Good Dimensional Accuracy Research Articles

Effect of Melt and Mold Temperature on Fiber Orientation during Flow in Injection Molding of Reinforced Plastics

Abstract Injection molding, a highly productive manufacturing process, is one of the most versatile production methods in plastic manufacturing industry. It is capable of producing intricate net shapes without requiring finishing treatment and with good dimensional accuracy. In injection molding of reinforced thermoplastics the properties of the final product highly depend on the state of fiber orientation. Tailoring the fiber orientation in the final product, in order to control the properties, is the basic motivation of this study. Among different parameters, which could affect the orientation patterns, this study is concerned on analyzing the effects of mold and melt temperature on the state of fiber orientation during flow. In contrast to the melt temperature, which has a limited range for variation, mold temperature provides wide range of possible input at different locations such that by revealing its effect it could become one of the most attractive parameters in controlling the properties of injection molded fiber reinforced thermoplastic products.

Electrochemical Deposition of Pure-Nickel Microstructures with Controllable Size.

Pure nickel microstructures have been widely used in MEMS and have great application potential as a sacrificial mandrel for fabricating terahertz micro-cavity components. The performance of MEMS and terahertz micro-cavity components can be significantly improved through the use of high-quality pure nickel microstructures. Up to now, microfabrication techniques, such as laser micromachining, wire electrical-discharge machining, and cold-spray additive manufacturing, have been used to machine various types of such microstructures. However, huge challenges are involved in using these micromachining techniques to fabricate pure-nickel microstructures with controllable size and good dimensional accuracy, surface roughness, and edge radius. In this paper, taking the example of a pure-nickel rectangular mandrel that corresponds to the size of the end face of a 1.7-THz rectangular waveguide cavity, the machining processes for the electrochemical deposition of pure-nickel microstructures with controllable size, high dimensional accuracy, and good surface roughness and edge radius are discussed systematically. This proposed method can be used to manufacture various types of high-quality pure-nickel microstructures.

Parametric Optimization for Quality of Electric Discharge Machined Profile by Using Multi-Shape Electrode.

The electrical discharge machining (EDM) process is one of the most efficient non-conventional precise material removal processes. It is a smart process used to intricately shape hard metals by creating spark erosion in electroconductive materials. Sparking occurs in the gap between the tool and workpiece. This erosion removes the material from the workpiece by melting and vaporizing the metal in the presence of dielectric fluid. In recent years, EDM has evolved widely on the basis of its electrical and non-electrical parameters. Recent research has sought to investigate the optimal machining parameters for EDM in order to make intricate shapes with greater accuracy and better finishes. Every method employed in the EDM process has intended to enhance the capability of machining performance by adopting better working conditions and developing techniques to machine new materials with more refinement. This new research aims to optimize EDM’s electrical parameters on the basis of multi-shaped electrodes in order to obtain a good surface finish and high dimensional accuracy and to improve the post-machining hardness in order to improve the overall quality of the machined profile. The optimization of electrical parameters, i.e., spark voltage, current, pulse-on time and depth of cut, has been achieved by conducting the experimentation on die steel D2 with a specifically designed multi-shaped copper electrode. An experimental design is generated using a statistical tool, and actual machining is performed to observe the surface roughness, variations on the surface hardness and dimensional stability. A full factorial design of experiment (DOE) approach has been followed (as there are more than two process parameters) to prepare the samples via EDM. Regression analysis and analysis of variance (ANOVA) for the interpretation and optimization of results has been carried out using Minitab as a statistical tool. The validation of experimental findings with statistical ones confirms the significance of each operating parameter on the output parameters. Hence, the most optimized relationships were found and presented in the current study.

Effects of remelting on the surface morphology, microstructure and mechanical properties of AlSi10Mg alloy fabricated by selective laser melting

Selective laser melting (SLM) is an additive manufacturing technology that uses laser and metal powder to directly manufacture metal parts. The process has good mechanical properties and dimensional accuracy and can be put into use with a simple post-treatment. However, spheroidisation and warpage can easily occur in the forming process, resulting in poor surface quality and high porosity, which are the main limiting factors for the direct application of the parts formed using this technology. Laser remelting is an effective solution to solve these problems. In this research, the microstructure and mechanical properties of AlSi10Mg fabricated by laser remelting using two different scanning strategies were studied, and it was found that both the laser remelting methods can effectively improve the surface quality, reduce the surface roughness (2.3 μm, 4.0 μm) and porosity (0.08%, 0.2%), refine the grains size and improve the hardness. The thermal conductivity and reflectivity of the metal solidification layer are high, the spreading property of molten pool worsens and the width and depth of the molten pool decrease.

