Authors: Ming Chu Kong, Wing Bun Lee, Chi Fai Cheung, Suet To
Abstract: The formation of tool marks in single-point diamond turning is a fundamental study of
the effect of materials swelling and recovery on surface roughness on a machined surface. A series
of orthogonal face cutting tests has been conducted among plate aluminum alloy, oxygen-free high
conductivity copper and electroless nickel phosphorus under the same cutting conditions by the use
of facet tools with different front clearance angles. The results show that the regular width of the
undulating pattern in tool marks could be explained by side swelling and the micro-waviness within
a tool mark is caused by burnishing and recovery.
544
Authors: Suet To, Bing Yan Jiang, Can Weng, Wing Bun Lee
Abstract: The aspheric VCD lens is hard to fabricate by injection moulding due to its small volume
and high precision requirement. The processing conditions have critical effects on the quality of the
moulded lenses. An optic lens needs precisely controlled surface contours, so determination of the
processing conditions for lens moulding becomes very complicated. This study’s purpose is to
investigate experimentally some effects of the moulding conditions on the form errors of injection
moulded lens. An aspheric VCD lens was moulded using polymethyl methacrylate. Different
combinations of moulding conditions were used focusing on moulding process parameters of the
ram speed, the mould temperature, the melt temperature and the packing pressure, The predicted
model of form errors was formulated by orthogonal and regression analysis. Finally, the predicted
model is proven to be valid based on the residual diagnostic plots.
123
Authors: Ling Bao Kong, Chi Fai Cheung, Suet To, Wing Bun Lee
Abstract: Optical freeform surface requires submicrometer form accuracy and nanometer surface
finish. Ultra-precision raster milling is an emerging technology in the fabrication of those surfaces
in which the dynamics factors are vital to achieve the surface quality. This paper presents a
theoretical dynamics model for ultra-precision raster milling. The cutting force is derived in the
depth of cut (DOC) planes in the feed and raster directions. Hence, a 3D cutting force model is
established. The cutting force induced deflection between tool and workpiece is determined which
can be employed to analyze the influence of the deflection on the surface generation in raster
milling. The dynamic model is useful for modeling of surface generation and further control of
vibration between the tool and the workpiece.
58
Authors: Wing Bun Lee, Chi Fai Cheung, Suet To
Abstract: A multi-scale model is proposed to explain the effect of material induced vibration and
the quantitative relation between cutting force and the surface quality from dislocations, grain
orientations, cutting tools, machine tools used in the simulation of the nano-3D surface topology
in single-point diamond turning. The model-based simulation system composes of several model
elements which include a microplasticity model, a dynamic model and an enhanced surface
topography model. The multi-scale model brings together knowledge from various disciplines to
link up physical phenomenon occurring at different length scales to explain successfully the surface
generation in single-point diamond turning of crystalline materials, and offers a new direction of
research in ultra-precision machining.
1009
Authors: Yi Ping Chen, Wing Bun Lee, Sandy To
Abstract: An accurate prediction of plastic anisotropy induced by initial texture in sheet metal
forming operations depends on the constitutive models adopted. Models of engineering interest
include both phenomenological formulations and crystal plasticity based on dislocation slip. In
addition to the above two approaches that are commonly adopted in FE analysis, now an alternative
is available which describes anisotropic behavior of polycrystalline sheet metals still by an analytic
yield function to keep the computing time as low as possible but at the same time which also takes
explicitly into account the crystallographic texture of the material to give a more precise description
of plasticity anisotropy. However, the locus of such a yielding potential determined by constitutive
coefficients upon invoking the rate-independent crystal plasticity may exhibit an unrealistic
concave shape, which will make it impossible to obtain a convergent solution. To circumvent the
difficulty, a detailed computation procedure is presented to calculate the constitutive coefficients
based on rate-dependent crystal plasticity. The combination of the coefficients obtained with
experimentally measured texture coefficients of an annealed FCC polycrystalline sheet metal will
provide a complete constitutive characterization of the material. As an application of the calibrated
model, the process of deep drawing by hemispherical punch is simulated, in which plastic
anisotropy (earring) corresponding to typical texture type is observed, thus demonstrating the
applicability of the coefficients found.
