chengcg – Page 36 – CNC Machining & Turning, Milling, Metal parts

CNC computer gong processing mold precision concept

Strengthen the understanding of mold precision concept

Die is a kind of precision forming tool used for batch forming, stamping and other products. Mold accuracy includes the accuracy of parts obtained in processing and the quality awareness of ensuring the accuracy of products in production, but generally speaking, mold accuracy mainly refers to the accuracy of working parts of mold.

① The concept of precision in mold processing refers to the degree of conformity between the actual geometric parameters and the design geometric parameters after the mold parts are processed and assembled.

② The concept of precision in mold production refers to a thinking mode and a quality consciousness formed gradually by enterprise employees in production practice to guide their production behavior. That is to say, the quality consciousness of grasping product precision is always carried out in the behavior of enterprise employees.

The mold precision includes four aspects: dimension precision, shape precision, position precision and surface precision. Because the mold is divided into two parts: upper mold and lower mold, the position accuracy between the upper mold and the lower mold is the most important among the four kinds of accuracy.

When the machining accuracy is very high, the mold often has more than enough force. Now the precision of a very good precision mold is about 0.1 ~ 0.01mm. Compared with the previous mold, the precision has been greatly improved. However, components such as engines require an accuracy of less than one thousandth of a millimeter, or even less. Therefore, it is impossible to completely replace cutting with mold now.

Difficulties in CNC machining stainless steel parts

The main difficulties are as follows: 1. Large cutting force, high cutting temperature of mechanical parts; high strength of this type of material, large tangential stress and plastic deformation during cutting, so the cutting force is large. In addition, the extremely poor thermal conductivity of the material causes the cutting temperature to rise, and the high temperature is often concentrated in the narrow area near the cutting edge, thus speeding up the tool wear.

Severe work hardening of stainless steel parts — austenitic stainless steel and some high temperature alloy stainless steel are austenitic structure, and the tendency of work hardening is large when cutting, which is usually several times of that of ordinary carbon steel. Cutting tools in the work hardening area shorten the tool life.
Stainless steel parts are easy to stick to the tool when machining — both austenitic stainless steel and martensitic stainless steel have the characteristics of strong chip and high cutting temperature. When the strong and tough chips flow through the rake face in the machining of Dongguan Mechanical parts, there will be adhesion, fusion welding and other adhesion phenomena, which will affect the surface roughness of the machined parts.
The tool wear of stainless steel parts is accelerated – the above materials generally contain high melting point elements, high plasticity and high cutting temperature. CNC machine tool processing accelerates the tool wear, and tool grinding and changing are frequent, which affects the production efficiency and improves the tool cost.

Precision inspection technology of CNC parts processing

In the selection of CNC complex parts processing, the best way, of course, is through a variety of ways to compare, so as to select the best quality CNC. Optical aspheric surface testing technology should be able to quickly judge the surface error in the process of mirror processing, give further correction instructions by random feedback, and solve the final inspection of parts.

At present, the most widely used method of aspheric surface measurement is light wave interferometry, which has higher measurement accuracy and better spatial resolution. It can measure the whole surface quickly, and the highest resolution can reach sub nanometer level. But for different optical aspheric surfaces, the corresponding optical template must be prepared to measure. The structure of this measurement system is usually very complex.

Aspheric surface can be measured by holographic interferometry, but a hologram must be made whether standard aspheric surface or CGH is used, and there must be corresponding holograms for aspheric surface with different equations. But up to now, the domestic technology of making hologram is only limited to some traditional technology, and the hologram for ultra precision measurement of aspheric surface basically depends on imports, which greatly limits the testing and processing of optical aspheric parts. At present, it costs about US $10000 to import a hologram for ultra precision measurement of aspheric surface, and we need to tell each other the equation of aspheric surface. For the model task, it involves confidentiality and other issues. Especially for some pre research or in research projects and unformed projects, due to the large variety and quantity of aspheric surfaces involved, the cost is very considerable, so it is urgent to develop the hologram for aspheric surface measurement.

At present, the most advanced technology abroad is to use computer generated hologram ram for aspheric surface measurement and laser writing system to make hologram, which not only greatly reduces the production cost, but also shortens the production cycle. The most typical prototype is the laser plotter clws300 laser engraving system developed by Stuttgart University in Germany. The diameter of laser recording point is 0.5 μ m, the positioning accuracy of radial coordinate is 0.08 μ m (RMS), and the positioning accuracy of angular direction is 0.1s “(RMS).

