CNC machining tool selection

December 17, 2022

When programming, it is important to choose the CNC tool correctly. The general requirements for CNC tools are easy installation and adjustment, good rigidity, high precision, and good durability. Based on this, the cutting performance of the workpiece material, the machining capability of the machine tool, the type of CNC machining process, the cutting amount, and the machine tool are taken into consideration. Numerous factors related to the working range of the numerical control device.

1. Factors Affecting CNC Tool Selection

When selecting the type and size of the tool, the following factors are mainly considered:

(1) Production properties

The production property here refers to the batch size of the parts, mainly considering the influence on the tool selection from the processing cost. For example, when special tools are used in mass production, it may be cost-effective. In single-piece or small-batch production, selecting a standard tool is more appropriate.

(2) Machine type

The effect of the CNC machine used to complete the process on the type of tool selected (drill, lathe, or milling cutter). High-productivity tools such as high-speed cutting tools and large-feed tools can be used under conditions that ensure the rigidity of the workpiece system and the tool system.

(3) CNC machining program

Different CNC machining programs can use different types of tools. For example, holes can be machined using drills and reamers, as well as drills and boring tools.

(4) The size and shape of the workpiece

The size and shape of the workpiece also influence the choice of tool type and specification. For example, the special surface must be machined with a special tool.

(5) Surface roughness

The roughness of the machined surface affects the structural shape of the tool and the amount of cutting. For example, rough roughing cutters can be used for roughing, and fine-tooth milling cutters are preferred for fine milling.

(6) Processing accuracy

The machining accuracy affects the type and shape of the finishing tool. For example, the final machining of the hole can be processed by drilling, reamer, reamer or boring tool.

(7) Workpiece materials

The material of the workpiece will determine the choice of tool material and geometric parameters of the cutting part. The tool material is related to the machining accuracy of the workpiece and the hardness of the material.

2. CNC tool performance requirements

Because the numerical control machine tool has the characteristics of high processing precision, high processing efficiency, centralized processing procedures and fewer parts clamping times, higher requirements are placed on the used CNC tool. In terms of tool performance, numerical control tools should be higher than those used by ordinary machine tools.

When selecting a numerically controlled tool, the first priority should be to use a standard tool, and when necessary, various high-efficiency compound tools and special special tools can be selected. When selecting the standard CNC tool, it should be combined with the actual situation, as far as possible the use of various advanced tools, such as indexable tools, solid carbide tools, ceramic tools and so on.

When choosing CNC machine tools, you should also consider the following issues:

(1) The types, specifications, and accuracy grades of CNC tools should be able to meet the machining requirements. The tool material should be compatible with the workpiece material.

(2) good cutting performance. In order to adapt the tool to rough cutting or machining of difficult-to-machine materials, the tool can adopt a large amount of back-feed and high feed. The tool should have the ability to withstand high-speed cutting and strong cutting. At the same time, the same batch of tools must be stable in terms of cutting performance and tool life, in order to achieve tool change by tool life or by the numerical control system tool life management.

(3) High precision. In order to meet the requirements of high-precision CNC machining and automatic tool change, the tool must have high precision. For example, the integral end mill has a radial dimension accuracy of up to 0.005mm.

(4) High reliability. To ensure that the accidental damage and potential defects of the tool will not be affected in the NC machining process, the cutting tool and its associated accessories must have good reliability and strong adaptability.

(5) High durability. CNC machining tools, whether roughing or finishing, should have a higher durability than the tools used in ordinary machine tools in order to minimize the number of times to replace or grind tools and tools, thereby improving the machining efficiency of CNC machine tools. And ensure the quality of processing.

(6) Good chip breaking and chip removal. In NC machining, chip breaking and chip evacuation are not handled in time as in the case of ordinary machine tools. Chips are easily wound on the tools and workpieces, which can damage the tool and scratch the workpiece surface, and even cause injuries and equipment accidents. Affects the processing quality and the safe operation of the machine tool, so the tool is required to have better chip breaking and chip removal performance.

