Before precise CNC machining line, each processing method has its processing sequence. Our operators need to process according to their processing order, but they can’t process at will, which will have a certain impact on the processed products or quality problems. Precision machining is one of them. What is the sequence of CNC machining? For precision parts, machining must be based on the structure of the parts and the condition of the blank, as well as the requirements of positioning and clamping. The key point is that the rigidity of the workpiece is not damaged. There are the following points
1、 The familiar understanding of precision parts processing technology can be divided into several points
How to deal with the previous process will not affect the positioning and clamping of the next process. The middle cross section has a general fine parts processing process.
First stop the adding process of the inner cavity, and then stop the shape processing process.
It is better to use the same positioning, clamping method or the same tool to stop the process, so as to reduce the times of repeated positioning, tool change and the number of moving platens. Dongguan Machinery processing factory method.
In the multiple processes stopped in the same device, the process of destroying the workpiece stiffness should be arranged first.
2、 Tool concentration sequence method: the whole process is divided according to the tools used by precision machining manufacturers, and all parts on the parts can be completed by using the same tools. Other parts can be completed successfully by using other tools. This can reduce the number of tool change, shorten the dead time and reduce unnecessary positioning error.
3、 Sorting method of processing parts: for parts with a large number of processing contents, according to their structural characteristics, processing parts can be partially red, such as internal shape, shape, surface or plane. Common processing plane, positioning surface, after processing hole; first processing simple geometry, and then processing complex geometry; first processing low precision parts, and processing high precision parts.
In the field of machining industry, what are the reasons for the influence of CNC machining accuracy?
The first is the error of position influence: it usually refers to the mutual position change or deviation degree of the actual surface, axis or symmetry plane of the machined part relative to its ideal position, such as perpendicularity, position degree, symmetry degree, etc.
Machine error: the error of the machine itself usually refers to the dead angle error. The main causes of position error are the machining error caused by the gap and elastic deformation of the transmission in the machining process of machine tool parts, and the position error caused by the friction that the tool head needs to overcome in the machining process. In the open-loop system, the position accuracy is greatly affected, while in the closed-loop servo system, the position accuracy mainly depends on the displacement detection.
Geometric error: machining accuracy error caused by geometric error of CNC machining. In the process of CNC machining, the geometric accuracy of the machine tool is affected by external factors such as external force and heat generated in the process. The geometric deformation of the parts processed on the machine tool will lead to geometric error. According to research, there are two main reasons for geometric error of CNC machine tools: internal factors and external factors. The internal factors that cause the geometric errors of machine tools refer to the geometric errors caused by the factors of machine tools, such as the levelness of machine tool table, the levelness and straightness of machine tool guide rail, the geometric accuracy of machine tools and fixtures, etc. The external factors mainly refer to the geometric errors caused by the influence of external environment and thermal deformation. For example, the geometric errors caused by the thermal expansion and deformation of cutting tools or parts in the cutting process will affect the machining accuracy of machine tools and parts.
Cumulative error: from the long-term data analysis and actual operation of parts processing, we can see the machining accuracy error caused by CNC machine positioning. The positioning of machine tool has a great influence on the machining accuracy of NC machine tool. From the structure point of view, the machining error of CNC machine tool is mainly caused by the positioning accuracy, and the feed system of machine tool is the main link affecting the positioning accuracy. The feed system of CNC machine tool is usually composed of mechanical transmission system and electrical control system. In structural design, positioning accuracy is related to mechanical transmission system. In the closed-loop system, CNC machine tools usually can prevent the position deviation of the main parts (such as ball screw and other parts) in the feed system by positioning detection device. However, for the open-loop system, due to many factors and complex conditions, it is impossible to carry out positioning monitoring, so the machining accuracy of CNC machine tools is greatly affected.
The above explanation is the reason for the influence of CNC machining accuracy in Dongguan. I hope it will be helpful to you after reading.
We need to understand a lot of precautions before processing, to avoid that we still have a lot of things we don’t understand in the later processing. After understanding, we can better help us work, reduce the occurrence of fault problems, and ensure the quality of products. These are closely related to the matters we need to pay attention to, so let’s understand the precision parts What should be paid attention to when processing?
Before mechanical work, check whether the moving part is filled with lubricating oil, then start and check whether the clutch and brake are normal, and idle the machine for 1-3 minutes. It is strictly forbidden to operate when the machine is faulty.
