Processing points of 90° counterbore and 90° countersunk screws

Cao or Xuan Qihang (China Air-to-Air Missile Research Institute, Luoyang, Henan 471099) L. However, in the actual machining process, due to the separate processing of the two parts, there is often a problem of countersinking and countersinking mismatch when assembling the site. According to the rework case of the on-site parts, the paper discusses the processability of the counterbore and countersunk screws during processing.

The long lines intersect and recognize >0, so there is a general process of a small countersunk cylinder with a diameter D of 1 90 counterbore "and 90 countersunk screws". Before the case analysis, introduce 90 counterbore and 90 countersunk screws. General process conditions.

90 counterbore on flat parts Generally speaking, the function of the counterbore is to hold the counterbore of the screw and the countersunk head of the countersunk head. The counterbore taper surface is closely attached to the countersunk cone surface, the 90 counterbore cone angle a' is processed by the difference, and the 90 countersunk cone angle a is processed by the difference, so a'< a, the maximum guaranteed countersunk head screw Capable of sticking to the counterbore; the diameter d' of the cylindrical section near the lower end surface of the counterbore is slightly larger than the size requirement of the large diameter d of the screw thread, indirectly ensuring that the translational amount of the flat plate is within the allowable range; near the counterbore of the upper end surface of the flat plate The diameter "D" of the bell mouth is larger than the diameter D of the cylindrical section of the head of the countersunk head screw for burying the countersunk head part, so that the upper end surface of the plate type part is flat, not "out of the head", so that the height H' of the counterbore cone surface is slightly larger than The height of the countersunk cone is H, and some of the counterbore forms a small cylindrical section directly at the "horn" as shown.

90 countersunk screws and cross recess 90 countersunk head countersunk head screws are concentrated on the groove shape of the cylindrical section and the countersunk end face after the natural end of the thread.

From the sum of the screw length L countersunk head end face and cone face extension Li Xiaoyu, Qian Zegang, Yang Qichao, and so on. Analysis of the status quo of compressed air energy storage technology. Liu Sunming, Lin Ziliang, Zhang Chengyan. Research on aerodynamic efficiency of compressed air systems. Fluid He Mingxun, Chen Guojuan. Energy consumption and energy saving analysis of compressed air systems. Fluid Machinery, 9 Chen Dong, Xie Jihong. Heat pump technology and its applications. Beijing: Chemical Industry Press, 2005. Han Weiguo, Jiang Yi, Guo Fei. Energy consumption analysis of various heating methods. HVAC (Editing Liming) gas storage, new energy utilization.

segment. The connection between the cylindrical surface of the thread closing section and the countersunk cone surface depends on the rounding r transition. At the same time, the height H of the countersunk cone increases as the nominal diameter d increases.

The processing of the word groove and the cross groove is processed in the screw head section, the word groove is the milling process, the cross groove is the stamping process, and the cross groove depth is greater than the "word groove depth", and the larger force area is provided for the screwdriver to tighten the thread.

After comparison, the machining tolerance of the counterbore is H13e, and the machining accuracy is not as good as the HB5800-1999 standard tolerance selected by the countersunk screw. There is a certain gap in the taper joint, but within the allowable range. Under normal circumstances, the counterbore can fit in the shape with the countersunk head of the countersunk head screw, and the screw can press the plate type parts. If there is a mismatch, the countersink is generally processed.

2 Rework of the countersunk and countersunk screws of the on-site parts The countersunk and countersunk screws are usually guaranteed to work together when they are processed separately. However, in actual production and processing, due to the design of the parts, not every type of plate parts has a sufficient thickness to ensure that the 90 counterbore and the 90 countersunk screws are properly matched, and there are also many parts with complicated shapes to process the counterbore. This requires repairing the counterbore or the screw according to the actual situation, and according to the universality of the situation, it is implemented into the part processing process to improve the processability of the sub-molding of the part. In the following, the rework of the counterbore and the strut parts on a rib is taken as an example to illustrate how to improve the processability of the part processing.

Since the thickness of the rib is thin, the tapered surface of the counterbore on the rib is better processed. However, the length 1' of the counterbore cylinder section near the joint surface is already smaller than the cylinder section 1 of the M2.5 countersunk screw thread end. The original part is connected to the threaded joint. When the thread is tightened, the end surface fails to stick to the rib. The pillar parts are loosened and the assembly fails.

As shown, the threaded hole chamfer of the strut part is 1x45. It is similar to the 90 counterbore, but does not match the countersunk head in depth, and cannot be buried in the counters at the end of the part. For this fault phenomenon, the counterbore on the rib is qualified, and the depth of the chamfering of the threaded hole of the strut part only serves as an auxiliary function, and does not accept the cylindrical section at the end of the countersunk screw thread. Overall, the countersunk screw is not suitable. At this point, the objects that need to be reworked are the screws and the struts.

Option 1: Machine the undercut for the cylindrical section at the end of the screw thread, as shown.

Ensure that the screw threads continue to tighten the threaded holes until the end faces of the posts stick to the ribs. D2 is the undercut diameter and 'is the undercut width. M2.5 pitch P=0.35 of the undercut diameter d2=d-0.6, width L' is between 0.6~1.05, d<3mm, the machining tolerance band is h12. Option 2: For the threaded hole of the pillar part The angle is machined to a 90. counterbore that is smaller than the diameter of the part. The length of the undercut is included in the counterbore, so that 1'+H2>1, you can continue to tighten and stick the ribs.

We have chosen a more economical solution. 2. Solution 1 Due to the small size of the screw, it is not easy to clamp, and the diameter is small. It is possible to break the part when machining the sipe, and at the same time, it will cut a part of the countersunk head, resulting in the countersunk head and the countersunk hole. The assembly surface is reduced, and the assembly process is reduced, which is not applicable to this failure. In Scheme 2, the similarity between the 45-hole chamfer and the 90 counterbore is used to change the threaded hole of the strut part into a counterbore to ensure the thread assembly. Option 1 is suitable for processing 90 countersunk screws, according to the assembly requirements, control the width and depth of the undercut, try to avoid cutting the countersunk part.

3 Conclusion For the case, from analyzing the phenomenon of failure, proposing the scheme, screening scheme, to the success of the implementation, the following experience can be summarized.

1 Most of the fault phenomena are derived from the general principle of 90 countersunk and 90 countersunk head screws. It is convenient to solve the related parts faults by mastering the general technical points. 2 The processing of the undercut of the screw thread is beneficial to the assembly processability of the parts, but the processing of the undercut should be placed in the process of screw processing, which should not be used during the processing. 3 Countersunk screws of the same specification are not suitable for rework. Therefore, the countersink must be machined with the screws used for it.

4 For irregular shape or countersinking on thin walls, the tooling must be reasonably supported, while ensuring that the lowest point of the counterbore can bury the countersunk screws.

90 countersunk screws.

GB/T152.2-1988 fasteners: countersunk holes for countersunk heads.

GB/T3-1997 ordinary thread finishing, shoulder distance, undercut and chamfering.

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