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| The Analysis and Comparison of the PCB Contour-milling Mode | | | 1. Purpose of Contour Milling
Generally speaking, there are two aims:
1.1 Separate the circuit board out of copper -clad board
1.2 The circuit board has special shape design, which request the finished product should be consistent with the drawing.
2. Form of Contour Milling
There are three main contour milling forms
2.1 Outer frame, request milling cutter outward migration
2.2 Inner frame, request milling cutter inward migration
2.3 Internal lines, line width should be considered. If line width is more than graver diameter, algorithm is as inner frame. If line width is less or equal to graver diameter, algorithm is as inner frame.
3. The Main Technical Difficulties of Contour Milling
As follows are the main technical difficulties, according to the different forms of contour milling.
3.1 Judgment of contour milling form
At first you should judge the outer frame, inner frame and internal lines from KEEPOUT lines. Then using different treatment methods according with different forms .That is the necessary precondition.
3.2 The influence of milling cutter's diameter
The milling cutter has its special width , if you ignore it, then the size of the finished product will be smaller than drawing requirement
A. Outer frame, request milling cutter outward migration
B. Inner frame, request milling cutter inward migration
C. Internal lines. The perfect practice is to dig out a inner frame according to the line width .But it becomes difficulty when the line width is smaller than the graver diameter. And sometimes many manufacturers begin cut form KEEPOUT center.
3.3 Contour milling need begin at inner stop at outer
General circuit board be fixed by double sided tape or locating pins.It can be moved when you cut the outer frame ,but then if you cut inner frame later ,the precision can not be promised and even cause tool injury.
Conventional cutting method is from internal lines first then inner frame, outer frame at last. But in practical applications, the order of internal lines and inner frame is not so important.
4. Contour Milling Mode
There are three familiar contour milling modes
4.1 Rectangle contour milling
Cut the circuit board according to the rectangle just by reading its size.
This mode has low technical difficulty, but can’t make special-shaped plate.
4.2 Center contour milling
Completely cut form keepout center. It can get to ideal effect through users' calculation and modification of the keepout layer. But this method suitable for the circuit board which is not digging out inside, because this method can't get the order that begin at inner stop at outer.
4.3 Intelligent contour milling
It can get to ideal effect in accordance with the circuit board requestion completely, but it can implementation hardly for the high difficulty of technology and complex algorithm.
5. Other factors
5.1 The contour milling depth, resistance and adhesive force are different because of different plate materials. Carving rate can be adjusted according to the different situation. If the rate is too fast, the graver will be broken easily.
5.2 At some special situation, contour milling step by step can be considered for reducing milling cutter’s burden. For example, when at the microwave control , you can split 3 times to complete and cut 3mm each time to make a 8mm thick board.
5.3 Once you find the circuit board isn’t firm fixation ,and appears these situations such as sloshing, dithering and easily broken of graver, you need stop contour milling immediately.
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