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The milling technology of CNC milling machines: The milling technology related to CNC milling machines for printed circuit boards includes selecting the cutting direction, compensation methods, positioning techniques, the structure of the frame, and the point at which the tool enters the workpiece. They are all important aspects in ensuring the precision of milling operations. Cutting direction, compensation method: When the milling tool cuts into the sheet metal, one of the surfaces being cut is always facing the cutting edge of the milling tool, while the other surface is always opposite to the cutting edge. In the former case, the machined surface is smooth and has high dimensional accuracy. The main shaft always rotates in a clockwise direction. Therefore, whether it is a CNC milling machine with the spindle fixed and the worktable moving, or one with the worktable fixed and the spindle moving, a counterclockwise tool path must be used when milling the outer contour of printed circuit boards. This is what is commonly referred to as back milling. When milling frames or grooves inside the circuit board, a feed-forward milling method is used. Plate milling compensation involves the machine automatically adjusting, during plate milling, the position of the milling tool so that it is offset by half of the tool diameter – in other words, a radial distance – from the center of the milling path, thereby ensuring that the shape produced matches what is specified in the program. At the same time, if the machine tool has a compensation function, it is necessary to pay attention to the direction of compensation and the commands in the usage procedure; using the compensation commands incorrectly can result in the dimensions of the circuit board increasing or decreasing by an amount equal to the diameter and width of the milling tool. Positioning method and cutting point: The positioning methods can be divided into two types ； One is internal positioning, and the other is external positioning. Positioning is also very important for process planners; generally, the positioning scheme should be determined during the early stages of circuit board production. Internal positioning is a universal method. Internal positioning refers to the use of mounting holes, plug holes, or other non-metallized holes in the printed circuit board as positioning points. The relative positions of the holes are aimed to be on the diagonal, with larger-diameter holes being selected as much as possible. Metalized holes cannot be used. Since differences in the thickness of the coating inside the holes can affect the consistency of the positioning holes chosen, it is also easy to damage the coating inside the holes and on their edges when removing the board. Under the condition of ensuring proper positioning of the printed circuit board, fewer pins are preferable. Generally, small plates use 2 pins, while larger plates use 3 pins. The advantages are accurate positioning, minimal deformation of the plate’s shape, high precision and good appearance, as well as fast milling speed. Its drawback is that there are various types of holes in the plate, requiring pins of different diameters to be available; if no positioning holes are available in the plate, it is necessary to discuss with the customer the addition of such holes during the initial design phase, which is a rather cumbersome process. Meanwhile, each type of plate requires different milling templates, which makes management complicated and increases costs. External positioning is another positioning method, which involves using positioning holes added outside the plate as the positioning holes for milling the plate. Its advantage is ease of management; if the standards are established in advance, there are generally around fifteen types of milling templates. Due to the use of external positioning, it is not possible to mill the board off in one go; otherwise, the circuit board can be easily damaged. This is especially true for multi-panel boards, as the milling tool and dust collection system may pull the board away, resulting in damage to the circuit board and breakage of the milling tool. With the method of segmented milling to leave joint points, the plate is first milled; once milling is complete, the program pauses and the plate is secured with tape, after which the second part of the program is executed, using a 3mm to 4mm drill bit to drill out the joint points. Its advantages include few templates, low costs, and ease of management; it can mill circuit boards without any mounting holes or positioning holes, making it convenient for staff with limited expertise to handle. In particular, the preparation process carried out by those responsible for CAM work can be simplified, while the utilization rate of the substrate can also be improved. The disadvantages are that, due to the use of drills, the circuit board has at least 2–3 protrusions on its surface, which is unsightly and may not meet customer requirements; moreover, the milling process takes a long time, resulting in higher labor intensity for the workers. Frame and cutting points: The fabrication of the frame is part of the initial stages of circuit board production. Frame design not only affects the uniformity of electroplating but also has an impact on the milling process; a poorly designed frame is prone to deformation, or it may result in small scraps during milling. These scraps can block the dust collection pipes or damage the rapidly rotating milling tools. Deformation of the frame can lead to deformation of the finished circuit boards, especially when positioning them for milling. Additionally, choosing the appropriate cutting points and processing sequence helps to maintain the maximum strength of the frame and enable faster processing. If the choice is poor, the frame is prone to deformation, resulting in the destruction of the printed circuit board. Milling process parameters: A cemented carbide end mill is used to mill the shape of the printed circuit board, with the cutting speed of the end mill typically ranging from 180 to 270 m/min. The calculation formula is as follows (for reference only): S = pdn/1000 (m/min). Where: p: PI (3.1415927); d: diameter of the milling tool, in mm; n ； The spindle speed in r/min; the feed rate that matches the cutting speed is the feed speed itself. If the feed rate is too low, the circuit board material softens or even melts and burns due to frictional heat, blocking the chip clearance of the milling tool and preventing cutting from taking place. If the feed rate is too high, the milling tool wears out quickly, the radial load it has to bear is large, the amount of tool deflection is significant, and the quality of the work is poor with inconsistent dimensions. How can one determine the speed of feeding? The following factors need to be considered: printed circuit board material, thickness, number of sheets per stack, diameter of the cutting tool, and chip removal grooves. It can generally be set based on the technical data provided by the tool supplier; due to differences in the material quality, brand, and manufacturing processes of the tools, the process parameters vary among different manufacturers. Only below the rated load can the speed of the spindle motor be maintained. As the load increases, the rotational speed drops until the milling cutter breaks. The problem of tool breakage during plate milling is usually caused by the following factors: First, the power of the spindle motor is insufficient, and it needs to be repaired or replaced. Second: it is because there are too many sheets per stack, the cutting load is too high, or the milling length exceeds the effective length of the milling tool. III: Milling tool quality issues. IV: Issues with speed and feed rate settings. 5: The clamping force of the drill chuck on the rotating shaft decreases, and the required rotational speed cannot be achieved when under load. 6: Misalignment occurs when the rotating shaft turns, resulting in wobbling. 7: There is a problem with the program design, such as the use of incorrect commands.