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Frequently Asked Questions and Solutions for Machining Small Internal Threads
The manufacturing unit of a machine is a part, and the parts are connected by a certain form to form a machine. One of the couplings between the parts is a threaded coupling, so the thread is often one of the most common structures on the part. The common methods of machining threads are car, attack, and roller compaction, and tapping is the most widely used method of internal thread machining. Especially for small-size internal threads, tapping is almost the only method of processing. There are two types of tapping methods, namely hand attack and machine attack. In order to facilitate the thread processing, the following issues will be discussed in the thread processing precautions, the problems that often arise, the causes of the problems, the solutions and the usual methods of taking out the broken taps. 1 Method for tapping threads with ordinary taps and precautions Methods and precautions for hand tapping threads At present, hand tapping threads still occupy a certain position in machining. Because in actual production, some threaded holes are not suitable for tapping threads because of the location or the shape of the parts. For the small hole thread, due to the smaller diameter of the threaded hole, the tap strength is lower, and the tap is easily broken by using the tapping thread, and the tap thread is generally used. However, the quality of hand tapping threads is greatly affected by human factors. Therefore, we can only ensure the quality of hand tapping threads by adopting the correct tapping method. The workpiece is clamped by the workpiece. Under normal circumstances, the workpiece should be tapped on one side, placed in horizontal or vertical position. It is easy to judge and keep the tap perpendicular to the base surface of the workpiece. The initial position of the tap starts when the thread is tapped. The tap is to be set up, and then the tap is set in one hand, and the other spindle is rotated slightly. When the tap rotates 1 or 2 turns, check whether the tap is perpendicular to the base surface of the workpiece from the front or side. If necessary, use a square to correct. Generally, after tapping 3 to 4 threads, the direction of the tap is basically determined. If you start to tap the thread incorrectly, you can screw out the tap, correct it with two cones, and then use the cone to tap the thread. When the cutting part of the tap all enters the workpiece, it will no longer need to apply axial force, relying on natural screw thread You can. When tapping threads, it is generally advisable to rotate 1/2 to 1 turn per thread. However, under specific circumstances, specific problems should be specifically analyzed. For example, taps below M5 should not be rotated more than 1/2 turn at a time. When fine threads or high-precision threads are used for hand tapping, each feed rate is also appropriate. Reduced; tapping of cast iron can be faster than tapping steel. After each precession, it is reversed by approximately 1/2 stroke of precession. When deeper threads are tapped, it is reduced to facilitate chip-breaking and chip-removal. The chipping phenomenon of the cutting edge ensures a sharp cutting edge, and at the same time, the cutting fluid smoothly enters the cutting position and plays a cooling and lubricating action. The swivel stroke is even larger, and requires several twists and turns. In addition, when tapping the blind hole thread, the tap must be frequently withdrawn and the chip removed to ensure the effective length of the threaded hole. When the force is required to rotate the hinge evenly, the operator's hands must be balanced. Do not use too much force and shake it. Otherwise, it will easily tear the thread profile and cause the tapped hole to expand and taper. If you feel very strenuous, you must not forcibly attack the thread. You should reverse the tap to remove the chips, or use a double tap to cut a few turns to reduce the load on the cutting portion of the nose cone. Then continue tapping the thread with the nose cone. If you continue If the tapping thread is still strenuous or intermittently sounding slightly or slightly, the cutting is abnormal or the tap wears. Tap the thread immediately to find the cause, otherwise the tap may break. The operating mode of exiting the tap taps the blind hole thread. When the end tappet is attacked and the tapping tap is loosened with a hinge, the tap is rotated out because the engagement of the tapped hole and the tap is loose, and the hinge is Heavy, if the tap is twisted with a hinge, it is prone to sway and vibrate, thus destroying the surface roughness of the thread. When tapping the through hole thread, the calibration part of the tap must not be fully out of the way so as not to enlarge or damage