Additive Manufacturing with Bioinspired Sustainable Product Design: A Conceptual Model

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Procedia Manufacturing 26 (2018) 880–891 Procedia Manufacturing 00 (2017) 000–000 www.elsevier.com/locate/procedia

46th SME North American Manufacturing Research Conference, NAMRC 46, Texas, USA 46th SME North American Manufacturing Research Conference, NAMRC 46, Texas, USA

Additive Manufacturing with Bioinspired Sustainable Product Additive Manufacturing with Bioinspired Sustainable Product Design: A Conceptual Model Manufacturing Engineering Society International Conference 2017, MESIC 2017, 28-30 June Design: A Conceptual Model 2017, Vigo (Pontevedra), Spain

Hao Zhang*, Jacquelyn K. Nagel, Abdulrahman Al-Qas, Evan Gibbons, Jenifer JooHao Zhang*, Jacquelyn K. Nagel, Abdulrahman Evan Gibbons, Jenifer JooYeon Lee Al-Qas, Costing models for capacity optimization in Industry 4.0: Trade-off Yeon Lee Madison University, 800 S Main St, Harrisonburg, VA 22807, USA betweenJames used capacity and operational efficiency James Madison University, 800 S Main St, Harrisonburg, VA 22807, USA

A. Santanaa, P. Afonsoa,*, A. Zaninb, R. Wernkeb

* Corresponding author. Tel.: +1-540-568-2711 a * Corresponding Tel.: +1-540-568-2711 E-mail address:author. [email protected] University of Minho, 4800-058 Guimarães, Portugal b E-mail address: [email protected] Unochapecó, 89809-000 Chapecó, SC, Brazil

Abstract Abstract Abstract The development of additive manufacturing (AM) has led to enormous opportunities for product design and manufacturing. The The development of additive (AM) has led to enormous opportunities for product design manufacturing. The industrial application of AM, manufacturing however, remains limited to aerospace, medical, and research arenas. Theseand limitations are largely industrial of however, remains limited toand aerospace, and research arenas. These limitations are largely Under theapplication concept ofAM, 4.0", production processes will bematerials pushed to equipment, be increasingly interconnected, due to AM’s weaknesses in"Industry process speed, surface finish, the costmedical, of raw and which prevent traditional due to AM’s process surface finish, the costbenefit of rawefficient. materials andthis equipment, prevent traditional industry awayweaknesses from adopting AM inspeed, their productions. Theand potential (e.g., material reduction andwhich higher product quality) information based on a inreal time basis and, necessarily, much more In context, capacity optimization industry from adopting AM in productions. Theindustry. potential benefit (e.g., material reduction and higher product from beyond AMaway is often overlooked traditional manufacturing Bioinspired design creates innovations in quality) product goes the traditional aim oftheir capacity maximization, contributing alsoproduct for organization’s profitability and value. from AMfor isless often overlooked traditional industry. Bioinspired suggest product design creates in product redesign material consumption, bettermanufacturing functionality, and lessapproaches environmental impact. The objective ofinnovations this paper is to develop Indeed, lean management and continuous improvement capacity optimization instead of redesign for less material consumption,tobetter functionality, andidentify less environmental Theprocess objective of this paper is to develop a conceptual model forstudy manufacturers productand and additive adoption opportunities, and maximization. The of capacityredesign optimization costing models manufacturing is impact. an important research topic that deserves aimplement conceptualAM model for manufacturers to redesign product and model identifyintegrates additive manufacturing process adoption and processes in production. conceptual concurrent considerations of opportunities, multiple additive contributions from both the practical andThis theoretical perspectives. This paper presents and discusses a mathematical implement AMdesign processes in production. conceptual integrates concurrent multiple additive manufacturing and bioinspired designThis factors includingmodel raw material quality (e.g. size,considerations shape, internal of porosity), processing model for capacity management based different costing models (ABC and TDABC). Ainternal generic model processing has been manufacturing design bioinspired designon factors including raw material quality size, shape, porosity), parameters (e.g., laserand power, roller speed), and functionality of the product (e.g.,(e.g. stress, strain, displacement). A case study is developed and it was used to analyze idle capacity and to design strategies towards the maximization of organization’s parameters (e.g., laser apower, roller speed), andwith functionality of thesintering product process. (e.g., stress, displacement). A case diamond study is conducted on making unit Titanium product selective laser Threestrain, structures were examined: value. The capacity maximization vs This operational efficiency ismethod highlighted and it is shown that capacity conducted ontrade-off making unit Titanium product with selective sintering process. Three structures were examined: diamond structure, honey comb astructure, and bone structure. studylaser reveals that the can be applied in additive manufacturing optimization might inefficiency. structure, honey combhide structure, and bone structure. This study reveals thatnew the method can begeometries applied in that additive manufacturing early product design and operational it assists researchers and engineers explore bioinspired could be used in © 2017product The Authors. by Elsevier B.V. and engineers explore new bioinspired geometries that could be used in early designPublished and it assists researchers manufacturing. Peer-review under responsibility of the scientific committee of the Manufacturing Engineering Society International Conference manufacturing. 2017. © 2018 The Authors. Published by Elsevier B.V. © 2018 Published Elsevier B.V. © 2018 The The Authors. Authors. Published by by B.V. committee of NAMRI/SME. Peer-review under responsibility of Elsevier the scientific Peer-review under responsibility of the scientific committeeIdle of the 46th SME North Efficiency American Manufacturing Research Conference. Keywords: Cost Models; ABC; TDABC; Capacity Management; Operational Peer-review under responsibility of the scientific committee ofCapacity; NAMRI/SME. Keywords: Additive manufacturing, Sustainable product design, Bioinspired design Keywords: Additive manufacturing, Sustainable product design, Bioinspired design

