When it comes to the characteristics of five-axis machine tools, and the traditional three-axis equipment to compare. Three-axis processing equipment in production is more common, there are vertical, horizontal and Longmen, and other forms.
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The common processing methods are end milling cutter edge processing, side edge processing. Copying machining of ball-end cutter and so on. But no matter which form and method has a common characteristic, that is, the direction of the cutter axis is always kept constant during the machining process, the motion of the tool in the space cartesian coordinate system can only be realized by the interpolation of X, Y and Z LINEAR axes. Therefore, in the face of the following products, the three-axis machine tool efficiency is low, poor surface quality or even unable to process the abuse was exposed.
Compared with three-axis CNC machining equipment, five linkage CNC machine tools have the following advantages: 1. Keep the best cutting condition and improve the cutting condition
As shown above, in the left-hand three-axis cutting mode, the cutting state gradually deteriorates as the cutting tool moves toward the top or the edge of the workpiece. And to maintain optimum cutting conditions here, you need to rotate the table. And if we want to complete an irregular plane, we have to rotate the table in different directions many times. As can be seen, the five-axis machine tool can also avoid the ball-end Milling Cutter Center Point Linear speed of 0, get better surface quality. 2. Effectively avoiding tool interference
As shown above, three-axis equipment can not meet the process requirements for the impeller, blade and integral blisk used in the aerospace field due to interference. And five-axis machine tools can meet. At the same time, the five-axis machine tool can also use shorter tools for processing, improve system rigidity, reduce the number of tools, to avoid the production of special tools. For our business owners, means in the cost of cutting tools, five-axis machine will give you money! 3. Reduce the number of clamping, one-time clamping to complete five-sided processing
As can be seen above five-axis machining center can also reduce the reference conversion, improve machining accuracy. In the actual processing, only one clamping, processing accuracy is easier to be guaranteed. At the same time, due to the shortening of the process chain and the reduction of the number of equipment, the number of fixtures, workshop floor area and equipment maintenance costs are also reduced. This means that you can use fewer fixtures, less plant area and maintenance costs, to achieve more efficient and high-quality processing! 4. Improve the processing quality and efficiency as shown in figure, five-axis machine tool can be used side edge cutting tool, processing efficiency is higher.
5. Shortening the production process chain, simplifying the production management of five-axis CNC machine tools complete processing greatly shorten the production process chain, production management and scheduling can be simplified. The more complex the work piece, the greater its advantage over a traditional, decentralized production method. 6. Shortening the research and development cycle of new products for enterprises in the fields of aerospace and automobile, some new product parts and forming molds have complex shapes and require high precision, therefore, the five-axis NC machining center with high flexibility, high precision, high integration and complete machining ability can solve the problem of machining precision and cycle of complex parts in the process of new product development, greatly shorten the research and development cycle and improve the success rate of new products. To sum up, five-axis machine tools really have too many advantages, but five-axis tool attitude control, CNC system, CAM programming and post-processing are more complex than three-axis machine tools! At the same time, we talk about five-axis machine tools, we have to say the question of true and false five-axis, we all know the biggest difference between true and false five-axis is the RTCP function, but what is RTCP, how did it come about and how should it be used? Let's take a closer look at RTCP and see what it really looks like, in combination with machine tool architecture and post-programming. 03 about RTCPTCP, in the high-end five-axis CNC system, that RTCP is a Rotated Tool Center Point, that is, we often say that the Point-of-a-knife follow function. In the process of five-axis machining, the additional motion of the tool point is produced due to the rotary motion when the tool point locus and the attitude between the tool and the workpiece are pursued. NC system control points often do not coincide with the tip point, so NC system should automatically correct the control points to ensure the tip point according to the instructions of the established trajectory movement. There are also features in the industry that call this technology TCPM, TCPC, or RMCP. In fact, the functional definition of these calls are similar to RTCP, strictly speaking, RTCP function is used in the Double Bob head structure, is the application of the BOB head rotation center point to compensate. And similar to the RPCP function is mainly used in the form of dual turntable machine tools, compensation is due to the rotation of the workpiece caused by the change in axis coordinates. In fact, all of these functions are to keep the tool center point and the actual contact point between the tool and the workpiece surface unchanged. So for the convenience of expression, this paper unifies this kind of technology as RTCP technology..
So how did the RTCP feature come about? Many years ago, when the five-axis machine tool was just popularized in the market, the RTCP concept was greatly promoted by the machine tool manufacturers. At the time, RTCP was more of a technology-for-technology stunt than a passion and hype for the technology itself. In fact, RTCP function on the contrary, it is not only a good technology, but also a good technology can bring benefits to customers and create value. The machine tool with RTCP technology (also known as the true five-axis machine tool in China) , the operator does not have to precisely align the workpiece with the axis of the turntable, random clamping, automatic offset compensation of the machine tool, greatly reducing the auxiliary time, while improving the processing accuracy. At the same time, the post-processing is simple, as long as the output point coordinates and vectors on the knife. As we said before, in the mechanical structure, five-axis CNC machine tools are mainly double pendulum head, double turntable, a pendulum a rotation and so on. Below we will double turntable high-end five-axis CNC system as an example, a detailed description of the RTCP function. The fourth axis and the fifth axis are defined in a five axis machine tool: the rotation of the fourth axis affects the attitude of the fifth axis in a double rotary table structure, and the rotation of the fifth axis can not affect the attitude of the fourth axis. The fifth axis is the rotational coordinate on the fourth axis.
