When CNC machining is carried out in CNC machining center, due to tool wear, regrinding or replacement of new tools, the parameters of related tools in the programmed machining program will be changed, and the tool running path will be changed. If the adjustment is not enough, the final machining accuracy of the workpiece will be affected. For example, calculate the tool path from the beginning, and correct the program. In this way, it is not only time-consuming and laborious, but also has a high error rate. The most convenient way is to call the tool radius compensation performance of CNC system. When programming the workpiece, we only need to prepare the processing program according to the appearance of the workpiece. The system will automatically calculate the tool center path, so that the tool deviates from the appearance of the workpiece by a radius value. Even if the tool parameters are changed, only the detailed tool parameters need to be changed without changing the whole machining program. This greatly improves the machining efficiency of the machining center.
1、 Establishment and revocation of tool radius compensation
In short, tool radius compensation can be divided into left compensation and right compensation. Farewell is defined by G41 and G42. When the tool center track is located on the right side of the part appearance, it is called the tool radius right compensation; otherwise, it is called the tool radius left compensation.
1. The establishment of tool radius compensation
The establishment of tool radius compensation is a process that the tool center track changes from coincide with the programmed path to deviate from a tool radius value with the programmed path when the tool approaches the workpiece at the feed speed from the starting point. G41 is responsible for the left compensation of tool radius; G42 is responsible for the right compensation of tool radius.
2. Cancellation of tool radius compensation
The cancellation of tool radius compensation is the same as the process of creating tool radius compensation. After the final section of tool radius compensation path of the workpiece is processed, the tool withdraws the workpiece and returns to the withdrawal point. In this process, the tool radius compensation should be cancelled, and its instructions are defined by G40. The undercut point shall also be located outside the part appearance, and the undercut point of the parts machined at intervals shall be close to the undercut point, which may be the same as the undercut point, and of course may not be the same.
2、 Concerns in CNC machining tool radius compensation input
The change of tool radius compensation usually occurs after machining in machining center for a period of time. For a continuous program segment, when the tool radius compensation amount changes, the vector at the end of a program segment needs to be calculated with the tool compensation amount specified in the program segment.
In the process of NC programming, we usually input the compensation amount of the tool radius into the compensation code as a positive value. If the compensation amount of the tool radius is set as a negative value, under the condition that the target of the tool path is fixed, it is equivalent to exchanging the compensation position command in the NC program, G41 and G42. It is possible that the processing center originally processed the outside of the workpiece into the inside plus There are some unexpected problems, so we must pay attention to the configuration of two compensation targets when inputting radius compensation.
Programmable logic controller is the logic control center of machine tools. In the future, all kinds of activities and efficiency instructions from CNC will be logically sequenced, so that they can operate safely and accurately, coordinately and orderly; all kinds of information and work information not from machine tool will be transmitted to CNC, so that CNC can quickly and accurately send out further control instructions, so as to complete the control of all machine tools.
The electrical hardware circuit of CNC lathe follows the function of PLC constantly. The main mission of electrical hardware circuit is the generation and control circuit of power supply, the part of barrier relay and all kinds of promotion appliances (relays and Contactors). There are few relay logic circuits.
CNC lathe (electrical part) includes all electric ideas, solenoid valves, brakes, various switches, etc. They are promoters of various behaviors of machine tools and reporters of various essential situations of machine tools. The possible main obstacles here are the breakage of electrical appliances and the disconnection or cracking of connecting wires and cables.
The spindle drive system of CNC lathe receives the drive instruction from CNC, and drives the main electric idea to rotate through the speed and torque (power) Regulation and transmission drive information, and receives the speed feedback together to promote the speed closed-loop control. At the beginning and the end, PLC announced that CNC was used to control the functions of the spindle.
The feed servo system receives the speed command from CNC for each active coordinate axis, drives the servo motor to rotate through the speed and current (torque) Regulation and transmission drive information, completes the machine coordinate axis activity, and receives the speed feedback information together to promote the speed closed-loop control.
