How to avoid burr at thread chamfer when machining metal workpiece

API 5B standard requires that the initial section of oil well casing thread should have chamfered buckle. When machining the initial section of thread, burr is easy to occur at the intersection of chamfer surface and thread. According to the angle effect of burr, the size of burr is related to the end angle of workpiece. When the angle of the end face of the workpiece increases, the supporting stiffness of the end of the workpiece is relatively improved, and burrs are not easy to occur in the cutting direction. Therefore, when making the cutting specification of oil well pipe thread, the cutting direction of the tool should be reasonably determined, so that the cutting outlet is located at a position with a large angle value (that is, the intersection angle of two adjacent surfaces) to prevent or reduce the generation of burrs. For round thread oil well casing with chamfer angle of 65, the included angle between guide surface and chamfer surface is 95, which is smaller than the included angle between bearing surface and chamfer surface (145) and the included angle between chamfer surface and end surface (115). Therefore, the guide surface can be effectively controlled by using the reverse cutting method (that is, cutting from the guide surface to the end surface). This method is mainly used for deburring. In order to avoid secondary burr, reverse cutting requires less feed, so the machining efficiency is low. The patent "Method of Removing Thread Burr by Side Cutting" (China PatentNo.: 97 103690.x) puts forward that feeding along the direction of thread tip where burr is located can greatly improve the machining efficiency of deburring. As shown in fig. 2, the two cutting edges of the deburring blade cut at the intersection of the incomplete thread and the chamfer surface, which makes the edges and corners larger and less prone to burr. When determining the angle of the deburring blade, the two angles formed by the left edge and chamfer surface and the guide wire side should be equal; The right edge forms two equal angles with the chamfer surface and the thread bearing surface respectively. θ is the half angle of thread profile, δ is the included angle between chamfer surface and thread axis, and ε is the half angle of thread taper. According to the geometric relationship between the angles, we can know that the left angle β 1 and the right angle β2 of the deburring blade are β 1 = 45-δ+θ 22β 2 = 45+δ+θ 22. The included angle ψ 1 between the feed direction of the deburring blade and the thread axis is 3. When deburring the black segment of trapezoidal thread, 0? 5"~ 13? 0? The incomplete thread length g of the sleeve of the 5 "offset ladder buckle is 1.984"), and its tooth tip is hollow (commonly known as "black leather buckle"). It is easy to form large burrs at the intersection of the two sides of the tooth groove of the black leather buckle section and the surface of the pipe body. After thread processing, it will turn to the inside of the tooth groove due to elastic deformation, which will affect the measurement of thread parameters and increase the tightening torque of the thread, so it is necessary to remove the black leather. Use a deburring blade with a wide tip to cut into the thread tooth slot. The top of the blade is parallel to the bottom of the thread tooth, and the two sides lean against the junction of the two sides of the incomplete thread and the tooth top. The left angle β 1 1 and the right angle β2 of the side edge should be greater than the corresponding side angles α 1 and α2. The selection of the top width L of the deburring blade should ensure that the blade can cut into the thread groove and cut off the burr at the junction of the bottom arc R and the surface. The minimum width Lmin and the maximum width Lmax of l can be calculated as follows: where ε-thread taper half angle p-thread pitch HN-the cutting point of the deburring blade with thread tooth height should be at the starting point of the incomplete thread, and the cutting angle should be greater than the thread taper angle, so as to avoid damaging the complete thread, and then it should be spirally fed and cut out along the outer surface direction. Compared with the burr at the beginning of the thread, the burr track of the black buckle section of trapezoidal thread is very irregular (depending on the surface condition of the pipe). Therefore, in order to effectively remove this burr, the deburring blade should be flexible, the radial direction of the blade is controlled by the spring, and it can be appropriately expanded and contracted according to the burr trajectory to deburr with a relatively constant cutting force. According to the geometric relationship and the known incomplete thread length g, the included angle ψ2 between the feed direction of deburring bayonet and the thread axis can be calculated as ψ2=arctan( x 1+x2+x3) g 4. SR 13 in the appendix of API 5CT standard on the burr control of sealing ring groove in the processing of sealing ring coupling is to process a coupling with sealing ring in the threaded section. If the burr generated during machining is too large, the mechanical damage of the sealing ring will occur when the threads are engaged, which will affect the normal use. Therefore, the metal on both sides of the ring groove can be cut off first, and then the sealing ring groove can be processed. At this time, the included angle between the two sides of the ring groove and the thread is greater than 90, so the support rigidity is obviously strengthened, and burrs are not easy to generate, thus achieving the effect of controlling burrs. The lower part shows the cutting path of the grooving knife. The width of the cutting edge of the grooving knife is greater than the tooth width b of the thread. First, cut the thread at the angle η 1, then cut the tooth width b at the thread taper half angle ε, and finally cut the thread at the angle η2. The angles η 1 and η2 are related to the thread pitch and tooth height, so it is necessary to ensure that the 1/2 incomplete thread at the intersection of the sealing ring groove and the thread is completely cut. The formulas of η 1 and η2 are η1= arctanp-ε h η 2 = arctanp+ε h, where p and h are tooth pitch and tooth height respectively. Conclusion To sum up, in the process of cutting oil well pipe thread, the burr produced by different processing methods at different parts of the pipe end can be removed or controlled by reasonable design of processing technology and cutting trajectory, and the most effective process method can be adopted to ensure the accuracy of thread inspection and the quality of thread connection.