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Boring machining of CNC machining center

The so-called boring is to enlarge or refine the original hole on the workpiece. It is characterized by correcting the eccentricity of the lower hole, obtaining the accurate position of the hole, and achieving high-precision roundness, cylindricity and surface finish. Therefore, boring as a high-precision machining method is often used in the final process. For example, the bearing holes of various machines and the processing of boxes and covers of various engines.

Compared with other machining, boring is a difficult process. It only needs to adjust one blade / (or blade holder /) to process micron sized holes such as H7 and H6. With the popularization of machining center, the boring process only needs programming and button operation. Because of this, it is necessary to have simpler, more convenient and more precise cutting tools to ensure the quality of products. This paper mainly analyzes the boring process of machining center from the perspective of tool technology.

Characteristics of boring process in machining center

2.1 tool rotation

Different from lathe processing, because of tool rotation in machining center, it is impossible to master the situation of tool tip in time to adjust the feed rate. It is impossible to change the machining diameter just by adjusting the NC button like the NC lathe. This has become a big obstacle to fully automated processing. It is also because the machining center does not have automatic diameter adjustment function (except for those with U-axis function), the boring cutter must have fine adjustment mechanism or automatic compensation function, especially in fine boring, sometimes it must be adjusted at micron level according to tolerance requirements.

In addition, due to the continuous change of chip flow direction during the boring of machining center, it is much more difficult to cool the tool tip, workpiece and chip discharge than when machining with a lathe. Especially when the longitudinal machining center is used for rough boring of steel blind hole, this problem has not been completely solved.

2.2 chatter

Chattering is the most common problem in boring. The main causes of chatter on machining center are as follows:

① Rigidity of tool system: including the rigidity of toolholder, boring bar, boring head and middle connecting part. Because of the cantilever machining, the rigidity of the tool system is particularly important when machining small holes, deep holes and hard workpieces.

② Balance of tool system: relative to the rotating axis of the tool system, if there is an unbalanced mass of the tool itself, the chatter will occur due to the action of unbalanced centrifugal force during rotation. Especially in high speed machining, the dynamic balance of the tool has a great influence.

③ Clamping rigidity of workpiece itself or workpiece: for example, some small and thin parts cannot be fully fixed with reasonable fixture due to insufficient rigidity or workpiece shape.

④ The geometry of edge /: the cutting resistance is different with different rake angle, escape angle, nose radius and chip breaking groove shape.

Tool setting and tool changing of machining center

Tool setting point is the reference point used to determine the position of workpiece coordinate system in the machine coordinate system after the workpiece is aligned and clamped on the machine tool.

The tool setting point can be selected on the workpiece or clamping positioning element, but there must be an accurate, reasonable and simple position corresponding relationship between the tool setting point and the workpiece coordinate point, so as to facilitate the calculation of the position of the workpiece coordinate point on the machine tool / (the machine coordinate of the workpiece coordinate point). The tool setting point should coincide with the workpiece coordinate point.

Tool change point: the machining center has a tool magazine and an automatic tool change device, which can automatically change tool according to the needs of the program. The tool change point should be in the position where there is no collision and interference among workpiece, fixture, tool and machine tool during tool change. The tool change point of machining center is usually fixed.

Tool setting method:

Tool setting in horizontal direction / (x, y coordinates)

(1) Lever dial indicator tool setting: the tool setting point is the center of the cylindrical hole;

(2) Tool setting with edge finder: round hole or reference edge

(3) The tool is set by touching or trial cutting.

Tool setting in Z direction / (Z coordinate /):

(1) On machine tool setting: use Z direction setter to set tool.

(2) Tool presetting outside the machine and tool setting on the machine.

(3) External tool setting instrument: measure the diameter, length, edge shape and angle of the cutter.

(4) Tool setting in multi position machining of horizontal machining center

EDM and WEDM

The non-traditional machine tools widely used in production mainly include EDM and WEDM. Therefore, this paper mainly describes the safety operation procedures of these two kinds of special machining machine tools.

