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How to improve the surface finish of precision parts

As engineers, we use our skills, knowledge and experience to make good appearance and accurate parts. We are very proud of the products we make. We hope the rest of us can see the conceit of the molded goods. But when we don’t get the result we want, what should we do? In terms of size, the parts meet the blueprint specifications, but the surface brightness and overall appearance are not very dream? When this happens, we need to return to the basics and make sure that we use the good processing methods we know.

We need to look at fixtures and other equipment to make sure that they are solid and that they do not contribute to harmonic problems or vibrations during processing. We need to make sure that we don’t use the long equipment we don’t need. These equipment can be easily turned to or added to the opportunity of waste. In high-speed process, we need to ensure the application of equipment with average quality, which has been rated according to the applied programming rpm. But if all the above are good, what should we do?

Study the following options:

1. Control chip: chip thinning is the main factor of excellent surface brightness. Controlling chips may be the first thing you should study. If the chip is in contact with the workpiece during machining, or if you are cutting the chip from scratch, it is likely to affect your surface brightness in a negative way. Study the possibility of changing the chip breaker style you are using to help break down the chip for better control.

Although the application of air and coolant is a good choice for chip removal, pay attention to the coolant. Prevent the application of coolant when cutting intermittently. Hot cracks in the cutting edge can occur… Due to intermittent heating and rapid cooling of the cutting edge… And can cause premature failure of the blade, which may at least initially affect your surface brightness, because of over stressed cutting edge and failure.

2. Speed up: This is more and more the case when using carbide tools. The increase in speed will ensure a shorter time for the material to come into contact with the tip… Thus reducing the edge accumulation on the tool, which may cause poor surface brightness. Increasing the rake angle of the cutting tool also helps to reduce and control edge accumulation.

3. apply accurate tip radius: larger tip radius will be suitable for faster speed. The inserts can be fed at about half of TNR per revolution and still have excellent results. If the TNR to IPR ratio is exceeded, the device will create more “linear” surface brightness, rather than the color and smooth surface you want. Therefore, the larger the TNR, the faster the feed rate it may contain, and the expected consequences still occur. However, the use of a considerable TNR can cause chatter – reduce cutting pressure – so pay attention to and study the speed required to cut raw materials – use TNR equipment that meets your needs.

It is also worth mentioning that the application of a larger tip radius means that you must leave more material for the finish. In order to ensure the normal operation of the equipment, you must have TNR equal to or greater than TNR, so as to complete the removal of the equipment.

If you run into waste around the corner, you may want to try a smaller TNR. Always apply a TNR smaller than the corner radius you are cutting – so you can “create” the radius you need – all the more on finishing equipment. This will help reduce cutting pressure and eliminate chatter.

When milling, try to use the fillet or spherical end milling cutter instead of the plane end milling cutter. Equipment with a fillet radius will give you higher brightness at sharp corners, and will certainly help to prolong tool life.

4. Try to insert the wiper: as far as possible. The wiper insert has a small flat area adjacent to the tip radius. When the device is fed along the workpiece, the plane essentially “wipes” the brightness and helps to eliminate the linear brightness that may be encountered by faster feed rates – this allows the use of smaller TNR to assist in flutter control.

5. Add the lead angle of the tool. A higher lead angle and a positive skew blade produce better surface brightness than a tool with a shallower cutting angle. For example, a face milling cutter with a 45 ° cutting angle will produce a better surface brightness than a face milling cutter with a 90 ° cutting angle.

6. Eliminate linger and pause: every time the equipment stops moving when contacting with the part surface, all traces will be left. Change the process if necessary, but try to make sure that the tool never stops or hesitates during the cutting process.

Die competitiveness determines product vitality in CNC lathe processing

Mould experts believe that the selection of advanced mould technology is the inevitable trend for fierce competition at the moment, and the most important thing is to increase the competitiveness of mould itself to meet the market demand. It is not only the requirement of mould industry development, but also the voice of automobile and other industries to improve the high precision of mould.

