Ju Long Yuan

Digital mammography image enhancement using improved unsharp masking approach

Characteristics of the lesions in digital mammography images will be more clear after image enhancement, which can increase the detection rate of early breast cancer. This paper proposes a modified unsharp masking approach based on an improved high-pass filter. Experimental result of digital mammography image enhancement proves that the proposed method can effectively extrude the edges of lesions and at the same time can suppress the noises in uniform background areas.

A semi-fixed abrasive machining technique

This paper proposes the technique of semi-fixed abrasive machining to reduce or eliminate the surface defects caused by large abrasive grains and improve the efficiency of ultra-precision processing. The method of semi-fixed abrasive machining is described, and a semi-fixed abrasive plate (SFAP) is manufactured. Under the condition of adding or not adding large grains, experiments of semi-fixed and loose abrasive machining for a workpiece of damage-free single crystal silicon are carried out. The surface roughness and SEM micrograph of the workpieces demonstrate that semi-fixed abrasive machining leads to less surface defects, and the existence of large grains has a slight effect on the surface roughness of the workpiece. Single crystal silicon workpieces with a roughness (Ra) of about 0.2 µm are semi-fixed abrasive processed, in order to investigate the influence of load and rotating speed of the SFAP on the surface roughness and material removal rate. No significant variation of the surface roughness is observed when the value of the load or SFAP rotating speed changes, and the material removal rate increases with the increase of the load or SFAP rotating speed, i.e. the machining efficiency can be improved by increasing the load or SFAP rotating speed while the surface quality of the workpiece does not decrease.

Particle Flow Simulation on the Influences of Property Parameters of Semi-Fixed Abrasive Plate on its ‘Trap’ Effect

This paper analyzes the property parameters influences of semi-fixed abrasive plate on the ‘trap’ effect with discrete element simulation by Particle Flow Code (PFC). The effects of the property parameters such as porosity, hardness and size of the abrasive particles, friction coefficient between the abrasive particles and the bonding agent concentration are simulated. The simulation results show that porosity, friction coefficient, bonding agent concentration has great influences on the ‘trap’ effect, while hardness and size of the abrasive particles almost have no effect. Grey incidence analysis is carried to determine the influence degree of porosity, friction coefficient, bonding agent concentration, and the results show that the most important factor is the porosity, followed by the friction coefficient, and then the bonding agent concentration.

Form and Texture Control of Free-Form Surface Polishing

In this paper, a new type of flexible sub-size polishing tool, and an advanced polishing technique for free-form surface based on the new type of tool will be researched. The configuration of the flexible polishing tool and the method of controlling the multi-DOF precessions of the flexible polishing tool will be introduced. The rectilineal movement along X,Y, Z axis and flirts on two polar coordinates rotational axis of the polishing tool are used to control the form precision and the surface texture of polished surface. This polishing technique is enable to change continuously the polishing pressure and contact area and makes the flexible polishing tool well suited both to control the texture of work-piece surface and to control the form of work-piece surface. The influence functions the flexible polishing tool is near-Gaussian, symmetrical, and lacks the high spatial frequencies and center-zero of removal. The example of multi-DOF precessions polishing for optic spherical and aspherical will be introduced. The results show that the form, the size and the movement mode of the polishing tool will have important effect to polishing quality and multi-DOF precessions polishing can obtain better surface texture quality, form precision and higher polishing efficiency than traditional pole-down polishing for free-form surface.

Simulation Study on the Developed Eccentric V-Grooves Lapping Mode for Precise Ball

A novel lapping mode is developed on the base of present eccentric v-grooves lapping mode for precise balls. The kinematics analysis shows that the ball spin axis can wiggle up to 180° under the developed mode, so the lapping trace will be dispersed onto the whole surface of the ball. The effect of offsetting and groove radius on the lapping uniformity in the developed eccentric v-grooves, the present eccentric v-grooves and the traditional v-grooves lapping mode are compared, and the advantage of the developed mode is that the impact offsetting is less while the groove radius has no impact.