Safe operation procedures for EDM machine tools

(1) Before starting the machine, carefully read the operation manual of the machine tool. If you are not familiar with the operation of the machine tool, you can avoid safety accidents.

(2) Before machining, pay attention to check the discharge gap, that is, a certain distance must be kept between the tool and the workpiece to form the discharge gap. It is generally 0.01-0.1mm. ,

(3) The clamping and calibration of the upper electrode must ensure that the feed direction of the tool electrode is perpendicular to the worktable plane.

Ensure that the output voltage pulse waveform of the pulse power supply on the workpiece and tool electrode added in the liquid medium is half

(5) There should be enough pulse discharge energy to ensure the metal melting or gasification in the discharge part.

(6) The discharge must be carried out in a liquid medium with constant insulation properties.

(7) During the operation, pay attention to check the filter element of the working fluid system. If the filter element is blocked, the working fluid should be replaced in time, which can automatically maintain a certain cleanliness.

(8) For the flammable type of working fluid in Sichuan, attention should be paid to fire prevention when using towel.

(9) To be civilized and strict, we must clean the working site and cut off the power supply of the system before leaving.

Safety operation rules of WEDM

Because WEDM is developed on the basis of EDM, it uses wire electrode / (copper or copper wire, etc.) to cut the upper part by spark discharge. Therefore, the safety operation regulations of WEDM machine tool are roughly the same as those of EDM plus machine. In addition, attention should be paid to the following aspects in operation.

(1) In order to reduce the pulling range of wire electrode and improve the machining accuracy, it is necessary to ensure that the wire electrode has a certain pre tightening force during wire winding.

(2) Check that the working fluid system is equipped with a resin cartridge to ensure that the working fluid can move freely and maintain a certain resistivity.

(3) In the process of EDM, it is necessary to make the working fluid fully surround the electrode wire to prevent the wire breaking phenomenon caused by the heat generated by the electrode wire passing through the large pulse current.

(4) Strengthen the regular inspection of the mechanical device of the machine tool

(5) To achieve civilized production, after the end of processing operation, cut off the power supply of the system before leaving. Mouth lubrication. Must clean the workplace, wipe clean machine tools, and cut off the power supply before leaving

Guide rail of CNC machining center

According to the motion track, the guide rail can be divided into linear motion guide rail and circular motion guide rail; according to the working nature, it can be divided into main motion guide rail, feed motion guide rail and adjustment guide rail; according to the friction property of contact surface, it can be divided into sliding guide rail, rolling guide rail and hydrostatic guide rail.

Sliding guide rail

The sliding guide has the advantages of simple structure, convenient manufacturing, good stiffness and high vibration resistance. The traditional cast iron cast iron and cast iron quenched steel guide rail has the disadvantages of large static friction coefficient, dynamic friction coefficient changes with speed, and the friction loss is large. It is easy to crawl at low speed / (1-60 mm / min /), which reduces the positioning accuracy of moving parts. Therefore, it is not used in other CNC machine tools except economical CNC machine tools. At present, most CNC machine tools use plastic guide, that is, a layer of plastic film soft belt composed of plastic and other chemical materials is pasted on the friction surface of moving guide rail.

There are two kinds of guide rail Plastics: PTFE soft belt and epoxy wear-resistant rail coating. The characteristics of plastic sliding guide are good friction characteristics, good wear resistance, smooth movement, good vibration damping and good technology.

Rolling guide

Rolling guide is to place ball, roller, needle and other rolling elements between the guide surfaces, so that the sliding friction between the guide surfaces becomes rolling friction. Compared with sliding guide, rolling guide has the following advantages: 1) high sensitivity, and little difference between dynamic friction coefficient and static friction coefficient, so it moves stably, and crawling phenomenon is not easy to appear when moving at low speed; (2) high positioning accuracy, repetitive positioning accuracy can reach 0.2 um; 8) low friction resistance, light movement, small wear, good accuracy retention and long service life. However, the anti vibration performance of rolling guide is poor, which requires high protection.

The rolling guide rail is especially suitable for the working parts of machine tools requiring uniform movement, sensitive motion and high positioning accuracy. This is the reason why rolling guide is widely used in CNC machine tools.