Machinability Study on CNC Turning of Stainless Steel 303 with CVD Multi-Layer (TiN/Al2O3/TiCN) Coated Carbide Insert by using Grey-Fuzzy Logic Approach

Manufacturing requires reliable models and methods for the prediction of output performance of machining processes as the demand for highly automated machine tools in the industry has been increased. The prediction of optimal machining conditions for good surface finish and dimensional accuracy plays a very important role in process planning. In the present work, dry turning of austenitic Stainless Steel (SS303) using CVD multi-layer (TiN/Al2O3/TiCN) coated carbide insert has been investigated. Cutting speed, feed rate, and depth of cut have been considered as the input process variables for the dry turning process. Taguchi's L9 orthogonal array has been utilized for designing the experiments. A Grey-Fuzzy logic approach has been employed to investigate the multi-objective optimization of turning process parametric combination to provide minimum Surface Roughness (SR) with the maximum Material Removal Rate (MRR). Analysis of Variance (ANOVA) technique has been employed to identify the most influencing input process variable for achieving minimum SR and maximum MRR. Morphology analysis has been performed on the machined surfaces and the chips generated during the machining processes using a Scanning Electron Microscope (SEM) in order to relate the surface quality with the input factor setting.

Evaluation of the roll elastic deformation and thermal expansion effects on the dimensional precision of flat ring rolling products: A numerical investigation

Ring rolling is a near-net shape forming process that produces ring products with relatively good dimensional accuracy. Two main factors that lower the precision of the final products are the inability to determine the effects of elasticity and the thermal expansion of rolls during the process. This work focuses on the creation and evaluation of suitable finite element models of a ring rolling process based on available experimental data found in literature. Through these numerical models, the elastic and thermal deformations of the rolls were thoroughly studied and the deformation effect on the produced ring was predicted. A difference of a few millimeters was calculated on the outer and inner diameters of the ring as a result of the two effects, which is far greater than the annotation levels of these products. On the other hand, the effects of the tools’ elasticity and thermal expansion of the ring rolling loads were proven negligible. Based on our analysis it was made clear that slight deformation deviations (thermal and elastic deformations) from the targeted values may cause instabilities to the process if the rolls fail to compensate for these deformations. Material combinations seem to influence the process. Regarding final dimensional deviations it can be concluded that thermo-elastic tool deformations are considerable in case of high product precision requirements.

Processing optimization, mechanical properties, corrosion behavior and cytocompatibility of additively manufactured Zn-0.7Li biodegradable metals

Biodegradable Zn-Li alloys exhibit superior mechanical performance and favorable osteogenic capability for load-bearing bone devices. Additive manufacturing (AM) endows freedom for the fabrication of bone implants of personalized structure to satisfy patient-specific needs. In this paper, AM of Zn-Li alloys was attempted for the first-time using laser powder bed fusion (LPBF), and the fabricated samples exhibited good fusion quality and high dimensional accuracy. The processing optimization, mechanical properties, in vitro corrosion behavior and cytocompatibility were investigated by using Zn-0.7Li bulk and porous samples. The ultimate tensile strength and elastic modulus of bulk samples respectively reached 416.5 MPa and 83.3 GPa, and both were the highest among various additively manufactured Zn alloys reported so far. Porous samples achieved compressive strength (18.2 MPa) and elastic modulus (298.0 MPa), which were comparable to those of cancellous bone. Porous samples exhibited a higher corrosion rate and alleviated the problem of slow degradation of Zn-Li alloys. Nevertheless, osteoblastic cells showed a more spreading and healthier morphology when adhering to the porous samples compared to the bulk samples, thus a better cytocompatibility was confirmed. This work shows tremendous potential to precisely design and modulate biodegradable Zn alloys to fulfill clinical needs by using AM technology. Statement of significanceThis paper firstly studied processing optimization during laser powder bed fusion of Zn-Li alloy. Bulk and porous Zn-0.7Li samples in customized design were obtained with high formation quality. The tensile strength of bulk samples reached 416.5 MPa, while the compressive strength and modulus of porous samples reduced to 18.2 MPa and 298.0 MPa, comparable to those of bone. The weight loss of porous samples was roughly 5 times that of bulk samples; osteoblastic cells showed a more spreading and healthier morphology at porous samples, indicating improved biodegradation rate and cytocompatibility. This work shows tremendous potential to precisely design and modulate biodegradable Zn alloy porous scaffolds to fulfill clinical needs by using additive manufacturing technology.

