Smooth Machined Surface Research Articles

Adverse effects of sterilization processes on the fundamental topographic properties of modified dental implant surfaces

The employ of sterilization processes are essential to investigate biomaterials aiming for experimental, preclinical, or clinical applications with biological tissues. However, responsive surface properties of biomaterials may be susceptible to sterilization processes, compromising important physio-chemical characteristics. For that reason, this in vitro study aimed to investigate the effects of three different processes for sterilization (humid heat under pressure, UVC-light exposure, and Gamma irradiation) on the major topographical properties of implant surfaces applied to dental bone-anchored implants and/or implant-abutments. Three groups of implant surfaces were developed: a smooth machined surface, a micro-texturized surface, and a hydrophilic micro-texturized surface. The implants were sterilized with three methodologies and characterized regarding surface morphology, elemental surface composition, roughness parameters, wettability characteristics, and compared to the samples as-developed. Surface morphology and roughness parameters were not modified by any of the sterilization processes applied. On the other hand, hydrophilic implants were negatively affected by autoclaving. After package opening, hydrophilic features showed to be sensible to atmospheric air exposition independently of the sterilization process performed. Our findings revealed significant chemical changes on the implant surfaces caused by autoclaving and UVC exposure; additionally, the results showed the importance of selecting an appropriate sterilization method when investigating hydrophilic implants so as not to generate imprecise outcomes.Graphical

Diamond machining of additively manufactured Ti6Al4V ELI: Newer mode of material removal challenging the current simulation tools

Single point diamond machining (SPDM) produces smooth machined surfaces that other production methods cannot match. While the mechanics of machining of cast alloys with SPDM is well-explored, the realm of SPDM for additively manufactured parts remains largely uncharted. This work reveals new insights into the surface generation process of an additively manufactured titanium alloy, specifically, a Ti6Al4V Extra Low Interstitials (ELI) alloy workpiece. Our examination of the chip morphology unveiled a distinct mode of chip removal, previously unrecorded in existing literature. During SPDM of additively made Ti6Al4V ELI workpiece, identification of numerous pores and discontinuities in the chips flowing on the tool rake face, indicating periodic intermittent cracking during the material's plastic flow was seen. To examine this phenomenon, a finite element analysis (FEA) model was developed. While the FEA model can well explain the machining mechanics and chip morphology of SPDM of cast Ti6Al4V ELI reported in the literature, it failed to describe the chip morphology that are obtained during machining of additively made workpiece in this work. This disparity underscores the need for innovative simulation approaches tailored for additively manufactured components. The experimental observations in this study highlight a unique form of chip formation in contrast to conventional Ti6Al4V alloy machining processes. At lower feeds, there was a presence of short, discontinuous chip formation with tearing at the outer periphery. Conversely, at higher feeds, a long, continuous ribbon-like chip formation was observed. In addition, some typical additive manufacturing defects appear on the machined surface and chips. Through optimisation of the SPDT parameters, a surface roughness (Ra) value of about 11.8 nm was achieved on additively manufactured Ti6Al4V ELI workpiece. This work provides a fresh perspective on the mechanics of SPDM for additively manufactured components, offering a stepping stone for subsequent studies.

Study on anisotropic heat transfer and thermal damage in nanosecond pulsed laser processing of CFRP

AbstractNanosecond pulsed laser processing is an efficient method of processing carbon fiber reinforced plastic(CFRP), which is widely used in the manufacturing field of aviation, medical, and auto industries. The anisotropic heat transfer of carbon fiber is a key factor degrading the surface integrity of laser processing CFRP. So it is urgent to explore the significant mechanism of anisotropic heat transfer of laser interacting with CFRP. A novel numerical model considering anisotropic heat transfer was established to analyze heat transfer and thermal damage of CFRP laser machining. By comparison of simulation and experiments, the average error of ablation depth and width ranges from 4.71% to 15.09%, so the model could precisely simulate the CFRP laser machining. It demonstrates that the heat conductivity along the axial carbon fiber is higher than that along the radial, resulting in an elliptical ablation morphology. And when the laser scanning direction is parallel to the direction of the carbon fiber, deeper and narrower microgrooves can be obtained. In addition, laser processing at the edge of the CFRP plate causes serious heat accumulation, leading to severe thermal damage. The simulation and experiments were conducted to explore the effect of parameters including laser energy, scanning speed, and scanning space on the depth and width of laser ablation. A deeper micro‐channel with a smooth machined surface and small thermal damage was obtained when laser energy E = 0.275 mJ, scanning speed v = 630 mm/s, and scanning space h = 21 μm.

