Metal Laser Sintering Technique Research Articles

Assessment, analysis and optimization for high temperature sliding wear process parameter with additive built nickel base superalloy

Abstract Superalloys are highly demanding alloy for high temperature application. The conventional production process and metallurgical sustainability of the superalloy against the applications is the preamble of the existing research. Based on the review it is clear to say that the development of nickel base superalloy with advanced technique without compensating the quality is open for research. The nickel base superalloy is developed through additive manufacturing process following a metal laser sintering technique. The developed alloy is used to perform high temperature sliding wear analysis with the different input process conditions. Applied load, sliding duration and the working temperature are the defined process environment for the investigation. The process conditions are designed with twenty-seven set of experimental trials for statistical analysis and process assessment. The responses on surface roughness and the material loss with respect to the input process parameters are technically assessed and justifications made with the electron microscopic images. The surface topography has influenced due to applied load and the sliding duration. Applied load has influenced the contact area prone with severe wear and the ridges are notice from the microscopic analysis. The statistical analysis has proved that the influence of temperature is less and negotiable compared to the load and time factor. From the optimization process, the optimal parameter for the experimental design is 10 N, 100 °C and 30 min is the ultimate condition to produce best results from the high temperature sliding wear analysis.

Lost-wax or laser sintering? Findings on marginal and internal adaptation of metallic copings

Marginal and internal adaptation are parameters of crucial importance to the success of prosthetic crowns. Automatized process creates an expectative of superior or equivalent results compared to restorations manufactured ​​by conventional lost-wax technique. The purpose of this study was to evaluate the marginal adaptation and internal adaptation (cement space) of metal-ceramic crown copings produced by lost-wax (LW) and direct metal laser sintering (DMLS) techniques. An artificial lower first molar was prepared for a full crown, duplicated in plaster and scanned. Twenty metal-ceramic crown copings were fabricated in cobalt-chromium by the two techniques (n=10). The copings were filled with low viscosity silicone and seated on the prepared tooth, resulting in a replica of the internal space. The pellicle formed was embedded in heavy body silicone, sectioned and captured by means of a stereomicroscope at 50x magnification, according to replica technique (RT). Shapiro-Wilk test followed by Holm-Sidak test were used for statistical analysis (α=.05). Marginal adaptation presented no difference between LW (101.5 ± 41.6) and DMLS (86.3 ± 39.9) groups (p=0.24). Conventional LW technique showed significantly lower occlusal (p<0.008) and axial spaces (p<0.03). Measurements of all regions showed numerically larger adaptation values than that defined during design​​ for DMLS group. Both the LW technique and the DMLS technique are within the clinically acceptable.

КЛИНИЧЕСКАЯ ОЦЕНКА ФИКСИРОВАННЫХ ЗУБНЫХ ПРОТЕЗОВ НА КОБАЛЬТ-ХРОМОВОЙ ОСНОВЕ

Subject. Ceramic-metal prostheses are distinguished by high wear resistance, resistance to deformation, and tight fit to the gums. However, there are relatively large differences in determining the success / survival of cobalt chromium based restorations. The article presents the results of a study of cobalt-chromium fixed dentures.
 Objectives — evaluate the effectiveness of cobalt-chromium fixed dentures made using the direct metal laser sintering (DMLS) technique. 
 Material and methods. 32 patients (mean age 41.8 ± 2.46 years) were found to have 54 fixed cobalt-chromium fixed bridges made using direct laser sintering of metals. Dentures were evaluated between 6, 12, 24, 36 months according to G. Ryge criteria. The survival rate of restorations is calculated according to Kaplan-Meyer. 
 Results. Assessment of fixed prostheses revealed the absence of criteria C and D in all 3 categories. A comparative analysis of prostheses showed no change in the period 6, 12, 24 months. After 36 months, chips that did not violate the function of the prosthesis were revealed in 5.5 % of cases, visible signs of a cleft in the category of “marginal adaptation” in 1.8 % of cases, edge discoloration of the surface in 3.7 % of cases. Radiographically, 1 patient showed signs of incipient proximal caries and periapical changes, respectively. During the study period of 6-24 months. survival rate was 1.0. The survival of the restoration over a 3-year period was 88.9 %. 
 Conclusion. The frequency of cleavage was 5.5 %, which is comparable to the usual performance of ceramic-metal restorations. The visible signs of a cleft in the regional adaptation was 1.8 %, and the regional color mismatch was 3.7 %. 1.8 % of restoration was detected. Signs of incipient proximal caries were 1.8 %, periapical changes — 1.8 %. Survival was 88.9 %.

Comparative evaluation of marginal fit and axial wall adaptability of copings fabricated by metal laser sintering and lost-wax technique: An in vitro study.