When working, keep the right posture, have enough spirit to deal with the work, if you find that you feel unwell, you should leave the job immediately and report to the leader. The operator must not operate in the state of irritability and fatigue, so as to avoid accidents and ensure operation safety. Before entering the post, all employees should check whether their clothes meet the work requirements. Slippers, high-heeled shoes and clothes affecting safety are not allowed. Those with long hair should wear safety helmets.
When replacing the die, first turn off the power supply, and then start to install and debug the die after the punch movement department stops running. After the installation and adjustment, move the flywheel by hand for trial punching twice to check whether the upper and lower dies are symmetrical and reasonable, whether the screws are firm, and whether the blank holder is in a reasonable position.
It is necessary to wait for all other personnel to leave the mechanical working area and take away the debris on the workbench before starting the power supply to start the machine.
When the machine works, it is forbidden to extend the hand into the slider working area, and it is forbidden to take and place the workpiece by hand. The standard tools must be used when taking and placing the workpiece in the die. In case of abnormal sound or machine failure, turn off the power switch immediately for inspection. After the machine is started, one person shall transport materials and operate the machine. Other people shall not press the electric building or step on the foot switch board, nor put their hands into the working area of the machine or touch the moving parts of the machine with their hands.
When off duty, turn off the idle power, and sort out the finished products, leftover materials and sundries on the post to ensure the clean and safe working environment.
CNC machining is also called numerical control machining
Before programming, it is necessary to analyze the process of the processed parts, draw up the processing plan, select the appropriate tool, and determine the cutting parameters. In programming, some technological problems such as tool setting and machining route need to be dealt with. Therefore, the process analysis in programming is very important. When processing parts on ordinary machine tools, the operation procedure of each process is specified by the process specification or process card, and the operator processes the parts according to the steps specified in the process card. When machining parts on CNC machine tools, it is necessary to program all the technological process, technological parameters and displacement data to control the machining of machine tools. The processing technology of NC machine tool is basically the same as that of ordinary machine tool in principle, but the whole process of NC machining is automatic, so it has its own advantages
Reduce the number of tooling, add the complex shape of Du parts, do not need complex tooling. If Dao wants to change the shape and size of parts, it only needs to modify the processing program of parts, which is suitable for the development and modification of new products.
The machining quality is stable, the machining accuracy is high, and the repetition accuracy is high, which can meet the machining requirements of aircraft.
In the case of multi variety and small batch production, the production efficiency is high, which can reduce the time of production preparation, machine adjustment and process inspection, and reduce the cutting time due to the use of the best cutting quantity.
It can process complex surface which is difficult to be processed by conventional methods, and even process some parts which cannot be observed.
The arrangement of working steps is more detailed
This is because the problems that need not be considered in the processing technology of ordinary machine tools, such as the arrangement of working steps in the process, the determination of tool setting point, tool changing point and processing route, can not be ignored when compiling the processing technology of CNC machine tools.
CNC machining has high efficiency, high machining accuracy, low labor intensity and strong adaptability to different workpieces.
Every processing technology has its own working principle. If we want to know what the working principle of a processing technology is, we only know that CNC processing is one of them. What is the working principle of CNC processing?
The control system of CNC machining center can generally control the machine tool to stop, change direction and speed automatically according to the digital program instruction. It can automatically control the feed speed, direction and processing path to process. It can select the cutting tool and adjust the cutting amount and walking track according to the cutting tool size, and can end all kinds of auxiliary actions required in the processing.
CNC machining structure CNC lathe is also composed of headstock, turret, feed transmission system, bed, hydraulic system, cooling system, lubrication system and other parts, but CNC lathe feed system and horizontal lathe feed system in the structure is essentially different, typical CNC lathe mechanical structure composition diagram. The movement of the horizontal lathe spindle is transmitted to the tool rest through the change gear frame, feed box and slide box to end the longitudinal and transverse feed movement. The CNC lathe is to select servo motor, through the ball screw to slide plate and turret, end Z direction (longitudinal) and set direction (transverse) feed movement. Fine CNC machining also has the function of various threads. The movement between spindle rotation and tool rest movement is controlled by CNC system.
Carving and milling machine, carving machine and machining center (computer gong) are very similar in appearance and structure. The following is a comparative analysis of the three
Conceptually
Machining center: Hong Kong, Taiwan and Guangdong are called computer gongs. They are highly automatic multi-functional CNC machine tools with tool magazine and automatic tool changing device. The first machining center appeared in the United States in 1958. It can realize the centralized processing of milling, drilling, boring, reaming, tapping and other processes after the workpiece is clamped once, with special emphasis on “milling”.