The high precision laser engraving system mainly includes the following aspects

Optical part: including laser, acousto-optic modulator, auto focusing system and the overall design and layout of optical path, etc;

Mechanical part: high precision air bearing, high precision motion guide rail, vibration isolation platform, etc;

Electric control part: motion and positioning control of high-precision mechanical system, laser, modulator and automatic focusing control, including coordination control of mechanical and optical systems

Method of deburring in CNC machining

This is to use electric energy and chemical energy to dissolve the anode and remove the burr. The anode is between the part and the positive pole of the DC power supply, and the cathode is between the forming tool and the negative pole of the DC power supply. There is a certain gap between the two poles to make the electrolyte circulate. When the anode and cathode are immersed in the solution and charged with direct current, the electrochemical reaction occurs on the anode surface, the dissolved metal and electrolyte form viscous liquid on the part surface, which is concentrated in the low concave part of the part surface, with higher resistance and less corrosion; while the burr protrudes from the part surface, under the influence of temperature difference, the liquid film is difficult to form, and the power line is highly concentrated in the burr after power on The burr nearest to the cathode will be dissolved at the fastest speed until the burr is completely dissolved, and the edge will gradually form a fillet, that is to achieve the purpose of deburring.

Electrolytic deburring machine can be used. When the production batch is not large, the rectifier can be used to convert alternating current into direct current to make simple equipment. According to the structure of the parts, the special fixture (tool cathode) with similar shape to the parts is made of brass or red copper and other conductive materials, and the unprocessed parts are coated with epoxy resin for isolation and protection. The commonly used electrolytes are NaCl, NaNO2 > and NaNO3.

This method is suitable for non-ferrous and ferrous metal parts, especially for parts with complex shape, inner holes, cross holes and inner surface burr which are difficult to remove by mechanical and manual methods. It can remove burr of extra hard parts such as molybdenum, nickel, titanium and quenched parts. The cleaned metal parts will be put into chemical solution (50 ℃), and the metal on the surface of parts will be transferred to the solution in the form of ions. These ions gather on the surface of the workpiece and form a layer of mucus film with high resistance and low conductivity by chemical reaction to protect the workpiece surface from corrosion, while the burr protrudes from the surface and the chemical action will remove the burr. When processing, only one slot is needed. According to different deburring materials, different chemical solutions are used. The main components of the base can be hydrochloric acid, phosphoric acid, sulfuric acid, dihydroxyaniline hydrochloride and water. Chemical deburring is suitable for small metal parts, which can remove the small burr with thickness less than 0.07 mm.

Milling: refers to the use of rotating multi edge tool cutting workpiece, is an efficient processing method. When the tool rotates (as the main motion) and the workpiece moves (as the feed motion), the workpiece can also be fixed, but at this time the rotating tool must also move (complete the main motion and feed motion at the same time). Milling machines include horizontal or vertical milling machines, as well as large gantry milling machines. These machine tools can be ordinary machine tools or CNC machine tools.

Main processing objects:

1) Plane parts

The characteristics of plane parts are that the surface can be parallel to the horizontal plane, or perpendicular to the horizontal plane, or at a fixed angle with the horizontal plane; at present, the vast majority of parts processed on the CNC milling machine belong to plane parts, and plane parts are the simplest type of parts in CNC milling, generally only need to use the two-axis linkage or three-axis linkage of the three-axis CNC milling machine Linkage can be processed. In the process of machining, the machining surface is in contact with the cutter, and the end milling cutter or nose cutter can be used for both rough and finish machining.

(2) Surface parts

The feature of curved surface parts is that the machined surface is a space curved surface. In the process of machining, the machined surface and the milling cutter are always in point contact. Ball end milling cutter is often used for surface finishing

Process classification of CNC machining parts

The process is to change the shape, size, relative position and nature of the production object on the basis of the process, so as to make it into finished or semi-finished products. It is the detailed description of each step and each process. For example, as mentioned above, rough machining may include blank manufacturing, grinding and so on, and finish machining may be divided into turning, fitter, milling machine, and so on. Each step requires detailed data For example, how much roughness and tolerance should be achieved. According to the product quantity, equipment conditions and workers’ quality, technicians determine the process to be adopted, and write the relevant contents into process documents, which are called process procedures. This is more targeted. Every factory may be different, because the actual situation is different. Generally speaking, the technological process is the program, the processing technology is the detailed parameters of each step, and the technological procedure is the specific processing technology compiled by a factory according to the actual situation.

