Yearly Archive September 25, 2020

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.

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

1. 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.
2. 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.
3. 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).
4. 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.

1. 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.
2. 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.
3. The tool change time of manipulator tool magazine is generally 4 seconds (from one cutting to another cutting).
4. The number of tools is generally more than that of disc magazine, and the conventional ones are 18, 20, 30, 40, 60, etc.
5. 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.

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.

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.

The biggest processing attribute of vertical machining center is that the consistency of batch workpiece size should be very high. We know that the traditional processing of workpiece from one process to another has to go through a clamping process. This process is difficult to achieve the complete consistency of the processing size of each part by human operation. Of course, this does not mean that the workpiece is out of tolerance, as long as the tolerance of the workpiece is within the tolerance All parts within the band are qualified parts, which means that some workpieces may be in large difference, some parts may be in medium difference, and some parts may be in small difference, so it is difficult to ensure the consistency of workpiece size.

Therefore, at present, the utilization rate of vertical machining center is the highest in small and medium-sized processing enterprises. Of course, the vertical machining center is also the most cost-effective machine tool in CNC machine tools. It has high processing efficiency and high processing precision. From these two aspects, it also solves the problem of maintaining the size consistency of workpieces. Of course, if the numerical control parameters are not set properly or the operation is improper, the vertical machining center will also appear the phenomenon of machining out of tolerance from time to time in the actual processing. This paper briefly introduces the causes and solutions of machining out of tolerance in vertical machining center

The out of tolerance of machining accuracy of vertical machining center mainly includes: high surface roughness of inner hole, out of roundness of reamed inner hole, out of tolerance of position precision of reamed hole, obvious edge of inner surface of hole, irregularity of center line of hole after reaming, increase and decrease of hole diameter.

1、 The position accuracy of reamed hole is out of tolerance

Causes: it may be caused by the wear of the guide sleeve of the vertical machining center, the distance between the bottom end of the guide sleeve and the workpiece, the short length of the guide sleeve, the poor accuracy and the looseness of the spindle bearing.

Solution: if the position accuracy of the hole is out of tolerance during reaming of the vertical machining center, the following maintenance can be carried out according to the above-mentioned problems. The guide sleeve shall be replaced regularly and the guide sleeve shall be lengthened to improve the matching accuracy of the clearance between the guide sleeve and the reamer, the machine tool shall be maintained in time, and the spindle bearing clearance shall be adjusted.

2、 The surface roughness of inner hole is high

Causes: the surface roughness of the inner hole machined by the vertical machining center is high, and there are many reasons, which may be caused by too high cutting speed, improper selection of cutting fluid, excessive reamer main deflection angle, too large reaming allowance, uneven or small reaming allowance, unsharp edge, too wide reaming edge, poor chip removal during reaming, excessive wear of reamer, and possibly selected milling Tool and part material mismatch and other reasons.

Solution: there are many reasons for the high machining roughness, so the solution is more complex. We can start from the following aspects: reduce the cutting speed, select the cutting fluid according to the processing materials, appropriately reduce the reaming allowance, improve the position accuracy and quality of the bottom hole before reaming, or increase the reaming allowance, increase the space of chip holding groove or use the reamer with edge inclination angle to make the chip removal smooth The reamer should be changed regularly and the cutting tool should be selected reasonably. For example, when machining steel parts, the suitable tool should be selected.

3、 Increase of machining aperture

Causes: the diameter of the reamer increases gradually when machining in the vertical machining center. The causes may be: the design value of the reamer’s outer diameter is too large or the reamer edge has burr, the cutting speed is too high, the feed rate is improper or the machining allowance is too large, the reamer’s main deflection angle is too large, the reamer is bent, the reamer edge adheres to the chip, the reamer edge swing is out of tolerance during grinding, the cutting fluid is not suitable, and It may be the problem of CNC machine itself. The spindle is bent or the spindle bearing is too loose or damaged.

Solution: according to the actual situation, the following countermeasures can be made: according to the specific situation, reduce the reamer outer diameter, reduce the cutting speed, adjust the feed rate or reduce the machining allowance, properly reduce the main deflection angle, straighten or scrap the bending reamer that can not be used, select the cutting fluid with good cold performance, adjust or replace the main shaft bearing, or replace the whole spindle.

4、 The reamed inner hole is not round

Causes: the machining of the inner hole is not round and the roundness is not enough. It is mainly due to the following factors: the reamer is too long, the rigidity is not enough, the vibration is generated during reaming, the reamer’s main deflection angle is too small, the reaming allowance is too small, there are gaps on the inner hole surface, cross holes, especially sand holes and air holes on the surface of the hole, as well as the looseness of the spindle bearing of the machine tool.

