Minimum Ra Value Research Articles

Study on Surface Roughness Improvement of Selective Laser Melted Ti6Al4V Alloy

To improve the surface quality of Ti6Al4V parts formed by selective laser melting (SLM), this paper systematically studies the effects of laser power, scanning speed and inclination angle on the different surface morphology and roughness of parts. On this basis, the effect of surface remelting and multi-layer profile scanning process strategies on improving the surface quality of parts is explored. The upper surface roughness varies parabolically with increasing line energy density, the line energy density value that minimizes the upper surface roughness is around 0.22 J/mm, and the minimum Ra value is 4.41 μm. The roughness of upper and lower sides increases significantly with the increase in scanning speed. As the inclination angle increases, the roughness of the upper and lower sides gradually decreases, which is caused by the combined influence of powder adhesion and step effect. The surface remelting process strategy can reduce the upper surface roughness by 35.68% and reduce its Ra value to 2.65 μm. The multi-layer profile scanning process strategy can reduce the upper side and vertical side roughness by more than 50%, down to Ra 5.10 μm and Ra 4.61 μm, respectively.

Development and investigation of the magnetorheological abrasive finishing (MRAF) system to nano-finish exterior cylindrical surfaces

ABSTRACT The invention of magnetorheological abrasive finishing (MRAF) techniques has been prompted by the ever-increasing demand for nano-finished exterior surfaces of cylindrical work samples. In the present study, a novel form of the MRAF system to nano-finish the exterior cylindrical surfaces of various diameters has been devised and their finishing mechanism is discussed. The finishing experiments have been carried out to examine the finishing capabilities of newly devised MRAF system. Taguchi’s parameter design approach has been employed to find the optimal combination of finishing parameters to achieve high-quality surface of S.S.-316 L cylindrical work-sample. The obtained results have been analyzed statistically which demonstrate that the chosen parameters namely F-to-S iron ratio, d.c. supply, work sample rotational speed and linear feed rate have significant effect on the percentage change in average surface roughness (%ΔRa). The effect of finishing time on Ra has also been explored, with the findings revealing that a minimum Ra value of 0.074 µm was attained after 60 minutes of finishing time, demonstrating the developed MRAF process’s superior capabilities.

Electrochemical trepanning in the presence of insulating particles

Electrochemical trepanning is a highly effective and economic manufacturing technology and often used to process ruled surface parts in the aerospace field. Stray corrosion in electrochemical trepanning causes poor processing localization, large tip taper, and low machining accuracy. This paper presents an innovative approach to the reduction of stray corrosion in electrochemical trepanning in which ceramic particles are used to form an insulating protective layer on the machined surface and thereby inhibit harmful stray currents. The electric field distribution and contour changes during the machining process are simulated using the finite element method in COMSOL software. The results suggest that the presence of the insulating particles can dramatically improve the electric field distribution and reduce stray currents and the taper angle. A series of experiments are performed to verify the simulation results. The experiments show that the particles have a significant effect on the taper angle, reducing it from 4.03° to 2.00° at the same machining speed of 1.0 mm/min. Further experimental results show that the size and quantity of insulating particles both affect surface quality. When the particle diameter is reduced from 2.5 to 1.5 mm, the surface roughness Ra decreases from 1.32 to 1.16 μm. As the particle quantity varies from 250 to 900, a minimum value of Ra = 0.86 μm is obtained for 650 particles.

Optimal Seeking Surface Roughness and Material Removal Rate Responses of Hardened AISI 4340 High Strength Low AlloySteel in Dry Sustainable Environment

The aim of this research is to study the machinability aspects of hardened AISI 4340 High Strength Low Alloy (HSLA) steel (50 ± 2 HRC (Hardness Rockwell C)). The experimental investigation using coated carbide inserts is carried out during the dry hard milling process in a sustainable environment. The input parameters in the study are speed, feed rate and depth of cut and the responses are Average surface Roughness (Ra) and Material Removal Rate (MRR) that are selected through screening. Central Composite Design (CCD) in response surface methodology has been utilized as the experimental design technique with twenty experiments. Analysis of variance has been employed to examine the momentous machining parameters and responses. A mathematical model has been developed to optimize the surface roughness and material removal rate. It has been observed that the most significant factor for Ra is feed rate while for MRR depth of cut is the most significant factor. The results show that the minimum value of Ra ~ 0.098 μm is achieved at speed ~ 1000 RPM, feed rate ~ 300 mm/min and depth of cut ~ 0.2 mm while the maximum value of MRR ~ 6.35 cm3/min is attained at feed rate ~ 500mm/min and depth of cut ~ 0.4 mm regarding less or no effect of speed ~ 500-1000 RPM. The average forecast error for the validation information has been observed to be 3.35%. for Ra and 3.2% for MRR. Further, it is investigated that good surface finish like grinding and dimensional accuracy can be achieved with coated carbide tools.

