Direct Laser Sintering Research Articles

Development and characterisation of direct laser sintering Cu-based metal powder

Direct laser sintering of metal powder is a promising manufacturing process to produce rapid moulds (or rapid tooling) because complex three-dimensional (3-D) metal parts can be created directly from computer-aided design (CAD) data without machining or use of additional tooling. However, material and process are still the crucial issues that restrict its wider adoption although the technology has been introduced more than 7 years. This paper characterises a self-developed Cu-based metal powder used for direct laser sintering. The material system is Cu-based alloy metal powder, which consists of two metal powders: high-purity Cu powder and pre-alloyed SCuP metal powder. The scanning electron microscope (SEM), XRD and energy dispersive X-ray (EDX) analyses show that the bonding mechanism of this process is liquid-phase sintering. The pre-alloyed SCuP metal powder with lower melting point (645°C) acts as the binder during laser sintering, while the Cu powder with higher melting point (1083°C) acts as the structure. The element phosphorus in the powder can act as flux to protect the Cu oxidisation. A case study on fabricating the inserts of a mobile phone cover mould was also carried out. The inserts were created in ambient atmosphere at room temperature. The total sintering time is 40h. Sixty five percent relative theoretical density and average surface roughness Ra 14–16μm were achieved with negligible distortion and curling. Epoxy infiltration was employed as post-process to improve the density and the strength of the sintered tooling. The mould inserts were used to inject ABS-PC mobile phone cover after polishing. No defects were found after moulding of 500 components.

Effects of laser sintering processing parameters on the microstructure and densification of iron powder

The densification behavior and the attendant microstructural features of iron powder processed by direct laser sintering were investigated. The effects of processing parameters such as laser power, scan rate, scan line spacing, thickness of layer, scanning geometry and sintering atmosphere were studied. A specific energy input ( ψ) was defined using the “energy conservation” rule to explore the effects of the processing condition on the density and the attendant microstructure of laser sintered iron. It was found that the sintered density increased sharply with increasing the specific energy input until a critical energy input had been reached ( ψ∼0.2 kJ mm −3). The microstructure consists of large pores (>0.5 mm) and elongated ferrite grains parallel to the building direction. The increase in the sintered density was followed with further increasing the specific energy, but at slower rate. Intensifying the energy input over 0.8 kJ mm −3 leads to the formation of horizontally elongated pores while the sintered density remains almost constant. The inter-agglomerates are fully dense and consist of elongated ferrite grains which are oriented parallel to the building direction. The iron powder was used as a model material so the outcomes are generic and can be applied to other material systems with congruent melting point or systems which melting/solidification approach is the mechanism feasible for the rapid bonding of metal powders in direct laser sintering.

Direct selective laser sintering of iron–graphite powder mixture

In the present work, laser sintering of a powder mixture of iron and graphite (99.22 and 0.78%, respectively) was carried out using a pulsed Nd-YAG laser. The paper reports experimental details with evolution of the microstructures and evaluation of some of the physical and mechanical properties of the resultant sintered material. The obtained results indicate suitability of the laser sintered material for some special applications.

Formation of Fe—Cu metal parts using direct laser sintering

The direct laser sintering process is currently being used to manufacture metallic parts for prototyping and tooling directly. This paper reports on the direct laser sintering of Fe—Cu metal powder using a 200 W CO2 laser. The effects of the ratio of Fe to Cu, the scan speed and atmosphere on the distortion, surface morphology and surface roughness have been investigated. The experiment also investigated the role of adding W particles to the Fe—Cu mixture. The result shows that adding W particles can reduce part distortion. To find the effect of gas protection in laser sintering, the three-dimensional specimens fabricated in both air and N2 atmosphere are also compared.

