Common tool setting methods of CNC machine tools and in-machine tool setting instruments

In the process of using CNC machine tools to produce product parts, there are many factors that affect the quality of parts, such as CNC machine tool accuracy, workpiece material, workpiece heat treatment, processing technology, coolant, cutting tools, and many other factors. Among them, the accurate setting of tool parameters has always been seldom concerned and valued by everyone. Here, we will focus on the characteristics and development trends of accurate tool setting on CNC machine tools.

Basic coordinate relations 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.

For the convenience of calculation and programming, we need to establish a workpiece coordinate system in the machine tool coordinate system. Use a certain point on the workpiece as the origin of the coordinate system (also called the origin of the program) to establish a coordinate system. 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.

Common tool setting methods of CNC machine tools and in-machine tool setting instruments

Under normal circumstances, the machine coordinate system of a machine tool is fixed, and the workpiece coordinate system can be established according to the actual requirements of the processing technology. For example, G54, G55, etc. can be used to select different workpiece coordinate systems.

When the purpose of tool setting is to perform numerical control processing, the path taken by the numerical control program is the movement track of the tool tip of the tool on the spindle. The movement trajectory of the tool position point needs to be controlled in the machine tool coordinate system from beginning to end, because the machine tool coordinate system is the base of the machine tool. It is impossible for programmers to know the specific dimensions of various specifications of tools when programming. In order to simplify programming, it is necessary to use a unified benchmark when programming, and then use the tool to process the exact length and radius of the tool. The size is offset relative to the datum to get the accurate position of the tool tip. Therefore, the purpose of tool setting is to determine the tool length and radius value, so as to determine the accurate position of the tool tip in the workpiece coordinate system during machining.

Commonly used tool setting methods External tool setting

The tool presetter is a measuring instrument that can pre-adjust and measure the length and diameter of the tool tip. If the instrument forms a DNC network with a CNC machine tool, it can also remotely input the tool length and diameter data into the tool parameters in the NC of the machining center . The advantage of this method is that the tool is calibrated outside the machine tool in advance, and it can be used when it is installed on the machine tool, which greatly saves auxiliary time. However, the main disadvantage is that the measurement result is a static value, and the tool wear or damage status cannot be updated in real time during the actual machining process, and the tool expansion and contraction caused by the thermal deformation of the machine tool cannot be measured in real time.

Trial cutting method

Trial-cutting tool setting means that the operator operates the machine tool in manual mode to perform a small amount of cutting on the workpiece before the workpiece is formally processed. The operator determines the current position of the tool tip based on the judgment of eyes and ears. Then proceed to formal processing. The advantage of this method is that it does not require additional investment in tools and equipment, and is economical. The main disadvantages are low efficiency, high requirements for the operator's technical level, and prone to 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.

In-machine tool setting

This in-machine tool setting method uses a measuring device (tool setting instrument) set on the worktable of the machine tool to measure the tools in the tool magazine according to a preset program, and then compare with the reference position or the standard tool to obtain the tool The length or diameter is automatically updated to the corresponding NC tool parameter table. At the same time, the tool can also be used to identify whether the tool is worn, damaged, or the installed model is correct or not.

In-machine tool setting instrument

The composition of the tool setting instrument in the machine

In-machine tool setting instrument generally consists of sensor, signal interface and tool setting macro program software.

According to the working mode of the sensor, the in-machine tool setting instrument can be divided into two types: contact tool setting instrument and laser tool setting instrument. The repetitive measurement accuracy of the contact type tool setting instrument itself is 1μm, and it can be further subdivided into the following categories according to the different signal transmission methods of the tool setting instrument: cable type tool setting instrument; infrared type tool setting instrument; radio type Knife instrument.

Cable-type tool setting instrument, because it does not require tool setting signal conversion parts and has a good one-piece cost performance, it is common in work, but its disadvantage is that there is dragging of the cable, which limits the application of the tool setting instrument. Mostly suitable for small and medium-sized three-axis milling machines/machining centers.

Infrared type tool setting instrument, the signal transmission range is generally within 6m. Its advantage is the use of encoded HDR (high-speed data transmission) infrared technology to avoid the inconvenience and potential safety threats caused by cable dragging. After the tool is set, it can be removed from the work surface at any time without occupying processing space, and it can be shared by multiple machine tools. A tool setting instrument reduces the overall cost. The disadvantage is that it is not cost-effective when used on a small machining center. Determined by its characteristics, this type of tool setting instrument is mostly used for medium-sized machine tools and large-scale CNC vertical lathes.

Radio-type tool setting instrument, the radio signal transmission range is generally more than 10 meters. The advantage is that the radio signal transmission range is large and it is not easily affected by the environment. After the tool is set, it can be removed from the work surface at any time without occupying processing space, and multiple machine tools can share a tool setter, which can reduce the overall cost. This type of tool setting instrument is mostly used for large/heavy machine tools.

Laser tool setting instrument, such as Hexagon’s LTS35.60. The basic principle of this product is to use a focused laser beam as the trigger medium. When the laser beam is shielded by the rotating tool, a trigger signal is generated. The essential difference from the contact type tool setting instrument is that the laser tool setting instrument adopts non-contact measurement, and there is no contact force during tool setting, so it can measure extremely small tools without worrying about the damage of small tools due to contact force. For example, the diameter of the tool that can be measured by LTS35.60 can be as small as 0.008mm (such as drills, taps or micro milling cutters, etc.), and its repeat measurement accuracy can reach 0.2μm. At the same time, since the tool rotates at a high speed at the processing speed during measurement, the measurement state is almost identical to the actual processing state, which improves the practical accuracy of tool setting. Due to the use of laser technology, the tool setting instrument can scan the shape of the tool to measure the contour of the tool, and can monitor the damage of a single edge of a multi-edged tool. The main disadvantage is that the structure is complex, an additional high-quality air source is required to protect the internal structure, and the cost is relatively high. It is mainly suitable for high-speed machining centers.