Jing He Wang

Effects of the Tool Angles on the Machined Surface Quality of KDP Crystal in Diamond Turning

In the ultra-precision machining of KDP crystal, there are many factors affecting the surface quality[1-3]. The experiments show that the rake angle and back angle of the tool have significant effects on machined surface roughness. Therefore, an efficient way to improve the surface roughness is to select a proper negative rake angle. In this study, the ANSYS static analysis method was employed to analyze the stress field distribution within the whole cutting region. A finite element simulation model was set up to calculate the residual stresses variation with tool’s angles, which can be considered to select optimal rake and back angles in the ultra-precision machining of KDP crystal. Results show that the optimal tool rake angle and back angle are -49° and 7°, respectively. Finally, by using different tool angles to process KDP crystal and utilizing AFM to analyze the surface roughness, it can be found that the measurement results agree well with what are deduced from theoretical calculation.

The Effect of Low Profile Additives on Unsaturated Polyester Resins During Curing at Low/Medium Temperature: Shrinkage Behavior Study

The cure of unsaturated polyester resins (UPR) is accompanied with a high degree of polymerization shrinkage of about 7-10%, which can generally be reduced by adding thermoplastics as low profile additive (LPA). Here the design of a dilatometer was presented for the measurement of the volume change of unsaturated polyester resin system containing low profile additives. According to experimental results, the shrinkage of the UPR system used during cure was not only related to temperature, LPA type, the molecular weight and the concentration of LPA, but also linked strongly with the competition between the shrinkage induced by resin polymerization and the volume compensation by LPA. PVAc was more effective for volume compensation than other LPAs (Polystyrene, Polymethyl methacrylate) and there existed an optimal concentration of LPA for shrinkage control, as were demonstrated in the paper.

Research on Influence of the Cutter Rake Angle to the Surface Quality during SPDT Machining of Crystal KDP

Influence of the cutter rake angle to the surface quality of crystal KDP is analyzed theoretically in this paper. Analysis result shows that the tension stress reaches minimum in the crystal KDP cutting region and optimal value of the surface quality is obtained as cutter rake angle is about -45°. Cutting experimental of different cutter rake angle is realized on the machine tool. Experimental results show that the surface roughness of the crystal KDP reach minimum (rms is 6.521nm, Ra is 5.151nm) as the cutter rake angle is about -45°, this experiment certifies the correctness of this theory analysis. Theory analysis and experimental results show that influence of the cutter rake angle to surface quality of the crystal KDP is very large, for ultra-precision machining of the crystal KDP, when large negative rake diamond cutter (-45°) is adopted, the super-smooth surface can be obtained.

Analysis of Mechanical Property of Crystal KDP and Simulation of Ultra-Precision Cutting Process in the Ductile Mode

In order to study mechanical property with different crystal-plane and different crystal orientation of the crystal KDP, nano-indentation experiments are first done. The mechanical properties of crystal KDP, such as elastic modulus, yielding stress, are obtained from the analysis of the experimental curve. To obtatin the stress-strain curves of crystal KDP, by using the spherical tip can get characteristic of continuous strain, the spherical indentation experiments is proposed firstly and carried out. According to obtained parameters, A finite element cutting model of crystal KDP is established. The cutting process of crystal KDP is simulated by the model, and the influence of rake angle and depth of cut on chip and surface quality is studied. The theory shows that when the cutter’s rake angle is in the range of -40° to -45°, an perfect super-smooth KDP crystal surface will be obtained. Finaly, the experiments is carried out on special ultra-precision machine tool for crystal KDP by ourself devoloping. Experiment results show that when the cutter’s rake angle is about -45°, an super-smooth surface (rms: 6.521nm and Ra: 5.151nm )is obtained on the plane (001), and this experiment certified correctness of theory analysis.

Research on Influence of Crystal KDP Anisotropy on Critical Condition of Brittle-Ductile Transition in Ultra-Precision Cutting

In order to machine high accuracy Potassium Dihydrogen Phosphate (KDP) crystal part, the indentation experiments are carried out with various loads and various orientation angles. The experimental results show that the critical condition of brittle-ductile transition of KDP has strong anisotropy. Therefore, the influence factors on the surface quality of crystal KDP was discussed, it is shown that influences of the tools geometry parameter, feed rate and Nominal depth of cut etc on the surface quality of KDP are main. Afterwards the cutting experimental study on crystal KDP material is carried out. The experimental results show that the super-smooth surface quality only can be obtained while KDP is ultra-precision machined in ductile mode.