Design, inverted vat photopolymerization 3D printing, and initial characterization of a miniature force sensor for localized in vivo tissue measurements

BackgroundTissue healthiness could be assessed by evaluating its viscoelastic properties through localized contact reaction force measurements to obtain quantitative time history information. To evaluate these properties for hard to reach and confined areas of the human body, miniature force sensors with size constraints and appropriate load capabilities are needed. This research article reports on the design, fabrication, integration, characterization, and in vivo experimentation of a uniaxial miniature force sensor on a human forearm.MethodsThe strain gauge based sensor components were designed to meet dimensional constraints (diameter ≤3.5mm), safety factor (≥3) and performance specifications (maximum applied load, resolution, sensitivity, and accuracy). The sensing element was fabricated using traditional machining. Inverted vat photopolymerization technology was used to prototype complex components on a Form3 printer; micro-component orientation for fabrication challenges were overcome through experimentation. The sensor performance was characterized using dead weights and a LabVIEW based custom developed data acquisition system. The operational performance was evaluated by in vivo measurements on a human forearm; the relaxation data were used to calculate the Voigt model viscoelastic coefficient.ResultsThe three dimensional (3D) printed components exhibited good dimensional accuracy (maximum deviation of 183μm). The assembled sensor exhibited linear behavior (regression coefficient of R2=0.999) and met desired performance specifications of 3.4 safety factor, 1.2N load capacity, 18mN resolution, and 3.13% accuracy. The in vivo experimentally obtained relaxation data were analyzed using the Voigt model yielding a viscoelastic coefficient τ=12.38sec and a curve-fit regression coefficient of R2=0.992.ConclusionsThis research presented the successful design, use of 3D printing for component fabrication, integration, characterization, and analysis of initial in vivo collected measurements with excellent performance for a miniature force sensor for the assessment of tissue viscoelastic properties. Through this research certain limitations were identified, however the initial sensor performance was promising and encouraging to continue the work to improve the sensor. This micro-force sensor could be used to obtain tissue quantitative data to assess tissue healthiness for medical care over extended time periods.

Fabrication and Automation of Drilling Machine by Using Arduino

For precision workpiece manufacturing, the system should have good dimensional accuracy and surface finish. In applications such as drilling, punching, marking, boring, tapping, etc., the workpiece is first positioned, and then the tool executes its action while the moving axis remains stationary. In the traditional method of such applications, manufacturers use very expensive CNC machines to program the cycle and perform the same work. Large manufacturers can afford such expensive machines, but for the small machinery manufacturing industry, we must consider low-cost solutions that can provide high-quality output. In this study, we tried to propose a low-cost design that can be used to achieve functions similar to CNC. By applying this machine in industry, multiple generations can be obtained in a short time. It is very difficult to estimate the drilling depth when manually drilling with a traditional drilling machine, and the work will usually fail due to over-drilling. In many cases, it is difficult to measure the depth after the drilling is completed; especially the depth of the fine hole cannot be measured. Therefore, an automatic drilling machine that performs the drilling function according to the generated drilling depth and transmitted to the control circuit is indispensable; therefore, undertaking the study, it exposed the technology of the dedicated drilling machine. The automatic drilling machine designed here is very useful for the mechanical workshop. The machine is built with power feed technology and is designed to drill the job to a certain specified depth.

Modeling and analysis of surface roughness in fused deposition modeling based on infill patterns

This paper presents an approach of modeling for surface roughness of Polylactic Acid (PLA) polymer components printed with Fused Deposition Modeling (FDM) based Additive Manufacturing (AM) process. With additive manufacturing technology one can build the components of metal, polymers and variety of composites with good dimensional accuracy. FDM is one of the additive manufacturing process which is used to build products of various polymers. In this investigation PLA components are built using FDM with different Infill Patterns viz. Zigzag, Triangles and Gyroid. Based on surface roughness measurement of components, predictive mathematical models for surface roughness are generated for different infill patterns. The analysis of surface roughness based on layer thickness and infill pattern is presented. The error between predictive surface roughness and experimental surface roughness ranges between 0.1 to 9.5%. For this investigation Gyroid infill pattern shows favourable results for surface roughness. The workable ranges for process parameter under investigation are infill percentage of 70 to 90 %, layer thickness of 0.2 to 0.22 mm and printing speed of 70 to 90 mm/s.