Strengthen the understanding of mould precision meaning

1. Die refers to the well formed equipment used for batch forming, stamping and other finished products. Mold accuracy includes the accuracy of parts obtained in machining and the quality consciousness of ensuring the accuracy of products during manufacturing. However, generally speaking, mold accuracy mainly refers to the accuracy of working parts of mold.

① Precision in die machining means that the essential geometric parameters of die parts after machining and assembly are in line with the design geometric parameters.

② Precision in mold making means that the enterprise employees gradually create a mode of thinking, a quality consciousness, which guides the employees to make actions. That is to say, in the actions of the enterprise employees, they always implement the quality consciousness of product precision.

2. The content of mould precision includes four aspects: dimension precision, form precision, position precision and surface precision. Due to the two parts of the upper die and the lower die during the working time of the die, the mutual position accuracy between the upper die and the lower die in the four kinds of accuracy is very important.

When the machining accuracy is very high, the mold often has more than enough force. Now the precision of a well-designed mold can reach within the range of 0.1-0.01 mm. Compared with the previous mold, the precision is still a big step higher. However, the accuracy of these components, such as engine, is required to be less than one thousandth of a millimeter, or even smaller. Therefore, it is impossible to replace the cutting process completely with the die at present.

Now, the brightness and roughness of the mould itself still have a great leap. However, the mold itself is also out of the machine tool manufacturing. If the accuracy of the machine tool manufacturing the mold itself can not pass the standard, the accuracy of the products manufactured out of the manufacturing will not be high.

The importance of CNC machining sequence

A CNC workpiece often has several surfaces to be machined. These surfaces not only have certain accuracy requirements, but also have certain position requirements between the surfaces. In order to achieve these accuracy requirements, the machining sequence of each surface of CNC machining parts can not be placed casually, but must be in accordance with the positive principle, that is, the selection and conversion of the positioning benchmark determines the processing sequence, and the principle that the previous process plans the positioning benchmark for the subsequent process.

1. Before the important surface machining, the precision datum should be trimmed once to ensure the machining accuracy of the important surface.

2. After finishing the fine datum machining, rough machining, semi finish machining and finish machining shall be carried out for the key surfaces with high precision requirements. The surface with unique high precision also needs finishing.

3. The surface used as the precision reference should be machined at the beginning of the CNC machining process, because it should be used to locate other surfaces in the subsequent process. That is, “benchmark before others”.

4. When machining the fine datum, it is necessary to use the coarse datum for positioning. In the process of single piece, small batch production and even batch production, for castings and forgings with complex form or large size, and workblanks with large size deviation, the marking process shall be arranged before the machining process, so as to provide the alignment benchmark for the precision machining.

5. As for the simple process of waste products, finishing and finishing can be properly placed in the front, and some secondary small surface processing can be placed later.

Spindle structure of CNC lathe

The accuracy of the horizontal spindle and vertical spindle on the base of CNC lathe plus Machine Tool Headstock decide the accuracy of the processed screw. At the same time, when the screw rotates at a high speed of several thousand revolutions in the shrinking machine, the screw with poor accuracy will cause the shrinking machine to have fever, vibration, low efficiency, fast wear and other phenomena. At present, there are two plans for the spindle structure of single screw machining machine in China.

1: The main shaft structure with non adjustable bearing radial clearance

The front bearing of the main shaft is composed of one double row cylindrical roller bearing and two thrust ball bearings. The main shaft uses the double row cylindrical roller bearing to receive the radial cutting force and two thrust ball bearings to receive the axial cutting force. The rear bearing of the main shaft usually adopts one double row cylindrical roller bearing or one centripetal ball bearing. The advantages of the spindle structure: the processing and equipping of the spindle are simple and the cost is low.

2: Spindle structure with adjustable bearing radial clearance

The front bearing of the main shaft is composed of a P4 level tapered double row cylindrical roller bearing and a P4 level double row radial thrust ball bearing. The spindle receives the radial cutting force by using the double row cylindrical roller bearing with tapered hole and the axial cutting force and partial radial cutting force by using the double row radial thrust ball bearing. The main shaft rear bearing is usually a P5 level tapered double row cylindrical roller bearing.

