Introduction. Turning means that turning is a part of machining. Turning mainly uses turning tools to turn rotating workpieces. Lathes are mainly used for machining shafts, discs, bushings and other workpieces with rotating surfaces and are the most widely used type of machining in machine building and repair enterprises.
The skill of a turner is limitless, and the most ordinary turner does not need too high skill. It can be divided into 5 types of auto workers, which are the most common in society.
1. Ordinary turners are easy to learn. Find a lathe department that's better than what you learned in school
2. Mold turner, especially precision plastic mold turner! Strict requirements for tools and precise dimensions
Need to know which steel has good glazing effect, i.e. mirror surface
Is the product of this mold set made of ABS or other materials? How Extensible are Plastic Parts === It is common knowledge that plasticine is an essential tool for this kind of automotive worker! ! !
The finish of the car is better, it is easy to polish, a plastic mold base is required to achieve a mirror effect, 4 grips are used very often, usually several templates are added to the car, the plastic mold threads need to be known. mastered! Difficulty higher!
3. Tool turning, processing of reamers, drills, alloy cutters == tool cores, this kind of turning is the easiest, best and most tedious
Usually produced in large quantities. The most commonly used are double centers, cone of turn and yield modulus. This is the fastest and easiest to do, and tool wear is kept to a minimum because the hardness of this kind of turning is not as good as your white steel knife is low! How well sharpened your alloy knife will totally affect your grades! !
4. Large-scale lathes, such lathe workers must have proficient skills, young people basically do not dare to drive! !
Learn more about using a vertical car. Example:
To break in the crankshaft, you first need to look at the drawings n times, which machine is the first and which is the second, whether it is the value of lost wear, or direct processing to size, or the thread is positive or negative... === Some best practices
5. CNC lathe, this kind of lathe is the simplest but also the most complex. First of all, you need to be able to read drawings, programming, conversion formulas and tool applications! ! !
If you know the theory of the lathe and have some knowledge of mathematics, mechanical engineering and CAD, you can quickly learn them.01 Introduction and interpretation
On a lathe, the shape and size of the workpiece is changed by the rotational movement of the workpiece and the linear or curvilinear movement of the tool, and processed in accordance with the requirements of the drawing.
Turning is a method of turning a workpiece on a lathe using rotation of the workpiece relative to the tool. The cutting energy in turning operations is mainly provided by the workpiece, not by the tool. Turningis the most basic and widespread method of machining, which occupies a very important place in production. Turning is suitable for rotating surfaces. Turning can process most workpieces with rotating surfaces, such as inner and outer cylindrical surfaces, inner and outer conical surfaces, ends, grooves, threads, and rotating forming surfaces. The tools used are mainly turning tools.
Among all types of metal cutting machines, lathes are the most widely used category, accounting for about 50% of the total number of machine tools. A lathe can not only turn a workpiece with a turning tool, but also perform drilling, reaming, threading and knurling operations using drills, reamers, taps and knurling knives. According to different technological characteristics, layout shapes and structural characteristics, lathes can be divided into horizontal lathes, floor lathes, vertical lathes, turret lathes and profiling lathes, etc., most of which are horizontal lathes</p >
Technical security issues
Turning is the most widely used type in mechanical engineering. There are a large number of lathes, a large number of personnel and a wide range of processing. Many tools and devices are used. Therefore, turning safety is just of particular importance, and its key tasks are as follows:
1. Chip damage and protective measures. All kinds of steel parts processed on a lathe have good toughness, and the chips generated during turning are full of plastic curl and have sharp edges. When cutting steel parts at high speed, hot and long chips will be generated, which can easily hurt people. In doing so, it is often wound on the workpiece, turning tool and tool holder. Therefore, iron hooks should be used to clean them in time or break them during operation. It should be stopped and removed, but it is strictly forbidden to remove or break it manually. To prevent chip damage, steps are often taken to break the chip, control chip flow, and add various baffles. The measure of chip breaking is the grinding of a chip breaker or step on a turning tool; use an appropriate chipbreaker and mechanically clamp the tool.
2. Workpiece clamp. There are many accidents in the turning process in which the machine is damaged, the tool breaks or breaks, and the workpiece falls or is thrown out due to incorrect clamping of the workpiece. Therefore, to ensure safe turning production, special attention must be paid to clamping workpieces. For detailsFor various sizes and shapes, appropriate fixtures should be selected, and the connection of three-jaw, four-jaw chucks or special fixtures with the main shaft should be stable and reliable. The workpiece must be clamped and clamped. A large workpiece can be clamped with a sleeve to ensure that the workpiece does not move, fall or be thrown out when it is rotated at high speed and cut under force. If necessary, it can be reinforced and fixed with a central frame and a central frame. Remove the key immediately after clicking.
