1. Knife site
The tool location is a reference point on the tool. The relative movement path of the tool location is the processing path, also called the programmed path.
2. Tool setting and tool setting
The tool setting refers to the fact that the operator positions the tool position and the tool setting point by a certain measuring method before starting the NC program. The tool setting tool can be used to set the knife, its operation is relatively simple, and the measurement data is also accurate. It is also possible to use a gauge block, a feeler gauge, a dial gauge, etc. after positioning a fixture and mounting a part on a numerical control machine tool, and use a coordinate cutter on a numerical control machine tool. For the operator, determining the tool-cut point will be very important and will directly affect the machining accuracy of the part and the accuracy of the program control. In the batch production process, the repeat accuracy of the tool point must be taken into account. The operator needs to deepen his understanding of the numerical control equipment and master more tool setting techniques.
(1) Selection principles for knife points Easy to find on the machine tool, easy to check in the process, easy to calculate when programming, and the tooling error is small. The tool point can select a point on the part (such as the center of the positioning hole of the part), or a point outside the part (such as a fixture or a point on the machine), but it must have a certain coordinate with the positioning reference of the part. relationship. Improve the accuracy and accuracy of the knife, even if the parts require less precision or program requirements are not strict, the selected part of the tooling accuracy should be higher than other positions of the machining accuracy. Select a site with a large contact surface, easy to monitor, and stable machining process as a tool point. The tool point should be unified with the design reference or the process reference as much as possible to avoid the decrease of the tool accuracy or even the machining accuracy due to the size conversion, and increase the difficulty of the numerical control program or the numerical control processing of the parts. In order to improve the machining accuracy of the parts, the tool point should be selected as far as possible on the design basis or process reference of the part. For example, the hole-positioned part is suitable for the center of the hole as a tool-cutting point. The precision of the tool-cutting point depends on the precision of the numerical control equipment, and also depends on the requirements of the parts processing. The precision of the tool-cutting is manually checked to improve the quality of the numerical control machining of the parts. In particular, in the batch production, the repetitive precision of the tool point must be taken into account. This accuracy can be checked by using the coordinate value of the tool point relative to the machine origin. (2) Selection method of knife point For numerical control lathe or milling and milling machining center type numerical control equipment, because the central position (X0, Y0, A0) has been determined by numerical control equipment, the entire machining coordinate system can be determined by determining the axial position. Therefore, it is only necessary to determine an end face in the axial direction (Z0 or relative position) as a tool setting point. For the three-axis CNC milling machine or three-axis machining center, the relative CNC lathe or turning and milling machining center is much more complex. According to the requirements of the NC program, not only the origin position (X0, Y0, Z0) of the coordinate system needs to be determined, but also the same processing coordinate system. The determination of G54, G55, G56, G57, etc. depends on the operator's habits. The tool setting point can be set on the machined part or on the fixture, but it must have a certain coordinate relationship with the positioning reference of the part. The Z direction can be determined simply by determining an easily detectable plane, and the X and Y directions Make sure you need to select the plane and circle related to the positioning reference according to the specific part. For the four-axis or five-axis numerical control equipment, the fourth and fifth rotation axes are added. Similar to the three-axis numerical control equipment, the tool selection point is similar. Because the equipment is more complex and the numerical control system is intelligent, more tool setting methods are provided. According to the specific numerical control equipment and specific processing parts to determine. The coordinates of the tool-cutting point relative to the machine tool coordinate system can be simply set to be related to each other. For example, the coordinate of the tool-cutting point is (X0, Y0, Z0), and the relationship with the machining coordinate system can be defined as (X0+Xr, Y0+). Yr, Z0+Zr), machining coordinate system G54, G55, G56, G57, etc., can be input through the control panel or other methods. This method is very flexible and very skillful, which brings great convenience for subsequent CNC machining.3. Zero drift
The phenomenon of zero drift is caused by the environmental influences of the numerical control equipment. Under the same cutting conditions, the same fixture, numerical control program, and tool are used for the same device. Or the phenomenon of reduced precision.
The phenomenon of zero drift is mainly manifested in the phenomenon of a decrease in precision in the numerical control machining process or it can be understood as the inconsistency in accuracy during numerical control machining. Zero drift is unavoidable in the CNC machining process. It is ubiquitous for numerical control equipment. It is generally affected by environmental factors surrounding the numerical control equipment. In severe cases, it will affect the normal operation of CNC equipment. There are many reasons that affect the zero drift, mainly temperature, coolant, tool wear, spindle speed and feed rate changes.4. Tool compensation
After a certain period of time after the NC machining, the wear of the tool is unavoidable. The main manifestation is the change of the tool length and the tool radius. Therefore, the tool wear compensation mainly refers to the tool length compensation and tool radius compensation.
5. Tool radius compensation
In the contour processing of parts, because the tool always has a certain radius such as the radius of the milling cutter, the movement path of the tool center is not equal to the actual trajectory of the part to be machined, but a tool radius value needs to be offset. This offset is customary. Become tool radius compensation. Therefore, the radius of the tool must be taken into account when machining the contour of the part. It should be pointed out that the UG/CAM NC program is programmed with an ideal machining state and an accurate tool radius. The tool motion path is the trajectory of the tool center and does not take into account the status of the CNC equipment and the degree of wear of the tool. influences. Therefore, regardless of contour programming or arbor programming, the implementation of UG/CAM NC program must take into account the effects of tool radius wear, and rational use of tool radius compensation.