1. Introduction

The cost of idle capacity is a fundamental information for companies and their management of extreme importance in modern©production systems. In general, it isB.V. defined as unused capacity or production potential and can be measured 2351-9789 2018 The Authors. Published by Elsevier 2351-9789 2018responsibility The Authors. Published by Elsevier B.V.hours Peer-review of the scientific committee of NAMRI/SME. in several©under ways: tons of production, available of manufacturing, etc. The management of the idle capacity Peer-review underTel.: responsibility the761; scientific committee NAMRI/SME. * Paulo Afonso. +351 253 of 510 fax: +351 253 604of741 E-mail address: [email protected]

2351-9789 © 2017 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the scientific committee of the Manufacturing Engineering Society International Conference 2017. 2351-9789 © 2018 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the scientific committee of the 46th SME North American Manufacturing Research Conference. 10.1016/j.promfg.2018.07.113



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1. Introduction

2.1. Additive manufacturing design

The development of numerous additive manufacturing processes have allowed industry to make 3D printing parts and products with multiple materials [1]. Especially for high value material products (e.g. stainless steel, titanium, copper) which suffer from high raw material cost and expensive endof-life management plans. One solution for reducing cost and environmental impact is designing high value parts with complex structure to reduce material use and meanwhile support the functionality of the part. The layer by layer processing method allows engineers to make these complex geometry that was difficult or impossible for conventional manufacturing processes [2–6]. This provides an opportunity for innovative product design targeting at higher product functional performance, lower cost, reduced environmental impact [7,8]. Designing for additive manufacturing, however, is a challenge, especially for designers that are used to develop parts for conventional manufacturing technologies like casting and machining [9]. The concept of learning from nature has deeply rooted in scientist and engineer’s spirit that design engineers now start to understand the natural structures and use them in products such as implants, aerospace, architecture, and automotive industry. Among the many biomimicry structures, a model of exploring bioinspired structures and applying in industrial products is desired. Design engineers also find it difficult to reference the functional, economic, and environmental properties in product design and application [10]. Presented herein is an overview of current challenges of additive manufacturing and bioinspired design. A conceptual systemic model is then presented to lay down the foundations to build a generalized system for assisting bioinspired product design for additive manufacturing. The proposed conceptual model is demonstrated with a case study on a Titanium product.

