Category Archive CNC Technology

CNC system is a numerical control system which uses computer to control machining function. According to the control program stored in computer memory, the CNC system of large-scale CNC machining performs some or all numerical control functions, and is equipped with interface circuit and servo drive device. CNC system consists of NC program, input device, output device, CNC device, PLC, spindle drive device and feed (servo) drive device (including detection device).

The core of CNC system is CNC device. Because of the use of computer, the system has software function, and PLC is used to replace the traditional logic control device of machine tools, which makes the system more compact, flexible, universal, reliable, easy to realize complex CNC functions, easy to use and maintain, and has the function of connecting with the upper computer and remote communication.

CNC high-speed precision parts processing mainly refers to the use of digital information recorded on the media to control the machine tool, so that it can automatically carry out the specified processing tasks. Numerical control machining can ensure the products to achieve high machining accuracy and stable processing quality; the operation process is easy to realize automation; the productivity is high and the production cycle is short; it can greatly reduce the process equipment, adapt to the needs of product rapid update; it is usually closely linked with CAD to realize the transformation of design ideas to the final product. In the whole process of CNC high-speed precision parts processing, students should focus on the relationship between the processes and the significance of each step. In a broad sense, the whole process consists of product analysis, graphic design, process planning, path generation, path simulation, path output, processing and inspection. In this section, a specific case is demonstrated, focusing on understanding the connection of each link. The case processing material is double color plate or plexiglass.

1. Product analysis through product analysis should obtain certain composition information and some specific processing requirements.
2. Graphic design the graphic design should be based on the detailed analysis of the product. For example, for the processing of the seal, we should determine the font, text size, seal type by analyzing the processing requirements.
3. Process planning is based on the analysis of the appearance and processing requirements of the workpiece products in the early stage, so as to reasonably establish each processing step from the overall processing situation.
4. In fact, the process of path generation is to realize the process planning through software, and optimize the tool path by setting parameters.
5. 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, thus reducing the actual processing scrap rate. The general inspection focuses on the effect of workpiece appearance, whether it is overcut or undercut, and whether the process planning of the path is reasonable.
6. Path output path output is a necessary step for software design and programming to realize on the machine tool. Through the path output, the relationship between the two can be established by the intermediate reference. If the students have the professional background of numerical control, they can also understand it as the post-processing of tool path.

1、 The machining accuracy of parts is poor

Generally, the feed dynamics between the shafts are not adjusted according to the error during installation and adjustment, or the transmission chain of each axis of the machine tool has changed (such as the change of lead screw clearance, pitch error, axial movement, etc.) due to wear and tear. It can be solved by readjusting and modifying the clearance compensation. When the dynamic tracking error is too large and an alarm is given, check whether the servo motor speed is too high; whether the position detection element is good; whether the position feedback cable connector is in good contact; whether the corresponding analog output latch and gain potentiometer are in good condition; whether the corresponding servo drive device is normal.

2、 When the machine tool is in motion, it causes poor machining accuracy

It may be that the acceleration and deceleration time is too short, so the speed change time can be appropriately prolonged; or the connection between the servo motor and the lead screw is loose or the rigidity is too poor, which can appropriately reduce the gain of the position ring.

3、 Roundness out of tolerance in two axes linkage

1. Axial deformation of circle

This deformation may be caused by mechanical adjustment. If the positioning accuracy of the shaft is not good or the gap compensation of the lead screw is improper, the roundness error will be produced when the image limit is exceeded.

1. Oblique ellipse error (ellipse in 45 degree direction)

At this time, the position deviation value of each axis should be checked first. If the deviation is too large, adjust the position loop gain to eliminate. Then check whether the interface board of rotary driver or inductosyn is adjusted properly, and then check whether the mechanical transmission pair clearance is too large and whether the gap compensation is appropriate.

1、 What is up milling and up milling of CNC milling machine

The rotation direction of the contact part between the milling cutter and the workpiece is the same as the feed direction of the workpiece, and vice versa. There is always a large or small gap between the nut and the lead screw of the milling machine. With the change of the horizontal milling component force, the table and the lead screw will move left and right. This periodic movement makes the table movement very unstable and easy to cause damage to the cutter teeth. However, the vertical milling component force of the forward milling presses the workpiece to the worktable, and the sliding and friction phenomenon between the cutter tooth and the machined surface is small, which reduces the friction The tool tooth wear, reducing work hardening and surface roughness are favorable. Therefore, when the clearance between the screw and nut of the worktable is adjusted to less than 0.03mm or when milling thin and long workpieces, it is better to use the down milling. In reverse milling, the workpiece is lifted up by the vertical force of milling, and the friction between the cutter tooth and the machined surface is increased. However, the horizontal force of milling is helpful for screw and nut to stick tightly, so that the table movement is more stable, and the cutter tooth wear caused by milling casting and forging is also small. Therefore, the general milling is usually up milling.

