How flexibility changes on a milling cutter with passive vibration dampening and how does it affect the service life of the tool. In addition, the flexibility of the turning tool has been tested in the previous process of turning, and now the results of this test are compared with the test results of the milling process, and the conclusions obtained from the next experiment are introduced.

　　During milling, the tool is subjected to alternating loads due to the process method. Such loads can be mechanical or thermal. In terms of mechanical loads, special mention is made of the inlet impact of the blades. The moment the cutting edge enters the material, the cutting force is significantly increased.

　　For example, when milling in the same direction of feed, the cutting edge of the tool will experience an input impact of the tool every time it enters the material. This effect is significantly enhanced by the brittle and hard oxide layer, which often occurs on cast or similar workpieces.

　　Lubricant enhances alternating loads

　　On the one hand, the process heat conducted by the tool will increase the heat load of the tool; On the other hand, temperature changes caused by cutting air on the cutting edge can also increase the heat load on the tool. The thermal alternating load is further exacerbated by the use of lubricants.

　　The Institute for Production Technology is sponsoring a project funded by the German Research Association to improve the service life of tools during cutting by changing flexibility at the input of the tool. The project explores mechanical overload and experimentally demonstrates that this mechanical overload can be minimized by changing the flexibility close to the point of action. The reason for initiating this research project is based on the results achieved in several previous works. These results show that the rigidity of the machine drive has a certain impact on the service life of the tool.

　　For example, a machine tool with a highly rigid motor spindle wears out faster than a machine tool with a less rigid drive. However, due to the many advantages of motor spindles that are currently widely used, there is a possibility of an option that is inexpensive and optimizes the parameters of flexibility and service life without changing the drive scheme. Conventional turning tools have a ground hard metal backing plate underneath the rotating punching blade to ensure a secure blade position. While the other parameters of the pad remain unchanged, we have modified the material of this backing board.

　　Similar to the trials done on lathes in the early stages of this project. First, a milling head tool holder was developed, which allowed materials with different flexibility to be placed on the tool. In order to make the test results as comparable as possible with those obtained in previous turning tests, the milling head tool holder is designed to accommodate the same rotating punching inserts as in the previous tests. The milling head tool holder is shown with a backing plate that is mounted between the rotating punching blade and the tool body.

　　When choosing the material of the backing plate used, the results of the previous test were referred to, and it was found that the material with low strength and low elastic modulus was not suitable. The materials used for the test, resin impregnated paper (elastic modulus 7GPa), acyl glass (4GPa), magnesium (40GPa) and aluminum (70GPa), showed that insufficient strength and too small elastic modulus would lead to excessive elastic deformation and excessive plastic deformation, which offset the prestress of the cutting blade and could not continue to be used.

　　For this reason, only materials with high strength and elastic modulus can be selected for backing plate materials. Specifically, it is the cast iron materials EN-GJS-250 (elastic modulus 110GPa), EN-GJS-600 (170GPa), and steel S 235 JR(210GPa)。 The use of the elasticity modulus of the backing plate as a landmark standard is because the modulus of elasticity is the only variable in the flexibility of the backing plate when the size remains the same.

　　Indexable blade breakage becomes the standard for service life

　　Two requirements are put forward for workpiece materials, one is that they will wear out the tool in the process of economical and fast operation, and the other is that they can be applied in daily cutting work. Finally, an aluminum alloy (AlSi10Mg) was chosen, which is a cast iron (EN-GJS) with multiple layers of graphite 260 Gr), and a structural steel (S 235 JR)。 The standard for service life is the breakage of indexable inserts detected when the cutting force increases are measured. Service life is defined as the impact of the indexable blade at the edge entrance before it breaks.

　　Some exceed the recommended maximum

　　The selected cutting test process parameters are adjusted to the corresponding cutting material and the indexable insert used, so that the cutting edge breaks within an appropriate period of time. This means that in specific cases, the parameters must be adjusted higher than the maximum recommended by the manufacturer.

　　S 235 JR、EN-GJS 260 Gr and AlSi10Mg, each of which is combined with three different backing plates. Ten trials were done in each series of nine possible combinations, running until the blade broke. In addition, when machining structural steel, the tool manufacturer Tübinger is used The original backing plates from Walter AG were also tested.

　　Cutting tests with aluminum alloys have not yielded usable results. Even when the cutting speed varies between 500 m/min and 3675 m/min, it does not cause edge breakage within an appropriate foreseeable period of time. So only the results of processing steel and cast iron materials are listed.

　　Machining S 235 The load cycles achieved by JR materials before the blade breaks are listed on the various pads for the elastic modulus of the corresponding material. It is clear from this that changes in the backing plate can have an impact on the service life of the tool. The use of steel pads can increase the average service life by 176% compared to hard metal original backing plates.

　　Conversely, the average lifespan of backing boards made of gray ductile iron was reduced by about 30%, while those made of multi-layer graphite cast iron increased by 42%.

　　EN-GJS 260 The test of GR for materials is a different situation. Compared to steel backing plates, both ductile iron (330% improvement) and multi-layer graphite cast iron (37% improvement) have clear advantages in terms of service life.

　　The individual extreme differences in tool life of machined cast iron materials are partly due to fluctuations in the results and require continued approval. These results are difficult to contrast with those obtained in the previous turning tests, because some of them are contradictory.

　　Backing plates are required for all processing

　　However, it seems that this does not answer the question of flexibility for universally applicable ****. Instead, the question should be asked, what kind of flexibility is for what kind of conditions. For example, there are various machining processes (milling, turning), and various workpiece materials that are difficult to compare with each other, and need to be judged according to the results, and different flexibility or backing plates are adjusted according to the corresponding processing situation.

　　The results of service life tests fluctuate greatly, and there is no universally applicable flexibility, which requires continued testing of the effects of flexibility while reducing interference. At the same time, the question is also raised whether the results achieved by making simple changes in flexibility on the basis of the pad will disappear in the range of fluctuations.

　　Later follow-up studies by the WBK Institute also showed that one possibility of achieving more reliable results was to design an active milling head that could be infinitely flexible and continue to enhance the desired effect. For example, a hydromechanical tool system with a variable pressure tank behind the indexable insert can be envisaged, allowing for variable flexibility and vibration damping.