While additive manufacturing can make complex structures, when designing additive manufactured parts, there are several challenges related to CAD model geometry, path generation, process selection, process resolution, feed material properties, and support materials. The quality of final product is affected by the feedstock quality. For metal product processing, the quality of powder is determined by its geometric features including particle size and distribution, particle shape and internal structure, surface area, morphology, and internal porosity. Physical characters such as flowability and apparent density also affect quality of final products [11]. The particle size determines layer thickness [12]. Higher layer thickness decreases the density of each powder layer, and thereby decreases density of the manufactured parts and causes rougher surfaces due to incomplete melting of larger particles [13]. Particle size ranges from 15 μm to 150 μm is often used to create higher density and lower surface roughness [14]. Particle shape and surface roughness also affects density of manufactured parts. Variables such as circularity, aspect ratio, elongation, dispersion, roundness, flatness, and perimeter to area ratio are often used to describe shapes of particles. Due to the high irregularity qualitative and quantitative descriptions are still challenging to researchers [15] [16]. High spherical shape particles with smooth and dry surfaces [17] are found to yield less internal fractioning which leads to higher layer density because the powders can be easily deposited with least interparticle friction and best flow ability [18]. Circularity and aspect ratio are usually used to measure spherical powders [19]. Porosity is a factor that affects mechanical properties of parts. Under tension, porosities are stress concentrators that may induce lower mechanical strength and cause damages from micro-cracks. Therefore, higher porosity results in lower stiffness of the parts [20]. Minimum feature size, surface roughness, and geometrical accuracy are of common concerns during the printing process. Heat source and the size of the feedstock determine the minimum feature size. Powder bed fusion (PBF) typically has the best

2. Literature Review This section reviews current knowledge on additive manufacturing design considerations, bioinspired product design, and sustainability of AM.

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resolution, with the resolution of Selective laser melting (SLM) slightly better than Electron beam melting (EBM) depending on parameters used [11]. For powder bed fusion processes, scanning speed and laser power directly affect solidification of the part. Edge effect happens when a heat source passes an edge and return to the edge before the heat has time to dissipate. Therefore, a good relationship between scanning speed and powder needs to be developed to ensure the heat transfer of the part and powders and avoid overheating of the melt surface [11,21,22]. Above are some common factors that need to be considered in additive manufacturing design. Engineers are recommended to holistically design the material and process conditions to achieve a desired quality of the finished part. 2.2. Bioinspired design for additive manufacturing Bioinspired design, also known as biomimicry, is a problem solving lens that looks at nature’s time-tested physical and non-physical characteristics to solve today’s engineering challenges in non-conventional ways while also considering the consequences of design decisions [23]. Taking a holistic approach such as bio-inspired design is similar to considering the multiple phases of a product’s life-cycle. Further, biological systems exhibit multi-functionality from physical characteristics (i.e., forms, shapes, geometries) as opposed to material which offers inspiration for product life-cycle management. To design a product holistically requires that the manufacturing process be considered. To fully exploit the potential of additive manufacturing, innovative approaches for material development and design through bio-inspired design have occurred. Recently, additive manufacturing researchers have taken inspiration from the physical characteristics (i.e., forms, shapes, geometries) of natural systems to achieve a variety of engineering requirements such as reduction of peak stresses, homogeneous stress distribution, minimization of weight, reduction of material diversity, reduction of waste, etc. Emmelmann et al. have identified key biological structures including honeycomb, bamboo, rhubarb, and diatom that enable lightweight design for structural components such as aircraft brackets [24,25]. Laser additive manufacturing is used to create the complex, optimized structures. Their process for incorporating the biological inspiration also includes topology optimization and FEA modeling to ensure

