Common faults and solving methods in turning screw thread

The thread is formed on the surface of the cylindrical workpiece, along the spiral line, and has the same section of the continuous bump and the groove. In the mechanical manufacturing industry, with the thread of the parts is very widely used. Machining thread by turning method is a common method used in machining. In horizontal lathe (such as CA6140) can turning metric, inches, the modulus and the diameter control four standard thread, whether turning which a thread, between the lathe spindle and tool must maintain strict movement: each revolution of the spindle a turn (i.e. workpiece a turn), the tool should be uniformly moving a (workpiece) by the distance. Their relationship is so that the spindle with workpiece rotate together, the movement of the spindle by the hanging wheel is transmitted to the feed box; by the feed box the transmission is in order to obtain a variety of pitch) and then to the screw; by the screw and the slide board box on the opening and closing of the nut with driven tool make linear movement, the movement of the rotation of the workpiece and tool are through the spindle drive to achieve, so as to ensure the strict movement relation between the workpiece and the cutting tool. In the actual cutting thread, due to various reasons, resulting in motion between the cutting tool from the spindle to, in a link problems, caused by turning the screw thread failure, affect the normal production, at this time should be promptly addressed. Common failures and solutions when turning threads are as follows:
One, eating knife fault analysis and solution: the reason is that the tool installed too high or too low, the workpiece is mounted clip is not firm or tool wear and tear is too large.
Tool installed too high or too low or too high, the depth to a certain depth, tool flank props against the workpiece. Increase the friction, and even the top curved workpiece, caused by eating knife phenomenon; is too low, the chip is not easy eduction, tool radial force direction is the workpiece center, and cross into the screw and the nut gap is too large, resulting in the depth of cut is continuously and automatically tend to deepen, thus the workpiece lift, appear to chew knife. At this time, should adjust the height of the tool, the tool tip and workpiece axis high (use tailstock tool). In the rough and semi finish car, tip position than the workpiece center height of about 1%D (D workpiece diameter).
Workpiece clamping is not firm, the rigidity of the workpiece itself cannot bear turning the cutting force, resulting in a large deflection, change the tool and the workpiece is the center height of the workpiece to be raised), increase in the formation of process of cutting depth, appear to chew knife. At that time, the workpiece clamping firmly, can make tailstock center and so on, in order to increase the rigidity of the workpiece.
The tool wear is too large, causing the increasing of cutting force, bending workpiece, appear to chew knife. The tool of grinding.
Two, random buckle failure analysis and solution: the reason is that when the screw to turn a turn, the workpiece is not turned around the integer.
When the ratio of the screw thread pitch and the work piece pitch ratio is not integral. If in the back of the knife, the opening closing nut, the bed saddle shake to the starting position, then closed the opening nut again occurs lathe tool tip is not in the car before the knife out of the spiral groove, resulting in arbitrary deduction.
Solution is to adopt the method of positive and negative car to retreat knife, namely at the first end of the trip, not to mention opening closing nut, knife along the radial exit, the spindle reversal, the tool along the longitudinal returned, again for a second trip, this back and forth in the process, because of the transmission of the spindle, screw and a holder not been separated turning always in the original spiral groove, it will not appear arbitrary deduction.
For turning the screw thread pitch of the lathe and the ratio of the distance between the workpiece and the workpiece to the integral multiple of the thread. The workpiece and the screw are in the rotation, lift the movable nut, will have to wait at least screw turned a turn, to re opening closing nut, such as a turn of the screw is turned, a workpiece rotating integer, the tool will be able to enter before the knife out of the spiral groove, it will not appear arbitrary deduction. It can be used to open the opening and closing nut, manual knife back. This knife is fast, it is conducive to improve productivity and maintain the accuracy of the lead screw, while the screw is also more secure.
Three. Failure analysis and solution of pitch:
Thread length is not the correct reason for the suspension wheel with improper or feed box handle position is incorrect, can re check the feed box handle position or check the hanging wheel.
Local incorrect causes are due to the local error of the thread pitch (usually caused by wear), which can be replaced by screw or local repair.
The reason is that the thread pitch is not uniform:
Axial movement of lead screw.
Axial movement of the main shaft.
The apron the split nut and the screw shaft caused by different meshing.
Apron dovetail guide wear caused by nut closed unstable.
Hanging wheel clearance is too large, etc..
By testing:
If it is caused by the axial movement of the screw, the adjusting nut of the connecting rod of the lathe and the feed box can be adjusted to eliminate the axial clearance of the thrust ball bearing at the connecting position.
If it is caused by the axial movement of the main shaft, the main shaft can be adjusted to adjust the nut to eliminate the axial clearance of the rear thrust ball bearing.
If the slip board box opening closing nut and screw to different axial caused by poor contact caused by dressing opening closing nut and adjust the opening and closing of the nut gap.
If the dovetail rail wear, can be prepared and dovetail guide strip, in order to reach the correct coordination requirements.
If the clearance is too large, can be used to re adjust the hanging wheel clearance.
Bamboo joint ripples is from spindle to between the screw gear transmission with periodic error caused, such as hanging gear box, gear,