Advantages and disadvantages of hard and linear guides machine center for CNC machine tools? Finally made it clear!
Small workers have always learned this: If a general machining center is used to make products, they buy linear rails. If they are processing molds, they buy hard rails. The accuracy of the linear rails is higher than the hard rails, but the hard rails are more durable.
Hard Track Features
First, the advantages of hard rail:
1. Able to withstand larger loads, suitable for roughing machine tools with large tool volumes and large feeds.
2. Because the contact area of the guide rail is large, the machine tool runs more smoothly, which is suitable for machine tools with high vibration requirements, such as grinding machines.
Disadvantages of hard rail:
1. The material is not uniform. Because it is generally cast and formed, casting defects such as sand inclusions, pores, and looseness are easy to occur in the material. If these defects exist on the guide surface, it will adversely affect the service life of the guide and the accuracy of the machine tool.
2. It is difficult to process, because this type of guide rail is generally integrated with the main components of the machine tool such as the base, column, table, slide saddle, etc., during the processing, its shape and position tolerances, roughness requirements, timeliness Processing, quenching and other processes are difficult to control, resulting in the processing quality of the parts can not meet the requirements of assembly.
3. It is difficult to assemble. The word "assembly" means that both installation and matching are required, and the matching process is a process of combining technology and physical strength. It cannot be completed by ordinary workers. It requires the relative number of technologies. The machine tool can be completed only by the assembly workers who have a good grasp of the overall accuracy. At the same time, it needs to be equipped with a shovel, a square ruler, a square ruler, a square ruler, a dial indicator, and a dial indicator.
4. The service life is not long. This can only be relatively speaking. Under the same maintenance and use conditions, the service life of common hard rails is shorter than the service life of wire rails, which is very different from their movement methods. In terms of friction, the hard rail runs with sliding friction, while the linear rail runs with rolling friction. As far as the frictional force is concerned, the friction of the hard rail is much larger than that of the linear rail, especially in lubrication. Inadequate conditions, the friction of the hard rail is even worse.
5. The maintenance cost is too high. The maintenance of the hard rail is much larger than the maintenance of the linear rail in terms of difficulty and maintenance cost. If the scraping margin is insufficient, it may involve disassembling all the large parts of the machine tool. After the new hardening treatment and mechanical processing, the large piece may be re-casted, and the wire gauge only needs to replace the corresponding wire rail, which basically does not greatly affect the use of the related large piece.
6. The running speed of the machine tool is low. Hard rails cannot usually withstand excessively fast running speeds because of their movement mode and excessive friction, which is inconsistent with the current machining concept. In particular, workers in many factories do not have the corresponding maintenance knowledge of machine tools. Many times they only know how to use machine tools, but they largely ignore the maintenance of machine tools. The maintenance of machine tool tracks is a top priority. Once the track lubrication is insufficient, Will cause burnout or wear transition, which are fatal to the accuracy of the machine tool.
Linear rail features
First, the advantages of linear rail
1. Assembly is easy and simple, with a little training, you can complete high-quality assembly. Because the accuracy of the machine tool is too large, the accuracy of the transmission mechanism is determined. The transmission mechanism is generally composed of a wire rail and a screw. That is to say, the accuracy of the wire rail and the screw itself determines the accuracy of the machine. They all exist in the form of standard parts. A
s long as you choose the corresponding accuracy provided by the manufacturer, there will usually not be a big problem.
2. There is a lot of choice, whether it is from the structural form or accuracy level of the rail, the lubrication method or load bearing capacity, the processing method to the running speed and other parameters can be selected. You can arbitrarily configure according to the specific conditions of your designed machine The type of rail you need.
3. The running speed is fast. Many machine tools now run extremely fast, especially the idling speed. This is largely due to the credit of the linear guide, because the rolling friction operation mode and high-precision processing ensure the machine tool. The accuracy and stability of high-speed operation has greatly improved the processing efficiency and processing accuracy.
4. High machining accuracy. As a linear guide, as a standard product, both the material and the processing method have entered a benign controllable range. Therefore, most of the machine tools in the field of precision machining use high-precision linear guides. As a machine tool guide, this also greatly guarantees the machining accuracy of the machine tool. Domestically done better are Nanjing technology, Hanjiang line guide, Taiwan has silver line guide, Germany has Rexroth company, Japan has THK line guide, etc. These brands have greatly enriched and fulfilled the market's needs for various rails of various requirements. Individuals prefer to use THK from Japan. The stable performance and fine workmanship are high prices.
5. Long service life, because the running mode of the line rail is rolling friction. The steel balls in the slider drive the movement of the feeding component by rolling on the rail. The friction force of this rolling friction is less than that of the hard rail. Many, so whether it is transmission efficiency or service life, the line rail should be much more ideal than the hard rail.
6. Low maintenance cost. No matter from the maintenance cost or convenience, the rail has its natural advantages and convenience, because as a standard part, the replacement form of the rail is the same as replacing a screw. Of course, there are still some adjustments in the accuracy of the reply, but compared to the hard track, it is really convenient.
7. The delivery cycle is short. The general delivery cycle of the line rail can be completed within half a month, unless you choose foreign brands, such as Rexroth and THK. In fact, these two brands also have corresponding processing plants in China. As long as the model of the rail you choose is not very biased, the delivery period of about half a month can still be guaranteed, and the line rail of Taiwan Shangyin can even achieve a one-week delivery cycle, but the same The hard track does not have such a good time to control. If the action is relatively large, such as recasting, the cycle may be uncertain for more than a few months.
Second, the shortcomings of the line rail
1. The carrying capacity is relatively small. This relatively small size is only for hard rails. In fact, the rails of many large factories have greatly improved their carrying capacity through some structural designs. Of course, they are relatively hard rails. In terms of carrying capacity, it is still relatively small.
2. The stability is relatively weaker than the hard rail, such as the ability to resist vibration, but I still want to emphasize that this weakness is relative to the hard rail. In fact, the smoothness of many line rails is also now Very well, as long as the equipment you design is not too special, it is generally able to meet the needs.
3. Pay special attention to the protection of the rails during transportation and assembly. As a standard part, its unique structural characteristics put it in an embarrassing situation that is relatively easy to be damaged, such as the slender shape leading to the rails. Insufficient rigidity, which is prone to bending and deformation during compression, leading to loss of accuracy; for example, because it is steel, if it is not rust-proofed, it is easy to contact water or other solvents during transportation and assembly. Phenomenon such as rust and corrosion can be caused, which leads to loss of accuracy.
The above are some rudimentary knowledge of hard rail and linear rail by a designer who has been engaged in machine tool design for more than 10 years. I hope it can help you.