The protective glass and reticle in photoelectric instruments, the substrate for manufacturing integrated circuits, and the flat panel display glass are flat panel optical parts with general accuracy requirements. Due to the increasing demand for such parts, the double-sided processing technology of such parts has gradually developed and matured.
Double sided processing technology refers to the technology of simultaneously processing two planes of flat optical parts. Obviously, this technology of simultaneous processing of two sides is much more efficient than the single processing of each side, but the corresponding equipment requirements and control requirements are also much higher.
1、principle of double sided processing
The early double-sided processing is to use the upper and lower flat dies on the general two axis machine, and use the retaining ring and separator to process the two surfaces of the flat plate at the same time. The device is shown in Figure 12-1, which mainly carries out the double-sided processing of fine grinding and polishing. During processing, the lower die 1 rotates with the spindle of the machine, and the upper die 5 swings under the drive of the swing frame and rotates with the rotation of the lower die. Its rotation has no power. The machined flat plate 2 is placed in the separation sheet 3, and the swinging upper die will drive the retaining ring, so as to drive the machined flat plate to move horizontally on the plane of the lower die. At the same time, the flat plate can also rotate with the rotation of the upper and lower dies in the separation sheet ring.
This kind of double-sided processing, the general speed is not high. The lower die is larger and the upper die is smaller, and the diameter of the retaining ring is larger and smaller than the upper die. By properly adjusting the swing of the upper die, the upper and lower surfaces of the flat plate can be finely ground or polished at the same time. When grinding or polishing, the abrasive or polishing powder is added to the surface of the lower mold and the flat plate intermittently manually. This low-speed double-sided processing improves the efficiency compared with single-sided processing, but the flatness and parallelism of the processed two sides cannot meet the high requirements, so it is only suitable for the processing of flat plates with general accuracy.
With the development of large-scale and very large-scale integrated circuit manufacturing technology, due to the needs of processing large quantities of semiconductor silicon wafers, double-sided high-speed machining machines have appeared abroad, which are suitable for double-sided grinding and polishing of semiconductor silicon wafers, and then are extended to high-speed grinding and polishing of optical flat plates in photoelectric instruments.
Figure 12-2 shows the layout of the high-speed double-sided processing machine tool in the workshop, and its processing principle is shown in Figure 12-3,
In the figure, the upper die 3 and the lower die 5 of high-speed double-sided machining have the same diameter and rotate around the spindle of the machine tool at the angular speed of the same size and opposite direction respectively. Between the upper and lower dies, there is also a planetary gear that drives the workpiece to be processed. It is meshed and driven by the internal gear and central gear concentric with the main shaft, and makes planetary motion around the center of the upper and lower dies, including revolution around the center and rotation around the self center of the planetary gear. The machined parts are put into the holes in the planetary gear that are consistent with the shape of the machined body. Therefore, the movement of the machined workpiece between the upper and lower dies is the synthesis of planetary motion and rotation motion. The slightly combined situation of the planetary gear supporting the machined parts is shown in Figure 12-4.
This kind of high-speed double-sided machining is mainly used in fine grinding and polishing processes. In the fine grinding stage, the self prepared granular abrasive fluid is used; In the polishing stage, use the polishing liquid prepared by yourself. When processing, first place the processed flat plate in the planetary gear of the lower die, drive the planetary gear to move with the rotation of the lower die, the rotation of the internal gear and the central gear, and the workpiece moves by the planetary belt. After the slow movement is normal, the upper die begins to contact and rotate in reverse, so that the motion of the workpiece enters the synthetic state. With the beginning and end of processing, the control system of the machine tool can gradually accelerate and decelerate, pressurize and depressurize the upper die, and control the recycling of grinding fluid and polishing fluid. Generally, the speed of the spindle can reach 200r/min~700r/min; The speed of the central gear can reach 10r/min~60r/min. After the processing parameters are set, the operation of the machine tool completely depends on program control.
High speed double-sided processing is relatively low-speed double-sided processing, which greatly improves the processing efficiency. Its processing feature is that the double-sided parallelism of the flat plate is very good, Generally, it can reach the level of less than 30 “, and its surface shape and surface quality can also meet the processing needs of general accuracy. After the process parameters are adjusted appropriately, setting the program of the processing machine tool can obtain a high part processing qualification rate. This processing certainty makes its process widely used in large-scale manufacturing.
Post time: Jul-21-2022