CNC Technology – Page 32 – CNC Machining & Turning, Milling, Metal parts

Abnormal rotation of computer gong spindle

During the work, it was found that there was abnormal sound in the spindle and gearbox when the spindle speed was below 500r / min. by observing the power meter of the motor, it was found that the output power of the motor was unstable, and the pointer swayed greatly. However, the abnormal sound disappeared again when it was used for more than 1201r / min. After startup, the power meter of the motor will swing automatically without rotation command, and the motor will drift and rotate automatically. After normal operation, the braking time is too long, and there is no alarm for the machine.

According to the phenomenon, the cause of the fault may be that the spindle controller is out of control, and the mechanical transmission or motor can not be eliminated. Due to the heavy workload of disassembling the mechanical part for inspection, the spindle controller of the electrical part is inspected first, and the controller is Siemens 6sc-6502. Firstly, check the preset parameters in the controller, and then check the control board, and there is no abnormality. After checking that the circuit board is dirty, clean the circuit board as required, but the power failure is still the same after it is installed. Therefore, the fault causes in the controller can be eliminated temporarily. In order to determine whether the fault is in the motor or the mechanical transmission part, the motor and the machinery must be separated. After the separation, it is found that when the motor speed command is close to 450R / min, the continuous abnormal sound begins to appear, but when the motor speed command is given to 1201r / min, the abnormal sound disappears again. For this reason, we analyzed the spindle part. The original 450R / min command at low speed and 4500r / min command at high speed are the same for the motor. At the highest speed, the motor is decelerated through the gear at low speed, so the fault can be basically determined in the motor part. After analysis, the abnormal sound may be caused by poor bearing.

When the motor was disassembled for inspection, it was found that the bearing was damaged. At high speed, the bearing was stuck, causing the load to increase, causing the power meter to swing and deflect. After stopping, the motor drifted and brake too slowly. After inspection, the encoder disc was scratched. After replacing the bearing and encoder, all the faults were eliminated. The main reason for the fault is that there is abnormal sound when the spindle rotates. Therefore, the sound source should be found out before checking. There is abnormal sound, common for mechanical friction, jam and bearing damage.

CNC machining center spindle orientation is usually used in three ways, magnetic sensor, encoder and mechanical orientation. When using the magnetic sensor and encoder, in addition to adjusting the position of the components, the machine parameters can also be adjusted. There is no alarm when orientation error occurs, and it can only be found when interruption occurs during tool change.

Once in a refitted CNC machining center, there was a fault of inaccurate orientation. At the beginning, the machine tool was often interrupted in the work, but the number of times was not very many. When the machine was restarted, it could work again, and the fault occurred repeatedly. After careful observation of the machine tool after the failure, it was found that the real cause of the failure was the position deviation of the spindle after orientation. It was strange that if the spindle was touched by hand after orientation (similar to the situation when the tool was inserted into the spindle during tool change), the spindle would drift in the opposite direction. There was no alarm in the electrical part, and the mechanical part was very simple.

The orientation of the machine tool uses encoder, so from the fault phenomenon and possible parts, the possibility of the electrical part is relatively small, the main mechanical part is the connection. So we decided to check the mechanical connection part. When we check the connection of the encoder, we found that the set screw of the coupling sleeve on the encoder is loose, which makes the coupling sleeve retreat, causing the gap between the coupling part and the spindle to be too large and the rotation is not synchronous. After the set screw is fixed as required, the fault is eliminated. If the spindle orientation fault occurs, it should be analyzed and handled according to the specific structure of the machine tool. Check the electrical part first, and consider the mechanical part after confirming that it is normal.

What is CNC three axis linkage

CNC machining center refers to the spindle axis and vertical machining center setting table, which is mainly suitable for processing plate, plate, shell and small complex parts. Vertical machining center can complete milling, boring, drilling, tapping and thread cutting process. Vertical machining center is at least 3-axis linkage device, generally can realize three-axis linkage. Some five axis and six axis controls can be implemented.

The height of the vertical machining center is limited, which reduces the processing range of the workpiece, which is the disadvantage of the vertical machining center. However, the workpiece clamping and positioning is convenient for vertical machining center; the cutting path is easy to observe and debug, the program inspection and measurement is convenient, the problems can be found in time, and the treatment or modification can be stopped; the cooling conditions are easy to establish, and the cutting fluid can directly reach the surface of the cutting tool and processing; the three-axis and Cartesian coordinate system, intuitive feeling, in line with the design point of view, the chip is easy to exclude and modify, Surface treatment to avoid scratches.