Optimization of machining parameters in drilling of LM6/B4C/Fly ash hybrid composites

Metal matrix composites (MMCs), innovative replacements for traditional materials, are currently achieving a growing trend in engineering and research for operations like aviation, nuclear power, and automotive. Machining of MMCs makes it challenging to get good dimensional accuracy, surface finish and lower tool wear. Drilling is a necessary and immensely useful tool for component assembly in the manufacturing sector. As a result, optimization of drilling process variables is unavoidable. The fundamental purpose of this study is to use the stir casting technique to manufacture LM6/B4C/Fly ash composites with 3, 6 and 9 wt.% of second phase materials. Taguchi's design of experiments strategy was used to drill with three levels of feed rate (F), spindle speed (S), drill material (D) and percentage of reinforcement (R) as input process parameters. Optimization of drilling variables for attaining lower surface roughness (SR) and burr height (BH) using single objective approach. The optimum process variable achieved for surface roughness is F1S3D3R2, i.e., 50 mm/min, 3000 rpm, TiN-coated drill bit and 6 wt.% of reinforcements (B4C and Fly-ash) and for burr height is F1S3D3R3, i.e., 50 mm/min, 3000 rpm, TiN-coated drill bit and 9 wt.% of reinforcements.

Multi objective optimization of 3D printing process using multi-attribute decision making methods

Fused deposition modeling (FDM) is one of the additive manufacturing (AM) methods widely used in many divisions, especially medical implants and aerospace, due to capabilities to build complex 3D objects and geometries. However, quality and dimensional accuracy of the FDM parts are significantly influenced by the various FDM process parameters including filament wire material. In the present work, new filament wire material Thermoplastic Polyurethane (TPU) was utilized to produce FDM parts. Hence, deciding the optimum process parameters is very critical to produce the FDM parts with good surface quality (Ra) and dimensional accuracy (Δd) concurrently using TPU material. In this paper, the author has contributed to determine the optimum 3D printing process parameters to improve the quality and accuracy for the new filament wire material Thermoplastic Polyurethane (TPU) using multi-attribute decision making (MADM) methods namely Gray Relational Analysis (GRA) and technique for order preference by similarity to ideal solution (TOPSIS). Further, the results of GRA and TOPSIS techniques were compared and concluded that TOPSIS method substantially reduced the surface roughness to a value of 12% contrast to the GRA method whereas the dimensional deviation accuracy increased to 6.25% over the GRA method.

Study and Design of Arduino Based CNC Laser Cutting Machine

For precise job manufacturing, system should possess good dimensional accuracy and surface finish. In applications like drilling, punching, marking, boring, tapping work piece is positioned firstly and then cutting tool performs its action while motion axes are kept stationary. In traditional approach for such applications, manufacturer uses highly expensive CNC machine for programming job cycle and executing the same. Big scale manufacturer can afford such highly expensive machines but for small scale mechanical job manufacturing industry we have to think of low-cost solution that can deliver high class output. In this project we are trying to propose low-cost design which gives similar functionality as that of high-cost CNC machine. By applying this machine in industry, it can acquire the multi generation brief time. In order to perform some operation which requires continuous cutting over a pre-defined curve, CNC machines are used as the traditional machines in the industry. Installation of a CNC machine requires a high financial investment and a skilled labour to perform the different operations on the machine. Apart from that the maintenance cost of such machine are also high. In small scale industries where the operations are performed on small job pieces, the installation of such high-cost CNC machine is very difficult; hence this project work is taken up in which a low-cost CNC laser cutting machine is designed using the Arduino. This CNC laser cutting machine will be quite useful for small scale industries where the job size is not very large. Also, the machine does not require a highly skilled labour to perform operations.

