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Computer gong processing – Measurement

3.2. Inspection standards before processing:

3.2.1. Divide the center and read the number. After each division, copy the working coordinates first, and then check again whether the distance from the center to both sides is consistent, to ensure that the center and reading are correct.

3.2.2. Tool selection, tool loading, tool setting and z-axis coordinate reading.

Select the appropriate tool according to the programming list. Clean the cutter head and nozzle thoroughly before installing the tool. After installing the tool, use the calibration table to check whether the tool has deflection. It is necessary to check again after the tool is set and the number is read, so as to avoid the wrong knife, which will bring great loss to the company.

3.2.3. transport program, start processing: before cutting, use single section execution, transfer speed and feed speed to the slowest, slow down the knife, watch the machine tool display Z axis allowance, check whether there is abnormal, if abnormal, press the pause button immediately, find out the reason to solve the anomaly, confirm that after normal, adjust to the right speed to start processing.

3.2.4. In the process of processing, always pay attention to observe whether the processing is abnormal and whether the tool is worn. If the tool wear is serious, the tool grinding shall be suspended to ensure the normal processing.

3.3. Mold kernel processing standards

3.3.1. After getting the drawing and workpiece, check whether the drawing is consistent with the die number of the workpiece.

3.3.2. Measure the actual size of the workpiece with measuring tools.

3.3.3. Check whether the direction of water transportation and reference angle on 2D drawing is consistent with that on the programming list.

3.3.4. Remove the rough edges at the bottom and around the workpiece with a 400 ා oilstone, and wipe the workpiece with cloth scraps.

3.3.5. Place the workpiece on the clamping tool of the machine platform, level the workpiece plane and perpendicularity with parallelism, and the perpendicularity tolerance is within ± 0.015,

Then fix the workpiece firmly and start to divide according to the position marked on the programming list and the size of z-axis collision. (pay attention to whether the edge finder collides with the workpiece during the separation) input the data of the mechanical coordinates x, y, Z into the corresponding coordinates.

3.3.6. According to the programming list, transfer all programs into the computer, simulate with the tool path simulation software, observe the processing area and the highest and lowest depth of processing, and determine the clamping direction, clamping reserved position and tool length of the workpiece.

3.3.7. Install the corresponding tool according to the programming list, and input the tool parameters automatically with the method of automatic tool setting.

3.3.8. Transfer the program to the machine for processing.

3.4. Copper processing standard

3.4.1. After getting the program sheet, find the appropriate copper material according to the mold number, size and quantity of copper on the program sheet.

3.4.2. According to the requirements of the programming list, process the coarse and young products. (the copper material is marked with a code, “a” stands for Yougong, and “B” for coarse material.

3.4.4. Check whether the tool on the program list is consistent with the tool on the machine tool magazine.

The program is simulated with tool path simulation software to observe the processing area and the highest and lowest machining depth to determine the clamping direction, reserved position and tool length of copper male.

3.4.5. Transfer the program to the machine for processing. The workpiece must be prepared for the next machine in the processing, so as to reduce the above preparation time.

3.5. Formwork processing standards

3.6.1. After the workpiece is processed, check whether the shape of the workpiece is consistent with that of the 3D drawing before getting off the machine, and then check whether the workpiece has missed processing, over cutting, and the position of joint connection.

3.6.2. According to the data marked on the programming list, use the calibration table or depth meter to measure the number, and use the needle gauge or plug gauge to measure some matching positions and positioning positions.

3.6.3. Parting surface measurement: according to the data provided by drawings or programmers, detect the coordinates of points (x, y, z) on several parting surfaces, and check whether the parting surface has been processed to the number.

3.6.6. Measure whether the depth of all flat positions reaches the number. For some positions that need to be connected smoothly, the processing shall be improved first, and then the connection shall be carried out slowly after painting the color on the connecting position.

3.6.7. Check all other position data that require CNC machining accuracy and confirm that it is OK before getting off the machine.

3.7 precautions:

3.7.1. Be careful when taking out the tool from the tool holder to avoid scratching fingers.

3.7.2. Do not allow the machine to run fully automatically when using the NC program that has not been tried out.

3.7.3. When the shaft is still rotating, adjust the coolant flow direction with great care.

3.7.4. In case of emergency, press the red emergency button on the controller.

Computer gong processing – knife alignment

The feed machining route of CNC lathe refers to the path that the tool moves from the point of alignment (or fixed origin of machine tool) until it returns to the point and ends the machining procedure, including the path of cutting and the path of cutting tool cutting and cutting out.