Direct laser sintering of a low-alloy PM steel

Direct laser sintering of a low-alloy PM steel

Direct Selective Laser Sintering of Hard Metal Powders: Experimental Study and Simulation

Direct selective laser sintering (SLS) technology can be used to produce 3D hard metal functional parts from commercial available powders. Unlike conventional sintering, it does not require dedicated tools, such as dies. Hence, total production time and cost can be reduced. The large shape freedom offered by such a process makes the use of, for example, sintered carbides components viable in domains where they were not applied before. Successful results have been obtained in the production of sintered carbide or hard metal parts through SLS. The investigation focuses on tungsten carbide-cobalt (WC-Co) powder mixture. This material is characterised by its high mechanical properties and its high wear resistance and is widely used in the field of cutting tools. This paper is devoted to the experimental study and the simulation of direct selective laser sintering of WC-Co hard metal powders.

The Potential of Plating Techniques in the Development of Rapid EDM Tooling

Electrodischarge machining (EDM) is a widely used process in the manufacturing of mould cavities for plastic products. EDM work typically accounts for a large portion of overall production time. A major cost and time element of EDM is electrode production, which can account for more than 50% of the total machining costs. A large complex electrode profile, which is very difficult to produce through machining and is also time consuming, can be easily produced using the rapid prototyping (RP) technique. The direct laser sintering of metal powders is a widely established RP process that can be employed for the rapid production of EDM electrodes. In this study, the above-mentioned technique has been employed. The powder mixture used in this process consists of copper, tin, nickel and phosphorus. An infra-red (IR) 200 W CO 2 laser is used to sinter the powdered metals layer-by-layer in order to form solid electrodes. Electroless copper and copper plating are then employed to improve the surface finishing and the conductivity of the sintered electrode as it deposits a uniform thickness of metal onto the substrate by chemical reaction, without building up at the edges and corners, and achieves unique physical characteristics. The performance of the newly developed electrode is very similar to that of conventional copper electrodes. It is found that integration of RP and electroless plating techniques can be a potential means of the rapid production of EDM electrodes at low cost.

Manufacture of RP tools with high quality surface finish using high temperature epoxy resin and electroless nickel plating

Rapid tooling is gaining increasing attention in the manufacturing sector, especially for the development of new products, owing to its distinctive characteristics. Rapid prototyping techniques can be used in this prospective manufacturing area to produce tooling either directly or indirectly. Although powder metal based rapid prototyping systems are considered most effective for rapid tooling, the requirements for injection moulding are not yet fully attained. In the present study, rapid tooling produced by direct laser sintering of metal powder has been investigated with the aim of improving its quality for industrial acceptance. High temperature epoxy resin was used to fill the pores to improve compressive strength, and electroless nickel plating was employed to enhance hardness, conductivity, ductility, lubricity, wear, and abrasion resistance without affecting dimensional accuracy. Results demonstrate that these techniques possess significant potential for rapid tool production.

Rapid Tooling by Using Metal Powder Reinforced Resin

As dies and molds have become more and more complicated in the recent years, the demand for lower cost and shorter production time is also growing stronger. Rapid prototyping and Tooling technologies are expected to be used for more rapid and lower cost tool fabrication. However the rapid tooling methods have not yet reached the level of application to the manufacturing of metallic dies and molds which require high dimensional accuracy. As the rapid tooling technology, there are the slurry casting, the powder casting, the direct laser sintering, and so on. Generally, in the slurry casting, the alumina powder and the water soluble phenol were mainly used. However, the mechanical properties of the phenol were not good enough to apply to molds directly. In this study, pure epoxy and two types of aluminium powder reinforced resin are applied to the slurry casting. The mechanical and thermal properties are better than phenol because the epoxy is the thermosetting resin. And mechanical characteristics such as shrinkage rate, hardness, surface roughness are measured for the sake of comparison. Metal powder reinforced resin molds are better than the resin tool form the viewpoint of shrinkage rate and hardness. Finally, it has been shown that the application possibility of this process is high, because the manufacturing time and cost savings are significant.

Laser Direct-Write of Materials for Microelectronics Applications

ABSTRACTWe demonstrate a laser direct-write method, a maskless process that transfers material directly from a ribbon to a substrate. This process offers the promise of fabricating passive electronic micro-components at a high speed with high spatial resolution. We are developing a workstation implementing this direct-write method, which integrates deposition, direct laser sintering, and micromachining capability on a single machine. Using this workstation we have deposited micro-patterns of conducting lines and resistors on alumina and polyimide substrates under ambient conditions that exhibit good electrical properties and substrate adhesion. From preliminary studies of laser sintering it was found that a wide range of sintering conditions may be used to arrive at silver conducting lines (∼60 µm × 10 µm) on alumina substrate with resistivity in the range of 5 to 10 times the resistivity of bulk silver. Preliminary results also indicate direct laser sintering of cermet resistor material can yield reproducible resistance values.