The inner ring and matching shaft diameter of tapered bore double row cylindrical roller bearing are both 1:12 tapered. If the bearing is locked with a round nut, a displacement will occur in the axial direction of the bearing and the inner ring of the bearing will expand, so as to reduce or eliminate the radial clearance of the bearing.

The advantage of this spindle structure: high spindle accuracy. Measure the end face runout of the spindle on the diameter of φ 230mm of the front end face of the spindle to be 0.010mm. Measure the radial run out value of the spindle on the outer circle of φ 230mm at the front end of the spindle to be 0.005mm. The accuracy of the second structure is 50% higher than that of the first one.

What are the material requirements for precision parts processing

Precision machining, not all raw materials can be carefully processed. Some raw materials are too hard, beyond the hardness of the processing machine parts, the machine parts may collapse, so these raw materials are not suitable for precision machining, unless they are made of unique raw materials, or laser cutting.

The raw materials for precision machining are divided into two categories: metal raw materials and non-metal raw materials.

As for the metal raw materials, the hardness is greater for stainless steel, followed by cast iron, followed by copper, followed by aluminum.

The processing of ceramics and plastics belongs to the processing of non-metallic materials.

1. First of all, the hardness of raw materials is required. For some scenes, the higher the hardness of raw materials is, the better it is. It is only limited to the hardness requirements of machining parts. The processed raw materials cannot be too hard. If they are harder than the parts, they cannot be machined.

2. Secondly, the material is of moderate hardness, at least one level lower than the hardness of the parts. At the same time, it depends on the function of the processed parts and the correct selection of materials for the parts.

In a word, precision machining still has some requirements for materials, not all materials are suitable for processing, such as too soft or too hard raw materials, the former is not necessary for processing, the latter is unable to process.

Therefore, before processing, we must pay attention to the density of the material. If the density is too large, it is equal to the hardness. If the hardness exceeds the hardness of the machine (lathe tool), it is impossible to process. It will not only damage the parts, but also cause danger, such as the tool flying out and hurting people. Therefore, generally speaking, for machining, the material of raw materials should be lower than the hardness of the machine tool, so that it can be processed.

报错

The cause and solution of the abnormal machining accuracy of CNC machine tools

1、 Causes of abnormal machining accuracy

The causes of abnormal machining accuracy are hidden and difficult to diagnose. Based on years of practical experience, the author sums up five main reasons: the feed unit of the machine tool is changed or changed; the zero point offset of each axis of the machine tool is abnormal; the reverse clearance of the axis is abnormal; the running state of the motor is abnormal, that is, the electrical and control parts are abnormal; the mechanical fault, such as the lead screw, bearing, coupling and other parts. In addition, the programming of machining programs, the selection of cutting tools and human factors may also lead to abnormal machining accuracy. Wechat for metal processing, good content, worthy of attention.

2、 Fault diagnosis principle of CNC machine tools

1. The first external and then internal CNC machine tool is a machine tool integrating mechanical, hydraulic and electrical, so the occurrence of its fault will also be comprehensively reflected by the three. The maintenance personnel shall check one by one from the outside to the inside first, and try to avoid opening and disassembling at will, otherwise the fault will be enlarged, the machine tool will lose precision and performance.

2. Generally speaking, mechanical fault is easy to detect, while the fault diagnosis of CNC system is more difficult. Before troubleshooting, first of all, pay attention to eliminate mechanical faults, which can often achieve twice the result with half the effort.

3. The machine tool can be powered on only when it is confirmed as a non-destructive fault through understanding, observation, test, analysis under the static state of power failure of the machine tool; under the operation condition, it can be dynamically observed, inspected and tested to find the fault.

For destructive faults, the danger must be eliminated before power on.