the last few threads. When tapping a group of taps, when tapping the tap with a tap, after tapping the head cone, the two cones or three cones should be screwed into the tapped holes by hand, and the hinges can be used until the rotation is stopped. Threads that are not allowed to be tapped in the previous tap have a random buckle phenomenon. Machine thread tapping method and precautions Due to the low efficiency and unstable quality of the hand tapping thread, in actual mass production, the thread is mainly used with high quality, high efficiency, and low production cost. However, in the process of tapping the thread, we must also use the machine and tool correctly. Otherwise, the quality of the threaded hole will also be affected. The self-precision of the machine tool's radial runout of the drill spindle should generally be adjusted within 0.05mm. If the precision of the tapped hole is high, the radial runout of the spindle should not exceed 0.02mm. The verticality error of the spindle center or the center of the tap should not exceed 0.05mm/100, and the coaxiality of the bottom hole of the workpiece and the tap should generally not exceed 0.05mm. Taping operation mode When the tap is about to attack the thread, the feed must be light and slow to prevent interference between the front end of the tap and the depth of the threaded bottom hole of the workpiece and damage the tap; when tapping the blind hole thread or deeper screw hole When used, tapping safety chucks should be used to withstand cutting forces. The cutting force that the safety chuck withstands must be adjusted according to the size of the tap, so as not to break the cone or attack; in the tapping stroke length of the tap cutting part, a uniform and appropriate pressure should be added to the drill feed handle. In order to assist the tap into the bottom hole, it can avoid the thread scraping when the spindle is pulled downwards by starting with a few incomplete screw threads. When the calibration part enters the workpiece, the reliable thread can be screwed into the hole to avoid attack. Teeth cut thin. When tapping the through-hole thread, it should be noted that the calibration part of the tap cannot be completely exposed. Otherwise, when the tap is reversed and quitted, it will produce a random buckle phenomenon. Cutting speed selection The cutting speed of the tapping thread is mainly determined by the cutting material, the diameter of the tap, the pitch, and the depth of the tapped hole. Generally, when the depth of the tapped hole is within 10 to 30 mm and the workpiece is the following materials, the cutting speed is approximately as follows: steel v=6 to 15 m/min, tempered steel or hardened steel v=5 to 10 m/min, Stainless steel v = 2 ~ 7m/min, cast iron v = 8 ~ 10m/min, under the same conditions, the tap diameter is relatively small to take a high-speed, tap diameter to take a relatively low speed, take a large pitch low speed. When the cutting fluid is selected by the cutting machine, the cutting fluid is mainly selected according to the material to be processed, and sufficient cutting fluid needs to be maintained. For the metal material, the emulsion is generally used; for the plastic material, the emulsified oil or the vulcanization cutting is generally adopted. oil. If the surface roughness of the threaded hole on the workpiece is required to be low, rapeseed oil, molybdenum disulfide, etc. can be used. The effect of soybean oil is also better. 2 The problems that often occur with ordinary tap tapping threads, the causes of the problems, and the methods for solving them are based on the actual production. By summing up and summarizing, it can be found that tapping the thread with an ordinary tap often results in broken taps, excessive diameter of the thread, and so on. These issues are summarized and analyzed as follows, and are provided to everyone in the form of a table to guide the actual production, reduce production accidents, and improve processing efficiency. Problem Cause Solution Tapped broken thread bottom hole processing, the bottom hole diameter is too small, the chip is not good cause blockage of the chip; when the blind hole is threaded, the depth of the hole is not enough; tapping speed is too high; tapping thread The diameter of the tap and the bottom hole of the thread is different; the selection of the tapping parameters of the tap is not suitable; the hardness of the workpiece is unstable; the use time of the tap is too long and excessive wear occurs. Correctly select the diameter of the bottom hole of the screw thread; use the edge of the sharpening edge or the spiral groove tap; the depth of the bottom hole of the drill must meet the specified standard; select the appropriate cutting speed and select according to the standard; correct the tap and the bottom hole when tapping the thread to ensure it