The milling technology of the circuit board CNC milling machine includes the selection of the cutting direction, compensation method, positioning method, frame structure, and cutting point. It is an important aspect to ensure the accuracy of milling.
Direction Of Cutting And Compensation Method
When the milling cutter cuts into the plate, one of the cut surfaces always faces the cutting edge of the milling cutter, and the other side always faces the cutting edge of the milling cutter. In the former, the processed surface is smooth and the dimensional accuracy is high. The spindle always rotates clockwise. Therefore, whether it is a spindle-fixed table movement or a CNC milling machine with a fixed spindle movement, counterclockwise cutting is used when milling the outer contour of the printed board. This is commonly referred to as reverse milling. While milling the frame or groove inside the circuit board, the down milling method is used. Milling plate compensation is that the machine tool automatically follows the set value when milling the plate, allowing the milling cutter to automatically offset the center of the milling line by half of the diameter of the milling cutter, that is, the radius distance, so that the shape and program of the milling are set. be consistent. 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 to use the program. If the compensation command is used incorrectly, the shape of the circuit board will be more or less than the length and width of the milling cutter diameter.
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 craftsmen. Generally, the positioning plan should be determined during the pre-production of the circuit board.
Internal positioning is a common method. The so-called internal positioning is to select the mounting holes in the printed board, insertion holes or other non-metallized holes as positioning holes. The relative position of the holes strives to be on the diagonal and to select as large a hole as possible. Metallized holes cannot be used. The difference in the thickness of the coating in the hole will affect the consistency of the positioning hole you choose. At the same time, it is easy to damage the plating layer in the hole and the surface edge of the hole when taking the board. Under the condition of ensuring the positioning of the printed board, the fewer the number of pins The better. Generally, the small plate uses 2 pins, and the large plate uses 3 pins. Its advantages are accurate positioning, small deformation of the plate shape, high accuracy and good shape, and fast milling speed. The disadvantages are that the various hole types in the board need to prepare pins of various diameters. If there is no positioning hole available in the board, it is more cumbersome to discuss with the customer to add the positioning hole in the board during the pre-production. At the same time, the different management of the milling plate template of each plate 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 board as the positioning hole of the milling board. The advantage is that it is easy to manage. If the pre-production specifications are good, the milling template is generally about fifteen kinds. Due to the use of external positioning, the board cannot be milled down at one time, otherwise the circuit board is very easy to damage, especially the puzzle, because the milling cutter and the dust suction device will bring the board out, causing the circuit board to be damaged and the milling cutter broken. In the method of segmented milling to keep the joint, the board is first milled. After the milling is completed, the program is suspended and then the board is fixed with tape. The second stage of the program is executed, and the joint is drilled using a 3mm to 4mm drill bit. The advantage is that the template has less cost and is easy to manage. It can mill all the circuit boards without mounting holes and positioning holes in the board. It is convenient for small craftsmen to manage, especially the production of pre-production personnel such as CAM can be simplified, and the substrate can be optimized Utilization rate. The disadvantage is that due to the use of a drill, there are at least 2-3 raised points on the circuit board shape, which may not meet the customer’s requirements, the milling time is long, and the labor intensity of the worker is slightly greater.
, Frame and cutting point:
The production of the frame belongs to the pre-production of the circuit board. The frame design not only affects the uniformity of the plating, but also affects the milling board. If the design is not good, the frame is easily deformed or some small pieces are generated during milling. Small waste block, the generated waste block will block the suction pipe or break the milling cutter rotating at high speed. The deformation of the frame will cause the deformation of the finished plate especially when positioning the milling plate externally. In addition, the choice of the cutting point and the machining sequence is good, which can make the frame Keep the maximum intensity and the fastest speed. The selection is not good, the frame is easily deformed and the printed board is scrapped.
Milling Process Parameters
The shape of the printed board is milled with a carbide milling cutter, and the cutting speed of the milling cutter is generally 180-270m / min. The calculation formula is as follows (for reference only): imported pump valve
S = pdn / 1000 (m / min)
In the formula: p: PI (3.1415927)
d: diameter of milling cutter, mm
n; cutter speed, r / min
The feed speed is matched with the cutting speed. If the feed rate is too low, the printed board material is softened or even melted or scorched due to frictional heat, blocking the chip flute of the milling cutter, and the cutting cannot be performed. If the feed is too fast, the milling cutter wears fast, the radial load is large, the amount of the cutter is large, the working quality is poor, and the size is inconsistent. How to judge the speed of feed? The following items should be considered: printed board material, thickness, number of blocks per stack, iron knife diameter, chip flute. Generally, it can be set according to the technical information provided by the tool supplier. Due to the difference in the material quality brand and manufacturing process of the tool, the tool process parameters of different manufacturers are different. Only below the rated load, the speed of the spindle motor can be maintained. The load increases and the speed decreases until the cutter breaks.
The problem of broken knife when milling the board is generally caused by these kinds of situations:
- The power of the spindle motor is insufficient and needs to be replaced.
- The number of plates per stack is too large, the cutting load is too large or the milling length exceeds the effective length of the milling cutter.
- The quality of the milling cutter.
- Rotation speed and feed speed setting problem.
- The clamping force of the drill chuck of the rotating shaft drops, and the required speed cannot be reached when the load is eaten.
- There is a problem with concentricity when the shaft rotates, and it will jump.
- There is a problem with the design of the program, such as using the wrong command.