Solution: we can start from the following aspects: the installation of reamer should adopt rigid connection, select qualified reamer, control the hole position tolerance of pre-processing process, adopt unequal pitch reamer, select qualified blank, timely adjust the spindle clearance of machine tool, etc.

5、 After reaming, the center line of the hole is not straight

Causes: when the vertical machining center is machining holes, the center line is not straight. The possible reasons may be: the hole is inclined when drilling, especially when the diameter is small, Due to the poor rigidity of reamer, the original bending can not be corrected, the reamer’s main deflection angle is too large and the guide is poor, so that the reamer is easy to deviate from the direction in reaming, the inverted cone of the cutting part is too large, and the reamer is displaced intermittently at the gap in the middle of the hole.

Solution: increase reaming or boring process to correct the hole, reduce the main deflection angle, adjust the appropriate reamer, replace the reamer with guide part or lengthening cutting part, and pay attention to correct operation.

The machining center has been developed from the basic CNC milling machine. It combines all the features and functions of the CNC milling machine. The only difference from the CNC milling machine is that the machining center has automatic tool changing device, which can realize the automatic tool changing function during processing. But NC milling machine has no automatic tool changing device, which can not realize the function of automatic tool change, which is the only difference between CNC milling machine and machining center.

The composition of automatic tool changing device in machining center

The automatic tool changing device of machining center is composed of tool magazine, manipulator and driving mechanism. The tool magazine is used to store the tools needed in the process. There are many types of tool banks, mainly classified according to the shape, such as the Douli type magazine, disc magazine and chain magazine, etc. the capacity of these repositories is several to hundreds of tools. In the market, there are two kinds of tool storehouses used in the common processing centers, namely, the Douli type and the disc type. However, chain type tool base is not used by any manufacturer because of its high price. Here is a small edition to introduce the way of tool change.

The way of changing the tool of the Douli type magazine

The tool changing method of the Douli type magazine is relatively simple, and there is no mechanical arm for such magazine, so it is not necessary to use the mechanical arm to complete the tool change. The tool changing mode of its magazine is that the magazine moves to the spindle to realize the tool change. This kind of tool has the advantages of high cost performance, convenient maintenance and simple structure, and the disadvantage is that the speed of tool change is slow.

The way of changing the tool of disc magazine

The tool changing mode of disc magazine is more complicated, mainly by the manipulator to complete the tool change action, and the manipulator takes the tool 180 ° from the magazine and rotates it into the spindle to complete the tool change. This kind of tool magazine has the advantage of fast tool changing, and its disadvantage is complex structure, inconvenient maintenance and high failure rate.

Although the tool changing mode, tool selection mode and tool structure of these tool banks are different, they are controlled by numerical control system, and the selection and exchange of tools are realized by motor, air pressure or hydraulic and manipulator.

As we all know, the structure of the tool magazine of machining center is very complex, especially the disc magazine. And in the normal work of the machining center, the tool magazine frequently transfers tools. Therefore, the machining center is prone to failure. According to statistics, 50% of the machine tool failures are related to the tool magazine. Therefore, when using the machining tool magazine, we must pay attention to some matters, and try to minimize the fault of the tool magazine of the machining center.

Precautions for tool magazine of machining center

1. It is forbidden to load the overweight and extra long tools into the tool magazine, which can prevent the tool from falling off or collision between the tool and workpiece and fixture during tool change.
2. When installing the tool into the tool magazine, we must pay attention to the correct installation according to the sequence of the tool magazine. After the installation, let the machining center idle to see whether the tool magazine replaced is consistent with the required tool, so as to prevent the adverse consequences caused by the wrong replacement
3. When the tool needs to be installed manually, make sure that it is installed in place and firmly. Check whether the locking device on the cutterhead is started and ensure these factors, otherwise unnecessary accidents will occur.
4. The operator of the machining center should check whether the tool magazine returns to the correct position at any time, simply return to zero, and then check whether the spindle of the machining center returns to the tool change position. If one of the two problems is found, it should be timely sorted out and fed back, otherwise the tool change can not be completed, affecting the work efficiency of the machining center.
5. The tool, handle and sleeve should be cleaned and maintained regularly. The tool, handle and sleeve must be kept clean.
6. When the machining center is started, if you want to make the machining center run at idle, check whether the tool magazine, manipulator and other moving parts are normal, especially if the travel switch and solenoid valve are working normally. The other is to check whether the hydraulic pressure value of the manipulator is within the normal range, whether the cutting tool is locked on the manipulator. If the above problems are found, they should be immediately fed back and dealt with in time.