For CNC milling parts, the quality of the finished workpiece is of vital importance. For CNC milling machine cutting, tool selection and effective determination of cutting parameters are both critical. To ensure that the processing meets the standards, programmers must accurately grasp the basic principles of tool selection and cutting parameters. At the same time, the characteristics of each part processing process are also highly valued.
How to Choose Cutting Tools for CNC Milling
CNC milling machines have high requirements for matching tools. The tools must have the characteristics of high precision, high strength, high rigidity, and can be easily installed and adjusted. Different tools have different lengths of shanks and cutter head shapes. When choosing, many factors should be considered, such as the installation and holding capacity of the milling machine, the material characteristics of the workpiece, and the processing method. On the premise of fully meeting other conditions, try to choose tools with short shanks to maximize the rigidity of the tool, meet the requirements of processing accuracy, and extend the service life of the tool.
Common Types of Milling Cutters
Due to the variety of materials and forms of the workpieces being processed, the types and forms of milling cutters are also different. At present, various types of milling cutters are usually classified according to materials, structures or cutter head shapes. Depending on the material, milling cutters can be divided into high-speed steel cutters, alloy steel cutters, diamond cutters, ceramic cutters, and cubic boron nitride cutters. Cutters of different materials have different hardness and rigidity, and are suitable for processing workpieces of different materials. According to the structure of the cutter, milling cutters can also be divided into integral cutters and inlaid cutters, among which inlaid cutters can be divided into welded and machine clamped types. According to the shape of the cutter head, milling cutters can be divided into ball-end cutters, flat-bottom cutters, taper cutters, T-shaped cutters, etc.
Factors Affecting the Selection of Milling Cutters
CNC milling is a rather complex operation. When selecting a milling cutter, the performance and characteristics of the processing material should be considered. For example, non-ferrous metals, ferrous metals, composite materials, and polymer materials all have different choices of cutters. In addition, the hardness, toughness, rigidity, wear resistance and other properties of the material should also be taken into account. In addition, the main processing capacity of CNC milling depends on CNC machine tools. Therefore, in the process of selecting cutters, the characteristics of CNC machine tools should also be considered, and the number of cutters should be minimized to achieve multiple processes in one clamping.
Uses of Common Cutters for CNC Milling Machines
- End mills: This type of cutter is suitable for processing shapes such as bosses or grooves on the surface of the workpiece, and can also be used for roughing, finishing and root cleaning.
- Keyway milling cutter: As the name suggests, this type of milling cutter is more suitable for processing various cavity grooves and keyway shapes on the workpiece.
- Ball cutter: This type of tool is more suitable for surface finishing with a small amount of cutting. Due to the small amount of cutting and low efficiency, it is generally not used for processing large shapes.
- Face milling cutter: Mainly used for processing large-area flat workpieces.
Principles of Tool Selection in Practice
In general, the selection of milling cutters should be based on the basic principles of easy installation and adjustment, ensuring the processing accuracy of the workpiece, and extending the service life of the tool. Under the premise of ensuring processing quality and efficiency, try to choose tools with shorter shanks to improve the working rigidity of the tool and extend the service life of the tool. The geometric shape of the workpiece is an issue that needs to be considered when selecting a milling cutter. Processing workpieces of different shapes has different requirements for the type of milling cutter and the shape of the cutter head. If the selection is inappropriate, it will seriously affect the processing quality of the workpiece, and even a large number of defective products will appear, causing losses.
Determination of Cutting Volume in CNC Milling
The processing of workpieces in CNC milling is achieved by cutting in different directions. Different cutting amounts have a significant impact on the speed, quality and service life of workpiece processing. The cutting amount mainly includes indicators such as cutting speed, back cutting amount and side cutting amount. Different cutting amounts should be selected for different situations, with the processing accuracy and surface finish of the workpiece as the main criteria. The cutting amount is set through scientific calculations to achieve a balance between processing quality, efficiency and reducing tool wear.
Determine the Cutting Speed
The selection of cutting speed needs to consider many factors such as workpiece hardness, tool material, and tool life. The cutting speed should be appropriately reduced during roughing operations because the cutting depth is usually large at this time. Once a higher cutting speed is selected, a higher operating temperature will be generated, reducing the service life of the tool. On the contrary, the cutting speed can be appropriately increased during fine processing operations to ensure the surface accuracy and work efficiency of the workpiece.
Determine the Feed Rate
The feed rate is an important indicator related to processing efficiency. It refers to the depth of cutting per minute, generally between 100 and 200 mm. When using high-speed steel tools or performing deep hole processing operations, the feed speed should be reduced according to the actual situation, generally maintained at about 20 mm to 50 mm per minute.
Determination of Cutting Depth
The determination of back cutting depth (side cutting depth) is related to the operational safety of the processing and the service life of the tool and machine tool. If the cutting depth is too large, it may cause a collision accident and damage the tool or machine tool. However, choosing the maximum cutting depth that can be tolerated within a certain range can reduce the number of passes and improve production efficiency.
