Abstract: Hard turning is an accepted process for finishing hardened workpiece materials. Compared with other processing technologies, it is flexible, efficient and economical. The transmission parts are easy to hard-turn, and the car synchronous meshing gears in this article use different tool concepts for machining. The number of different parts of the part highlights the advantages and limitations of the different concepts used.
Hard turning is an accepted process for finishing hardened workpiece materials. Compared with other processing technologies, it is flexible, efficient and economical. Since its introduction, hard turning has continued to achieve significant performance improvements with the help of machine tool builders, the development of new PCBN grades and the improvement of tool manufacturing methods.
The transmission parts are easy to hard-turn, and the car synchronous meshing gears in this article use different tool concepts for machining. The number of different parts of the part highlights the advantages and limitations of the different concepts used.
Although the choice of hard turning a few years ago was quite limited, it will be as many as there are options available today. Therefore, the machining process should be around the user's needs, and the technology of the machine tool is designed according to the user's output, which is very important.
Hard turning basic technology
When it comes to the basic technology of hard turning, the reference is to use a standard ISO blade geometry on a standard shank to machine hardened parts to form the desired part profile. Typical hard turning parts are shown in Figure 1. The machining process usually involves a variety of machining operations, such as the inner hole of the car, the end face of the car, the end face of the car, and the tapered surface of the synchronous meshing gear. Since the machining can be done in one setup, the direct benefit compared to grinding is the reduction of parts that are scrapped due to poor positional accuracy. Dimensional accuracy and surface roughness can be met by adjusting the processing parameters. Part clamping and machine stability also play an important role. This technology has been used very successfully since the late 1980s and continues to be the basis for replacing grinding.
High productivity processing technology
For all developing technologies, once the basic concepts have been accepted, there will inevitably be a modified concept. In terms of hard turning, current emphasis is placed on increasing productivity. Interestingly, one process is low feed machining, and another process that everyone expects is high feed finishing.
Insert technology
Plunging essentially uses a significant portion of the length of the cutting edge to create a machined surface. This concept is not completely new, as it has been used very successfully for the seat of the engine cylinder head. However, with the development of the world's first and currently the only integrated PCBN grade CBN100 for finishing, the concept of plug-in has expanded to other applications. The overall CBN100 is much more economical. For example, a triangular blade provides six cutting edges for the insert, which makes the product ideal for both inserting and conventional turning.
Compared with traditional hard turning, the main advantage is to shorten the processing cycle, which is between 75 and 90%.
Indicates the basic principle of the car.
The process relies on a number of key factors: First, the quality of the cutting edge of the insert is very important for good surface finish and longest tool life. It is also necessary to increase the cutting speed and reduce the feed rate. This reduces cutting forces and ensures excellent dimensional accuracy. In order to maintain dimensional accuracy, the blade allows for empty feed during the last 2 to 3 revolutions of the cut. In order to avoid the cutting edge profile affecting the surface roughness, a small axial movement is made. With the application of these technologies and good machine configuration, it is feasible to achieve consistent surface roughness and part accuracy. In gear turning, the insert has been used to machine the tooth flanks and the synchronous meshing cones. The maximum length that has been machined with PCBN is 16 mm.
Wiping edge technology
The wiper technology has been tried and tested in cemented carbide tools. The advantage of using a wiper blade is the ability to process at higher feed rates. . In fact, the principle of the wiper blade is to place a large arc or a large arc after the arc of the tool tip. Since the contact area is wider and the ratio of peaks to troughs of the hard turning generation surface can be reduced, this gives the blade the same effect as a large circular arc or a circular blade. This also makes the surface roughness not deteriorate after the feed amount is increased.
With the advancement of tool manufacturing technology, it is feasible to apply this principle to PCBN blades. The benefits of using wiper technology for hard turning have two advantages: first, to increase productivity, and second, to shorten contact time and provide longer tool life. In gear machining, the wiper blade is typically used to machine the bore.
