B. K. A. Ngoi

Dry machining: Machining of the future

Abstract Machining without the use of any cutting fluid (dry or green machining) is becoming increasingly more popular due to concern regarding the safety of the environment. Most industries apply cutting fluids/coolants when their use is not necessary. The coolants and lubricants used for machining represents 16–20% of the manufacturing costs, hence the extravagant use of these fluids should be restricted. However, it should also be noted that some of the benefits of cutting fluids are not going to be available for dry machining and also dry machining will be acceptable only whenever the part quality and machining times achieved in wet machining are equalled or surpassed. This paper presents recent developments in the dry machining operation.

Applying spatial representation techniques to the container packing problem

This paper describes an efficient method of packing boxes into a container using a unique spatial representation technique. Unlike other algorithms, the packing algorithm in this paper is not constrained by the physical packing sequence, that is, back to front, or bottom to top. This extra flexibility allows the program to pack the boxes more efficiently. The packing plan can be generated to suit the actual packing sequence. The program is implemented on an IBM PC and a comparison has been made with a similar software. The results, in terms of packing efficiency and packing time, are promising.

Brittle–ductile transition in the diamond cutting of glasses with the aid of ultrasonic vibration

Abstract High efficiency mirror surface machining of brittle materials such as glasses and ceramics has become more important as these materials have become used more widely in optical and electronic devices. In this work, the ultrasonic vibration diamond cutting of glasses was performed in order to investigate the effect of tool vibration on the brittle–ductile transition mechanism. The effect of cutting speed on the critical depth of cut was studied by groove cutting experiments. The value of critical depth of cut has been found to vary with the ratio of vibration speed to cutting speed. The characteristics of the surface generated in the ductile mode have been examined and the measures for minimizing the influence of tool vibration on surface finish are suggested. The reason for the increase in the critical depth of cut is discussed based on the analysis of the ultrasonic vibration cutting process and the measured data of cutting force.

Material removal mechanisms in precision machining of new materials

Abstract Modern-day products are characterised by high-precision components. A wide range of materials, including metals and their alloys, ceramics, glasses and semiconductors, are finished to a given geometry, finish, accuracy and surface integrity to meet the service requirements. For advanced technology systems, demands for higher fabrication precision are complicated by the use of brittle materials. For efficient and economical machining of these materials, an understanding of the material removal mechanism is essential. This paper focuses on the different material removal mechanisms involved in machining of brittle materials.

Applying linear programming to tolerance chart balancing

This paper explores an important aspect of tolerance charting, i.e. tolerance chart balancing. A mathematical model for tolerance chart balancing, based on the “rooted tree” representation technique, has been established. The mathematical model, which represents a resource allocation problem, is then solved by using the linear programming approach. An example is used to illustrate the method. A comparison between the results generated by the proposed method and the manual method is also included.

A complete tolerance charting system

Abstract Manual computation of tolerance charts is both tedious and time-consuming. This paper presents an efficient method of automatically determining the working dimensions and their balanced tolerances. With this method, the feasibility of different process plans can be evaluated efficiently and economically. A unique algorithm, based on a special path tracing technique, is developed to reduce the unknown working dimensions to a system of linear equations. The Gauss elimination technique is then employed to solve for the working dimensions. The tolerance balancing process is accomplished using a separate mathematical model. The complete system, comprising the tolerance charting and optimization modules, is finally tested on an example.

In-plane deformation measurement using the atomic force microscope moiré method

In this paper, a new scanning moire method is developed to measure the in-plane deformation of mica using an atomic force microscope (AFM). Moire patterns are formed by the scanning line of the CRT in the AFM system, and the atomic lattice of the mica or high-orientated pyrolytic graphite (HOPG). The measurement principle and the techniques employed for grating preparation are described in detail. This new method is used to measure the residual deformation of a mica plate after irradiation by a Nd-YAG laser, and to determine the residual strain of HOPG under a tensile load. Some interesting results are obtained. The successful results verify the feasibility of this method for measuring deformation in the nanometre range using the lattice of the material as the model grid.

Computer-aided tolerance charting

We present a simplified approach of deriving the working dimensions between surfaces of a workpiece during tolerance charting. Unlike other methods, it does not require any representation of the machining sequence. The dimensional chains are first formulated into a matrix and it is then solved by applying the Gauss elimination technique. We also describe an elegant method of deriving the balanced tolerances of a workpiece during tolerance charting. The process links between surfaces are derived by using a special tracing technique. With the process links obtained, the balanced tolerances are solved by using a separate mathematical model. An example is used to illustrate the method.

Phase-shifting interferometry immune to vibration

A modification of phase-shifting interferometry is proposed for microsurface profiling of flat surfaces under vibrating conditions. With this technique the required phase shift, achieved by quarter-wave plates and polarizers, is free of errors associated with motion. A nearly common optical-path configuration is achieved, and the effect of environment is reduced. The effect of environment on the optical system is also studied. Moreover, the measurement of phase is instantaneous, which increases the versatility of this technique to measure vibrating objects. Experiments were carried out on a smooth mirror surface excited with high-frequency vibrations, and the technique was found to be immune to vibrations of both high and low frequency.

Angular dispersion compensation for acousto-optic devices used for ultrashort-pulsed laser micromachining

Ultrashort pulsed laser material processing is a new micromachining method that is gaining interest. Its capability of submicrometer machining has been proved. To obtain high speed and highly flexible beam steering, a two-axis acousto-optic deflector is employed. However, dispersion associated with acoustic-optic interaction will cause serious spatial deformation on the writing spot. The compensation for dispersion is proposed and studied. Experiments show promising results. An additional advantage of the proposed compensation method is that it can also precisely control the pulse number, and, hence improve the quality of ablation.