The rolling of titanium seamless pipe is generally processed by a reciprocating (ie, Peel format) cold rolling mill. During the machining, two-roll (LG) and multi-roll (LD) rolling mills are generally used for multi-pass rolling. With the rotation and feeding of the rolling mill during the deformation process, the titanium pipe gradually reduces the wall and reduces the diameter. The pipe of the unit length generally undergoes 5-10 times of rolling and finishing in one rolling pass to obtain the process requirements. Pipe size specifications. The cold-rolled tube machine can perform large diameter reduction and wall reduction machining, but the dimensional accuracy after rolling is low, and the tube end is prone to cracking, unevenness and other phenomena. It can be solved by the same method; for the uneven pipe end, which is similar to the “fish mouth” phenomenon, it needs to be flattened in the subsequent machining process, otherwise it will cause a plug car accident.
Therefore, this article analyzes from the aspects of process, tooling and mold, equipment, etc., in order to find out the cause of the unevenness of the pipe end and take effective measures to solve it. The spline gap at the connection between the mandrel and the mandrel trolley is too large and the resulting serious displacement of the mandrel position is the main reason for the unevenness of the end of the tube after the tube billet is rolled this time.
When the pure titanium tube is rolled through the billet, it is usually finished many times in one pass. After rolling to the required titanium tube specification, the end of the tube will generally have a slight fluctuation of 1 ~ 2mm. The raw materials and processes of this batch of titanium tubes are no different from the previously produced tubes, but there are more serious bumps and bumps, the length is up to 70mm, accounting for 1% of the length of the tube. From the test results of outer diameter and wall thickness before and after machining, The sample wall thickness fluctuated greatly. The average measured wall thickness of the convex part was 2.33mm, and the average measured wall thickness of the concave part was 2.60mm. The difference between the two wall thicknesses reached 0.27mm. The end of the titanium tube after normal rolling The wall thickness deviation is 0.05 ~ 0.10mm, and the wall thickness deviation will inevitably cause the difference in elongation coefficient. It can be said that the uneven wall reduction during rolling of the end pipe is the direct cause of the unevenness of the pipe end. Therefore, the pipe end The unevenness may be caused by equipment or tools.
The wall thickness caused by the tool and die does not all have factors such as the installation of the gear rack, the alignment of the mold, and the opening of the mold. After measurement, the openings of the upper and lower mold holes differ by 0.05. ; The gap between the feeler gauge and the measuring hole is 0.05mm, and the gap between the gear and the rack is about 1.6mm; the rack is fixed on the frame without loosening, and the positioning block is not deformed; the hole is cut by .02mm, and the zero line is aligned. The above measurement data shows that the installation of the mold is within the scope of the design requirements. The thickness of the wall caused by the equipment is not all due to the amount of feed, the angle of rotation, and the coordination of the movement. Rolling speed and feed rate are carried out according to the process requirements. During the operation of the equipment, the rotation and feed at the rear dead center and the rotation at the front dead point are coordinated. There is no phenomenon of advance and lag of the rotary feed operation; in the equipment design Within the required range; continue to measure the feeding amount during rolling, and find that the feeding amount is uniform, but it is found that when the titanium tube is fed, the core rod coaxial with the tube blank moves forward and backward, reaching 10mm, according to the requirements The back and forth movement of the mandrel during rolling should not be greater than 0.5mm, otherwise it will seriously affect the accuracy of the position of the mandrel during rolling. Further inspection revealed that the spline gap at the connection between the mandrel and the mandrel trolley is 20mm, exceeding the gap 8mm requirement. When the titanium tube is fed at the rear dead center, the gap between the spline and the core rod is too large, which will inevitably cause the core rod to advance when the titanium tube blank advances, so that the position of the core rod connected to the core rod during rolling occurs A larger change has been made, that is, the position of the mandrel and the hole pattern is no longer the position set by the process, but is moved forward.
In this way, when rolled to the front dead point, the tube is actually rolled to a thinner size; but although the mandrel is following the tube blank, the spring at the front of the spline has been stressed at this time. At the front dead center, the inner hole of the pipe is separated from the mandrel. At this time, the spring pushes the mandrel back, so that the mandrel also retreats. At this time, the hole pattern is carried out on the thicker side wall of the titanium tube after rolling Leveling, but due to the retreat of the mandrel, the thickened part of the leveling wall is not leveled, thus causing a large difference in wall thickness. Adjust the spline gap at the connection between the core rod and the core rod trolley. After adjustment, it was found that the pipe end unevenness disappeared.