Vertical machining center

Mainly used for:

Using grease and oil circulation in machining center will produce abnormal heating.
Spindle, need high-definition washing, high-speed bearing sealing place

Working principle: using compressed air flow pipe, the continuous flow of transmission oil along the pipe, stirring and transportation of oil and gas processing center spindle and other parts of the screw need lubrication. The constant pressure dry compressed air (bar) 5 – 8 continuous supply, according to the spindle and lubricating oil lubrication, screw oil and other parts of the fuel consumption different quantitative supply. Therefore, each lubrication circuit must use a separate micro pump power supply of oil. After the oil pump, it must enter the oil and natural gas mixing valve. In the oil and natural gas mixing valve, the compressed air flow blows into small oil drops and adheres to the wall to form an oil film. The flow direction of the air flow between the oil film and the pipe wall, and the thickness of the medium oil film gradually becomes thinner, but not together.

Four processing stages of CNC model

When the requirements of surface precision and roughness of parts are relatively high, it is often impossible to complete the processing in one process, and it is divided into several stages for processing.

Four processing stages in the process of making CNC model

(1) Rough machining stage. Rough machining is mainly to cut off most of the machining allowance on each surface to make the shape and size of the blank close to the finished product. This stage is characterized by the use of high-power machine tools, the selection of larger cutting tools, as far as possible to improve productivity and reduce tool wear.

(2) Semi finishing stage. Semi finishing is to finish the machining of secondary surface and prepare for the finishing of primary surface.

(3) Finishing stage. Finish machining is to ensure that the main surface meet the requirements of the drawing.

(4) Finishing stage.

Finishing is a kind of surface with high requirements for surface roughness and machining accuracy, and it also needs finishing. This stage can not be used to improve the position accuracy of parts.

It should be pointed out that the division of processing stages is based on the whole process of parts processing, and cannot be judged by the processing of a certain surface or the nature of a certain process. At the same time, in the specific application, it can not be absolute. For some heavy parts or parts with small allowance and low precision, rough and finish machining can be completed after one clamping.

The transformation brought by CNC machining

NC machining skills have been widely promoted. Most of the machining workshops have NC machining ability. The most common NC machining methods in typical machining workshops are NC milling, NC lathe and NC EDM wire cutting. Because the machining center can complete a variety of processes in a centralized and automatic way, it can avoid man-made operation errors, reduce the time of workpiece clamping, measurement and machine tool adjustment, as well as the time of workpiece turnover, transfer and storage, greatly improve the processing efficiency and accuracy, so it has good economic benefits.

There are many kinds of large CNC machining and CNC lathe machining; from the main categories, there are special CNC lathe machining and general CNC lathe machining; from the processing varieties, there are CNC lathe machining shell, CNC milling machine, processing base, CNC lathe machining shaft, turning center, cam CNC grinder, etc.; from the control request of CNC lathe machining, there are Single axis CNC Abrasive Belt polishing machine includes five linkage CNC gear cutting machine and CNC hob grinding machine; from the complexity of control, there are simple CNC and multi-channel CNC; from the driving method, there are stepper motor, DC servo motor, communication synchronous servo motor, communication asynchronous servo motor and linear motor; from the spindle driving method, there are three parts, There are DC spindle motor, communication spindle motor and communication motorized spindle; in terms of azimuth response method, there are full closed loop response, half closed loop response and open loop control.

The parts processed by CNC lathe should be able to give full play to the technical characteristics of multi process centralized processing of CNC grinder. When CNC grinder processes parts, the condition of grinding wheel cutting workpiece is completely the same as that of corresponding non CNC grinder, but it can carry out some complex processing with machining accuracy requirements. For example, in the grinding range, the general grinder is mainly used for grinding cylindrical and circular CNC lathe The end face of conical surface or stepped shaft shoulder is usually ground by lathe. In addition, CNC cylindrical grinder can also grind torus, as well as the complex combination of the above forms.