Direct laser freeform fabrication of high performance metal components

This paper focuses on recent advances in direct freeform fabrication of high performance components via selective laser sintering (SLS). The application, known as SLS/HIP, is a low cost manufacturing technique that combines the strengths of selective laser sintering and hot isostatic pressing (HIP) to rapidly produce low volume or “one of a kind” high performance metal components. Direct selective laser sintering is a rapid manufacturing technique that can produce high density metal parts of complex geometry with an integral, gas impermeable skin. These parts can then be directly post‐processed by containerless HIP. The advantages of in situ encapsulation include elimination of a secondary container material and associated container‐powder interaction, reduced pre‐processing time, a short HIP cycle and reduction in post‐processing steps compared to HIP of canned parts. SLS/HIP is currently being developed under a DARPA/ONR program for INCONEL® 625 superalloy and Ti‐6Al‐4V, the demonstration components being the F‐14 turbine engine vane and the AIM‐9 missile guidance section housing base respectively.

Effect of sintering conditions on dimensional change in iron base powder compacts: J. Takata, N. Kawai. (Kobe Steel Ltd., Takasago, Japan.) J.Japan Soc. Powder and Powder Metallurgy, vol 42, no 7, 1995, 827–832. (In Japanese.)

The densification behavior and the attendant microstructural features of iron powder processed by direct laser sintering were investigated. The effects of processing parameters such as laser power, scan rate, scan line spacing, thickness of layer, scanning geometry and sintering atmosphere were studied. A specific energy input (ψ) was defined using the “energy conservation” rule to explore the effects of the processing condition on the density and the attendant microstructure of laser sintered iron. It was found that the sintered density increased sharply with increasing the specific energy input until a critical energy input had been reached (ψ∼0.2 kJ mm−3). The microstructure consists of large pores (>0.5 mm) and elongated ferrite grains parallel to the building direction. The increase in the sintered density was followed with further increasing the specific energy, but at slower rate. Intensifying the energy input over 0.8 kJ mm−3 leads to the formation of horizontally elongated pores while the sintered density remains almost constant. The inter-agglomerates are fully dense and consist of elongated ferrite grains which are oriented parallel to the building direction. The iron powder was used as a model material so the outcomes are generic and can be applied to other material systems with congruent melting point or systems which melting/solidification approach is the mechanism feasible for the rapid bonding of metal powders in direct laser sintering.

Experimental Study of the Basic Process Mechanism for Direct Selective Laser Sintering of Low-Melting Metallic Powder

Due to the still limited mechanical properties of the materials which can be processed using industrially available rapid prototyping techniques, work is currently being undertaken to develop methods of manufacturing metallic prototypes directly. This paper reports on the process development of Selective Laser Sintering (SLS) for direct sintering of bronze as a low-melting metallic powder on a laboratory test facility. The experimental investigations with single spots, lines and layers on the powder bed indicate successful direct sintering of bronze powder without polymer binder or preheating. Besides the process parameters such as laser beam power, scanning speed and hatching distance, material parameters such as particle size distribution exert an influence on the melting behavior and should, therefore, be considered in terms of further process development.

Direct selective laser sintering of metals

A method of fabricating a fully dense, three dimensional object by direct laser sintering is disclosed (flow chart). In a chamber (evacuated) with a partial pressure atmosphere, a degased powder layer is dispensed over a target surface and a beam of directed energy melts metallic powder in order to form a solid layer cross section. Another layer of powder is deposited and melted, along with a portion of the previous layer. The energy beam typically is in the form of a laser, scanning along a path resembling a parametric curve or another, arbitrary piecewise parametric curve (vector scan). In another embodiment, the previous layer is not remelted, thus creating an oxide film that acts as a clean stop to prevent unwanted downward growth.