CNC processing to choose the right way to go, so that you double the processing efficiency!
With the development of modern manufacturing technology, CNC machining equipment and CAM system have been widely used and developed. The tool path generated by CAM system is the core of controlling the machining operation of the machine, which directly affects the accuracy of the workpiece, the Surface roughness, the total machining time, the service life of the machine tool, etc. , ultimately determines productivity.
Through the analysis of the different characteristics of the cutting ways and some factors affecting the selection of the cutting ways, and the comparison of the cutting ways and the cutting methods in the milling process, the paper provides a reference for how to choose the appropriate cutting ways.
1. The way of cutting
1. Basic concepts of tool walking
In numerical control machining, the tool path is the path planning method when the tool completes the workpiece cutting. In the processing of the same part, many kinds of cutting ways can meet the size and precision requirements of the part, but the processing efficiency is not the same.
2. Classification of tool paths
There are 4 kinds of cutting ways: one-way Cutting, reciprocating cutting, circular cutting and compound cutting. Compound feed is the first three kinds of mixed feed. The use of one-way or reciprocating tool, from the processing strategy is the line cutting tool. Therefore, according to the different processing strategies, tool path can be divided into line cutting, ring cutting and other special ways. Line and girth cuts are usually used.
The line cutting method is beneficial to the maximum feed speed of the machine tool, and the surface quality of the machine tool is better than the ring cutting method. However, when a complex planar cavity is provided with multiple bosses to form multiple internal contours, an additional tool lift is often performed, that is, at a certain point in the tool path, or to avoid interference between the tool and the boss, or in order to return the tool to the remaining raw area, the tool should be raised to a certain height from the machining surface, then translated to the start of another tool path, and then continue cutting action.
The tool path of line cutting is mainly composed of a series of straight lines parallel to a fixed direction, so the calculation is simple. It is suitable for simple cavity finish machining or rough machining with large allowance removed. Figure 1 -- Reciprocating knife path.
The Tool Path with similar boundary contour in ring cutting is composed of a set of closed curves, which can ensure that the tool keeps the same cutting state when cutting parts. It is complicated and time-consuming to calculate the next annular trace by constructing the current annular trace graph with continuous offset. It is suitable for machining complex cavity and curved surface. Image 2: A loop cutter.
2. The factors that affect the way of cutting
1. The shape and geometry of the workpiece itself: The shape and geometry of the workpiece include the geometry of the machining area, the size and location of the island, etc. . This is the inherent characteristics of the workpiece itself, is an immutable factor, but it is the fundamental factor in determining the way of cutting.
2. The technological route: The technological route is the direct process of realizing the aim of machining, and is the direct basis of choosing the way of cutting. Process routes determine the sequence of processing areas, island merger and Split, roughing, semi-finishing, finishing, and so on. There are a variety of process routes to achieve the goal, which determines the different choice of tool path.
3. workpiece material: workpiece material is also one of the factors that determine the way of cutting, workpiece material is the direct processing object, does not directly affect the way of cutting, but will have an impact on the choice of cutting tool materials, size, processing methods, etc. , which indirectly affects the way of cutting. The shape and size of the workpiece blank will result in whether the machining allowance is distributed evenly among the parts of the workpiece. At the same time, the different size and shape of the blank can be used to select the workpiece, it will change the way of clamping, the redistribution of the processing area and so on, which will affect the processing strategy and lead to the adoption of different cutting ways.
4. The clamping and fastening methods of the workpiece: The clamping and fastening methods of the workpiece also indirectly affect the tool-walking methods, such as the influence of the new “island” produced by the clamping plate, and the influence of the fastening force on the cutting parameters, resulting in the change of the tool-walking methods, influence of vibration on tool path.
5. Tool Selection: tool selection includes tool material, tool shape, tool length, tool tooth number, etc. . These parameters determine the size and frequency of tool-workpiece contact area, thus determines the unit time of cutting material volume size and machine load, its wear-resistant degree and tool life determines the length of cutting time. And the tool size (i. e. diameter) has a direct impact on the tool path. Because the tool with different diameter is selected, the size of the residual area will be affected, and the machining path will be changed, which will lead to the different tool path. Do not want to work at the bottom, want to get rid of the status quo, want to learn UG programming, can find plus teacher Qq: 770573829 learning CNC technology.
