CNC machining tools must be adapted to the high speed, high efficiency, and high degree of automation of CNC machine tools. They generally include general-purpose tools, general-purpose connecting tool holders, and a small number of special-purpose tool holders. Tool holders connect the tools and are mounted on the machine tool's power head, and therefore have gradually become standardized and serialized.
1. Based on the tool structure, they can be divided into: ① integral type; ② insert type, which uses welding or mechanical clamping connection. Mechanical clamping type can be further divided into non-indexable and indexable types; ③ special types, such as composite tools, vibration damping tools, etc.
2. Based on the materials used to manufacture cutting tools, they can be divided into: ① high-speed steel cutting tools; ② cemented carbide cutting tools; ③ diamond cutting tools; ④ cutting tools made of other materials, such as cubic boron nitride cutting tools, ceramic cutting tools, etc.
3. From the perspective of cutting process, they can be divided into: ① Turning tools, including external turning, internal turning, threading, cutting tools, etc.; ② Drilling tools, including drills, reamers, taps, etc.; ③ Boring tools; ④ Milling tools, etc.
In order to meet the requirements of CNC machine tools for durable, stable, easy-to-adjust, and replaceable cutting tools, indexable tooling has been widely used in recent years, accounting for 30 to 40% of all CNC cutting tools and removing 80 to 90% of the total metal.
The main features are as follows: ① Good rigidity (especially for roughing tools), high precision, and small vibration and thermal deformation resistance; ② Good interchangeability, facilitating quick tool changes; ③ Long tool life, stable and reliable cutting performance; ④ The tool size is easy to adjust to reduce tool change adjustment time; ⑤ The tool should be able to reliably break or roll chips to facilitate chip removal; ⑥ Serialization and standardization to facilitate programming and tool management.
Tool selection is performed in the human-machine interface of CNC programming. The correct tool and tool holder should be selected based on the machine tool's machining capabilities, workpiece material properties, machining processes, cutting parameters, and other relevant factors.
Easy to install and adjust, with good rigidity, durability, and high precision. While meeting machining requirements, choose the shortest possible tool shank to improve tool rigidity during machining. When selecting tools, ensure the tool size is compatible with the surface dimensions of the workpiece. In production, end mills are commonly used for machining the peripheral contours of planar parts; carbide insert end mills should be selected for milling planes; high-speed steel end mills are used for machining bosses and grooves; carbide insert-embedded corn end mills can be selected for machining rough surfaces or roughing holes; ball end mills, ring end mills, tapered end mills, and disc end mills are commonly used for machining some three-dimensional surfaces and variable angle contours.
When machining free-form surfaces (molds), the cutting speed at the tip of a ball end mill is zero. Therefore, to ensure machining accuracy, the cutting path is generally close at the tip, making ball end mills commonly used for finishing curved surfaces. However, flat end mills are superior to ball end mills in terms of surface finish and cutting efficiency. Therefore, provided that overcutting is avoided, flat end mills should be the preferred choice for both roughing and finishing of curved surfaces.
In addition, the durability and precision of cutting tools are closely related to their price. It is important to note that, in most cases, while choosing good cutting tools increases the cost of the tools themselves, the resulting improvement in machining quality and efficiency can significantly reduce the overall machining cost.
In machining centers, various cutting tools are mounted on tool magazines, and tool selection and changing are performed according to the program. Therefore, standard tool holders must be used to ensure that standard tools for drilling, boring, reaming, and milling operations can be quickly and accurately mounted onto the machine tool spindle or tool magazine. Programmers should understand the structural dimensions, adjustment methods, and adjustment range of the tool holders used on the machine tool to determine the radial and axial dimensions of the tools during programming. Currently, machining centers in my country use the TSG tool system, which includes two types of tool holders: straight shank (3 specifications) and tapered shank (4 specifications), encompassing a total of 16 different types of tool holders for various purposes.
In the machining process of economical CNC machine tools, since tool sharpening, measurement, and replacement are mostly performed manually, which takes up a lot of auxiliary time, it is essential to rationally arrange the tool arrangement sequence. Generally, the following principles should be followed: ① Minimize the number of tools; ② Once a tool is clamped, it should complete all the machining steps it is capable of performing; ③ Roughing and finishing tools should be used separately, even if they are tools of the same size and specification; ④ Milling should precede drilling; ⑤ Surface finishing should be performed first, followed by two-dimensional contour finishing; ⑥ Where possible, the automatic tool changer function of the CNC machine tool should be utilized to improve production efficiency, etc.
During roughing, the primary focus is on maximizing productivity, but economic efficiency and machining costs should also be considered. During semi-finishing and finishing, the goal is to ensure machining quality while simultaneously balancing cutting efficiency, economic efficiency, and machining costs. Specific values should be determined based on the machine tool manual, cutting parameters handbook, and experience.
Specifically, the following factors need to be considered: ① Depth of cut t. When the rigidity of the machine tool, workpiece, and cutting tool allows, t is equal to the machining allowance, which is an effective measure to improve productivity. To ensure the machining accuracy and surface roughness of the parts, a certain allowance should generally be left for finishing. The finishing allowance of CNC machine tools can be slightly smaller than that of ordinary machine tools. ② Cutting width L. Generally, L is directly proportional to the tool diameter d and inversely proportional to the depth of cut. In the machining process of economical CNC machine tools, the general range of L is: L = (0.6～0.9)d. ③ Cutting speed v. Increasing v is also a measure to improve productivity, but v is closely related to tool durability. As v increases, tool durability decreases sharply, so the selection of v mainly depends on tool durability. In addition, the cutting speed is also greatly related to the material being machined. For example, when milling 30CrNi2MoVA alloy steel with an end mill, v can be around 8 m/min; while when milling aluminum alloy with the same end mill, v can be selected to be above 200 m/min. ④ Spindle speed n (r/min). The spindle speed is generally selected based on the cutting speed v. The calculation formula is: v = nd/1000. CNC machine tools typically have a spindle speed adjustment (multiplier) switch on the control panel, allowing for integer adjustments to the spindle speed during machining. ⑤ Feed rate vF. vF should be selected based on the machining accuracy and surface roughness requirements of the part, as well as the material of the tool and workpiece. Increasing vF can also improve production efficiency. When the surface roughness requirement is low, a larger vF can be selected. During machining, vF can also be manually adjusted using the adjustment switch on the machine tool control panel, but the maximum feed rate is limited by the rigidity of the equipment and the performance of the feed system.
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