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Burrs after machining are annoying, and the metal cutting process is often accompanied by the generation of burrs. The existence of burrs not only reduces the machining accuracy and surface quality of the workpiece, but also affects the performance of the product, and sometimes even causes accidents. For the generated burr problem, people usually use the deburring process to solve it. Deburring is a non-productive process, which not only increases product cost and prolongs product production cycle, but also causes the entire product to be scrapped due to improper burr removal, resulting in economic losses.
This paper firstly analyzes the main factors that affect the formation of end milling burrs, and discusses the methods and technologies for reducing and controlling milling burrs from the structural design to the whole process of manufacturing.
1. The main forms of burrs in end milling
According to the cutting motion-tool cutting edge burr classification system, the burrs generated in the end milling process mainly include burrs on both sides of the main edge, burrs in the cutting direction on the sides, burrs in the cutting direction on the bottom edge, and in and out feeds Five forms of direction burrs
Generally speaking, compared with other burrs, the burrs in the cutting direction of the bottom edge are large in size and difficult to remove. Therefore, this paper takes the burr in the cutting direction from the bottom edge as the main research object to carry out research. According to the different size and shape of the burr in the cutting direction in the end milling, it can be divided into the following three types: I-type burr (larger size, difficult to remove, and high removal cost), II-type burr (smaller size small, can not be removed or removed easily) and type III burrs i.e. negative burrs.
2, The main factors affecting the formation of end milling burrs
The formation of burrs is a very complex material deformation process. Various factors, such as workpiece material properties, geometry, surface treatment, tool geometry, tool cutting path, tool wear, cutting parameters, and coolant usage, all directly affect burr formation. Figure 3 is a block diagram of the influencing factors of end milling burrs. Under specific milling conditions, the shape and size of end milling burrs depend on the combined effect of various influencing factors, but different factors have different effects on the formation of burrs.
1. Tool entry/exit
Under normal circumstances, the burr generated when the tool is rotated out of the workpiece is larger than the burr generated when the tool is rotated into the workpiece.
2. Plane cut out corners
The plane cutting angle has a great influence on the formation of burrs in the cutting direction of the bottom edge. The plane cutting angle is defined as when the cutting edge is rotated out of the workpiece end face, in the plane perpendicular to the axis of the milling cutter at a point on the cutting edge, the direction of the cutting speed (the vector combination of the tool speed and the feed speed) at this point is the same as that of the cutting edge. The angle between the workpiece end face directions. The direction of the workpiece end face is from the tool screw-in point to the tool screw-out point. .
The test results show that the burr height changes with the change of cutting depth, that is, the burr changes from I-type burr to II-type burr with the increase of cutting depth. The minimum milling depth that produces Type II burrs is usually referred to as the limit depth of cut, expressed by dcr.
The larger the plane cut-out angle, the greater the limit cutting depth; when the plane cut-out angle is greater than 120°, the size of the I-type burr is larger, and the limit cutting depth of the transition to the II-type burr is also larger. Therefore, a small plane cut-out angle is conducive to the generation of type II burrs, because the smaller the Ψ, the higher the support stiffness of the terminal surface, and the more difficult it is for the burrs to form.
The size and direction of the feed speed will have a certain influence on the size and direction of the composite speed v, which will then affect the plane cutting angle and burr formation. Therefore, the larger the offset angle α between the feed speed and the exit edge, the smaller Ψ, which is more conducive to suppressing the formation of large burrs
3. Tool tip exit sequence EOS
During end milling, the burr size is largely determined by the exit sequence of the tool tip.
4. The influence of other factors
① Milling parameters, milling temperature, cutting environment, etc. will also have a certain impact on the formation of burrs. Some of the main factors such as feed speed, milling depth, etc. are reflected through the plane cutting angle theory and the EOS theory of the tool nose exit sequence. This will not be repeated;
②The better the plasticity of the workpiece material, the easier it is to form I-type burrs. In the process of end milling brittle materials, if the feed rate or the plane cutting angle is large, it is conducive to the formation of type III burrs (deficiencies);
③ When the angle between the end surface of the workpiece and the machined plane is greater than a right angle, the formation of burrs can be suppressed due to the increased support rigidity of the end surface;
④The use of milling fluid is beneficial to prolong the life of the tool, reduce the wear of the tool, lubricate the milling process, and then reduce the size of the burr;
⑤ Tool wear has a great influence on the formation of burrs. When the tool wears to a certain extent, the arc of the tool tip increases, not only the size of the burr in the exit direction of the tool, but also the formation of burr in the cutting direction of the tool, the mechanism needs to be further Research in depth.
⑥ Other factors such as tool material also have a certain influence on the formation of burrs. Under the same cutting conditions, diamond tools are more conducive to inhibiting burr formation than other tools.
3. Basic ways to control the formation of milling burrs
The formation of end milling burrs is affected by many factors, which are not only related to the specific milling process, but also related to the workpiece structure, tool geometry and other factors. To reduce end milling burrs, it is necessary to control and reduce the generation of burrs from many aspects.
1. Reasonable structural design
The formation of burrs is largely affected by the structure of the workpiece. With different workpiece structures, the shape and size of the burrs at the edges after processing are also very different. If the workpiece material and surface treatment are predetermined, the workpiece geometry and edges are an important factor in determining burr formation.
2. Proper processing sequence
The machining sequence also has a certain influence on the shape and size of the end milling burr. Different burr shapes and sizes have different deburring workloads and related costs. Therefore, selecting an appropriate processing sequence is an effective way to reduce deburring costs.
3. Avoid tool exit
Avoiding tool withdrawal is an effective way to avoid burr formation, because tool withdrawal is the main factor for burr formation in the cutting direction. Under normal circumstances, the burr generated by the milling cutter when it is rotated out of the workpiece is larger, and the burr generated when it is rotated into the workpiece is smaller. Therefore, the milling cutter should be avoided as far as possible during the cnc machining process.
4. Select the appropriate tool path
It can be seen from the previous analysis that when the plane cut-out angle is less than a certain value, the size of the burr produced is small. The plane cut-out angle can be changed by changing the milling width, feed rate (magnitude and direction) and rotation speed (magnitude and direction). Therefore, the generation of I-type burrs can be avoided by choosing an appropriate tool path
5. Select appropriate milling parameters
End milling parameters (such as feed per tooth, end milling width, end milling depth, and tool geometry angle, etc.) have a certain influence on the formation of burrs.
The formation of end milling burr is affected by many factors, among which the main influencing factors are: tool exit/entry, plane cutting angle, tool nose exit sequence, milling parameters, etc. The final shape and size of the burr is the result of a combination of factors.
Starting from the whole process of workpiece structure design, machining process arrangement, milling amount and tool selection, this paper analyzes the main influencing factors of milling burr, and proposes the method of controlling the milling cutter route, selecting the appropriate processing sequence and improving the structure design. The technologies, processes and methods for suppressing or reducing milling burrs, such as methods, provide feasible technical solutions for actively controlling the size of burrs, improving product quality, reducing costs and shortening production cycles in milling.
