Chunze Yan

The effect of processing parameters on characteristics of selective laser sintering dental glass‐ceramic powder

Purpose – The purpose of this paper is to report a study about the rapid prototyping method of dental glass‐ceramic restoration.Design/methodology/approach – Dental glass‐ceramic restoration materials have excellent physical and chemical, mechanical, aesthetic and biocompatibility characteristics. However, casting methods adopted at present have complicated procedures and high costs; the forming qualities are especially difficult to control. These problems greatly restrict their clinical application and promotion. Therefore, a new forming process based on selective laser sintering (SLS) technology is proposed. First, dental glass‐ceramic is processed into fine powder through a special heat treatment process. Then, the dental restoration parts are manufactured using SLS without any moulds. In this paper, the effects of processing parameters including laser power, scan speed, scan spacing and preheating temperature on the relative density and mechanical properties of the sintered parts are studied.Findings ...

Effects of the unit cell topology on the compression properties of porous Co-Cr scaffolds fabricated via selective laser melting

Purpose Selective laser melting (SLM) is an additive manufacturing process suitable for fabricating metal porous scaffolds. The unit cell topology is a significant factor that determines the mechanical property of porous scaffolds. Therefore, the purpose of this paper is to evaluate the effects of unit cell topology on the compression properties of porous Cobalt–chromium (Co-Cr) scaffolds fabricated by SLM using finite element (FE) and experimental measurement methods. Design/methodology/approach The Co-Cr alloy porous scaffolds constructed in four different topologies, i.e. cubic close packed (CCP), face-centered cubic (FCC), body-centered cubic (BCC) and spherical hollow cubic (SHC), were designed and fabricated via SLM process. FE simulations and compression tests were performed to evaluate the effects of unit cell topology on the compression properties of SLM-processed porous scaffolds. Findings The Mises stress predicted by FE simulations showed that different unit cell topologies resulted in distinct stress distributions on the bearing struts of scaffolds, whereas the unit cell size directly determined the stress value. Comparisons on the stress results for four topologies showed that the FCC unit cell has the minimum stress concentration due to its inclined bearing struts and horizontal arms. Simulations and experiments both indicated that the compression modulus and strengths of FCC, BCC, SHC, CCP scaffolds with the same cell size presented in a descending order. These distinct compression behaviors were correlated with the corresponding mechanics response on bearing struts. Two failure mechanisms, cracking and collapse, were found through the results of compression tests, and the influence of topological designs on the failure was analyzed and discussed. Finally, the cell initial response of the SLM-processed Co-Cr scaffold was tested through the in vitro cell culture experiment. Originality/value A focus and concern on the compression properties of SLM-processed porous scaffolds was presented from a new perspective of unit cell topology. It provides some new knowledge to the structure optimization of porous scaffolds for load-bearing bone implants.

Investigation and development of large-scale equipment and high performance materials for powder bed laser fusion additive manufacturing

The current available selective laser sintering (SLS) and selective laser melting (SLM) systems have relatively small effective building volumes, which do not offer capability to integrally manufacture a large dimension component. Therefore, our research team in Huazhong University of Science and Technology, China, has broken through some key techniques such as the large powder bed preheating system and multi-laser scanning technique, and then successfully developed a series of large-scale SLS systems with effective building volumes up to 1400×1400×500 mm3, and an SLM system with an effective building volume of 500×250×400 mm3. These large-scale SLS/SLM systems will not only offer new capability to make large complex prototypes and products, but also provide higher volume production capability to make numerous small parts rapidly and cost-effectively. In addition, several high performance materials have been developed for the large-scale SLS/SLM systems.

Study on the selective laser sintering of a low-isotacticity polypropylene powder

Purpose Semi-crystalline polymers such as polyamide-12 can be used for selective laser sintering (SLS) to make near-fully dense plastic parts. At present, however, the types of semi-crystalline polymers suitable for SLS are critically limited. Therefore, the purpose of this paper is to investigate the processibility of a new kind of semi-crystalline polypropylene (PP) with low isotacticity for SLS process. Design/methodology/approach The SLS processibility of the PP powder, including particle size and shape, sintering window, degree of crystallinity and degradation temperature, was evaluated. Effects of the applied laser energy density on the surface micromorphology, density, tensile strength and thermal properties of SLS-built PP specimens were studied. Findings The results show that the PP powder has a nearly spherical shape, smooth surfaces, an appropriate average particle size of 63.6 μm, a broad sintering window of 21 oC and low crystalline degree of 30.4 per cent comparable to that of polyamide-12, a high degradation temperature of 381.8°C and low part bed temperature of 105°C, indicating a very good SLS processibility. The density and the tensile strength first increase with increasing laser energy density until they reach the maximum values of 0.831 g/cm3 and 19.9 MPa, respectively, at the laser energy density of 0.0458 J/mm2, and then decrease when the applied laser energy density continue to increase owing to the degradation of PP powders. The complex PP components have been manufactured by SLS using the optimum parameters, which are strong enough to be directly used as functional parts. Originality/value This paper provides a new knowledge for this field that low-isotacticity PPs exhibit good SLS processibility, therefore increasing material types and broadening the application of SLS technology.

Preparation and selective laser sintering of nylon‐coated metal powders for the indirect SLS process

Purpose – The purpose of this paper is to report a new method, the dissolution‐precipitation process, to prepare nylon‐coated metal powders for the indirect selective laser sintering (SLS) process.Design/methodology/approach – The nylon‐12 coated carbon steel powders were prepared by the dissolution‐precipitation process. The powder characteristics are examined by scanning electron microscope (SEM) and laser diffraction particle size analysis. The effect of the applied laser energy density on the three‐point bend strength and dimensional accuracy of the SLS specimens are studied. The influence of nylon‐12 content on the bend strength are also investigated.Findings – The SEM and laser diffraction particle size analysis results indicate that the steel particles are well coated by nylon‐12 resin. The bend strength of the SLS specimens increases with increasing the applied energy density until it reaches a maximum value, and then further increasing energy density will cause the decrease in the bend strength. ...