The quality of tool alignment in CNC machining directly affects the accuracy of machined parts and also affects the operation of CNC machine tools. The so-called tool alignment refers to placing the tool position of the tool on the starting point (tool alignment point) in the workpiece coordinate system, under the control of the CNC program, so that the machining surface cut by the tool has the correct dimensional relationship with the positioning reference, thereby ensuring the machining accuracy requirements of the part. In CNC machining, the basic methods of tool alignment include trial cutting method, tool alignment instrument, ATC tool alignment, and automatic tool alignment.

1. Trial cutting method

According to the different position detection devices used in CNC machine tools, the trial cutting method can be divided into two types: relative and absolute. In the relative trial cutting method for knife alignment, three methods can be used:

One method is to measure directly with measuring tools (such as steel rulers) and align them with the tool size. This tool alignment method is simple but not accurate.

The second method is to move the tool away to the tool size after aligning the tool position with the working surface of the positioning block. The accuracy of tool alignment in this method depends on the accuracy of aligning the tool position with the working surface of the positioning block.

The third method is to first polish the machining surface of the workpiece, measure the size of the workpiece, and indirectly calculate the tool size. This method is the most accurate.

In the absolute trial cutting method for tool alignment, a reference tool needs to be used, and then the deviation between the tool position of other tools and the reference tool needs to be measured directly or indirectly as the set tool compensation value for other tools.

The above trial cutting method adopts a tool setting mode of "trial cutting measurement adjustment (compensation)", which takes up more machine time and has lower efficiency. However, due to its simplicity and the need for fewer auxiliary equipment, it is widely used in economical low-end CNC machine tools.

2. Knife setting instrument

There are two types of tool setting instruments: internal tool setting instruments and external tool setting instruments. The in machine tool alignment instrument is used to directly install the tool in a fixed position on the machine tool (for lathes, the tool is directly installed on the tool holder or re installed on the tool holder through a tool clamp). This method is commonly used in turning CNC machine tools.

The external tool alignment instrument must be installed on the tool holder (lathe) through a tool clamp, and together with the tool clamp, it must be calibrated outside the machine tool in advance. Then, the tool can be installed on the machine tool to be used. This method is currently mainly used in boring and milling CNC machine tools, such as machining centers.

The use of a tool setting instrument requires the addition of auxiliary equipment for tool setting, which is costly and labor-intensive for tool loading and unloading. However, it can save tool setting time and improve tool setting accuracy. It is generally used in CNC machine tools with high precision requirements.

3. ATC knife alignment

AIC tool alignment is a method of automatically calculating tool length on machine tools using a tool alignment microscope. Due to manual operation and visual inspection during the operation of the tool alignment mirror and tool alignment process, there is still a certain degree of tool alignment error.

Compared to the tool setting device, it is only easier and more convenient to load and unload tools. Automatic tool alignment utilizes the tool detection function of CNC devices to automatically and accurately measure the length of the tool in various coordinate directions, automatically correct the tool compensation value, and directly process the workpiece without stopping.

Compared with the previous tool alignment method, this method reduces tool alignment errors, improves tool alignment accuracy and efficiency, but requires an automatic tool alignment system composed of tool inspection sensors and tool position detection systems. Moreover, the CNC system must have auxiliary functions for tool automatic detection, which is more complex and requires a large investment. It is generally used in high-end CNC machine tools.