mm.
02
Pull-controlled riveting process
The pull riveting of the riveted nut is another way to complete the pull riveting that is different from adjusting the compression stroke.
The installation process is by giving the riveted nut enough axial tension, under the action of axial load, the thin wall deformation area of the riveted nut will quickly achieve complete plastic deformation, avoiding the partial deformation ability of the riveted nut due to the incomplete match between the stroke and the plate thickness.
In order to achieve the above purpose, the load needs to meet two conditions: the riveted nut deformation area can be completely plastic deformation, and does not exceed the load capacity of the riveted nut thread. The axial loads required for the complete plastic deformation of riveted nuts of different specifications can be obtained through experiments.
The axial load and deformation curves recorded by the tension sensor (see Figure 1 to Figure 4) are obtained when the specifications M8 and M10 rivet nuts of a certain brand on the tension machine are bonded with aluminum test plates of different plate thicknesses.
It can be seen from the load deformation curve that when the axial load of the riveted nut reaches a certain value, there is an obvious inflection point of plastic deformation and elastic deformation on the curve, that is, the critical load required for the force value of the riveted nut to the elastic transformation.
According to the deformation curve found by the load, M8/M10 When two kinds of rivet nuts are bonded with different plate thickness test plates, the rated load capacity of plastic-two kinds of rivet nuts (see Table 2) has different critical loads during the elastic transformation process.
Rivet nut plastic - Elastic transformation of critical load
For riveted nuts of the same specification, the thicker the cleat thickness, the smaller the plastic deformation area, and the larger the critical load of the required elastic-plastic transition.
For a certain type of riveted nut, the maximum plate thickness suitable for similar tests is selected to obtain the critical load of its elastic to plastic transition, which is also suitable for the pull riveting of other plate thickness products.
The load can be defined as the nominal riveting load of the riveted nut. During the riveting process, just set the riveting load on the tension control riveting tool according to the riveting nut type, and the riveting nut can be riveted on different plate thicknesses without worrying about the influence of plate thickness.
03
Proposed
The pull riveting nut is installed on the aluminum alloy car body, and the pull riveting process is quick and convenient with stroke adjustment, but it is greatly affected by the plate thickness, and there is a risk that the pull riveting is not in place, which will lead to the reduction of the preload and torque of the riveting nut, thus affecting the reliability of the product. In order to avoid this risk, the plate thickness of each workpiece needs to be accurately measured before installation, which is cumbersome and laborious, especially for structures with limited space.
The nominal riveting loads of all kinds of riveted nuts were obtained by test. During the riveting process, products of different thicknesses can be riveted continuously by simply setting the load on the riveting tool according to the riveting nut type.
Compared with the stroke mediation riveting process, this installation method fundamentally avoids the impact of plate thickness on the riveting process, and can effectively ensure that the riveted nut is ultimately extremely demanding in the high-speed aluminum alloy body manufacturing field, which is worth promoting.