High grade and efficient universal active metal cutting machine tool, fine numerical control system with CNC standardization function, computer gong processing can realize the vast majority of drilling, milling, boring, expanding, twisting and other active processing technology, accurately and efficiently finish all kinds of chaotic cam, template, die, arc groove and other typical parts active processing, and can process DNC chaotic parts through RS232 serial port.

As far as the hydraulic buffer for machinery is concerned, it has been oriented to all-round customized planning. For example, it can be used in field and military machinery, crane, high temperature and humid places, etc. Therefore, in planning, it needs to withstand long-term testing before it can become a functional and all-weather commodity. In manufacturing technology, the surface and interior of this type of commodity are highly hardened, heat treated to HRC60 degree and chrome plated, rust resistant and anti-corrosion treatment.

In the high-speed machining base, because the cutting speed is greatly improved, the active tool changing equipment and tool magazine equipment should consider shortening the tool changing time as much as possible, and then cooperate with the high-speed cutting machine tool. The tool changing equipment in the base is generally composed of tool magazine and tool communication organization, and the commonly used methods are manipulator type and non manipulator type. The way and position of tool magazine are also different. In order to meet the needs of high-speed movement, the structure of high-speed machining base is different from that of traditional machining base. It has become the main stream of high-speed machining base planning to reduce the quality of moving parts mainly by tool movement.

Main body description of high speed CNC system

NC machining process is completed in a NC machining process system composed of NC machine tool, cutting tool, fixture and workpiece. CNC plus program controls the movement path of cutting tool relative to workpiece. Therefore, the unity of CNC machine tools, fixtures, tools and workpieces is called CNC machining process system.

numerical control machine. The machine tool that adopts numerical control technology or is equipped with numerical control system is called numerical control machine tool. Numerical control machine tool is a kind of machine integration processing equipment with relatively high technology intensity and automation degree. It is the main body of numerical control processing and the working machinery of parts processing.

High speed CNC fixture. In mechanical manufacturing, the device used to clamp the workpiece and guide the tool is called fixture. In the process of mechanical manufacturing, fixture is widely used, from blank manufacturing to product assembly and testing of each production link, there are many kinds of fixture. The fixture is used to fix the workpiece and keep the correct position, which is the link to realize the data processing.

Tool. Metal cutting tool is an important tool in modern machining, whether it is ordinary machine tool or CNC machine tool, must rely on the tool to complete the cutting work. Tool is the bridge to realize NC machining.

Main elements of high speed CNC programming technology

According to the principle of giving full play to the function of CNC machine tool, the reasonable machining method and process route are determined.
When designing and selecting NC machining tools, the factors such as machining methods, cutting parameters and workpiece materials should be considered to meet the requirements of convenient adjustment, good rigidity, high precision and good durability. When designing and selecting NC machining fixture, it should be able to quickly complete the positioning and clamping process of the workpiece, so as to reduce the auxiliary time. And try to use modular fixture to shorten the production preparation cycle. In addition, the fixture used should be easy to install on the machine tool to coordinate the dimensional relationship between the workpiece and the machine coordinate system.
The selection of high-speed CNC tool setting point is the starting point of program execution. The selection should be based on the principles of simplifying programming, easy alignment, easy inspection in machining process and reducing CNC machining error. The tool setting point can be set on the workpiece to be processed, or on the fixture or machine tool. In order to improve the machining accuracy of parts, the tool setting point should be set on the design basis or process basis of parts as far as possible.
In order to improve the utilization rate of the machine tool, the pre adjustment outside the machine tool should be used as far as possible, and the pre adjustment size should be input into the CNC system in time before running the program, so as to realize the tool compensation.
CNC machining route is determined to ensure the accuracy and surface roughness requirements of the machined parts; shorten the tool path as far as possible, reduce the empty tool travel; it is conducive to simplify the numerical calculation, reduce the number of program segments and programming workload. The process route is formulated to process the parts on the machining center. Due to the many processes of parts processing and the variety of tools used, rough machining, semi finish machining and finish machining have to be completed even under one-time clamping.
The cutting parameters include cutting depth, spindle speed and feed speed. The specific value of cutting parameters should be comprehensively considered according to the provisions of the manual of CNC machine tool, the material of the workpiece to be processed, the processing content and other high-speed CNC process requirements, and combined with the experience data.