Experimental study on the quality of drilled holes in Sabai grass reinforced composites

Hole quality in composites plays very important role in the production of close tolerance holes in automobile parts. Through drilling experiments in Sabai Yarn reinforced composite, this study examines the impact of different input parameters like feed rate, rpm, and tool diameter. The circularity of hole was measured with the help of CMM. The circularity error was reported in the range of 0.037 to 0.1628 mm. Design of experiments and Taguchi method have been used to study the effect of process parameters. The circularity of hole mainly depends on feed rate and rpm in the drilling process of Sabai yarn composite. The circularity error and delamination are minimum in treated reinforcement in yarn (0°) and woven yarn (0°/90°) compared to the untreated reinforcement yarn (0°) and woven yarn (0°/90°). Due to strong bound strength fibres cannot pull-out its cut with tool edge so that it gives smooth machined surface in treated reinforcement. The chip formation in drilling depends on the feed rate and tool diameter. Chips are discontinuous at the higher feed rate and higher rpm.

Abrasive slurry jet machining system using polyurethane@silica core-shell particles for internal surfaces of axisymmetric x-ray mirrors.

Abrasive machining has been used for inner surface processing of various hollow components. In this study, we applied an in-air fluid jet as a precision machining method for the inner surface of an axisymmetric x-ray mirror whose inner diameter was less than 10mm. We employed an abrasive with a polyurethane@silica core-shell structure, which has a low density of about 1.2 g/cm3 and a relatively large particle size of about 15 µm. By using this abrasive, a practical removal rate and a smooth machined surface were simultaneously obtained. We performed figure corrections for an axisymmetric mirror and improved the circumferential figure accuracy to a sub-10nm root mean square level. To evaluate the machining performance in the longitudinal direction of the ellipsoidal surface, we also performed periodic figure fabrication on the inner surface of a 114 mm-long nickel ellipsoidal mirror. X-ray ptychography, an optical phase retrieval method, was also employed as a three-dimensional figure measurement technique of the mirror. The wavefield of the x-ray beam focused by the processed ellipsoidal mirror was observed with the ptychographic system at SPring-8, a synchrotron radiation facility. The retrieval calculations for the wavefront error confirmed that a sinusoidal waveform with a period of 12mm was fabricated on the mirror surface. These experimental results suggest that a nanoscale figure fabrication cycle for the inner surface consisting of jet machining and wavefront measurement has been successfully constructed. We expect this technique to be utilized in the fabrication of error-free optical mirrors and various parts having hollow shapes.

Ultraviolet Treatment of Titanium to Enhance Adhesion and Retention of Oral Mucosa Connective Tissue and Fibroblasts.

Peri-implantitis is an unsolved but critical problem with dental implants. It is postulated that creating a seal of gingival soft tissue around the implant neck is key to preventing peri-implantitis. The objective of this study was to determine the effect of UV surface treatment of titanium disks on the adhesion strength and retention time of oral connective tissues as well as on the adherence of mucosal fibroblasts. Titanium disks with a smooth machined surface were prepared and treated with UV light for 15 min. Keratinized mucosal tissue sections (3 × 3 mm) from rat palates were incubated for 24 h on the titanium disks. The adhered tissue sections were then mechanically detached by agitating the culture dishes. The tissue sections remained adherent for significantly longer (15.5 h) on the UV-treated disks than on the untreated control disks (7.5 h). A total of 94% of the tissue sections were adherent for 5 h or longer on the UV-treated disks, whereas only 50% of the sections remained on the control disks for 5 h. The adhesion strength of the tissue sections to the titanium disks, as measured by tensile testing, was six times greater after UV treatment. In the culture studies, mucosal fibroblasts extracted from rat palates were attached to titanium disks by incubating for 24, 48, or 96 h. The number of attached cells was consistently 15–30% greater on the UV-treated disks than on the control disks. The cells were then subjected to mechanical or chemical (trypsinization) detachment. After mechanical detachment, the residual cell rates on the UV-treated surfaces after 24 and 48 h of incubation were 35% and 25% higher, respectively, than those on the control surfaces. The remaining rate after chemical detachment was 74% on the control surface and 88% on the UV-treated surface for the cells cultured for 48 h. These trends were also confirmed in mouse embryonic fibroblasts, with an intense expression of vinculin, a focal adhesion protein, on the UV-treated disks even after detachment. The UV-treated titanium was superhydrophilic, whereas the control titanium was hydrophobic. X-ray photoelectron spectroscopy (XPS) chemical analysis revealed that the amount of carbon at the surface was significantly reduced after UV treatment, while the amount of TiOH molecules was increased. These ex vivo and in vitro results indicate that the UV treatment of titanium increases the adhesion and retention of oral mucosa connective tissue as a result of increased resistance of constituent fibroblasts against exogenous detachment, both mechanically and chemically, as well as UV-induced physicochemical changes of the titanium surface.