Deconstruction of CNC Milling Machine Cutting Process
Rough Machining Process
The overall improvement of production efficiency is the key to choosing the rough machining process. The so-called rough machining specifically refers to the maximum material removal rate that can be achieved within a unit time range. Specifically, it refers to the machining allowance of the blank surface, which ensures that the shape and size of the blank are as close as possible to the finished product. Generally speaking, after rough machining, the material can form the outline of a semi-precision workpiece. In the whole process, speed plays an important role, and a tool with a larger diameter is selected for operation. Not only can the overall improvement of production efficiency be achieved, but also the probability of tool wear can be avoided. For CNC milling machines, only any two of the three coordinates are controlled, which can achieve the purpose of two-dimensional control.
Semi-finishing Process
Unlike rough machining, semi-finishing pays more attention to the organic coordination of efficiency and quality. After semi-finishing, the surface of the workpiece should be relatively smooth and the allowance should be uniform. And the purpose of this process is to lay a solid foundation for the development of finishing, in order to achieve the goal of secondary surface machining. It should be noted that in the actual machining process, the excess material on the surface of the part should be effectively removed as much as possible. Ensure that the surface of the machined parts is in a flat state and finally meet the standard requirements of accuracy.
Angle Cleaning Process
The processing technology of workpiece corner cleaning does not require processing speed, but focuses on the uniformity and coordination of the mold surface. It should be noted that the purpose of workpiece corner cleaning is to completely remove excess material. It effectively paves the way for the subsequent finishing operations and further promotes the comprehensive development of finishing work. If a tool with a smaller diameter is used in this process, it is difficult to complete the cutting operation in one go, so it is necessary to perform at least two cutting operations and stop only when the specific requirements are met. However, the tool diameter should not exceed the diameter of the finishing tool.
Finishing Process
The finishing process is the last processing process, which requires that the dimensional accuracy, surface roughness and shape accuracy of each part must meet the requirements of the drawing. Generally speaking, a specific allowance will be reserved on the finishing surface. The main purpose is to ensure that the blade can be in a stable state during cutting, minimize the error of workpiece processing, and ensure that the performance effect meets the standard. In the process of finishing, it is necessary to choose to use a processing tool with a smaller diameter. The best finishing process is as follows: machining external contour → machining convex parts → machining step surfaces and free-form surfaces → machining recesses → machining other low auxiliary surfaces.
In the mold manufacturing process, for high-speed finishing of curved surface cores and cavities, the following should be noted: when cutting, it is necessary to ensure that the contact point between the tool and the workpiece can follow the slope of the curved surface and the change of the selected tool radius to show corresponding changes.
If the curved surface of the mold to be machined has strong complexity, it must be ensured that it can be completed in one process at a time, effectively reducing the number of cuts and effectively preserving the mold surface. In addition, during the cutting process, it is necessary to ensure that the direction of the tool feed is presented in an arc shape, so that the cutting surface is continuous and smooth, and has a certain stability characteristic. Finally, in the actual processing process, the occurrence of processing pauses should be avoided as much as possible.
Once the tool stops suddenly, it is easy to cause a slight deformation problem on the surface of the mold, which will eventually have a negative impact on the accuracy of the processing, and even dents will appear at the position where the tool stops, thereby affecting its surface quality.
Effective Improvement of Cutting Process of CNC Milling Machine
Ways to Improve Rough Machining Process
First, the cutting surface area can be accurately calculated with the help of machining simulation software, and the cutting rate of the cut material should also be calculated accordingly. Only in this way can the tool load and wear rate be balanced at all times during cutting, and the tool wear probability can be reduced as much as possible while further enhancing the machining quality.
Secondly, in actual cutting, the CNC milling machine should choose to cut in or out obliquely as much as possible. At the same time, the vertical cutting and cutting problems should also be effectively avoided for machining mold cavities. If conditions permit, spiral cutting should be selected as shown in Figure 1 as much as possible to effectively reduce the tool load.
Thirdly, if large excess parts are required to be processed, climbing methods should be used. The most prominent advantage of this method is that it can effectively reduce the cutting force, ensure that the degree of cutting hardening is appropriately improved, reduce the heat generated by cutting, and ensure that the actual quality of part cutting is comprehensively enhanced.
Finally, when cutting with a CNC milling machine, do not suddenly change the direction of the tool feed, otherwise it will directly affect the cutting speed, ultimately significantly reducing the cutting quality and causing residue or overcutting, and in severe cases, causing immeasurable safety accidents.
Ways to 我改善 年代emi-finishing 磷流程
For the improvement of semi-finishing process, cutting spacing and tolerance value are very important. To ensure stable cutting, the above order must be strictly followed to avoid damage to the tool as much as possible. In addition, to ensure the continuity of cutting, the processing procedures should be arranged reasonably to avoid frequent tool withdrawal or tool change.
Ways to 我改善 Corner Cleaning 磷流程
The surface of the workpiece is relatively uniform on the basis of semi-finishing, but the machining allowance at the concave profile position is still large. Once the machining allowance uniformity is poor, it will inevitably affect the stability of cutting and even have a direct impact on the final accuracy of machining. Therefore, a reasonable corner cleaning process must be arranged to remove excess material.
Ways to 我改善 F完成 磷流程
The finishing process has high requirements for quality and accuracy, so the cutting program must be optimized. In order to avoid vertical cutting and a large number of tool lifting problems, the surface of the parts should be damaged as much as possible. In addition, in the process of finishing milling, the down milling method should be adopted to avoid sliding problems. The selection of the tool path should also attach great importance to the problem of machining deformation. If necessary, try to increase the number of tool passes. The most important thing is to ensure the optimization of the tool path.