Engraving machine: its spindle speed is high, suitable for small tool processing, torque is relatively small, focusing on the “engraving” function, such as wood (special processing of wood called wood engraving machine), two-color board, acrylic board and other low hardness plate, not suitable for strong cutting of large workpieces. At present, most of the products on the market under the banner of engraving machine are mainly for processing handicrafts with low cost. Due to the low precision, they are not suitable for mold development; but there are exceptions, such as wafer engraving machine.
Carving and milling machine: as the name suggests. It can be carved or milled. On the basis of engraving machine, the power of main shaft and servo motor is increased, and the bearing force of bed is increased. At the same time, the high speed of main shaft is maintained, and more importantly, the precision is very high. Engraving and milling machine is also developing at a high speed, commonly known as high-speed machine. It has stronger cutting ability and very high machining accuracy. It can also directly process materials with hardness above HRC60 for one-time forming.
In terms of appearance and volume
The volume of machining center is the largest, the volume of large 1690 machine is 4m * 3M, and that of small 850 machine is 2.5m * 2.5m; carving and milling machine is the second, and that of large 750 machine is 2.2m * 2m; carving machine is the smallest.
In terms of mechanical structure
Machining centers generally use cantilever type, carving and milling machines and carving machines generally use gantry type structure, gantry type is divided into pillar type and fixed beam type, at present, carving and milling machines are mostly fixed beam type.
In terms of index data
Spindle maximum speed (R / min): 8000 machining center; carving and milling machine is the most common 240000, high-speed machine is the lowest 30000; engraving machine is generally the same as carving and milling machine, engraving machine for high gloss processing can reach 80000, but it is not ordinary motorized spindle, but air floating spindle.
Spindle power: machining center is the largest, from thousands of watts to tens of kilowatts; carving and milling machine is the second, generally within ten kilowatts; carving machine is the smallest.
Cutting capacity: machining center is the largest, especially suitable for heavy cutting, roughing; carving and milling machine is the second, suitable for finishing; carving machine is the smallest.
Speed: because the engraving and milling machine and engraving machine are relatively light, their moving speed and feed speed are faster than the machining center, especially the high-speed machine equipped with linear motor, the maximum moving speed can reach 120m / min
Accuracy: the accuracy of the three is almost the same.
From the processing dimension: the area of the worktable can better reflect this. The smallest worktable area (unit mm, the same below) of domestic machining center (computer gong) is 830 * 500 (850 machines); the largest worktable area of engraving and milling machine is 700 * 620 (750 machines), and the smallest is 450 * 450 (400 machines); engraving machine generally does not exceed 450 * 450, the common is 45 * 270 (250 machines).
In terms of application objects: machining center is used to complete the processing equipment of large amount of milling work pieces, large molds and materials with relatively high hardness, which is also suitable for roughening of ordinary molds; engraving and milling machine is used to complete the finishing of small amount of milling work pieces and small molds, which is suitable for copper and graphite processing; low-end engraving machine is inclined to wood, two-color board, acrylic board and other materials with low hardness Plate processing, high-end suitable for wafer, metal shell polishing.
people say that
Machining center, engraving and milling machine can do both products and molds, engraving machine can only do products.
Tool magazine: Machining Center, there is a tool magazine is the machining center, no tool magazine is called computer gong or CNC milling; carving and milling machine generally does not equipped with tool magazine, even if the optional tool magazine is 12 knife umbrella tool magazine, or 6 knife in-line tool magazine; carving without tool magazine.
supplement
There is no CNC engraving and milling machine in foreign countries. Strictly speaking, engraving is a part of milling, so there is only the concept of machining center in foreign countries, and the concept of small machining center is derived to replace engraving and milling machine. Purchase engraving machine or purchase CNC milling machining center is often to ask their own questions, to see the actual production needs. In addition, there is the popular high-speed cutting machine (hscmachine), which is called high-speed machine in China.