Parametric Analysis and Optimization of Rotary Ultrasonic Machining of Zirconia (ZrO2) Ceramics

Micro-channels are considered as the essential part of several medical applications such as microfluidics devices, lab on a chip, microbiology, etc. In most applications, fluid flow is required to pass through certain microchannels. The fluid flow characteristics such as flow rate and fluid dynamics are mainly accomplished based on the surface quality and dimensional accuracy of the microchannels. In this study, the microchannels are fabricated on zirconium oxide (ZrO2) using rotary ultrasonic machining (RUM). A full factorial design of experiments is employed in order to detect the influences of key input parameters of RUM including cutting speed (S), feed rate (FR), depth of cut (DOC), frequency (F) and amplitude (A) on surface roughness (Ra), edge chipping (EC), depth error (DE) and width error (WE) of the milled microchannels. Multi-objective genetic algorithm (MOGA) was employed to determine the optimal parametric conditions for minimizing the values of Ra, EC, DE, and WE of the fabricated microchannels. Results revealed that the minimum value of Ra = 0.26 μm, EC = 10.1 μm, DE = 4.2% and WE = 7.2% can be accomplished through the multi-objective optimization at higher levels of frequency and amplitude and lower levels of feed rate, depth of cut and cutting speed.

Optimization of wood machining parameters in CNC routers: Taguchi orthogonal array based simulated angling algorithm

In the present study, two mathematical models were developed to optimize the surface roughness for machining condition of Cedar of Lebanon pine (Cedrus libani). Taguchi approach was applied to examine the effect of CNC processing variables. Quality characteristics parameters were selected as arithmetic average roughness (Ra) and average maximum height of the profile (Rz) for wood material. Analysis of variance (ANOVA) was used to determine effective machining parameters. Developed mathematical models using response surface methodology (RSM) were optimized by a combined approach of the Taguchi’s L27 orthogonal array based simulated angling algorithm (SA). Optimum machining levels for determining the minimum surface roughness values were carried out three stages. Firstly, the desirability function wasused to optimize the mathematical models. Secondly, the results obtained from the desirability function were selected as the initial point for the simulated angling algorithm. Finally, the optimum parameter values were obtained by using simulated angling algorithm. Minimum Ra value was obtained spindle speed of 17377 rpm, feed rate of 2.012 m/min, tool radius of 8 mm and depth of cut of 2.009 mm by using desirability function based simulated angling algorithm. For Rz these results were found as 16980 rpm, 2.004 m/min, 8.001mm and 2.003 mm. The R-square values of the Ra and Rz were 95.91 % and 96.12 %, respectively. The proposed models obtained the minimum surface roughness values and provided better results than the observed values.

Experimental evaluation of surface topographies of NMQL grinding ZrO2 ceramics combining multiangle ultrasonic vibration

Nanofluid minimum quantity lubrication (NMQL) technique has many technological and economic advantages in grinding operation. NMQL can improve grinding performance in terms of cooling and lubrication and is ecofriendly because it consumes a small amount of grinding fluid. Ultrasonic machining can improve grinding performance owing to its reciprocating vibration mechanism and furrow widening. Consequently, the simultaneous utilization of these techniques is anticipated to improve the surface quality, especially for hard brittle materials. In this research, multiangle two-dimensional (2D) ultrasonic vibration is utilized in zirconia ceramic grinding. Results reveal that the adhesion and material peeling phenomenon on the workpiece surface is obviously reduced compared with dry grinding without ultrasonic vibration. The synergistic effect of multiangle 2D ultrasonic and NMQL is also studied. With increased angle, the roughness value is found to initially increase (from 45° to 90°) and then decreases (from 90° to 135°). Moreover, the lubricating effect under 90° is the poorest, with the highest Ra and RSm values of 0.703 μm and 0.106 mm, respectively; conversely, the minimum Ra value (0.585 μm) is obtained under 45°, and the lowest RSm value (0.076 mm) is obtained under 135°.

