China Southern Aviation Industry Group Co., Ltd. (Zhuzhou 412002, Hunan Province) Qu Quping Yuan Peng cold processing cold heading has the advantages of high productivity, high material utilization rate, good surface quality and internal comprehensive performance, and consistent metal flow lines.
Compared with machined parts, the mechanical properties of cold heading parts can generally be increased by about 10%, some even up to 20%, the processing efficiency can be more than 50 times, and the material utilization rate can be improved by nearly 100%. Bolts, screws, rivets, etc. are tight. Nearly 80% of the firmware is produced using the cold heading method, which is the preferred process for fastener processing. However, as a separate process, Lengbu has not received enough attention, and there is very little information on the cold heading process and mold design. And most of the fastener materials of civilian products are carbon steel. Due to the harsher environment and higher performance requirements of aero-engine fasteners, many materials are high-strength structural steel, high-temperature alloy or titanium alloy, etc. The difficulty of coldness. At present, an aero-engine company's basic processing of cold-rolled parts blanks should have a smaller pumping pressure. The flushing method is as shown.
4. Monitoring of the machining process When EDM is ready, the machine process can be started as shown. In recent years, aircraft accidents caused by fastener cracks and the like have occasionally occurred. It can be seen that the quality of fasteners that seem to be simple in shape is still not to be underestimated. This paper analyzes the quality problem of a certain hexagonal head bolt of an aero-engine company, finds out the main cause of cold heading defects, and uses the finite element volume simulation software to simulate the cold heading process, and then optimizes the mold design, so that the product quality is greatly improved. It provides better value for cold die design.
Start processing. In the process of processing, the processing status should be monitored at any time. The corresponding treatment method is adopted in time for the abnormal discharge state in the process to ensure the smooth progress of the processing. It is mainly to prevent the occurrence of arcing. Generally, the discharge condition can be improved by modifying the parameters of the lifting knife, cleaning the electrode and the workpiece, and adjusting the parameters of the electrical standard.
At present, the machining performance of CNC EDM machine tools has been greatly improved, and the intelligent control technology of some advanced CNC EDM machines can almost replace manual monitoring. During the processing, the state of the gap of the EDM is monitored and judged by the computer, and the processing conditions that maximize the processing efficiency are automatically selected within the range of maintaining the stable arc. However, the intelligent control technology of the machine tool is not omnipotent, and the role of manual monitoring cannot be ignored. Especially in some special processing occasions such as deep hole machining, large taper machining, and large area machining, manual monitoring has its significance. A MW material is a hex head bolt of GH2132. It is cold-twisted on a two-flush cold heading machine CH-6L. After cold heading, the outer circumference of the bolt head is creased and even cracks occur. Similar defects are shown. Because the defect is too deep, the car can not meet the corresponding acceptance requirements after the machining allowance, and the production cannot continue.
There are many reasons for creases/cracks in the cold heading process. There are some reasons for the material itself, such as serious segregation of materials, high hardness, scratches on the surface, etc. There are reasons for cold heading, such as rough mold cavity design is not reasonable. The volume of the precision die is not correct, the gap between the die cavity is too large/too small, the distance of the scissors die is large/small, the clamping of the scissors die is too tight, and the concave and convex cavity is misaligned; at the same time, the bevel angle of the blank is too large, lubrication Poor results, instability of the cold heading machine may cause creases/cracks. Since the materials re-inspected all the indicators meet the relevant acceptance criteria, the equipment operation is relatively stable, so the problem of crease/crack defects is mainly solved from the mold side.
(1) Analysis of blank forming For the material of a certain specification, the smaller the upsetting ratio is, the easier it is to process. When the upsetting is relatively large, the number of upsetting should be increased appropriately when formulating the process. The relationship between the upsetting ratio and the number of upsetting is shown in the table. 1 is shown.
Table 1 Relationship between upsetting ratio and upsetting times Table upsetting ratio S 镦 forging times / n hex head bolts before cold heading total length L = 25.5mm, diameter 1mm, cold heading required blank head 12.5mm, bolt head The height is 2.65mm. Through calculation, the hex head bolt upsetting ratio is S = 13/3.1.4.19, the degree of cold heading deformation is = (13-2.65) / 13x100% = 79.6%. The upsetting ratio S is close to the secondary upset forging The limit, and the general material upsetting ratio of 3, the upset is easy to produce a double drum shape; after more than 3, the blank is prone to a longitudinal bending similar to the compression of the pressure bar. In addition, the cut surface of the blank cannot be completely flattened, so that the rough material is interfered by a component force perpendicular to the axis, which increases the longitudinal bending tendency. It shows the deformation of the blank after the rough adjustment process (only the deformation of the bolt head is concerned during the test, so the length of the rod in the non-deformed area is inconsistent in the figure). It can be seen from the figure that the side bend is very obvious when the rough is rough (the speed is too slow and will aggravate the defect to some extent), which makes it impossible to make up for this defect when it is fine, so it is easy to form similar to the one shown. Creases. At the same time, the degree of deformation of the part is large, and the fine material partially approaches or exceeds the allowable deformation degree of the material, so that the bolt head is cracked.