4. Simple first, then complex. When there are many kinds of faults interwoven and covered up, and there is no way to start for a while, the easy problems shall be solved first, and then the difficult problems shall be solved. Often after simple problems are solved, difficult problems may become easy.

CNC machining

3、 Fault diagnosis method of CNC machine tools

1. Intuitionistic method (looking, hearing, asking and cutting) – machine tool fault phenomenon, processing status, etc.; look at CRT alarm information, alarm indicator light, capacitor and other components deformation, smoke burning, protector tripping, etc.; listen to abnormal sound; listen to electrical components burnt smell and other peculiar smell; touch heat, vibration, poor contact, etc. Wechat for metal processing, good content, worthy of attention.

2. Parameters of parameter inspection method are usually stored in RAM, sometimes the battery voltage is insufficient, the system is not powered for a long time or external interference will cause parameter loss or confusion, so relevant parameters shall be checked and calibrated according to fault characteristics.

3. Some faults of isolation method are difficult to distinguish whether they are caused by numerical control part, servo system or mechanical part. Isolation method is often used.

4. In the same kind of method, the spare board with the same function is used to replace the suspected faulty template, or the templates or units with the same function are exchanged with each other.

5. The function program test method compiles some small programs for all the instructions of G, m, s, t and functions, and runs these programs when diagnosing faults to judge the lack of functions.

Why does the precision of precision hardware parts become worse

The accuracy of hardware parts almost determines the quality of products. The more sophisticated the hardware parts, the higher the accuracy requirements. Why does the processing accuracy of sophisticated hardware parts become worse? Here is the answer for everyone:

The first factor is the poor machining accuracy of the parts themselves. Generally speaking, if the dynamic deviation between the shafts is not adjusted well during the installation, it may also be that the change of the shaft transmission chain due to wear will affect the accuracy of the parts. Generally speaking, the accuracy caused by the deviation of this variety may be adjusted from the beginning. If the deviation is too large or even if there is an alarm, it is necessary to check the servo motor to see if its speed is too high.

The second factor is that the overshoot of the machine tool during operation will also affect the machining accuracy. It may be that the acceleration and deceleration time is too short, and the transformation time is appropriately prolonged. Of course, it may also be that the link between the lead screw and the servo motor is loose.

The third factor is that the roundness of the two shafts is out of tolerance, the axial deformation of the circle is caused by the mechanical failure to be adjusted properly, and the compensation for the clearance of the screw of the shaft is not correct, or the displacement of the shaft positioning may affect the accuracy of the fine parts.

The existing problems of high-end CNC lathe independently developed in China

The CNC lathe profession is a basic profession, and the elites in demand are also increasing year by year. With the acceleration of the upgrading pace of the Chinese system homework, the demand for CNC lathe is greatly increased. However, according to statistics, the market is now dominated by imports, and the development of domestic high-end CNC lathe is suffering. In such a case, the success of the CNC lathe industry should have a lot of outstanding lost.

At present, the added value of CNC lathe profession in China is relatively low, and the effect of self-developed high-end CNC lathe is not obvious. This is related to the low position of “made in China” in the world system and the low position of division of labor. Some experts have made an examination and analysis of why the market is dominated by imported CNC lathes, while the domestic CNC lathes are struggling, and obtained the following information: the State encourages the import of advanced skills and equipment, and expands the import of products of advanced CNC lathes

At present, the salary of CNC lathe elites in China is not very popular. For example, the research staff of a CNC lathe factory can get a salary of 3000 yuan in the third or second tier cities. Imagine that such a salary level can be obtained even if it is right or wrong for a high skilled type of work.

So the value of the creation of high skilled workers is more than 3000 yuan. Chinese machine tool enterprises are still unable to meet the urgent dream of engineers. During this period, a very important reason is that the domestic CNC lathe can not sell well. For products of the same model, the value of domestic products is much cheaper than that of overseas enterprises, so that the wife of the enterprise does not look at the product parameters, but only at the value can identify whether they are domestic products or foreign products. On the other hand, the management of Chinese enterprises seems not to be deeply aware of the importance of high-end skilled engineering staff.