Purpose:The present study aims to compare and evaluate the marginal fit and axial wall adaptability of Co-Cr copings fabricated by metal laser sintering (MLS) and lost-wax (LW) techniques using a stereomicroscope.Materials and Methods:A stainless steel master die assembly was fabricated simulating a prepared crown; 40 replicas of master die were fabricated in gypsum type IV and randomly divided in two equal groups. Group A coping was fabrication by LW technique and the Group B coping fabrication by MLS technique. The copings were seated on their respective gypsum dies and marginal fit was measured using stereomicroscope and image analysis software. For evaluation of axial wall adaptability, the coping and die assembly were embedded in autopolymerizing acrylic resin and sectioned vertically. The discrepancies between the dies and copings were measured along the axial wall on each halves. The data were subjected to statistical analysis using unpaired t-test.Results:The mean values of marginal fit for copings in Group B (MLS) were lower (24.6 μm) than the copings in Group A (LW) (39.53 μm), and the difference was statistically significant (P < 0.05). The mean axial wall discrepancy value was lower for Group B (31.03 μm) as compared with Group A (54.49 μm) and the difference was statistically significant (P < 0.05).Conclusions:The copings fabricated by MLS technique had better marginal fit and axial wall adaptability in comparison with copings fabricated by the LW technique. However, the values of marginal fit of copings fabricated that the two techniques were within the clinically acceptable limit (<50 μm).

Marginal fit and microleakage of cast and metal laser sintered copings—An in vitro study

PurposeThis study aimed to compare the marginal fit and microleakage of metal laser sintered Co–Cr alloy copings and conventional cast Ni–Cr alloy copings using a stereomicroscope. MethodsForty extracted maxillary premolars were randomly divided into two groups. One group was subjected to coping fabrication using conventional lost wax (LW) technique while the other group was subjected to coping fabrication using metal laser sintering (MLS) technology. The marginal fit of these copings were compared before and after ceramic addition using images obtained with a steromicroscope and an ImageJ analysis software. All the specimens were cemented using Type 1 glass ionomer cement and were subjected to thermocycling. The specimens were evaluated for microleakage using stereomicroscope and 2% methylene blue die used as a tracer. The data were subjected to statistical analysis using paired t-test, Mann–Whitney test and Chi-Square test. ResultsThe mean marginal fit of copings before and after ceramic addition in Group B (MLS) was better than the copings in Group A (LW) and was statistically significant (P<0.05). The influence of ceramic firing had a significant (P<0.05) increase in mean marginal gap in Group A (LW) but not in Group B (MLS). And the difference in mean microleakage between the groups was not statistically significant (P≥0.05). ConclusionThe copings fabricated using MLS technique had a better marginal fit and an observable decrease in microleakage when compared to the copings fabricated using the conventional lost wax (LW) technique.

Combined Treatment with Laser Sintering and Zirconium: A Case Report of Dentinogenesis Imperfecta

Osteogenesis imperfecta (OI) is a heterogeneous disorder of connective tissue that manifests mainly as skeletal deformity and bone fragility. Dentinogenesis imperfecta (DI) is sometimes an accompanying symptom of OI. The treatment protocol of these patients varies according to the clinical appearance. The case report here describes complete mouth rehabilitation of an 18-year-old male patient with OI and DI using direct metal laser sintering (DMLS) technique of metal-ceramic restorations and zirconium all-ceramic crowns. DMLS is an additive metal fabrication technology that is simpler, more precise, and healthier than conventional manufacturing and can be remarkably cost effective. Moreover, the technique affords highly accurate production of fixed partial dentures with ideal marginal fit and excellent mechanical properties. The patient was treated using a multidisciplinary strategy that focused on controlling caries, protecting teeth from further wear, obtaining an appropriate vertical dimension, and providing soft tissue support to return the facial profile to a normal appearance using new technology in the field of prosthetics.

An intelligent parameter selection system for the direct metal laser sintering process

As one of the promising Rapid Prototyping (RP) processes, the Direct Metal Laser Sintering (DMLS) technique is capable of building prototype parts by depositing and melting metal powders layer by layer. Metal powder can be melted directly to build functional prototype tools. During fabrication, four important resulting properties of interest to the users are: the processing time, mechanical properties, geometric accuracy and surface roughness. By adjusting an identified set of process parameters, these properties can be properly controlled. The process parameters involve: the laser scan speed, laser power, hatch density, layer thickness and scan path. But the relationships between these parameters and their resulting properties are quite complicated. In many cases, the effects of different parameters on the resulting properties contradict one another. In this paper, an intelligent system to assist the RP user to choose the optimal parameter settings based on different user requirements is presented. For the accurate prediction of the resulting properties of the laser-sintered metal parts, a method based on the feed-forward neural network (NN) with backpropagation (BP) learning algorithm is described. Through experiments, some input–output data pairs have been identified. After continuous training by using the data pairs, this NN constructs a good mapping relationship between the process parameters and their resulting properties. The system developed can determine the most suitable parameter settings containing the process parameters and predict resulting properties from the database built based on different process requirements automatically. It is very useful to RP users for saving material cost and reducing processing time.