Five-axis linkage milling parallel motion machine

Does the spindle only rely on tiny basket-type legs connected to the frame to machine steel? Is the entire machine frame with only the welding accuracy suitable for tool and mold manufacturing? The conclusion is yes, this machine is competent. The machining performed by this type of machine can be illustrated in the following article.

When the parallel movement mechanism is first seen, the above-mentioned problems will almost certainly arise. Interested people certainly want to know, so that the structure of such a thin line can really be solid enough in actual production? First of all, it should be explained what the parallel movement organization is. Parts (such as spindles) that are moved on a parallel kinematic machine are connected to the frame using a certain number of support bars and universal hinges. A typical six-legged machine tool has six lifting cylinder type support rods of variable length. When a suitable type of universal hinge is selected and the hinge on the frame is coupled with the hinge on the part to be moved by means of a support rod, the six degrees of freedom of the moving part can be manipulated by means of changes in the length of the support rod. The length of any one of the support rods can be manipulated individually without jamming.

For machines using five support rods, for example a parallel motion machine developed by the company Metrom () in Chemnitz, five degrees of freedom can be manipulated. In the case where the universal hinge is appropriately arranged, the degree of freedom of no longer manipulating is overlapped with the degree of freedom of rotation about the axis of the spindle. In this case, it means to reduce to five support rods, but it does not limit the degree of freedom necessary to achieve five-axis motion. However, the use of five support bars allows for greater oscillating motion than a conventional six-legged parallel kinematic machine tool. The deflection angle can be greater than 90 degrees. If the workpiece is fixed on the rotary table, the workpiece can be processed on five sides in one clamping.

Although the machine tool uses five support rods, and through suitable hinge connections, all the accelerations of the spindle mass can only produce axial forces on the support rods. For the parallel motion machine tool of Metrom, the support rod as a ball screw has high rigidity in the axial direction.

Machining of steel parts with larger material removal

Chemnitz machine tool specialists use a 63 mm diameter ball screw drive on the P1000. The configuration of the support rod is optimal, so that the spindle has a high rigidity in the large working range, both in the upright position and in the horizontal position. Metrom designs racks according to the same principles. The support rods of the frame are mainly subjected to tensile loads and pressure loads. In this way, important conditions are fulfilled, for example in order to be able to adjust higher jerk limit values ​​(500 m/s3). The rotary direct drive can accelerate the acceleration by more than 10m/s2 with higher adjustment. Due to the lighter weight of the movement, the energy consumption and output power are very low.

In addition, the main shaft of this machine can have 88Nm and 130Nm (S1/S6) torque (S1 represents the load of the electric spindle during 100% operation time, S6 represents the load at 40% operation time. S6> S1, which is Due to the short turn-on time, the motor spindle is allowed to temporarily overload the input and 27 kW of power. The performance of the machine tool is not limited to these limit values. Therefore, the P1000 parallel motion machine tool can process steel and other hard materials with a large material removal amount. At the same time, the so-called acceleration and jerk as well as the adjustment amplification allow a high dynamic five-axis linkage trajectory movement. Therefore, using the same machine tool can also be used to efficiently process light material workpieces.

How rigid is the parallel movement mechanism?

Metrom's parallel movements in Chemnitz City have been used for many years to directly mill cast dies that are bonded by sand. This material allows higher cutting speeds when machining, so parallel motion mechanisms are suitable for this type of machining.

Based on years of use, what do you think about wear and tear? In sand milling, sharp-edged particles are thrown at higher speeds throughout the process area. The results show that even if the sand is flying, the equipment is not damaged, Metrom company thinks. Because in any spindle position, the direction of sand flow is perpendicular to the axis of the spindle. The support rod itself can be protected against sand with a corrugated sleeve in a simple manner. For a parallel-moving machine tool, there is no need for a guide rail for the machine tool of this structure. Both ends of the ball screw drive are supported by universal joints. In this way, due to structural reasons, there is no bending load in the transverse direction that causes severe wear of the ball screw drive.

Prevent collision

In order to prevent collisions, the spindle is not allowed to enter certain positions in the work area. This collision may occur because the hinge angle of the gimbal hinge is too large, the spindle collides with the frame components, or the support rods collide with each other. In this case, Metrom uses a control system to handle and identify any collision hazards in a timely manner through the control system. However, the control system cannot prevent the collision between the spindle and the workpiece. Even if parts are damaged, the advantages of this machine structure can still be shown here. Because of the modular machine tool structure, the repair cost is relatively reduced. And after replacing the damaged parts and recalibrating them, the accuracy will not be affected, even if the entire rack is deformed due to a collision.

Is machining a workpiece bigger than a machine tool?

The mechanical structure of Metrom's parallel motion machine tool consists of five support rods, including a gimbaled hinge, a spindle part and a rigid frame. The frame can be manufactured with greater tolerances without affecting the accuracy of the machine.

After installing the support rod into a rack that can be easily calibrated, the calibration procedure is started. Through this procedure, the motion parameters are determined and these parameters are input into the NC control system. Using these information control systems, each spindle position pre-determined in the ordinary coordinate system is converted into the position of all the feed drives. Through this model of machine tool construction, a new approach has been opened up for the reprocessing of large workpieces. One idea that has been endorsed is the moveable modular milling center. For such a machine tool, the workpiece is not transferred. A frame is simply constructed within the scope of the workpiece to be machined, and the support rod is attached to the frame with the universal hinge. After a large part of the automated calibration process is completed, processing can begin. The machine parts can then be easily removed and can be used again in the future. This kind of machine tool is beneficial to be productive and to process large parts at a low cost.

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