Modeling and prediction for 3D surface topography in finish turning with conventional and wiper inserts

Wiper insert have the characteristics of achieving an excellent surface finish and improving the productivity in turning processes. Wiper insert can provide twice feed rate while maintaining the comparable surface roughness compared to that provided by the conventional insert. In the present study, surface topographies in finish turning with conventional and wiper inserts are investigated. The key element of this work is that the cutting edge path equation in the cutting tool coordinate system is transformed into the machine tool and workpiece coordinate system by the use of spatial coordinate transformation. Following that a surface topography simulation algorithm based on the cutting edge path equation and cutting parameters is put forward. The output of this work is that both the simulated surface topography and surface roughness profile are good agreement with the experimental results. Both the simulated and the actual machined surface results show that better surface topography is obtained in finish turning with the wiper insert than that with conventional insert. Burnishing effect of the wiper insert leads to half decrease of the Ra and Rz. The actual surface profiles are no longer regular wave shapes due to ploughing effect and side flow existing in the cutting zone. In addition, a surface roughness map has also been developed to optimize the selection of wiper radius and feed rate to satisfy the requirement of surface finishing with higher productivity. From the viewpoint of cutting tool design, the wiper radius with five times larger than tool nose radius can fully come into its role. This provides a novel insight into the design of wiper insert over conventional techniques. Above all, the proposed model gives a better prediction of surface roughness in finish turning process compared to the previous empirical and regression roughness models. The prediction of surface roughness in finish turning with wiper insert is also realized.     

An investigation into material-induced surface roughness in ultra-precision milling

This paper presents a theoretical and experimental investigation into the effect of the workpiece material on surface roughness in the ultra-precision milling process. The influences of material swelling and tool-tip vibration on surface generation in ultra-precision raster milling are studied. A new method is proposed to characterize material-induced surface roughness on the raster-milled surface. A new parameter is defined to characterize the extent of surface roughness profile distortion induced by the materials being cut. An experiment is conducted to compare the proposed method with surface roughness parameters and power spectrum density analysis method by machining three different workpiece materials. The results show that the presence of elastic recovery improves the surface finish in ultra-precision raster milling and that, among the three materials being cut in the experiment, aluminum bronze has the greatest influence on surface finish due to its highest elastic recovery rate and hardness. The results also show that, in the case of faster feed rates, the proposed method more efficiently characterizes material-induced surface roughness.     

Influence of machining parameters on surface roughness in finish cut of WEDM

Surface roughness is significant to the finish cut of wire electrical discharge machining (WEDM). This paper describes the influence of the machining parameters (including pulse duration, discharge current, sustained pulse time, pulse interval time, polarity effect, material and dielectric) on surface roughness in the finish cut of WEDM. Experiments proved that the surface roughness can be improved by decreasing both pulse duration and discharge current. When the pulse energy per discharge is constant, short pulses and long pulses will result in the same surface roughness but dissimilar surface morphology and different material removal rates. The removal rate when a short pulse duration is used is much higher than when the pulse duration is long. Moreover, from the single discharge experiments, we found that a long pulse duration combined with a low peak value could not produce craters on the workpiece surface any more when the pulse energy was reduced to a certain value. However, the condition of short pulse duration with high peak value still could produce clear craters on the workpiece surface. This indicates that a short pulse duration combined with a high peak value can generate better surface roughness, which cannot be achieved with long pulses. In the study, it was also found that reversed polarity machining with the appropriate pulse energy can improve the machined surface roughness somewhat better compared with normal polarity in finish machining, but some copper from the wire electrode is accreted on the machined surface.     

Design optimization of diamond disk pad conditioners

Chemical mechanical planarization (CMP) is the major manufacturing step used to planarize semiconductor wafers and obtain mirror surface finish. In CMP, diamond disk pad conditioning is traditionally employed to restore pad planarity and surface roughness. The conditioning tool typically consists of a metal disk with one side embedded with protruding diamond grits (abrasives). The conditioner design has a significant effect on the pad conditioning process and hence the wafer planarization process. This paper proposes the application of engineering optimization methods such genetic algorithm to the conditioner design problem for the first time. A new metric to evaluate conditioning performance based on the conditioning density generated by a specific conditioner design is developed. The metric is applied in a genetic algorithm to optimize conditioner design parameters (including geometric arrangement of diamonds, grit density and disk size). The model searches for the design parameters that produce a desired CMP pad surface texture. Results show that the model can effectively serve as a platform to evaluate and tune conditioner design for different applications in CMP.     