Machining process includes: five axis machining, ceramic machining, chemical numerical control machining, electrical discharge machining, electrical discharge drilling, numerical control titanium, emergency construction / on-site machining, casting machining, grinding, micro machining (micro parts machining), plastic machining, turning, spiral machining, Swiss turning, CNC machining, etc.

The reduction of loading times avoids the error accumulation caused by positioning datum conversion. At the same time, most of the current turn milling compound processing equipment has the function of on-line detection, which can realize the in-situ detection and precision control of the key data in the manufacturing process, so as to improve the processing accuracy of the product; the high-strength integrated bed design improves the gravity processing ability of the difficult cutting materials; the high-strength integrated bed design improves the processing ability of the hard cutting materials; The machine is equipped with an automatic feeding device, which can realize automatic feeding for continuous operation and basically realize the assembly line operation of a single machine.

Reduce floor space and production cost.

Compact and beautiful shape design, improve the space utilization, maintenance and repair more convenient, so that customers get the maximum satisfaction; Although the single unit price of turn milling compound processing equipment is relatively high, due to the shortening of manufacturing process chain and the reduction of equipment required for products, as well as the reduction of the number of fixtures, the floor area of workshop and equipment maintenance costs, it can effectively reduce the investment, production operation and management costs of the overall fixed assets.

Shorten the manufacturing process chain and improve production efficiency.

It can install a variety of special tools, new tool layout, reduce the tool change time, improve the processing efficiency, turn milling composite processing can achieve a clamping to complete all or most of the processing procedures, thus greatly shortening the product manufacturing process chain. In this way, on the one hand, the auxiliary production time caused by the change of clamping is reduced, and the fixture manufacturing cycle and waiting time are also reduced, which can significantly improve the production efficiency.

Flexible shaft machining

When turning long and thin parts that cannot be supported in the middle, turning milling can prevent the parts from bending. Compared with turning, in theory, milling can cut parts under very small pressure. But in fact, a lot of technical problems need to be solved.

Long time processing

In the cutting of difficult to machine materials, the service life of a turning tool is very short, and the milling cutter can be used for a long time because it distributes the cutting load through multi edge cutting. Because the milling cutter has a long service life, it can save the trouble of changing the cutter many times during cutting.

Discontinuous cutting

Turning tools are usually not very good for discontinuous cutting, while milling tools can do very well. Milling is often defined as a kind of discontinuous cutting. Therefore, in the case of discontinuous cutting, it should be thought of turning to turn milling.

Excellent chip breaking process

It has been proved by many machining practices that turning milling instead of turning can eliminate the “bird’s nest” chip phenomenon in the past. Because the milling process with the advantage of natural chip breaking is combined in cutting, the continuous chips are broken into small pieces which are easy to be eliminated

Machining characteristics of CNC high speed computer gong

Processing characteristics of high speed CNC computer gong

Reasonable selection of equipment. High machining accuracy is required. Roughing is mainly to cut off most of the machining allowance. Rough machining should be carried out on the machine tool with high power and low precision, while finish machining should be carried out on the machine tool with high precision.
In order to ensure the machining accuracy, rough and finish machining should be carried out separately. The amount of cutting is large, because when rough machining. For some parts with high machining accuracy. After roughing and before finishing, low temperature annealing or aging treatment should be arranged to eliminate the internal stress. The cutting force and clamping force of the workpiece are large, the calorific value is large, and there is a significant work hardening phenomenon on the surface of the workpiece. There is a large internal stress in the workpiece. If the rough and rough machining is carried out continuously, the precision of the finished part will be lost quickly because of the redistribution of the stress.
Heat treatment process is often arranged in machining process. In order to improve the mechanical properties of parts, quenching and tempering are generally arranged after machining. The location of heat treatment process is as follows: in order to improve the cutting performance of metal, such as annealing, normalizing, quenching and tempering, it is generally arranged before machining. In order to eliminate the internal stress, such as aging treatment, quenching and tempering treatment, it is generally arranged after rough machining and before finishing.

Requirements of power supply for CNC machine tools

The power supply is the energy support part to maintain the normal operation of the system. The direct result of its failure or failure is the shutdown of the system or the destruction of the whole system. In addition, some operation data, setting data and processing programs of the CNC system are generally stored in the RAM memory. After the power failure of the system, they are maintained by the backup battery or lithium battery of the power supply. As a result, the downtime is relatively long, plug power or memory may cause data loss, so that the system can not run.

