Achievable Surface Roughness Research Articles

Experimental investigations into rotating workpiece abrasive flow finishing

Abrasive flow finishing (AFF) is used to deburr, polish or radius surfaces and edges by flowing a semisolid abrasive medium over the intended surface to be finished. Such finishing operations play a crucial role in manufacturing process of machine parts. The cost escalates sharply when the requirement is to achieve surface roughness values near nano levels. The need for finishing is to avoid power losses due to friction, increase the wear resistance and to provide a long serviceable life to the equipment. AFF is used in the industries especially in the case of finishing complex internal and external shapes. However, AFF is a time consuming process and any effort to reduce the process time even marginally saves production time and cost of the finished product. In the present study, an effort is made towards improving the performance of AFF process by providing rotary motion to the workpiece (R-AFF: rotational abrasive flow finishing). Preliminary experimental comparative study is done on AFF and R-AFF processes to compare their process performance in terms change in R a (Δ R a) and material removal. Later complete experimental study on R-AFF is conducted using central composite rotatable design and the responses are plotted using response surface methodology. The workpiece materials used in the present study are Al alloy, Al alloy/SiC (10%) and Al alloy/SiC (15%) metal matrix composites (MMCs). The results of R-AFF are encouraging. The present study shows that rotational speed of workpiece has significant effect on output responses (Δ R a). Indigenously developed semi solid abrasive laden medium is used in the present study. Overall, the experiments have shown that R-AFF has a very promising future for the industries in terms of better finishing.

Roughness characteristic length scales of belt finished surface

Surface integrity, dynamic properties and mechanical characteristics of belt finished surfaces strongly depend on the achieved surface roughness produced by the abrasion process. A new approach based on the scaling analysis of the roughness characterization is introduced on a surface obtained by a set of roughness process parameters. Experimental results show that range roughness amplitude depends on the scan size and that roughness amplitude follows two stages. Stage I presents a linear power-law roughness distribution—a linear relation. Stage II presents a non-linear power-law roughness distribution. The latter is divided into two sub-stages: the first sub-stage (sub-stage II.a) characterizes the fractal behaviour of the surface until a critical length where the second sub-stage (sub-stage II.b) starts and characterize roughness by extreme values statistics. Fractal parameters, extreme values estimators and transition scale threshold between stages II.a and II.b are shown to be related to the abrasion process. As a result, an original probabilistic model based on the generalized lambda distribution is proposed to estimate the extreme range amplitude roughness values in stage II, depending on the observation scale. Finally, the maximal roughness amplitude PDF is estimated, at a scale higher than the scanning length with the aid of a bootstrap protocol coupled with a Monte-Carlo simulation.

A study on the fine-finish die-sinking micro-EDM of tungsten carbide using different electrode materials

In recent years, tungsten carbide (WC) and its composites (WC–Co) are widely used in the die and mold industries due to their unique combination of hardness, strength and wear resistance. Micro-EDM is one of the most effective methods for machining these extremely difficult-to-cut materials. However, numerous applications of WC often involve intense mechanical demands at the surface. Therefore, fine-finish micro-EDM of WC is becoming an imminent and important issue. In this study, investigations have been conducted with view of obtaining fine surface finish in the micro-EDM of WC using tungsten (W), copper tungsten (CuW) and silver tungsten (AgW) electrodes. It was found that the surface characteristics are dependent mostly on the discharge energy during machining. The fine-finish micro-EDM requires minimization of the pulse energy supplied into the gap. In addition, the surface finish was found to be influenced greatly by the electrical and thermal properties of the electrode material. The performance of the electrodes for the finishing micro-EDM was evaluated based on the achieved surface roughness and surface characteristics with respect to material removal rate (MRR) and electrode wear ratio (EWR). It was found that AgW electrode produces smoother and defect-free nanosurface with the lowest R a and R max among the three electrodes. Besides, a minimum amount of material migrates from the AgW electrode to the WC workpiece during the finishing micro-EDM. On the other hand, CuW electrodes achieved the highest MRR followed by AgW. In the case of electrode wear, the W electrode has the lowest wear followed by CuW and AgW. Finally, considering all the performance parameters, AgW appears to be the best choice for finish die-sinking micro-EDM of WC.

Focused ion beam iodine-enhanced etching of high aspect ratio holes in InP photonic crystals

The authors investigate the focused ion beam (FIB) fabrication of photonic crystal (PhC) holes in InP combining physical sputtering using 30 keV gallium ions and iodine-enhanced etching at 150 °C with a protective platinum or tungsten layer. The authors show that it is equivalent to conventional dry-etching methods such as inductively coupled plasma reactive ion etching in terms of achievable aspect ratio (>10), surface roughness (12.6 nm rms), and stoichiometry. The protective layers can be selectively removed after fabrication. This new FIB fabrication method lifts the previous constraints of funnel-shaped holes and limited aspect ratios of physical sputtering and reduces the Ga implantation and amorphous layer. Thus, rapid prototyping (5 s fabrication time per hole) of planar PhCs or planar PhC elements, such as PhC Y splitters, becomes feasible.

