How to align Chuck?

Tool setting is a major operation and an important skill in CNC machining. Under certain conditions, the accuracy of tool setting can determine the machining accuracy of the part, and at the same time, the efficiency of tool setting also directly affects the efficiency of CNC machining. Only know the tooling method is not enough, but also know the CNC system of various tooling settings, as well as these ways in the processing program call method, at the same time to know the advantages and disadvantages of various tooling methods, use conditions, etc..

Tool setting principles

The purpose of tool setting is to establish the workpiece coordinate system, intuitively speaking, tool setting is to establish the position of the workpiece in the machine table, in fact it is to seek the coordinates of the tooling point in the machine coordinate system.

For CNC lathes, the first thing to do before machining is to select the tooling point, which is the starting point of the tool movement relative to the workpiece when machining the workpiece with a CNC machine. The tooling point can be located on the workpiece (such as the design benchmark or positioning benchmark on the workpiece), but also on the fixture or machine tool, if located on the fixture or machine tool at a certain point, the point must maintain a certain accuracy of the dimensional relationship with the positioning benchmark of the workpiece.

When tool setting, it should make the tool position point and the tooling point coincide, the so-called tool position point refers to the positioning reference point of the tool, for turning tools, the tool position point is the tool tip. The purpose of tool setting is to determine the absolute co-ordinate value of the tool point (or workpiece origin) in the machine tool co-ordinate system and to measure the deviation value of the tool position. The accuracy of the tool setting point has a direct impact on the machining accuracy.

In the actual machining of workpieces, the use of one tool is generally not sufficient to meet the machining requirements of the workpiece and multiple tools are usually used for machining. When using more than one turning tool, the geometric position of the tool tip point will differ after the tool change position remains unchanged, which requires different tools to start machining in different starting positions to ensure the normal operation of the program.

In order to solve this problem, the machine tool CNC system is equipped with the function of tool geometry position compensation, the use of tool geometry position compensation function, as long as the prior to each tool relative to a pre-selected reference tool position deviation measured out, input to the CNC system tool parameters correction column specified group number, in the processing program using the T command, you can automatically compensate for tool position deviation in the tool path. The measurement of the tool position deviation is also carried out by means of a tool setting operation.

Tool setting methods

In CNC machining, the basic methods of tool setting are test cutting, tool setting and automatic tool setting. This paper takes CNC milling machine as an example and introduces several common tool setting methods.

1. Trial cut on the tool method

This method is simple and convenient, but will leave cutting marks on the surface of the workpiece, and tool setting accuracy is low. Take the tool setting point (where it coincides with the origin of the workpiece coordinate system) in the centre of the workpiece surface as an example and use the bilateral tool setting method.

(1) Tool setting in the x and y directions.

① Mount the workpiece on the table by means of a fixture. When clamping, all four sides of the workpiece should be left for tool setting.

② Start the spindle to rotate at medium speed and move the table and spindle quickly so that the tool moves quickly to a position close to the left side of the workpiece at a safe distance, then reduce the speed to move closer to the left side of the workpiece.

③ close to the workpiece when the change to fine-tuning operation (generally with 0.01mm) to close, so that the tool slowly approach the left side of the workpiece, so that the tool just touch the surface of the left side of the workpiece (observation, listen to the cutting sound, look at the cut marks, look at the chips, as long as a situation that the tool contacted the workpiece), and then back 0.01mm. note down at this point in the machine tool coordinate system to show the coordinate value, such as -240.500.

④ Retreat the tool in the z-positive direction to above the surface of the workpiece, approach the right side of the workpiece in the same way and write down the value of the coordinates shown in the machine tool coordinate system at this point, e.g. -340.500.

⑤ Accordingly, the workpiece coordinate system origin in the machine coordinate system coordinate value of ｛-240.500 + (-340.500)} /2 = -290.500.

(6) Similarly, the coordinate value of the origin of the workpiece in the machine tool coordinate system can be measured.

(2) z-direction tool setting.

① Move the tool quickly to the top of the workpiece.

② Start the spindle to rotate at medium speed, move the table and spindle quickly, let the tool move quickly to a position close to the upper surface of the workpiece with a certain safety distance, and then reduce the speed to let the tool end close to the upper surface of the workpiece.

③ close to the workpiece with fine adjustment operation (generally with 0.01mm) to close, so that the tool end surface slowly approach the workpiece surface (note that the tool, especially the end mill, is best in the edge of the workpiece under the knife, the end of the knife contact the surface of the workpiece area is less than half a circle, try not to make the centre hole of the end mill under the workpiece surface), so that the tool end just touches the upper surface of the workpiece, and then the axis will be raised again, write down the machine tool at this time The z value in the machine tool coordinate system, -140.400, then the workpiece coordinate system origin W in the machine tool coordinate system coordinate value of -140.400.

(3) Input the measured x, y and z values into the machine workpiece coordinate system storage address G5* (generally use the G54 to G59 code to store the tooling parameters).

(4) Enter panel input mode (MDI), enter "G5*", press start (in auto mode) and run G5* to make it effective.

(5) Check if the tool setting is correct.

2. plug ruler, standard mandrel, block gauge on the knife method

This method is similar to the test cut tool setting method, except that the spindle does not rotate during tool setting, and a stopper (or standard mandrel, block gauge) is added between the tool and the workpiece to the extent that the stopper cannot be drawn freely, so that the thickness of the stopper should be subtracted when calculating the coordinates. Because the spindle does not need to rotate cutting, this method will not leave traces on the surface of the workpiece, but the accuracy of tool setting is not high enough.

3.Tool setting method using edge finder, eccentric rod and axis setter and other tools

The procedure is similar to the test cut tool setting method, except that the tool is replaced by an edge finder or eccentric bar. This is the most commonly used method. It is efficient and guarantees accurate tool setting. Care must be taken when using the edge finder so that the ball part is in light contact with the workpiece and the workpiece to be machined must be a good conductor with a good surface finish on the positioning datum. z-axis setters are generally used for the transfer (indirect) tool setting method.

4. Transfer (indirect) tool setting

Machining a workpiece often requires the use of more than one tool, the length of the second tool is not the same as the length of the first tool loading, the need to re-zero, but sometimes the zero point is machined off, can not directly find the zero point, or do not allow the destruction of the machined surface, and some tools or occasions are not good for direct tool setting, this time can be used to find the zero method indirectly.

(1) For the first knife

① The first tool is still the first to use the test cut method, the plug method, etc. Write down the machine coordinates of the workpiece origin z1. Note down the machine coordinates of the workpiece origin z1. after the first tool is processed, stop the spindle.

② Place the tool setter on a flat surface of the machine table (e.g. the large surface of the vise).

③ In handwheel mode, use the hand crank to move the table to a suitable position, move the spindle downwards, press the top of the tool setter with the bottom end of the tool, the dial pointer turns, preferably within one revolution, note down the number of the axis setter at this point and zero the relative coordinate axes.

(4) Raise the spindle exactly and remove the first tool.