2、 Characteristics of down milling and up milling of CNC milling machine

Features of down milling:

In down milling, the cutting thickness of each tool changes gradually from small to large. When the cutter tooth is just in contact with the workpiece, the cutting thickness is zero. Only when the cutter tooth slides over a certain distance on the cutting surface left by the previous cutter tooth, and the cutting thickness reaches a certain value, the cutter tooth can really start cutting. Up milling makes the cutting thickness change from large to small, and the sliding distance of cutter teeth on the cutting surface is also very small. Moreover, the distance of the cutter teeth on the workpiece is shorter than that of the reverse milling. Therefore, under the same cutting conditions, the tool is easy to wear when using up milling. In down milling, the cutter teeth are cut from the surface of the workpiece each time, so it is not suitable for processing the workpiece with hard skin. The average cutting thickness is large and the cutting deformation is small during the down milling, and the power consumption is less than that of the up milling.

Features of up milling:

Because the horizontal cutting force acting on the workpiece by the milling cutter is opposite to the feed movement direction of the workpiece, the screw rod and nut of the worktable can always keep one side of the thread tightly fit. However, it is not the case in down milling. Because the direction of horizontal milling force is consistent with the direction of workpiece feed motion, when the force of cutter teeth on the workpiece is large, due to the existence of the gap between the table screw rod and nut, the table will move, which not only destroys the stability of the cutting process, but also affects the processing quality of the workpiece, and in serious cases, it will damage the cutter. Due to the large friction between the cutter teeth and the workpiece, the cold and hard phenomenon on the machined surface is serious.

Conclusion: both forward milling and reverse milling have their own advantages and determination. The specific milling method should be based on the requirements of the workpiece to be processed. If the surface smoothness is required to be high, the forward milling should be used, and the reverse milling should be used.

There are few and no composite materials processed by machining center, but it is strict to process composite materials with machining center, and there are some precautions:

Now the amount of composite materials has been rising, so the use of machining centers to add composite materials has also been rising. In the past, we used to drill and cut the edge by hand, but now we use machinery to finish it. Using machining center to process composite materials is much faster than manual processing, and the precision is high. However, once there is a problem, there will be serious loss. Therefore, the process, tool selection and processing parameters are particularly important for processing composite materials.

Matters needing attention in selecting cutting tools for machining composite materials

1、 Generally, the size of composite auxiliary materials is relatively large, and its workpiece structure is complex, and its hardness and strength are very high. The cutting force used in the machining process is relatively large, and the heat produced by the processing is difficult to transfer out, which may severely scorch the resin or soften the resin, resulting in severe tool wear. Therefore, the tool used must have carbon fiber, and the cutting speed should be greater than 500 / min, and the feed speed must be small. In the process of edge cutting, carbide hobbing cutter, electroplated diamond grinding wheel, diamond inlaid milling cutter and copper based diamond grain saw blade should be selected.

2、 The cutting effect of the three new types of special milling cutters for machining monolithic cemented carbide composites is better. They all have some common characteristics: high rigidity, small helix angle, even 0 ° angle. The specially designed herringbone blade can effectively reduce the axial cutting force and delamination, and their machining efficiency and effect are very good.

3、 The interlaminar strength of carbon fiber composites is low, and it is easy to produce delamination under the action of cutting force. Therefore, the axial force should be reduced when drilling or trimming. High speed and small feed are required for drilling. The rotating speed is generally 3000 ~ 6000r / min, and the feed rate is 0.01 ~ 0.04mm/r. It is better to select three tips and two edges or two tips and two edges for the drill bit. The sharp tip can cut off the carbon fiber layer first. The two edges play a repair role on the hole wall. The diamond embedded drill head is sharp and wear-resistant. It is a difficult problem to drill the interlayer between composite and titanium alloy. Generally, the integral cemented carbide bit is used to drill according to the cutting parameters of drilling titanium alloy. From the titanium alloy side, the drilling is carried out until the drilling is through. Lubricant is added during drilling to alleviate the burn of composite materials. Boeing company specially developed PCD combined bit for interlayer drilling.

