Song Lin Ding

Finite Element Analysis of Machining Thin-Wall Parts

In an attempt to decrease weight, new commercial and military aircraft are designs with unitised monolithic metal structural components which contains of thinner ribs (i.e., walls) and webs (i.e., floors). Most of the unitised monolithic metal structural components are machined from solid plate or forgings with the start-to-finish weight ratio of 20:1. The resulting thin-walled structure often suffers a deformation which causes a dimensional surface error due to the action of the cutting force generated during the machining process. To alleviate the resulting surface errors, current practices rely on machining through repetitive feeding several times and manual calibration which resulting in long cycle times, low productivity and high operating cost. A finite element analysis (FEA) machining model is developed in this project to specifically predict the distortion or deflection of the part during end milling process. The model aims to provide an input for downstream decision making on error compensation strategy when machining a thin-wall unitised monolithic metal structural components. A set of machining tests have been done in order to validate the accuracy of the model and the results between simulation and experiment are found in a good agreement.

Chatter Detection in High Speed Machining of Titanium Alloys

Chatter is a complex phenomenon characterized by unstable, chaotic motions of the tool and by strong anomalous fluctuations of cutting forces. The situation becomes more serious in the milling of titanium alloys because of their low Young modulus and extended elastic behaviour. This paper presents an online chatter detection system based on the analysis of cutting forces, which is one of the integrated modules of a multi-sensor chatter detection system consisting acoustic and acceleration sensors. The cutting force is transformed into frequency domain by applying Fast Fourier Transform (FFT). Chatter frequency is identified in the frequency domain by comparing its power spectrum with predefined threshold. Experiments were carried out to validate the mythology.

Experimental study of wheel rotating speed effect on electrical discharge grinding

Electrical discharge grinding is used to machine polycrystalline diamond layer of cutting tools, which can effectively drill composite/titanium stacks in modern aircraft frames. In the machine, an electrode wheel is rotated to accelerate debris flushing to quickly recover the dielectric fluid between a spark gap. The aim of this study was to investigate the effect of the wheel speed on polycrystalline diamond removal rate for high erosion efficiency. Multiple wheel speeds were applied in a electrical discharge grinding machine under various pulse on-times and the volumetric removal rates were calculated by the precise position feedback of this machine over the time, which was obtained by the electrical waveform of discharges. The experimental results show that the removal rate increases with the wheel speed up to a limit at the low range and then declines at the high range. This indicates that the wheel speed needs to be optimized for high erosion efficiency under various discharge conditions such as different materials and pulse on-times.

Chips Morphology Analysis under Graphene Oxide Suspension with Tungsten Carbide Tool in Drilling Ti-6Al-4V

Recently, titanium alloys have been widely used in industry owing to their excellent physical and mechanical properties. However, the severe cutting conditions such as abrasion, adhesion and high temperature accelerate the rate of chip formation and strongly affect the quality of machined surface. This paper investigates that the effect of the conventional coolant (CC) and graphene oxide suspended (GO) on the drilling process of titanium alloy Ti-6Al-4V using tungsten carbide tools. Here are two main chip formation could be found that zigzag chips and spiral chips. Through the analysis of chip morphology, it was found that under graphene oxide suspended fluid. It can be found that using conventional coolant would form the zigzag chips, while it formed spiral chips when graphene oxide suspended fluid applied. In addition, by analysing the chip free surfaces, the chip lamella stuck and chip flaw happened when conventional fluid used. While the back surfaces could be found that less chip stuck and crack occurred when graphene oxide suspended coolant applied. Finally, chip thickness were investigated that thinner chip thickness was found when graphene oxide suspended fluid used.

The development of an economic model for the milling of Titanium alloys

This paper presents a model for the determination of optimal cutting parameters in the milling of Titanium alloys based on real manufacturing data collected from cutting tests. The objective of the optimal function is to achieve the lowest overall costs. Design of Experiment and Taguchi methods are applied in the design of cutting tests. Optimal cutting parameters such as cutting speed, feed, depths of cut are obtained by solving the economic model which is developed according to workshop-specific data.

Online Tool Life Prediction in the Machining of Titanium Alloys

In order to reduce the risk of expensive tool failure in the machining of Titanium alloys, the paper presents a tool life prediction approach based on the analysis of cutting forces. Regression analysis was applied to develop the prediction model. Detailed steps of implementation are presented. Prediction logics and criteria are introduced. Cutting tests were carried out to validate the reliability of the proposed method. When compared with empirical methods the proposed approach which is based on the analysis of cutting force measured in the machining process appears far more effective in predicting tool life.

Residual Stress Analysis of Polycrystalline Diamond after Electrical Discharge Machining

The extreme hardness of Polycrystalline Diamond (PCD) makes it an ideal choice for the machining of hard materials as a cutting tool. Due to the high hardness, fabrication of PCD tools relies on conventional abrasive grinding which suffers from low machining efficiency. Electrical discharge machining (EDM) is an advanced machining process and can be utilised to fabricate complicated PCD tools. High temperature of sintering and EDM processes creates residual stress inside PCD and can result in unmatured failure of PCD tools. This paper analyses the distribution of residual stress in PCD after electrical discharge machining process.

Electric Discharge Grinding of Polycrystalline Diamond Materials

The poor electric conductivity of polycrystalline diamond (PCD) makes it difficult to machine with the conventional EDM process. Inappropriate selection of parameters of the power generator and the servo system leads to unstable working condition and low material removal rate. This paper introduces a method to find optimal parameters in the Electrical Discharge Grinding (EDG) of PCD materials with Taguchi method. The theory and detailed procedures are presented, experimental results are analyzed. The optimized configuration was validated through confirmation tests.

Measurement of Polycrystalline Diamond Craters in Electrical Discharge Machining

The electrical discharge grinding method is widely used to machine polycrystalline diamond tools because diamond is the hardest material and the traditional abrasive grinding method leads to high tool wear rate. The aim of this study was to find a method to precisely measure the individual diamond crate morphology during the electrical discharge process. A 3D microscopy with the focus-variation technique was chosen to obtain the stereolithography file of the polycrystalline diamond craters. The measurements were shown that the polycrystalline diamond crater morphology is more complex than that of normal tungsten carbide material. This finding can help build more accurate model of polycrystalline crater formation during electrical discharge process.

Dynamic In-Process Stock Based Tool Path Generation for High Surface Finish Rough Machining

This paper presents a new tool path generation strategy for rough machining based on the dynamic in-process stock model of the workpiece. Compared to conventional roughing method, the new tool paths result in a better surface finish but consume the same machining time. The cutter locations in the tool path are determined by removing the peak portion of the residual materials on the stock. The geometric information of remaining stocks is updated dynamically in the in-process model once each cutting pass is completed. The overall machining time is no longer than the conventional method since no additional tool paths are added. The proposed method was implemented in Catia and has been validated by simulation and cutting tests with flat end and ball nose cutters on a 3-axis CNC milling machine.