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Article
Publication date: 7 August 2007

P. Regenfuss, A. Streek, L. Hartwig, S. Klötzer, Th. Brabant, M. Horn, R. Ebert and H. Exner

The purpose of the paper is the elucidation of certain mechanisms of laser material processing in general and laser micro sintering in particular. One major intention is to…

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Abstract

Purpose

The purpose of the paper is the elucidation of certain mechanisms of laser material processing in general and laser micro sintering in particular. One major intention is to emphasize the synergism of the various effects of q‐switched laser pulses upon metal and ceramic powder material and to point out the non‐equilibrium character of reaction steps.

Design/methodology/approach

Recent results and observations, obtained in development of “laser micro sintering,” are surveyed and analyzed. By breaking down the overall process into relevant steps and considering their possible kinetics, an approach is made towards interpreting specific phenomena of laser micro sintering. Thermodynamics upon heating of the material as well as its photo‐electronic response to the incident radiation are considered.

Findings

The findings corroborate a model whereby short pulses of high intensity provide non‐equilibrium pressure conditions at the location of incidence, that allow for the melting of metal powder with an almost immediate expansion of a plasma and/or vapor bulb. Thereby the molten material is condensed and propelled towards the substrate. A final boiling eruption after each pulse is the reason for the morphology of the laser micro‐sintered surfaces and can prevent oxidation when the process is conducted under normal atmosphere. In sintering of ceramics, the short pulsed and intensive radiation increases the chance to excite the material even with photon energies below the bandgap value and it lowers the risk of running into a destructive avalanche.

Research limitations/implications

Owing to the stochastic character of the respective sintering event, that is initiated by each individual pulse, the gathered data are not suitable yet for the formulation of an exact quantitative function between sintering behavior and laser parameters.

Practical implications

The qualitative findings yield a good rule of thumb for the choice of parameters in laser sintering on a micrometer scale and the model is conducive for advanced interpretation of other phenomena in laser material processing besides sintering.

Originality/value

The kinetics and thermodynamics of laser sintering with q‐switched pulses are approached by a qualitative explanation. The heterogeneous and non‐equilibrium character of the processes is taken into account; this character is often neglected by researchers in the area.

Details

Rapid Prototyping Journal, vol. 13 no. 4
Type: Research Article
ISSN: 1355-2546

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Article
Publication date: 26 August 2021

Hong-Chuong Tran, Yu-Lung Lo, Trong-Nhan Le, Alan Kin-Tak Lau and Hong-You Lin

Depending on an experimental approach to find optimal parameters for producing fully dense (relative density > 99%) Inconel 718 (IN718) components in the selective laser melting…

541

Abstract

Purpose

Depending on an experimental approach to find optimal parameters for producing fully dense (relative density > 99%) Inconel 718 (IN718) components in the selective laser melting (SLM) process is expensive and offers no guarantee of success. Accordingly, this study aims to propose a multi-scale simulation framework to guide the choice of processing parameters in a more pragmatic manner.

Design/methodology/approach

In the proposed approach, a powder layer, ray tracing and heat transfer simulation models are used to calculate the melt pool dimensions and evaporation volume corresponding to a small number of laser power and scanning speed conditions within the input design space. A layer-heating model is then used to determine the inter-layer idle time required to maximize the temperature convergence rate of the solidified layer beneath the power bed. The simulation results are used to train surrogate models to construct SLM process maps for 3,600 pairs of the laser power and scanning speed within the input design space given three different values of the underlying solidified layer temperature (i.e., 353 K, 673 K and 873 K). The ideal selection of laser power and scanning speed of each process map is chosen based on four quality-related criteria listed as follows: without the appearance of key-hole melting; an evaporation volume less than the volume of the d90 powder particles; ensuring the stability of single scan tracks; and avoiding a weak contact between the melt pool and substrate. Finally, the optimal laser power and scanning speed parameters for the SLM process are determined by superimposing the optimal regions of the individual process maps.

Findings

The feasibility of the proposed approach is demonstrated by fabricating IN718 test specimens using the optimal processing conditions identified by the simulation framework. It is shown that the maximum density of the fabricated parts is 99.94%, while the average density is 99.88% and the standard deviation is less than 0.05%.

Originality/value

The present study proposed a multi-scale simulation model which can efficiently predict the optimal processing conditions for producing fully dense components in the SLM process. If the geometry of the three-dimensional printed part is changed or the machine and powder material is altered, users can use the proposed method for predicting the processing conditions that can produce the high-density part.

