Studies in the punching of polyester glass laminates

Pritchard, R.H. (1978) Studies in the punching of polyester glass laminates. (MPhil thesis), Kingston Polytechnic, .


A considerable volume of electrical and electronic printed circuit boards are manufactured, by the punching process, from paper based and glass fibre re-inforced laminates. The effects, of the constituent elements of GFR laminate, upon the punching characteristics of the board were studied by means of a specially designed press dynamometer located within a standard press-tool die set used on a mechanical crank press. Both hot and cold punching techniques were developed initially by the use of commercially supplied samples of both paper and GFR laminates. Laboratory manufactured polyester laminates were produced with different resins, filler sizes and forms of glass fibre re-inforcement. These experimental boards were punched and analysed in respect to specific punching criteria and laminate punched quality. The punch quality (PQ) was assessed by a quanti tative technique using a magnified image of the punched contour and a graticule; the punch contour used was of a special design to incorporate the PQ requirements and provide the extreme crack propagation geometry. The surface density of the glass fibre re-inforcement was found to' be a primary factor influencing the main punch load and shear energy criteria used. The ladder stripping load required to remove the ladder from the punch was also investigated by means of a strain-gauged stripper-pad, and showed an important sensitivity to punching temperature, which could be utilized in industry when ladder stripping is a problem. Additional to the main programme of work already outlined above, a series of test punchings were also made at different punch velocities on three other sets of equipment, one of which was an Instron testing machine using a punch and die accessory conforming to BS.2782 requirements for shear testing of plastic sheet etc. From this basic Instron shear load information a simple mathematical model was developed to quantify the relative shear energy functions of the different punching equipments used; for the crank press die-set the specific shear energy (SSE) absorbed was found to be considerably higher than for the remainder of the test rigs used, thus some consideration was given to this result. One factor influencing this result was found to be related to the punch/die clearance deduced from the re-plotted -punch data. Some suggestions for future punching research work have been made, particularly in respect to die-set punching energy and small hole production which could be of great significance to industrial PCB manufacturers.

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