A study on strengthening and machining integrated ultrasonic peening drilling of Ti-6Al-4V

In aircraft assembly filed, introducing compressive residual stress by cold expansion around the fastening hole is considered as a common method to enhance hole fatigue resistance. However, the conventional cold expansion technology inevitably extends the processing cycle of fastening hole. Therefore, this study proposes a strengthening and machining integrated ultrasonic peening drilling (UPD) to solve this problem by introducing ultrasonic vibration perpendicular to the hole surface during drilling. Both the strengthening principle and dimension accuracy improvement mechanism in UPD were analyzed to better understand the cutting mechanism. The feasibility experiments of UPD of Ti-6Al-4V were conducted to evaluate surface integrity and machining accuracy. The results show that compared to conventional drilling (CD), smoother machined surface and narrower dimensional tolerance were obtained with UPD. Moreover, the subsurface plastic deformation was increased by as high as 4 times with severer deformation degree. Accordingly, the surface residual stress and the depth of circumferential residual stress in the subsurface was increased by 115.7% and 125% respectively. In addition, surface micro-hardness and subsurface hardening layer depth were also significantly increased. The results demonstrated that UPD achieved the integration of strengthening and precision-machining and could be a promising method for finish drilling of aircraft fastening holes.

A new optimized predictive model based on political optimizer for eco-friendly MQL-turning of AISI 4340 alloy with nano-lubricants

Metal cutting using flood cooling has serious impacts on the environment and operator health. Therefore, the minimum quantity lubricant (MQL) technique has been proposed as a promising alternative to the conventional flood cooling technique. Replacing mineral oils by eco-friendly vegetable oils gives another environmental advantage to MQL metal cutting. In this study, two types of nanoparticles (Al 2 O 3 and CuO) are added to rice bran vegetable oil to obtain eco-friendly nanofluid with enhanced thermophysical properties, which utilized as a cutting fluid in the so-called MQL-turning with nano-lubricants (MQL-TNL). The experimental plan was designed according to Taguchi L 16 method. The effects of the main cutting parameters such as cutting speed, cutting depth, and feed on the cutting force, surface roughness, tool wear are investigated. Among all cutting parameters, cutting speed has the highest effect on all process responses. The use of CuO/oil nanofluid as a cutting fluid produces smooth machined surfaces with little tool wear compared with that of Al 2 O 3 /oil nanofluid. Moreover, an improved random vector functional link (RVFL) model trained using experimental results is utilized to predict the responses of the cutting process. The accuracy of the model is enhanced via incorporation with a metaheuristic optimization algorithm called political optimizer (PO), which used to obtain the optimal RVFL parameters. The predicted results obtained by the developed RVFL-PO model are compared with the experimental ones as well as those obtained by standalone RVFL and hybrid RVFL-PSO (particle swarm optimization). The accuracy of the three models is assessed using various statistical measures. The RVFL-PO shows the best accuracy among others. The lowest coefficient of determination of the predicted results for all investigated cases was 0.768, 0.844, and 0.961 for RVFL, RVFL-PSO, and RVFL-PO, respectively.

Assessment of implant surface and instrument insert changes due to instrumentation with different tips for ultrasonic-driven debridement

BackgroundTo assess the changes of implant surfaces of different roughness after instrumentation with ultrasonic-driven scaler tips of different materials.MethodsExperiments were performed on two moderately rough surfaces (I—Inicell® and II—SLA®), one surface without pre-treatment (III) and one smooth machined surface (IV). Scaler tips made of steel (A), PEEK (B), titanium (C), carbon (D) and resin (E) were used for instrumentation with a standardized pressure of 100 g for ten seconds and under continuous automatic motion. Each combination of scaler tip and implant surface was performed three times on 8 titanium discs. After instrumentation roughness was assessed by profilometry, morphological changes were assessed by scanning electron microscopy, and element distribution on the utmost surface by energy dispersive X-ray spectroscopy.ResultsThe surface roughness of discs I and II were significantly reduced by instrumentation with all tips except E. For disc III and IV roughness was enhanced by tip A and C and, only for IV, by tip D. Instrumentation with tips B, D and E left extensive residuals on surface I, II and III. The element analysis of these deposits proved consistent with the elemental composition of the respective tip materials.ConclusionAll ultrasonic instruments led to microscopic alterations of all types of implants surfaces assessed in the present study. The least change of implant surfaces might result from resin or carbon tips on machined surfaces.

