1, break the principle of chips
Whether the chipping is fragile or not, during metal cutting, is directly related to the deformation of the chipping, so in the study of the principles of chipping and fracture, it is necessary to start the study of the law of chipping the deformation.
The chippings formed during the cutting process will have higher hardness as well as significantly lower plasticity and toughness due to the relatively large plastic deformation. This phenomenon is called cold work hardening. After cold curing, the chipping becomes hard and brittle and breaks easily under alternating bending or impact loads. The greater the plastic deformation that chipping undergoes, the more pronounced the phenomenon of hardness and brittleness, and the easier it breaks. When cutting high-strength, high-plasticity, high-toughness materials that are difficult to break, it is necessary to try to reduce the plasticity and toughness and increase the deformation of chipping in order to achieve the purpose of chip breaking.
The chipping deformation consists of two parts.
The first part is formed during the cutting process where we call the basic transformations. The chipping deformation measured when the flat rake face cutter is freely cut is relatively close to the value of the basic deformation. The main factors that affect the basic deformation are the rake angle of the tool, negative chamfering, and cutting speed. The smaller the rake angle, the wider the negative chamfer, and the slower the cutting speed, the greater the deformation of the chipping and the better the chip breakage. Therefore, reducing the rake angle, widening the negative chamfer, and slowing the cutting speed can be used as a means to promote chip breakage.
2, the influence of the chip breaker on (curl) chipping
The chip breaker not only acts as an additional variant for chipping, but also has an important effect on the shape of the chipping and the breaking of the chipping. In the cutting process, people use different shapes and sizes of insert breakers, as well as the tilt angles of the insert breaker and main cutting edge to control chipping curl and breakage. To better understand and master these laws, we specifically analyze the shape and size of the chip breaker and the effect of the tip breaker and main cutting edge tilt angle on the chipping shape and chipping fracture.
(1) Shape of chip breaker
The shape of the chip breaker is linear arc type, linear type, full arc type.
- (1) A straight arc-shaped chip breaker (see FIG. 5a) is connected to the straight line by an arc. The straight portion constitutes the rake face of the cutter, and the radius Rn of the groove bottom has a certain effect on the curl and deformation of the chipping. When Rn is small, the chipping curl radius is small and the chipping deformation is large. When Rn is large, the chipping curl radius is large and the chipping deformation is small. (See Figure 6). Medium depth of cut (cut depth ap = 2-6 mm) or less, generally optional
Rn = (0.4 to 0.7) B, B is the width of the chip breaker.
- (2) A straight tip breaker (see Figure 5b) is formed by the intersection of two straight lines. The bottom angle of the groove is 180 ° -σ (σ is called the chipboard wedge angle), and the bottom angle of the groove (180 ° -σ) replaces the action of the arc Rn. When the bottom angle of the groove is small, the curling radius of the chipping is small and the chipping deformation is large. When the groove bottom angle is large, the curling radius of chipping is large (see FIG. 7). For medium cuts, the plywood wedge angle is generally selected from 60 ° to 70 °.
The above two shapes of chip breakers are suitable for processing carbon steel and alloy structural steel, and the front angle is generally γ. It is in the range of 5 to 15 °.
3. The main parameters of the full arc type chip breaker are groove width B, groove bottom arc radius Rn, and rake angle γ (see Figure 5c).
Full-arc insert breakers are often used when cutting highly plastic materials such as copper and stainless steel. Due to the high plasticity material, the tool rake angle is chosen to be relatively large (γ0 = 25 ° -30 °). The same large front angle, full arc cutting tip cutter is more practical as it has a relatively strong cutting edge and shallow grooves for convenient tipping .
Width of chip breaker
The width B of the chip breaker is related to the feed rate f and the depth of cut ap. When the feed amount f is increased, the cutting thickness becomes thicker, so that it is necessary to increase the width of the chip breaker accordingly. The cutting depth is deep and the groove must be widened properly.
Fixed the effect of changing the width B of the chip breaker on the curl and deformation of the chip. FIG. 9a shows that the groove width and feed amount are basically adapted and the insert curls and deforms to break into a C shape. FIG. 9b shows that the groove is not wide enough, the tip has a small curl radius, a large deformation, and breaks into short C-shapes or chipped pieces after collision. In FIG. 9c, the grooves are too narrow and the chips are narrowed down to small rolls. Clogs do not easily flow into the grooves and chips can even damage the cutting edge. In FIGS. 9d and 9d, the groove is too wide, the tip curl radius is too large, and the deformation is not sufficient. It’s not easy to break. Sometimes it does not even flow through the bottom of the groove, forming a freely formed strip.
In general, if the width of the chip breaker is selected by feed rate to cut carbon steel, the relationship between width B and feed rate f is about B = 10f. When cutting alloy steel, B = 7f can be taken to increase chip deformation.
The width B of the chip breaker must also match the depth of cut ap. In general, the slot width B can also be selected approximately according to p. If ap is large, then B should be large. When ap is small, B should be reduced appropriately. If the notch is large and the groove is too narrow, the chips will widen and will not curl easily in the groove, so the chips will not flow into the bottom of the groove and will often form a strip on their own. If there are few cuts and the groove is too wide, the chips will be thin, the flow will be relatively free, the deformation will be insufficient, and it will be difficult to break.
Link to this article：Relationship between tip breaker and cutting edge shape
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