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The purpose of this paper is to develop a quantitative model to assess probability of errors and errors correction costs in parts feeding systems for assembly lines.

Event trees are adopted to model errors in the picking-handling-delivery-utilization of materials containers from the warehouse to assembly stations. Error probabilities and quality costs functions are developed to compare alternative feeding policies including kitting, line stocking and just-in-time delivery. A numerical case study is included.

This paper confirms with quantitative evidence the economic relevance of logistic errors (LEs) in parts feeding processes, a problem neglected in the existing literature. It also points out the most frequent or relevant error types and identifies specific corrective measures.

While the model is general purpose, conclusions are specific to each applicative case and are not generalizable, and some modifications may be required to adapt it to specific industrial cases. When no experimental data are available, human error analysis should be used to estimate event probabilities based on underlying modes and causes of human error.

Production managers are given a quantitative decision tool to assess errors probability and errors correction costs in assembly lines parts feeding systems. This allows better comparing of alternative parts feeding policies and identifying corrective measures.

This is the first paper to develop quantitative models for estimating LEs and related quality cost, allowing a comparison between alternative parts feeding policies.

The purpose of this paper is to investigate the polyamide 12 (PA12) powder properties deterioration in the laser sintering (LS) process and propose a methodology for more efficient powder recycling. The main goals are: to recommend a level of input PA2200 powder properties which could guarantee acceptable part quality in the LS process; and selection of the refresh rate in order to minimise the consumption of fresh material.

The paper analyses the LS processing conditions and current recycling practices in relation to the deterioration or ageing of the PA12‐based powders. Samples of new and recycled grades of PA2200 powder were artificially aged in a temperature‐controlled oven and then tested using melt flow rate (MFR) indexer. Also, un‐sintered powder samples collected from different locations within various builds, and different LS machines (EOSINT P700 and Sinterstation^® 2500 HiQ) were tested.

The powder exposed at higher temperature and longer time experiences a much higher deterioration rate. The temperature and the time at which the un‐sintered material was exposed are the most influential parameters for the powder aging. It was confirmed that the MFR index is a very sensitive indicator of the changes in the powder properties and provides a relatively fast and inexpensive method of measuring the rate of the powder degradation because of the LS process. The powder located in the periphery and the top of a build has a higher MFR and therefore is less deteriorated. In contrast, powder located in the centre, or in the bottom of a long build has much lower MFR and therefore is less usable.

Based on the findings, a methodology for powder recycling is proposed. It allows a better control of the input material properties, a consistent quality of the fabricated parts, and more efficient use of the LS material.

The paper provides some useful information for the properties deterioration of PA12‐based powders (PA2200) in relation to the temperature and time at which the material is exposed in the LS.

A pine/co-PES composite (PCPES composite) was proposed as the feedstock for powder bed fusion (laser sintering, LS). This paper aims to provide some necessary experimental data and the theoretical foundation for LS of pine/co-PES, especially for the application of using the laser-sintered pine/co-PES parts as complex structural patterns in investment casting.

The PCPES composites with different pine loadings were mixed mechanically. The composite’s preheating temperature and processing temperature during LS were determined experimentally based on the material’s thermal behavior. The effects of pine powder on the binding mechanism of PCPES composites were discussed through analyzing the microstructure of the laser-sintered parts’. Mechanical properties and dimensional precision of laser-sintered PCPES parts in different pine loadings were tested, and the parts’ mechanical properties were strengthened by wax-infiltration post-processing. The influence extents of process parameters on the mechanical properties of laser-sintered 20 Wt.% pine/co-PES parts were investigated using a 1/2 fractional factorials experiment.

20 Wt.% pine/co-PES is considered to be a promising wood-plastic composite for laser sintering. The relationship between mechanical strength of its laser-sintered parts and process parameters was built up using mathematical formulas. Experimental results show density, tensile strength, flexural strength and surface roughness of laser-sintered 20 Wt.% pine/co-PES parts are improved by 72.7-75.0%, 21.9-111.3%, 26.8-86.2%, 27.0-29.1% after post-process infiltration with a wax. A promising application of the wax-infiltrated laser-sintered parts is for investment casting cores and patterns.

The proper process parameters and forming properties of laser-sintered parts are limited to the results of laser sintering experiments carried on using AFS 360 rapid prototyping device.