Underwater Laser Turning of Commercially-Pure Titanium

Underwater laser machining process is a material removal technique that can minimize thermal damage and offer a higher machining rate than the laser ablation in ambient air. This study applied the underwater method associated with a nanosecond pulse laser for turning a commercially pure titanium rod. The effects of laser power, surface speed and number of laser passes on machined depth and surface roughness were investigated in this work. The results revealed that a deeper cut depth and smoother machined surface than those obtained from the laser ablation in ambient air were achievable when the underwater laser turning process was applied. The machined depth and surface roughness were found to significantly increase with the laser power and number of laser passes. The findings of this study can disclose the insight as well as potential of the underwater laser turning process for titanium and other similar metals.

Reducing overcut in electrochemical micromachining process by altering the energy of voltage pulse using sinusoidal and triangular waveform

In electrochemical micromachining (ECMM), improved material dissolution localization and generation of the smooth machined surface under pulsed voltage condition is attributed to the fact that short pulse-duration time results in the generation of relatively less volume of dissolution products. The intermittent supply of voltage provides idle time to flush the hydrogen bubbles and sludge from the machining zone and, also increases control over the dissolution process. From the last few decades, various studies have been carried out to analyze the effect of short pulse voltage to ultra-short pulsed (rectangular) voltage. Development of such a sophisticated system capable of supplying ultra-high frequency voltage pulses is challenging, cost in-effective and complex. Also, the compromising ways of reducing the pulse energy by reducing the duty cycle and increasing the pulse frequency impose increased voltage requirement and idle time while machining. In this study, an approach of reducing pulse energy per unit time by changing the waveform of the voltage pulse (while keeping the pulse-duration time the same) for reducing the overcut is presented. A theoretical model is developed first to quantify the input energy per pulse for rectangular, sinusoidal, and triangular voltage pulses. This ensured that by changing the shape of voltage pulses of same on-time, the energy input per pulse can be further altered. A function generator based pulsed power supply is then developed with the capability of generating rectified voltage pulses of different waveforms. The process of ECMM for generating micro dimples on a flat surface is modeled in two dimensions using finite element method in MATLAB (R2018b). Three numerical models for sinusoidal, rectangular and triangular voltage pulses are developed for predicting the current density and anode shape. Simulation results demonstrated that triangular voltage pulse yields minimum diameter of micro-dimple as compared to sinusoidal and rectangular pulse respectively. Results from the developed model are also validated using experimental observations and a good correlation between the two was observed (with an average deviation of 18%).

Enhanced Surface Properties and Microstructure Evolution of Cr12MoV Using Ultrasonic Surface Rolling Process Combined with Deep Cryogenic Treatment

In this study, the enhanced surface properties and microstructure evolution of quenched and tempered cold work die steel Cr12MoV, which were induced by ultrasonic surface rolling process combined with deep cryogenic treatment (UDCT), were systematically investigated. The results indicated that UDCT had an advantage over conventional ultrasonic surface rolling process (USRP) in improving surface mechanical properties, including smaller surface roughness and smoother machined surface with less cracks and defects; higher surface microindentation hardness with the value of ~ 890 HV (increased by ~ 6.2% compared with USRP); and lower friction coefficient. Such enhancements in surface properties are mainly attributed to the martensitic transformation of retained austenite, the dispersion strengthening of small secondary carbides and the homogenized carbides distribution during UDCT.