Effect of process parameters during electric discharge machining of maraging steel and optimization using Taguchi-DEAR method

Purpose The electric discharge machining (EDM) involves electrons discharged from the electrode and machining progresses due to the removal of the material from the component. This a thermal-based machining process primarily used for hard to machine components with conventional methods. This process is used to make intricate cavities and contours. The fabricated part is the replica of the tool material with high surface finish and good dimensional accuracy. This study aims to evaluate the comprehensive effect of process parameters on electric discharge machining of maraging steel. Design/methodology/approach Multiple criteria Decision making (MCDM) techniques are used to select the best parameters by comparing several responses to achieve the desired goal. There are different MCDM techniques available for optimization of machining parameters. In the current investigation, multi-objective optimization by data envelopment analysis based ranking (DEAR) approach was used for machining Maraging C300 grade steel. Findings The Taguchi L9 runs were planned with process parameters such as current (Amp), Tool diameter (mm) and Dielectric pressure (MPa). The effect of process parameters on the responses, namely, material removal rate (MRR), tool wear rate (TWR) and surface roughness (SR) were evaluated. High MRR is found at 15 A current, 14 mm tool diameter and dielectric pressure of 0.2 MPa. Optimum process parameters experiment showed reduced crack density. Originality/value An effort was made successfully to enhance the responses using the DEAR method and establish the decision making of selecting the optimal parameters by comparing the results obtained by machining maraging steel C300 grade.

Optimization of process parameters in turning of nuclear graded steel alloy (AISI-410) for sustainable manufacture

Metal cutting operations involve intense heat generation owing to plastic deformation of the work piece and due to friction at the tool-work piece and tool-chip interface. The heat generated in metal cutting unfavourably affects the quality and thus the functional performance of the product. It is known that quality and functional performance is the function of roughness and dimensional accuracy. To maintain a longer component life, along with the robust material choice, a component should have good surface finish and dimensional accuracy. While, for the organization to monitor and control their environmental issues in a holistic manner, emphasis in adopting eco-friendly practices and protecting environment has been growing continuously across all the business sectors. In this study, an attempt is made to optimize the process parameter of stainless steel AISI-410 alloy, a nuclear graded material, for better surface finish. For this, Taguchi L9 orthogonal array was utilise to identify the process parameter and cutting environment. Analysis of variance (ANOVA) was also conducted to highlight the significant parameter that affects the surface finish most. A statistical model to forecast the surface roughness was also developed and was validated by an experiment with a maximum error of 12%. Results indicates that feed rate is the most critical factor that effects the surface roughness with the contribution of 91.5%, followed by environment with 5.22% contribution, cutting speed and depth of cut with 2.7 % and 0.4 % respectively. The correlation coefficient of 0.9213 and conformation tests reveals that developed statistical model predicts surface roughness with the statistical error limit.

LiDAR-based Computational Fluid Dynamics heat transfer models for bushfire conditions

Post-bushfire damage assessments show no significant reduction in property damage when compared with past bushfire events. Other than the severity of the attack and the behaviour of the bushfires, the architectural design of the houses, construction materials and, many other factors affect bushfire house ignition. These are generally ignored in the simulations using simplified models. An improved bushfire risk assessment can be conducted if the exact surrounding and the architectural design of the existing houses are considered. However, this is not widely practised due to associated high cost and time, which can be minimised by the adaptation of modern technologies in an efficient way. This study proposes a novel approach to assess the effect of bushfires on individual building structures (houses) in bushfire-prone areas, through heat transfer modelling. It utilises ground and airborne Light Detection and Ranging (LiDAR) point cloud to model individual building structures with all their complex features and the surroundings with good dimensional accuracy. These point cloud maps were used to develop heat transfer models by using Fire Dynamics Simulator (FDS) to investigate wind velocities, temperature profiles and pressure distributions during bushfires. A case study was conducted for a selected house (elevated building structure) using the proposed approach and the results were compared against a simplified cuboid model of the same house. The simulation results show that the proposed approach is capable of identifying the most vulnerable locations of the building structure compared to the simplified model, which emphasises its applicability in bushfire planning and damage mitigation.