3. Safe operation. Before operation, the machine should be completely inspected, and it can only be used after confirming its serviceability. Clamping the workpiece and cutting tool ensures a correct, strong and secure position. During processing, when changing tools, loading and unloading workpieces, and measuring workpieces, the machine must stop. The workpiece must not be touched with hands or wiped with cotton silk when it is rotating. It is necessary to correctly select the cutting speed, feed and depth of processing, processing overload is not allowed. Blanks, fixtures and other equipment are not allowed to be placed on the head of the bed, handrest and bed. When using a file, move the turning tool to a safe position with your right hand in front and your left behind to prevent tangling of the sleeve. The machine must be used and maintained by a special person, and other personnel are not authorized to use it.2 notes
The processing technology of the CNC lathe is similar to that of the conventional lathe, but since the CNC lathe is a one-time clamp, and continuous automatic processing completes all turning processes, the following aspects should be paid attention to.
1. Reasonable choice of cutting quantity:
For high-performance metal cutting, the main elements are the workpiece material, cutting tools and cutting conditions. They determine the machining time, tool life and machining quality. An economical and efficient machining method should be a reasonable choice of cutting data. The three elements of cutting conditions: cutting speed, feed rate and depth of cut directly cause tool damage. With an increase in cutting speed, the temperature of the tool tip will increase, which will cause mechanical, chemical and thermal wear. Cutting speed increased by 20%, tool life decreased by 1/2. The relationship between feed conditions and wear on the back of the tool is in a very small range. However, the feed rate is large, the cutting temperature rises, and the rear wear is large. This has less effect on the tool than cutting speed. Although the influence of the depth of cut on the tool is not as great as the cutting speed and feed rate, when cutting with a small depth of cut, the workpiece material will form a hardened layer, which will also affect the tool life. tool. The user must select the cutting speed according to the material to be machined, hardness, cutting condition, material type, feed rate, depth of cut, etc. The selection of the most appropriate machining conditions is selected based on these factors. Regular constant wear until the end of the service life is an ideal condition. However, in actual use, the choice of tool life depends on tool wear, size change, surface quality, cutting noise, processing heat, etc. When determining the processing conditions, it is necessary to study the actual situation. For difficult-to-machine materials such as stainless steel and high temperature alloys, coolant or a hard cutting edge can be used.
2. A smart choice of tools:
(1) In rough turning, it is necessary to select a tool with high strength and durability to meet the requirements of large cutting capacity and large feed in rough turning.
(2) When finishing a car, it is necessary to select a tool with high precision and durability to meet the requirements for machining accuracy.
(3) To reduce tool change time and facilitate tool setting, use mechanical clamping tools and mechanical clamping blades as often as possible.
3. A smart choice of fixtures:
(1) Try to use general purpose clamping fixtures and avoid using special fixtures;
(2) The part position base is the same to reduce the position error.
4. Define the machining path: The machining path refers to the movement path and direction of the tool relative to the workpiece during the machining process on a CNC machine.
(1) Must provideprocessing accuracy and surface roughness requirements;
(2) The machining path should be as short as possible to reduce tool downtime.
5. Relationship between processing route and processing permission:
Currently, provided that the CNC lathe has not yet become widespread, as a rule, excess allowance for the workpiece, especially the allowance containing forged and cast hard layers of leather, should be processed on a conventional lathe. If it needs to be machined on a CNC lathe, attention should be paid to flexible program layout.
6. Luminaire installation points:
Currently, the connection between the hydraulic chuck and the hydraulic clamping cylinder is by means of a link. Pull it out, and then use a wrench to unscrew the chuck fixing screw, after which the chuck can be removed</p > 3 general rules
General Code of Practice for Turning (JB/T9168.2-1998)
Clamping turning tools
1) The tool post of the turning tool should not protrude too far from the tool post, and the total length should not exceed 1.5 times the height of the tool post (excluding turning holes, grooves, etc.)</ p>
2) The center line of the turning tool holder must be perpendicular or parallel to the direction of the cutting tool.
