De Ping Yu

Ultraprecision machining of micro-structured functional surfaces on brittle materials

Ultraprecision micro-structured functional surfaces on hard and brittle materials, e.g. ceramic and glass, are gaining increasing application in a range of areas such as engineering optics and semiconductor and biomedical products. However, due to their tendency of being damaged in brittle fracture in machining, it is challenging to achieve both a high surface finish and complex surface shapes. In this paper, ultraprecision machining of micro-structured functional surfaces on brittle materials by fast tool servo diamond turning is studied. A machining model has been developed to ensure ductile regime machining of the brittle material, in which the material is removed by both plastic deformation and brittle fracture, but the cracks produced are prevented from being extended into the finished surface. Based on the model, an iterative numerical method has been proposed to predict the maximum feed rate for producing crack-free micro-structured surfaces. Machining experiments on typical micro-structured functional surfaces have been carried out to validate the effectiveness of the proposed method for producing ultraprecision micro-structured functional surfaces.

An automatic form error evaluation method for characterizing micro-structured surfaces

Ultra-precision micro-structured surfaces are becoming increasingly important in a range of application areas, including engineering optics, biological products, metrology artifacts, data storage, etc. However, there is a lack of surface characterization methods for the micro-structured surfaces with sub-nanometer accuracy. Although some research studies have been conducted on 3D surface characterization, most of them are on freeform surfaces, which are difficult to be applied on the micro-structured surfaces because of their limited characterization accuracy and the repeated surface feature patterns in the micro-structured surfaces. In this paper, an automatic form error evaluation method (AFEEM) is presented to characterize the form accuracy of the micro-structured surfaces. The machined micro-structured surface can be measured by any 3D high resolution measurement instrument. The measurement data are converted and pre-processed for the AFEEM, which mainly consists of a coarse registration and a fine registration process. The coarse registration estimates an initial position of the measured surface for the fine registration by extracting the most perceptually salient points in the surfaces, computing the integral volume descriptor for each salient point, searching for the best triplet-point correspondence and calculating the coarse registration matrix. The fine registration aligns the measured surface to the designed surface by a proposed adaptive iterative closest point algorithm to guarantee sub-nanometer accuracy for surface characterization. A series of computer simulations and experimental studies were conducted to verify the AFEEM. Results demonstrate the accuracy and effectiveness of the AFEEM for characterizing the micro-structured surfaces.

Design of a Fast Tool Servo Based Diamond Turning Machine for Fabricating Micro-Structured Surfaces

Increasing demand for ultraprecision components with micro-structured surfaces has attracted focus on diamond turning research. In this paper, a fast tool servo (FTS) based diamond turning machine is presented for fabricating micro-structured surfaces with high accuracy. A design criterion is established to serve as a guide in choosing or designing a suitable type of FTS for a micro-structured surface. Experiments on fabricating sampled micro-structured surfaces are carried out to demonstrate the effectiveness of the designed FTS based diamond turning machine.

Ductile-Regime Machining for Fast Tool Servo Diamond Turning of Micro-Structured Surfaces on Brittle Materials

Micro-structured surfaces on brittle materials, e.g. ceramic and glass, are gaining increasing application in a range of areas. In this paper, fast tool servo (FTS) diamond turning has been applied to machine micro-structured surfaces on brittle materials and the machined surfaces has been observed to study its machining mechanism. A machining model is presented to enable ductile-regime machining of the brittle material. Based on the model, machining characteristics can be predicted for given cutting conditions. Experimental investigation on machining of a micro-structured surface verified that ductile-regime machining can be ensured on the entire surface through path planning simulation based on the machining model.

Automatic Surface Characterization for Micro-Structured Surfaces Fabricated by Fast Tool Servo Diamond Turning

Fast tool servo diamond turning is a promising machining method for precision and complex micro-structured surfaces with spatial wavelength above tens of microns. It is crucial to measure and characterize the micro-structured surfaces to sub-micrometer form accuracy. The general purpose measurement instruments are not able to evaluate the true form accuracy between the measured surface and designed surface. Therefore, in this paper an automatic surface characterization method is proposed to evaluate the form accuracy for micro-structured surfaces. The fabricated surfaces can be measured by any high-resolution measurement instruments. After the surface measurement, an iterative closest point (ICP) algorithm is modified to align the measured surfaces to the designed surfaces with the form error evenly distributed over the whole surface. After alignment, the designed surface height corresponding to each measured point is calculated to form the areal error map. 3D surface parameters are chosen and calculated from the error map to characterize the surface form error. Experimental results demonstrate the effectiveness of the proposed surface characterization method.

Innovative Design of Pin Tumbler Lock Based on TRIZ

Pin tumbler lock is widely used due to its important role in security. However, the existing pin tumbler locks are not safe enough as they can be easily opened by many specific tools. Although many pin tumbler lock patents have been proposed to enhance the security level, these revealed designs still exhibit different deficiencies. In addition, the traditional method for lock designing is of low efficiency as it is based on inspiration and experience. Therefore, the TRIZ tool, which is the inventive problem solving method, is applied to lock designing in this paper. An innovative design of magnetic pin tumbler lock has been proposed through analyzing the traditional pin tumbler lock system, finding contradictions and solving them by using TRIZ tools such as separation principle, inventive principle, contradiction matrix and substances - field analysis. The proposed magnetic pin tumbler lock is double encoded and can effectively prevent specific tools from opening.

Research on a New Scanning Process for the Flexible Forming Using Plasma Arc

Flexible forming using plasma arc (FFUPA) is a newly developed process of sheet metal forming, which can deform the sheet metal without mould and die, and thus is a promising method for rapid prototyping and short-run production. To achieve a large bending angle, it is unavoidable to scan the sheet metal for multiple times. However, the average bending angle reported in literature for each time is limited. To obtain a larger bending angle by each scan, this paper proposes a new scanning process, in which an assistant heat source is placed ahead of the plasma arc. The proposed scanning process has been studied by numerical simulation and optimized for the optimal processing parameters.