Investigation of Elastic Deformation Machining Method for Aspheric Surface Generation

The mechanics of elasticity is a novel aspheric fabrication technology that could transform aspheric optical fabrication technology into sphere optical fabrication technology. The shape accuracy of the optical lens changes significantly with deformation conditions and various parameters of machining process. Considering Polymethyl-methacrylate (acrylic PMMA) characteristic and elastic deformation aspheric surface generated by the load is uniformly distributed over the inner portion of the plate, the investigation of elastic deformation machining method for aspheric surface generation is introduced in this paper. The subject of this study is to determine finished surface shape of acrylic after lapping process. The experiment results are compared with the finite element analysis (FEA) and theoretical results. The mentioned finite element models were established using the software Abaqus/CAE. The experiment result showed that the error of deformation curves between analytical and experimental result is smaller than FEA and experimental result. The theoretical of deformation curves obtained close to the experiment curves. The results indicate that the experimental investigation of elastic deformation machining method can be used to fabricate the aspheric surface with simple machining process and high efficiency.

Study on Fixed Abrasive Lapping Technology for Ceramic Balls

To improve low lapping efficiency of silicon nitride balls in conventional lapping process, fixed abrasive lapping technology for ceramic balls is investigated in this paper. Diamond abrasives and photosensitive resin are used to fabricate the fixed abrasive plate. The lapped ball surface is observed with microscopy to identify the dominant wear mechanism. The results show that the material removal rate of the fixed abrasive lapping is about 20 times of that of conventional free abrasive lapping process, and the roughness is close to the conventional one. The experimental results indicate that the fixed abrasive lapping technology is a promising process to instead of conventional free abrasive lapping process for ceramic balls in rough and semi-finishing process.

Numerical Simulation of Machining Distortion of Residually Stressed Aircraft Aluminum Components

The presence of residual stress in aircraft aluminum components can give rise to distortion after machining. Excessive distortion may result in the rejection of a part or the need for costly and time-consuming rework prior to placement in service. The purpose of this research was to develop a methodology for the prediction of machining-induced distortions of residually stressed aircraft aluminum components. Numerical simulation results show that the magnitude of machining distortion is strongly related to the square root of Stain Energy Density W or Stress Range σ . The experimental results demonstrate good agreement with the predicted machining distortions of 7075T73 bulkheads. It included that the original residual stress in the blocks of aircraft aluminum component is one of key factors to cause machining distortion.

Research on Material Removal Characteristics in Plane Lapping Method for Aspherical Surface Using Elastic Deformation

Plane lapping method using the elasticity of materials has many advantages comparing with current machining method for aspherical surface machining. Due to the deformation of the workpiece, the material removal characteristics of this method are different from the traditional lapping process of flat surface. In this paper, based on the Preston equation and plate theory, the theoretical model of the material remove rate is built in the case of proving experiment. Then the proving experiment of elastic deformation method is carried out, the recorded values fit well with theoretical ones, which shows that the theoretical model of material removal property is valid and the variation of MRR is related to the deformed profile of workpiece.

An Investigation to Semi-Fixed Abrasives Plate Characteristics

The most typical example of hard and brittle material is advanced ceramics, for its ultra-precision machining difficulty and wide applications, now it becomes a focus of attention. Semi-fixed abrasive plate (SFAP) is newly developed for preventing larger particles from doing workpiece surface damage in machining advanced ceramics, for larger particles from grain size dispersion or from outside of processing area could bring uneven load distribution on processing region of advanced ceramics. In this paper, Shearing strength, surface hardness and Young’s modulus as characteristics of SFAP are investigated. They were influenced by Grain size and abrasive weight ratio are analyzed and discussed, as well as the qualitative estimation of these influences on the characteristics of SFAP are deduced.