The quality of NC process design will directly affect the size accuracy and surface quality of NC machining, the length of processing time, the consumption of materials and labor, and even directly affect the safety of processing. Using large computer gong to process CNC machine parts, the general process from parts drawing to qualified products is as follows:

According to the shape and size of the workpiece, material and technical requirements specified in the part drawing, the large-scale computer gong processing carries out the design and calculation of the process program (including the processing sequence, the relative movement path of the cutter and the workpiece, the stroke and the feed speed, etc.).
Then, according to the form of “numerical control device identification code”, it can be programmed.
The control medium (such as perforated paper tape) is made according to the number code, text code and symbol number on the part processing program sheet.
Through the photoelectric reader, the perforated paper tape converts the optical signal with or without holes into electrical signal and inputs it to the numerical control device.

Processing method of computer gong

Computer gong processing is a complex processing by computer-controlled machine tools. The most complex part of the computer gong is the control system. The computer sends all kinds of instructions to control the three-axis servo motor of the machine. According to the established route, it cooperates with each other to process all kinds of complex processes and ensure high machining accuracy.

What are the common computer gong processing methods

Plane hole parts

Generally, point and line control computer gong machine tools (such as computer gong drilling machine) are used for processing. When selecting the process route, the two principles of processing accuracy and processing efficiency are mainly considered.

Rotating parts

Commonly used computer gong lathe or grinder processing.

a. Consider the processing efficiency: when processing on the lathe, usually the machining allowance is large, we must reasonably arrange the rough machining route to improve the processing efficiency. In actual programming, it is generally not suitable to use cycle instruction (otherwise, there are too many empty tools at work speed). A better way is to cut off the material as soon as possible with rough turning, and then finish turning.

b. Consider the strength of the tool tip: low strength tools are often used in computer gongs and lathes to process small grooves.

Plane contour parts

Commonly used computer gong milling machine processing. It should be noted that:

a. Cut in and cut out direction control: radial cut in, there are pits on the surface of the workpiece; horizontal cut in and cut out, the surface of the workpiece is smooth.

b. First approximation method selection: when machining irregular curve contour, the computer gong machine tool with only linear and circular interpolation function needs to use small linear segment or circular segment to approximate the machined contour (its error is called first approximation error). When approaching, the workpiece error should be within the qualified range, and the number of program segments should be less.

In the production and processing, there are two main forms: solid heat treatment and melt heat treatment. There is a certain difference between the two ways to make precision hardware processing parts. What’s more, they use different steel to make different workpieces.

CNC lathe is composed of bed, headstock, turret feed system, cooling and lubrication system and CNC system. Different from the ordinary lathe, the feed system of CNC lathe is qualitatively different from the ordinary lathe. It does not have the traditional tool box, slide box and change gear frame, but directly uses the servo motor or stepper motor to drive the slide and tool through the ball screw to realize the feed movement. The NC system consists of NC unit, input and output module and operation panel.

(1) Processing methods of precision hardware parts

Solid solution strengthening: because the solute atoms enter into the gap or node of the solvent lattice, the lattice will be distorted and the hardness and strength of the solid solution will be increased. This phenomenon is called solid solution strengthening.
Compound: a new crystal solid structure with metallic properties is formed by the combination of alloy components.

Mechanical mixture: an alloy consisting of two crystal structures. Although it has two kinds of crystals, it is a component with independent mechanical properties.

Ferrite: interstitial solid solution of carbon in a-Fe (body centered cubic iron).
Austenite: interstitial solid solution of carbon in g-fe.
Cementite: stable compound (Fe3C) formed by carbon and iron.
Pearlite: a mechanical mixture of ferrite and cementite (F + Fe3C contains 0.8% carbon)
Ledeburite: a mechanical mixture of cementite and austenite (containing 4.3% carbon) Metal heat treatment is one of the important processes in mechanical manufacturing. Compared with other processes, heat treatment generally does not change the shape and overall chemical composition of the workpiece, but endows or improves the performance of the workpiece by changing the microstructure inside the workpiece or the chemical composition on the surface of the workpiece.

How to electrify CNC machining center

CNC machining center in the process of work, if there is no power on, how to solve the problem

There are two lights on the power supply of CNC machining center unit, one is the power indicator light, which is green, and the other is the power alarm light, which is red. Here, the power supply unit includes the power input unit and the power control part.

