Wahyudin P. Syam

Rapid prototyping and rapid manufacturing in medicine and dentistry This paper presents an overview of recent developments in the field of rapid prototyping and rapid manufacturing with special emphasis in medicine and dentistry

The fundamentals and latest developments of Rapid Prototyping (RP) and Rapid Manufacturing (RM) technologies and the application of most common biomaterials such as titanium and titanium alloy (Ti6Al4V) are discussed in this paper. The issues while fabricating pre-surgical models, scaffolds for cell growth and tissue engineering and concerning fabrication of medical implants and dental prostheses are addressed. Major resources related to RP/RM technology, biocompatible materials and RP/RM applications in medicine and dentistry are reviewed. A large number of papers published in leading journals are searched. Besides the titanium and titanium alloys which were established as bio-compatible materials over five decades ago, other biocompatible materials such as cobalt-chromium and PEEK have also been increasingly used in medical implants and dental prosthesis fabrication. For over a decade RP technologies such as Selective Laser Sintering (SLS) and Selective Laser Melting (SLM) along with the Fused Depositing Modelling (FDM) are predominantly employed in the fabrication of implants, prostheses and scaffolds. Recently Electron Beam Melting (EBM) has been successfully employed for fabrication of medical implants and dental prostheses with complex features. In dentistry crown restoration, the use of thin copings of Ti6Al4V made by the EBM process is an emerging trend. This review is based upon the findings published in highly cited papers during the last two decades. However the major breakthrough in the field of RP/RM for medical implants and dental prostheses took place in the last decade. The fabrication of medical implants and prostheses and biological models have three distinct characteristics: low volume, complex shapes and they are highly customised. These characteristics make them suitable to be made by RM technologies even on a commercial scale. Finally, current status and methodology and their limitations as well as future directions are discussed.

Preliminary fabrication of thin‐wall structure of Ti6Al4V for dental restoration by electron beam melting

Purpose – The purpose of this paper is to investigate the potential application of electron beam melting, as a layered manufacturing process, to fabricate dental coping of metal‐ceramic crown restoration using Ti6Al4V powder.Design/methodology/approach – This experiment was conducted in two steps: shrinkage study to determine scale up factor for shrinkage compensation and parameter selection study, based on thickness, hardness, and surface roughness, to select process parameter of electron beam melting.Findings – A promising result of fabricating metal coping of Ti6Al4V via electron beam melting was shown. Ti6Al4V coping was successfully fabricated, with an average thickness of 0.52 mm required for dental coping. Total average hardness of 333.35 HV that is comparable to casted Ti6Al4V with considerably high roughness of RSm of 382 μm.Originality/value – The paper presents a novel application of electron beam melting to fabricate metal coping for metal‐ceramic crown restoration.

Loose powder detection and surface characterization in selective laser sintering via optical coherence tomography.

Defects produced during selective laser sintering (SLS) are difficult to non-destructively detect after build completion without the use of X-ray-based methods. Overcoming this issue by assessing integrity on a layer-by-layer basis has become an area of significant interest for users of SLS apparatus. Optical coherence tomography (OCT) is used in this study to detect surface texture and sub-surface powder, which is un-melted/insufficiently sintered, is known to be a common cause of poor part integrity and would prevent the use of SLS where applications dictate assurance of defect-free parts. To demonstrate the capability of the instrument and associated data-processing algorithms, samples were built with graduated porosities which were embedded in fully dense regions in order to simulate defective regions. Simulated in situ measurements were then correlated with the process parameters used to generate variable density regions. Using this method, it is possible to detect loose powder and differentiate between densities of ±5% at a sub-surface depth of approximately 300 μm. In order to demonstrate the value of OCT as a surface-profiling technique, surface texture datasets are compared with focus variation microscopy. Comparable results are achieved after a spatial bandwidth- matching procedure.

Hybrid chaos optimization and affine scaling search algorithm for solving linear programming problems

In this study, we addressed Single Objective Linear Programming (SOLP). This article proposed a new combination of Chaos Optimization Algorithm (COA) with Affine Scaling Search (AFS) to be used as a Hybrid COA and AFS algorithm (Chaos AFS) for solving SOLP. The potential of COA as an emerging optimization algorithm to improve efficiency and effectiveness of AFS is investigated. Chaos AFS method is so-called numerical search algorithm that searches through the domain of decision variables of SOLP to obtain final feasible solution. An initial solution point, obtained from COA, will be used as starting solution point in AFS algorithm to improve the performance of AFS algorithm. The result shows that Hybrid COA and AFS for solving SOLP problems significantly improves the results of objective value compared to pure AFS and reduces the number of iteration steps compared to simplex and pure AFS.

Performance Verification of a 4-Axis Focus Variation Co-Ordinate Measuring System

The performance verification of a co-ordinate measuring system (CMS) is important for instrument acceptance, reverification, comparability, and measurement traceability to the definition of the meter. The state-of-the-art ISO 10360 standard series is the reference text about the procedure of verification for the CMS. Specifically, ISO 10360-8 considers optical distance sensor-based CMSs. This paper proposes procedures and artifacts for the performance verification of focus variation-based CMS for a simultaneous 4-axis measuring mode. The proposal is inspired by, but goes beyond, the ISO 10360 standard, proposing an original solution for simultaneous linear and rotational axes verification.