Welding repair of mechanical parts is more difficult than that of steel structure parts, because welding repair parts not only need to meet the requirements of strength and rigidity, but also need to meet the requirements of overall size, shape and position accuracy and machinability after repair. For the welding repair of large and complex parts, the welding repair process must be formulated and strictly implemented according to the wear and damage conditions of the parts. Generally, the key points of parts welding repair process are as follows.
① Pre welding planning. In addition to equipment planning, pre welding planning mainly includes preparation of welding groove and preheating of weldment.
Y-groove is used for single side welding (plate thickness ≤ 30mm), double V-groove is used for double side welding (plate thickness > 30mm), and U-groove is used for butt welding of shaft parts. Groove is formed by machining, or by gas cutting or gouging, but oxide skin must be eliminated. The groove shall be clean and free of oil stain and rust. The groove of butt welding shall be symmetrical to ensure good positioning. The groove of the crack depends on the depth and length of the crack, which shall be convenient for welding and reduce the filler metal.
The preheating temperature of the welding repair parts is determined by the carbon content of the base metal. Some steels which maintain austenite structure at normal temperature have no hardening condition and can not be preheated.
② Tack welding. When one side of the shaft parts or some parts welded and butted has been broken from the whole, the butt position of the parts to be welded shall be accurate to prevent excessive deformation during welding. For this reason, tack welding shall be carried out first: spot welding shall be carried out with the welding rod whose diameter is smaller than that of welding, and then the position shall be corrected again, and spot welding shall be carried out at several symmetrical points.
③ Selection of weld passes and electrode diameter. The wide or deep weld needs to be completed with multiple weld layers, and the weld procedures are interwoven. The functions can be improved, and the annealed weld bead can be applied. The weld bead shall be welded symmetrically. For the thicker part of the welding layer, the welding rod with good toughness or austenitic stainless steel welding rod shall be used to weld near the working size first, then the welding rod shall be used to weld to the required size, and machining allowance shall be reserved if necessary. For multi pass welding, the first 1-3 passes of fine-diameter electrode can be used to fully weld the bottom corner, and then the rest passes can be completed with coarse-diameter electrode. The diameter of the bead shall be smaller than that of the electrode used for welding, so as to control the temperature of the part during the bead welding.
1、 First, explain the processing method of stainless steel parts for everyone:
Stainless steel parts are widely used in equipment and machinery, and their processing methods and processes are becoming more and more advanced. Here are six processing methods of key stainless steel parts:
1. Forging method: use the swaging machine to stretch at the end or part of the pipe to reduce the outer diameter. The common swaging machines are rotary type, connecting rod type and roller type;
2. Bulge method: one is to place rubber in the pipe, and shrink it with a punch to make the pipe protrude; the other is to bulge the pipe with hydraulic pressure, and fill the middle of the pipe with liquid. The liquid pressure bulges the pipe into the required form, which is mostly used in the production of wave pipe;
3. Bending forming method of stainless steel elbow: there are three commonly used methods, one is stretching method, the other is stamping method, the third is roller method, there are 3-4 rollers, two unchanging rollers, one adjusting roller, adjusting unchanging roller distance, forming article pipe fittings is bending;
4. Stamping method: the pipe end is expanded to the required size and form by the core with taper on the punch;
5. Rolling method: usually without mandrel, suitable for the inner circular edge of thick wall pipe;
6. Roller method: the core is placed in the pipe, and the outer circumference is pushed and pressed by roller, which is used for round edge processing.
