Advanced Materials Research Vols. 126-128

Abstract: This study investigates a spiral polishing mechanism in polishing the inner wall of stainless bore with the mixture grinding material of silicon carbide and polystyrene. The delicate polishing process is verified to be more efficient, cost-saving, and environment friendly than traditional processes. Varied sets of polishing parameters, including SiC grain size, SiC weight, polystyrene(PS) weight, viscosity of silicon oil, revolution speed of the driving screw, and machining time, are examined through the Taguchi Methods for optimum polishing effects. Impacts of different combinations of the six polishing parameters on surface roughness and texture are probed into and analyzed in the process of the experiment. The findings suggest that with the increase of time, the fluidity and stickiness of the abrasive medium improve, resulting in a finer polished surface within delicate spiral polishing process. It appears that significant differences are observed through the use of a mixture of 60 grams of SiC (with size of 7 μm) and 70 grams of polystyrene, silicon oil of 1000 mm2/s viscosity under the speed of 3500 rpm screw revolution speed for 30-minute machining time, improving the surface roughness from 0.90 μm to 0.158 μm Ra. The finding thus lends support to the effect of spiral polishing mechanism, which can be further developed.

Abstract: Grinding is a commonly used process in precision machining. This paper is aimed to establish a model for predicting surface roughness and hardness with respect to grinding parameters, including wheel speed, feed rate and depth of grinding for the SKD11 molding steel. The Adaptive Network based Fuzzy Inference (ANFIS) is used to construct the grinding model that is trained by experimental data from grinding the SKD11 steel. Test experiments are then conducted to verify the model. Results from the test experiments showed that the average error between surface roughness predicted by the model and the measured data is 3.94%. The average different of the hardness between the measured data and that predicted by the model is less than 0.06%. It verifies that the model can be used to predict surface roughness and hardness for different grinding parameters.

Abstract: Multi-wire sawing process has been widely used for wafer slicing of silicon substrates for solar cells. Usually there are two different kinds of wire saw in multi-wire sawing process including free abrasive wire sawing with SiC grits and fixed abrasive wire sawing with diamond wire. For free abrasive wire sawing process, the material removal mechanism can be considered as lapping and the fixed abrasive wire sawing can be considered as grinding. This paper is to investigate the characteristics of the surface texture of silicon substrate fabricated by these two wire sawing process. Experimental results have been observed by white light interferometry and SEM. Some different properties of both processes have compared been with variant characteristics including 2-D and 3-D surface roughness parameters. Results of this paper can be further used to evaluate the feasibility of wire sawing process of silicon substrates for solar cells.

Abstract: ‘Trap’ effect of the newly developed semi-fixed abrasive tool (SFAT) plays key role in decreasing the surface damages of advanced ceramics caused by the undesirable large particles emerging in machining area. Influences of characteristics of the large particle, such as size, shape and concentration, on the ‘trap’ effect of SFAT are studied with Particle Flow Code (PFC) simulation and lapping experiments. A normalized normal force is defined to evaluate the ‘trap’ effect in PFC simulation, and surface roughness is taken as an indicator in lapping experiments. The results show that the change of surface roughness is according to the one of normalized normal force. Bigger normalized normal force is better for ‘trap’ effect and surface roughness. ‘Trap’ effect works well when the large particle is in small size, sharp shape, and low concentration. In this study, the followed characteristics of the large particle are good for ‘trap’ effect of SFAT made of 1000# SiC abrasive: size <17µm, corner angle < 60°, and concentration <18 particles per mm2.

Abstract: The selection of the cutter type is of crucial importance to maximise the advantages of mechanical rock excavation systems. Specific energy (SE), cutter forces, and rock properties are used to decide what type of cutter is most suitable for economical excavation of the rock based on laboratory rock cutting tests. This study is concerned with the preliminary results of an ongoing rock cutting program in which a mini-disc has been compared with a point-attack pick in laboratory linear cutting tests simulating a cutterhead on a Helidon sandstone block. Analysis of the preliminary results has shown that the mini-disc experienced lower mean cutting forces and was seven times more efficient than the pick in first layer cuts. However, the mini-disc had mean normal forces 1.5 times higher than the pick. Additionally, first layer cuts taken on the trimmed surfaces required more forces and SE than completely relieved cuts in pick cutting.