At the same time, because the CNC machine tool uses three-phase AC 380V power supply, so the safety is also an important part of the pre installation work of CNC equipment

The fluctuation of power grid voltage should be controlled between + 10% and – 15%. However, the fluctuation of power supply in China is large, the quality of power supply is poor, and the interference such as high-frequency pulse is hidden, plus human factors (such as sudden switch off, etc.). During the peak period of electricity, such as about an hour before going to work or leaving work in the daytime and at night, there are often more out of tolerance, even up to ± 20%. It makes the machine alarm and cannot work normally, and damages the power supply system of the machine. It even leads to the loss of parameter data. This phenomenon has happened in CNC machining center or turning center, and the frequency is high, so we should pay attention to it.

It is suggested that the workshop with more centralized CNC machine tools should be equipped with AC voltage stabilizing power supply system with automatic compensation and regulation function; a single CNC machine tool can be equipped with AC voltage stabilizer separately to solve the problem.

It is recommended to connect mechanical and electrical equipment to a single power supply. If it is necessary to use other power supply to supply some parts of electrical equipment (such as electronic circuit, electromagnetic clutch), these power supply should be taken from the components (such as transformer, transducer, etc.) that are part of mechanical and electrical equipment as far as possible. For large and complex machinery, including many machines that work together in a collaborative way and occupy a large space, more than one power supply may be needed, which depends on the configuration of the site power supply.

Unless the mechanical and electrical equipment is directly connected to the power supply by plug / socket, it is recommended that the power line be directly connected to the power terminal of the power cut-off switch. If this is not possible, a separate terminal block shall be provided for the power cord.

The handle of the power cut-off switch shall be easy to access and shall be installed between 0.6m and 1.9m above the easy operation position. The upper limit is suggested to be 1.7m. In this way, the power can be cut off quickly in case of emergency, and the losses and casualties can be reduced.

CNC equipment for compressed air supply system requirements, CNC machine tools generally use a lot of pneumatic components, so the plant should be connected to clean, dry compressed air supply system network. The flow and pressure should meet the requirements. The compressed air machine should be installed far away from the CNC machine. According to the layout of the plant and the amount of gas consumption, it should be considered to install the chilled air in the coal machine, air filter, gas storage tank, safety valve and other equipment for the compressed air supply system network.
The requirements of CNC equipment for working environment precision CNC equipment generally has the requirements of constant temperature environment, only in constant temperature condition, can ensure the accuracy and processing degree of machine tool. Ordinary CNC machine tools have no specific requirements for room temperature, but a lot of practice shows that when the room temperature is too high, the failure rate of CNC system increases greatly.

Humid environment will reduce the reliability of CNC machine tools, especially in the humid environment with large acid gas, it will rust the printed circuit board and connectors, and increase the electrical failure of machine tools. Therefore, some users in southern China should take dehumidification measures in summer and rainy season.

1) The working environment temperature should be between 0 ℃ and 35 ℃. Computer gong processing, mechanical parts processing, CNC machine tool processing, Dongguan high-speed computer gong processing should avoid direct sunlight on CNC machine tools, and the room should be equipped with good lighting equipment.

2) In order to improve the accuracy of machining parts and reduce the thermal deformation of the machine tool, if possible, the CNC machine tool can be installed in a relatively closed workshop with air conditioning equipment.

3) The relative humidity of working environment should be less than 75%. CNC machine tools should be installed in the place far away from liquid splashing, and prevent plant dripping.

4) Keep away from excessive dust and corrosive gas.

Difficulties in machining stainless steel with CNC lathe

Severe work hardening of stainless steel parts — austenitic stainless steel and some high temperature alloy stainless steel are austenitic structure, and the tendency of work hardening is large when cutting, which is usually several times of that of ordinary carbon steel. Cutting tools in the work hardening area shorten the tool life.
Stainless steel parts are easy to stick to the tool when machining — both austenitic stainless steel and martensitic stainless steel have the characteristics of strong chip and high cutting temperature. When the strong and tough chips flow through the rake face, there will be adhesion and fusion welding, which will affect the surface roughness of machined parts.
The tool wear of stainless steel parts is accelerated – the above materials generally contain high melting point elements, high plasticity and high cutting temperature. CNC machine tool processing accelerates the tool wear, and tool grinding and changing are frequent, which affects the production efficiency and improves the tool cost.