Hydrostatic guide

Hydrostatic guideway can be divided into hydrostatic guideway and aerostatic guideway.

There is an oil chamber between the two guide working faces of hydrostatic guideway. After the lubricating oil with certain pressure is injected, the hydrostatic oil film can be formed, which makes the working surface of the guide rail in pure liquid friction, without wear, and has good accuracy retention. At the same time, the friction coefficient is also very low, which greatly reduces the driving power rate; at low speed In addition, the oil has the function of absorbing vibration and good vibration resistance. Its disadvantage is that the structure is complex, there must be an oil supply system, and the cleanliness of the oil is required to be high. Hydrostatic guideway is widely used in machine tools. The hydrostatic guideway of CNC turret punch press can be divided into open type and closed type. Figure 2.25 shows the working principle of the open hydrostatic guideway.

The aerostatic guideway can form a static pressure air film after passing a certain pressure between the working faces of the two guide rails, so that the two guide surfaces of the CNC punch press can be evenly separated to obtain high-precision movement. At the same time, the friction coefficient is small, and it is not easy to cause heating deformation, but it will change with the air pressure fluctuation, and the bearing capacity is small, which is often used in occasions with small load 。 In addition, we must pay attention to the dust on the guide rail surface, because the dust falling into the air guide surface will cause damage to the guide rail.

Core features of CNC system

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.

Engraving and milling machine and vertical machining center

Many friends often ask me what is the difference between engraving and milling machine and CNC machining center. It seems that the two kinds of machine tools are similar. In fact, their functions are different. Today, let’s learn about the difference between engraving and milling machine and machining center.

When machining small dies with small cutting tools, the machining center is unable to meet its needs and the cost is very high. The advantage of engraving machine is carving. If the hardness of processing material is relatively large, it will also appear to be inadequate. The emergence of engraving and milling machine can be said to fill the shortage of both.

The machining center can realize the centralized processing of milling, drilling, boring, reaming, tapping and other processes after the workpiece is clamped at one time. The function of the machining center is especially emphasized on “milling”. The speed of the CNC system required by the machining center is general, and the spindle speed is about 0 ~ 8000 rpm, which is especially suitable for heavy cutting. The rough machining center is generally cantilever type with large volume.

Engraving and milling machines generally use gantry structure. Gantry type is divided into pillar type and fixed beam type. At present, fixed beam type is the main type of engraving and milling machines. It can be carved or milled. On the basis of the engraving machine, the power of the spindle and servo motor is increased, and the bearing force of the lathe bed is maintained. At the same time, the high speed of the spindle is maintained, and more importantly, the precision is very high. Engraving and milling machine is also developing to high speed, generally known as high-speed machine, with stronger cutting ability and high machining accuracy. It can also directly process materials with hardness above HRC60, and can be formed once, which is suitable for finishing. Engraving and milling machine requires high-speed CNC system, spindle speed of 3000 ~ 30000 rpm.

CNC milling and machining center is used to complete a large amount of milling workpiece processing equipment. CNC engraving and milling machine is used to complete small amount of milling, or soft metal processing equipment. High speed cutting machine is used to finish medium milling amount and reduce grinding amount to the minimum.

Disc type tool magazine of machining center

The tool magazine of machining center is generally divided into three types, hat type, disc type and chain type. The most commonly used forms of general machining center are disc type tool magazine and manipulator tool changer magazine.

1、 Features of disc magazine

Disk type tool magazine should be called fixed address tool changer magazine, that is, each tool position has a number, which is usually from 1 to 12, 18, 20, 24, etc., which is the tool number address. After the operator installs a tool into a certain tool position, no matter how many times the tool is replaced, it is always in the tool position

