The main discussion below is for some unique processing techniques for large steam rooms.
(1) Pre-treatment of welded parts For the large-scale welded parts of this type, the residual stress of welding should be eliminated as much as possible. The partial pretreatment is carried out here, that is, a part of the parts are welded and then pretreated to eliminate the welding residual stress of the part. The role of partial pretreatment is to create a relatively stress-free welding environment for the remaining parts welding and control the welding deformation; the second is to create conditions for reducing the overall welding stress of the welded parts in the later stage. For this large steam chamber, the portion shown in Fig. 4 is first welded, and the welding stress is locally removed by annealing or vibration aging treatment. After the partial treatment, it is welded to the welded part shown in Fig. 3, and then subjected to integral annealing treatment.
Figure 4 Lower steam chamber pretreatment parts
In the welding process, due to the large size of the large steam chamber, it is difficult to level after welding, so various measures should be taken to ensure the flatness of the plane after welding, as shown in Figure B. Appropriate use of B-side and D-face staggered welding, symmetrical welding and other measures to achieve the ultimate avoidance of excessive welding stress. In the welding process, for the convenience of group welding and to prevent new deformation during the welding deformation and heat treatment, some struts can be used for support, as shown in Figure 5.
Figure 5 steam room tooling struts
In the daily general engineering practice, it is not necessary to accurately measure the residual stress of each part, but it is necessary to understand the residual degree of residual stress for the workpiece with high precision. At this point, the spot welded struts can play a clever application. Before opening the struts, measure the relevant dimensions and make detailed records. The measuring points are marked accordingly. After the struts are opened, the same points are repeatedly measured, and the measured dimensions are compared before and after, and the deformation is verified to be changed. If the dimensional change before and after is large, it means that the previous pretreatment does not really achieve the purpose of eliminating the welding stress. In addition, when the struts are opened, it can be observed whether the last opened solder joint is disconnected by itself, and if it is self-disconnected, there is still a large welding stress. Depending on the circumstances, heat treatment should be repeated if necessary.
(2) Reasonable selection of the clamping point of the workpiece Reasonable selection of the reference and clamping point is the key to ensure the processing quality. When selecting the reference and the nip point, in addition to the requirements of the pattern, it is necessary to fully understand the working condition of the workpiece. Since the wall thickness is easy to cause clamping deformation and cannot be directly clamped radially, a feasible method is to uniformly weld some clamping process blocks on the circumference, and clamp the process block to achieve the purpose of clamping the workpiece, as shown in FIG. After the processing is completed, these process blocks are removed.
Image 6
(3) The use of clamping tooling requires large parts of the interior and exterior surfaces of large steam to be processed, and it is not convenient to install the reinforcing tooling inside, but there is a problem of poor rigidity when directly processing. The C surface in Fig. 7 is one of the processing difficulties. When the cutting force is applied, the portion belongs to the cantilever beam structure, and it is easy to vibrate the knife and deform during processing. Choosing the right auxiliary clamping tool can equalize the clamping force, reduce the adverse effect of the clamping force, and avoid the vibration knife.
Figure 7
As shown in Fig. 7, the auxiliary clamping tool is bolted to the rotary table of the large vertical car. In practical application, the bolt of the upper end is in contact with the lower steaming circle, and the rigidity of the steam chamber is strengthened by the rigidity of the work table and the auxiliary clamping tool. The number of the clamping fixtures is determined to be 8 pieces according to the steam chamber, and is uniformly distributed on the circumference. When adjusting, pay attention to ensure that the force is appropriate and the contact stress of each piece with the steam chamber should be the same. When the contact stress is inconsistent, after the tool is removed, the surface to be turned may have an elliptical shape, and the surface roughness cannot be guaranteed.
How to adjust the contact stress between the bolt and the workpiece is the key to the realization of this processing technology. The force uniformity can be adjusted at the site by a dial indicator. The specific method is: install the dial indicator contact near the bolt, adjust the bolt to observe the change of the dial indicator, and the jump amount is 0.5mm, indicating that the contact stress between the bolt and the steam chamber is basically the same. In different processing stages such as roughing, semi-finishing and finishing, the different contact stresses can be adjusted by this method, which can be combined to obtain different processing effects and improve the processing efficiency. This processing technology plays a key role in the processing quality such as roundness, size and surface roughness of the C-face.
(4) Turning over and repeating processing and intermediate stress processing The repetition principle here refers to when a workpiece has different processing surfaces, as shown in the B side and the C side of Fig. 3 . When processing the B-face for the first time, the size of the pattern is not processed first, and then the second processing is performed after the amount is retained, so that the repeated processing can ensure the processing precision. Repeat processing can be considered to homogenize and reduce processing stress. Due to the large size of the large steam chamber and the thinness of the cylinder part, there is a certain processing allowance on the B side, C side and D side. The cutting force fluctuates greatly during the cutting process, and the sensitivity of the part size to the residual cutting stress is also higher. Big. Try not to process in one position in one process, turn over more, and process all the processing surfaces once and then coarsely finish the car in place.
After the rough surface of the B side and the C side, the workpiece is loosened, and the accuracy of the shape and position of each processing surface is detected by using a dial gauge. If the deformation amount exceeds 0.5 mm, the cutting stress treatment may be arranged in the middle. When using vibration aging treatment, the vibration exciter should be rigidly clamped on the processing surface, the vibration direction is perpendicular to the direction of the machining during machining, and the vibrator is clamped away from the amplitude and try to make the part resonate at its natural frequency. .
After the previous analysis, the processing route of the large steam chamber is as follows (the following steam chamber is taken as an example): blanking → partial welding → partial welding parts vibration aging → remaining parts welding → overall annealing treatment → drawing each surface processing line → roughing B face, C face retention 5mm → vibration aging treatment → turn over → rough car D face retention 5mm → vibration aging treatment → turn over → rough car, semi-finished car B, C face → rough car, semi-finish car, fine car D Face → turn over → fine car B, D face → draw the remaining holes → drill the remaining holes.
In addition, since the cylinder of the large steam chamber is relatively thin and needs to be turned over to achieve the purpose of the transposition processing, in order to prevent the workpiece from colliding with the ground and causing deformation and bumping of the processing surface, the air overturning technique should be adopted. The air overturning is to use the main and auxiliary hooks of the vehicle to replace the lifting point of the wire rope to achieve the purpose of the workpiece not falling over.
Conclusion
Today, with the rapid development of modern processing technology, only by effectively planning and designing the entire manufacturing process, it is possible to develop practical manufacturing technology, and it is possible to ultimately guarantee the quality of the product. The main purpose of this paper is to provide a feasible idea for the processing of large parts through the research and development and practice of processing technology in large steam chambers. It is worth noting that in the machining industry, it is also necessary to promote overall consideration, pay attention to the on-site, and constantly adjust the processing technology according to the actual situation on the spot, and finally solve the technical problems encountered in production and promote the level of processing technology. Innovation and development.
For more information, please see Metalworking (Cold Processing), Issue 24, 2012 or other related articles on Metalworking Online.
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