3) Tool tip height adjustment:
(1) In face turning, taper turning, thread turning, forming surface turning, and solid workpiece cutting, the tip of the tool should generally be at the same height as the axis of the workpiece.
(2) The outer circle of rough turning, the fine turning hole, and the tip of the tool should generally be slightly above the axis of the workpiece.
(3) When turning thin shafts, rough holes, and cutting hollow workpieces, the tip of the tool should generally be slightly below the axis of the workpiece.
4) The nose angle bisector of the thread turning tool must be perpendicular to the axis of the workpiece.
5) When clamping a turning tool, the spacers under the tool shank should be few and flat, and the screws holding the turning tool should be tightened.
1) When using a three-jaw self-centering chuck to clamp a workpiece in rough or finish turning, if the workpiece diameter is less than 30mm, the overhang should not exceed 5 times the diameter; if the workpiece diameter is greater than 30 mm, its overhang length should not exceed the diameter by more than 3 times.
2) When clamping heavy, irregular workpieces with single-action four-jaw chucks, faceplates, angles (bent plates), etc., a counterweight must be added.
3) When machining shaft blanks between centers, adjust the center axis of the tailstock to match the axis of the lathe spindle before turning.
4) When processing thinala between the two centers, a steady rest or a central steady rest should be used. Pay attention to the adjustment of the upper tightening force during processing, and pay attention to the lubrication of the dead center and stable frame.
5) When using a tailstock, the sleeve should be kept as short as possible to reduce vibration.
6) When clamping a workpiece with a small footprint and a large height on a vertical lathe, use raised jaws, and press the workpiece with a link or pressure plate at the appropriate position.
7) When turning wheel and sleeve castings and forgings, they should be centered on the rough surface to ensure uniform wall thickness of the workpiece being machined.
1) When turning a stepped shaft, in order to ensure rigidity during turning, generally turn the larger diameter part first and then the smaller diameter part.
2) When grooving a shaft blank, this should be done before final turning to prevent deformation of the blank.
3) When finishing a threaded shaft, generally the non-threaded part must be machined after threading.
4) Before drilling, the end surface of the workpiece must be leveled. If necessary, the center hole should be punched first.
5) When drilling a deep hole, a pilot hole is drilled first.
6) When turning holes (Φ10-Φ20) mm, the diameter of the tool holder should be 0.6-0.7 times the diameter of the hole to be machined; when machining holes with a diameter of more than Φ20mm, generally, a tool post with a clamping head should be used.
7) When turning a multi-start thread or a multi-start worm, try cutting after adjusting the change gear.
8) When using an automatic lathe, the mutual position of the tool and the workpiece should be adjusted according to the machine setting chart. After the adjustment, a trial lathe should be carried out, and the first part can only be processed after passing the pass; pay attention to tool wear and the size of the workpiece at any time during machining and surface roughness.
9) When turning on a vertical lathe, do not arbitrarily move the beam after adjusting the tool post.
10) When a position tolerance is required for the corresponding surface of the workpiece, try to complete turning in one clamp.
11) When turning a spur gear blank, the hole and base end face must be machined in one clamp. If necessary, the marking line should be drawn near the circumference of the ring gear at the end.4 error compensation
Modern mechanical engineering technologies are developing towards high efficiency, high quality, high precision, high integration and high intelligence. Precision andultra-precise machining has become an essential component and direction of development of modern mechanical engineering and has become a key technology for increasing international competitiveness. With the wide application of precision machining, turning error has become a hot research topic. Since thermal errors and geometry errors make up the majority of various machine tool errors, reducing these two errors, especially thermal errors, has become a major goal. Error compensation technology (abbreviated as ECT) appears and develops along with the continuous development of science and technology. Losses caused by thermal deformation of machine tools are significant. Therefore, it is highly necessary to develop a high-precision and low-cost thermal error compensation system that could meet the actual production requirements of the factory, in order to correct the thermal error between the spindle (or workpiece) and the cutting tool, in order to improve the processing accuracy of the machine tool, reduce waste, improve production efficiency and economic benefits.
Basic definition and characteristics of error compensation
The basic definition of error compensation is the artificial creation of a new error in order to compensate or greatly reduce the original error that is currently a problem. Through analysis, statistics, induction and study of the characteristics and laws of the original error, a mathematical model is created. error is set. Try to make the error caused by artificial and original error equal in value and opposite in direction, so as to reduce the processing error and improve the dimensional accuracy of the part.