Abstract: Wear mechanism on the flank of a cutting tool is caused by friction between newly machined surface and the cutting tool, which plays predominant role in determining tool life. Detailed study on wear mechanism at the cutting edge of carbide tools were carried out at cutting speed of 55 – 95 m/min, feed rate of 0.15 – 0.35 mm/rev and depth of cut of 0.10 – 0.20 mm. The wear on the cutting tools was occurred predominantly on the nose radius, as effect of lower feedrate and nose radius selected. Various wear observed on both coated and uncoated cutting tool such as abrasive wear, adhesive wear, adhering chip on the cutting edge, flaking, chipping, coating delamination of coated tool, crack and fracture. The abrasive wear predominantly occurred on the flank face while the flaking on the rake face. Abrasive wear occurred at nose radius due to the depth of cut selected was low therefore, the contact area between the cutting tool and the workpiece material was small. Adhesion or welded titanium alloy onto the flank and rake faces demonstrated a strong bond at the workpiece-tool interface. The adhesion wear takes place after the coating has worn out or coating delamination has been occurred. The crack occurred possibly due to machining at high cutting speed and high depth of cut. Cutting at high cutting speed caused more heat generated at the cutting edge and at high depth of cut caused more cutting forces on the insert.

Abstract: In the case of turning workpieces having high aspect ratios, i.e. length divided by diameter, it is not so easy to obtain high cylindricity because of the elastic deformations due to the thrust forces taking place under operations. In this paper, the generating mechanism of geometrical errors is discussed and its suppressing method is proposed. That is, applying previously established controlling method of thrust forces to turning cylinders with high aspect ratios, it is confirmed that geometrical errors of workpieces due to the action of thrust forces can be suppressed.

Abstract: In TFT-LCD manufacturing process, the ACF is an essential material. To make the driving circuit conductive, the ACF attach process is used in bonding process. Since the total manufacturing cost becomes lower year by year, the ACF material occupies a great deal of manufacturing cost. The boding technology has been changed from the conventional long bar type into short bar type to save the material usage. The parameter setting of the short bar type machine was not initially optimized. The NG rate of short bar type ACF attach process is higher as compared to the long bar type. The rework cost and material cost may increase in the short bar type process. Therefore, the parameter optimization for the associated short bar type ACF attach process becomes an essential problem. The response surface method is adopted to model the problem. The yield rate is selected as objective function for study. In the analysis of response surface method, the plasma clean speed, ACF peeling speed and ACF cutter spring setting are selected three key factors for discussion. Results reveal that the yield rate can be improved up to 99.35%, which is very helpful to improve the manufacturing process.

Abstract: To obtain some knowledge to predict the tool life caused by breakage, a series of slotting experiments was performed at various feed rates for high carbon steel by using coated carbide square end mills of 0.5mm in diameter. The main results obtained are as follows, (1) There found a possibility to obtain an optimum feed rate for the maximum slotting distance. (2) Lower feed rate caused chatter but higher feed rate rarely caused chatter. (3) A newly defined cumulative damage seems to be useful in some extent to predict tool life by monitoring cutting force.

Abstract: The chemical vapor deposition (CVD) diamond and diamond-like carbon (DLC) films are deposited on the cobalt cemented tungsten carbide (WC-Co) cutting tools respectively using the hot filament chemical vapor deposition (HFCVD) technique and the vacuum arc discharge with a graphite cathode. The scanning electron microscope (SEM), optical interferometer profiler and Raman spectroscopy were adopted to characterize the as-deposited diamond and DLC films. The cutting performance of as-fabricated CVD diamond and DLC coated milling tools is evaluated in dry milling SiC particulate reinforced Al-metal matrix composite material (Al/SiC-MMCs), comparing with the uncoated WC-Co milling tool. The milling results demonstrate that the uncoated WC-Co milling tool suffers severest wear in its circumferential cutting edge, while the wear of DLC coated milling tool is slightly lower. Comparatively, the CVD diamond coated milling tool exhibits much stronger wear resistance. The wear on its circumferential cutting edge is less than 0.07 mm at the end of milling test, only a half of that of DLC coated milling tool. This result is attributed to the extremely high hardness and strong adhesive strength of CVD diamond film covered on the WC-Co milling tool.