829
Authors: Wing Bun Lee, Yi Ping Chen, Sandy To
Abstract: A rate-dependent crystal plasticity constitutive model together with Marciniak-
Kuczynski(M-K) approach is employed to perform numerical simulations of forming limits
diagrams(FLDs). An initial imperfection in terms of a narrow band is adopted to initialize the sheet
necking. Homogeneous deformations inside and outside the band are assumed and the enforcement
of compatibility and equilibrium conditions is required only on the band interface. Constitutive
computations are carried out on two aggregates of FCC crystal grains, with each representing one of
the two zones, respectively. Taylor homogenization assumption is employed to establish the link of
stress between single crystal and polycrystal, and to derive an average response of the aggregates.
The same initial texture is imparted to the two aggregates and their evolutions will be traced in the
necking process. Factors affecting the FLDs prediction, such as imperfection intensity, initial
texture, strain rate sensitivity and crystal elasticity will be taken into account. The above procedure
will be applied to an annealed aluminium alloy sheet metal
179
Authors: Jian Guang Li, Wing Bun Lee, Chi Fai Cheung, Sandy To, J.J. Du, Z.Q. Yin
Abstract: Virtual manufacturing (VM), which primarily aimed at reducing the lead times to market
and costs associated with new product development, offers various test-beds for the time-consuming
and expensive physical experimentation. Since surface roughness and form accuracy play essential
roles in the functional performance of the products machined with ultra-precision machining
technology. An optimizer, VSPDT (virtual single point diamond turning) system was developed for
the purpose of form error compensation and optimal cutting parameters selection. In this paper, the
keys issues for developing VSPDT using virtual manufacturing technology were highlighted such as
framework of system, virtual workpiece, virtual machining and inspection, etc. At the end of the
paper, A VSPDT was developed and applied to predict and compensate the form error, select optimal
cutting parameters by using a 2-axis CNC ultra-precision turning machine.
447
Authors: Ling Bao Kong, Chi Fai Cheung, Wing Bun Lee, Sandy To
Abstract: This paper presents an integrated platform for modelling and measurement of freeform
surface generation in ultra-precision raster milling. It is composed of several components which are
optics design component, tool path generator, modelling system, measurement system, evaluation
component, compensation component and optimization component, respectively. The research
emphasizes on modelling and simulation of freeform surface generation, the prediction of the cutting
performance and hence the optimization of cutting strategy in the ultra-precision raster milling of
freeform surfaces. A measurement system is also proposed to carry out a fast and efficient
measurement plan of freeform surfaces. Non-uniform Rational B-Spline (NURBS) will be employed
for the development of the integrated platform which will meet Standard for the Exchange of Product
model data (STEP).
422
Authors: H.F. Li, Chi Fai Cheung, Ling Bao Kong, Wing Bun Lee, Sandy To
Abstract: Ultra-precision freeform surfaces have become widely used in advanced optics
manufacture. Although these surfaces can be fabricated by ultra-precision freeform machining
technology with sub-micrometer form accuracy and surface finish in nanometer range, our current
understanding on the evaluation of surface quality of these surfaces is still far from perfect. In this
paper, a study of measurement technology for ultra-precision freeform surfaces is presented.
417
Authors: Su Juan Wang, Chi Fai Cheung, Sandy To, Wing Bun Lee
Abstract: Recently, the high quality and high productivity in fabrication of freeform optics has been
of primary interest in manufacturing industries, such as die and mould manufacturing, aerospace part
manufacturing, and so forth. However, the fabrication of freeform optics is currently expensive and
vastly complex. Ultra-precision raster milling can produce non-rotational symmetric surfaces with
sub-micrometric form accuracy and nanometric surface finish without the need for any subsequent
post polishing. While, there is little research work focus on this kind of machining method. This paper
presents a framework of a tool path generation system for freeform surface ultra-precision raster
milling. This system includes model of freeform optics, tool path generator, interference monitor and
an optimization model of machining parameters. The tool path generation system can generate
interference free and optimal tool path for machining freeform surfaces. Some simulation results have
been presented to illustrate the performance of the system.
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