Common problems and solutions of machining small i

Common problems and solutions in processing small-size internal threads

the manufacturing unit of the machine is a part, which is connected to form a machine through a certain form. One of the connection forms between parts is thread connection, so thread is often one of the most common structures on parts. The commonly used methods for machining threads are turning, tapping, rolling, etc., and tapping is the most widely used method for machining internal threads. Especially for small internal threads, tapping is almost the only processing method. There are generally two methods of tapping thread, namely hand tapping and machine tapping. In order to facilitate thread processing, the following will discuss a series of problems in thread processing, such as precautions, common problems, causes, solutions, and common methods of taking out broken taps

1 method and precautions of tapping with ordinary tap

1) method and precautions of tapping by hand

at present, tapping by hand still occupies a certain position in machining. Because in actual production, some threaded holes are not suitable for machine tapping due to the limitations of their location or part shape. For small hole threads, due to the small diameter of the thread hole and the low strength of the tap, it is easy to break the tap with machine tapping thread, and generally hand tapping thread is also often used. However, the quality of hand tapping thread is greatly affected by human factors, so only by adopting the correct tapping method can we ensure the processing quality of hand tapping thread

a. the clamping of the workpiece should be correct when being processed. Generally, the side of the workpiece that needs tapping shall be placed in a horizontal or vertical position. It is convenient to judge and keep the tap perpendicular to the workpiece base

b. the initial position of the tap is to put the tap right at the beginning of tapping, then hold the tap right with one hand and gently turn the hinge screw with the other hand. When the tap rotates for 1 ~ 2 turns, observe whether the tap is perpendicular to the workpiece base surface from the front or side. If necessary, use a square to correct it. Generally, the direction of the tap is basically determined after tapping 3 ~ 4 turns of thread

if the tapping is not correct at the beginning, screw out the tap, correct it with two taps, and then tap the thread with a head tap. When the cutting part of the tap enters the workpiece completely, it is no longer necessary to apply axial force, and it can be naturally screwed in by the thread

the operation mode of tapping. When tapping, it is generally appropriate to screw in 1/2 ~ 1 turn each time. However, in special cases, specific problems should be analyzed in detail, for example: the one-time screw in of taps below M5 should not be greater than 1/2 turn; When tapping fine thread or thread with high precision, the feed rate should be appropriately reduced each time; The speed of tapping cast iron can be appropriately faster than that of tapping steel. After each screw in, reverse it to about 1/2 of the screw in stroke; When tapping deep threads, in order to facilitate chip breaking and chip removal, reduce chip sticking on the cutting edge, ensure a sharp edge, and make the cutting fluid smoothly enter the cutting part to play the role of cooling and lubrication. The rotation stroke should be larger, and it needs to be screwed back and forth for several times. In addition, when tapping the blind hole thread, the tap should often be withdrawn to remove the chips, so as to ensure the effective length of the threaded hole

c. the force should be uniform. When rotating the hinge bar, the force of the operator's two hands should be balanced. Do not use too much force and shake left and right, otherwise it is easy to tear the thread profile and cause the thread hole to expand and taper. If you feel very laborious, don't tap the thread forcibly. Turn the tap upside down to remove the chips, or tap with a double tap for several rounds to reduce the load of the cutting part of the tap, and then continue tapping with the tap. If it's still hard to continue tapping the thread or the sound of "cluck, cluck" is intermittent, the cutting is abnormal or the tap is worn. Stop tapping the thread immediately to find the cause, otherwise the tap may break

d. when tapping the blind hole thread by withdrawing the operation mode of tap, when the end tap is tapped and the tap is loosened by screwing back with reaming screw, it is easy to screw the tap out, because the tapped thread hole is loosely matched with the tap, and the reaming screw is heavy. If the tap is screwed out with reaming screw, it is easy to swing and vibrate, thus damaging the surface roughness of the thread. When tapping through-hole threads, the calibrated part of the tap should not be out of the head as far as possible to avoid expanding or damaging the last few threads

e. application of group tap when tapping the thread with group tap, after tapping the head tap, the second or third tap should be screwed into the threaded hole by hand until it can't be screwed, and then the reaming screw can be used to prevent disordered threading caused by inaccurate tapping of the previous tap

2) tapping methods and precautions for machine taps

due to the problems of low efficiency and unstable quality of hand tapping threads, machine tapping threads with good quality, high efficiency and low production cost are mainly used in actual mass production. However, in the process of machine tapping, we must also use machines and tools correctly, otherwise, it will also affect the processing quality of threaded holes

a. the radial runout of the spindle of the drilling machine with inaccurate speed control of the machine tool should generally be adjusted within 0.05mm. If the accuracy of tapping threaded holes is high, the radial runout of the spindle should not be greater than 0.02mm, the perpendicularity error between the fixture positioning support surface of the workpiece and the center of the spindle or tap of the drilling machine should not be greater than 0.05mm/100, and the coaxiality of the threaded bottom hole of the workpiece and the tap should generally not be greater than 0.05mm

