Printed Circuit Board High-speed NC Drilling Machine And Research On Dynamic Characteristic

Printed circuit board (PCB) are widely applied in many areas such as information, communication, photoelectricity, consumer products, automotive, aerospace, military, precision instrument and industrial products. At present, the PCB with multi-layer, thin wide spacing, small hole and special function are rapidly developed. The number of PCB micro-holes with diameter of less than 0.3mm increased dramatically, which was made by high-speed NC drilling machines. The overall level of NC drilling machine for PCB still has a big gap with foreign developed countries. Whereas the manufacturing standards plays an important role in the drill’s fracture and processing quality. The processing quality is also closely related to the vibration of workpiece system, and drilling system and the processing chatter. The drill’s structure parameters and overhang are very important for improving the stiffness of the drill, optimizing the drilling parameters and improving the characteristics of vibration drilling process. The above aspects are all the problems and to be solved urgently.Based on the detailed investigation to the high-speed NC drilling machines for PCB, this paper studys the design principles to the drilling machine and puts forward the main consideration factors, layout plan and design scheme when making the general layout of PCB. The whole structure and all the parameters of the drilling machine are determined. Moreover, it gives the whole design process of the drilling machine. Through unremitting efforts, we have produced a high-speed NC drilling machine for PCB with spindle speed 250KRPM. The drilling force can be tested. The spindle can be changed quickly. Then we do some debugging for spindle, movement body, automatic tool changer, detection, system and control PC, analysis and test the drilling machine by laser interferometer, dynamic test device, optical measuring holes device and so on.This paper studys the NC machine’s vibration characteristics’ relationships to the hole position accuracy and drilling parameters, these provide basis and method of the machining process optimization, drilling machine design and improving the stability of drilling machine. Using modeling design and finite element theory technology, the paper set the micro-drill’s solid model and finite element model. Using model analysis method, this paper computes the micro-drill’s natural vibration frequency under different overhang and different structural parameters, the optimized drill structure is given. The conclusions are as follows:(1)While designing the high-speed printed circuit board NC drilling machine, the machine must have high precision, high speed, high rigidity and high reliability. The general layout of the PCB drilling machine must consider its movement, the size and shape of the PCB and the convenience of processing operations, adjustment and maintenance. Another factors must be considered such as small volume and manufacturing cost. The moving set beam gantry structure for NC’s workbench can improve the dynamic performance of the drilling machine.(2)The contents for design of the PCB high-speed NC drilling machine mainly include overall structure, spindle system, feeding system, NC system, shields and overall appearance, safe protection, pneumatic drive system, as well as other important parts as insert, cutting tool, tool mearuring system, etc. Some performance comparison were completed within relevant product.(3) To the printed circuit board high-speed NC drilling machine we have made a series of tests including the geometry precision test, position accuracy and reiteration precision test, dynamic performance test and actual drilling hole position accuracy test. The developed equipment can achieve the desired index and requirements.(4) The research of micro-drill’s vibration characteristics to Hitachi triaxial and six axials drilling machine at the diameter of 0.1mm to 0.5mm demonstrate that, the Z-vibration presents variability as the change of drilling parameters. With different drilling parameters, the rules of micro-drill’s vibration in different diameters to drilling parameters are different. For different drilling equipment, the rule of micro-drill’s vibration in same diameters to drilling parameters are also different. According to different machines and drill diameter and the corresponding variation rule of vibration, we choose the appropriate drill and processing parameters.(5) Using Pro/E design software we get a drill solid model approximate to the actual model. Through rational simplification such as ignoring the small size characteristics as chamfering, using free grids strategy, choosing suitable unit types and precision, finally we get the micro-drill’s finite element model in different structures.(6) Micro-drill’s overhang, length of transition and thickness can assure the drill’s some properties, as the number of vibration of strong mode is less or under a small range the vibration happens, only within a certain range. The micro-drill’s vibration characteristics is well when the diameter is 0.1 mm, the length of transition chooses 4mm or 6mm and the thickness takes 0.04 mm.