What Are the Different Types of Milling Equipment?

High-speed milling with high feed rates and small cutting parameters.

High-speed milling

ordinary

(1) Reduce tool quality, reduce the number of tool components, and simplify the tool structure

The relationship between the fracture limit of different tools of the same diameter obtained from experiments and the quality of the tool body, the number of tool components and the number of contact surfaces of the tool. After comparison, it was found that the lighter the tool mass, the fewer the number of components and the contact surface of the tool, and the tool The higher the limit speed of rupture. It is found that the use of titanium alloy as the material of the tool body reduces the mass of the component, and can increase the tool's fracture limit and limit speed. However, due to the sensitivity of the titanium alloy to the incision, it is not suitable to manufacture the cutter body, so some high-speed milling cutters have used high-strength aluminum alloys to produce the cutter body.

In the structure of the tool body, attention should be paid to avoiding and reducing stress concentration. The grooves on the tool body (including the tool holder groove, the chip groove,

With the development of high-speed cutting technology, the application of high-speed milling technology is becoming more and more widespread, and it has attracted more and more attention from manufacturing companies and scientific researchers. A research institute of the Ministry of Information Industry purchased the first HSM-700 high-speed vertical milling center from the Swiss company MIKRON in July 1999, and in October 2001 purchased three more HSM-700 high-speed milling machines for production. The author conducted in-depth and detailed investigations on the processing efficiency of this batch of advanced high-speed milling machines, compared the processing efficiency of different milling machines, and deduced the calculation formula for high-speed milling processing efficiency.

Calculation of high-speed milling processing efficiency

According to the traditional cutting theory, the cutting efficiency ZW (cm3 / min) can be calculated by the following formula: ZW = v · f · ap (1)

Where v --- cutting speed; f --- feedrate; ap --- cutting depth

According to analysis and research, we believe that formula (1) is not applicable to the calculation of high-speed milling processing efficiency, for two main reasons:

1) The spindle speed of the high-speed milling machine is quite high (such as the highest speed of the HSM-700 high-speed milling machine is 42000r / min, and the speed when machining the plane is also 35000r / min, or more). Cutting metal

2) In actual machining, the set speed and feedrate are only the maximum speed and feedrate, and the actual tool speed and feedrate are always changing (the self-test function of the HSM-700 machine tool can show the entire cutting process Changes in the process), the actual speed and feed rate during the cutting process always quickly reach the higher value from the lower value and then quickly fall to the lower value. Such repeated changes are an objective reflection of the milling process, and not Speed and feed can be kept constant during turning processes.

Therefore, we propose to use the metal removal amount Z (cm3 / min) per unit time to represent the processing efficiency, that is,

(2)

Where W --- total metal removal during cutting (cm3)

t --- cutting time (<0,)

Formula (2) is more in line with the actual situation of high-speed milling. Using formula (2), it is easy to calculate the processing efficiency of high-speed milling, and it is also convenient to compare the processing efficiency of different milling machines.

For example, the parts shown in Figure 1 were originally processed on ordinary milling machines. In order to shorten the production cycle, some parts are now processed by high-speed milling machines. In this way, the processing efficiency of the two processing equipments can be compared by processing the part. Because the surface quality of this part is not high, high-speed milling and ordinary milling can meet the requirements. In fact, the surface roughness of parts produced by high-speed milling is 1-2 levels lower than that of ordinary milling.

Figure 1 Schematic diagram of parts

The processing efficiency is represented by the amount of metal removed per unit time Z = W / t (cm3 / min). In the test, several time periods in the milling process are taken, the processing time is recorded, the volume difference between parts before and after processing is measured, and the Z value is calculated by formula (2). The average value of Z is calculated through multiple measurements, and the average value can be regarded as a more accurate Z value. For the high-speed milling process of the part shown in Figure 1, the Z value calculated by equation (2) is

Calculated according to the traditional cutting theory according to formula (1)

Comparing Z high speed and ZW, it is clear that ZW and the actual high speed milling processing efficiency of this part are very different.

Comparison of machining efficiency of different milling machines for high-speed milling

In addition to the HSM-700 high-speed milling machine, the milling machine currently used by a research institute also has domestic vertical milling machines and imported milling centers. The domestic milling machine is an XK5040-1 type vertical lifting table milling machine (hereinafter referred to as a domestic ordinary milling machine) produced by Beijing First Machine Tool Plant purchased in the early 1990s. It is mainly used for rough machining of parts and a small amount of cast iron and steel. Processing of imported parts; the imported milling center is a VF-0 HAAS type milling center (hereinafter referred to as imported ordinary milling machine) made in the United States, which can be used for roughing and finishing.

For the parts shown in Figure 1, the cutting efficiency of machining on a domestic ordinary milling machine is

The cutting efficiency of processing on imported ordinary milling machines is

Comparing Z high speed with Z national general and Z Jin general respectively, there are

From the above calculations and comparisons, it can be seen that the metal removal rate of this part on the high-speed milling machine is quite high, and its advantages are more obvious than domestic ordinary milling machines. Milling machine is 10 times faster). Of course, the processing efficiency of different milling machines is not the same for parts with different materials, different shapes and different processing requirements. For large parts with large processing areas or parts with particularly complex shapes, high-speed milling machines have a more significant processing efficiency advantage. The efficiency advantages of high-speed milling machines are mainly reflected in high tool speed n and high feed speed Vf. In actual processing, the influence of the feed rate Vf on the processing efficiency is often greater.