The feed route of finishing is basically carried out in the order of the outline of parts. Therefore, the key to determine the feed route is to determine the feed route of rough machining and empty stroke.

In the NC lathe processing, the determination of the processing route should follow the following principles.

① The accuracy and surface roughness of the workpiece to be processed shall be guaranteed.

② The shortest processing route, reducing the time of empty travel and improving the processing efficiency.

③ The work of numerical calculation and the processing procedure are simplified as much as possible.

④ For some reuse programs, subroutines should be used.

CNC advantages and disadvantages CNC machining has the following advantages:

① A large number of tooling is reduced, and complex tooling is not needed for parts with complex shapes. To change the shape and size of parts, only the part processing procedure needs to be modified, which is suitable for the development and modification of new products.

② The machining quality is stable, the processing precision is high, the repetition precision is high, which is suitable for the machining requirements of the aircraft.

③ The production efficiency is high under the condition of multi variety and small batch production, which can reduce the time of production preparation, machine tool adjustment and process inspection, and reduce the cutting time due to the use of the best cutting quantity.

④ The complex profile which can be processed by conventional methods is difficult to process, and even some parts which cannot be observed can be processed.

The disadvantage of NC machining is that the machine tool equipment is expensive, and it requires the maintenance personnel to have a high level.

Computer gong processing — milling head

1、 Computer gong processing — milling head of computer gong:

The milling head part is composed of two parts: a stage (or stepless) gearbox and a milling head. The main shaft of Dongguan high-speed computer gong machining milling head is supported on high-precision bearing to ensure high rotation accuracy and good rigidity of the spindle. The spindle is equipped with a quick tool change nut, and the front cone adopts 105 taper. The spindle adopts mechanical stepless speed change, which has wide adjustment range, stable transmission and convenient operation. The brake mechanism can make the main shaft brake quickly, which can save auxiliary time. When braking, the main shaft can be braked immediately by expanding the stop ring through the brake handle. When starting the main motor, attention should be paid to loosening the spindle brake handle. The milling head part is also equipped with servo motor, inner toothed belt pulley, ball screw pair and spindle sleeve. They form a vertical (Z-direction) feed transmission chain to make the spindle move in a vertical straight line.

The table and the saddle are supported on the wide horizontal guide rail of the lifting table, and the longitudinal feed of the table is driven by a servo motor installed at the right end of the table. The precision ball screw is driven by the inner toothed belt wheel, so that the worktable can obtain longitudinal feed. The left end of the table is equipped with a hand wheel and a dial for manual operation. Turclle B is used on the longitudinal and transverse guide rail surfaces of the bed saddle, so as to improve the wear resistance, stability and accuracy of the guide rail, and eliminate the phenomenon of low-speed crawling.

2、 Computer gong processing: the main functions of computer gong are as follows:

Point position control function the point position control of CNC milling machine is mainly used for hole processing of workpiece, such as center drill positioning, drilling, reaming, countersinking, reaming and boring.
The continuous control function can mill the plane and surface of the workpiece through the linear interpolation, circular interpolation or complex curve interpolation of the CNC milling machine.
Tool radius compensation function of Dongguan mold processing.
If programming directly according to the workpiece contour line, the actual contour line will be larger than the cutter radius value when machining the inner contour of the workpiece; when machining the outer contour of the workpiece, the actual contour line will be reduced by another tool radius value. Using the method of tool radius compensation, the NC system automatically calculates the tool center path, which makes the tool center deviate from the workpiece contour by one tool radius value, so as to process the contour meeting the drawing requirements. By using the function of tool radius compensation, the tool radius compensation can be changed, and the tool wear and machining error can be compensated to realize the rough machining and finish machining of workpiece.
The tool length compensation function can change the compensation amount of tool length. The machining of Dongguan Mechanical parts can compensate the length deviation after tool change, change the plane position of cutting process, and control the axial positioning accuracy of the tool.
The fixed cycle processing function can simplify the processing program and reduce the workload of programming by applying the fixed cycle processing instructions.
Subroutine function if the same or similar parts of the workpiece are processed, it is written into a subroutine, which is called by the main program, so as to simplify the program structure. CNC machining is divided into several modules according to the working procedure of the machining process. Subprograms are written respectively and called by the main program to complete the processing of the workpiece. This modular program is easy to debug and optimize the processing technology.

