Advanced Materials Research Vols. 126-128

Abstract: To evaluate the cutting performance of CVD diamond coated silicon nitride insert, two kinds of CVD diamond films, namely microcrystalline diamond (MCD) and composite diamond films, are deposited on silicon nitride (Si3N4) inserts using the hot filament chemical vapor deposition (HFCVD) method. The characterization of as-deposited diamond films is conducted using the scanning electron microscope (SEM), optical interferometric profiler, X –ray diffraction (XRD) and Raman spectrum. The turning tests for as-fabricated MCD and composite diamond coated insert, as well as uncoated silicon nitride insert, are performed in dry turning aluminum silicon alloy, where the cutting speed, feed rate and depth of cut are fixed as ν = 2000 r/min, f=0.1 mm/r and ap=1 mm. The results demonstrate that the main tool failure is the tool wear. As compared with the uncoated silicon nitride insert, the woking life time of the diamond coated insert can be increased by a factor of above 7.

Abstract: Single-point fly cutting and nanoindentation test of quartz glass were performed using three different cutting tools, namely, a V-shaped cutting tool, a Vickers indenter and a spherical indenter, to investigate the elastic and plastic behaviors of quartz glass in ductile-regime machining. It was found that these behaviors depend on tool shape and that the V-shaped cutting tool is most effective for removing quartz glass material followed by the Vickers indenter and spherical indenter.

Abstract: In this paper, the technology of pre-stressed machining suitable for ceramic materials was presented. Using the cluster method, the discrete element method (DEM) model of SiC ceramic was established to simulate the crack’s initiation and propagation in cutting processes with different pre-stress value. The scratching tests were carried out to confirm the validity of simulation. Both the DEM simulation and the experimental investigation showed that: with the increasing of pre-stress, the number of radial cracks reduced and the transverse cracks replaced the radial cracks to some extent, and also caused the material removal in the form of smaller fragments. Using pre-stressed machining can decrease the machining damage and improve the surface quality, and further prove that using DEM to simulate the machining process of ceramic materials was feasible.

Abstract: This paper describes the cutting characteristics of lithium niobate, which is used for surface acoustic wave type micropumps, regarding the formation of micro grooves by direct cutting. Since lithium niobate is a brittle material with a strong crystal orientation dependency, significant differences were observed in the characteristics of the finished surface according to different directions of cutting. The ductile mode cutting of lithium niobate was found to be feasible with cutting depths of approx. 5 μm or less. Also, results of the study show the feasibility of the formation of minute grooves through the cutting of lithium niobate, using milling with an end mill.

Abstract: This paper describes ultrasonically assisted fly cutting for finishing advanced ceramics for hot-press dies used to fabricate glass lenses. Fly cutting can perform shallow machining, which realizes ductile-mode cutting of hard, brittle materials. Ultrasonically assisted machining can increase the critical cutting depth (i.e., the maximum cutting depth for ductile-mode machining of a surface). The technique proposed in this paper combines both techniques and enables precise finishing of advanced ceramics at a high machining efficiency. Ultrasonic assisted fly cutting was found to reduce tool fracture and improve the finished surface quality compared with conventional fly cutting.

Abstract: Making holes in glass or ceramic with conventional twist drills is difficult because of the hard and brittle properties of the workpieces, but the drilling-grinding process with diamond core-tools has found application in the field due to its high efficiency and low cost. However, small hole drilling-grinding with the core tools is still a challenge because the small core tools have a limited strength and chip-removal capacity. In this paper, the small hole drilling-grinding in glass and ceramic by diamond core-tools with 4mm diameter is experimentally investigated, the drilling-grinding force and heat are measured and calculated, the performances of two types of electroplating diamond core tools are compared.

Abstract: This research investigates machining schemes for dicing soda lime glass in order to reduce the damage in the processes. Ductile machining and brittle machining of glass are first analyzed based on fracture mechanics and then verified by experiments. Experiments with various machining schemes including scribing-then-breaking, direct-dicing and dicing-then-breaking processes for soda lime glass are then conducted. Experimental observations showed the following results. (i) The critical depth of cut (CDOC) for soda lime glass is between 0.4μm and 0.8μm that matches theoretical prediction, 0.78μm, based on fracture analysis. (ii) The scribing-then-breaking machining scheme results in less damage than the regular slicing process. The DOC of scribing, however, must be in the ductile-brittle region to achieve this result. (iii) Defect due to dicing on the back surface is higher than that on the front surface in one-step dicing through process. Dicing defects can be effectively reduced by decreasing the feed rate or increasing the dicing speed.

Abstract: Chemical mechanical polishing has been widely used to achieve global planarization of wafers. In this paper, an improved designed test rig is used to acquire the signals on chemical mechanical polishing. The shear force and temperature-rise are measured during chemical mechanical polishing process. The polishing temperature is measured by T-type thermocouples screwed behind the polishing interface of the carrier. The shear force is measured by a load transducer mounted on the lever and connected with the polishing head. The parameters including down force, rotation speed, particle size and volume flow rate of slurry are investigated. The experimental results provide a good index to end-point-detection. The theoretical simulation by the average lubrication equation coincides with the experimental results. This study contributes to the understanding of chemical mechanical polishing mechanism.

Abstract: It is well known that dishing occurring in chemical mechanical polishing of plug structures leads to considerable wafer surface non-planarity and reduces the current/charge conduction. Thus, a closed-form solution for quantitative prediction of dishing is needed. A contact-mechanics-based approach to describe the steady-state dishing occurring in chemical mechanical polishing of plug structures is presented. The model is then applied to investigate the effect of pattern geometry on dishing in details. It was shown that plug dishing strongly depends on plug size, but minimally on pattern density. In addition, the maximum value of dishing occurs at a critical pattern density for fixed pitch.

Abstract: As a new fixed-abrasive machining method, chemo-mechanical grinding (CMG) is developed from chemical mechanical polishing (CMP), with the obvious advantage of geometric accuracy determinacy and no slurry. To improve material removal rate and enhance the popularity of CMG, this paper introduces a combined grinding method, i.e., two dimensional ultrasonic vibration assisted CMG (2D-UACMG). Si wafer is taken as the workpiece and the influence of ultrasonic vibration modes and process parameters on the surface roughness and the material removal is examined. The results show 2D-UACMG can obtain better surface quality with little surface damage at nanometer level compared with the conventional CMG without the ultrasonic vibration.