First of all, we need to know if the power indicator (green) doesn’t light up when the CNC machining center can’t be connected. The fuse F1 and F2 of the power supply unit have been blown. This is caused by the high input voltage, or the components of the power supply unit itself have been damaged.

The input voltage of CNC machining center is low. Please check the voltage entering the power supply unit. The allowable voltage is ac200v + 10%, 50 Hz ± 1 Hz. The power supply unit is bad, the internal element is damaged, the power indicator light is on, the alarm light also disappears, but the power supply cannot be connected. This is because the power on condition is not satisfied. By the following switch circuit, the conditions of power on are as follows:

There are three conditions for CNC to be connected

First, the source on button is closed.

Second, close the power button.

Third, the external alarm contact is opened.

The alarm light of power supply unit of CNC machining center is on: the fuse of 24 V output voltage is fused, and the + 24 V voltage is used for 1.9 “display screen, as shown in the figure below. Check whether the + 24 V is short circuited to the ground. 2. Poor display / manual data input board.

The above introduction is about how to deal with when the power supply unit of CNC machining center cannot be powered on.

Lathe processing – computer gong processing

Lathe processing is a part of mechanical processing. There are two main processing forms of computer gong processing: one is to fix the turning tool to process the unformed workpiece in rotation, and the other is to fix the workpiece to carry out precision processing through the high-speed rotation of the workpiece and the horizontal and vertical movement of the turning tool (tool holder).

It is easy to ensure the accuracy of each processing surface of the workpiece; during processing, the workpiece rotates around a fixed axis, and each surface has the same rotation axis, so it is easy to ensure the requirements of coaxiality between processing surfaces;
The cutting process is relatively stable; in addition to the intermittent surface, generally, the processing process of Dalang lathe is continuous, unlike milling and planing, in the process of one tool feed, the cutter teeth have multiple cuts in and out, resulting in impact;
It is suitable for finish machining of non-ferrous metal parts; for some non-ferrous metal parts, because of the low hardness and good plasticity of the material itself, it is difficult to obtain a smooth surface with other machining methods;
The cutting tool is simple; turning tool is the simplest one of the cutting tools, which is very convenient for manufacturing, grinding and installation, so it is convenient to select a reasonable angle according to the specific processing requirements

Operation safety of lathe

It is forbidden to put on the protective clothing when the machine is operating. It is forbidden to put on the protective clothing when the machine is operating. It is forbidden to put on the protective clothing when the machine is operating. Must wear a helmet, braids should be put into the hat, not to wear skirts, slippers. Wear protective glasses to prevent eye injury caused by splashing iron chips.
It is necessary to carefully check whether the machine tool operates safely and reliably according to the requirements of no-load operation for 2 ~ 3 minutes, and carefully check whether the machine tool operates safely and reliably.
When loading and unloading chucks and large pieces, check whether there are obstacles around, pad wood to protect the bed surface, and block, hold firmly and frame well. When the car is too heavy, balance should be done according to the weight. The clamping of workpieces and tools should be tightened to prevent workpieces or tools from flying out of the fixture. The chuck wrench and socket wrench should be removed.
When the machine tool is running, it is strictly forbidden to wear gloves to operate; it is strictly forbidden to touch the rotating part of the machine tool with hands; it is strictly forbidden to transfer objects across the lathe during the operation of the lathe. The machine should be stopped to load and unload the workpiece, install the cutter, refuel and clean the chip. Brush or hook shall be used to remove iron filings. Hand cleaning is forbidden.
When the machine tool is running, it is not allowed to measure the workpiece, and it is not allowed to use the hand to brake the rotating chuck; when using sandpaper, it should be placed on the file, and it is strictly prohibited to wear gloves to operate with sandpaper. It is not allowed to use the worn sandpaper, it is not allowed to use the file without handle, it is not allowed to use the brake of the front and back brake, it should go through the intermediate braking process.
The cutting parameters are selected according to the technical requirements of the machine tool to avoid accidents caused by overload of the machine tool.
When cutting, the cutter should be withdrawn when stopping. The center frame must be used for machining long axis of mechanical parts to prevent the workpiece from bending and deforming to hurt people; the length of the bar extending into the head of the bed shall not exceed the vertical axis of the head of the bed, and it shall be processed slowly, and attention shall be paid to protection when extending.
When cutting at high speed, there should be a protective cover. The workpiece and tools should be fixed firmly. When the iron chips splash seriously, a baffle should be installed around the machine tool to isolate it from the operation area.
When the machine tool is running, the operator can’t leave the machine tool. If the machine tool doesn’t work properly, stop the machine immediately and ask the repairman to check and repair it. In case of sudden power failure, shut down the machine immediately and exit the tool from the working position.
When working, you must stand sideways in the operating position, and it is forbidden to face the rotating workpiece.
At the end of the work, cut off the power supply of the machine tool or the main power supply, withdraw the cutting tool and workpiece from the working position, clean and place the tools, clamps and measuring tools used, and clean the machine tool. Now because the automatic lathe processing market is not perfect and sound, small stamping parts market is very mature in some areas.