报错

What are CNC machining center systems in machining

Today’s CNC machining for you to understand the CNC machining center system in machining? Let’s get to know.

CNC system is the core component of machine tool. If the CNC system controls the behavior of machine tool, the CNC system can accurately control the position, angle, speed and other mechanical and switching values of machine tool. In China, all middle and high-level machine tools will be equipped with imported CNC systems, while domestic CNC systems are usually seen in low and medium-level machines. It is impossible to configure domestic CNC systems on some high-level machines, because domestic CNC systems are not as good as imported CNC systems in performance, stability and reliability, so the general manufacturers of machine tools will not equip domestic CNC systems to a high level It is a good choice to configure the imported CNC system on the advanced computer. The performance, stability and reliability of the imported CNC system are very good.

What are the imported CNC products

There are many imported CNC systems in China, only a few of which are well-known. For example, Siemens of Germany, FANUC and Mitsubishi of Japan, Baoyuan and Xindai of Taiwan are all well-known CNC systems in China. At present, FANUC numerical control system of Japan accounts for a large market share in Chinese numerical control system, followed by Siemens of Germany and Mitsubishi of Japan. These imported CNC systems use their advanced data and the performance advantages of the CNC system to quickly seize the Chinese CNC market, so the domestic CNC system has little market share in the Chinese market.

Features of imported CNC

As there are many brands of imported CNC system with similar characteristics, it seems too slow to talk about the characteristics one by one. Besides, the small editors can’t talk about it. Take the FANUC numerical control system of Japan, which is used by Chinese machine tools, for example. The FANUC numerical control system has the characteristics of high quality, high performance, full performance, application and various machine tools and machine tools. Fanuc CNC system focuses on the following aspects:

1. The structure is simple, easy to disassemble, and each control board is highly integrated, so the reliability is greatly increased, and the maintenance and exchange are simple.

2. Its CNC system is suitable for working environment temperature of 0-45, relative humidity of 75%. It can be seen that FANUC CNC system is suitable for environment strength.

3. Fanuc numerical control system is equipped with complete software comparison, which can meet the general requirements of machine tool operation.

After the above understanding of CNC processing, I hope to be able to help you.

How to select blank for precision parts machining

1、 Casting

The forging method should be used to manufacture the parts with complex forms. At present, most castings are forged by sand mold, which can be divided into wood mold manual type and metal mold mechanical type. It has low precision, large machining surface allowance and low production efficiency. It can be used for single small batch production or forging of large parts. Metal mold machinery has high production rate and casting precision, but the cost of equipment is high and the component of casting is limited, so it can be used in a large number of small and medium-sized castings. Secondly, special forging can be selected for small castings with high quality requirements, such as pressure forging, centrifugal manufacturing and investment forging.

2、 Forging

For steel parts with high mechanical strength requirements, forging blanks are usually used. There are two kinds of Forgings: free forging and die forging. The free forging forging can be obtained by hand forging (small blank), mechanical hammer forging (medium blank) or press forging (large blank). This kind of forging has the advantages of low precision, low production rate, large machining allowance, and simple structure. It is applicable to single piece and small batch production, and large forgings.

The small braid in the well-organized parts processing field tells you that the accuracy and surface quality of die forgings are better than that of free forgings, and the form of forgings can be more complex, so the machining allowance can be reduced. The production efficiency of die forging is much higher than that of free forging, but it needs unique equipment and forging die, so it is used for large batch of medium and small forgings.

3、 Profile

Profiles can be divided into round steel, square steel, hexagonal steel, flat steel, angle steel, channel steel, I-beam and other profiles with unique sections. There are hot rolled and cold drawn sections. The hot-rolled profile has low precision but low value, which is used for the blank of common parts; the cold drawn profile has small size and high precision, which is easy to complete the automatic feeding, but it has high value, which is mostly used for the production of large batch, and it is practical for the processing of self-propelled bed.