Papers by Author: Yong Wei Zhu

Abstract: The self-conditioning of hydrophilic fixed abrasive lapping based on the principle of two-body (pad-wafer) abrasion has great importance on the MRR (material removal rate) of wafer. The physical and mechanical properties of pad were taken as set of available alternatives. Fuzzy comprehensive evaluation principle was applied to establish a model for the self-conditioning of FAP. The swelling ratio, the slurry abrasive ratio and pendulum hardness were selected to be the set of alternatives for self-conditioning evaluations in this paper .The five types of matrix formations of fixed-abrasive pad were prepared, and the matrix were ranked in order of comprehensive evaluation index. The results show that the fuzzy evaluation is rational. The tests of MRR verified the self-conditioning of FAP. The machining of pad can be evaluated in advance of lapping processes. Moreover, the self-conditioning evaluation will be important reference for determination of FAP during choosing the matrix formations.

Abstract: The choice of abrasive particle size is crucial to improve the lapping efficiency and surface quality in lapping of sapphire wafer by fixed abrasive (FA) pad. A model for the penetration depth of a single abrasive is developed with fixed abrasive pad. A serious of lapping tests were carried out using FA pads embedded with different size of diamond particles to verify the validity of the developed model. Results show that the penetration depth of abrasive is related not only to the particle size, but to the hardness ratio of the work-piece to the pad as well. The material removal rate of sapphire is proportional to the square of abrasive particle size, while the average surface roughness is proportional to the abrasive particle size.

Abstract: The processing technology of sapphire with a high material removal rate a good surface quality is critical for its applications. The experiment of sapphire lapping and polishing was carried out by using three different fixed abrasive pad (FAP). Their material removal rate (MRR) and surface roughness (Ra) were measured and analyzed. Results indicate that a MRR of 5.6μm/min reaches in rough lapping and a MRR of 0.4μm/min in fine lapping. The average surface roughness Ra of rough lapping and fine lapping is 142nm and 1.2nm respectively. The processing efficiency of sapphire wafer is effectively improved and a good surface quality is obtained when FAP adopted.

Abstract: Fixed-abrasive lapping (FAL) is a new machining technology and is adopted to manufacture hard brittle materials to obtain the high surface quality. In the same machining condition, K9 glasses are lapped by abrasives and fixed-abrasive, respectively. Two grain sizes of diamond abrasives are adopted in every lapping means. Differential chemical etch method (DCEM) is employed to measure the depth of subsurface damage (SSD) of different lapping means. Surface damages are compared by Microscope. The results show that the depth of SSD is 53 and 15.2μm after abrasives lapping (AL) by 40 and 28μm diamond abrasives. FAL with 40 and 28μm diamond abrasive leads to 4.5 and 3.4μm subsurface damage depth, respectively. FAL can get smaller surface damage and shallower depth of SSD than AL. And FAL can obtain the higher surface quality than AL.

Abstract: Differential chemical etch method (DCEM) was employed to study the effect on the surface/subsurface damage depth of K9 glass lapped by different particle sizes of fixed diamond abrasives. The advantage of DCEM is that both the lapped and substrate samples are placed in the chemical etch at the same time to decrease or eliminate the effect of etching condition variation. K9 glasses are firstly fixed-abrasive lapped with 40, 28, 14 and 10μm diamond abrasives, respectively. Surface damages of K9 glass after FAL are measured by Microscopy. The results show that the corresponding subsurface damage (SSD) depths of K9 glass are 4.5, 3.4, 2.8 and 1.6μm when the fixed diamond abrasive particle size are 40, 28, 14 and 10μm.With the decreasing of diamond particle size, the SSD depth decreases obviously and surface quality of K9 glass is improved significantly.

Abstract: This paper presents a model for the determination of optimal cutting parameters in the milling of Titanium alloys based on real manufacturing data collected from cutting tests. The objective of the optimal function is to achieve the lowest overall costs. Design of Experiment and Taguchi methods are applied in the design of cutting tests. Optimal cutting parameters such as cutting speed, feed, depths of cut are obtained by solving the economic model which is developed according to workshop-specific data.

Abstract: Chatter is a complex phenomenon characterized by unstable, chaotic motions of the tool and by strong anomalous fluctuations of cutting forces. The situation becomes more serious in the milling of titanium alloys because of their low Young modulus and extended elastic behaviour. This paper presents an online chatter detection system based on the analysis of cutting forces, which is one of the integrated modules of a multi-sensor chatter detection system consisting acoustic and acceleration sensors. The cutting force is transformed into frequency domain by applying Fast Fourier Transform (FFT). Chatter frequency is identified in the frequency domain by comparing its power spectrum with predefined threshold. Experiments were carried out to validate the mythology.

Abstract: The polishing pad plays a significant role in the Chemical Mechanical Polishing (CMP) process and its wear influences the surface accuracy of the polished wafer. A new polishing pad wear model is introduced and the law of pad wear along the pad radius is discussed, thus a new FAP with optimized pattern is designed and prepared in order. The flatness of the wafer lapped with a uniform pattern pad and that with an optimized pattern was compared. Results show that the PV value of the latter is lower that of the former.

Abstract: The polishing pad’s wear influences the surface accuracy of the polished wafer. A new polishing pad wear model is established using the idea of Finite Element Analysis (FEA) and the effect of polishing parameters on the wear of polishing pad is discussed.

Abstract: The anisotropy of LBO crystal leads to the different properties of different crystal faces, such as thermal expansion coefficient, which results in trouble of ultra-precision machining. Chemical mechanical polishing of a face (001), b face (010) and c face (001) of LBO crystal by adopting Logitech PM5 Precision Lapping & Polishing Machine in the same process conditions was investigated. The effect of anisotropy on MRR and surface roughness was studied. In the same CMP process conditions, c face of LBO crystal is the highest MRR, b face is inferior to and a face is the lowest. And surface roughness of c face is the best, b face is followed and a face is the worst. The results also show that the anisotropy leads to the different MRR and surface roughness on different crystal faces. In CMP of LBO crystal, the higher MRR is, and the better surface roughness is in the scope of experiment.