Earliest error compensation was implemented in hardware. Hardware compensation is a mechanical fixed compensation. To change the amount of compensation when the error of the machine changes, it is necessary to redo the parts, calibration scales or re-adjust the compensation mechanism. Hardware compensation has the disadvantages of not being able to eliminate random errors and lack of flexibility. The recently developed software compensation is characterized by the comprehensive use of modern various compensation methods without making any changes to the machine itself. The discipline's advanced technology and computer control technology are used to improve the processing accuracy of machine tools. Software compensation overcomes many of the difficulties and shortcomings of hardware compensation and takes compensation technology to the next level.
Error compensation (technology) has two main characteristics: scientific and engineering.
The rapid development of scientific error compensation technology has greatly enriched the theory of precision mechanical design, precision measurements and all precision engineering and has become an important branch of this discipline. Error compensation technologies include detection technology.fishing, detection technology, signal processing technology, photovoltaic technology, material technology, computer technology and control technology. As a branch of new technology, error compensation technology has its own independent content and features. Further study of error compensation technology, its theorizing and systematization will be of great scientific importance.
The technical significance of engineering error compensation technology is very high. It has three meanings: first, the use of error compensation technology can easily achieve a level of accuracy that "hard technologies" can only achieve at great expense; second, the use of error compensation technology can solve a level of accuracy that cannot usually be achieved with "hard technologies"; Thirdly, if error compensation technology is used to meet certain accuracy requirements, the manufacturing cost of instruments and equipment can be greatly reduced, which has a very significant economic benefit.
Occurrence and classification of thermal errors in turning
As the requirements for machine tool accuracy continue to increase, the proportion of thermal error in the total error will continue to grow, and thermal deformation of machine tools has become a major obstacle to improving machining accuracy. Machine tool thermal errors are mainly caused by thermal deformation of machine components caused by internal and external heat sources such as motors, bearings, transmission parts, hydraulic systems, ambient temperature and coolant. The geometrical error of the machine tool arises from the manufacturing defects of the machine tool, the fit error of the machine components, the dynamic and static misalignment of the machine components, etc.
Basic error compensation method
Summarizing the above and related links, rotation errors are usually caused by the following factors:
Inaccuracy of thermal deformation of machine tools;
Geometric errors of machine parts and structures;
Error caused by cutting force;
Tool wear error;
Other error sources such as machine shaft servo error, CNC interpolation algorithm error, etc.
There are two main methods to improve the accuracy of a machine: the error prevention method and the error compensation method.
Error prevention is an attempt to eliminate or reduce potential sources of error through design and manufacturing practices. The error prevention method is effective in reducing the temperature rise of the heat source, balancing the temperature field, and reducing the thermal deformation of the machine to a certain extent. But it is impossible to completely eliminate thermal deformation, and it is very expensive;
The application of the thermal error compensation law opens up an effective and economical way to improve the accuracy of machine tools.
The study of turning error is an essential component and direction of development of modern mechanical engineering and has become a key technology for increasing international competitiveness. Turning accuracy and technical requirements.
Error compensation technology can achieve the high precision and low cost required by the actual production in the factory. Thermal error compensation technology can correct the thermal drift error between the spindle (or workpiece) and the cutting tool, improve the processing accuracy of the machine tool, reduce waste and improve efficiency production and economic benefits.5 frequently asked questions
When turning threads with a large pitch on conventional lathes with force, sometimes the saddle will vibrate. If it is light, it will cause ripples on the workpiece, and if it is strong, it will break the knife. When cutting, students often experience the phenomena of a stabbing or breaking knife. There are many reasons for the above problems, now we mainly discuss this phenomenon and its solution through the analysis of the strength of the tool.
1 Origin and cause of the problem
We know that when threading with a small pitch, the rectilinear method of cutting is mainly used (feed along a straight line perpendicular to the axis of the workpiece); When threading with a large pitch, in order to reduce the cutting force, the method of cutting with the left and right knife is often used (by moving the small sliding plate, the thread turning tool can be cut with the left and right cutting edges, respectively).