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Article
Publication date: 10 June 2014

Linda Ke, Haihong Zhu, Jie Yin and Xinbing Wang

– The purpose of this paper is to report the influence of the peak laser power on laser micro sintering 4-μm nickel powder using Q-switched 1064-nm Nd:YAG laser.

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Abstract

Purpose

The purpose of this paper is to report the influence of the peak laser power on laser micro sintering 4-μm nickel powder using Q-switched 1064-nm Nd:YAG laser.

Design/methodology/approach

Experimental study has been performed. Nickel powder with grain size of 4 μm has been utilized. A Q-switching duration of 20-25 μs and rate of 20-40 kHz have been used.

Findings

The peak power intensity is so high that the metal particles and molten pool are blown away, leading to laser micro sintering not being successfully proceeded. The scanning line obtained by continuous-wave (CW) laser looks like a rod owing to balling effect. Using a suitable peak power intensity, a good-shaped sintering line can be obtained because the plasma can protect the molten metal from oxidation, and improve the wettability of the system. In addition, the plasma flattening effect may also contribute to the form of the good-shaped sintering line in pulsed laser sintering regime.

Originality/value

The role of plasma induced by pulsed laser with high peak power intensity has been found during pulsed laser sintering under an ambient environment.

Details

Rapid Prototyping Journal, vol. 20 no. 4
Type: Research Article
ISSN: 1355-2546

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Article
Publication date: 11 January 2013

Haihong Zhu, Linda Ke, Wenjuan Lei, Cheng Dai and Baijin Chen

The purpose of this paper is to investigate the effect of the Q‐switching parameters on the sintering behavior of laser micro sintering Cu‐based metal powder, using Q‐switched…

566

Abstract

Purpose

The purpose of this paper is to investigate the effect of the Q‐switching parameters on the sintering behavior of laser micro sintering Cu‐based metal powder, using Q‐switched 1064 nm Nd‐YAG laser.

Design/methodology/approach

An experimental study has been performed. Metal powder mixture with Cu and Cu‐P alloy powders has been utilized. Q‐switching duration of 15 μs∼25 μs, rate of 25 kHz∼45 kHz have been used.

Findings

The results show that as the Q‐switching rate and duration increases, the peak laser power decreases and the densification enhances. However, an optimal peak laser power exists and if the peak laser power is too low, the density of the sample is also low. The densification regime of laser micro‐sintering is not only caused by the liquid phase filling the pores, but is also caused by the Cu powder migrating and by coalescence, e.g. including initial stage and intermediate stage of the traditional furnace liquid phase sintering. However, the degree of these stages depends on the peak power and input laser energy.

Originality/value

The effect of the Q‐switching parameters on sintering behavior of laser micro sintering Cu‐based metal powder using Q‐switched 1064 nm Nd‐YAG laser has been obtained. It is found that the densification behavior is Q‐switching parameters dependent, although the average laser power is same. The densification regime of laser micro‐sintering includes initial stage and intermediate stage of the traditional furnace liquid phase sintering, but the degree is Q‐switching parameters dependent.

Details

Rapid Prototyping Journal, vol. 19 no. 1
Type: Research Article
ISSN: 1355-2546

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Article
Publication date: 8 February 2016

Richard Slack and Matthias Munz

A change in leadership can signal a shift in corporate strategy to drive future value creation. To help achieve this, a different emphasis may be placed upon the intellectual…

1747

Abstract

Purpose

A change in leadership can signal a shift in corporate strategy to drive future value creation. To help achieve this, a different emphasis may be placed upon the intellectual capital (IC) resources within the organisation. The purpose of this paper is to examine the changes in volume, composition and emphasis of IC disclosure in annual reports mapped against the re-orientation of corporate strategy and associated leadership change.

Design/methodology/approach

A longitudinal period of over three decades (1979-2010) is examined. Adopting a case-based approach, Daimler AG is purposively selected for this research having a number of distinct changes in strategy over the period, reflective of leadership change. Using content analysis, annual report IC-related disclosures (structural, relational and human capital) by Daimler AG are examined, by category and more detailed sub-categories, against corporate strategy.

Findings

The composition and emphasis of IC disclosures found in the annual reports changes over the longitudinal period and is reflective of the prevailing corporate strategy at that time. There were four identified periods of strategy, each associated with leadership change. The prevalence and qualitative focus of IC disclosures relevant to each period reflects the importance of respective IC components in corporate value creation.