Computer gong oil leakage

(1) Influence of clearance factor

The leakage is directly proportional to the size of the seal gap, and the larger the gap, the greater the leakage.

(2) Influence of internal and external pressure difference

The leakage is directly proportional to the internal and external pressure difference of the seal, and the greater the pressure difference, the greater the leakage.

(3) Influence of medium viscosity

The leakage of computer gong processing is inversely proportional to the viscosity of medium. The smaller the medium viscosity, the easier the leakage occurs.

(4) Effect of seal length

In the gap damping, the leakage is inversely proportional to the seal length. The larger the seal length is, the less likely it is to leak.

(5) Influence of ambient temperature

The leakage rate is directly proportional to the ambient temperature. Generally, with the increase of temperature, the viscosity of liquid medium becomes thinner, and the molecular motion of gaseous medium intensifies, which makes the leakage increase.

(6) Performance influence of sealing materials

Including the compactness, pressure flexibility, wear resistance, aging resistance, corrosion resistance, high temperature resistance and processability of the material, the change of leakage condition can be determined.

(7) The velocity effect of relative motion

In rotating shaft or reciprocating movement of the seal, high-speed computer gongs processing its relative speed has the greatest impact on the leakage. Generally speaking, the higher the rotating speed of the rotating shaft, the faster the medium leakage. Moreover, in reciprocating motion, the leakage of medium is also related to the direction of motion.

(8) Influence of vibration and shock on machine tools

The vibration and impact produced by the machine itself or by external forces have a direct impact on the medium leakage.

In order to completely eradicate the oil leakage phenomenon of machine tools, attention should be paid to all aspects of design, manufacturing, use and maintenance. Dongguan Mechanical parts processing ensures that the work in each stage fully meets the requirements of relevant standards. In the actual work of CNC machining, it is necessary to investigate and study the leakage of existing equipment, find out the parts of oil leakage, analyze the causes of oil leakage, and take effective measures At the same time, information feedback should be done to ensure that the same leakage problem will not happen again.

CNC Machining Shop

CNC Machining Shop. CNC Machining Shop is a China CNC precision machining manufacturer and Chinese CNC machining company with state-of-the-art CNC manufacturing factory based in China. We provide custom 3-5 axis CNC Machining Services, CNC milling services, CNC turning services and manufacture CNC Machined Parts in our China precision CNC machining factory.

On the processing of computer gongs

Computer numerical control: computer numerical control, referred to as CNC, generally known as CNC abroad, rarely use the concept of NC. Numerical control machine tools refers to the machine tools equipped with computer numerical control system, referred to as CNC machine tools. We have seen CNC machines, but we don’t understand them very well. Let’s take a look at CNC precision parts processing machine tools.

It usually controls the position, angle, speed and other mechanical quantities and the switch value related to the mechanical energy flow direction. The generation of numerical control of computer gong machining depends on the emergence of data carrier and binary data operation. In 1908, the perforated sheet metal interchangeable data carrier came out; at the end of the 19th century, the paper-based control system with auxiliary functions was invented; in 1938, Shannon carried out fast data calculation and transmission at MIT, laying the foundation for modern computers, including computer digital control systems. The numerical control technology of high-speed computer gong machining is developed in close combination with machine tool control. In 1952, the first CNC machine tool came out, which became a great pioneering work in the history of world machinery industry.

characteristic

Compared with ordinary machine tools, CNC precision parts machining machine tools have the following characteristics:

High machining precision and stable machining quality;

It can carry out multi coordinate linkage and process parts with complex shapes;

When the machining parts are changed, only the NC program needs to be changed, which can save the production preparation time;

The machine tool itself has high precision and rigidity. It can choose favorable processing amount and high productivity (generally 3 ~ 5 times of ordinary machine tool);

High degree of automation of machine tools can reduce labor intensity;

Mass production, easy control of product quality;

The requirements for the professional quality of operators are low, and the technical requirements for maintenance personnel are high.

In CNC precision parts processing, the staff should have a very familiar understanding of the machine tool. Mold processing is a kind of artificial intelligence, which is completed by computer control machine tool. The most complex part of the computer gong lies in the control system. The computer processing the computer sends various instructions to control the three axis servo motors of the machine to cooperate with each other according to the established route, so as to process various complex processes and ensure high machining accuracy.

