Figure 1 The tip radius of the indexable insert transitions from 2.7mm to 12.7mm. In this way, the chips produced during cutting will become thinner because the shallower depth of cut meets the requirements of this surface for indexable inserts, allowing the feed rate to be increased from the Robertson EDM company name itself to be clearly aware As a result, the company was not a specialized processing workshop that began with machining centers. The shop is located in Edgerton, Ohio, and has four EDM wire-cutting machines and one EDM tooling machine, but currently only one CNC machining center - this is a Mazak VTC purchased in the shop -16B vertical machining center, performance is very reliable. However, with the continuous success of the workshop and the continuous improvement of the business volume, the scope of work and the opportunities for work have also continued to expand. For example, in order to undertake turning operations for large-diameter workpieces, the workshop recently invested in the acquisition of a Johnford ST-40A slant bed turning center from Absolute Machine Tool Co., Ltd., and the bed has a swing diameter of 787 mm ( 31in). At present, the workload of this machining center is continuously increasing. In order to meet new challenges, the machining shop has implemented a high-speed machining method on a vertical machining center such as VMC. The term "high-speed machining", especially in the field of steel machining applications, is often aimed at high-speed operation on a spindle and a shallow cutting depth for a high-speed feed of a small tool. Although the depth of cut is shallow, with this method, the cutting speed is very fast and a very high metal removal rate can be achieved. If the ball end mill is used, the speed of the pass can even be further increased. Although the ball end mill has a shallow depth of cut, it has the advantage of making the axial chips thinner. Because of this effect, the chip thickness is smaller than the advancement per tooth. This means that the forward speed per tooth can be further increased, and the linear feed rate of several inches per minute can be increased accordingly, even exceeding the allowable range of high-speed spindles. This is high speed machining. But on the contrary, Robertson's machine tools do not have particularly high spindle speeds, and no complicated 3D milling work can benefit from small-diameter ball-end tools. For this processing plant, the thinning of chips in order to increase the feed rate in high-speed machining is still a really valuable idea. In order to increase its own metal cutting speed, the shop used a tool designed by Iscar to achieve the purpose of thinning the chips. This indexable insert is called a "feed milling cutter" and its profile has a curved surface that makes it possible to thin the chips. In other words, it is not necessary to use a ball end mill or a small-diameter tool for chip thinning. At least this aspect of high-speed machining can be applied on medium-speed machines to achieve a more standard roughing purpose.
Figure 2 The gearbox cover is another part machined with a high-speed feed tool. The practical application of the chip thinning process has also been mentioned previously in this machined part. Mr. Jeffrey Robertson is one of the main partners of this workshop. Iscar’s representative responsible for local machine tool sales and applications is Mr. Greg Mallett. Mr. Mallet and Mr. Robertson also saw the opportunity for the application of axial chip thinning indexable inserts and jointly planned the tools used for the new turning machining center. Robertson Electric Machining Co., Ltd. used a cold-rolled steel material to rough process a fixture part. The shop's method of machining this part provided a good basis for comparison. Because this part is too large, the stroke of the machining center is not enough, so the workshop had to use a partial processing method to process this part. After the first half of the part was machined with a 19.05mm (0.75 in) radius indexable insert tool, the shop agreed to use the 19.05mm radius indexable insert cutter to cut the other half of the part. The tool with the latter indexable insert uses one tooth rather than two teeth for cutting, but it also uses a shallow depth of cut. However, due to the thinning of the chips, a higher feed rate is obtained, so the productivity is improved. The service life of the tool has also increased. The surface of the indexable insert begins with a 2.7 mm (0.106 in) radius and then transitions to a 12.7 mm (0.5 in) radius. The shallow depth of cut created by this curved surface allows each tooth to advance faster because the chip thickness is less than the advancement of each tooth, not equal.
The size of this part is slightly over the working area, and two different types of indexable end mills are used during machining to set up the machine in two stages. Two different cutting performances were obtained after the shop used indexable inserts that made the chips thinner. See the table for details. Indexable milling cutters using the advantages of chip thinning Previously used indexable roughing end mills Tool diameter (mm) 19.05 19.05 Number of teeth 1 2 Cooling medium air air speed (r/min) 3000 2000 Depth of cut (mm) 1.02 1.27 Cutting width (mm) 12.7 12.7 Feed amount (mm/z) 1.02 0.22 Feed speed (mm/min) 3048 889 Tool life (number of bits/blade) 20 15 Cutting time (s) 584 977 Mr Mallett says that tool life The extension is also due to the curved surface of the tool. He said that Robson Electric Machining Co., Ltd. has been able to improve the tool life mainly because of its stable machining. In the case of ball end mills, the material is only in contact with the tool surface at one point below the full radius of the tool. The resulting cutting force is not exactly transverse thrust, but an upward thrust toward the center point of the ball end. In other words, only a part of the cutting force moves in the X-axis and Y-axis directions. Other cutting forces are in the direction of the Z-axis, that is, the direction of the spindle. In the three axes, the rigidity of the spindle is the best. Since the force received along one side of the tool is relatively small, the chance of tool offset is much less, so the cutting is more stable. In fact, the production capacity of the processing center in the workshop has been greatly improved. Nowadays, the tool shop often uses this type of tool for the rough machining of steel, for example, it is used to process the gearbox cover shown in FIG. 2 , which is another example of such a tool being suitable for machining a certain part. With the continuous development of the processing plant, there is no doubt that the number of machining centers will continue to increase, and perhaps a high-speed machining machine will be added later. However, in the current situation, the excess production capacity provided by the faster roughing feed rate is sufficient to meet current production needs. What is the axial chip thinning process? 
With ball-end milling cutters, the cutting conditions differ from the standard milling cutters in that the cutting contact surface with the tool is smaller than the full radius of the curved surface. The chip thickness and advancement per tooth will also be different - less cut thickness. The principle is shown in the figure. Since the chips are thin, the amount of advance per tooth can be increased, resulting in a higher linear feed rate, resulting in higher metal cutting speeds. For applications that have adopted relatively shallow depths of cut, this is the case. The process is more appropriate. This effect is usually closely related to the ball end mill in high speed machining. However, it is also advantageous for milling cutters that use round indexable inserts and tools that use curved surfaces to achieve the goal of thinning the chips (such as the "feed milling cutter" mentioned in this article). The direction of force can also be seen from the figure. The tool force shown in the figure is not transverse but extends from the material to the center point of the surface along the diagonal line indicated by the dashed line. In other words, some forces do not move exactly along the X-axis and Y-axis, but move along the Z-axis. This is the most rigid spindle in the machine tool, which can make the cutting more stable. status.
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