Processing steps of CNC lathe

Introduction of high speed CNC computer gong processing process

Product analysis through product analysis should obtain certain composition information and some specific processing requirements.
Graphic design graphic design should be based on the detailed analysis of the product, determine the type of graphics by analyzing the processing requirements, and draw through the graphics software.
Through the analysis of the appearance and processing requirements of the workpiece products in the early stage of process planning, each processing step is reasonably established from the overall situation of machining.
Path generation the process of path generation is that we realize the process planning by software, and optimize the tool path by setting parameters.
After the path simulation path is generated, we generally have no intuitive sense of its final performance on the machine tool. Here we can check the possible problems through path simulation, so as to reduce the scrap rate of actual processing. The general inspection focuses on the effect of the workpiece appearance, whether it is overcut or undercut, and whether the process planning of the path is reasonable.
Path output path output is a necessary step for software design and programming to realize on the machine tool. Through path output, the intermediate reference can establish a connection between the two. If you have NC professional background, it can also be understood as the post-processing of tool path.

In the whole CNC process, we should focus on the relationship between the processes and the significance of each step. In a broad sense, the whole process of NC machining includes product analysis graphic design process planning path generation path simulation path output processing inspection.

Product analysis through product analysis should obtain certain composition information and some specific processing requirements.
Graphic design graphic design should be based on the detailed analysis of the product, determine the type of graphics by analyzing the processing requirements, and draw through the graphics software.
Through the analysis of the appearance and processing requirements of the workpiece product in the early stage of process planning, each processing step is reasonably established from the overall situation of processing.
Path generation the process of path generation is that we realize the process planning by software, and optimize the tool path by setting parameters.
After the path simulation path is generated, we generally have no intuitive sense of its final performance on the machine tool. Here we can check the possible problems through path simulation, so as to reduce the scrap rate of actual processing. The general inspection focuses on the effect of the workpiece appearance, whether it is overcut or undercut, and whether the process planning of the path is reasonable.
Path output path output is a necessary step for software design and programming to realize on the machine tool. Through path output, the intermediate reference can establish a connection between the two.

Causes of errors in CNC engraving and milling machine

Troubleshooting of CNC engraving and milling machine error

（1） . use environment

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

The voltage should be stable to 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 the equipment that seriously affects the signal transmission of engraving and milling machine, such as strong electricity and strong magnetism. Such as welding machine, transmitting tower, etc.
Use three core power supply to ensure good grounding of engraving and milling machine and reduce interference.

（2） 2. Processing problems

Operators

The proficiency and 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, machine parts processing with the passage of time, machine wear will reduce the accuracy of the machine.

Rationality of processing technology

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

Tool use

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

（3） . maintenance and maintenance

CNC engraving and milling machine is mostly used in processing business, which produces more powder and dust. Pay attention to keep the screw rod, polished rod and other parts clean and lubricated in use, clean the dust and oil the transmission parts in time; the operator shall clean and oil in time, and it is strictly prohibited to plug and pull with electricity.

（4） . software usage

CNC engraving and milling machine has many engraving and milling software for use. In order to meet your carving and milling requirements, please choose the correct operation software.

The continuous operation time is less than 10 hours per day to ensure the cleaning of the cooling water and the normal operation of the water pump. The water spindle motor must not be short of water. The cooling water should be replaced regularly to prevent the water temperature from being too high. If the working environment temperature is too low in winter, the water in the water tank can be changed into antifreeze.
Every time the machine is used, pay attention to cleaning, be sure to clean up the dust on the platform and transmission system, and lubricate the transmission system (x, y, z axes) regularly (weekly). (Note: the X, y, Z three-axis polished rod shall be maintained with engine oil; the screw rod part shall be added with high-speed grease; if the working environment temperature is too low in winter, the screw rod and polished rod (square guide rail or circular guide rail) part shall be washed and cleaned with gasoline first, and then the CNC machine tool shall be used for processing, and then the engine oil shall be added, otherwise the resistance of the machine transmission part will be too large, resulting in the machine dislocation.)
When the electrical appliances are maintained and checked, the power supply must be cut off. It can only be carried out after the monitor has no display and the main circuit power indicator is off.
After about three months of use, the fasteners should be inspected, and the connecting screws on both sides of the gantry, the fastening screws of the lead screw nuts, and the fastening screws of the motors on both sides should be tightened.