Research limitations/implications

The research is based on annual report IC disclosures within one case company and hence reflect the messages conveyed by that company over the longitudinal period. Additionally, the authors recognise that the annual report is only one source of corporate information, but as a historic record it serves to consistently capture management disclosure over a long-time period. Future research, adopting an econometric approach, could further test the linkages between leadership change, strategic shift and IC-related disclosure.

Practical implications

The research reveals how IC-related disclosure shifts to reflect leadership and strategic change within a case company. Through such disclosure, the authors are able to gain greater insight into how a specific business seeks to create value drawing on the components of IC underpinning corporate strategy.

Originality/value

The research provides new insights into IC disclosure by mapping its content and emphasis against changes in corporate strategy. This has contemporary significance due to the wider disclosure debate concerning strategy and value creation in the annual report, for instance through integrated reporting. Further, the research shows the value of annual reports for longitudinal disclosure research.

Details

Journal of Applied Accounting Research, vol. 17 no. 1
Type: Research Article
ISSN: 0967-5426

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Article
Publication date: 18 April 2017

Swee Leong Sing, Wai Yee Yeong, Florencia Edith Wiria, Bee Yen Tay, Ziqiang Zhao, Lin Zhao, Zhiling Tian and Shoufeng Yang

This paper aims to provide a review on the process of additive manufacturing of ceramic materials, focusing on partial and full melting of ceramic powder by a high-energy laser…

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Abstract

Purpose

This paper aims to provide a review on the process of additive manufacturing of ceramic materials, focusing on partial and full melting of ceramic powder by a high-energy laser beam without the use of binders.

Design/methodology/approach

Selective laser sintering or melting (SLS/SLM) techniques are first introduced, followed by analysis of results from silica (SiO2), zirconia (ZrO2) and ceramic-reinforced metal matrix composites processed by direct laser sintering and melting.

Findings

At the current state of technology, it is still a challenge to fabricate dense ceramic components directly using SLS/SLM. Critical challenges encountered during direct laser melting of ceramic will be discussed, including deposition of ceramic powder layer, interaction between laser and powder particles, dynamic melting and consolidation mechanism of the process and the presence of residual stresses in ceramics processed via SLS/SLM.

Originality/value

Despite the challenges, SLS/SLM still has the potential in fabrication of ceramics. Additional research is needed to understand and establish the optimal interaction between the laser beam and ceramic powder bed for full density part fabrication. Looking into the future, other melting-based techniques for ceramic and composites are presented, along with their potential applications.

Details

Rapid Prototyping Journal, vol. 23 no. 3
Type: Research Article
ISSN: 1355-2546

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Article
Publication date: 1 May 2005

Isabel Diéguez Castrillón and Ana I. Sinde Cantorna

The aim of this article is to gain insight into some of the factors that determine personnel‐training efforts in companies introducing advanced manufacturing technologies (AMTs)…

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Abstract

Purpose

The aim of this article is to gain insight into some of the factors that determine personnel‐training efforts in companies introducing advanced manufacturing technologies (AMTs). The study provides empirical evidence from a sector with high rates of technological modernisation.

Design/methodology/approach

Ad hoc survey of 90 firms in the manufacturing sector with advanced manufacturing technologies in production processes.

Findings

Managerial decision to develop training is determined by a factor that is extraneous to the investment in new production technologies, that is to say, recruitment policies. As for the existence of a specific training budget, implementation of AMTs does not appear to determine a company's decision to allocate specific budget items to personnel‐training programmes. It is concluded that training policies are strongly influenced by factors outside the inner context of the organisation.

Research limitations/implications

Similar research could be conducted on informal corporate training, working with additional variables to determine how they affect company training policies. The propositions were tested in a specific industry and area. Further research would be convenient in different regions and sectors.

Originality/value

Contributes to the literature in human resources about the adaptation of human resources strategy to necessary changes in the workplace.

Details

Journal of European Industrial Training, vol. 29 no. 4
Type: Research Article
ISSN: 0309-0590

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Article
Publication date: 12 November 2020

Abid Ullah, HengAn Wu, Asif Ur Rehman, YinBo Zhu, Tingting Liu and Kai Zhang

The purpose of this paper is to eliminate Part defects and enrich additive manufacturing of ceramics. Laser powder bed fusion (L-PBF) experiments were carried to investigate the…

271

Abstract

Purpose

The purpose of this paper is to eliminate Part defects and enrich additive manufacturing of ceramics. Laser powder bed fusion (L-PBF) experiments were carried to investigate the effects of laser parameters and selective oxidation of Titanium (mixed with TiO2) on the microstructure, surface quality and melting state of Titania. The causes of several L-PBF parts defects were thoroughly analyzed.

