Microencapsulation of Finely Divided Ceramic Powders

Polymer coated alumina particles have been prepared by spray drying alumina powder with a polymer emulsion. Powders containing a maximum of 50% wt. were obtained. The coated particles were compared to mixtures of alumina and polymer. Oven sintering tests show the coated material to compact more than the mixed and pure polymer materials. Strong, well defined parts with layer thicknesses of 0.002" were produced from both coated and mixed materials by the Selective Layer Sintering process.Mechanical Engineerin

Thermal Properties of Powders

This paper presents measurements of the specific heats of various powders, including nylon, ABS, PVC, and two kinds of wax. An unsteady-state conduction technique is also presented for measuring the thermal conductivities of these powders at temperatures below those where sintering occurs. Both specific heats and thermal conductivities are found to be functions of temperature.Mechanical Engineerin

Prediction of the Thermal Conductivity of Beds Which Contain Polymer Coated Metal Particles

Structural parts of ceramics or metals can, in principle, be made by laser sintering polymer coated ceramic or metal powders, followed by conventional methods for removing the binder and sintering in ovens. Understanding the laser sintering of coated materials requires knowledge of the behavior of beds containing composite particles. Many correlations for predicting the effective thermal conductivity of a bed of solid particles exist in literature, but little work has been done on beds of coated particles. We coated lead shots(high conductivity) with a styrene acrylic acid copolymer (low conductivity) to study the effect of coating thickness on the thermal conductivity. The thermal conductivity ofthe coated particle·hed was found to •drop rapidly in the beginning·· and then level off with increasing coating thickness. We also developed an equation that yields the equivalent conductivity of a coated spherical particle subjected to axial heat flow. The predicted results with the experimental measurements of bed conductivity obtained by an unsteady state method.Mechanical Engineerin

Relating Operating Parameters between SLS Machines which have Different Scanner Geometries and Laser Spot Sizes

As the number of SLS machines in operation increases, the opportunities to share operating parameters with other SLS operators also increases. However, if the machines are not identical down to the spot size of the laser beam, the quality of parts made on each machine can be different. The most likely differences between two SLS machines are the laser spot size and the scanning radius of the optics. The total energy flux to the powder surface is a function of the spot size and the scan speed. The algorithms defined to correct for machine differences are verified both experimentally and numerically using a one-dimensional empirical SLS model.McDonald Observator

Effect of Polymer Coatings as Intermediate Binders on Sintering of Ceramic Parts

It has been proposed that a thin polymer layer applied to the surfaces of finely divided ceramic powders would serve as a suitable intermediate binder for Selective Layer Sintering of ceramic pans. In this study, the effects of completeness and fraction of coa nd particle size distribution on sintering rates and strengths of coated ridized glass are examined. The effect of the coating as a binder during Selective Layer Sintering as well as the binder's burnout capability during post processing steps are also investigated.Mechanical Engineerin

Laser Sintering Model for Composite Materials

A computer model for the sintering of ceramic/polymer composite materials has been established based on empirical sintering rate data. The model calculates sintering depths which result from variations in the operating parameters which include laser power, beam speed, scan spacing, scan vector length, and initial temperatures of the powder and surroundings. Sintering depths measured in multiple layer parts made of polymer coated ceramic powders are compared to sintering depths calculated by the sintering model.Mechanical Engineerin

Drying of Colloidal Binder Infiltrated Ceramic Green Parts Produced by Selective Laser Sintering™

Colloidal ceramic binders have been used to strengthen ceramic green shapes produced by Selective Laser Sintering. This paper focuses on the effectiveness of the colloid infiltration with respect to the physical properties of the colloidal binder. Mass gains, strength gains, and dimensional changes resulting from infiltration were monitored. Controlled drying experiments were conducted to predict the factors influencing drying times for complex shapes.Mechanical Engineerin

Solid Freeform Fabrication An Advanced Manufacturing Approach

Solid freeform fabrication (SFF) is the production of freeform solid objects directly from a computer model without part-specific tooling or human intervention. SFF has been realized in the last ten years through the merging of several previously distinct technologies: computer science, mechanical design, controls, high-energy beam technology and materials science and engineering. Their combination has produced over a relatively short time..frame numerous SFF methods. The value of SFF to the commercial sector is usually articulated in terms of reduced time to market (prototyping), low production "one-of-a-kind" parts and patterns for casting. The purpose of this introductory paper is to describe briefly some of the approaches to SFF as a background for the articles included in this proceedings.Mechanical Engineerin

Ceramic Structures by Selective Laser Sintering of Microencapsulated, Finely Divided Ceramic Materials

The feasibility of producing ceramic green parts by Selective Laser Sintering from microencapsulated, finely divide ceramic powders has been reported in an earlier paper. Post-processing of a silica/zirconium orthosilicate system and an alumina system, both utilizing a polymer binder in the form of a coating, are discussed in this paper. Ceramic green parts require postprocessing to remove the intermediate polymer binder and to impart strength properties to the ceramic bodies. In this paper, the use of ceramic cements and high temperature firing to realize strengths will be discussed. The effects of cement concentration and controlled drying rates on the strengths and dimensional accuracy of the ceramic bodies are also discussed.Mechanical Engineerin

Selective Laser Sintering of Bioceramic Materials for Implants

Selective Laser Sintering (SLS) process is employed for fabrication of biocerarnics for orthopedic implants. Hydroxyapatite and Calcium Phosphate ceramics are coated with polymer as a intermediate binder by using a spray drier. Polymer coated materials are SLS processed to make green parts, which are infiltrated and fired to remove the polymer. SLS processed green parts of hydroxyapatite have low density due to the small particle size with large specific surface area. This paper discusses the possibilities and problems in free-form fabrication of bioceramic.Mechanical Engineerin