Search results

dding dopants to a powder bed could be a cost-effective method for spatially varying the material properties in laser powder bed fusion (LPBF) or for evaluating new materials and processing relationships. However, these additions may impact the selection of processing parameters. Furthermore, these impacts may be different when depositing nanoparticles into the powder bed than when the same composition is incorporated into the powder particles as by ball milling of powders or mixing similarly sized powders. This study aims to measure the changes in the single bead characteristics with laser power, laser scan speed, laser spot size and quantity of zirconia nanoparticle dopant added to SS 316 L powder.

A zirconia slurry was inkjet-printed into a single layer of 316 SS powder and dried. Single bead experiments were conducted on the composite powder. The line type (continuous vs balling) and the melt pool geometry were compared at various levels of zirconia doping.

The balling regime expands dramatically with the zirconia dopant to both higher and lower energy density values indicating the presence of multiple physical mechanisms that influence the resulting melt track morphology. However, the energy density required for continuous tracks was not impacted as significantly by zirconia addition. These results suggest that the addition of dopants may alter the process parameter ranges suitable for the fabrication of high-quality parts.

This work provides new insight into the potential impact of material doping on the ranges of energy density values that form continuous lines in single bead tests. It also illustrates a potential method for spatially varying material composition for process development or even part optimization in powder bed fusion without producing a mixed powder that cannot be recycled.

Additive manufacturing (AM) is readily capable of producing models and prototypes of complex geometry and is advancing in creating functional parts. However, AM processes typically underperform traditional manufacturing methods in mechanical properties, surface roughness and hermeticity. Solvent vapor treatments (vapor polishing) are commonly used to improve surface quality in thermoplastic parts, but the results are poorly characterized.

This work quantifies the surface roughness change and also evaluates the effect on hermeticity and mechanical property impacts for “as-printed” and acetone vapor-polished ABS tensile specimens of 1-, 2- and 4-mm thicknesses produced by material extrusion (FDM).

Vapor polishing proves to decrease the power spectral density for surface roughness features larger than 20 µm by a factor of 10× and shows significant improvement in hermeticity based on both perfluorocarbon gross leak and pressure leak tests. However, there is minimal impact on mechanical properties with the thin specimens showing a slight increase in elongation at break but decreased elastic modulus. A bi-exponential diffusion decay model for solvent evaporation suggest a thickness-independent and thickness-dependent time constant with the latter supporting a plasticizing effect on mechanical properties.

The contributions of this work show vapor polishing can have a substantial impact on the performance for end-use application of ABS FDM components.

Projection sintering, a system for selectively sintering large areas of polymer powder simultaneously with a high-power projector is introduced. This paper aims to evaluate the suitability of laser sintering (LS) process parameters for projection sintering, as it uses substantially lower intensities, longer exposure times and larger areas than conventional LS.

The tradeoffs in sintering outcomes are evaluated by creating single layer components with varied exposure times and optical intensities. Some of these components were cross-sectioned and evaluated for degree of densification, while the single-layer thickness and the maximum tensile force was measured for the rest.

Shorter exposure times and higher intensities can create thicker and therefore stronger parts than when equal energy is applied over longer exposures. This is different from LS in which energy input (Andrew’s Number) is accepted as a reliable process variable. This difference is likely because significant thermal energy is lost from the sintering region during the exposure time – resulting in reduced peak temperatures. These thermal losses can be offset by imparting additional energy through increased exposure time or light intensity.

Most methods for evaluating LS process parameters, such as the energy melt ratio and Andrew’s Number, estimate energy input from basic process parameters. These methods do not account for thermal losses and assume that the powder absorbs all incident light. These methods become increasingly inaccurate for projection sintering with visible light where exposure times are much higher (>1s) and a larger portion of the light is reflected from the power’s surface. Understanding the appropriate sintering criteria is critical for the development of long-exposure sintering.

A new method of selectively sintering large areas is introduced that could sinter a wider variety of materials by enabling longer sintering times and may increase productivity relative to LS. This work shows that new processing parameters are required for projection sintering as traditional LS process parameters are inadequate.

Solid freeform fabrication processes such as three‐dimensional printing (3DP) and selective laser sintering (SLS) produce porous parts. Metal parts produced by these processes must be densified by sintering or infiltration to achieve maximum material performance. New steel infiltration methods can produce parts of standard alloy compositions with properties comparable to wrought materials. However, the infiltration process introduces dimensional errors due to both shrinkage and creep — particularly at the high temperatures required for steel infiltration. Aims to develop post‐processing method to reduce creep and shrinkage of porous metal skeletons.

The proposed process treats porous metal parts with a nanoparticle suspension that strengthens the bonds between particles to reduce creep and sintering shrinkage during infiltration. The process is tested by comparing the deflection and shrinkage of treated and untreated cantilevers heated to infiltration temperatures. The method is demonstrated with an iron nanoparticles suspension applied to parts made of 410 SS powder.

This process reduced creep by up to 95 percent and shrinkage by 50 percent. The best results were obtained using multiple applications of the nanoparticles dried under a magnetic field. Carbon deposited with the iron is shown to provide substantial benefit, but the iron is critical to establish strong bonds at low temperatures for minimal creep.