PCBN; One of the latest advances in wiper technology is the development of the Secomax CBN100 CrossbillTM wiper blade. This unique blade combines the advantages of a monolithic PCBN with a left and right hand wiper design. Until recently, monolithic PCBN; the wiper design on the blade was limited in its ability to face the step. This is due to the fact that the wiper design on one cutting edge is the opposite of the design of the rounded corners. CBN100; The introduction of the CrossbillTM blade has solved this problem by supplying both right-hand and left-handed blades. It can be used for axial turning towards the step (making full use of the wiper technology), and thanks to this design, it can also produce a perfect arc.
Apply high productivity technology
The wiper and insert technology can be used in a range of different high volume production applications. In gear turning, the combination of the insert and the wiper is usually the best solution. Typical synchromesh gears including technical requirements such as dimensional accuracy and surface roughness. The first key point is to synchronize the tapered faces of the gears. There are three options for machining this surface: (i) conventional turning, (ii) inserting, and (iii) finishing edge technology.
Conventional turning is a trial cut and serves as a benchmark against plug-in and wiper technology. In conventional turning, the cutting speed and feed rate used are 150-200 m/min and 0.1 mm/rev, respectively. The parameters used for the insertion: Vc=300m/min f=0.04mm/rev. As mentioned earlier, successful insertion depends on increasing the cutting speed and reducing the feed rate.
The insert used was a one-piece Secomax CBN100 triangular insert with a negative angle groove type, each blade providing six cutting edges. In the insertion process, the positional accuracy of the tool is critical as it will be copied to the workpiece. When machining a taper, a special 'custom' shank is required to provide a taper of 6.5°, and the final adjustment of the taper needs to be done on the machine.
The main benefit of inserting the car is to shorten the processing cycle. The feed rate of the inserted car is 0.04mm/rev, the cutting depth is 4 turns plus a very small air feed, and the total contact time is completed within 0.04 seconds, while the traditional turning requires 4.96 seconds, and the difference is more than 100 times.
Surface roughness result - cone surface
Processing time of turning the end face of the synchronous meshing gear
Analysis of the surface residual stresses of the machined surface has also shown that the insertion has a definite benefit depending on many factors, such as the state of the cutting edge, the processing parameters, and the like. It is feasible that the entire surface of the machined part is in a compressive stress state. This is of course of interest for parts that are subjected to dynamic loads. The surface of the inserted car also removes the problem of affecting the surface roughness associated with the spiral surface, which is the tool path of the spiral.
The use of the wiper technology on the tapered surface is an option when it is necessary to shorten the machining cycle compared to conventional turning; however, this will require the blade to be adjusted to match the taper to ensure the effectiveness of the wiper effect.
The inner hole of the gear can be machined using both conventional blades and wiper blades. It is the reason of the length of the inner hole that the insertion of the car cannot be a feasible solution. The main benefit of using a wiper blade is to increase the margin of resection without affecting the surface roughness of the part. The use of a wiper blade at low feed rates has little or no advantage, and thanks to the design of the wiper blade, the feed can be three times higher than conventional turning, and it has two potential advantages. The first is to shorten the processing cycle, and secondly, less contact time provides potentially longer tool life.
One variation of using the wiper principle is to use a blade with a larger radius of the tool tip, such as a round blade. This modification is acceptable for through-hole or unobstructed external turning, and it is not acceptable to encounter the step during processing, which limits its application. The use of a wiper blade or a round blade has a larger contact area, which does increase the pressure during cutting, but due to the low cutting force of hard turning, there is usually no problem of achieving dimensional accuracy.
Typically, the front end face and/or the rear end face are machined. All three options are possible, and of course the processing tempo is low in all cases because of the small area, but there is still an opportunity to minimize cutting time by applying the insertion technique.
in conclusion
As the industry places great emphasis on increasing productivity by reducing processing cycles, the two new processing techniques discussed in this paper have made important contributions. Although both techniques have some limitations, it has been shown that when the geometry of the part allows the use of the insert and wiper technology, the processing cycle is significantly improved and thus the productivity is increased.
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