The blank after the rough test is a set of software specially developed for metal plastic forming developed by SFTC of the United States. It is one of the most popular metal processing numerical simulation softwares in the world. In the mold design stage, the finite element simulation can analyze the flow law of the material, predict whether defects are generated, and thus verify the rationality of the mold shape and size design, and optimize the mold design and other process parameters.
First, according to the actual size required by the process, in the Pro/E3.0, the blank, rough mold, fine mold, cold head die shape is saved as. Stl grid. Then, it is imported into Deform3D software. In the simulation process, in order to reduce the calculation amount, it is assumed that the mold is a rigid body, and no deformation occurs during the cold rolling process. The blank material selects the US grade A286 in the software material library (equivalent to this hexagonal head material GH2132). Set the simulation parameters and simulate according to the part cold forming process. The simulation results are as shown. From the visible, the simulation results are basically consistent with the results of the cold heading production of the blank. Therefore, in order to solve the crease/crack defect, the rough side bend must be minimized or avoided.
The design principle of the roughing die for cold rolling A is: firstly, it is required to have the largest possible deformation ratio to prepare for the second upset forming; secondly, to avoid (b) fine simulation of Deform3D simulation results without metal fiber Produces longitudinal bending. The conventional rough model cavity is a simple conical structure. In order to make the rough deformation as much as possible to make the two formations uniform, it is only necessary to increase the cone angle, but as the angle increases, the longitudinal bending of the blank during the forming process The tendency is also increasing. In order to balance the two aspects, based on the experimental exploration, the design scheme of the cylindrical cavity + spring structure rough die is proposed. While ensuring a large amount of rough deformation, the positioning guide is strengthened by adding a cylindrical cavity at the small end of the rough mold cavity, thereby increasing the stability of the blank during deformation, as shown. A spring ram structure is adopted for the problem that the positioning cavity increases the sticking tendency of the blank to a certain extent. This not only helps to reduce the influence of the unevenness of the end face of the blank, but also avoids the occurrence of the sticking condition of the blank when the mold is not well lubricated.
The main parameters of the new rough mold are /3, h, y and (. The rough die angle can be shown in Table 2. Since the hex head bolt upsetting ratio and deformation rate are both large, it is basically reasonable to ensure the coarse and fine boring deformation. In the case of the case, try to use a large angle. Deform3D is used to simulate the shape of the blank after the rough forming of the rough model cavity angle, and a basic angular range is confirmed. The combined angles are 0.5mm, 1.0mm, 2 at various angles. When the height of the positioning cavity of 5mm is used, the rough test condition of the blank is simulated. It can be seen that with the increase of the height of the positioning cavity within a certain range, the positioning guiding effect is enhanced and the side bending is gradually eliminated. For the two upset forming parts, Generally, the height after roughing is 2/3 of the total height of the original deformation part. Therefore, if the value of h is too large, the amount of deformation of the rough will be reduced; and if the angle of cone/3 is too large, the stability during the forming of the blank will be weakened. Comparing the simulation test, the hexagon head bolt, the positioning cavity height h=1.82.3mm, the taper angle/3 is 34. Combined with the clamping condition of the cold heading machine tool, considering the mold positioning cavity and the taper angle/3, consider The volume of the blank before and after upsetting is basically not In principle, the y value in the determination is obtained.
Table 2 Relationship between upsetting ratio and rough die forging angle Table upsetting ratio (average) New structure design effect By adopting a new rough die design scheme, the blank cavity is strengthened during the forming process, and the cylindrical cavity is strengthened to guide the blank positioning. The process is more stable, and the rough side bend phenomenon of a hexagonal head bolt of the large upsetting ratio is completely eliminated. In addition, the spring has the function of ejecting, and the sticking phenomenon does not occur. The final thickness of the product is qualified, and the appearance quality meets the relevant acceptance criteria. .
By adopting a new type of rough die: cylindrical cavity + spring ejection structure, the problem of side bend defects of a large die-turning ratio and large deformation amount of a die-type two-punching equipment is solved, which provides a very good design for cold die design of similar parts in the future. Good idea.
The finite element numerical simulation software Deform3D provides very good value for the analysis of cold heading problems and mold design, and can play a big role in the field of cold heading. MW cold working
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