Experiment and analytical model of laser milling process in soluble oil

The liquid-assisted laser machining process is a promising method to cut materials with minimum thermal damage caused by laser, and water is typically used in the process due to its high thermal conductivity, nontoxicity, and relatively low price. However, water can intrinsically oxidize ferrous metals and in turn deteriorate the workpiece through corrosion during laser ablation in water. This study has for the first time proposed laser ablation in soluble oil to effectively cut the ferrous metals by using laser in a high cooling rate and low potentiality of corrosion to the metals. A nanosecond pulse laser was used to scan over the AISI H13 steel sheet to create a square cavity, while the workpiece surface was covered by a thin and flowing soluble oil film throughout the laser milling process. The effects of laser scan overlap, traverse speed, and liquid flow rate on cavity dimensions and milled surface morphology were experimentally examined. The results revealed that a clean and uniform cavity with a smooth machined surface can be attained by using 70% scan overlap, 6 mm/s traverse speed, and 3.9 cm3/s soluble oil flow rate. Furthermore, analytical models based on heat transfer equations were formulated to predict the cavity profile and cooling of molten droplets in flowing liquid. The predicted profile was found to correspond well to the experiment, and the calculated temperature of cut particles can endorse the experimental findings on debris deposition and recast formation. The implications of this study could bring a new technological approach for damage-free fabrication and fine-scale manufacturing.

Comparative study between wear of uncoated and TiAlN-coated carbide tools in milling of Ti6Al4V

As is recognized widely, tool wear is a major problem in the machining of difficult-to-cut titanium alloys. Therefore, it is of significant interest and importance to understand and determine quantitatively and qualitatively tool wear evolution and the underlying wear mechanisms. The main aim of this paper is to investigate and analyse wear, wear mechanisms and surface and chip generation of uncoated and TiAlN-coated carbide tools in a dry milling of Ti6Al4V alloys. The quantitative flank wear and roughness were measured and recorded. Optical and scanning electron microscopy (SEM) observations of the tool cutting edge, machined surface and chips were conducted. The results show that the TiAlN-coated tool exhibits an approximately 44% longer tool life than the uncoated tool at a cutting distance of 16 m. A more regular progressive abrasion between the flank face of the tool and the workpiece is found to be the underlying wear mechanism. The TiAlN-coated tool generates a smooth machined surface with 31% lower roughness than the uncoated tool. As is expected, both tools generate serrated chips. However, the burnt chips with blue color are noticed for the uncoated tool as the cutting continues further. The results are shown to be consistent with observation of other researchers, and further imply that coated tools with appropriate combinations of cutting parameters would be able to increase the tool life in cutting of titanium alloys.

Precise micromachining of yttria-tetragonal zirconia polycrystal ceramic using 532 nm nanosecond laser

High quality micro-sized steps and blind hole structures without microcracks, chips or spatter deposition were machined on yttria-tetragonal zirconia polycrystal (Y-TZP, 3mol% yttria) by nanosecond laser (wavelength=532nm, pulse width ~6ns). The diameter of blind hole is 500μm and each step is 500±10μm wide and 100±5μm deep. The 1.35mm3/min removal rate and the smooth machined surface with Ra=2.824μm roughness depicting the high precise and efficient processing were achieved. The ablation characteristics of nanosecond laser process of Y-TZP ceramic were also studied. Based on the study, a reasonable design of the processing path for micromachining of a finer embedded step with 24±2μm width (smaller than the 60μm focused spot size) around the inner-wall of a 2×2mm2 cavity was developed. These results and discussion offer new possibilities in the manufacturing of bio-ceramic products by nanosecond laser with high processing quality and efficient.

The Experiment Investigation of the Tool Wear in Diamond Ultra-Precision Cutting of Aluminum Alloy Mirror

Due to its relatively low mass density, low cost, high strength, the aluminum alloy is an ideal optical material to fabricate the large metal mirror of infrared band optical systems. The diamond ultra-precision cutting can produce ultra smooth machined surfaces without other finishing processes. Consequently, it can be used as a effective method to fabricate the large metal mirror. However, the tool wear is severe during the ultra-precision processes, which will ruduces the surface error of the large metal mirror. In this work, the ultra-precision cutting tests were performed to investigate the tool wear. The tool wear was examined by using a scanning electron microscope (SEM), and the chip was examined by using x-ray energy dispersive spectrdmeter (EDS). The tool wear mechanism and the influence of the chutting parameters on the tool wear were investigated. The results show that the daimond tool occurred abrasive wear and diffusing wear in the diamond ultra-precision cutting of aluminum alloy. The average clearance wear width increases with an increase of the cutting speed and the feed rate. There is a slight rise in the average clearance wear width as the depth of the cut increases in the range of 5μm-15μm. The average clearance wear width obviously increases when the depth of the cut reaches to 20μm.

