7 practical experiences of lathe processing
The mechanics of lathes are endless and can be roughly divided into the following five categories of lathes:
1) Ordinary mechanical lathes are easy to learn. Finding a lathe processing department is better than what you learned in school.
2) Mold lathe, especially precision mold lathe. Strict requirements on tools and precise dimensions. You need to know what kind of steel has a good glazing effect, that is, a mirror surface; the product of this set of mold is ABS material or other material, the elasticity of the plastic parts is a few wires... a lot of common knowledge, such as plasticine An essential tool for lathe workers. The car comes out with a better finish, easy to polish, and to achieve a mirror effect. It needs a plastic mold base. 4 claws are commonly used. Generally, several templates are added together. Plastic mold thread knowledge must be mastered. It is more difficult.
3) Tool turning, machining reamers, drills, alloy cutter heads, etc... This kind of turning is the simplest, best dry, and the most tiring, usually mass production, the most commonly used is the double top, Turning taper and flow modulus should be the fastest and easiest to reduce tool wear to a minimum, because the products processed by this turning machine are not much harder than your white steel knife, and your alloy knife is well ground. It completely affects your grades.
4) Large-scale equipment lathes. Such lathes must have senior skills, and young people basically dare not car. There are many times when using a standing car. Example: When you turn a crankshaft, you have to read the drawings repeatedly n times, which one is the first to be the second, which is the amount of grinding, or directly processed to the size, whether the thread is positive or negative, and other advanced technologies.
5) CNC lathe. This lathe looks simple, but it is also the most difficult. You have to look at the drawings, programming, conversion formulas, tool applications, as long as you master its lathe theory and have a certain knowledge of mathematics, machinery, CAD Get up quickly.
1. Problems that should be paid attention to when turning a slender shaft at high speed when do lathe processing
"The lathe is afraid of the rod." This sentence reflects the difficulty of turning slender rods. Due to the characteristics and technical requirements of the slender shaft, when turning at high speed, it is easy to produce defects such as vibration, polygon, slub, cylindricity difference and bending. If you want to drive it smoothly, you must pay full attention to the problems in the process.
1) Machine tool adjustment, the connection between the center line of the lathe spindle and the tailstock and the large guide rail of the lathe must be parallel to the upper and lower, left and right, the tolerance should be less than 0.02mm; the workpiece is installed, during the installation, try not to over-position, use chuck to clamp At one end, do not exceed 10mm; cutter, use κr=75°～90° offset cutter, pay attention to the secondary clearance angle α′0≤4°～6°, it should not be large. When the tool is installed, it should be slightly higher than the center.
2) After the tool holder is installed, it must be trimmed. The trimming method can be grinding, reaming, boring, etc., so that the arc surface contacting the claw of the tool holder and the workpiece R≥ the radius of the workpiece, and it must not be less than the radius of the workpiece To prevent polygons. When adjusting with the tool holder claw, make the claw contact with the workpiece, do not use force to prevent the occurrence of slubs.
3) Auxiliary support. When the length-to-diameter ratio of the workpiece is greater than 40, an auxiliary support should be added during the turning process to prevent the workpiece from vibrating or centrifugal force to throw the workpiece. Pay attention to the adjustment of the top during the cutting process, it is better to just top the workpiece, not tight, and adjust at any time to prevent the workpiece from thermal expansion, deformation and bending.
2. Problems that should be paid attention to when turning a slender rod with a reverse tool when do lathe processing
There are many methods for turning slender rods, generally using the forward tool post for forward or reverse tool turning. However, reverse tool turning has many advantages over forward tool turning, and most of them are used.
There are two kinds of problems that are easy to occur in turning. One is polygonal, which is mainly due to the large back angle of the tool, which is inconsistent with the R of the tool holder claw and the diameter of the workpiece. The other is the slub problem. It is caused by the cutting edge and the tool holder, when the tool is set and the tool is moved to the cutting surface, the cutting depth changes from a very small to a sudden increase, the cutting force changes, the workpiece produces an outward tool, and the diameter suddenly changes Large, when following the tool holder to a large diameter, the diameter of the car becomes smaller again, so the cycle makes the workpiece processed into a slub shape.