When turning the threads, the movement of the seat is carried out by the rotation of the long lead screw, which drives the split nut. There is axial clearance in the long screw bearing, as well as axial clearance between the long screw and split nut. When using the left and right borrowing method to force the rotation of a right worm with a right main cutting edge, the tool perceives the force P generated by the workpiece (without considering the friction between the chip and the front surface, as shown in Fig. 1), and the force P is decomposed into the axial component of the force Px and the radial force component are combined, while the axial force component Px coincides with the tool feed direction, and the tool transfers the axial force component Px to the bed seat, thereby moving the bed seat to the side where there is a gap. Make quick and jerky movements back and forth, as a result, the tool will move back and forth, which will cause ripples in the workpiece or even break the knife. However, when cutting with the left main cutting edge, there is no such phenomenon. When cutting with the left main cutting edge, the axial component of the force Px perceived by the tool is opposite to the feed direction and moves in the direction of eliminating the gap. At this time, the bed saddle moves at a constant speed.
When cutting off, the movement of the middle slide plate is realized by rotating the lead screw of the middle slide plate to drive the movement of the nut. There is an axial clearance in the lead screw bearing, and there is also an axial clearance between the lead screw and the nut. When cutting on a lathe, the front surface of the tool (with a rake angle) is acted upon by the force P created by the workpiece (without taking into account the friction between the chip and the front surface, as shown in Fig. 2), and the force P is decomposed into the force Pz and the component of the radial force, in which the component of the radial force coincides with the feed direction of the cutting tool, points towards the workpiece, pushes the tool against the workpiece, which will pull the middle slider to move in the direction of the gap, causing the cutting knife to sharply pierce the hand parts, resulting in piercing (breaking) of the knife or warping of the workpiece .
When the turning pitch is large and the thread is cut by the left-hand and right-hand cutting method, in addition to adjusting the relevant parameters of the lathe, it is also necessary to adjust the corresponding gap between the seat and the bed guide. make it a little tighter increase the friction force nWhen moving, it reduces the possibility of seat displacement, but the gap should not be adjusted too tight, and it is better to rock the saddle smoothly.
Adjust the gap between the middle sliding plate and try to minimize the gap; adjust the tightness of the small slip plate to be slightly tighter to prevent the turning tool from shifting during turning. The protruding length of the workpiece and toolbar should be as short as possible, and the left main blade should be used for cutting as much as possible; when cutting with the right main blade, reduce the amount of back cut; the front angle of the right main blade should be increased, and the blade edge should be straight and sharp, so as to reduce the axial component of the force Px carried by the tool. Theoretically, the larger the front angle of the right main blade, the better.6 formulas for sharpening car knives
Types and materials of frequently used turning tools, selection of grinding wheelsFive types of commonly used turning tools with different cutting purposes,Outer circle, inner hole and thread, cutting and forming are also widely used;Shape turning tool is divided into three types: straight and compound;There are many types of materials for turning tool, commonly used carbon steel, alumina,tungsten carbide, silicon carbide, choose the grinding wheel according to the material;Particles The grinding wheel are divided into different sizes, do not use them indiscriminately; br>Round grinding wheels are used for grinding coarse turning tools, while fine grinding wheels are used for fine turning tools.7 Skills and Precautions for Sharpening Turning Tools
Inspect the grinder first, the safety of the equipment is the most important;After the speed of the grinding wheel is stabilized, grasp the side of the vertical knife wheel with both hands;Close your waist with both elbows. , smoothly sharpen and prevent shaking;Car. The height of the knife must be controlled, and the center of the grinding wheel must be horizontal;The force of the knife pressing the grinding wheel is moderate, and the reaction force is too large and slides easily;Hold the turning tool with your hand so that it moves evenly if the temperature high and hot, leave it temporarily;The knife must be careful when leaving the grinding wheel to protect the tip of the knife and lift it first;HSS knives can be cooled with water to prevent annealing and maintain hardness;Do not water harden hard alloys, as sudden cooling can easily lead to cracking of the tool; Stop grinding first, then stop, and people will turn off the power from the computer room
890°, 75°, 45°, etc. Turning tool sharpening steps according toouter circle
For rough grinding, first grind the main back, and the tail of the shank is to the left of the main deflection;The cutting head is flipped 38 degrees to reduce back corner friction; Then, grind the back of the sub and finally sharpen the front surface; The front of the rake angle is ground at the same time, first coarsely and then sequentially fine;Final grinding first grinds the front, and then sharpens the back of the main back and auxiliary;When sharpening the arc of the knife tip with your left hand, hold front fulcrum;Turn the shank of the rod with your right hand, and the arc of the knife tip has a natural shape;The flat edge is straight and stable, and the correct angle is the key;Carefully inspect the corner square of the sample, and it can be visually checked with rich experience.