The main component of the body part of the computer gong processing is casting, which is also a major reason affecting the accuracy of the computer gong machine tool. It can even be said that the quality of casting determines the grade of machine tool and the stability of future use. What are the requirements for casting manufacturing, that is, no deformation and enough rigidity. CNC machining does not deformation refers to the actual processing process after leaving the factory, the accuracy of the machine tool remains good, deformation will affect the accuracy. The machining rigidity of mechanical parts is enough for the machine tool to meet the needs of heavy chip processing.

Turn milling compound machining

According to the accuracy requirements, that is, the dimensional accuracy, positioning accuracy and surface roughness of the workpiece, the control accuracy of the CNC lathe is selected. Reliability is the guarantee to improve product quality and production efficiency. The reliability of CNC machine tool means that the machine tool can run stably for a long time without failure when it performs its functions under specified conditions. That is, the average time between failures is long, even if there is a fault, it can be recovered in a short time and put into use again. Select the machine tools with reasonable structure, excellent manufacturing and mass production. Generally, the more users, the higher the reliability of CNC system.

Turning center 2. Machine tool accessories and tool selection

Machine tool accessories, spare parts and their supply capacity, cutting tools are very important for CNC lathes and turning centers that have been put into production. When selecting machine tools, the matching of tools and accessories should be carefully considered.

Pay attention to the identity of control system

Manufacturers generally choose the same manufacturer’s products, at least the same manufacturer’s control system, which brings great convenience to the maintenance work. Teaching units, due to the need for students to be knowledgeable, choose different systems, equipped with a variety of simulation software is a wise choice.

Select according to the performance price ratio

Do not idle and waste functions and accuracy, and do not choose functions irrelevant to your own needs.

Protection of machine tool

If necessary, the machine tool can be equipped with fully enclosed or semi enclosed protective devices and automatic chip removal devices.

When selecting CNC lathe and turning center, the above principles should be considered comprehensively.

Determine the process requirements of typical parts and the batch of processed workpieces. The function of NC lathe is to prepare well in the early stage, and the precondition of reasonable selection of CNC lathe meets the process requirements of typical parts.

The process requirements of typical parts are mainly the structural size, processing range and precision requirements of the parts. According to the accuracy requirements, that is, the dimensional accuracy, positioning accuracy and surface roughness of the workpiece, the control accuracy of the CNC lathe is selected. Reliability is the guarantee to improve product quality and production efficiency. The reliability of CNC machine tool means that the machine tool can run stably for a long time without failure when it performs its functions under specified conditions. That is, the average time between failures is long, even if there is a fault, it can be recovered in a short time and put into use again. Select the machine tools with reasonable structure, excellent manufacturing and mass production. Generally, the more users, the higher the reliability of CNC system.

Turning center 2. Machine tool accessories and tool selection

Pay attention to the identity of control system

Select according to the performance price ratio

Do not idle and waste functions and accuracy, and do not choose functions irrelevant to your own needs.

Protection of machine tool

If necessary, the machine tool can be equipped with fully enclosed or semi enclosed protective devices and automatic chip removal devices.

When selecting CNC lathe and turning center, the above principles should be considered comprehensively.

Firstly, determine the process requirements of parts and the batch of processed workpieces, draw up the functions that the CNC lathe should have, prepare well in the early stage, and reasonably select the preconditions of CNC lathe to meet the process requirements of typical parts. The process requirements of typical parts mainly include the structural dimension, processing range and precision requirements of the parts. According to the accuracy requirements, that is, the dimensional accuracy, positioning accuracy and surface roughness of the workpiece, the control accuracy of the CNC lathe is selected. Reliability is the guarantee to improve product quality and production efficiency. The reliability of CNC machine tool means that the machine tool can run stably for a long time without failure when it performs its functions under specified conditions. That is, the average time between failures is long, even if there is a fault, it can be recovered in a short time and put into use again. Select the machine tools with reasonable structure, excellent manufacturing and mass production. Generally, the more users, the higher the reliability of CNC system. General import system has Japan Sanling, farnac, Germany’s Siemens, domestic Guangshu, Kandi, new generation more commonly used

CNC lathe processing materials are: 304, 316 stainless steel, carbon steel, copper, aluminum, alloy, plastic, POM, etc. However, the products of different materials need to choose different quality cutting tools to ensure the accuracy required by each product. Composite machining is one of the most popular machining technologies in the field of mechanical processing. It is an advanced manufacturing technology. Compound machining is to realize several different processing technologies on one machine tool. Compound machining is the most widely used and the most difficult one is turn milling compound machining. Turning milling compound machining center is equivalent to the compound of a CNC lathe and a machining center.