Simplified stiffness model for spherical rough contacts

Abstract

Obtaining a surface with negligible roughness is very expensive, time consuming and unnecessary. The influence of surface roughness on the contact stiffness is of great importance. The extra cost associated with unnecessary surface finish can be limited by eliminating the unnecessary machining operations beyond the required surface finish. In this article, a simplified solution is presented to calculate the stiffness of rough contact between the workpiece and spherical locator; also, the effect of surface roughness on the stiffness and deformation of rough spherical contact is studied for different applied loads to find an ‘economic roughness’ under machining forces.     

Effect of lighting conditions in the study of surface roughness by machine vision - an experimental design approach

In the evaluation of surface roughness by machine vision technique, the scattered light pattern reflected from the machined surface is generally captured and optical surface finish parameters from the images are correlated with the actual roughness. Capturing of the image at appropriate conditions is required for the good correlation of the optical parameters with the roughness. Lighting conditions is a major factor that influences the image pattern and hence the optical parameters. In this work the lighting conditions like grazing angle, the light to specimen distance, the orientation of the striations on the surface to the light are varied and its influence on the optical surface finish parameter are studied. A plan of experiments based on the techniques of Taguchi was designed and executed for conducting the trials and to obtain valid conclusions. The analysis of variance and the signal to noise ratio of robust design are employed to investigate the influence of different lighting conditions on the optical surface finish parameter. The results of both the approaches confirm that grazing angle is the most influencing factor affecting the image parameter.     

Simulation and measurement of surface roughness via grey scale image of tool in finish turning

Study on the surface roughness of specimen is a significant field of research because this parameter affects the performance of the machined parts. Meanwhile, the evaluation of surface roughness of specimens using a vision system via the images captured from the specimen is an interesting method which is widely used. Although the effect of flank and crater wear has been investigated extensively in the past researches on surface profiles, some reports indicated that, in finish turning, the nose radius wear has a greater effect on the surface profile of specimen. Although, vibration can affect the surface profile of a specimen in rough turning, the final surface profile in the product used is usually shaped by finish turning that may not be affected by vibration using the robust machine tool. In this work, a machine vision was used to capture the images of the tool tip in-cycle. The 2-D images of the nose area of tool tips were used to simulate the surface profile of specimens in finish turning. The simulated images of specimens in a range of machining condition were detected using the algorithm of this work. The results showed that this method can be used successfully to simulate and evaluate the surface profile of a specimen in finish lathe machining as a fingerprint of the tool tip. This method can be used for forecasting the final surface profile in order to control the performance of products.     

Optimization of tool geometry parameters for turning operations based on the response surface methodology

This investigation focuses on the influence of tool geometry on the surface finish obtained in turning of AISI 1040 steel. In order to find out the effect of tool geometry parameters on the surface roughness during turning, response surface methodology (RSM) was used and a prediction model was developed related to average surface roughness (Ra) using experimental data. The results indicated that the tool nose radius was the dominant factor on the surface roughness. In addition, a good agreement between the predicted and measured surface roughness was observed. Therefore, the developed model can be effectively used to predict the surface roughness on the machining of AISI 1040 steel with in 95% confidence intervals ranges of parameters studied.     

An investigation into the assessment of surface finish by microwave reflection

Non-contact methods are ideal for in-process monitoring of surface finish. In this context, the application of microwave reflection for the assessment of roughness assumes significance. It is well known that surface roughness affects the reflection of microwaves, and the energy loss in their transmission is considerably influenced by the finish of the wave guides. Experimental investigations were conducted with a sweep oscillator and reflectometer to find the feasibility of this technique in monitoring the roughness of manufactured surfaces. A number of surface specimens produced with different machining operations were measured for the return loss, and these compared with the normal roughness values. This paper deals with the experiments conducted and results obtained in these investigations.     

EFFECT OF CRYSTALLOGRAPHIC ORIENTATION ON CUTTING FORCES AND SURFACE FINISH IN DUCTILE CUTTING OF KDP CRYSTALS

In order to investigate the influence of material anisotropy in ductile cutting of Potassium Dihydrogen Phosphate (KDP) crystals, experiments of face cutting of (001) plane of KDP crystals are carried out by using an ultra-precision lathe with a single point diamond tool. The cutting forces, surface finish, and surface roughness in all crystallographic orientations of the machined surface are measured, and a power spectrum analysis method is used to reveal the cutting force patterns. The experimental results show that the cutting forces and surface roughness vary greatly with different crystallographic orientations of KDP crystal, and that amplitude variation of cutting forces and surface finish is closely related with the cutting parameter of the maximum undeformed chip thickness. With the maximum undeformed chip thickness below 30 nm, the amplitude variation of cutting force and surface finish is minimized, and a super-smooth surface with consistent surface finish in all the crystallographic orientations can be achieved. The surface roughness is 2.698 nm (Ra) measured by Atomic Force Microscope (AFM). These findings provide criteria for achieving a large-scale KDP crystal with consistent super-smooth surface using ductile cutting technology.