This work shows that dimensional stability of porous metal skeletons during infiltration processes can be significantly improved by treatment with nanoparticles. The increased dimensional stability afforded by this technique can combine the excellent properties of homogenous infiltration with substantially improved part accuracy and open up new applications for this manufacturing technology.

The work shows how solid freeform fabrication processes can be improved.

The purpose of this paper is to evaluate the performance of 3D printed materials for use as rapid tooling (RT) molds in low volume thermoforming processes such as in manufacturing custom prosthetics and orthotics.

3D printed specimens of different materials were produced using the Z‐Corp process. The parts were post processed using both standard and alternative methods. Material properties relevant to the 3D printed parts such as pneumatic permeability, flexural strength and wear rate were measured and compared to standard plaster compositions commonly used.

Three‐dimensional printing (3DP) can replicate the performance of the plaster materials traditionally used in prosthetic/orthotic applications by using modified post process techniques. The resulting 3D printed molds can still be modified and adjusted using traditional methods. The results show that 3D printed molds are feasible for thermoforming prosthetic and orthotic devices such as prosthetic sockets while providing new flexibility.

The proposed method for RT of a mold for prosthetic/orthotic manufacturing provides great flexibility in the manufacturing and fitting process while maintaining proven materials in the final device provided to patients. This flexibility increases the value of digital medical records and efforts to develop model‐based approaches to prosthetic/orthotic device design by providing a readily available process for recreating molds. Depending on the needs of the practitioners and patients, 3DP can be incorporated at a variety of points in the manufacturing process.

The purpose of this paper is to evaluate the use of a simple printed geometry to estimate mechanical properties (elastic modulus, yield strength) with inexpensive test equipment.

Test geometry is presented that enables controlled strains with manual deformation and repeatable measurement of vibrational frequencies. This is tested with multiple fused deposition modeling (FDM) machines to assess measurement accuracy and repeatability. Printing orientation and some printing parameters are varied to assess the measurement sensitivity.

The test methods show good correlation with manufacturer material specifications in the X-Y plane and reported elastic strain limits. It is also sensitive to printing orientation and printing parameters.

Further work is needed to assess the sensitivity of the method to particular defects and parameter errors expected in particular applications.

This method supports process monitoring in production environments and inexpensive assessments of material properties for hobbyist and do-i- yourself users. While it is tested with FDM, it should be applicable to other additive manufacturing processes.

Towards the end of the nineteenth century Paris was the global capital of art and fashion. Today it remains a key hub in the global cultural economy. Male and female artists/designers develop new products and production techniques and marketing techniques are used to gain an international reputation. The top designers are embedded in a supportive milieu of cooperative competition, where ideas are exchanged and resources accessed. The purpose of this paper is to draw on archival documents to examine the privileged role cities have played as centres of cultural and economic activity, with specific reference to Paris and haute couture.

The paper employs a case study approach, accessing data from a number of sources including secondary sources and grey literature, the analysis of archival material, and in‐depth interviews with key stakeholders in examining the role of Parisian haute couture.

Parisian haute couture developed using the system pioneered in the nineteenth century by the Englishman Charles Worth. Their ideas inspired fashion trends globally, and this persisted for over a century. The salons tended to be owned at least partially by the artist/designer. The most successful designers based their reputations on a specific and well defined fashion innovation. A further strategy adopted by couturiers was the use of subsidiary lines of products to offset uncertainties in the market for fashionable clothing, the principal one being perfume.

The paper links the work of French and Anglo‐American writers on the cultural economy, and highlights, using case studies, the pivotal role Paris has played in shaping global fashion trends since the nineteenth century.

This paper sets out to evaluate the financial security consequences of the terrorists attack on the USA of 11 September 2001 with specific regard to money laundering.

The study itemises in minute detail the litany of actual and potential financial legislation in the wake of 9/11 in both the USA and the UK.

Basically, the study finds the depriving criminals of the proceeds of their crimes is illusory and ineffectual, since they never have sufficient funds available for confiscation in the first place.

The paper arguably represents the most comprehensive evaluation to date of the financial issues, both real and hypothetical, thrown up on both sides of the Atlantic by the events of 9/11.

This paper aims to introduce the concept of institutional CSR and explains its antecedents, key characteristics and the potential implications arising from private firms providing public goods and services in developing economies.

The paper conceptualises institutional CSR using key insights from institutional theory along with legitimacy theory. It integrates the antecedents of CSR at the state and society levels and shows how firms may respond to these antecedents within an integrated institutional CSR framework.

The paper derives six distinct characteristics of institutional CSR and presents a conceptual model to inform how institutional CSR occurs in practice.

This paper brings to the attention the need for private firms that undertake institutional CSR activities to engage more closely with the state to ensure better societal outcomes.

The paper identifies the importance of resource coordination between the state and the firm for the efficient and effective provision of public goods and services. Without such coordination, moral hazard, resource imbalances and long-term viability concerns pose a risk for institutional CSR activities. It furthermore highlights important implications for societal governance.

The paper makes an important contribution to the literature on CSR practices within developing economies by conceptualising institutional CSR in providing public goods and services.