CNC milling of the hottest circuit board

2022-08-08
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The milling technology of the NC milling machine for circuit board includes the selection of the cutting direction, the compensation method, the positioning method, the structure of the frame and the cutting point. Are important aspects to ensure milling accuracy. Cutting direction and compensation method when the milling cutter cuts into the plate, there is a cutting surface that always faces the cutting edge of the milling cutter, and the other side is always against the cutting edge of the milling cutter. The former has smooth machined surface and high dimensional accuracy. The spindle always rotates clockwise. Therefore, when milling the external contour of the printed board, the CNC milling machine with fixed spindle and fixed spindle should adopt counterclockwise cutting. This is commonly known as reverse milling. However, when milling the frame or groove inside the road slab, the forward milling method is adopted. Milling plate compensation is that when milling plate, the machine tool automatically installs the set value so that the milling cutter automatically offsets half of the set milling cutter diameter with the center of the milling line, that is, the radius distance, so that the milling shape is consistent with the program setting. At the same time, if the machine tool has the function of compensation, it is necessary to pay attention to the direction of compensation and the command of using the program. If the error of using the compensation command will make the shape of the circuit board more or less equal to the length and width of the milling cutter diameter. There are two kinds of positioning methods: positioning method and cutting point positioning method; One is internal positioning, the other is external positioning. Positioning is also very important for process developers. Generally, the positioning scheme should be determined during the pre production of road slab. Internal positioning is a general method. The so-called internal positioning is to select the mounting hole, plug hole or other non-metallic hole in the printed board as the positioning hole. The relative position of the hole shall be on the diagonal and the hole with large diameter shall be selected as far as possible. Metallized holes cannot be used. Because the difference of coating thickness in the hole will affect the consistency of the positioning hole you choose, and it is easy to cause coating damage in the hole and the edge of the hole surface when taking out the board. Under the condition of ensuring the positioning of the printed board, the fewer the number of pins is, the better. Generally, two pins are used for small plates and three pins are used for large plates. Its advantages are accurate positioning, small deformation of plate shape, high accuracy, good shape and fast milling speed. Its disadvantage is that there are many kinds of hole diameters in the plate, and pins of various diameters need to be prepared. If there is no available locating hole in the plate, it is more cumbersome to discuss with customers to add locating holes in the plate during early production. At the same time, the milling template of each kind of plate is different, and the management is more troublesome and the cost is higher. External positioning is another positioning method, which is to add a positioning hole on the outside of the plate as the positioning hole of the milling plate. Its advantage is that it is easy to manage. If the production specification is good in advance, there are generally about 15 kinds of milling plate templates. Due to the use of external positioning, the board cannot be milled down at one time, otherwise the circuit board is very easy to be damaged, especially the panel, because the milling cutter and dust suction device will bring out the board, causing the circuit board to be damaged and the milling cutter to break. The method of milling and cutting the joint point by sections is adopted. When the milling is finished, the program is suspended, and then the plate is fixed with tape. The second section of the program is executed, and the joint point is drilled off with a 3mm to 4mm drill bit. Its advantage is that the template is less, the cost is small, and it is easy to manage. It can mill all circuit boards without installation holes and positioning holes in the board. It is convenient for small craft personnel to manage. In particular, the production of early production personnel such as cam can be simplified, and the utilization of substrate can be optimized at the same time. The disadvantage is that due to the use of drill bits, at least 2-3 convex points are left in the shape of the circuit board, which is not beautiful, and may not meet the requirements of customers. The milling time is long, and the labor intensity of workers is slightly high. The fabrication of the frame and the lower tool point frame belongs to the early fabrication of the circuit board. The frame design has an impact not only on the uniformity of electroplating, but also on the milling board. For example, if the design is not good, the frame is easy to deform, or some small waste blocks installed in small blocks are generated during milling, which will block the dust suction pipe or break the high-speed milling cutter. The deformation of the frame, especially when positioning the milling board externally, will cause the deformation of the finished board, In addition, if the cutting point and processing sequence are well selected, the frame can maintain the maximum strength and the fastest speed. The selected ultrasonic level switch is not good after the cost decreases, and the frame is easy to deform, making the printing machine 3. Balancing machine (including on-site balancing instrument); The blackboard newspaper is discarded. Process parameters of milling: use carbide milling cutter to mill the shape of printed board, and the cutting speed of milling cutter is generally 180 ~ 270m/min. The calculation formula is as follows (for reference only): s=pdn/1000 (m/mi, but in terms of technology classification and application classification hardware, according to the national standard gb/t2611 (2) 007 "general technical requirements for laboratory machines", it has been clearly stated that electrical equipment should have the ability to protect personal safety and avoid electric shock, and it is sometimes difficult to distinguish that fine, so these 20 relatively miscellaneous classifications can also be simply reduced to 4 types n) in the formula: D: milling cutter diameter, mm n; The milling cutter speed, r/min, and the cutting speed are matched by the feed speed. If the feed speed is too low, the printed board material will soften or even melt or scorch due to friction heat, blocking the chip removal slot of the milling cutter, and cutting cannot be carried out. If the feed is too fast, the milling cutter will wear fast and bear large radial load, resulting in large tool quantity, poor working quality and inconsistent size. How to judge the speed of feeding? The following items should be considered: printed board material, thickness, number of blocks per stack, iron knife diameter, chip removal slot. Generally, it can be set according to the technical data provided by the tool supplier. Due to the difference of the material quality brand and manufacturing process of the tool, the tool process parameters of different manufacturers are different. The speed of the spindle motor can be maintained only when it is lower than the rated load. The load increases and the speed decreases until the milling cutter breaks. There are usually several conditions that cause the problem of tool breaking during milling: first, the power of the spindle motor is insufficient and needs to be repaired and replaced. 2: There are too many plates in each stack, the cutting load is too large, or the milling length exceeds the effective length of the milling cutter. 3: Milling cutter quality problems. 4: Speed and feed speed setting problems. 5: The clamping force of the drill chuck of the rotating shaft decreases, and the required speed cannot be reached when taking the load. 6: There is a concentricity problem when the rotating shaft rotates, resulting in runout. 7: There are problems in the design of the program, such as using the wrong command

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