2、 Requirements of stainless steel parts for welding technology:
Due to the different sizes of stainless steel parts, the special welding places of stainless steel parts shall be followed, and the heat input shall be reduced as much as possible. Therefore, manual arc welding and argon arc welding shall be used. For d > Φ 159mm, argon arc welding shall be used as the backing and manual arc welding cover. D ≤ Φ 159 mm. Requirements for welding technology of stainless steel parts are as follows:
1. In manual arc welding, DC reverse connection is used for welding machine and DC positive connection is used for argon arc welding;
2. Before welding, the welding wire shall be brushed with stainless steel wire to remove the oxide skin on the surface and washed with * *; the welding rod shall be dried at 200-250 ℃ for 1H and used as needed;
3. Before welding, the oil stain within the 25 mm boundary line on both sides of the workpiece groove shall be cleaned, and the 25 mm boundary line on both sides of the groove shall be washed with * *;
4. During argon arc welding, the diameter of nozzle is Φ 2 mm, and the specification of tungsten electrode is Φ 2.5 mm;
5. When argon arc welding stainless steel, the reverse side must be filled with argon for protection to ensure the reverse forming. The flow rate is 5-14l / min and the flow rate of argon on the opposite side is 12-13l / min. During backing welding, the thickness of the weld shall be thin, with excellent fusion with the root, and it shall be in a gentle slope shape during arc closing. If there are arc closing shrinkage holes, they shall be ground off with a grinder. Make sure to start and extinguish the arc in the groove, and fill the crater during arc extinguishment to prevent the crater crack.
Using CNC processing equipment for processing, high efficiency, good quality, but if the process design is not properly placed, it can not well reflect its advantages. From the experience of some CNC processing plants, there are some problems as follows:
1. Over distribution of CNC process
The reason for this problem lies in the fear of complexity (referring to planning time), the simple programming, the simplified manipulation and processing, the use of a knife for processing, the easy adjustment of the tool, and the habit of ordinary processing. In this way, it is not easy to guarantee the goods (location yamen) and the production efficiency can not be well developed. Therefore, CNC processing staff and operators should have a comprehensive understanding of CNC processing knowledge, try more to be in charge of the related knowledge, and try to select the way of process set for processing, and use more times, which will naturally reflect its advantages. After the selection of working procedures, the unit processing time increases. We have deployed two equipment face to face, and completed the operation of two equipment by one person. The efficiency has been greatly increased, and the quality has been well guaranteed.
2. Sequential bifurcation theory of CNC processing
Some CNC processing operators study some problems in planning, and often put the processing order in a very different way. NC machining is usually carried out according to the requirements of normal machining process planning, such as first coarse and then fine (tool change), first inside and then outside, correct selection of cutting parameters, etc., so that the quality and efficiency can be improved.
Careful use of G00 (g26, G27, g29) quick positioning instruction has brought great convenience to programming and application. However, if it is not properly configured and used, it will usually lead to adverse consequences such as overshoot when returning to zero due to excessive speed configuration, precision drop, equipment guide rail surface pull, etc. The route of returning to zero is not concerned, which is easy to cause safety incidents of collision with workpieces and equipment. Therefore, when studying and using G00 instruction, we should study carefully and not casually.
In NC machining, more and more attention should be paid to strengthening the retrieval and test run of programs. After the program is input into the control system, the operator should swindle the SCH key and the ↑, ↓, ←, → mobile key to search indefinitely and positively, and correct the program if necessary to ensure the accuracy of the program. At the same time, before the formal implementation of the program processing, the program test run must be carried out from the beginning to the end (turn on the power amplifier) to confirm whether the processing route is the same as the design route.
The above are some common problems and solutions when using CNC processing equipment. There may be some other problems in the essential work, but as long as the CNC processing engineering technicians and operators are open-minded and carefully in charge of the related CNC knowledge and technology, the CNC equipment can well promote the benefits for the enterprise
(1) NC machining open-loop: this kind of machine has no feedback information from the position sensor. The CNC system processes the part program, transmits the digital instruction to the servo system, and drives the machine to move. The structure of the CNC system is simple, economical and easy to care for, but the speed and precision are low, which is suitable for the small and medium-sized machine tools with low precision requirements, and it is mostly used for the CNC transformation of the old machine tools.
(2) NC machining closed-loop: this kind of machine tool is equipped with a position detection device, which directly measures the displacement of the workpiece; its precision is high, but the system design and adjustment are troublesome, the structure is complex, and the cost is high. It is mainly used in some boring and milling machines, ultra-fine lathes, ultra-fine milling machines, machining centers, etc. with high precision requirements.