Comparison of cost-effective machining efficiency in high-speed milling

The comparison of processing efficiency must have certain constraints, and the relationship between processing efficiency and production costs should be considered in combination with the actual situation of the enterprise. Divide the processing efficiency Z obtained by formula (2) by the processing cost C to represent the processing efficiency E (cm3 / min · 10,000 yuan) considering the cost factor, that is,

In equation (3), for simplicity of calculation, let the processing cost C be mainly the manufacturing cost (including equipment cost, equipment maintenance cost, tool loss cost, etc.), and assume that the daily maintenance costs of high-speed milling machines, domestic ordinary milling machines, and imported ordinary milling machines are equal. . In order to objectively reflect the actual machining efficiency, the comparison of the use of machine tools in the longer period from January 2001 to May 2002:

Swiss MICRON HSM-700 high-speed milling machine is worth RMB C0 high speed = 2 million yuan; due to the high price of machine tool parts, the costs for non-routine maintenance of the machine tool (including troubleshooting, replacement of parts, etc.) are C2 high speed = 95,000 The tools used on high-speed milling machines are imported milling cutters, which are more expensive. In addition, the lack of specifications for cutting tools and parts materials makes high-speed milling cutters more expensive. Therefore, from the beginning of last year to the present The high-speed milling cutter wear cost is C3 high-speed = 14,548.13 yuan.

The U.S.-made VF-0 HAAS milling center was an ordinary milling center imported in 1998. At that time, the value was RMB C0 Jinpu = 800,000 yuan; the machine tool has good performance. Except for routine maintenance, no faults that require maintenance have occurred. General = 0.45 million yuan; like high-speed milling machines, the tools used are imported milling cutters, except for normal tool wear, there is very little abnormal tool wear, and the cost of milling cutter loss is C3 Jinpu = 2,195.26 yuan.

XK5040-1 type vertical lifting table milling machine purchased from Beijing No. 1 Machine Tool Factory in 1992. At that time, the value was RMB C0 Guopu = 600,000 yuan; currently it is mainly used for rough machining of parts. Although the accuracy is not high, the performance is relatively stable In addition to routine maintenance, no major failures occurred. In 2000, the operating system was remodeled (Siemens operating system was replaced). The cost of the transformation and overhaul was C2 Gp = 64,500 yuan. Both imported tools and domestic tools were used on this machine. C3 national standard = 1,377.62 yuan.

Let the service life of the machine tool be 20 years. According to the straight line depreciation method, the machine tool is depreciated by 5% per year. By 2002, the current costs of the three milling machines are:

According to formula (3), the processing efficiency of three different milling machines when considering cost is E high speed = Z high speed = 0.1291 cm3 / min

It can be seen from the calculation results that after considering the cost factors, high-speed milling no longer has a significant efficiency advantage (close to the processing efficiency of imported ordinary milling centers). This comparison result shows that the current cost of high-speed milling is still relatively high (its equipment costs, maintenance costs and tool wear costs are much higher than ordinary machine tools).

Although economical cutting efficiency is currently not achieved with high-speed milling, it does not mean that high-speed milling has no advantages. First of all, the above analysis of the milling efficiency economy only considers the production cost and does not consider the time efficiency. With the rapid development of technology today, time is often a more important economic factor. The advantage of high-speed milling in terms of shortening the processing time is obvious. Secondly, the comparison of the machining efficiency made above is based on the premise that both high-speed milling machines and ordinary milling machines can process the same part. In fact, many parts that are not suitable (or cannot) be processed on ordinary milling machines (such as thin-walled parts or Machined parts with high surface quality requirements) can only be processed with high-speed milling machines. Third, high-speed milling technology is undergoing a continuous development process in China as a new processing technology. In order to obtain the economic processing efficiency of high-speed milling, it is necessary to deeply study the high-speed milling mechanism, accelerate the scientific research and development of high-speed milling technology, and strengthen production Management to improve the quality of operators. It is believed that with the continuous deepening of research on high-speed milling technology, problems such as machining economics will be solved very well.

High-speed milling conclusions

1) Production practice shows that the high-speed milling machine covers a wide range of parts, and is especially suitable for precision parts with large processing areas and complex shapes. Parts are processed with high precision and low reject rate.

2) The traditional cutting efficiency formula is not suitable for high-speed milling. It is more accurate to express the processing efficiency of high-speed milling with the amount of metal removed per unit time.

3) From the perspective of the cutting efficiency of the machine tool alone, the high-speed milling machine is several times higher than the ordinary milling machine, but the current high-speed milling machine has a higher cost. When choosing a process plan, you can consider rough milling with ordinary milling machines and semi-finishing and finishing with high-speed milling machines.

4) Only by in-depth scientific research and development of high-speed milling technology can the processing efficiency advantages of high-speed milling machines be fully utilized.