Peck milling
Peck milling (see Figure 5-8) is that the milling cutter first drills downward, and then the end teeth of the milling cutter play a cutting role: then the direction of the pass is turned 90° to mill with the circumferential teeth of the milling cutter. This is the traditional way of keyway milling.
The state of the vertical downward milling section of pecking milling is not very favorable for the tool. When milling downward, the actual cutting angle near the center of the end tooth will form a negative actual relief angle, which is easy to cause damage at the end edge of the milling cutter near the center. Therefore, pecking milling is only suitable as an alternative.
5-8
Circular interpolation/helical interpolation
Circular interpolation/helical interpolation milling can essentially be regarded as a deformation of ramp milling, that is, the original straight line path in the direction of the vertical axis is changed to a circumferential pass, as shown in Figure 6-9.
But there are some other problems that can be found after changing the straight line to a circumferential route. Rhodium cutter center programmed pass speedWhen the milling cutter turns the straight path into a circumferential path, there is a gap between the horizontal trajectory of the milling cutter center and the trajectory formed by the outer circle of the milling cutter. This gap is related to the interpolation method such as interpolating holes/interpolating outer circles, as well as the diameter of the milling cutter and the diameter of the cylinder.
The diagram of the outer circle interpolation calculation is shown in Figure 6-10, and the formula is as follows:
where "is the programmed horizontal pass speed (mm/min) at the center of the milling cutter during cylindrical interpolation; D, is the large diameter of the milling cutter (mm); D. is the large diameter of the milled workpiece (mm); n is the rotational speed (r/min); / is the feed per tooth (mm/z); It is the number of teeth.
The basic principle is that the horizontal pass speed on the outer circle of the cutter at the point of the large diameter of the workpiece is the same as the calculated pass speed of the straight pass.
When external interpolation is used, the actual cutting width A also changes slightly from the original cutting width, and the calculation formula is as follows:
where D is the outer diameter of the blank (mm): the remaining variables are described in Eq. (6-1).
Figure 6-11 illustrates the calculation of the inner hole interpolation, and the formula is as follows:
where "is the programmed horizontal pass speed (mm/min) at the center of the milling cutter during bore interpolation; The meaning of other variables is explained in Eq. (6-1).
When using internal hole interpolation, the actual cutting width a. is also slightly different from the original cutting width, and the calculation formula is as follows:
where D, is the diameter of the inner hole of the blank (mm); The remaining variables are described in Eq. (6-1).
In addition to the standard outer and inner hole interpolation, the corners of some cavities are actually part of the inner hole interpolation. The machining of cavity fillets often has a local overload.
Conventional corner milling methods (see Figure 6-12) can place very heavy loads. Sandvik Coromant gives an example of when the radius of the arc is equal to the radius of the cutter, if the cutting width of the straight edge is 20% of the cutter diameter, then at the corner, the cutting width will increase to 90% of the cutter diameter and the contact arc center angle of the cutter teeth will reach 140°.
The first recommended solution is to use an arc-shaped path for machining. In this case, it is recommended that the diameter of the cutter be 15 times the radius of the arc (e.g. a radius of 20 mm is suitable for a radius of about 30 mm). As a result, the maximum milling width has been reduced from 90% of the cutter diameter, which was not ideal, to 55% of the cutter diameter, and the contact arc center angle of the cutter teeth has been reduced to 100°, as shown in Figure 6-13. Further optimizations (see Figure 6-14) include further increasing the radius of the cutter pass arc and further reducing the cutter diameter. When reducing the diameter of the cutter to equal the radius of the arc (i.e. the radius of the arc is twice the radius of the cutter, an arc with a radius of 20mm is suitable for a milling cutter of about 40mm). In this way, the maximum milling width is further reduced to 40% of the cutter diameter, and the contact arc center angle of the cutter teeth is further reduced to 80°
6-12
The diameter of the cutter for internal milk interpolation
When interpolating the inner hole on a solid material, special attention needs to be paid to the selection of the diameter of the milling cutter. A cutter diameter that is too large or too small can cause problems.
Figure 6-15 shows the relationship between the diameter of a milling cutter and the diameter of the inner hole when it is interpolated.
To mill a solid flat-bottomed hole, the cutter should exceed the centerline radially at the highest point in the axial direction (see Figure 6-15). If the cutter diameter is too small, a residual column will be created in the middle, and a nail-like bump facing up in the middle of the lighter hole bottom will be left (see Figure 6-16). When the cutter diameter is equal to one time the diameter of the hole being machined, the insert fillet or round insert cutter leaves a red peg-like bump (red on the diagram) after completing a circumferential pass. This peg-like bulge can only be avoided if the highest point of the end teeth of the cutter exceeds the center of the cutter. As shown in Figure 6-17, a flatter hole bottom is obtained when the nail bumps that may be left behind by the fillet of the cutter insert can be covered. The formula is as follows
D.-2(D-r)
(6-5)
The ratio of the diameter of the interpolated hole to the diameter of the cutter should not be too close, as too close to each other will cause flash at the bottom of the hole (see Figure 6-18 in red at the bottom).
To avoid flashing, it is necessary to increase the diameter of the milling cutter appropriately, as shown in Figure 6-19. The minimum bore diameter D- that can be interpolated by a milling cutter with a diameter D is determined by the following formula
D-2(D-r-b,)(6-6), where D. is the minimum inner hole diameter (mm) that the milling cutter can interpolate; D is the diameter of the milling cutter (mm); " is the radius of the corner radius of the cutter insert tip (mm); b is the length of the wiper edge of the milling cutter insert (mm).
Therefore, the diameter of the inner hole that can be interpolated by the milling cutter with a diameter of D, a corner radius of the insert tip and a length of 6 insert trimming edges should be between 2 (D--b) and 2 (D-), that is, the milling cutter can process very few non-through holes with a flat bottom by only garden-shaped interpolation, and its range is only equivalent to the length of two trimming blades. Taking a true 90° end mill with a tip radius of R0.8mm and a wiper length of B=1.2mm as an example, the size limits of non-through holes that can be interpolated by several diameters of milling cutters are shown in Table 6-1 (green and yellow).
However, it should be noted that the needle bulge only has an effect on the interpolation of non-through holes, and it is limited to the use of pure perimeter interpolation. If the method described in the next section of the inner cavity is used to interpolate a non-through hole, the interpolation milling is only affected by the smallest diameter, and there is almost no restriction on the maximum diameter.
There is also a method of expanding the diameter of the inner hole of the non-through hole, that is, the circular interpolation is completed first, which allows a column-shaped island to be left in the middle (see the middle image of Figure 6-15). Then, with a straight line through the center line of the hole, the middle island is completely cut off by relying on this straight line. This method requires that the effective diameter of the bottom of the cutter (which takes into account the effect of insert fillet) completely cover the islands in a straight pass, including the part of the insert fillet that is affected when the islands are formed.
In this case, the maximum diameter of the round hole that can be machined by circular interpolation and a single straight pass is
D... 3D.-4r6-7) is much larger than the maximum diameter of interpolation by arc (see Table 6-1, blue column) than the maximum diameter of interpolation by arc (see Table 6-1, yellow column). Table 6-2 shows the Walter AD.. 120408 The size of the interpolated part at the time of the insert refers to the size limit of the interpolated via.