2、 Analysis from the angle of numerical control
— the CNC milling center requires a general speed for the CNC system, and the spindle speed is about 0 ~ 8000rpm
— the engraving and milling machine requires a high-speed numerical control system, and the spindle speed is about 3000 ~ 30000 rpm
High speed cutting machine tools require high-speed CNC system and excellent servo motor characteristics. The spindle speed is about 1500 ~ 30000 rpm
What points should be paid attention to when machining and installing workpieces with gantry milling machine
When machining and installing workpieces with gantry milling machine, if it is necessary to use pad iron, a certain thickness of copper plate (about 5mm) should be padded between the pad iron and the worktable, and a thin copper sheet should be padded between the pad iron and the worktable to prevent the surface of the worktable and workpieces from producing marks. When using pad iron, pay attention to the pad iron and the fixing screw as low as possible, And the iron pad should be placed outside a certain area of the workpiece processing range, in order to avoid the damage caused by the impact of the iron pad on the tool head and tool chuck. When loading and unloading workpieces, it is necessary to handle them with care to reduce the friction and movement of workpieces on the worktable as far as possible. It is forbidden to drag workpieces on the worktable of the machine tool by using the edges and corners of many workpieces as support points (this will seriously scratch the worktable of the machine tool and affect the flatness of the worktable). It is forbidden to place tools such as socket, screw wrench, screw, rubber hammer, oilstone, file, etc. on the worktable of the machine tool to prevent damage Damage the working table of the machine tool. Operation method of gantry milling: before starting the machine, first check whether the lubricating oil is appropriate and whether the machine is in normal state, then turn on the machine power (turn the knob from “off” to “on” when turning on the machine power), then turn on the power switch of the control panel and turn out the emergency stop key.
After the machine is started, the origin of the machine tool will return and the tool magazine will return to zero. Before the origin return, check whether the position of the tool relative to the workpiece is safe, and then determine how to return the origin (the machine tool can return to the zero position according to the sequence of axes). Select zero return (machine tool origin return); select arc manual → press Magazing zero return (tool magazine return). Check the shift record to make clear today’s tasks and precautions. For each workpiece, check in advance whether the processing program is complete, whether the tools are complete and in good condition, number the tools, and write the tool number on the tool with a marker pen. Easy to check. According to the programmer’s requirements, prepare the workpiece and fixture, and determine the method of clamping the workpiece (the bottom of the work should be polished with an oilstone).
The worktable of gantry machining center is basically rectangular. Large castings such as worktable, bed, column, crossbeam and RAM are made of mihanna cast iron. The inner cavity of the castings is honeycomb composite arrangement structure. The design is advanced. All of them are treated by aging and secondary tempering to eliminate residual internal stress, stabilize the material, ensure the stability of workpiece processing accuracy and machine life.
2 Longmen
The gantry consists of a beam and two columns. It can be divided into three types: fixed beam, locking sectional lifting beam by positioning block and arbitrary lifting beam.
3 RAM
The structure of RAM can be divided into open type and closed type. The ram with open structure is clamped on the spindle box by pressing plate, and the cross-sectional area of ram is large; the ram with closed structure is clamped in the spindle box, and the cross-sectional area of ram is small.
4 tool magazine
There are three basic types of tool magazine: turret type, drum type and chain length type.
Attachment 5
The processing of large and complex parts usually needs a lot of accessories. The accessory head is specially designed according to the processing requirements of the workpiece, which is generally divided into right angle head, extended head, special angle head and universal head.
6 CNC system
The CNC system generally adopts SINUMERIK 840C and 840D of Siemens company of Germany or 31I series of FANUC company of Japan, and the CNC axis adopts full closed-loop control.
7 accuracy
The accuracy of machine tool refers to the original accuracy of machine tool without external load. The accuracy is usually expressed by the deviation between its opposite side and ideal state (error for short). The smaller the error is, the higher the accuracy is.
CNC machining center must meet the following four conditions
1、 Environmental requirements for machining center location
The machining center should be located far away from the vibration source, avoid the influence of direct sunlight and thermal radiation, and avoid the influence of humidity and airflow. If there is a vibration source near the CNC machine tool, the anti vibration groove should be set around the machining center. Otherwise, it will directly affect the machining accuracy and stability of CNC machine tools, make the electronic components in poor contact, cause failure, and affect the reliability of the machining center.
2、 Power requirements
The general machining center installed in the machining workshop, not only the environmental temperature changes greatly, the use of poor conditions, and a variety of mechanical and electrical equipment, resulting in large fluctuations in the power grid. Therefore, the installation position of machining center needs strict control of power supply voltage. The fluctuation of power supply voltage must be within the allowable range and keep relatively stable. Otherwise, it will affect the normal work of CNC system of machining center.