Special attention: the composite chip is powder, which is harmful to human health. High power vacuum cleaner should be used for dust collection, and water cooling can also effectively reduce dust pollution

The cutting fluid plays a very important role in the machining of workpiece in CNC machining center. Cutting fluid will be used in any material processed by CNC machining center. Therefore, cutting fluid is an indispensable liquid in CNC machining center. The main function of the cutting fluid is lubrication, cooling, anti-corrosion, anti rust, etc. if there is no cutting fluid for processing, the workpiece will be easy to deform and rust under high temperature. Therefore, CNC machining center must use cutting fluid to avoid this undesirable phenomenon.

There are many kinds of cutting fluids. Today, we will talk about several commonly used in the market. These are emulsion, chemical synthetic cutting fluid and cutting oil added with extreme pressure additives. Today, we will introduce these three common cutting fluids.

Advantages and disadvantages of cutting oil with EP additive

Advantages: the general use and cutting speed is not higher than 60m / min, the main cutting speed is not higher than 60m / min, regardless of any material cutting processing. Disadvantages: in high-speed cutting, due to the large amount of heat, oil-based cutting fluid heat dissipation effect is poor, so in high-speed cutting will produce stable and high smoke or fire. Therefore, due to high stability will have a certain impact on the workpiece, such as workpiece deformation, poor machining accuracy and other adverse phenomena.

Advantages and disadvantages of emulsion

Advantages: the biggest advantage of emulsion is strong heat dissipation, can clean the workpiece and high cost performance, which is conducive to the health and safety of operators. Therefore, the general metal processing plant is to choose the use of emulsion processing. In addition to the materials that are particularly difficult to machine, emulsion can be used for almost all light and medium load cutting and most heavy load processing, especially for processing thread grinding, groove hemp cutting and other complex grinding. Disadvantages: the biggest defect of emulsion is that it is easy to make bacteria and mold multiply, and make the effective components in emulsion decompose and stink and deteriorate In general, organic fungicides with low toxicity should be added.

Advantages and disadvantages of chemical synthetic cutting fluid

Advantages: it has the advantages of high cost performance, fast heat dissipation, strong cleaning ability and excellent workpiece visibility. It is very easy to control the size of the workpiece. Its stability and anti-corruption ability are better than emulsion. The disadvantage is that the lubrication ability is not strong, it is easy to suck the adhesion and wear of the moving parts of the machining center. Moreover, the viscous residue left by the chemical synthesis will affect the movement of the parts of the machining center and cause the rust of the overlapping surfaces of the parts.

Many friends who are new to machining centers don’t know much about machining centers, so occasionally some customers will ask what kind of CNC machining centers there are. CNC machining center we have had a lot of introduction, to introduce the types of CNC machining center, CNC machining center in the end what kind? After reading the following content introduction, you will understand.

1、 What kinds of CNC machining centers are there

In fact, CNC machining centers can be divided into vertical machining centers and horizontal machining centers according to the structure of CNC machining centers. CNC machining centers can be divided into vertical machining centers and horizontal machining centers according to their structures, which can be divided into vertical machining centers, vertical machining centers, vertical machining centers, and horizontal machining centers Horizontal machining center, gantry machining center, high-speed machining center, drilling and drilling center are all types of CNC machining centers.

2、 Recommendation of different products of CNC machining center

We have already talked about the types of CNC machining centers. At present, the types of CNC machining centers of mingwan machine tools include vertical machining center, gantry machining center, high-speed machining center and drilling and drilling center. Let’s introduce their respective advantages. Vertical machining center is our most commonly used machining center, and so are our small machining center A kind of vertical machining center, with the characteristics of miniaturization and high cost performance, gantry machining center is called the terminator of Dali Canada. Our gantry machining center can replace vmc1270, vmc1370 and vmc1580. With many advantages, the price is lower than Dali plus. The high-speed machining center is mainly used to make high-precision and high-finish products, with 12000 rotary direct spindle. Drilling and tapping center tool library is different, mainly used for making precision 3C products.

Five axis machining centers are not new to you. Five axis vertical machining centers generally have five moving axes, which are three linear axes / (XYZ /) and two rotating axes / (AB /) or / (AC /), which are represented by different representation methods according to their installation positions. Today, I mainly introduce the installation position of a and C rotating shafts of five axis vertical machining center.

