Influence of molecular weight average, degree of crystallinity, and viscosity of different polyamide PA12 powder grades on the microstructures of laser sintered part

Laser Sintering (LS) allows functional parts to be produced in a wide range of powdered materials using a dedicated machine, and is thus gaining popularity within the field of rapid prototyping. It offers the user the ability to optimise part design in order to meet customer requirements with few manufacturing restrictions. A problem with LS is that sometimes the surface of the parts produced displays a texture similar to that of the skin of an orange (the so-called “orange peel” texture). The main aim of this research is to develop a methodology of controlling the input material properties of PA12 powder that will ensure consistent and good quality of the fabricated parts. Melt Flow Rate (MFR) and Gel permeation chromatography (GPC) were employed to measure the flow viscosity and molecular weight distributions of Polyamide PA12 powder grades. The experimental results proved that recycle PA12 powder with higher melt viscosity polymer has a higher entanglement with a longer molecule chain causes a higher resistance to flow which cause poor and rough surface finished on laser sintered part

Effect of employing different grades of recycled polyamide 12 on the surface texture of laser sintered (LS) parts

Laser sintering (LS) is one of the most versatile rapid prototyping (RP) processes currently available. One of the main advantages of employing this technology is that the non-sintered powder can be recycled and reused for further fabrication. Current powder recycling methodologies using a constant refresh rate with a very high portion of new material being added to the existing material reserve in order to maintain part quality and integrity. If the amount of the new powder is insufficient or if the recycled material is too “old” (i.e. has been recycled too many times), then the fabricated parts experience variation in their quality. Typical quality defects include; higher shrinkage rates and rougher than average surface textures often known as “orange peel”. This paper reports on an experimental study to investigate the significance of different deteriorated recycle Polyamide 12 (PA12) powders on the surface quality of products. The main aim of this research is to determine and acceptable ratio quantities of virgin to recycled powder that can be used before adversely affecting product surface texture. In this experiment, the melt flow rate (MFR) is chosen as a criterion to measure the recycled powder quality. The microstructures of external surface and cross sectional parts which employed the different grades of recycled powder quality were examined. The results of experiment suggested that the refresh powder target must be at least 27MFR in order to produce a LS good part surface

Investigation of the thermal properties of different grades Polyamide 12 (PA12) in improving laser sintering process (SLS)

Selective Laser Sintering (SLS) is a combined technology of computer and laser to produce complex 3D prototypes directly from CAD modeling. One of the main advantages of employing this technology is that the non-sintered powder can be recycled and reused for another fabrication. However, the fabricated part could be affected by rough and unacceptable surface texture. As a result, the parts may have to be scrapped and the build has to be repeated with a higher ratio of new material. This paper presents an experimental study of the thermal properties of new and recycled of PA12 powder in the Laser Sintering process. The influence of melting temperature, glass transition temperature and crystallization temperature on these properties is investigated. The experimental results have shown that PA12 powder with high melt flow rate, low melting temperature, low glass transition temperature and low degree of crystallization temperature could improve the sintering process

Environmental dimensions of additive manufacturing: mapping application domains and their environmental implications

Additive manufacturing (AM) proposes a novel paradigm for engineering design and manufacturing, which has profound economic, environmental, and security implications. The design freedom offered by this category of manufacturing processes and its ability to locally print almost each designable object will have important repercussions across society. While AM applications are progressing from rapid prototyping to the production of end-use products, the environmental dimensions and related impacts of these evolving manufacturing processes have yet to be extensively examined. Only limited quantitative data are available on how AM manufactured products compare to conventionally manufactured ones in terms of energy and material consumption, transportation costs, pollution and waste, health and safety issues, as well as other environmental impacts over their full lifetime. Reported research indicates that the specific energy of current AM systems is 1 to 2 orders of magnitude higher compared to that of conventional manufacturing processes. However, only part of the AM process taxonomy is yet documented in terms of its environmental performance, and most life cycle inventory (LCI) efforts mainly focus on energy consumption. From an environmental perspective, AM manufactured parts can be beneficial for very small batches, or in cases where AM-based redesigns offer substantial functional advantages during the product use phase (e.g., lightweight part designs and part remanufacturing). Important pending research questions include the LCI of AM feedstock production, supply-chain consequences, and health and safety issues relating to AM

Methodology – A Review of Intelligent Manufacturing Scope, Strategy and Simulation

This paper presents a critical review of some existing modelling, control and optimization techniques for energy saving, carbon emission reduction in manufacturing processes. The study on various production issues reveals different levels of intelligent manufacturing approaches. Then methods and strategies to tackle the sustainability issues in manufacturing are summarized. Modelling tools such as discrete (dynamic) event system (DES/DEDS) and agent-based modelling/simulation (ABS) approaches are reviewed from the production planning and control prospective. These approaches will provide some guidelines for the development of advanced factory modelling, resource flow analysis and assisting the identification of improvement potentials, in order to achieve more sustainable manufacturing

A useful study of entrepreneurship

REFERENCE to Éîðäàí Êîåâ. Îñíîâè íà ïðåäïðèåìà÷åñòâîòî. Âàðíà, Èçä. êúùà “Þòåíî”, 2002.

Recycling of polyamide 12 based powders in the laser sintering process

PurposeThe purpose of this paper is to investigate the polyamide 12 (PA12) powder properties deterioration in the laser sintering (LS) process and propose a methodology for more efficient powder recycling. The main goals are: to recommend a level of input PA2200 powder properties which could guarantee acceptable part quality in the LS process; and selection of the refresh rate in order to minimise the consumption of fresh material.Design/methodology/approachThe paper analyses the LS processing conditions and current recycling practices in relation to the deterioration or ageing of the PA12‐based powders. Samples of new and recycled grades of PA2200 powder were artificially aged in a temperature‐controlled oven and then tested using melt flow rate (MFR) indexer. Also, un‐sintered powder samples collected from different locations within various builds, and different LS machines (EOSINT P700 and Sinterstation® 2500 HiQ) were tested.FindingsThe powder exposed at higher temperature and longer time experiences a much higher deterioration rate. The temperature and the time at which the un‐sintered material was exposed are the most influential parameters for the powder aging. It was confirmed that the MFR index is a very sensitive indicator of the changes in the powder properties and provides a relatively fast and inexpensive method of measuring the rate of the powder degradation because of the LS process. The powder located in the periphery and the top of a build has a higher MFR and therefore is less deteriorated. In contrast, powder located in the centre, or in the bottom of a long build has much lower MFR and therefore is less usable.Practical implicationsBased on the findings, a methodology for powder recycling is proposed. It allows a better control of the input material properties, a consistent quality of the fabricated parts, and more efficient use of the LS material.Originality/valueThe paper provides some useful information for the properties deterioration of PA12‐based powders (PA2200) in relation to the temperature and time at which the material is exposed in the LS.</jats:sec