CNC Milling Technology

The milling technology of the circuit board CNC milling machine includes selecting the direction of the cutting tool, the compensation method, the positioning method, the structure of the frame, and the lower knife point. All are important aspects to ensure the accuracy of milling.

First, go knife direction, compensation method:

When the milling cutter cuts into the plate, one of the cut surfaces always faces the cutting edge of the milling cutter, while the other side always opposes the cutting edge of the milling cutter. In the former, the surface to be processed is smooth and the dimensional accuracy is high. The spindle always rotates clockwise. Therefore, whether it is a CNC milling machine with a fixed spindle movement or a fixed spindle movement of the table, counterclockwise cutting is used when milling the outer contour of the panel. This is what is commonly referred to as milling. The milling method is used to mill the frame or groove inside the circuit board. The compensation of the milling plate is the automatic setting of the machine when the panel is milled. The milling cutter automatically sets half the diameter of the milling cutter with the center offset of the milling line, that is, the radius distance, so that the milling shape and program setting be consistent. At the same time, if the machine tool has a compensation function, it must 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 the size of the length and width of the cutter diameter.

Second, the positioning method and the next tool 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 developers. Generally, the positioning plan should be determined during the pre-production of circuit boards.

Internal positioning is a common method. The so-called internal positioning is to select mounting holes, insertion holes or other non-metallized holes in the printed board as positioning holes. The relative position of the holes strives to be on the diagonal and to pick as large diameter holes as possible. Metallized holes cannot be used. Because the difference in plating thickness in the hole will affect the consistency of the positioning holes you have chosen, it is easy to cause damage to the plating in the hole and the edge of the hole when the board is removed. The smaller the number of pins is under the condition of ensuring the positioning of the printed board. The better. Generally, the small plate uses two pins, and the large plate uses three pins. The advantages are accurate positioning, small plate deformation, high accuracy, good shape, and high milling speed. The disadvantages of the various types of aperture in the board need to prepare a variety of diameter pins, such as the board has no available positioning holes, in the pre-production need to discuss with the customer to add positioning holes in the board, more cumbersome. At the same time, the management of the milling template of each plate is more troublesome and the cost is higher.

External positioning is another positioning method that uses positioning holes on the outside of the board as positioning holes for the board. The advantage is that it is easy to manage. If the pre-production specifications are good, there are generally about 15 types of paneling templates. Due to the use of external positioning, it is not possible to cut the board one at a time, otherwise the circuit board is very easy to damage, especially the puzzle, because the milling cutter and the dust collection device will cause the circuit board to be damaged and the cutter broken due to taking out the board. The method of using segmental milling to leave the joints is used. After the milling board is finished, the program pauses and then the board is fixed with tape. In the second stage of the program, the drill joint is drilled with a 3 to 4 mm drill bit. The advantages are that the template is less costly and easier to manage. It can mill all circuit boards without mounting holes and positioning holes in the board. The management of the small craftsman is convenient. In particular, the production of advanced production personnel such as CAM can be simplified, and the substrate can be optimized at the same time. The utilization rate. The disadvantage is that due to the use of drills, the shape of the circuit board leaves at least 2-3 protruding points unattractive, may not meet customer requirements, milling time is long, and the labor intensity of workers is slightly larger.

Third, the framework and the next knife:

The production of the frame belongs to the manufacture of circuit boards. The design of the frame not only affects the uniformity of electroplating, but also affects the milling. If the design is not good, the frame may be easily deformed or some small blocks may be generated when the plate is assembled. Small waste blocks, resulting in waste blocks will block the vacuum tube or high speed rotating milling cutter, deformation of the frame, especially when the external positioning of the plate caused by the deformation of the finished board, in addition to the lower point and the processing sequence selection of good, can make the frame Keep the fastest strength at the fastest speed. The selection is not good, the frame is easily deformed and the printed board is scrapped.

Fourth, the milling process parameters:

Carbide milling cutters are used to mill the board shape. The cutting speed of the cutters is generally 180-270m/min. The formula is as follows (for reference only): Import pump valve

S=pdn/1000(m/min)

Where: p:PI (3.1415927)

d: cutter diameter, mm

n; milling cutter speed, r/min

Matching the cutting speed is the feed rate. If the feed rate is too low, the printed board material softens or even melts or scorches due to the frictional heat, blocking the flutes of the milling cutter and cutting off. If the feed is too fast, the milling cutter wears fast and the radial load is large, so that the large amount of the cutter, the work quality is poor, and the dimensions are inconsistent. How to determine the speed of feed? Consider the following: printed board material, thickness, number of stacked blocks, diameter of the iron knife, chip flutes. Generally, according to the technical data provided by the tool supplier, the tool process parameters of different manufacturers are different due to the difference between the material quality brand of the tool and the manufacturing process. Only under rated load, spindle motor speed can be maintained. The load increases and the speed drops until the cutter breaks.

The problem of broken knife when cutting board is generally caused by these kinds of situations: First, it is the power of the spindle motor that is in need of repair and replacement. Two: There are too many piles per stack, the cutting load is too large or the milling length exceeds the effective length of the milling cutter. Three: cutter quality problems. Four: speed and feed speed settings. Five: The clamping force of the drill chuck of the shaft is reduced, and the required rotation speed cannot be achieved when the load is consumed. Six: There is a problem with concentricity when the shaft rotates. Seven: There are problems with the design of the program, such as the use of wrong commands.