The A and C rotation axes of the five axis machining center can be installed in different positions. For example, the A and C rotation axes can be installed on the worktable or the spindle, or they can be installed on the workbench or the spindle respectively. The A and C rotation installation positions of the five axis machining center are mainly determined by the product. In the market, the A and C rotation of the common five axis vertical machining center are both Installed on the workbench, there are few other types of installation. Now let’s introduce it to you.

Five axis machining center a, C rotation axis is installed on the worktable

In general, the A, C rotating shaft is installed on the worktable in this way, and it is the most seen in the market. Because of the limited size of the workpiece, this kind of installation method can not process large workpieces or load the machining center, because the bearing capacity of a rotation is limited.

Five axis machining center a, C rotation axis is installed on the spindle

There are few ways to install a and C rotating shafts on the main shaft. This kind of a and C rotating shaft installation mode is used to process large workpieces, and its load capacity is stronger than that of installing a and C rotating shafts on the workbench. Therefore, this kind of a, C rotating shaft installation method will be used in processing large-size workpieces.

The A and C rotating axes of the five axis machining center are respectively installed on the worktable and the spindle

In general, the a-axis is installed on the main shaft, while the c-axis is installed on the table. This kind of a-axis and c-axis installation mode is also relatively rare. It can process large-scale workpieces and grab the load capacity.

After using the belt drive spindle machining center for a long time, it is found that the spindle box belt has abnormal noise, whether it is in forward or reverse rotation, there will be some noise. According to many years of experience, most of them are belt problems. As long as we start from the belt of the main shaft, we can find out the key problem of making noise.

The belt tension of the spindle connected to the servo motor is too high

The tension of the belt connecting the main shaft to the servo motor should not be too tight. If it is too tight, it will easily lead to the wear of the belt, slip and make abnormal noise,

The belt tension between the spindle and the servo motor is too low

The tension of the belt connecting the spindle to the servo motor should not be too low. If the tension is too low, it will appear that the belt connecting the spindle to the servo motor is too loose. In this way, it is easy to cause slipping and make abnormal noise during heavy cutting.

The belt connecting the spindle to the servo motor is damaged

In general, the machining center has been used for a long time, and it is inevitable that there will be some defects, such as the transmission belt, which will wear after a long time, which is also one of the reasons for the abnormal noise of the belt. Therefore, the better quality of the drive belt to use a longer time, poor quality drive belt use time is shorter.

The tooth profile of the drive belt does not match that of the servo motor and the spindle

As the drive belt of the machining center is used for a long time, it will cause some wear, so many customers purchase the drive belt to replace it in order to save the cost. After replacement, it is found that the tooth shape of the drive belt is not consistent with that of the servo motor and the spindle, which will cause abnormal noise during use. It is suggested that customers should pay attention to whether the model of the purchased drive belt is the same as that of the removed worn belt. If different types of drive belts are used persistently, the abnormal noise of the belt in the transmission process will be caused, and even the gear wear of servo motor and spindle will be caused, resulting in serious consequences.

Vice clamp is installed on the working table of machining center

In fact, the installation method of vice clamp is very simple. Firstly, move the vice onto the workbench of the machining center, correct it to the pre-determined position, and then fix the locating block under the Vice Clamp in the T-groove of the working table of the machining center. This method is to prevent the vice clamp from deviated from the position corrected before the re cutting process, and also confirm the vice clamp position The parallelism and verticality of the fixture. This will allow the fixture to be installed.

Key points for installation of workpieces

Just after the vice clamp has been installed, then it will introduce how to install the workpiece on the clamp just now.

1. Before installing the workpiece, the parallelism and verticality of the workpiece shall be confirmed. If the parallelism and verticality are poor, the clamping force after the installation of the workpiece cannot be guaranteed.
2. It is necessary to ensure that the workpiece is installed in the middle of the clamp, and the clamping force of the clamp is consistent with the center of the workpiece, and there will be no offset.
3. Pay attention to not too hard when installing workpiece clamping, otherwise excessive force will cause deformation and poor machining accuracy.
4. The two used gasket must be of the same model. The same type of gasket referred to here is the same size and material of gasket. If the gasket is not the same type, the parallelism and verticality of the workpiece will be poor, which directly affects the processing accuracy of the workpiece.