In order to prevent the slub shape, when the B section of the rack is finished, carefully follow the knife holder, and then reverse the knife after the knife, when the tip of the knife is approaching point A, use the middle carriage handle and eat deep ( 0.04～0.08)mm, but it should be flexibly controlled according to the cutting depth.
3. Roll straightening method when do lathe processing
In mechanical processing, rolling processing is often used to improve the surface hardness, fatigue resistance and wear resistance of the workpiece, reduce the surface roughness of the workpiece, and extend the service life of the workpiece. At the same time, in the process of rolling, the metal can be plastically deformed under the action of external force to change the internal stress to straighten the shaft and rod workpieces with better rigidity.
In the process of rolling the workpiece, the rolled workpiece bends due to uneven hardness of the surface layer under the action of external force. At a high point in the center of rotation of the bend, the rolling pressure is high, and the plastic deformation is also large, which makes the bending degree of the workpiece more increased. This phenomenon is particularly prominent when using rigid rolling tools.
The method of rolling straightening is to check the radial runout of the workpiece after the first rolling of the workpiece, mark the concave part, and adjust the concave part of the workpiece to the height of the center of rotation of the machine tool with a four-jaw chuck , Proportional to the bending size of the workpiece, and then perform the second rolling, and then use a dial indicator and adjust the jaws of the four-jaw chuck to correct the workpiece. Then use a dial indicator to check the bending condition. If it still bends, adjust the workpiece using the above method and perform the third rolling until the required straightness of the workpiece is reached. The length of the knife passed after the second time should be according to the specific situation. It is not necessary to go through the whole process, and the reverse pass should be used.
Rolling straightening is generally used in the process of rolling the workpiece, which not only does not damage the surface of the workpiece, but also makes the outer surface of the workpiece more uniformly rolled, does not cause dead bends, and is easy to operate.
4. Screw straightening method when do lathe processing
For the larger diameter and longer length, there are several bent screws, the use of extrusion straightening, the effect is very good.
(1) Working principle. Using a straightening tool, under the action of external force, the bottom surface of the screw thread is squeezed to plastically deform the surface and extend axially to change the internal stress of the screw and straighten it.
(2) Straightening method. First measure the bending position and direction of the screw on the lathe or the platform, and then move the curved concave part upward and the convex side down to contact the metal backing plate. Within the range of 200-300 mm in the recess, use a special flat shovel and a hammer to strike the bottom of the screw, deform the metal of the small diameter of the screw, and achieve the purpose of straightening. Throughout the process of straightening, the bending is detected, and the flat shovel is pressed against each other alternately until the screw is straightened. This method is simple and easy to apply, not only for large and small screws, but also for straightening shaft blanks, and it is not easy to recover after straightening.
(3) Problems that should be noted. The size R of the special flat shovel used for straightening should be greater than half of the diameter of the screw bottom, b is less than the width of the tooth bottom, and α is less than the tooth shape angle; the R section in contact with the workpiece should be ground out of the arc; after straightening, Use a file to flatten the squeezed teeth.
5. Processing of rubber thread when do lathe processing
Because the hardness of rubber is very low, the elastic modulus is only 2.35N, which is equivalent to 1/85000 of carbon steel. Under the action of external force, it is very easy to deform and it is difficult to cut. Especially cutting some special-shaped threads is more difficult.
In order to solve the processing of rubber threads, install a grinding head that can adjust the spiral angle arbitrarily on the lathe, or in the case of low thread accuracy requirements, it can also be replaced by an air-driven grinding head. The grinding wheel adopts white corundum grinding wheel with diameter Φ60mm～Φ80mm and granularity of 60#～100#. After the grinding wheel is installed, the shape of the grinding wheel is trimmed with a diamond pen. The shape of the grinding wheel is the normal cross-sectional shape of the thread.
