Tool setting is the most basic operation in CNC machining. The accuracy of tool setting will affect the machining accuracy of parts. At the same time, the tool setting efficiency also directly affects the processing efficiency. The essence of tool setting is to determine the exact position of the tool nose of different tools in the machining coordinate system. The main task of tool setting is to determine the offset parameters of the current tool, including the length or diameter of the tool setter, and the change of tool parameters with the state of the machine tool bed, so that the CNC system can compensate for the production of parts.
Under the historical background of industrial upgrading and transformation, the metal processing manufacturing industry is also undergoing a comprehensive upgrade of numerical control. Numerical control is a comprehensive process with the overall popularization and application of CNC machine tools as the core, so that the quality, accuracy and reliability of the products are comprehensively improved.
In the process of using CNC machine tools to manufacture product parts, there are many factors that affect the quality of parts, such as the accuracy of CNC machine tools, workpiece materials, workpiece heat treatment, processing technology, coolant, tools and so on. Among the many influencing factors, the accurate setting of tool setting parameters has received little attention. However, processing the workpiece to the required size range, and meeting the geometric tolerance requirements are the basic requirements for the precise setting of the tool setting parameters.
1) Basic coordinate relationship
Generally speaking, two coordinate systems are usually used: one is the machine coordinate system, and the other is the workpiece coordinate system. The machine tool coordinate system is the inherent coordinate system of the machine tool, and the origin of the machine tool coordinate system is called the machine origin or the machine zero point.
In order to facilitate calculation and programming, we need to establish a workpiece coordinate system in the machine tool coordinate system. The coordinate system is established by taking a certain point on the workpiece as the origin of the coordinate system (also called the origin of the program), and this coordinate system is the workpiece coordinate system. In our daily work, we should try our best to make the programming benchmark coincide with the design and assembly benchmarks.
Normally, the machine coordinate system of a machine tool is fixed. The workpiece coordinate system can be established according to the actual needs of the processing technology. For example, G54, G55, etc. can be used to select different workpiece coordinate systems.
2) The purpose of tool setting
When performing CNC machining, the path taken by the CNC program is the movement track of the tool nose of the tool setter on the spindle. The movement track of the cutter location point of the tool setter needs to be accurately controlled in the machine tool coordinate system from beginning to end, because the machine tool coordinate system is the only datum of the machine tool.
It is impossible for programmers to know the specific dimensions of tool setters of various specifications when programming. In order to simplify programming, it is necessary to adopt a unified benchmark when programming. When the tool setter is used for processing, the accurate length and radius of the tool setter are offset relative to the datum, so as to obtain the accurate position of the tool tip of the tool setter. Therefore, the purpose of tool setter is to determine the exact length and radius of the tool setting device, so as to determine the exact position of the tool nose in the workpiece coordinate system during processing.
① Tool setting outside the machine
The advantage of this method is that the tool setter is calibrated outside the machine tool in advance so that it can be used when it is installed on the machine tool, which greatly saves auxiliary time. But the main disadvantage is that the measurement result is a static value. In the actual machining process, the wear or damage status of the tool setter cannot be updated in real time, and the tool expansion and contraction caused by the thermal deformation of the machine tool cannot be measured in real time.
② Trial cutting method for tool setting
The advantage of this method is that it is economical and does not require additional investment in tools and equipment. The main disadvantage is low efficiency. It requires high technical level of the operator and is easy to introduce human error. In actual production, there are many derivative methods for the trial cutting method, such as the gauge block method and the coloring method.
③ In-machine tool setting
This kind of in-machine tool setting method uses a measuring device (tool setter) installed on the worktable of the machine tool to measure the tool setter in the tool storage according to a pre-set program. Then compare with the reference position or standard tool to get the length or diameter of the tool, and automatically update it to the corresponding NC tool parameter table. At the same time, the detection of the tool can also realize the identification of whether the tool is worn, damaged or the installed model is correct.