Skillful use of 4 types of CNC Machining technology

First, the undercut knife method

  1. Outer convex processing
    As shown in FIG. 1, when the outer opening is projected outward, the processing can be performed by using the “planar contour processing” method. Usually, the tool is selected from the outer point P1 (A’B’C’D’) of the blank material, so a vertical knife can be used and a linear cutting method can be used. If you choose to cut the knife from a point on the surface of the solid material, you can only use the spiral knife method or the linear progressive method. Otherwise, a pre-drill is required (a small hole with a drill bit is pre-drilled and cut vertically with a vertical cutter to the pre-drill of a flat drill). If you do not understand this, using the tool as a drill directly under the physical material of the knife can easily damage the tool.
    Assume that the size of the blanks A’B’C’D’is 100×100 and the size of the projection is 60×60. For φ24 end mills, the manual programming of the vertical lower blade is as follows.
    X42Y65 (P 1 outside the entity)
    Z-2 (Vertical to the lower blade, cutting depth 2 mm) G01Y-42F300 (straight line cutting)
    For example, if you are using a Φ16 end mill and want to use a smaller milling cutter, you will need multi-knife machining (ie, multi-row machining). As shown in Figure 2, this outsole should be cut “outside to inside”. This not only removes the tool from the outside of the body, but also makes it easy to finish the finishing allowance. For flat knives, the roughing line spacing (line spacing) can be between 0.7% and 0.8% of the tool diameter.
  2. Internal cavity treatment
    When machining cavities, it is inevitable to cut the knife from solid material.
    When machining parts with a CNC machining center, you can pre-drill small holes with a center drill and then use the “planar machining” method.
    If you are working on a regular CNC mill, you do not need to drill in advance. Place the tool using “Spiral Low Knife Mode” and then perform flattening (save tool change time). Manual programming in spiral disconnect mode is as follows:

X-6Y-6 (Lumen for processing knife points on XY plane P1)
Z10 (Z direction that slows down the height of the point blade)
G01Z1F100 (Starting point of spiral knife in Z direction)
G91G03I0J6Z-1L3 (helical lower knife, depth of cut 2 mm)
G90 G03I-3J0 (This statement cannot be omitted; otherwise, an untreated clean mark remains on the bottom of the workpiece)
G01Y6F300 (first “planar cavity machining” from inside to outside)
In addition to the outer spiral style under the knife, the knife can also be used with a straight tilt,
Or a straight knife that gradually turns off the knife mode.

2, wise use of finishing allowance
Finishing allowances in machine manufacturing technology and automatic programming software finishing allowances are different.

The former refers to the margin to be removed during processing, and the latter refers to the margin left after the 5 axis cnc machining is completed.
For example, if the final dimension of the inner hole is Φ800 + 0.2 and the current machining is final machining, the “residual tolerance” of automatic programming should be set to “0”. If you need to keep 0.1mm in this process for finishing, you need to set the “Mask Margin” to “0.1” during programming.

We can use it skillfully to solve the intermediate size calculation problem of asymmetric tolerance. In manual programming, the “intermediate size” is usually programmed to ensure that the actual dimensions of the machined part are within the required dimensional tolerances. For asymmetric tolerances, calculating the median size is often cumbersome. In automatic programming, this problem can be easily solved by setting the machining allowance.
As shown in Figure 7a, the low deviation is the base deviation of 0 and the upper deviation is +0.2. Therefore, the programming software will automatically calculate the trajectory according to an intermediate size of 60.1 mm only if the machining tolerance is set to 0.05.
The top offset of the part shown in Figure 7b is 0, the lower bound deviation is -0.2, and the machining margin is -0.05, so the programming software can automatically calculate the trajectory with an intermediate dimension of 59.9 mm.
Further, the outer contour adopts “outside to inside”, and the inner contour is cut as “inside to outside”. Roughing of parts is also easy using the residual tolerance setting.

3, corner transition mode
In the trajectory design of CAXA automatic programming software, it is necessary to set the “corner transition mode”, which is the machining mode when a corner is encountered during cutting. CNC automatically recognizes the corners of the inner corners. For internal angle machining, the center trajectory of the tool at the corner must pass through the intersection P of the equidistant lines of the profile trajectory, as shown in Figure 8.

That is, in a corner where one contour is machined into another, the center locus of the tool is the intersection of two equidistant lines (the intersection of 1P and 2P, the tool radius is the distance).
FIG. 9b shows the arc transition mode. In other words, in the corner where one contour is machined to the other contour, the trajectory at the center of the tool is an arc (the arcs 1-2 in the figure). The start point is the end point of the previous curve, the end point is the start point of the next curve, and the radius is equal to the tool radius.
From the point of view of cutting technology, in semi-closed or closed internal and external contouring, the rest during machining should be avoided as much as possible. The “parts machining machine” machining system is temporarily in a dynamic equilibrium state and an elastic deformation state during machining, so that when the feed is suddenly stopped, the cutting force is significantly reduced.
The original process system is out of balance and the tool leaves scratches and dents that affect the surface quality of the part.

Obviously, from a process point of view, you should choose corner transitions whenever possible. However, when a sharp corner transition occurs, the tool will move longer than the arc transition. In particular, when the angle α of the part is small, the intersection of the tool center trajectories at the corners becomes farther, which affects the cnc machining china efficiency. Therefore, the principle of corner transition selection is generally to select “arc transition” for rough cutting and “spike transition” for finishing (especially if the corners are sharp and surface quality is high).
In manual programming, there are also cusp transitions and arc transitions. The instruction codes corresponding to sharp corner conversion are G451 (SIEMENS system) and G61 (FANUC system), and the codes corresponding to arc conversion are G450 (SIEMENS system) and G64 (FANUC system).

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