From the current situation, there are some problems in the automatic lathe processing market, some production capacity is oversupplied, and some stamping plants in the main engine factory can’t put it or hold it.

Measurement error classification – computer gong processing

When manufacturing large batch parts, there are many factors that affect the accuracy of the data in the measurement process. The following small series for us to introduce the measurement error, measurement error can be divided into three categories: random error, systematic error, gross error.

Random error. Under the same condition, the size and direction of the error change when measuring the same measurement, and there is no change rule, this kind of error is random error. The causes of the random errors are the gap and deformation of the measuring instrument, the change of the measuring force, and the judgment error of the visual measurement or estimation. The elimination method is mainly from the source of the error to eliminate (reduce the temperature fluctuation, control measurement force, etc.), but also according to the normal distribution probability budget random error size.
System error. Under the same conditions, the size and direction of errors in repeated measurement of the same measurement remain unchanged. Maybe when the measurement conditions change, the errors change according to certain rules. This kind of error is a system error. The causes of system errors include inaccurate calibration of measuring tools or measuring instruments, errors in proofreading of measuring tools or measuring instruments, and the ambient temperature is not at 20 ℃ during fine measurement. There are several ways to eliminate system errors. Before measurement, it is necessary to verify all measuring instruments, which should be corrected according to regulations to eliminate errors. Dongguan high speed computer gong processing, to ensure that the scale alignment zero, it is necessary to measure before carefully checking measuring tools to ensure the accuracy of the requirements.
Gross error. Gross errors are errors that obviously distort the measurement results. The reason for this kind of error is that the measuring staff will not concentrate and ignore the carelessness, such as reading error, recording error, calculation error, and other abnormal disturbing factors from the outside world. Measurement values with gross errors are called bad values, which probably need not be eliminated.
The oxide scale of the parts shall be removed. There shall be no scratch, scratch and other defects on the surface of the parts, and the burr and flash shall be removed;
After quenching and tempering, the parts are subjected to high-frequency quenching, tempering at 350-370 ℃, hrc40-45, carburizing depth of 0.3mm, and high-temperature aging treatment.
The undeclared shape tolerance should meet the requirements of gb1184-80, the allowable deviation of undeclared length dimension is ± 0.5mm, and the casting tolerance zone is symmetrical to the basic dimension configuration of the blank casting;
The fillet radius R5 is not noted, the chamfer is 2 × 45 ° and the acute angle is blunt;
The temperature shall not exceed 100 ℃. After the gear is assembled, the contact spot and backlash on the tooth surface shall comply with the provisions of GB10095 and gb11365;
When assembling the hydraulic system, it is allowed to use sealing filler or sealant, but it should be prevented from entering the system. The parts and components (including purchased parts and outsourcing parts) that enter the assembly must have the qualification certificate of the inspection department before they can be assembled.

How to choose CNC machine tool system

The numerical control system includes numerical control device, feed drive (feed speed control unit and servo motor), spindle drive (spindle speed control unit and spindle motor) and detection element. The selection of numerical control system should include the following contents.

Selection of numerical control device

(1) Selection of types

Generally speaking, CNC drilling, milling, EDM and other devices should be selected according to their types.

(2) The choice of performance

The performance of different CNC devices varies greatly. The number of input control axes is single axis, 2 axis, 3 axis, 4 axis, 5 axis, or even more than 10 axis, 20 axis; the number of linkage axes is 2 or more than 3 axis, the maximum feed speed is 10m / min, 15m / min, 24m / min, 240m / min; the resolution is 0.01mm, 0.001mm, 0.0001mm. According to the actual needs of machine tools, for example, 2-axis or 4-axis (double turret) control should be selected for general turning, and more than 3-axis linkage should be selected for plane parts processing.