(3) NC machining semi closed loop: this kind of NC machine selects the angle measuring element installed on the feed lead screw or the end of the electric motor to measure the rotation angle of the lead screw, to obtain the position feedback information tactfully; it can obtain the more desired accuracy and speed, and numerous NC machine tools choose it, such as the numerical control lathe, NC milling machine and machining center.
CNC machining, also known as CNC machining, refers to the machining with CNC machining tools. Because NC machining is controlled by computer after programming, CNC machining has the advantages of stable machining quality, high machining accuracy, high repetition accuracy, complex profile machining and high machining efficiency. In the actual processing process, human factors and operating experience, to a large extent, will affect the processing quality. Next, let’s take a look at 12 valuable experiences summed up by an old driver with ten years of CNC processing experience
1. How to divide CNC process
The division of CNC machining process can be generally carried out according to the following methods:
The method of tool centralized sequence is to divide the working procedure according to the tool used, and use the same tool CNC to finish all the parts that can be finished. Use the second knife and the third to finish other parts they can finish. In this way, the number of tool changes can be reduced, the empty travel time can be compressed, and the unnecessary positioning error can be reduced. For parts with a lot of CNC machining content, the machining part can be divided into several parts according to its structural characteristics, such as internal shape, shape, curved surface or plane, etc. Generally, plane and positioning surface are processed first, then hole; simple geometry is processed first, then complex geometry is processed; parts with lower precision are processed first, then parts with higher precision requirements are processed. For the parts that are easy to deform in CNC machining, the method of sorting by rough and fine CNC machining needs to calibrate the shape due to the possible deformation after rough machining, so generally speaking, the process should be separated for the parts that need rough and fine machining. To sum up, in the process division, it is necessary to flexibly grasp the structure and process of the parts, the function of the machine tool, the number of CNC machining contents of the parts, the installation times and the production organization of the unit. In addition, it is suggested that the principle of process concentration or process dispersion should be adopted, which should be determined according to the actual situation, but must be reasonable.
2. What principles should be followed in the arrangement of CNC processing sequence
The arrangement of the processing sequence should be considered according to the structure of the part and the condition of the blank, as well as the need of positioning and clamping. The key point is that the rigidity of the workpiece will not be damaged. Generally, the sequence shall be in accordance with the following principles:
The CNC machining of the previous process can not affect the positioning and clamping of the next process, and the machining process of universal machine tool inserted in the middle should also be considered comprehensively. First, process the internal cavity, then process the shape. It is connected by the same positioning and clamping method or the same tool CNC processing process to reduce the number of repeated positioning, tool change and moving of pressing plate. For multiple processes in the same installation, the process with small damage to workpiece rigidity shall be arranged first.
3. What should be paid attention to in the determination of workpiece clamping mode
The following three points should be paid attention to when determining the positioning datum and clamping scheme:
Strive to unify the design, process and programming calculation standards. Reduce the number of clamping as much as possible. After one positioning, all surfaces to be machined can be processed by CNC. Avoid manual adjustment of occupation plan. The fixture shall be smooth, and its positioning and clamping mechanism shall not affect the cutter (such as collision) in CNC machining. In such cases, it can be clamped by means of vise or screw extraction with base plate. 4. How to determine the tool setting point is reasonable? What is the relationship between workpiece coordinate system and programming coordinate system?
1. The tool setting point can be set on the part to be machined, but it must be the reference position or the part that has been finished. Sometimes the tool setting point is damaged by CNC machining after the first process, which will cause the second process and the subsequent tool setting point cannot be found. Therefore, when the first process is used for tool setting, it is necessary to set a relative pair at the place that has a relatively fixed dimension relationship with the positioning benchmark Knife position, so that the original tool setting point can be retrieved according to the relative position relationship between them. This relative tool setting position is usually set on the working table or fixture of the machine tool. The selection principles are as follows:
Alignment is easy. Easy to program. The tool setting error is small. It is easy to check during processing.