This investigation not only provides a new feedstock for laser sintering with the advantages of low cost and fabricability but also uses an advanced technique to produce personalized wood-plastic parts efficiently. Mathematical models between mechanical properties of laser-sintered PCPES parts and LS process parameters will guide the further LS experiments using the 20 Wt.% pine/co-PES composite. Besides, the laser-sintered PCPES parts after wax-infiltration post-processing are promising as complex structural patterns for use in investment casting.

The purpose of this paper is to develop an efficient hybrid method that can collectively address assembly sequence generation (ASG) and exploded view generation (EVG) problem effectively. ASG is an act of finding feasible collision free movement of components of a mechanical product in accordance with the assembly design. Although the execution of ASG is complex and time-consuming in calculation, it is highly essential for efficient manufacturing process. Because of numerous limitations of the ASG algorithms, a definite method is still unavailable in the computer-aided design (CAD) software, and therefore the explosion of the product is not found to be in accordance with any feasible disassembly sequence (disassembly sequence is reverse progression of assembly sequence). The existing EVG algorithms in the CAD software result in visualization of the entire constituent parts of the product over single screen without taking into consideration the feasible order of assembly operations; thus, it becomes necessary to formulate an algorithm which effectively solves ASG and EVG problem in conjugation. This requirement has also been documented as standard in the “General Information Concerning Patents: 1.84 Standards for drawings” in the United States Patent and Trademark office (2005) which states that the exploded view created for any product should show the relationship or order of assembly of various parts that are permissible.

In this paper, a unique ASG method has been proposed and is further extended for EVG. The ASG follows a deterministic approach to avoid redundant data collection and calculation. The proposed method is effectively applied on products which require such feasible paths of disassembly other than canonical directions.

The method is capable of organizing the assembly operations as linear or parallel progression of assembly such that the assembly task is completed in minimum number of stages. This result is further taken for EVG and is found to be proven effective.

Assembly sequence planning (ASP) is performed most of the times considering the geometric feasibility along canonical axes without considering parallel possibility of assembly operations. In this paper, the proposed method is robust to address this issue. Exploded view generation considering feasible ASP is also one of the novel approaches illustrated in this paper.

The purpose of this paper is to improve the quality of additive manufactured optically translucent parts by investigating the manufacturing issues, analyzing lithophane production criteria and identifying the best translucent material and additive manufacturing (AM) technology.

Figured lithophanes were laser sintered on a 3D Systems SinterStation® HiQ™ with varying layer thickness and plate thickness. Laser sintered (LS) polyamide (PA) 12 blanks were cyanoacrylate infiltrated and polished. Optical properties and performance were compared with the original LS blanks. Lithophanes and blanks were manufactured using 3D systems stereo lithography apparatus (SLA)® Viper ™si2 station, and optical properties and lithophane performance were compared with the LS specimens.

When building in the XY plane, it is optimal to sinter with the minimum layer thickness (0.076 mm) and maximum plate thickness (5 mm). Cyanoacrylate infiltration and polishing assists in reducing the LS PA 12 plate surface roughness, but polishing does not affect the lithophane performance. The best LS candidate should have an absorption coefficient of 0.5/mm using a white light source. Improved resolution but reduced contrast was observed on stereolithography (SL) specimens compared to LS parts.

Transmittance experiments were performed on three SL parts which was not sufficient for optical property calculation. Limited literature was found for new material exploration.

It is the first effort to study systematically quality improvement issues of LS PA optically translucent parts. A comparison is made of optical performance between parts made using LS and SL.

Part building orientation (PBO) is an important factor affecting the quality of laser powder bed fusion (L-PBF), which can affect the surface quality and manufacturing cost. The purpose of this paper is to propose a PBO optimization method to optimize the surface roughness and molding time of parts at the same time on the premise of small calculation scale and arbitrary resolution.

Efficient and accurate evaluation is an important index of PBO optimization method. In this paper, a PBO optimization method based on scaling enumeration method is proposed, and the surface roughness and molding time of L-PBF parts are modeled as the objective evaluation function of PBO optimization process. To realize multi-objective optimization, an expert system is established, and the fuzzy multiple-attribute group decision-making theory is used to provide weights for each objective evaluation function.