Low manufacturing cost. The main components are the tool magazine body and index plate. As long as the machining accuracy of these two parts is guaranteed, the indexing of the tool magazine in the moving parts uses the very classic “Markov mechanism”, and the cylinder is mainly used for the forward and backward, up and down movement. It is convenient to assemble and adjust, and easy to maintain. General machine tool manufacturers can make their own.
Counting principle of tool number. Generally, a contactless switch is installed at tool change position, and baffle plate is installed on tool position 1. The tool magazine must “return to zero” after the machine tool is started. When the tool magazine rotates, as long as the baffle plate is close to the contactless switch (the distance is about 0.3 mm), the CNC system will default to No.1 tool. With this as the counting benchmark, the “Markovian mechanism” has been turned several times, and the current number of knives. As long as the machine tool is not turned off, the current tool number will be memorized. When changing the tool, generally according to the principle of the nearest distance rotation, the tool number is counter clockwise. If the number of tool magazine is 18 and the current tool number is 8, tool No. 6 needs to be changed. According to the principle of tool change according to the nearest distance, the tool magazine rotates anticlockwise. If you want to change tool No.10, the tool magazine will rotate clockwise. The tool memory is cleared after the machine is shut down.
The tool change time of fixed address tool changer is relatively long, and domestic machine tools generally take more than 8 seconds (from one cutting to another cutting).
The total number of tools in the disc type magazine is limited and should not be too much. Generally, there are no more than 24 pieces of 40 pieces of tool holder, and no more than 20 pieces of 50 pieces of tool. Large gantry machine tools also change the disc into chain structure, and the number of tools is up to 60.

2、 Characteristics of manipulator magazine

Manipulator tool magazine tool change is a random address tool change. There is no serial number on each tool sleeve. Its greatest advantage is that the tool can be changed quickly and reliably.

High manufacturing cost. The tool magazine has a chain combination of tool sets, and the tool changing action of manipulator is controlled by cam mechanism, so the machining of parts is more complicated. Assembly and debugging is also more complex, generally produced by professional manufacturers, machine tool manufacturers generally do not self-made.
Counting principle of tool number. Like the fixed address tool selection, it also has a reference tool number: No. 1 tool. But we can only understand it as tool sleeve No.1, not tool No.1 in part program: T1. There is a tool list in the system. It has two columns. One column is the tool set number, and the other column is the current program tool number corresponding to the tool set number. If we compile a three tool processing program, the tool placement starts with No.1 tool set T1 (No.1 tool set), No.2 tool set T2, No.3 tool set T3. We know that when T1 on the spindle is being processed, tool T2 is ready. After tool change, T1 is replaced by No.2 tool sleeve. Similarly, if working time is added at T3, T2 is installed in No.3 tool sleeve. After a cycle, the former tool is installed in the latter tool sleeve. The memory of tool set number and tool number in CNC system is permanent. After the machine is shut down, the tool magazine can be restored to the state before shutdown without “returning to zero”. If “return to zero”, the corresponding tool number in the tool set number must be modified in the tool table.
The tool change time of manipulator tool magazine is generally 4 seconds (from one cutting to another cutting).
The number of tools is generally more than that of disc magazine, and the conventional ones are 18, 20, 30, 40, 60, etc.
The gear oil for lubrication and cooling shall be replaced regularly for cam box of tool magazine.

3、 How to choose the two

These two types of tool magazine have their own advantages and disadvantages. When selecting them, we need to combine them with practice. The most important one is the price and which type of parts to process. Take 20 knives in 40 pieces of knife magazine as an example. The price of disc magazine is about 35000, and that of manipulator is 65000. In general, it is better to use disc type tool magazine for single piece small batch production, and manipulator magazine for mass production. In addition, we also know that the reliability of manipulator magazine is higher than that of disc magazine, but the maintenance of disc magazine is simple and convenient.

4、 Fault condition of tool magazine

The failure probability of disc type magazine is higher than that of manipulator magazine. The main vulnerable parts are the needle roller bearing on the fork in “horse mechanism”. If the magazine is loaded or overloaded for a long time. The guide pair will wear and the bearing in the center of the disc will also wear. But the replacement is more convenient.

The tool magazine of manipulator is simple and reliable, which is mainly accomplished by cam mechanism. Usually as long as the oil in the cam box can be replaced on time. Long service life. If the cam groove is not replaced after wear to a certain extent, the tool magazine can not be used.

