Nc drilling machine, milling process
PCB nc milling machine milling technology including the choice of feeding direction, compensation method, positioning method and frame structure, the cutting point. Are all important aspects of guarantee milling machining accuracy.
Feeding direction, compensation methods:
When the milling cutter cut sheet, is there a cutting face always with the cutting edge of milling cutter, and the other side is always against the cutting edges of the milling cutter. The former, the size of the processed surface is bright and clean, high precision. The spindle is always clockwise rotation. So whether the spindle fixed worktable movement or workbench fixed spindle of CNC milling machine, when the external contour milling printed circuit board, feeding the counterclockwise. This is called inverse milling. And within the circuit board and down milling in slot milling box. Milling board compensation is in milling plate machine automatically according to set value for automatic milling cutter in milling lines set by the center of the migration of the milling cutter of the diameter of the half, the radius distance, make the milling shape consistent with the procedures set. At the same time, such as machine tool compensation function must pay attention to the direction of the compensation and the use of program command, such as using the error compensation command will make the circuit board shape more or less equivalent to the size of the milling cutter diameter, length and width.
Positioning method and the cutting point:
Locating methods can be divided into two; One is in positioning, the other is outside. Positioning for the process to formulate personnel is also very important, generally in the circuit board positioning scheme should be determined when the pre-production.
Location is within the general method. In the so-called positioning is to choose the PCB mounting holes, call waiting bore holes or other nonmetallic mineralization as positioning. The relative position of holes to on the diagonal and choose the large diameter hole as much as possible. Cannot use hole metallization. Because hole plating thickness difference will affect you selected a consistency of hole, at the same time take when the plate is easy to cause hole and the hole on the edge of the surface coating damage, under the condition of ensure the PCB positioning, pin number the less the better. General small plate use 2 pin, large plate use 3 pin, its advantage is accurate, the board shape deformation good appearance, high precision milling speed. Its shortcomings within plate, various types of aperture are documented the diameter of the pin, if you can't available within plate positioning hole, in the early production need to discuss with the customer and locating hole is on the plate and more cumbersome. At the same time, each plate milling plate template different management more trouble, cost is higher.
Location is another location method, is used on the outside of the board and locating holes as milling plate positioning hole. Its advantage is easy to manage, if early production specification, general milling plate template at about 15 kinds. Due to outside positioning so you can't use a plate milling, otherwise the circuit board is very easy to damage, especially the makeup, because of milling cutter and the board will be out of the dust collection device damage of circuit board and the cutter broken. And adopt the method of section milling leave combining site, when milling milling plate after plate pause then board with adhesive tape, the executor of the second paragraph, use 3 mm to 4 mm drill bit will point to drill out. Its advantage is the template cost little less easy to govern, but within all plate milling circuit board without mounting holes and positioning hole, small technology personnel management convenient, especially in the production of CAM and other early production personnel can be simplified, and the utilization rate of substrate can be optimized. Defect is due to the use of drill bit, circuit board shape with at least two or three convex point not beautiful, may not conform to the requirements of the customers, milling time is long, little older workers labor intensity.
Under the framework and knife point:
Frame production belongs to the circuit board with the first production, the frame design not only have an effect on uniformity of electroplating, at the same time also has an effect of milling plate, such as bad design framework is easy to deformation or part during milling plate on a small piece of small pieces of waste produced by waste may clog vacuum tube or touch off high speed rotating cutter, frame deformation especially when foreign positioning milling plate caused the finished plate deformation, in addition the knife point selection and processing order is good, can keep the framework's biggest strength the fastest speed. Framework of choice is not good, easy to deformation and make the PCB scrap.
Milling process parameters:
Using hard alloy cutter milling PCB shape, cutter cutting speed is generally 180 ~ 270 m/min. Computation formula is as follows (for reference only) :
S = PDN / 1000 (m/min)
Type: p: PI (3.1415927)
D: milling cutter diameter, mm
N;The milling speed, r/min
Match the cutting speed is the feeding speed. If the feed speed is too low, due to the friction heat to soften the PCB material even melting or burning, jam the chip groove of milling cutter, cutting can't. If you feed fast, quick wear of cutter, bear radial load is big, big knife and poor quality of work, the size is not consistent. How to determine the feed speed? To consider the following the items: PCB material, thickness, each pile of blocks, iron dao, chip removal tank diameter. General technical data set according to the cutting tool suppliers, due to the cutting tool material quality brands and manufacturing process, the difference between different vendors tool parameters have distinction.
Only under the rated load, the speed of the spindle motor to maintain. Load increases, the speed down, until the cutter broken. Generated when cutting knife plate milling generally have these leads to the result: a: is the spindle motor power is not enough, need repair replacement. 2: is each pack number too much, cutting load is too big or milling length more than the effective length of the milling cutter. Three: milling quality problems. 4: speed and feed speed setting problem. Five: rotation of drill chuck clamping force drops, eat loads are not up to the required speed. Six: shaft rotates concentricity have problems. Seven: the design of the program has a problem, such as using the wrong command.
