Joel Oliveira Correia Vasco

Laser micromachining for mould manufacturing: I. The influence of operating parameters

Purpose – Laser milling is a recent process in mould making, providing several advantages over traditional mould making technologies by reducing manufacturing time, shortening the number of machining operations and avoiding expensive electrodes. This paper investigates the influence of the operating conditions on both the surface quality and material removal for two types of materials commonly used in mould making.Design/methodology/approach – Laser scanning strategies and operating parameters like scanning speed and laser frequency and power were tested, regarding surface quality and material removal rate. The most representative parameter of the real surface quality, Rk, the core roughness parameter, is used to characterise the surface finishing on all cavities.Findings – The findings of this research work suggest that it is possible to significantly reduce processing time by increasing the hatch spacing up to a value close to the laser beam spot diameter, without compromising surface quality. Lower pul...

Innovative Developments in Design and Manufacturing: Advanced Research in Virtual and Rapid Prototyping -- Proceedings of VRP4, Oct. 2009, Leiria, Portugal

The use of rapid prototyping has increasingly begun to reveal itself as a tool of great value in supporting medical activity. From two-dimensional medical images from computed tomography (CT) or magnetic resonance imaging (MRI) it is possible to obtain three-dimensional models. The models produced by rapid prototyping technologies are useful both in educational and medical-surgical environments. It can simplify the diagnosis of certain diseases, the development of complex surgical procedures, the prostheses and medical devices manufacture and the visualization of anatomical structures in educational environment produce models and prototype parts (Alves & Braga 2001). One of the main applications of Rapid Prototyping is the fast way that is allowed in verifying new concept projects in the earlier stages or even in advanced phases of conception. In all Rapid Prototyping processes, a 3D CAD model is used that is translated into an STL (Stereolithography) format file, (Souza et al. 2003) where all the model surfaces are converted in a triangle mesh. In Biomedical Engineering field, using Rapid Prototyping techniques it is possible to produce several types of anatomical models and implant replica with educational purposes or to better understand a specific patient pathology. The models, depending of available techniques, can be made of paper, wax, ceramic, plastic or metal (Antas & Lino 2008). These models can be produced without finishing or color or have these finishing operations done later to improve visualization. For educational purpose it is possible to manufacture implant replica with much lower cost than the implant value. A great interest can be found in anatomical models manufacture from patient tomographic images. These models allow students from biomedical field to have an easier view of a specific pathology and compare it with normal anatomical models. To better understand image techniques and anatomy, it is also possible to simultaneously compare the original image (TC or MRI) and 3D solid model. Medical professionals cooperate with other field professionals to optimize pre-surgical pathology analysis, shorten surgical times, create personalized tools, facilitate the communication with patients and, simultaneously, to explore the capabilities this technology offers in personalized prosthesis design (Antas & Lino 2008). Vertebral Spine replica are particularly useful to diagnose, plan and simulate surgical procedures as it also allows the patients to understand the nature of their pathologies as well the need for surgical procedures (Madrazo et al. 2008) Several manufacturing processes are available today, as Fused Deposition Modeling (FDM), Stereolithography (SLA), Selective Laser Sintering (SLS), Tridimensional Printing (TDP or 3DP) and Laminated Object Manufacturing (LOM) among other specific processes. A brief description of the most used Rapid Prototyping processes is presented as follows: • Fused Deposition Modeling (FDM): This prototyping process build the prototypes by depositing an extruded thermoplastic material. The injection head draw transversal section perimeters and fills them building, this way, each layer. The most used material is ABS once it has good mechanical properties. More recently have been developed equipments that allow the used of materials such as polycarbonate and polyphenilsulfone (PPSU) that have better mechanical and thermic properties than ABS. • Stereolitography (SLA): This system builds the prototype by polymerizing a photosensitive liquid resin by applying an ultraviolet light formed by a laser. The solidifying process is made layer by layer, allowing obtaining a good surface finished prototype. • Selective Laser Sintering (SLS): This process allows physical models building by using dust materials like ceramics or metal. These materials are processed in an inert and thermally controlled environment inside a chamber. In here, the melting point (sintering) is achieved by action of a CO2 laser. After one layer being sinterized, another layer is deposited until the prototype is finished. This method demands a post-processing work to obtain a better surface. • Three Dimensional Printing (TDP or 3DP): In this process, models are built from a dust material (which can be a blend using materials like composite, cellulose among others) infiltrated with a liquid binder. This binder is applied through a printing head as used in traditional printing. The prototype is removed having the dust blended with the binder and needing operations of cleaning and medium consolidation. • Laminated Object Manufacturing (LOM): In LOM, most of the times, the models are obtained by gluing successive layers of paper which are cut by a laser beam. All the paper not used in the model is cut in square or rectangle forms to make easier prototype remove. To ensure the needed rigidity a frame is also built. Model definition will result from paper thickness and quality. Sometimes, instead paper there can be, also, used glass fibres, ceramics or metal (Alves & Braga 2001).

Thermo-rheological behaviour of polymer melts in microinjection moulding

Microinjection has proven to be one of the most efficient replication methods for microcomponents and microsystems in various domains of microengineering. The use of available commercial microinjection equipment to evaluate the polymeric flow in microchannels would surely contribute to enhancing knowledge on polymeric flow at the microscale under industrial conditions. This approach is appropriate since rheological phenomena such as wall slip, surface tension, melt pressure drop and polymer flow length can be studied. These aspects are not fully dealt with in current commercial simulation software packages. In this study a micromould was designed to assess and characterize the flow in microchannels under realistic industrial conditions.

Laser micromachining for mould manufacturing: II. Manufacture and testing of mould inserts

Purpose – Laser milling is a non‐conventional layer‐by‐layer material removal technology suitable for machining a wide range of materials. This technology is particularly suitable to produce microstructures inside cavities, also obtained by other conventional processes, though with larger material removal rates, or for the direct development of microcavities not requiring high removal rates. This paper seeks to evaluate the capacity of laser milling for manufacturing of mould inserts.Design/methodology/approach – The paper examined several specific features of laser milling, important for the manufacturing of mould inserts, such as walls verticality, unselected illuminating areas, due to an incorrect STL removal volume definition, aspiration process and orientation, to prevent welding of re‐solidified particles on the surface. Two mould inserts were produced too, assembled on a metallic mould frame and tested with different injection conditions.Findings – The findings suggest that laser milling is a suita...