Micro-USAL technique for the manufacture of high quality microstructures in brittle materials

Abstract In the paper, microultrasonic assisted lapping (USAL) is proposed as a flexible alternative to micro-system technologies for the manufacture of high surface quality microstructures in brittle materials. The authors first introduce the background and principles of micro-USAL of microstructures, analyze obstacles in implementing and using this technique, and configure a micro-path-controlled USAL test-rig with the integration of on-line AE (acoustic emission) monitoring system. They then discuss the effectiveness of automatic tool–workpiece contact detection and tool wear compensation using AE-based feedback, of which both are important for a stable micro-USAL. They also identify the influence of the AE's positional dependence which was recognized by the authors for the first time. The AE's positional dependence was identified to be inherently attributed to the ultrasonic generator and, under certain conditions, it caused a misjudgment of AE-based feedback. In the paper, they also demonstrate the highly flexible capability of the new micro-USAL in generating microstructures of various geometrical patterns through a number of machining experiments, as well as its current limitations in achievable concave feature sizes, aspect ratios and surface roughness. Also in the paper, the authors finally discuss, in detail, micro-USALed surface properties, effects of process parameters and lapping media, and the newly proposed chemo-mechanical way to improve the micro-USALed surfaces with the achieved minimum roughness of R a 7 nm.

Machining characteristics of novel-abrasion resistant iron

Novel-abrasion resistant iron (N-AR iron) is a new cast iron, which basically is a high-Cr white cast iron alloyed with cemented carbide (13wt.%). The cemented carbide can be either powder from cemented carbide tool or use of recycled carbide tool. The characteristic properties for the material are the castability and its superior wear resistance which means that the N-AR iron has a high potential as tool material in many industrial applications, for example, in sheet metal forming processes and other tools exposed for abrasive wear. In presented paper, machining characteristics or machinability of N-AR iron was investigated in order to select suitable tool material and cutting parameters for this material with respect to achievable surface roughness (Rz), dimensional accuracy, material removal rate and tool wear rate. Cutting forces and chip shape of the N-AR iron material were also examined during the investigation to clarify the reason why the tool rate is so high in the machining.

A Model for Surface Roughness in Ultraprecision Hard Turning

Numerical modelling procedures to predict surface roughness in turning processes have been in use for more than forty years. However, the procedures available to date do not correlate well with hard turning. A novel numerical model is presented which incorporates process disturbances such as tool cutting edge defects and machine vibration in hard turning and thus their effect on the achievable surface roughness. It includes a material partition equation to address the behaviour of chip removal and deformations during the cutting process; it also allows additional information to be derived about the mechanism of generation involved at a given point on the surface. Experimental results show good correlation of calculated with measured roughness parameters even at low feed rates.

102 Ultrasonic Assisted Lapping for the Manufacture of High Surface Quality Microstructures on Brittle Materials

Ultrasonic assisted lapping (USAL) is proposed as a cost-effective alternative to micro-system based technologies, such as lithography, etching, and electron or ion beam micromachining, for manufacturing high surface quality and complex microstructures. The chosen target materials in this research are silicon, glass and advanced ceramics, which are hard-brittle and are not diamond turnable. First this paper describes the principles of USAL for microstructures, followed by obstacles in implementing and using the technique. Then, a path-controlled USAL system with an integrated on-line monitoring AE (Acoustic emission) system is presented. To evaluate the feasibility of the proposed technique, machining experiments were conducted to fabricate linear, spiral and other 2-D arbitrary patterns using a 50μm carbide tool. Further experimental results focus on the achievable surface roughness and observed tool wear as well as on improving the surface roughness by reducing the material removal unit.

Rapid fabrication and replication of metal, ceramic and plastic mould inserts for application in microsystem technologies

The process strategy for the rapid fabrication of microcomponents made of polymers will be presented. Different fabrication routes have been developed at Forschungszentrum Karlsruhe GmbH within the microsystem technology programme focusig on replication techniques. Single prototypes can be generated by the direct patterning of plastics with excimer laser radiation. For the fabrication of very small series laser-assisted micromachining, neodymium-doped yttrium aluminium garnet (Nd:YAG) and krypton fluorine (KrF) excimer laser radiation allows for the rapid manufacturing of microstructured mould inserts made of plastics, steel, cemented carbide or ceramics. The applied mould insert material depends on the achievable low surface roughness values essential for the subsequent moulding process. Plastic replication such as hot embossing, injection moulding or reaction injection moulding of the generated microstructured mould inserts gives access to mouldings carrying structural details in the micrometre range and/or high aspect ratio microstructures.

On the interrelationships of some machinability parameters in finish turning with cermet chip forming tool inserts

This paper presents results of an experimental study on finish turning of steels with cermet chip forming tool inserts. Three major machinability parameters were investigated: chip breakability; surface roughness; and specific cutting pressure. The interrelationships among these three parameters were established with a view to developing methodologies for optimum solutions in finish turning operations. The basic analysis presented in the paper includes a new method for determining the chip breakability level and the achievable surface roughness ( R a) for a given chip groove, work material and a set of cutting conditions (feed, depth of cut and cutting speed). Based on this analysis, the paper proposes the need for establishing a “total machinability” assessment criterion for optimum machining performance of a “cutting tool-work material-machine tool” system.