2. The origin position of the workpiece coordinate system is set by the operator himself. After the workpiece is clamped, it is determined by tool setting, which reflects the distance position relationship between the workpiece and the zero point of the machine tool. Once the workpiece coordinate system is fixed, it is generally not changed. The workpiece coordinate system and the programming coordinate system must be unified, that is, when machining, the workpiece coordinate system and the programming coordinate system are the same.
4. How to choose the cutting route
Tool path refers to the path and direction of the tool relative to the workpiece in the process of NC machining. The reasonable choice of machining route is very important, because it is closely related to the CNC machining accuracy and surface quality of parts. The following points are mainly considered in determining the tool path:
Ensure the machining accuracy of parts. It is convenient for numerical calculation and reduces programming workload. In order to improve the efficiency of CNC machining, it is necessary to find a short CNC machining route and reduce the time of blank cutting. Minimize the number of program segments. To meet the requirements of the surface roughness after CNC machining, the contour should be processed by a continuous cutter. The advance and retreat (cut in and cut out) routes of the tool should also be carefully considered to minimize the tool marks caused by tool stop (elastic deformation caused by sudden change of cutting force) at the contour, and avoid cutting vertically on the contour surface and scratching the workpiece.
The plastic guide rail of CNC lathe is a kind of plastic soft belt with the same static and dynamic conflict coefficient on the sliding guide rail matching with the bed guide rail, which is wear-resistant and vibration absorbing. Maybe the plastic guide rail is made by injection molding between the fixed and dynamic guide rails. This kind of plastic guide rail has excellent conflict characteristics, wear resistance and vibration absorption, so it is commonly used in CNC lathe.
The plastic soft belt is based on polytetrafluoroethylene, with bronze powder, molybdenum disulfide, graphite and other fillers added, sintered and made into a soft belt. China has already made a TSF soft belt for guide rail, and a matching DJ adhesive. The process of using the guide rail soft belt is simple, as long as the surface roughness of the guide rail paste surface is semi-finished to ra1.6-3.2um, after cleaning the paste surface, the adhesive is used for bonding, after pressure curing, and then the finish machining can be carried out. Because this kind of guide rail soft belt adopts the bonding method, it is usually called “stick plastic guide rail”.
The raw materials for guide rail injection molding are epoxy resin and molybdenum disulfide as the matrix, plasticizer is added, and the mixture is a two-component plastic with paste shape as one component and curing agent as another component. The Chinese brand is hNT. The injection molding process of the guide rail is simple. After adjusting the mutual position accuracy between the constant guide rail and the movable guide rail, the two-component plastic is injected. After curing, the fixed and movable guide rails are separated into plastic guide rails. The plastic guide rails manufactured in this way are customarily called “injection molding guide rails”
The machining method of CNC workpiece surface depends on the technical requirements of machining surface. However, it should be noted that these technical requirements are not necessarily the requirements of the regulations of the part drawing, and may occasionally be higher than the requirements of the part drawing in some aspects due to technological reasons. For example, the machining requirements for the surface of some CNC machining parts are raised due to the misalignment of datum. Or higher machining requirements may be put forward because it is used as a precision reference.
After understanding the technical requirements of each CNC workpiece surface, we can choose the final processing method that can guarantee the requirements, and we will definitely need several processing steps and processing methods of each step. The selected machining method of CNC machining parts should meet the requirements of parts quality, excellent machining economy and high manufacturing efficiency. For this reason, the following factors should be studied when choosing the processing method:
1. There is an equal boundary between the machining accuracy and the surface roughness of any CNC machining method, but only in a narrow boundary is economic. The machining accuracy of this boundary is economic machining accuracy. Therefore, when choosing the processing method, we should choose the corresponding processing method which can obtain the economic processing precision.