CNC high speed precision parts processing process

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.

Product analysis through product analysis should obtain certain composition information and some specific processing requirements.
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.
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.
In fact, the process of path generation is to realize the process planning through 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, 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.
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.

Belt type spindle of machining center

1、 Belt type spindle of machining center

There are several kinds of spindles that can be used in machining center, such as belt type spindle, straight spindle, gear spindle and motorized spindle. Among them, the belt spindle is the most commonly used spindle form in machining centers, and it is also the standard spindle of many machining centers. Why is the standard spindle of machining center belt type? Is the belt of machining center the spindle?

Not all machining centers use belt type spindle as standard configuration, high-speed machining center and drilling center are not included. This kind of high-speed machine tool is equipped with straight spindle as standard, and belt type spindle cannot be used. The belt spindle is not as high as the direct spindle and motorized spindle, and the maximum speed can only reach 10000 rpm. However, the cutting force of belt spindle is better than that of the straight spindle and motorized spindle, next to the gear spindle. And the price will not be too high, so many machining center standard spindle are belt type spindle. Belt type spindle is enough to meet the needs of most customers and is a very good spindle.

2、 What is the belt spindle used for processing

Since the belt spindle is the most widely used spindle, what can it be processed? Belt spindle is used in both small and large machining centers. It can process large workpieces and small parts. Most of the time, large vertical machining centers are engaged in heavy cutting, including the processing of cast iron and steel castings and the processing of molds. The belt type spindle is competent in this respect, but some alloys with high hardness are not suitable for belt spindle processing, but gear spindle is selected.

Many customers of small machining centers are used for the processing and production of small hardware parts or products, and some of them are also used for the processing of small molds. In other words, the workpieces processed by small machining centers are relatively small. Generally, belt type spindles can meet the requirements of small machining centers, and their small machining centers are less used for processing alloys with high hardness, so the small ones on the market are small 99% of the machining centers use belt type spindles. It can be seen that belt type spindles are very good spindles.

3、 Model recommendation of belt spindle machining center

Most of the machining centers of mingwan machine tools use belt type spindle as standard configuration. Large vertical machining centers include vmc850, 1060, 1270, 1370, 1680, etc., and small machining centers include vmc650, 550, 420, etc., which are very good machining centers with high cost performance. The vertical machining center of mingwan machine tool can meet most of the requirements of most customers and is highly praised by customers. It is the only choice for the brand of cost-effective machining center.

Characteristics of hard rail vertical machining center

1、 Characteristics of hard rail vertical machining center — hard rail

For the hard rail, we talk less, especially the vertical machining center. Isn’t it easy to use? It’s not. So, what are the characteristics of the hard rail vertical machining center? With such a question, mingwan machine tool small series for you to summarize the characteristics of the hard rail vertical machining center. Hard rail refers to the machine tool bed, column and other fixed parts of the direct processing guide rail into a whole, through the sliding seat and workbench or other moving parts connected. The rigidity of the hard rail is better, the weight it can bear is relatively large, and the ability of heavy cutting is also very strong. Through direct transmission, the three axis linkage, large axial thrust, wide base and four rail supporting structure are adopted. Therefore, the vertical machining center is suitable for large and medium-sized workpiece processing, especially for mold processing.

2、 Characteristics of hard rail vertical machining center

It has the characteristics of low damping and low friction coefficient to cast castings with mikhanna material.

The lubrication system lubricates the transmission parts to reduce the friction resistance and increase the service time of the machine tool;

Equipped with special chip removal machine for systematic chip removal;

The cooling system and oil cooler are used to cool the machining cutting and spindle, so the cooling efficiency is high;

It can be equipped with tool magazine to implement automatic tool change, saving tool changing process time;

With the fourth axis and rotary table, the horizontal / (fourth axis /) movement can be realized, and complex workpieces can be processed.

Mingwan machine tool uses Taiwan Science and technology, specializing in manufacturing high-level, cost-effective products. If you are interested in hard rail vertical machining center, you may as well contact us, we will give you the most satisfactory products.