At present, most of the turn milling compound machining is completed on the turning center, while the general turning center only changes the ordinary turret turret of CNC lathe into the turret turret with power tool, and the spindle adds the c-axis function. Due to the limitation of turret structure and dimension, the power of power head is small, and the speed is not high

CNC engraving and milling machine

The spindle speed of engraving and milling machine is high, which is suitable for processing small cutting tools, and its torque is relatively small. It focuses on the “carving” function, such as wood (wood carving machine for special processing of wood), dual color board, acrylic plate and other plates with low hardness. It is not suitable for CNC processing of large workpieces with strong cutting. At present, most of the products marked with engraving machine banner are mainly for processing handicrafts with low cost, Due to the low precision, it is not suitable for mold development, but there are also exceptions, such as wafer engraving machine. Advantages: it can carry out relatively small processing and high machining accuracy. High speed machining is possible for soft metals; disadvantage: heavy cutting is not possible due to poor rigidity.

Troubleshooting of CNC engraving and milling machine

（1） . usage environment

CNC engraving and milling machine is a high-tech mechatronics equipment, which has certain requirements for the working environment.

The voltage is required to be stable and avoid large fluctuation. It is better to use voltage regulator.
The machine should not work in strong acid and alkali environment for a long time.
Avoid strong electricity, strong magnetism and other equipment that seriously affect the signal transmission of engraving and milling machine. Such as: welding machine, launch tower, etc.
Use three core power supply to ensure good grounding of engraving and milling machine and reduce interference.

（2） . processing problems

Operators

The proficiency and sense of responsibility of operators also have a great impact on the machining accuracy.

Wear and tear of the machine

CNC engraving and milling machine wear is inevitable in the process of use, with the passage of time, machine wear will reduce the accuracy of the machine.

Rationality of processing technology

In addition to CNC engraving and milling machine to ensure the machining accuracy, reasonable processing technology is also very important. CNC machining in order to ensure the accuracy of processing, please pay attention to the rationality of the processing technology.

Tool use

The machining accuracy is affected by the manufacturing process and accuracy of the tool itself. Therefore, please select the suitable tool for machining.

（3） . maintenance and maintenance

CNC engraving and milling machine is mostly used in processing business, which produces a lot of powder foam and dust. During use, attention should be paid to keep the screw rod, polished rod and other parts clean and lubricated, timely clean up the dust and add oil to the transmission parts; the operator should clean and add oil in time, and it is strictly forbidden to plug and plug with electricity.

（4） . software usage problems

There are many engraving and milling software for CNC engraving and milling machine. In order to meet your engraving and milling requirements, please select the correct operation software. At present, most enterprises in CNC cutting machine tool industry rely on reducing the product price to obtain the market. The result is that the product price is low, the added value is low, the profit is low, and the enterprise does not have enough funds for sustainable development. Low price competition, imitation and OEM production are limited to a certain historical stage. With the development of the industry and the upgrading of competition, it is the best choice for enterprises to improve the technical content of products, have independent patents and designs, and pay attention to brand building and marketing.

The decorative development trend of CNC machine tools can be seen. CNC cutting machine tools emphasize more on mechanical properties, simple operation, economic price, stable processing accuracy and so on. Nowadays, with the increasing demand for popularization and batch processing of metal materials, CNC cutting machine tools should not only meet the above functions, but also have the applicability of multiple cutting methods. At present, CNC cutting machine tools can be divided into flame cutting and plasma cutting. In recent years, with the continuous improvement of downstream industry demand, the CNC machine tool accessories put forward greater demand and higher requirements.

It is understood that the next few years will be the high-speed development and shock period of CNC machine tool industry. The direct consequence of this high-speed shock is that the polarization trend in the current decoration CNC machine tool brand camp is more obvious and expanded. CNC machining is expected to be able to survive in the market in the next few years, the number of CNC machine tool enterprises will drop sharply. However, the high-speed vibration of CNC machine tool industry will also bring great opportunities to make the market operation more rational and standardized.