Research shows that the scaling-enumeration method can optimize the surface roughness and molding time at the same time and get the best PBO. Compared with the traditional method, the surface roughness and molding time are reduced by 1.1% and 0.58%, respectively, and the operation scale of the scaling-enumeration method is reduced by 99% compared with the traditional method. PBO with arbitrary angular resolution can be achieved.

This paper presents a new method to optimize the forming direction of L-PBF parts. This method has small operation scale and accurate results, so it is meaningful for industrial application.

The purpose of this paper is to develop an optimization model allowing the choice of parts feeding policy to assembly lines in order to minimize total cost.

An integer linear programming mathematical model is developed to assign the optimal material feeding policy to each part type. The model allows choice between kitting, line stocking and just in time delivery policies.

The choice of assembly lines feeding policy is not trivial and requires a thorough economic comparison of alternatives. It is found that a proper mix of parts feeding policies may be better that adopting a single material delivery policy for all parts.

The model is aimed at single-model assembly lines operating in a deterministic environment, but can be extended to the multi-model line case. While relevant quantitative cost drivers are included, some context-related qualitative factors are not included yet. The model assumes that information about product structure and part requirements are known and that a preliminary design of the assembly system has been carried out.

Production managers are given a quantitative-decision tool to determine the optimal mix of material supply policies at an early decision stage.

Respect previous simplified literature models, this approach allows to quantify a number of additional factors which are critical for successful implementation of cost-effective parts feeding systems, allowing comparison of alternative policies on a consistent basis.

This paper aims at developing a multi-objective mathematical model of circular economy that integrates key concept of leasing as a strategy in addition to reuse, refurbishing, primary recycling, secondary recycling and disposal.

This paper proposes multi-objective fuzzy mixed integer linear programming mathematical model considering multi-product, multi-echelon and multi-capacitated concepts of the circular economy. The three objectives of the proposed model, namely, economic, environmental and social are solved simultaneously using constraint approach to obtain balanced trade-off between the objective functions. The model is validated by solving a case study from the literature. The proposed model is made pragmatic for industrial application by considering multi-external suppliers multi-customer zones, multi-disassembly centers, multi-collection centers and multi-refurbishing centers and accounting for purchasing, processing, transportation, set-up costs and capacity constraints at the same time.

The results show that the leasing of the products improves the economic function in addition to the known environmental improvements. The proposed model also shows that the circular economy can generate the jobs for the unskilled people at different locations.

The proposed model can be further improved by considering the non-linearity due to economy of scale at various centers and in transportation. The model can be further extended to make it multi-period model.

The proposed model of circular economy can be used by the organizations as a policy tool to decide the optimum number of collection centers, disassembly centers, refurbishing centers, recycling centers and disposal centers and their optimum locations and allocations. The organizations can also trade-off among economic, environmental and social benefits of their proposed decisions in circular economy.

The originality of the proposed mathematical model is consideration of leasing as a strategy to have better control over the supply chain for circularity; considering the training of unskilled people for backward supply chain jobs and accounting for primary recycling and secondary recycling separately for economical computation.

The use of laser sintering (LS) in the medical sector has increased dramatically in recent years. With the move towards direct use of these parts in clinical applications, there is a greater need to understand the effects of standard processes on the part properties. The purpose of this study is to determine the effect that steam sterilisation has on the mechanical properties of LS polyamide 12 parts.

The research presented here focusses on the effect of a single steam sterilisation cycle on the mechanical properties of polyamide 12 parts manufactured using LS. The influence of water content on the properties was investigated, with additional drying steps trialled to establish the potential to reverse any changes observed and to determine their root cause.

The results show that steam sterilisation has a significant effect on the mechanical properties of LS polyamide 12 parts, with a 39% reduction in elastic modulus, a 13% decrease in ultimate tensile strength and a 64% increase in the elongation at break. These properties were also all found to correlate with the water content, suggesting that this was the cause of the difference. The original properties of the parts were able to be recovered after oven drying.

These results show that with an additional drying step, LS polyamide 12 parts can be steam sterilised with no effect on the mechanical properties.

This is believed to be the first investigation into the effects of steam sterilisation in isolation on LS polyamide 12 parts, the first instance of drying parts to recover mechanical properties and the first instance of multiple water content measurements being directly linked to the mechanical properties.

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.

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.

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.

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.