High-precision micro-through-hole array in quartz glass machined by infrared picosecond laser

Circle and triangle micro-through-hole arrays without cracks, chips, and debris were machined in 0.3-mm-thick quartz glass by picosecond laser (wavelength = 1064 nm, pulse width ~12 ps) in air ambient. The diameter of each circle through-hole was 550 μm, and the side length of each triangle hole is 500 μm; 30 μm spacing between the adjacent hole edges and the smooth machined surface with R a = 0.8 μm roughness depicted the high precision of the high-density micro-through-hole arrays. The fundamental properties of the ps laser processing of quartz glass were investigated. The laser ablation threshold fluence of the quartz glass was determined as 3.49 J/cm2. Based on the fundamental investigation, a quantitative design of the cutting path for micro-machining of the through-holes with various geometries in quartz glass was developed. The work presents a more practical ps laser micro-machining technique for micro-through-hole arrays in glass-like materials for industrial application due to the precise quality, flexibility in geometries, ease of manipulation, and large-scale application.

Multi Objective Optimization of Cutting Parameters in Machining Cellulose Based Hybrid Composites

Cellulose based hybrid composites are gaining popularity in the growing green communities. With extensive studies and increasing applications for future advancement, the need for an accurate and reliable guidance in machining this type of composites has increased enormously. Smooth and defect free machined surface are always the ultimate objectives. The present work deals with the study of machining parameters (i.e. spindle speed, feed rate and depth of cut) and their effects on machining performance (i.e. surface roughness and delamination) to establish an optimized setup of machining parameters in achieving multi objective machining performance. Cellulose based hybrid composites consist of jute (a bast fiber) and glass fiber embedded in polyester resins. Response Surface Methodology (RSM) using Box-Behnken Design (BBD) was chosen as the design of experiment approach for this study. Based on that experimental approach, 17 experimental runs were conducted. Mathematical model for each response was developed based on the experimental data. Adequacy of the models were analyzed statistically using Analysis of Variance (ANOVA) in determining the significant input variables and possible interactions. The multi objective optimization was performed through numerical optimization, and the predicted results were validated. The agreement between the experimental and selected solution was found to be strong, between 95% to 96%, thus validating the solution as the optimal machining condition. The findings suggest that feed rate was the main factor affecting surface roughness and delamination .

SURFACE ROUGHNESS AND ROUNDNESS ERROR PREDICTION MODELS IN TURNING LOW CARBON STEEL

Cutting tests were conducted to longitudinally turn low carbon steel using HSS tools with cutting fluid. The experimental design used was based on response surface methodology (RSM) using a central composite rotatable (CCD) design. The primary cutting tests confirmed the use of proper specimen design with length to diameter ratio (L/D) of 2 in the subsequent cutting tests of this research. Further cutting tests were carried out to turn low carbon steel with L/D=2 to determine the effect of using different cutting conditions on the surface roughness and roundness error (out of roundness) of the machined surfaces. At the end of each cutting test, the surface roughness and roundness error measurements were taken and analyzed using “DESIGN EXPERT 8” experimental design software. Mathematical models of responses (surface roughness and roundness error) as functions of the conditions (cutting speed, feed, and depth of cut) were obtained and studied. A quadratic predicted model for surface roughness showed that the feed, cutting speed and their squares and interactions were more effective than the depth of cut because of its little influence on the surface roughness. Also, the resultant two-factor interaction (2FI) model for roundness error exhibited that cutting speed, feed and the interaction of feed and speed were significant parameters, while the depth of cut had no effect. The predicted models indicated that at higher cutting speed and various feed levels, both responses decreased, resulting in a smooth machined surface with lower roundness error. But, both models exhibited that at lower cutting speed and higher feeds, the surface roughness and roundness error increased, producing a rough machined surface with higher out of roundness error.

A new method for fabricating zirconia copings using a Nd:YVO4 nanosecond laser.

The purpose of this work was to fabricate zirconia copings from fully sintered Y-TZP blocks using a Nd:YVO4 nanosecond laser in order to avoid complicated procedures using conventional CAD/CAM systems. To determine the most appropriate power level of a Nd:YVO4 laser, cuboid fully sintered Y-TZP specimens were irradiated at six different average power levels. One-way ANOVAs for the average surface roughness and laser machining depth revealed that an average power level of 7.5 W generated a smooth machined surface with high machining efficiency. Y-TZP copings were then machined using the proposed method with the most appropriate power level. As the number of machining iterations increased, the convergence angles decreased significantly (p<0.01). The accuracy of the machined copings was judged to be good based on 3D measurements and traditional metal die methods. The proposed method using the nanosecond laser was demonstrated to be useful for fabricating copings from fully sintered Y-TZP.