2. The nature of raw materials for CNC machining should be studied.
3. To study the structure and size of CNC parts.
4. To study the production rate and economic requirements. When making a large number of products, we should choose advanced technology with high efficiency. It is even better to fundamentally change the manufacturing mode of blank, which can reduce the workload of machining.
5. To study the existing equipment and technical conditions of the workshop or workshop, we should fully defraud the existing equipment, tap the potential of the enterprise, and develop the enthusiasm and creativity of the workers when choosing the processing mode. But it is also necessary to study and constantly improve the existing processing methods and equipment, select new technology and improve the level of technology.
Precautions in the processing of CNC lathe. The machining process of CNC lathe is the same as that of ordinary lathe. However, since CNC is a clamping process, all the turning processes are finished continuously and automatically, the following aspects should be paid attention to.
1. Correct selection of cutting parameters
In terms of high efficiency metal cutting, the raw materials to be processed, cutting equipment and cutting conditions are three major factors. These decisions determine machining time, tool life and machining quality. The economic and useful machining method must be the correct choice of cutting conditions.
Three factors of cutting conditions: cutting speed, feed rate and cutting depth directly lead to tool damage. With the increase of cutting speed, the temperature of tool tip will rise, and mechanical, chemical and thermal wear will occur. If the cutting speed increases, the tool life will be reduced by 1 / 2.
The relationship between the feed condition and the wear of the back edge of the tool occurs within a very small boundary. But the feed rate is large, the cutting temperature rises, and the rear edge wear is large. It has less influence on the cutting tool than the cutting speed. Although the influence of cutting depth on the tool is not as high as the cutting speed and feed rate, when the cutting depth is small, the hard layer of the material to be cut will also affect the tool life.
Users should choose the cutting speed according to the raw material, hardness, cutting shape, raw material variety, feed rate, cutting depth, etc. The following table:
The selection of suitable processing conditions is based on these factors. Regular and stable wear and tear is the condition of dream.
However, in the essential work, the choice of tool life is related to tool wear, dimension change, surface quality, cutting noise, machining heat, etc. When confirming the processing conditions, the requirements are discussed according to the nature. As for stainless steel and heat-resistant alloy and other hard to process raw materials, it is advisable to choose a coolant or a rigid blade.
2. Select tools correctly
1) During rough turning, the cutter with high strength and good durability shall be selected to meet the requirements of large back draft and large feed during rough turning.
2) When finishing, the cutting tools with high accuracy and good durability shall be selected to ensure the requirements of machining accuracy.
3) In order to reduce the time of tool change and make the tool setting easier, we should choose the clip knife and clip knife.
3. Select fixture correctly
1) Although the general fixture is used to clamp the workpiece, the special fixture shall not be used;
2） The positioning datum of parts are overlapped to reduce the positioning deviation.
4. Confirm the processing route
Machining route refers to the moving track and target of the tool relative to the part in the process of NC machining.
1) It shall be able to meet the requirements of machining accuracy and surface roughness;
2) It is necessary to reduce the processing route and the time of tool empty travel.
5. Correlation between machining route and machining allowance
At present, under the condition that the CNC lathe has not been widely used, it is usually necessary to place too much allowance on the blank, especially the allowance containing forging and casting hard skin layer on the ordinary lathe for processing. If the CNC lathe must be used for machining, it is necessary to pay attention to the sensitive placement of the program.
6. Key points of fixture installation
At present, the connection between hydraulic chuck and hydraulic clamping cylinder is completed by pull rod. The key points of hydraulic chuck clamping are as follows: first, remove the nut on the hydraulic cylinder with the handle, remove the pull tube, and pull it out from the rear end of the main shaft, and then remove the constant screw of the chuck with the handle to remove the chuck.
The polishing edge on the tool refers to a small section of the edge which is parallel to the tool tip milled by the target of the deviation angle of the back edge pair of the tool edge, which is mainly used for the second cutting after the cutting of the tool edge, which is equivalent to the direction burr in the finishing process. The goal is to increase the surface roughness of the workpiece, which is mostly used for the tool of finishing.