The thread lead is small, and the nameplate of the lathe is available, which can be obtained by directly pulling the handle of the lathe. When there is no nameplate on the lathe, the required change wheels must be calculated. Generally, you can check the manual, or you can use the calculation method to find and manufacture the required hanging wheels.
Generally, when the thread lead is greater than 300mm, the spindle speed must be reduced to avoid affecting the quality of the thread grinding due to the high spindle speed, but also make the operation tight or damage the parts into the tool box. The methods of deceleration are: changing the diameter of the active and passive pulleys; adding a reduction box outside the lathe.
The method of splitting is the same as the method of turning multiple threads.
The use of grinding rubber threads on a lathe is a high-efficiency and high-quality processing technology. The grinding method is adopted successively. The processing lead is (1.5 to 1280) mm single-head and multi-head rubber threads, and their quality is in line with Claim.
6. The method of step deep hole turning when do lathe processing
When turning a hole with a length-diameter ratio greater than 4 on a lathe, due to the poor rigidity of the cutter bar and vibration during cutting, the cutting efficiency and the quality of the processed surface are affected, which makes it difficult to turn. Especially when the hole diameter is large and the hole is deep, and there are steps, the machining is more difficult due to the influence of the tool bar and the rigidity of the machine tool. In order to improve the quality and efficiency of workpiece processing, tooling was designed and manufactured, and the deep hole of the step was turned, and the effect was very good.
First install the workpiece on the lathe with the chuck and the center frame, use the inner hole cutter to process the short holes at both ends of the workpiece, and each is equipped with a sleeve and a special cutter bar. When turning the middle long hole, first put the support at the left end into the workpiece hole, then install the workpiece on the lathe, adjust the extension length of the cutter head on the tool bar, and install it into the inner hole of the workpiece together with the support sleeve at the left end , Adjust the height of the arbor with the knife pad, fix the arbor on the lathe square tool table, so that the arbor can slide freely in the sleeve, the workpiece can be rotated, and the cutter starts to cut until the longitudinal depth of the workpiece. When the work piece is finished, move the large carriage in the reverse direction, and withdraw from the work piece together with the support sleeve and cutter bar at the right end to unload the work piece. When processing the second piece, first install the left end support sleeve, clamp the workpiece, then extend the shank into the left end support sleeve of the workpiece, and install the right end support sleeve to start turning of the second workpiece.
The characteristics of the tooling: the support sleeves are used to support the cutter bar at both ends, which greatly increases the rigidity of the cutter bar, so that the cutting is free of vibration, and the roughness of the processed surface is ensured; the support sleeves at both ends are used to support the turning of the cutter bar to ensure the clearance between the holes Position accuracy; easy to operate, the efficiency is more than 5 times higher than the traditional reaming method.
7. Method for adjusting the center frame when turning large hollow workpieces when do lathe processing
When turning the inner hole and end face of a hollow workpiece with a relatively large length and diameter, a center frame is required. If the center frame is not adjusted well, and the axis of the workpiece does not coincide with the axis of the spindle of the machine tool, the center of the face and the taper error of the bulge and hole will occur during processing. In severe cases, the work piece comes out of the chuck, causing an accident.
When installing this kind of work piece, one end of the work piece adopts three-jaw chuck or four-jaw chuck, and the other end is placed on the center frame. Then plug a piece of wood in the hole of the work piece or paste a piece of paper with butter on the end face of the work piece, put the tip of the tailstock tip against the wood or paper surface, select a lower spindle speed, and rotate the work piece for a week or two At this time, a circle is drawn by the center on the board or paper, and then the three brackets of the center frame are adjusted so that the center of the circle is aligned with the tip of the center. This basically makes the center line of the workpiece and the axis line of the machine tool spindle Basically coincide. After semi-finishing, such as measuring the out-of-plane flatness of the end face and the cylindricity of the hole, the three brackets of the center frame are adjusted slightly to eliminate them.