Offset of tool point in computer gong machining

The materials for computer gong machining are usually free cutting steel and copper. The free cutting steel has higher sulfur content and phosphorus content. Sulfur and manganese exist in the steel in the form of manganese sulfide. Manganese sulfide plays a lubricating role in the steel, making the steel easier to cut, thus improving the production progress of lathe bed. So what should be paid attention to when CNC lathe processing?

When aligning the workpiece, it is only allowed to move the chuck by hand or turn on the lowest speed for alignment, and do not turn on the high speed for alignment.
When changing the rotation direction of the spindle, the spindle should be stopped first and then. It is not allowed to change the rotation direction suddenly.
When loading and unloading the chuck, only rotate the V-belt manually to drive the spindle to rotate. It is absolutely forbidden to directly start the machine tool and force it to loosen or tighten. At the same time, a board should be placed on the bed to prevent accidents.
The tool installation should not extend too long, the gasket should be flat and straight, and the width should be consistent with the width of the tool bottom surface.

In order to set the knife conveniently, the imaginary point P is often used to set the knife. If there is no tool tip radius compensation, undercut will occur when turning cone or arc. When the accuracy of the part is high and there is a cone or arc, the solution is to calculate the trajectory size of the tool tip arc center, and then compile and calculate the local compensation.

Is the tool position compensation caused by the radius r of tool tip arc when turning dimensional surface. When the tool position compensation is carried out in Z and X directions at the same time, the actual contact point a between the cutting edge and the workpiece moves to the set point P of the tool tip during programming. The compensation amount of R can be calculated by the following formula: when programming the conical surface of the workpiece, the base point coordinates are the coordinates of the base point of the workpiece contour (Z and x) plus the compensation amount of the radius of the tool tip arc R (DZ and DX), thus solving the problem that there is no compensation for the radius of the tool tip arc Questions. Because there is an arc at the tool tip, the workpiece contour is formed by the tool motion envelope, so the motion path of the tool location does not coincide with the contour of the workpiece. In the full function CNC system, the tool compensation instruction can be used to program conveniently according to the contour size of the workpiece. In the economical CNC system, the path of the cutter location can be calculated according to the contour size of the workpiece and the cutter. According to this programming, it can also be solved by the method of local compensation.

In order to improve the work efficiency and reduce the errors of various operations, the safe operation that should be paid attention to in the process of C is summarized as follows:

Try to install the clamping material first and then the cutting tool to prevent the hand from touching the tool when installing the clamping material. If the tool has been installed, the worktable should first be moved to the outside to ensure that the clamping material will not interfere with the tool, so as to avoid injury or breakage of the tool.
After stopping, it is necessary to observe whether the spindle stops rotating when disassembling the tool.
Don’t hold or pinch the edge of the knife when unloading it to avoid scratching.
In the process of machining mechanical parts, operators are not allowed to observe the cutting position closely to prevent chips from falling into eyes.
The wrench should be placed in the tool storage area after use, not on the y-axis shield or beam.
Before CNC machining, check the position of the oil nozzle before opening the oil pump switch to avoid spraying to other positions when flushing oil.
When suspending observation during machining clearance, the worktable must be moved away from the cutting position.
Inspection. After processing, before disassembling the workpiece, it is necessary to conduct preliminary inspection on the size or appearance of the workpiece. The workpiece can only be disassembled after passing the inspection, so as to avoid positioning problems of secondary processing and scrapping of the workpiece after disassembly. For some key dimension data of the disassembled workpiece, further inspection is needed to meet the requirements.

Surface roughness of computer gongs

Because the spindle speed and range of CNC machine tools are far higher than ordinary machine tools, and the output power of the spindle is large, compared with the traditional processing methods, higher requirements are put forward for the CNC machining tools, including high precision, high strength, good rigidity, high durability, and the size stability, convenient installation and adjustment, and the characteristics of the spindle drive system of CNC machine tools. This requires that the structure of the tool is reasonable, the geometric parameters are standardized and serialized. NC tool is one of the preconditions to improve the machining efficiency. Its selection depends on the geometry of the parts to be processed, the material state, the fixture and the rigidity of the selected tool. The following aspects should be considered:

(1) The cutting tool is selected according to the cutting performance of the part material. If turning or milling high strength steel, titanium alloy, stainless steel parts, it is recommended to select indexable carbide tool with good wear resistance.