3、 Temperature conditions
The environment temperature of NC machining center is less than 30 degree, and the relative temperature is less than 80%. Generally speaking, there are exhaust fans or air coolers in the CNC electric control box to keep the working temperature of electronic components, especially the CPU constant or the temperature difference changes little. Too high temperature and humidity will reduce the life of control system components and increase the number of faults. With the increase of temperature and humidity, more dust will bond on the integrated circuit board and lead to short circuit.
4、 Use the machining center according to the instruction
Users are not allowed to arbitrarily change the parameters set by the manufacturer in the control system when using the machining center. The setting of these machining center parameters is directly related to the dynamic characteristics of machining center components. Only the gap compensation parameters can be adjusted according to the actual situation.
The following aspects should be considered when selecting a blade or cutter
The workpiece materials are steel materials (carbon steel, low alloy steel, tool steel, stainless steel). And other complex materials, such as copper, iron and non-metallic materials.
The material properties of machined parts include properties, toughness, microstructure, etc.
The categories of cutting technology include turning, milling, boring, drilling; machining, superfinishing; inner hole, outer circle, plane, groove; cutting flow state, tool displacement time interval, etc.
The geometric shape of the workpiece affects the continuous cutting or intermittent cutting, the cutting in or out angle of the tool. Part accuracy (dimensional tolerance, geometric tolerance, surface roughness) and machining allowance.
Cutting parameters of blade (tool) (back feed, cutting speed)
Production site conditions (operation interruption time, feed rate, cutting speed)
Processing of workpieces and production batch. Economic life of blade (cutter)
2、 Selection of boring tools:
In the selection of boring tools, the main problem is the rigidity of the tool bar, and the vibration should be prevented or eliminated as far as possible. The main points for consideration are as follows;
The diameter of the reverse bar should be as large as possible, close to the boring diameter.
Select the short arm (working length) as far as possible. When the working length is less than 4 times the diameter of the tool bar, steel tool bar can be used. When machining holes with high requirements, cemented carbide tool bar is best used. When the working length is 7-10 times the diameter of the arbor, the small hole is made of cemented carbide arbor, and the drilling is made of shock absorber arbor. When the working length is 7-10 times the diameter of the cutter bar, the damping cutter bar should be used.
The main deflection angle is more than 75 ° and close to 90 °
Select the blade without coating to reduce the radius of cutting arc and tool tip.
The positive cutting edge (positive rake angle) blade and tool are used for finish machining, and the negative cutting edge (negative rake angle) blade and tool are used for rough machining.
When boring deep through holes, cooling measures should be taken. Compressed air (air cooling) or cutting fluid (chip removal and cooling) can be used.
Choose the right and fast boring tool holder.
3、 Selection of milling cutter:
Indexable carbide milling cutter should be used when milling plane on CNC machine tool. It can be divided into two steps. One rough milling and one finish milling. When continuous cutting. The diameter of rough milling cutter should be reduced. The diameter of the finishing cutter should be larger, and it is better to contain the whole width of the surface to be machined. When the machining allowance is large and the machined surface is uneven, the tool diameter should be selected smaller. Otherwise, when rough machining, it will affect the machining quality due to the deep tool mark.
High speed steel end mills are mostly used to process boss and groove, so it is better not to use them to process blank, because there are hardening layer and cracks in the blank. It will accelerate the tool wear.
The machining allowance is small and the surface roughness is required to be low, so the CBN end mill or ceramic end mill should be used.
The end milling cutter with carbide insert can be used for machining groove, concave surface, convex surface and blank surface.
The end milling cutter with cemented carbide can be used for powerful cutting. Milling the surface of the blank and rough machining the hole.
When machining the groove with high accuracy requirements, the end milling cutter with diameter smaller than the groove width can be used. Firstly, the middle part of the groove is milled, and then the two sides of the groove are milled by using the radius compensation function of the cutter until the accuracy requirements are met.
When drilling on CNC milling machine, the drill die is generally not used. When the depth of the hole is about 5 times of the diameter, it is easy to break the drill bit. Fixed cycle program can be used to advance and retreat automatically for many times to facilitate cooling and drainage. Before drilling, it is better to drill a central hole with a central drill or to drill the bottom hole with a section drill with good rigidity for positioning
When drilling on the milling machine, the drilling die is not generally used. When the depth of the hole is about 5 times of the diameter, it is easy to break the drill bit, and fixed circulation can be used