Technological Parameters Forming the Surface Texture in Hyper Productive Surface Plastic Deformation Processing

The hyper productive surface plastic deformation processing technology called as wide burnishing (WB) was developed in Russian Federation. The mechanics of new WB technology is different from the classic SPD technologies (rolling or burnishing). For example applied force during processing of burnishing is 150-300 N, of WB is 2500-5000 N due to condition of process implementation in mass production with limited processing time (3-4 turnovers of workpiece). WB also has a high degree of deformation due to a multiple deformation passes. To determine the optimal WB processing parameters single and double instrumental devices were implemented and tested. Specimens made of steel 40 and high-strength cast iron 75-50-03 were tested. Initial roughness of steel 40 specimen’s surface was Ra = 0.5 microns and high-strength cast iron was Ra = 0.85 microns. Results of surface texture parameters of processed parts such as surface roughness Ra of steel 40 and high-strength cast iron 75-50-03 under varying load values P and number of cycles (the number of workpieces revolutions during the period of burnishing) were acquired. It was established that the minimum Ra value of the processed surface correspond with values of P = 210 N/mm2 for steel 40 and P = 410 N/mm2 for high-strength cast iron 75-50-03 regardless of number of burnishing cycles. Plastic deformation mechanism (processing time and pressure on the surface) influences on the processed surface roughness formation. It is possible to assume that straining state forms at the optimal values of P in terms of achieving a minimum value of Ra in which the reached degree of hardening allows to minimize the height of the microscopic irregularities of the previous grinding processing. In this case there is no plastic flow of the metal surface layer.

Dependence of the Cutting and Polishing Ability of Magnetic-Abrasive Powders on the Form and Structure of the Particles

It is shown that fragmented particles are preferable to spherical particles for magnetic-abrasive finishing. The cutting elements of such powders are microscopic projections that determine the roughness of the finished surfaces. For a given volume of magnetic-abrasive powder, a decrease in the diameter of the particles increases the number of cutting centers. To maximize metal removal over the duration of the polishing operation and shorten the amount of time needed to reach the minimum value of Ra, it is necessary to use progressively finer abrasive powders as Ra decreases during polishing.

Effects of Number of Inserts and Insert Materials on Surface Roughness of Cast-Iron Work Produced by Face Milling

In this work, the effects of two key factors of face milling including the number of inserts and insert material on surface roughness of cast-iron turbine housing work were systematically studied using full factorial designed experiments. Three insert materials including uncoated cemented carbide (TH10), commercial TiAlN/TiN coated cemented carbide (AH120) and tungsten carbo-nitride (WCN) coated cemented carbide were selected while the number of inserts was varied from 1 to 3 in this study. The results showed that both factors were statistically significant and the optimal parameters that yielded minimum Ra-value of 0.495 μm were the commercial TiAlN/TiN coated cemented carbide material (AH120) and three inserts.

Stability of an Initially, Stably Stratified Fluid Subjected to a Step Change in Temperature

The onset of convective instability in an initially quiescent, stably stratified fluid layer between two horizontal plates is analyzed with linear theory. The bottom boundary is heated suddenly from below, subjected to a step change in surface temperature. The critical time t c to mark the onset of Rayleigh-Benard convection is predicted by propagation theory. This theory uses the length scaled by $\sqrt{\alpha_t}$ , where α denotes thermal diffusivity. Under the normal mode analysis the dimensionless disturbance equations are obtained as a function of τ(=αt/d 2) and ζ(=Z/ $\sqrt{\alpha_t}$ ), where d is the fluid layer depth and Z is the vertical distance. The resulting equations are transformed to self-similar ones by using scaling and finally fixing τ as τc under the frame of coordinates τ and ζ. For a given γ, Pr and τc, the minimum value of Ra is obtained from the marginal stability curve. Here γ denotes the temperature ratio to represent the degree of stabilizing effect, Pr is the Prandtl number and Ra is the Rayleigh number. With γ=0, the minimum Ra value approaches the well-known value of 1708 as τc increases. However, it is inversely proportional to τc 3/2 as τc decreases. With increasing γ, the system becomes more stable. It is interesting that in the present system, propagation theory produces the stability criteria to bound the available experimental data over the whole domain of time.