(3) Function selection

A numerical control system has many functions, including the basic function — the essential function of the numerical control device; the selection function — the function for the user to choose. Some of the selection functions are to solve different processing objects, some to improve processing quality, some to facilitate programming, some to improve operation and maintenance performance. Some of the selection functions are related, and you have to select another one to select this one. Therefore, it is necessary to select according to the design requirements of the machine tool, not without analysis, but with too many steps to select the function, and the relevant functions are omitted, which will reduce the function of the CNC machine tool and cause unnecessary losses.

There are two kinds of PLC in the selection function: built-in PLC and independent PLC. It is better to choose the built-in type, which has different models. First of all, it should be selected according to the number of input and output signals between the numerical control device and the machine tool. The selected points should be a little more than the practical points. One cup may meet the needs of adding and changing the control performance. Secondly, the size of sequential program should be estimated and the storage capacity should be selected. With the increase of the complexity of the machine tool, the storage capacity of the program increases, which should be reasonably selected according to the specific situation. There are also processing time, command function, timer, counter, internal relay and other technical specifications, the number should also meet the design requirements.

(4) Xu Ze of price

Different countries, different manufacturers of numerical control devices, produce different specifications of products, the price is very different, should meet the control type, performance, function selection, on the basis of comprehensive analysis of the performance price ratio, choose the numerical control device with high performance price ratio, in order to reduce the cost.

(5) The choice of technical service

When selecting the CNC device that meets the technical requirements, we should also consider the reputation of the manufacturer, whether the product instructions and other documents are complete, and whether the users can be trained in programming, operation and maintenance personnel. Whether there is a special technical service department to provide long-term spare parts and timely maintenance services, so as to give full play to technical and economic benefits.

Selection of feed drive

(1) AC servo motor is preferred, because it has small inertia, good dynamic response, large output power, high speed, simple structure, low cost and unlimited application environment compared with DC motor.

(2) Through the correct calculation of the load conditions on the motor shaft to select the appropriate specifications of the servo motor.

(3) The feed drive manufacturer provides a series of complete products for the feed speed control unit and servo motor, so after the servo motor is selected, the corresponding speed control unit is selected by the product manual.

Selection of spindle drive

(1) The mainstream spindle motor is preferred, because it does not have the limitation of commutation, high speed and large capacity as DC spindle motor, has large range of constant power speed regulation, low noise and low price. At present, 85% of CNC machine tools are driven by AC spindle.

(2) Select the spindle motor according to the following principles:

① According to different machine tools to calculate the cutting power, the selected motor should meet this requirement; ② according to the required spindle acceleration and deceleration time, the calculated motor power should not exceed the maximum output power of the motor; ③ when the spindle is required to be frequent The output power of the motor must be within the range of the required constant power and the constant speed of the surface, which should be controlled continuously.

(3) The spindle drive manufacturer provides a series of complete products for the spindle speed control unit and the spindle motor, so after the spindle motor is selected, the corresponding spindle speed control unit is selected by the product manual.

(4) When the spindle orientation control is needed, the position encoder or magnetic sensor is selected to realize the spindle orientation control according to the actual situation of the machine tool.

Selection of detection elements

(1) According to the position control scheme of the CNC system, the linear displacement of the machine tool is measured directly or indirectly, and the linear or rotary detection elements are selected. At present, the closed-loop pulse rotary encoder and rotary transformer are widely used for angle measurement

(2) According to the accuracy or speed required by CNC machine tools, the position or speed detection elements (test generator, pulse encoder) are selected. Generally speaking, large machine tools mainly meet the speed requirements, while high-precision, medium and small machine tools mainly meet the accuracy requirements. The resolution of detecting element is generally one order of magnitude higher than the machining accuracy.

(3) At present, the photoelectric pulse encoder is the most commonly used detection element of CNC machine tools. It selects the corresponding specifications of pulse encoder according to the ball screw pitch of CNC machine tools, the minimum moving speed of CNC system, command rate and detection rate.

(4) When selecting the detecting element, the corresponding interface circuit of the numerical control device should be considered.