Research On Micro Forming Technology Of Metallic Glass And Its Application In Injection Molding

In the injection molding process of micro/nano devices,there are some shortcomings,such as insufficient mold precision and short service life.As the lack of mechanical properties of traditional mold materials,and the complexity of micro structure processing technology.It leads to the problems of high cost and low yield in the processing of micro/nano structures.In addition,the low impact resistance of the micro structure,which reduces the service life of the mold,there are still great challenges in injection molding micro/nano devices.Metallic glass shows the characteristics of increasing fluidity and decreasing viscosity with the increase of temperature in the supercooled liquid region,which makes it simpler to form micro/nano structures and has a unique processing method,such as hot embossing process which can easily process nanoscale structures,and it does not have defects such as crystal lattice,grain boundary,dislocation and so on.It shows more excellent impact resistance and other mechanical properties than traditional alloy,which just solves the shortcomings of traditional injection molding technology.However,the metallic glass is prone to oxidation and crystallization in the process of preparing structure,which leads to the sharp decline in processing accuracy and performance.In order to solve these problems,we have carried out the following three different ways of microstructure forming of metallic glass:(1)Wire electrical discharge machining-low speed(WEDM-LS).Compared with the traditional EDM,this method has higher precision and smaller machining size.The machining process was always carried out in oil,which effectively avoided the oxidation and crystallization phenomenon during machining.The micro structure was formed through the pulse discharge between the copper wire electrode and the metallic glass surface.Under the observation of scanning electron microscope(SEM),micro grooves less than 150 μm wide have been successfully machined on the surface of metallic glass.(2)A controllable millisecond resistance heating forming method.The metallic glass and mold were placed in two electrode plates.By applying voltage at the upper and lower levels,the metallic glass has quickly reached the supercooled liquid region,and squeezed the metallic glass into the mold under the effect of pressure.This method shaped the metallic glass within 270 milliseconds.The results of scanning electron microscopy showed that the size of the sample from macro to micro has a good replication ability and this method minimizes the crystallization time,so as to avoid the crystallization of metallic glass.After forming,the mechanical properties of the sample were consistent with those of the metallic glass in the casting state.(3)Hot embossing.This method was to place the metallic glass in the cavity of high vacuum,raised the temperature of the metallic glass to the supercooled liquid region through the heating device,and finally pressed the metallic glass into the mold under the effect of pressure,so as to form the metallic glass with micro/nano structure.The heating time of this kind of technology was relatively slow,but the smaller structure and the brighter surface obtained.All of the above three methods have effectively avoided the oxidation and crystallization of metallic glass,and successfully formed the microstructure.Then,the micro injection molding experiment was carried out by using the metallic glass with micro structure after the WEDM-LS as the injection mold.Under the observation of SEM,in addition to the effect of plastic shrinkage during the whole injection molding process,plastic products have well copied the structure of the metallic glass mold.Then the service life of the metallic glass mold was analyzed,this material still maintained the microstructure of the metallic glass surface after 10000 cycles,and its service life was up to 7 years under the working environment of520 K.All in all,the use of resistance welding,hot embossing and WEDM-LS speed to process the metallic glass microstructure will greatly improve the application of metallic glass in industry.At the same time,the use of metallic glass mold with micro/nano structure in injection molding technology will also bring a qualitative leap to the production of plastic micro/nano devices.