3. Tool selection method

The choice of tool is one of the important contents in the numerical control processing technology. It not only affects the machining efficiency of the machine tool, but also directly affects the machining quality of the part. Because the spindle speed and range of CNC machine tools is much higher than that of ordinary machine tools, and the spindle output power is larger, compared with the traditional processing methods, higher requirements are put forward for CNC machining tools, including high precision, high strength and rigidity. Good, durable, and requires a stable size, easy installation and adjustment. This requires a reasonable tool structure, standardization of geometric parameters, and serialization. CNC tooling is one of the prerequisites for improving the machining efficiency. Its choice depends on the geometry of the part being machined, the state of the material, the fixture and the rigidity of the tool selected by the machine tool. The following should be considered:

(1) Select the tool according to the cutting performance of the part material. Such as car or milling high-strength steel, titanium alloy, stainless steel parts, it is recommended to choose a good wear-resistant indexable carbide cutting tools.

(2) Select the tool according to the machining stage of the part. That is to say, the roughing stage is mainly based on removing the margin, and the tool with better rigidity and lower precision should be selected. The semi-finishing and finishing stages are mainly used to ensure the machining accuracy and product quality of the part. The high durability and accuracy should be selected. For high cutting tools, the accuracy of the tools used in the roughing stage is the lowest, and the accuracy of the tools used in the finishing stage is the highest. If the same tool is used for rough and finish machining, it is recommended to use the tools that are eliminated during the roughing process because the wear of the tools that are eliminated during the finishing process is mostly due to slight wear of the blades, the wear of the coating is lighted, and the continued use will affect the finish machining. Processing quality, but less impact on roughing.

(3) Select tools and geometric parameters according to the characteristics of the processing area. When the part structure allows, a tool with a large diameter and a small aspect ratio should be selected; the center-end angle of the over-center milling cutter for cutting thin-walled and ultra-thin-wall parts should have enough tangential angle to reduce the cutting of the tool and the cutting part. force. When processing aluminum, copper and other softer material parts, choose an end mill with a slightly larger front rake and do not use more than 4 teeth.

When selecting a tool, the size of the tool must be adapted to the surface dimensions of the workpiece being machined. In production, the peripheral contours of plane parts are often machined with end mills. When milling planes, hard alloy insert milling cutters are selected. When machining bosses and grooves, high-speed steel end mills are selected; surface roughing or rough machining is performed. In the case of holes, corn milling inserts with carbide inserts can be selected. For the machining of some three-dimensional profiles and variable bevel outlines, ball-end cutters, ring cutters, taper cutters, and disc-type cutters are often used.

In the free-form surface machining, since the cutting speed of the end of the ball-end tool is zero, in order to ensure the machining accuracy, the cutting spacing is generally very small, so the ball-end milling cutter is suitable for the surface finishing. The end mill is far superior to the ball end mill both in terms of surface machining quality and machining efficiency. Therefore, in the premise of ensuring that the parts are not over-cut, the rough end and semi-finishing surfaces are selected as much as possible. Milling cutter. In addition, the tool's durability and precision are highly related to the tool's price. It must be noticed that, in most cases, selecting a good tool increases the tool cost, but the resulting increase in machining quality and machining efficiency. , you can greatly reduce the cost of the entire process.

In the machining center, all the tools are pre-installed in the magazine, and the corresponding tool change actions are performed through the NC program's tool selection and tool change commands. The corresponding standard tool holders suitable for the machine tool system specifications must be selected so that the tools for NC machining can be quickly and accurately mounted on the machine tool spindle or returned to the tool magazine. The programmer should be able to understand the structure of the shank used in the machine tool, adjust the method and adjust the scope of the content in order to ensure the radial and axial dimensions of the tool in the programming, a reasonable arrangement of the order of the tool.

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Author:

Ms. Mirada Kuo

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