Chip types and control
1. The type of chip
Due to the different materials of the workpiece and the different cutting conditions, the chip shapes generated during the cutting process are varied. There are four main types of chip shapes: band, knot, granular, and crushed, as shown in Figure 1-7.
1) Banded chips. This is the most common type of chipping. Its inner surface is smooth and its outer surface is hairy. processing
In the case of plastic metals, such chips are often formed under the conditions of small cutting thickness, high cutting speed, and large tool rake angle.
2) Knobular chips. Also known as extruded chips. Its outer surface is zigzag, and the inner surface is sometimes cracked. These chips are often produced at low cutting speeds, large cutting thicknesses, and small tool rake angles.
3) Granular chips. Also known as unit chips. During chip formation, if the shear stress on the shear surface exceeds the breaking strength of the material, the chip unit falls off the material being cut, forming granular chips.
4) Crushing chips. When cutting brittle metal, due to the small plasticity of the material and low tensile strength, after the tool is cut, the cutting layer metal is brittle under the action of tensile stress without obvious plastic deformation under the action of the front of the tool, forming an irregular shape then the crumbling chips. When machining brittle materials, the greater the cutting thickness, the easier it is to get these chips. The first three types of chips are common types of chips when machining plastic metals. When the ribbon chip is formed, the cutting process is the most stable, the cutting force fluctuation is small, and the surface roughness value of the machined surface is small. The cutting force fluctuates the most during cutting when granular chips are formed. The first three chip types can be converted to each other depending on the cutting conditions, for example, in the case of knotted chip formation, it is possible to obtain granular chips if the rake angle is further reduced, the cutting speed is reduced, or the cutting thickness is increased; Conversely, if the cutting speed is increased or the cutting thickness is reduced, strip chips can be obtained.
2. Chip control
In production practice, we see different chip evacuation situations. Some chips are rolled into snails and break off by themselves when they reach a certain length; Some chips are broken into C-shapes and 6-shapes: some are broken into needles or small pieces, splashing everywhere and sounding safely; Some ribbon chips are wound around the tool and workpiece, which is easy to cause accidents. Poor chip evacuation will affect the normal progress of production, so chips
The control is of great importance, which is especially important when processing on automated production lines. After the chips are violently deformed in the deformation zone of [ and II, the hardness increases, the plasticity decreases, and the properties become brittle. In the process of chip discharge, when encountering obstacles such as behind the tool, on the transition surface on the workpiece or on the surface to be machined, if the strain in a certain part exceeds the breaking strain value of the chip material, the chip will break. Figure 1-8 shows the chip breaking off when it hits the workpiece or behind the tool.
Studies have shown that the greater the brittleness of the workpiece material (the smaller the fracture strain value), the greater the chip thickness, and the greater the chip curl radius, the easier it is for the chip to break. The following measures can be taken to control the chips. 1) Chip breaker is adopted. By setting the chip breaker, a certain binding force is exerted on the chips in the flow, so that the chip strain increases and the chip curl radius decreases. The size parameters of the chip breaker should be adapted to the size of the cutting amount, otherwise the chip breaking effect will be affected. Commonly used chip breaker cross-section shapes are polyline, straight, arc, and full arc, as shown in Figure 1-9. When the rake angle is large, the strength of the tool with a full arc chip breaker is better. There are three types of chip breakers located on the front: parallel, outward, and inward, as shown in Figure 1-10. The external oblique type often forms C-shaped chips and 6-shaped chips, which can achieve chip breaking in a wide range of cutting amounts;
1) a chip breaker is used. By setting the chip breaker, a certain binding force is exerted on the chips in the flow, so that the chip strain increases and the chip curl radius decreases. The size parameters of the chip breaker should be adapted to the size of the cutting amount, otherwise the chip breaking effect will be affected. Commonly used chip breaker cross-section shapes are polyline, straight, arc, and full arc, as shown in Figure 1-9. When the rake angle is large, the strength of the tool with a full arc chip breaker is better. There are three types of chip breakers located on the front: parallel, outward, and inward, as shown in Figure 1-10. The external oblique type often forms C-shaped chips and 6-shaped chips, which can achieve chip breaking in a wide range of cutting amounts; The internal oblique type often forms long tight screw coil chips, but the chip breaking range is narrow; The parallel chip breaking range is somewhere in between.
2) Change the tool angle. Increasing the entering angle and cutting thickness of the tool is conducive to chip breaking. Reduced tool rake angle, chips are easy to break. The blade inclination angle λ can control the flow direction of the chips, ^, when the value is positive, the chips are often curled and broken after hitting the back to form C-shaped chips or naturally flow out to form spiral chips: when the input is negative, the chips are often curled and broken into C-shaped chips or 6 after hitting the machined surface chips.
3) Adjust the amount of cutting. Increasing the feed increases the cutting thickness, which is beneficial to chip breaking: but the increase will increase the roughness value of the machined surface. Appropriately reducing the cutting speed increases the cutting distortion and is also good for chip breaking, but this will reduce the efficiency of material removal. The cutting amount must be appropriately selected according to the actual conditions.
