Optimization of powder layer density in selective laser sintering

An important parameter for the overall quality of SLS parts is the density of powder layers before sintering. Previous studies have shown that the control of powder particle shape and size distribution can increase the density of non-packed powder beds. However, these studies concerned beds several orders of magnitude larger than the SLS layers. The purpose of this study is to determine if, and to what extent, the density of thin powder layers can be increased. Experiments show that the density of thin layers increases from 53% to 63% when adding 30% fine powder to the coarse powder, with a coarse-to-fine ratio of 1:10. Compared with the bulk experiments, this density improvement method is less efficient, because the particles do not arrange as efficiently, and the wall effects can become predominant

Thermal behavior of parts made by direct metal laser sintering

The Direct Metal Laser Sintering (DMLS) manufacturing technique induces thermal stresses in parts. When such parts are used at elevated temperatures, residual stresses are relaxed and the part can suffer significant distortion. This study presents values of geometrical distortion for two laser exposure strategies and for different heat treatment temperatures and durations, Surface and bulk hardness data are provided as well as porosity measurements. At temperatures above 300 degrees C, the geometrical changes become important. A stabilization treatment at 600 degrees C can help reduce distortions

Direct rapid tooling: a review of current research

Rapid prototyping technologies are now evolving toward rapid tooling. The reasons for this extension are found in the need to further reduce the time-to-market by shortening not only the development phase, but also the industrialization phase of the manufacturing process. The present state of rapid tooling is reviewed and the direct rapid tooling concept, aimed at developing direct and rapid tool manufacturing processes, is presented, along with three promising methods. Their intrinsic properties are outlined and compared. Necessary research and development are described in terms of direct rapid tooling requirements

Thermal Behavior of Parts Made by Direct Metal Laser Sintering

The Direct Metal Laser Sintering (DMLS) manufacturing technique induces thermal stresses in parts. When such parts are used at elevated temperatures, residual stresses are relaxed and the part can suffer significant distortion. This study presents values of geometrical distortion for two laser exposure strategies and for different heat treatment temperatures and durations. Surface and bulk hardness data are provided as well as porosity measurements. At temperatures above 300 the geometrical changes become important. A stabilization treatment. at 600°C can help reduce distortions.Mechanical Engineerin

Injection Molds Behavior and Lifetime Characterization

This paper presents the concept of a standard method used to determine the durability of injection molds. In particular, some Rapid Tooling molds are less resistant to abrasive plastics than conventional steel molds. Some evidence of wear in a conventional mold is given, and a specific mold is designed for this test; polymer materials are defined and the test methodology is outlined. Numerical simulation is utilized to show the areas ofthe mold subject to high shear stresses.Mechanical Engineerin

Injection molds behavior and lifetime characterization - Concept and design of a standard measurement method

This paper presents the concept of a standard method used to determine the durability of injection molds. In particular, some Rapid Tooling molds are less resistant to abrasive plastics than conventional steel molds. Some evidence of wear in a conventional mold is given, and a specific mold is designed for this test; polymer materials are defined and the test methodology is outlined. Numerical simulation is utilized to show the areas of the mold subject to high shear stresses

Modeling of near infrared pulsed laser sintering of metallic powders

Using pulsed near infrared laser radiation for selective laser sintering bears several advantages compared to cw sintering such as low required average power, less residual heat and improved lateral precision. By adapting the pulse length (and thus the heat diffusion length during the pulse) to the grain size of the used metal powder, the laser pulse energy can mainly be deposited in the skin of the powder particles where heating and melting is obtained, whereas the centers of the grains remain at much lower temperature and act as heat sinks after consolidation. The model described here was numerically implemented and experimentally tested with a pulsed Nd:YAG laser on titanium powder. The results of the model predictions and the performed experiments are in good agreement