6. Selection of machining area: In the milling process, when the complex planar cavity with multiple convex to form a number of internal contour, for the line-cutting will often produce additional lifting action; for the ring-cutting will make the machining trace longer. This additional tool lift action or longer machining path, it will seriously reduce the efficiency of cutting. How to minimize the number of such situations is therefore a major concern for us.
The whole cutting area is divided into several sub-areas according to the need of machining, each sub-area is processed separately, the tool lifting takes place between the sub-areas, and these sub-areas are merged or divided according to the way of cutting, or even neglected. This kind of different selection of machining area can not only reduce the Times of tool lifting but also not make the relative length of machining path longer, but also can adopt the most reasonable way to the new area and improve the machining efficiency.
3. Reasonable selection of cutting way
1. The basic principles of choice
Two points should be considered when choosing the tool path: one is the length of the processing time, the other is whether the machining allowance is even. In general, the method of ring cutting is based on the shape of the workpiece tool path, machining allowance more uniform. But the machining allowance of the line-cutting method is not uniform. If you want to leave more uniform allowance after the line-cutting processing, you usually need to increase the ring-cutting tool path around the boundary. If the non-uniformity of the allowance is ignored, the length of the tool path is usually shorter; if the non-uniformity of the allowance is taken into account and the tool path of the ring is increased, when the boundary of the machining area is longer (for example, in the case of many islands) , the ring cutting tool path around the boundary has an obvious effect on the total processing time, and the line cutting tool path is generally longer than the ring cutting tool path. It is easy to calculate the cutter position of the line cutting tool, and it takes up less memory, but the number of tool lifting is more. When circular tool path is used, it is necessary to offset the edge of the loop and clear the self-intersecting loop.
2. Choose based on physical features
The shape characteristics of the workpiece determine the way of cutting. According to the different machining objects, the workpiece can be simply divided into two classes: Planar cavity class and free-form surface class. Generally, the plane cavity is machined by row cutting, because most of the workpieces of this kind are formed by whole drawing and milling, such as box body, base, etc. . The machining allowance is large, and the row cutting method is favorable to bring into play the maximum feed speed of the machine, at the same time, the cutting surface quality is better than that of ring cutting.
The free-form surfaces are usually machined by ring-cutting, which is mainly due to the non-uniformity of the allowance and the high precision of the surface Secondly, compared with the row-cutting method, the ring-cutting method has better surface machining characteristics and can approximate the real shape of the surface.
3. Choose according to the processing strategy
The machining of parts can be divided into three stages: rough machining, semi-finish machining and finish machining, and sometimes finishing machining. Because the traditional machining mode has relatively single function, the boundary of each stage can be clearly seen in the process route, but under the NC milling mode, the boundary is relatively hollow, and there may be cases of blending (for example, there may be finishing content in the rough machining stage, and there may also be traces of rough machining in the finishing stage) . In order to ensure the quality of machining, it is necessary to divide the stages of NC machining, however, in order to reduce the clamping time and simplify the cutting motion, how to determine the processing content of each stage may be different from the traditional processing technology.
The main goal of rough machining is to achieve the material removal rate per unit time and to prepare the geometry of the workpiece for semi-finish machining. Therefore, the use of line-cut mode or composite mode for slicing. The main goal of semi-finish machining is to make the workpiece contour smooth and the surface finish machining allowance uniform. Therefore, more use of circumferential way. The main goal of finish machining is to obtain the workpiece whose geometry size, shape accuracy and surface quality meet the requirements. According to the geometrical features of the workpiece, the inner part should be cut in line, and the edge and joint should be cut in ring.
4. Choose based on your programming strategy
In programming, the following principles are used to determine the tool path: to ensure the machining accuracy of the parts and the requirements of the Surface roughness; to shorten the machining route as far as possible, and to reduce the time of the Empty Path Movement of the tools; to make the numerical calculation simple and the number of program segments small; To reduce the amount of programming effort. Generally speaking, the cutting method is used to divide the machining domain in order to reduce the Times of tool lifting, and the ring-cutting method is used to approximate the shape of free-form surface. The size of blank shape will affect the choice of programming. By increasing the blank shape, the machining of the shape which is not easy to be clamped can be transformed into the machining of the line-cutting mode of easy to be clamped Or the free-form surface processed by ring-cutting will be changed to line-cutting method to increase the machining efficiency.