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B provide the best and most design oriented solutions to automobile manufacturers Tapping operation mode when the tap is about to finish tapping, the feed should be light and slow to prevent interference and impact between the front end of the tap and the depth of the thread bottom hole of the workpiece and damage the tap; When tapping blind hole threads or deep screw holes, the tapping safety collet should be used to bear the cutting force. The cutting force borne by the safety collet must be adjusted according to the size of the tap to avoid breaking the tap or being unable to attack; Within the tapping stroke of the length of the cutting part of the tap, a uniform and appropriate pressure should be applied to the feed handle of the drilling machine to help the tap enter the bottom hole, so as to avoid scraping the thread when the spindle is pulled down by the first few incomplete threads. When the calibration part enters the workpiece, the reliable thread should be naturally screwed for tapping, so as to avoid cutting the tooth shape thin. When tapping through-hole threads, it should be noted that the calibrated part of the tap cannot be fully exposed, otherwise when reversing and exiting the tap, disordered threading will occur

c. selection of cutting speed the cutting speed of tapping is mainly determined by the cutting material, tap pitch, pitch, depth of threaded hole, etc. Generally, when the depth of the threaded hole is within 10 ~ 30mm and the workpiece is made of the following materials, the cutting speed is roughly as follows: steel v=6 ~ 15m/min, Quenched and tempered steel or hard steel v=5 ~ 10m/min, 1. How to solve the problem of sensor displacement by electronic universal testing machine? Stainless steel v=2 ~ 7m/min, cast iron v=8 ~ 10m/min. under the same conditions, the relatively high speed is selected for the small tap diameter, the relatively low speed is selected for the large tap diameter, and the low speed is selected for the large pitch

d. selection of cutting fluid when tapping threads, the cutting fluid is mainly selected according to the processed material, and enough cutting fluid needs to be maintained. For metal materials, emulsion is generally used; Generally, emulsified oil or vulcanized cutting oil can be used for plastic materials. If the surface roughness of the threaded hole on the workpiece is required to be low, rapeseed oil and molybdenum disulfide can be used, and the effect of soybean oil is also better

2 common problems, causes and solutions of tapping with ordinary taps

according to the actual production, through induction and summary, it can be found that tapping with ordinary taps often leads to taps breaking and thread pitch diameter out of tolerance. For these problems, we summarize and analyze them as follows, and provide them to you in the form of tables, so as to guide the actual production and reduce production accidents, Improve processing efficiency

causes and solutions of the problem when the tap breaks the thread bottom hole, the diameter of the bottom hole is too small, and the chip is blocked due to poor chip removal; When tapping blind hole threads, the depth of drilling is not enough; Tapping speed is too high and too fast; The taps used for tapping are different from the diameters of thread bottom holes; The selection of tap grinding parameters is not appropriate; The hardness of the workpiece is unstable; The tap has been used for too long and is excessively worn. Correctly select the diameter of threaded bottom hole; Sharpen the inclination of the cutting edge or select spiral groove tap; The depth of bottom hole drilling shall meet the specified standard; Reduce the cutting speed appropriately and select according to the standard; When tapping, calibrate the tap and bottom hole to ensure that their coaxiality meets the requirements, and select floating tapping chuck; Increase the front angle of the tap and shorten the length of the cutting tap; Ensure that the hardness of the workpiece meets the requirements, and select the safety chuck; If the tap is worn, it should be replaced in time. The front angle of the tap is too large; The cutting thickness of each tooth of the tap is too large; The quenching hardness of tap is too high; The tap is seriously worn. Properly reduce the front angle of the tap; Appropriately increase the length of the cutting cone; Reduce the hardness and replace the tap in time. The tap is worn too fast, and the speed is too high when tapping the thread; Improper selection of tap grinding parameters; Improper selection and insufficient use of cutting fluid; The material hardness of the workpiece is too high; When the tap is sharpened, burns occur. Reduce the cutting speed appropriately; Reduce the front angle of the tap and lengthen the length of the cutting cone; Choose cutting fluid with good lubricity; Carry out proper heat treatment on the processed workpiece; Sharpen the tap correctly. The pitch diameter accuracy grade of the tap with too large pitch diameter of the thread is improperly selected; Unreasonable choice of cutting fluid; Tapping speed is too high; The coaxiality between the tap and the workpiece thread bottom hole is poor; Improper selection of tap grinding parameters; Burr occurs when grinding the tap; Tap cutting tap length is too short. Select the pitch diameter of tap with appropriate accuracy grade; Select the appropriate cutting fluid and reduce the cutting speed appropriately; Correct the coaxiality of tap and thread bottom hole when tapping; Adopt floating chuck; Properly reduce the front angle and the back angle of the cutting cone; Eliminate burrs generated by grinding taps, and appropriately increase the length of cutting taps. The pitch diameter of thread is too small, and the pitch diameter accuracy grade of tap is improperly selected; Tap grinding parameters are not appropriate; The tap is worn; The selection of cutting fluid is inappropriate. Select the pitch diameter of tap with appropriate accuracy grade; Appropriately increase the front angle and cutting taper of the tap; Replace the excessively worn tap; Choose cutting fluid with good lubricity. The surface roughness of thread and the grinding parameters of big taper are not appropriate; The material hardness of the workpiece is too low; Poor grinding quality of tap and improper selection of cutting fluid; The cutting speed of tapping thread is too high; The tap is worn heavily. Appropriately increase the front angle of the tap and reduce the cutting taper; Carry out heat treatment and appropriately improve the hardness of the workpiece; Ensure that the cutting surface of the tap has a low surface roughness value; Choose cutting fluid with good lubricity; Reduce the cutting speed appropriately; Replace the worn tap

3 method of taking out the broken tap from the screw hole

when machining small-size internal threads, because the tap diameter is small and the strength is low, the tap breaking phenomenon often occurs. Therefore, how to correctly take out the broken tap is also an important problem that needs to be studied. First of all, before taking out the broken tap, the cutting chips and tap chips in the screw hole should be cleaned first to prevent being caught between the thread and the tap from hindering the withdrawal of the tap. The specific methods are as follows:

when the broken part of the tap is exposed outside the hole, it can be screwed out with pliers; Or gently pick it out with a sharp chisel; You can also weld a hexagon nut on the broken cone, and then gently pull the hexagon nut with a wrench