6. Tool length compensation
In numerically controlled milling and boring machines, when the tool is worn or the tool is changed, the position of the tool's tool tip is not at the programmed position of the original machining. The change in size must be compensated by lengthening or shortening the offset value of the tool length. Ensure that the depth of processing or the position of the machined surface still meets the original design requirements.
7. Machine coordinate system
The naming convention of numerically-controlled machine tools is that Cartesian coordinates are used for the linear motion of the machine tool, and the coordinates are named X, Y, and Z, which are generally called the basic coordinate system. The X, Y, Z coordinate axes or the motions centered on the coordinate axis parallel to the X, Y, and Z coordinate axes are called the A axis, B axis, and C axis, and the positive direction of A, B, and C is right-handed. The law of the spiral is determined.
Z-axis: Normally, the axis that transmits the cutting force is defined as the Z-axis. For the tool rotating machine, such as boring machine, milling machine, drilling machine, etc., the axis of the tool rotation is called Z axis. X-axis: The X-axis is usually parallel to the workpiece clamping surface and perpendicular to the Z-axis. For machine tools that rotate tools, such as horizontal and horizontal boring machines, the right-hand direction is the positive direction of the X-axis when viewed from the direction of the tool's main axial workpiece. When the Z-axis is vertical, for a single-column machine tool, such as a vertical milling machine, Look in the direction of the main column of the tool and the right-hand direction is the positive direction of the X-axis. Y-axis: The Y-axis is perpendicular to the X-axis and the Z-axis, and the direction can be determined according to the determined X-axis and Z-axis, and the right-handed Cartesian coordinate system. The definition of the rotation axis is also in accordance with the right-hand rule, the rotation around the X axis is the A axis, the rotation around the Y axis is the B axis, and the rotation around the Z axis is the C axis.The axis of the CNC machine tool is shown in the figure below.
CNC machine axes
The machine origin is the coordinate origin of the machine coordinate system. There are some fixed reference lines on the machine tool, such as the centerline of the spindle; there are also some fixed reference planes, such as the workbench, the spindle end, and the side of the workbench. After the axes of the machine tool are manually returned to their respective origins, the position of the machine's origin can be determined by the distance between the reference line on each axis component and the reference plane. This point is described in the operating instructions of the CNC machine tool.8. Part machining coordinate system and coordinate origin
The workpiece coordinate system, also known as the programming coordinate system, is a coordinate system established by the programmer when the part machining program is programmed with a fixed point on the workpiece as the origin. The origin of the part coordinate system is called the part zero (part origin or program zero), and the tool trajectory coordinates are programmed according to the coordinates of the part in the part coordinate system.
The origin of the machining coordinate system is called the adjustment point in the machine coordinate system. During processing, the part is mounted on the machine tool with the fixture. The fixture location of the part is fixed relative to the machine tool, so the position of the part coordinate system in the machine coordinate system is also determined. At this time, the distance between the measured part origin and the machine origin is called the part zero offset. This offset needs to be stored in advance in the CNC system. During machining, the origin offset of the part can be automatically added to the part coordinate system, so that the CNC system can determine the absolute coordinate value when machining according to the machine coordinate system. Therefore, the programmer can ignore the actual installation position and installation accuracy of the part on the machine tool, and use the offset function of the numerical control system to compensate the position error of the part on the machine tool through the offset value of the original point of the part. Now all CNC machine tools have This feature is very convenient to use. The position of the part coordinate system uses the machine tool coordinate system as a reference point. On a CNC machine tool, multiple part coordinate systems can be set and stored in G54/G59, etc. The part zero is generally set at the design reference and process reference of the part. For easy calculation of dimensions. General CNC equipment can preset multiple working coordinate systems (G54 ~ G59), these coordinate systems are stored in the machine memory, the working coordinate system is based on the machine origin as a reference point, respectively, their respective offsets from the origin of the machine Need to input the CNC system in advance, or set the coordinate system before machining. The machining coordinate system (MCS) is the positioning reference for all the tool path output points of the part machining. The machining coordinate system is represented by OM-XM-YM-ZM. With the machining coordinate system, it is not necessary to consider the installation position of the workpiece on the machine tool during programming, as long as it is programmed according to the characteristics and dimensions of the workpiece. The origin of the machining coordinate system is the workpiece machining zero point. The position of the zero point of workpiece machining is arbitrary, which is selected by the programmer according to the characteristics of the part when preparing the NC machining program. The workpiece zero can be set on the machined workpiece or on the fixture or machine tool. In order to improve the machining accuracy of the parts, the zero point of the workpiece is selected as far as possible on the machining surface with higher accuracy; in order to facilitate data processing and simplify programming, the zero point of the workpiece should be set as far as possible on the design basis or process reference of the part. For symmetrical parts, the best The zero point of the workpiece is set on the center of symmetry, which is easy to identify and check.9. Mounting origin
The origin of clamping is common in CNC machine tools and machining centers with swivel (or swinging) tables, such as swivel centers. The offset from the machine reference point can be stored in the origin offset register of the CNC system for the CNC system. Origin offset calculation.
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