The threads are continuous projections and grooves of the same profile formed along the spiral on the surface of the cylindrical workpiece. In the mechanical manufacturing industry, threaded parts are used in a wide range of applications. It is a commonly used processing method to machine threads by turning. On horizontal lathes (such as CA6140), four standard threads of metric, inch, modulus and caliper can be turned. No matter which thread is turned, the strict relationship between the spindle and the tool must be maintained: One revolution (ie, one turn of the workpiece), the tool should evenly move the distance of one (the workpiece) lead. Their movement relationship is guaranteed as follows: the main shaft rotates with the workpiece, and the movement of the main shaft is transmitted to the feed box through the hanging wheel; after the shifting of the feed box (mainly to obtain various pitches), it is transmitted to the screw; The screw and the opening and closing nut on the slide box cooperate to drive the tool holder to move linearly, so that the rotation of the workpiece and the movement of the tool are realized by the spindle, thereby ensuring a strict motion relationship between the workpiece and the cutter. . In the actual turning of the thread, due to various reasons, the movement from the spindle to the tool, problems occur in a certain link, causing failure when turning the thread, affecting normal production, and should be resolved in time. Common faults and solutions for turning threads are as follows:
First, the sickle
Fault analysis and solution: The reason is that the turning tool is installed too high or too low, the workpiece is not clamped tightly or the turning tool is worn too much.
1. The turning tool is installed too high or too low
If the knife is too high, the knives of the turning tool will bear against the workpiece, increase the friction, and even bend the workpiece to cause a boring phenomenon. The direction is the center of the workpiece, and the gap between the lead screw and the nut is too large, so that the depth of the knife is constantly deepened, so that the workpiece is lifted and a file is formed. At this time, the height of the turning tool should be adjusted in time so that the tool tip is at the same height as the axis of the workpiece (the tip of the tailstock can be used to align the blade). In roughing and semi-finishing, the tool tip position is about 1%D higher than the center of the workpiece (D indicates the diameter of the workpiece to be machined).
2. The workpiece is not clamped tightly
The rigidity of the workpiece itself cannot withstand the cutting force during turning, thus causing excessive deflection, changing the center height of the turning tool and the workpiece (the workpiece is raised), forming a sharp increase in cutting depth, and a file is generated. The workpiece is clamped firmly, and the tailstock tip can be used to increase the rigidity of the workpiece.
3. The tool wear is too large
Causes the cutting force to increase, the workpiece is bent at the top, and the file is formed. At this point, the turning tool should be ground.
Fault analysis and solution: The reason is that when the lead screw turns one turn, the workpiece is not rotated through the integer.
1. When the ratio of the screw pitch of the lathe to the workpiece pitch is not a multiple
If the opening and closing nut is used to open the opening and closing nut to the starting position, then when the opening and closing nut is closed again, the turning edge of the turning tool will not be in the spiral groove of the former one, so that it appears Chaos.
The solution is to use the forward and reverse method to retract the knife, that is, at the end of the first stroke, without lifting the opening and closing nut, after the knife is radially exited, the spindle is reversed, so that the turning tool is retracted in the longitudinal direction, and then the first step is performed. The second stroke, in this reciprocating process, because the transmission between the spindle, the lead screw and the tool holder is not separated, the turning tool is always in the original spiral groove, and there will be no disorder.
2. Threads that are integral multiples of the screw pitch of the turning lathe and the workpiece pitch ratio
The workpiece and the lead screw are rotating. After lifting the opening and closing nut, at least the screw must be rotated a turn to reclose the opening and closing nut, so that when the lead screw rotates one turn, the workpiece turns an integral multiple, the turning tool It can enter the spiral groove of the previous knife, and there will be no disorder, so you can open the opening and closing nut and manually retract the knife. This quick retraction is beneficial to increase productivity and maintain screw precision, while the lead screw is also safer.
Third, the pitch is incorrect
Fault analysis and solution:
1. The length of the thread is incorrect.
The reason is that the hanging wheel is not properly matched or the position of the feed box handle is incorrect. You can recheck the position of the feed box handle or check the hanging wheel.
2. Partially incorrect
The reason is due to the local error of the pitch of the lathe screw itself (generally caused by wear), the screw can be replaced or partially repaired.
3. The pitch of the thread is not uniform over the entire length
The reason is that:
o The axial movement of the lead screw.
o Axial movement of the spindle.
o The opening and closing nuts of the slide box are not aligned with the different axes of the lead screw.
o The slide box swallowtail guide is worn out and the opening and closing nuts are unstable when closed.
o The clearance of the hanging wheel is too large.
o If the screw is axially moved, adjust the adjusting round nut at the joint between the lathe screw and the feed box to eliminate the axial clearance of the thrust ball bearing at the joint.
o If the spindle is axially tilted, adjust the spindle rear adjustment nut to eliminate the axial clearance of the back thrust ball bearing.
o If the opening and closing nut of the slide box is not properly meshed with the different shaft of the screw, trim the opening and closing nut and adjust the gap between the opening and closing nuts.
o If the dovetail rail is worn, the dovetail rails and inserts can be formulated to achieve the correct fit.
o If the clearance of the hanging wheel is too large, you can re-adjust the hanging wheel clearance.
4. Bamboo streaks appear
The reason is that the gear transmission from the main shaft to the lead screw is caused by periodic errors, such as gears in the hanging wheel box, gears in the feed box, manufacturing errors, or partial wear, or eccentric mounting of the gears on the shaft. The rotation center is low, which causes the periodic rotation of the screw to be uneven, which causes the periodicity of the movement of the tool to be uneven, which leads to the occurrence of the slubs and can replace the gears with errors or wear.
Fourth, the medium diameter is not correct
Fault analysis and solution: The reason is that the knife is too large, the dial is not allowed, and it is not measured in time. The solution is to check whether the dial is loose when finishing the car, the balance of the fine car should be appropriate, the cutting edge of the turning tool should be sharp, and it should be measured in time.
Five, the surface of the thread is rough
Fault analysis and solution: The reason is that the cutting edge of the turning tool is not smooth, the cutting fluid is not suitable, the cutting speed and the workpiece material are not suitable, and the vibration generated during the cutting process is successful.
The solution is to correct the grinding wheel or use the oil stone to grind the tool; select the appropriate cutting speed and cutting fluid; adjust the lathe pressure plate of the lathe and the insert of the middle and small slide dovetail guides to ensure the accuracy of the gap between the guide rails and prevent cutting. Generate vibration.
In short, the types of faults generated when turning the thread are various, both for the reasons of the equipment, as well as for the reasons of the cutters, operators, etc., in the case of troubleshooting, the specific situation should be analyzed in detail, through various detection and diagnostic means, to find out the specific Influencing factors and taking effective measures.
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