Effect of Process Parameters on the Quality of Laser-Cut Stainless Steel Thin Plates

At present, laser cutting is currently employed to cut metallic plates, due to their good finish and dimensional quality, as well as because of the flexibility of the process to obtain different shapes. In the present paper, surface roughness, dimensional accuracy, and burr thickness of thin plates of 0.8 mm are studied as functions of different process parameters: pulse frequency, pulse width, and speed. Eight different experiments were performed according to a full 23 factorial design, with two replicates each. Square specimens of 10 mm × 10 mm were cut. Arithmetical mean roughness Ra was measured with a contact roughness meter, and the dimensions and burr thickness with a micrometer. Ra values ranged between 1.89 and 3.86 µm, dimensional error values between 0.22 and 0.93%, and burr thickness between 2 and 34 µm. Regression analysis was performed, and linear models were obtained for each response. Results showed that roughness depends mainly on frequency, on the interaction of frequency and pulse width and on pulse width. Dimensional error depends on pulse width, frequency, and the interaction between pulse width and speed. Burr thickness is influenced by frequency, pulse width, and the interaction between frequency and speed. Multi-objective optimization showed that, in order to simultaneously minimize the three responses, it is recommended to use high frequency (80 Hz), high pulse width (0.6 ms), and high speed (140 mm/min). The present study will help to select appropriate laser cutting conditions in thin plates, in order to favor good surface finish and dimensional accuracy, as well as low burr thickness.

Performance evaluation of newly designed nozzle on abrasive jet machining characteristics of laminated composites

PurposeThe purpose of the study is to machine the composites at lower machining time with higher accuracy without causing delamination.Design/methodology/approachAbrasive jet machining is the technology appropriate for machining composite materials to obtain good dimensional accuracy without causing de-lamination. The central composite design was followed in deciding the number of experiments to be carried out.FindingsThe influence of abrasive jet machining process parameters on machining time, material removal rate (MRR) and kerf characteristics were investigated. The experimental results proved the newly designed internal threaded nozzle increased MRR, thereby reducing the machining time.Originality/valueMachining of glass fibre reinforced polymer (GFRP) is one of the challenging tasks given its non-linear and in-homogeneous properties. In this investigation, newly developed threaded and unthreaded nozzles in machining were used for making holes on the GFRP composites.

Experimental assessment of compensated distortion in selective laser melting of Ti6Al4V parts

Selective laser melting (SLM) is a well-established Additive Manufacturing technique for the fabrication of end-use metal components. Process reliability and maximum product quality are ensured by 20 years of technology development. Nevertheless, depending on the complexity of the part geometry and on the operator experience, different trials are often needed before getting a part first time right. To reduce the number of failed jobs, simulation software packages predict residual stresses and related distortions in SLM parts and propose a compensated geometry for the “right first time” production of the product. In this works, the simulation routines of Amphyon software by Additive Works are experimentally calibrated and validated for the fabrication of a reference geometry by means of an EOSINT M270 machine and Ti6Al4V powder. The calibration of Amphyon is performed using three cantilever specimens and the calibrated SLM simulation is then used to compute the compensated shape of the reference part. The validation of the compensated shape by comparison to the real part geometry shows that Amphyon routines have good prediction capability and dimensional accuracy.

Knife-edged crown fabricated by 3-dimensional gel deposition and soft milling

Statement of problemRestorations with knife-edge margins are more prone to margin chipping during the manufacturing process. Three-dimensional gel deposition shows potential for fabricating zirconia restorations with good margin quality, but studies on its performance in fabricating knife-edged crowns are lacking. PurposeThe purpose of this in vitro study was to compare the 3-dimensional trueness, surface morphology, and margin quality of self-glazed zirconia and soft-milled zirconia crowns with knife-edge margins. Material and methodsAn abutment with a knife-edge finish line design was prepared and scanned with a laboratory scanner. Anatomic contour crowns were designed and fabricated by 3-dimensional gel deposition and soft milling (n=5). The crowns were digitalized, and the scan data were superimposed on the computer-aided design (CAD) data for 3-dimensional deviation analysis. Surface morphology and margin quality were characterized with microscopic examination. ResultsThe self-glazed zirconia crowns showed a smooth and glossy appearance. The soft-milled crowns showed traces left by the removal of support bars and numerous micropits of various sizes. In internal areas, no significant difference was found in root mean square values between the 2 groups (P＞.05). For the external surface, self-glazed zirconia showed statistically lower root mean square values than the soft-milled crowns (P＜.05). When observed at ×5 magnification, all the self-glazed zirconia crowns showed smooth edges with no defects, whereas small or large margin defects were found in the soft-milled crowns. When characterized at ×200 magnification, minor margin flaws were observed in the self-glazed zirconia crowns. More and larger margin defects were found in the soft-milled crowns. ConclusionsThree-dimensional gel deposition forms a smoother and more homogeneous surface than soft milling. Knife-edged self-glazed zirconia crowns have good dimensional accuracy and margin quality.