All right, let's go over the definitions. As shown above, axis 4 of the machine tool is axis A, axis 5 is axis C. The workpiece is placed on a c-axis turntable. As axis 4 rotates, because axis C is mounted on axis A, axis C attitude is also affected. In the same way, if we place the workpiece on the turntable, if we program the cutting tool center, the change of the rotation coordinate will cause the change of the X, Y, Z coordinates of the straight line, resulting in a relative displacement. In order to eliminate this displacement, it is necessary to compensate the machine tool, RTCP is to eliminate this compensation and the resulting function. So how does the machine tool compensate for this offset? So let's look at how that happens. Want to learn UG CNC programming plus QQ Group 579401268 can help you. From the foregoing, we know that the shift in the axis of a straight line is caused by a change in the rotation coordinates. So it is very important to analyze the center of rotation of the axis of rotation. For double-turntable machine tools, the C axis is the fifth axis of the control point is usually in the table of the machine tool rotary center. The fourth axis usually selects the midpoint of the fourth axis as the control point.
In order to realize 5-axis control, the relationship between 5-axis control point and 4-axis control point should be known. That is, the initial state (machine tool A, C axis 0 Position) , the fourth axis control point for the origin of the fourth axis rotation coordinate system, the fifth Axis Control Point Position Vector [ U, V, W ] . You also need to know the distance between the axes of A and C. For Double turntable machine tools, examples are shown in the following figure.
At this point, you can see that for the RTCP function of the machine tool, the control system to keep the tool center in the programmed position. In this case, the programming is independent and independent of the machine's motion. When you program on a machine tool, you don't have to worry about the motion and length of the tool. All you have to think about is the relative motion between the tool and the workpiece. The rest of the work control system will be completed for you. For example,：
As shown above, the control system does not consider the tool length without the RTCP switch. The cutter rotates around the center of the shaft. The tip of the knife is removed from its position and is no longer fixed.
As shown above, with the RTCP function on, the control system only changes the direction of the cutter, the position of the cutter tip remains unchanged. The necessary compensatory motions on the X, Y, and Z axes have been calculated automatically. But for the five-axis machine tools and CNC system without RTCP, how to solve the PROBLEM OF LINEAR AXIS OFFSET? We know that many domestic five-axis CNC machine tools and systems belong to the false five-axis, the so-called false five-axis, in fact, refers to the non-RTCP function of machine tools. True and false five axis, neither look at the appearance is not to see whether the five axis linkage, to know that false five axis can also do five axis linkage. The difference of the pseudo-five-axis is that there is no real five-axis RTCP algorithm, that is to say, the pseudo-five-axis programming needs to consider the swing length of the spindle and the position of the rotary table. This means that the use of pseudo-five-axis CNC system and machine programming, must rely on Cam programming and post-processing technology, pre-planning good tool path. For the same part, when the machine tool is changed or the cutting tool is changed, the CAM programming and post-processing must be carried out again. And the false five-axis machine tool needs to ensure the workpiece in its table rotation center position, which means that the operator needs a large number of clamping alignment time, and accuracy can not be guaranteed. Even if it is to do dividing processing, false five axis is also a lot of trouble. And true five axis only need to set up a coordinate system, only need a knife, you can complete the processing. The following illustration illustrates the coordinate transformation of the false five axes with an example of the NX POST-PROCESSING EDITOR SETUP: . The pseudo-five-axis is based on post-processing technology, which shows the relation between the center of the fourth axis and the fifth axis of the machine tool to compensate the displacement of the rotation axis to the linear axis. The generated CNC programs x, Y and Z are not only the programming approach point, but also the necessary compensation on the x, Y and Z axes. The result of this processing will not only lead to low precision, low efficiency, the generated program is not universal, the human cost is also very high. At the same time, due to the rotation parameters of each machine tool are different, there must be corresponding post-processing files, for the production will also cause great inconvenience. Moreover the false five-axis its generation procedure can not change, realizes the manual five-axis programming basic not to have the possibility. At the same time, because there is no RTCP function, many of its derivatives of five-axis high-level functions can not be used, such as five-axis knife repair function. In fact, for five-axis machine tools, it is only in order to achieve our processing results, there is no distinction between true and false. What is important is that our process determines which way to choose processing, relatively speaking, the true five-axis machine tool cost-effective。