Difference between high speed machining (HSC) and high efficiency machining (HPC)

High speed machining (HSC), which emerged in the late 1980s, greatly shortens the machining time and improves the surface quality and machining accuracy of the workpiece because it significantly improves the cutting speed and feed speed. Therefore, it can reduce processing procedures and simplify production process, and promote the transformation of production mode in some industries, which effectively promotes the development of the whole production technology. High speed machining integrates the two contradictory characteristic parameters of “productivity” and “flexibility”, so that the flexible production system composed of high-speed machining center can replace the traditional rigid automatic line, and promote the transformation of production mode in medium and large volume production industries such as automobile.

High speed machining leads to process substitution, which simplifies the production process. In mold manufacturing, using high-speed hard milling instead of EDM is a very typical example. The hardened workpiece can be processed into finished products by rough milling and high-speed finish milling under one clamping. The application of high-speed hard milling has created conditions for mold manufacturing to realize the integration of cad-cam-hsc. High-speed hard milling technology has undoubtedly brought a major change to mold manufacturing technology.

Since the rise of high-speed machining for more than ten years, high-speed machining technology has been widely popularized and applied. In production, through high-speed machining, the basic time is significantly shortened, and the proportion of auxiliary time to basic time is correspondingly increased (from 7%: 93% in the past to 35%: 65% at present. For the processing of aluminum alloy workpiece, this proportion reaches 50%: 50%). From the current technical situation, the potential to further reduce the basic time through high-speed machining is not great.

In recent years, in order to further improve production efficiency, more and more high-efficiency machining (HPC) – increasing material removal per unit time and significantly reducing auxiliary time – are used to further reduce the basic time and auxiliary time in the cutting process.

The difference between high speed machining (HSC) and high efficiency machining (HPC) is that it is not limited to increasing the cutting speed and feed speed, but puts the optimization of material removal rate in the first place, aiming to further reduce the processing cost by increasing the material removal amount per unit time and reducing the processing time (basic time and auxiliary time).

The material removal rate (q) depends on the side cutting amount (AE), back cutting amount (AP) and feed rate (VF). For milling, the feed rate (VF) depends on the feed rate per tooth (Fz), the number of cutter teeth (z) and the speed of milling cutter (n).

The material removal amount per unit time can be expressed by q = AE · AP · VF / 1000 = AE · AP · FZ · Z · n / 1000 (cm3 / min).

From this expression, we can see that the material removal rate is related to five cutting parameters. Therefore, efficient machining can but does not have to include high-speed machining, which means that there is no obvious boundary between efficient machining and high-speed machining.

Aviation industry is the first department to apply the new technology of high-speed machining and high-efficiency machining. The load-bearing components such as beams, frames and large wall panels of aircraft adopt integral structural parts, and 75% ~ 95% of the blank materials will be cut off during processing. For this particularly high cutting amount, it is undoubtedly the most appropriate to adopt efficient processing. Eads (European aeronautical defense and space company) in Augsburg, Germany, used HSC process to process an aluminum alloy integral component of a military aircraft in the 1990s. The main purpose is to simplify the production process, obtain high surface quality with fewer processes, rather than improve the material removal rate. 54 cutting tools were used during processing, and it took 25 hours to complete the processing. In order to further tap the potential of productivity, it was natural to turn to high-efficiency processing later. 40 cutting tools were used, and the processing time was only 12 hours, which was reduced by more than half.

Especially for milling, the material removal rate that can be achieved by milling cutter has become an important index to measure the processing economy of milling cutter. In recent years, many tool manufacturers have developed many milling cutters with high feed speed. Although the structural forms of these milling cutters are different, one common feature is that they have a blade geometry suitable for high-speed feed. The characteristic of this geometry is that the cutting edge has a large arc radius, which slightly limits the back draft (AP) of the milling cutter, and the radial cutting force acting on the milling cutter is greatly reduced due to the small main deflection angle, which is conducive to the use of high feed per tooth for machining.

For example, when roughing the blow mold of 40crmnmos86 glass bottle, Franken tool factory in Germany compared the milling effect of milling cutter with three round blades and high feed speed milling cutter with three time-s-cut blades. The cutting parameters of the former are VC = 250m / min, FZ = 0.3mm, AP = 0.75mm and AE = 18mm. Cold compressed air is used for cooling during processing, and the processing time is 9 minutes. In the latter, AP was reduced to 0.5 mm, while FZ was increased to 1.0 mm. As a result, the processing time was only 4 minutes. The time saving reached 55%, that is, the hourly use of the machine tool saved 55%.

It can be seen from here that by using higher cutting parameters, high material removal rate can be obtained and the processing time can be significantly shortened. However, efficient machining can not only adopt high cutting parameters, but also implement efficient machining through other machining strategies that can significantly reduce auxiliary time. For example, the use of composite tools (such as composite step drilling, thread drilling and milling tools and other composite tools for comprehensive processing), multifunctional end milling tools for circular feed milling and other advanced tools can significantly reduce the number of tool changes and reduce the auxiliary time, so as to significantly improve the production efficiency.

The compound tool integrates multiple machining processes on a tool, and often realizes the comprehensive machining of multiple machining parts in one machining stroke. The use of this tool not only eliminates the tool change, but also helps to improve the machining accuracy, and saves the accuracy measurement between processes, so as to significantly improve the production efficiency.

When the multi-functional end milling cutter is used to mill holes on the machining center, the number of tool changes can also be reduced. When milling holes, the rotating milling cutter makes spiral interpolation movement around the Z axis, and the holes of the required size can be processed in one working stroke. For example, if a hole with a diameter of 285 mm is processed, the milling cutter with a diameter of 160 mm can complete the processing task in one working stroke, which can save 73% of the processing time and five reaming procedures compared with the conventional process.

In recent years, the advent of high efficiency deep hole drill has significantly improved the efficiency of deep hole drilling. A double-edged whole fried dough twist drill developed by G hring l/D has been used in deep hole with a bore diameter ratio (l/D) of 20. It uses a high rate of 10~12 times than the traditional large flow wet drilling, and does not need to chip in the drilling process, which greatly improves the machining efficiency. Moreover, when drilling, the radial offset of the bit is particularly small, which can obtain better surface quality.

In production, high-speed machining and high-efficiency machining processes have been widely popularized and applied. The common feature of these two processes is that they can significantly reduce the machining time and shorten the production process. The different feature is that high-speed machining adopts high cutting speed in order to obtain high surface quality and simplify the process flow. Therefore, high-speed machining is more suitable for finish machining; High efficiency machining mainly adopts high cutting parameters to obtain high material removal per unit time, so as to significantly shorten the machining time. For efficient machining to obtain high material removal rate, it is suitable for rough machining. In actual production, these two processing processes can be applied to process a workpiece at the same time. For example, when machining the die, high-efficiency machining can be used for rough milling (to achieve high material removal rate), while high-speed machining (to obtain better surface quality and high machining accuracy) can be used for fine milling.

At present, both the popular high-speed machining and the emerging high-efficiency machining should be attributed to the promotion of the continuous development of tool technology, especially the continuous development and optimal combination of tool materials, blade geometry and coating, which provides a foundation for the continuous development of high-efficiency tools with different structures. The production practice shows that in order to significantly shorten the processing time, improve the production efficiency and reduce the manufacturing cost of parts, the key is to adopt new high-speed machining and efficient machining processes.