Yong Wei Zhu

Fixed Abrasive Lapping and Polishing of Hard Brittle Materials

Fixed abrasive lapping and polishing (FALP) is a new machining technology and was adopted to manufacture hard brittle materials and obtain the high productivity because of fixed abrasive. The preparation process of fixed abrasive pad (FAP) was described. FALP of K9 glass, mobile panel glass and Si were investigated with fixed 5-10 µm diamond abrasives. The effect on material removal rate (MRR) and surface quality of different materials was studied. The results show that in the same FALP process conditions, Si is the highest MRR and reaches 4428 nm/min, mobile panel glass is inferior to and K9 glass is the lowest. And surface quality of mobile panel glass that surface roughness Sa is 2.10 nm and little and less damages is the best, Si is followed and K9 glass is the worst. So FALP can obtain the higher MRR and reaches several micrometers per minute and the better quality that surface roughness Sa can reach nanometer level for different materials.

Chatter Detection in High Speed Machining of Titanium Alloys

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.

Research on Subsurface Damage After Abrasives and Fixed-Abrasive Lapping of K9 Glass

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.

The development of an economic model for the milling of Titanium alloys

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.

Study on Subsurface Damage after Fixed-Abrasive Lapping with Different Particle Size

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.

Preparation and Evaluation of Hydrophilic Fixed Abrasive Pad

The swelling ratio and the pencil hardness of pad were introduced to evaluate the properties of hydrophilic fixed abrasive (FA) pad. The effect of pad composition on its swelling ratio and pencil hardness was studied. Results show that the swelling ratio increases with the rise of content of Trimethylopropane Triacrylate (TMPTA) and Urethane Acrylate (PUA) and the pad gets harder while there is more TMPTA and less PUA. Results also show that a low swelling ratio corresponds to a high material removal rate (MRR), and a low wet pencil hardness to a low surface roughness in each group.

Modeling of Polishing Pad Wear in Chemical Mechanical Polishing

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.

Effect of Anisotropy on Chemical Mechanical Polishing of LBO Crystal

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.

Mechanism of Brittle-Ductile Transition of Single Silicon Wafer at Different Temperatures

Formation, propagation and length of crack and hardness of single silicon wafer were investigated at different temperatures by means of Vickers indentation, using lower temperature testing unit with semiconductor refrigerating chip and higher temperature testing unit with closed electric furnace. The results show that the hardness of single silicon wafer decreases with the increase of temperature, while the length of crack increases with the increase of temperature. Ductile-brittle transition of the single silicon wafer can occur at different temperatures with the increase of load. When the load is smaller and temperature is lower, no cracks can be found.

Nanodiamond Modified with SHP

A stirring mill, an ultrasonic bath and a high-speed shearing emulsifier were adopted to modify the surface characteristics of nanodiamond (ND) respectively. The ζ-potential, size distribution and Fourier transform infrared spectroscopy (FT-IR) of ND were measured to evaluate its properties. Results show that the ζ-potential of ND modified with SHP (either by Mechano-chemical Modification or Ultrasonic measurement) drops sharply. Results also show that the rotating speed of the emulsifier exerts little influence on the size D5 but great influence on the size D95 of ND.