Forecasting of Surface Roughness and Cutting Force in Single Point Diamond Turning for KDP Crystal

The method of single point diamond turning is used to machine KDP crystal. A regression analysis is adopted to construct a prediction model for surface roughness and cutting force, which realizes the purposes of pre-machining design, prediction and control of surface roughness and cutting force. The prediction model is utilized to analyze the influences of feed, cutting speed and depth of cut on the surface roughness and cutting force. And the optimal cutting parameters of KDP crystal on such condition are acquired by optimum design. The optimum estimated values of surface roughness and cutting force are 7.369nm and 0.15N, respectively .Using the optimal cutting parameters, the surface roughness Ra, 7.927nm, and cutting force, 0.19N, are obatained.

Nanoindentation Size Effect of KDP Crystal by Instrumented Indentation Testing

Indentation tests and single-point scratch tests are probably the simplest methods of measuring the elastic, plastic and fracture behavior of brittle materials. In this paper, the nearsurface mechanical properties of KDP single crystal have been investigated including the elasticity like Young’s modulus E, and the plasticity like the hardness H. These material properties can be used to predict the material responses in optical manufacturing operations. Hardness and elastic modulus on different crystal plane of KDP single crystal have been examined under different loads by nanoindentation test, and the influence of the indentation load on hardness and elastic modulus have been also analyzed systematically. The results show the nanoindentation size effect, that is, the hardness and elastic modulus increase as the indentation load decreases. The hardness and elastic modulus have strong anisotropy in the different crystallographic orientation of the same crystal plane.

Critical Cutting Condition for Brittle-Ductile Transition of KDP Crystals in Ultra-Precision Machining

In this paper, mechanical characteristics of KDP crystal anisotropy are analysed theoretically. Vickers indentation experiments are adopted to validate the variation rule of hardness and fracture toughness in different orientation of KDP crystal plane (100), and a model to calculate critical cutting thickness of brittle-ductile transition is proposed for the KDP crystals. The result shows that, on the crystal plane (100), the minimum value of critical cutting thickness of KDP crystal in brittle-ductile transition appears in the direction [110], but the maximum appears in the direction [010]. Finally, the ultra-precision machining of KDP crystal is performed, and the results agree well with the theoretical conclusions. Super-smooth surface with a roughness RMS of 6.6nm is reached as machined in the crystal direction [010], and 11.2nm to the direction [110].

Atomic Force Microscopy-Based Investigation on the Elastic Properties of Oligodendrocytes

As the leading killer of human health in the current age, cancer is concerned widely in the medical profession. As the popularizations of atomic force microscopy (AFM) in micro-biology, measuring the mechanical properties of cells by AFM is gradually applied in the diagnosis and treatment of cancer. In this paper, the scanning parameters were optimized and the indentation experiments in different parts of oligodendrocytes were carried out to test the elastic modulus of oligodendrocytes. In order to evaluate the elastic modulus accurately, nine areas on each cell were selected, and for each area, a small matrix of indentation point was made. The results indicated that elastic modulus of the center part of cancer cell is softer than that in the edge, and the one of the normal cell are 3 order of magnitude harder than the cancer cell.

Research on Nanoscale Material Removal Process Using Atomic Force Microscopy

Nanomachining tests have been conducted on single-crystal Al using atomic force microscope to simulate single-blade machining process of single gain. The influences of nanomachining experimental parameters (lateral feed and velocity) on the properties of engineering surface, material removal and chip formation were studied. Results indicated that the cutting depth of nanomachined surface increased as the lateral feed decreased. Insensitivity of cutting depth to velocity at same normal load was revealed. The different chip behaviors of nanomachined surface were investigated through scanning electron microscope (SEM). Results indicated that different lateral feeds caused different chip behaviors. Three typical chip behaviors were characterized as the lateral feed increased. In addition, the chip behavior and the volume of material removed were observed having no evident linear transformation with the evolution of the velocity by SEM graphics. Furthermore, it was concluded from the chip behaviors in nanomachining process that the material at high loads was removed by plastic deformation with no fracture or crack happened.