Concentricity meets the requirements, and use floating tapping chuck; increase the front angle of the tap, shorten the length of the cutting cone; ensure that the workpiece hardness meets the requirements, select the safety chuck; found that the tap wear should be replaced in time. The tap angle of the tapping tooth tap is too large; the cutting thickness of each tap is too large; the quenching hardness of the tap is too high; the tap wear is severe. Appropriately reduce the rake angle of the tap; increase the length of the cutting cone; reduce the hardness and replace the tap in time. Tap wear too fast when tapping thread speed is too high; Tap grinding parameters are not suitable; Improper selection of cutting fluid and insufficient use; Material hardness of the workpiece is too high; Burning occurs when the tap wears. Reduce the cutting speed properly; reduce the rake angle of the tap and lengthen the length of the cutting cone; select the cutting fluid with good lubrication; perform appropriate heat treatment on the workpiece being machined; The medium diameter precision of thread diameter is too large to be selected; the selection of cutting fluid is unreasonable; the speed of tapping is too high; the coaxiality of the bottom hole of the tap and workpiece thread is poor; the tapping parameters of the tap are not suitable; Burr; tap cone length is too short. Select the appropriate tap diameter of the precision grade; select the appropriate cutting fluid and reduce the cutting speed properly; correct the tap and thread bottom hole coaxiality when tapping; use the floating chuck; reduce the front angle and the back angle of the cutting cone; eliminate Sharpen the burr produced by the tap and increase the length of the cutting cone. The medium diameter precision grade of the thread medium diameter is too small. The tap grinding parameters are not suitable. The tap wear is not suitable. Select the tap diameter suitable for the accuracy grade; appropriately increase the rake angle and cutting taper; replace the tap with excessive wear; choose a good cutting fluid with good lubrication. Thread surface roughness large taps Grinding parameters are not suitable; the material hardness of the workpiece is too low; the quality of the tap grinding is poor, the cutting fluid is not properly selected; the cutting speed of the tapping thread is too high; the tap wear is large. Appropriately increase the rake angle of the tap to reduce the taper; Heat treatment, improve the hardness of the workpiece; Ensure that the rake face of the tap has a low surface roughness value; Select a good cutting fluid with good lubricity; Taps. 3 How to remove the broken tap from the screw hole When the small size female thread is processed, because the tap diameter is small and the strength is low, the tap breaking phenomenon occurs frequently. Therefore, how to correctly remove the tapped tap is an important issue that needs to be studied. First, before removing the broken tap, the chips and tap debris in the screw hole should be first removed to prevent the screw thread from blocking the exit of the tap. The specific methods are as follows: When the broken part of the broken tap is exposed outside the hole, it can be screwed out with pliers; or it can be lightly removed with a pointed tweezers; a hexagon nut can also be welded on the broken cone, and then the wrench can be used gently. Move the hex nut to remove the broken wire. When the broken part of the tap is in the hole, two nuts can be screwed on the broken tap with a square tap, and the steel wire (with the same number of taps as the number of taps) is inserted into the empty groove of the tap and the nut, and then pressed with a hinge. Pull out the direction and pull the broken tap. The breakage of the tap often occurs abruptly under high stress, causing the cutting edge of the half tap broken in the screw hole to be tightly wedged in the metal, generally making it difficult to remove the cutting edge of the tap from the metal. In order to loosen the tap in the screw hole, a sharp chisel can be used to abut against the flutes of the tap, and the hammer can be tapped repeatedly in the forward and reverse directions of the thread until the tap is loosened. Use acetylene flame or torch to anneal the tap, then use a drill to drill. The diameter of the drill should be smaller than the diameter of the bottom hole, and the hole should be centered to prevent the thread from drilling. After the hole is drilled, a flat or square shape is drilled. The punch then uses a wrench to unscrew the tap. EDM equipment will be broken off the broken tap. When tapping stainless steel materials, stainless steel is resistant to nitric acid corrosion, while taps made of high-speed steel can be quickly corroded in nitric acid. Therefore, the workpiece can be put into nitric acid solution and eroded. .