(2) Select the tool according to the hardware parts processing stage. That is to say, in the rough machining stage, the cutting tool with better rigidity and lower precision should be selected; in the semi finishing and finishing stage, the machining accuracy and product quality of the parts should be guaranteed; the tools with high durability and high precision should be selected; the precision of the tools used in the rough machining stage is the lowest, while that in the finishing stage is the highest. If the same tool is selected for rough machining and finish machining, it is recommended to select the tool eliminated from finish machining during rough machining, because most of the tool wear out of finishing machining is slight wear on the edge, and coating wear and polishing. Continuous use will affect the quality of finish machining, but the impact on rough machining is small.

(3) According to the characteristics of NC lathe processing area, the tool and geometric parameters are selected. The tool with large diameter and small ratio of length to diameter should be selected if the structure of the part is allowed; the end edge of the cross center milling cutter for cutting thin-walled and ultra-thin-wall parts should have enough centripetal angle to reduce the cutting force of the cutter and cutting parts. When processing aluminum, copper and other soft material parts, the end mill with larger front angle should be selected, and the number of teeth should not exceed 4.

When selecting the tool, the size of the tool should be compatible with the surface size of the workpiece to be processed. In production, end milling cutter is often used for peripheral contour processing of plane parts; when milling plane, carbide blade milling cutter should be selected; when machining boss and groove, high-speed steel end milling cutter should be selected; when hardware processing blank surface or rough machining hole, corn milling cutter with cemented carbide blade can be selected; Ball end milling cutter, ring milling cutter, conical milling cutter and disc milling cutter are often used in the machining of solid surface and variable bevel profile.

In the process of free-form surface machining, because the cutting speed of the ball end cutter is zero, in order to ensure the NC machining accuracy, the cutting row spacing is generally very small, so ball end milling cutter is suitable for surface finishing. The end milling cutter is far better than the ball end milling cutter in both surface processing quality and processing efficiency. Therefore, under the premise of ensuring that the parts can not be cut, the end milling cutter should be selected as far as possible when rough machining and semi finishing surface machining. In addition, the durability and accuracy of cutting tools are closely related to the price of cutting tools. It must be noted that in most cases, although the selection of good tools increases the cost of cutting tools, the improvement of processing quality and efficiency brought about by this can greatly reduce the whole processing cost.

In the machining center, all the tools are pre installed in the tool library, and the corresponding tool change action is carried out through the tool selection and tool change instructions of the NC program. It is necessary to select the corresponding standard tool holder suitable for the machine tool system specification, so that the tool for NC machining can be quickly and accurately installed on the machine tool spindle or returned to the tool magazine. The programmer should be able to understand the structure size, adjustment method and adjustment range of the tool holder used by the machine tool, so as to ensure that the radial and axial dimensions of the tool can be determined and the arrangement order of the tool can be arranged reasonably.

The surface geometric characteristics of NC machining include surface roughness, surface waviness and surface texture. Surface roughness is the basic unit of geometric characteristics of machined surface. When machining workpiece surface with metal cutting tools, surface roughness is mainly affected by geometric factors, physical factors and NC machining process factors.

(1) Geometric factors

From the geometric point of view, the shape and geometric angle of the tool, especially the radius of the tool tip arc, the main deflection angle, the secondary deflection angle and the feed rate in cutting parameters have a great influence on the surface roughness.

(2) Physical factors

Considering the physical essence of the cutting process, the metal material plastic deformation is caused by the corner of the cutting edge and the extrusion and friction behind the tool, which seriously worsens the surface roughness. When the plastic material is processed by numerical control lathe to form strip chip, it is easy to form chip accretion with high hardness on the rake face. It can replace the rake face and cutting edge for cutting, so that the geometric angle of the cutter and the back feed can be changed. The contour of the chip accretion is very irregular, so that the depth and width of the workpiece surface are constantly changing. In CNC machining, some chips are embedded in the workpiece surface, which increases the surface roughness. The vibration during cutting increases the surface roughness parameters.

(3) Technological factors

From the perspective of technology, the influence on the surface roughness of metal parts is mainly related to cutting tools, workpiece materials and CNC processing conditions.