Design/methodology/approach

Laser power and scanning speed were varied within a specific range (50–125 W and 170–200 mm/s, respectively). Furthermore, varying loads of Ti (1%, 3%, 5% and 15%) were mixed with TiO2, which was selectively oxidized with laser beam in the presence of oxygen environment.

Findings

Part defects such as cracks, pores and uneven grains growth were widely reduced in TiO2 L-PBF specimens. Increasing the laser power and decreasing the scanning speed shown significant improvements in the surface morphology of TiO2 ceramics. The amount of Ti material was fully melted and simultaneously changed into TiO2 by the application of the laser beam. The selective oxidation of Ti material also improved the melting condition, microstructure and surface quality of the specimens.

Originality/value

TiO2 ceramic specimens were produced through L-PBF process. Increasing the laser power and decreasing the scanning speed is an effective way to sufficiently melt the powders and reduce parts defects. Selective oxidation of Ti by a high power laser beam approach was used to improve the manufacturability of TiO2 specimens.

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Article
Publication date: 11 January 2013

Jan Wilkes, Yves‐Christian Hagedorn, Wilhelm Meiners and Konrad Wissenbach

The purpose this paper is to develop an additive manufacturing (AM) technique for high‐strength oxide ceramics. The process development aims at directly manufacturing fully dense…

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Abstract

Purpose

The purpose this paper is to develop an additive manufacturing (AM) technique for high‐strength oxide ceramics. The process development aims at directly manufacturing fully dense ceramic freeform‐components with good mechanical properties.

Design/methodology/approach

The selective laser melting of the ceramic materials zirconia and alumina has been investigated experimentally. The approach followed up is to completely melt ZrO2/Al2O3 powder mixtures by a focused laser beam. In order to reduce thermally induced stresses, the ceramic is preheated to a temperature of at least 1,600°C during the build up process.

Findings

It is possible to manufacture ceramic objects with almost 100 percent density, without any sintering processes or any post‐processing. Crack‐free specimens have been manufactured that have a flexural strength of more than 500 MPa. Manufactured objects have a fine‐grained two‐phase microstructure consisting of tetragonal zirconia and alpha‐alumina.

Research limitations/implications

Future research may focus on improving the surface quality of manufactured components, solving issues related to the cold powder deposition on the preheated ceramic, further increasing the mechanical strength and transferring the technology from laboratory scale to industrial application.

Practical implications

Potential applications of this technique include manufacturing individual all‐ceramic dental restorations, ceramic prototypes and complex‐shaped ceramic components that cannot be made by any other manufacturing technique.

Originality/value

This new manufacturing technique based on melting and solidification of high‐performance ceramic material has some significant advantages compared to laser sintering techniques or other manufacturing techniques relying on solid‐state sintering processes.

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Article
Publication date: 26 July 2013

Dai Cheng, Haihong Zhu and Linda Ke

This paper aimed to investigate the plasma characteristics of selective laser micro sintering Cu‐based metal powder using spectra method.

549

Abstract

Purpose

This paper aimed to investigate the plasma characteristics of selective laser micro sintering Cu‐based metal powder using spectra method.

Design/methodology/approach

Temporal and time integrating plasma induced during selective laser micro sintering Cu‐based metal powder with a Q‐switched pulsed YAG laser have been detected and analyzed. Boltzmann plot and Stark broadening of the spectra line are utilized to analyze the electron temperature and density, respectively. The influences of the Q‐switching rate and duration on the plasma temperature and electron density have been investigated.

Findings

The results show that the plasma temperature decreases from 9,600 to 9,000 K with the increase of the Q‐switching rate from 5 to 35 kHz if Q‐switching duration of laser is kept at a constant value. The plots of temporal temperature and electron density show that the electron density varies in a faster speed than plasma temperature and the entire expansion process takes about 700 ns‐1 μs in this experiment. Evolutional images of the plasma plume using Q‐switching rate of 5 kHz and 5 μs have been registered by the ICCD with a 10 ns exposure time, which shows that the plasma plume takes about 100 ns to get to the maximum size and 600 ns to disperse.

Originality/value

The plasma spectra of selective laser micro sintering Cu‐based metal powder have been diagnosed experimentally. The plasma characteristics of selective laser micro sintering Cu‐based metal powder have been analyzed.

Details

Rapid Prototyping Journal, vol. 19 no. 5
Type: Research Article
ISSN: 1355-2546

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