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the designs meet the engineering requirements. Similarly, Kamps et. al [26] have defined a methodology that uses CAD/CAE optimization to design load-adapted structures for lightweight design specifically for additive manufacturing. TRIZ serves as a logic framework for identification of the engineering functions to be fulfilled, and a biomimetic database serves as the source for finding biological inspiration. Bio-inspired design has also been applied through additive manufacturing to increase product recyclability through minimization of material diversity while still achieving desired functions [27]. Leveraging bioinspired geometries that achieve multiple functions enables maximization of existing materials and manufacturing methods. This approach is focused on the re-design of multi-material systems such that they can be manufactured with a single, recyclable material to facilitate integration with centralized recycling processes. Bio-inspired design for additive manufacturing has also resulted in composite materials with multifunctional abilities. Gu et. al [28] studied how advanced 3D-printing techniques can be used to mimic the architectures, basic building blocks, and functions of natural materials (bone, nacre, hair, and spider silk) to create bio-inspired composites. A unique aspect of this work is the use of a multi-material 3D printer to create soft and stiff building blocks that are optimized and tuned for specific mechanical properties. In a similar vein, Dimas and Buehler [29] have used biological inspiration to design composite materials with tunable fracture mechanical properties. Experimental tests of the flaw-tolerant materials confirmed computational predictions. Significantly, macroscale composites were design and manufactured taking inspiration from microscopic features of biological systems [29]. 2.3. Sustainability of additive manufacturing Sustainability studies on additive manufacturing primarily focus on cost assessment on AM processes [8,30], environmental impact assessment on AM processes or product life cycles [31–33], sustainable product design [34–37], process optimization to reduce environmental impact, and safety issues around AM materials and processes [38]. Traditional sustainability assessment methods can be used to assess additive manufacturing processes. Activity based model [39] where each cost is

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associated with a particular activity can also be utilized to assess AM process cost [30]. A wellconstructed cost model should consider several factors in the system such as material costs, machine cost, build envelope and envelope utilization, build time, energy consumption and labor [8]. Life cycle costing categories cost items through product or system life cycle and has been proved to be an effective method to evaluate process costs [40]. From life cycle perspective, cost model should include material extraction, material refining, manufacturing, and transportation among other things. Current research on additive manufacturing costs reveals that material costs and AM system are two major cost factors in the total cost. AM can be cost effective for manufacturing small batches with continued centralized manufacturing. However, with increased automation distributed production may be cost effective. Current studies are limited in the scope of cost assessment due to lack of examining supply chain effects such as inventory and transportation costs. The general approach for environmental impact assessment is life cycle assessment which has been practiced for two decades on various traditional manufacturing processes and systems [41–44]. LCA is a method to systematically evaluate environmental impact through a product or system’s life cycle [45]. LCA on additive manufacturing should take into account two aspects, one is in the whole life-cycle stages of the part and the second is on the process’s objectives to estimate quantitatively all the resource consumption of the set part process [46]. A cradle to cradle life cycle assessment should include life cycle stages such as raw material extraction, material processing, manufacturing, distribution, use, and end of life. While studies have shown that AM shows a reduced environmental impact on the process and material use [47]. However, research on material processing, distribution, and end of life stages remain to be challenging due to the immaturity of the additive manufacturing supply chain. Social impact assessment of additive manufacturing mainly focuses on the human safety risks due to different routes of exposure to metal powders. Workers on AM processes that use metals and in particular metal powders can come into contact with them in various ways, such as inhalation exposure,

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exposure oral, and dermal exposure. Safety regulations shall be designed properly to avoid such risks [38]. However, social impact assessment shall also consider broader impact along the additive manufacturing supply chain. Social life cycle assessment [48,49] can be employed to investigate societal impact (e.g. worker, consumer, local community, society, and value chain actors) from AM manufacturing development and transition from traditional manufacturing systems. 3. Conceptual model In this section, a conceptual model for bioinspired sustainable product design for additive manufacturing is presented (Figure 1). The impact of bioinspired design on product life cycle, the concept of library of bioinspired geometries, and sustainable additive manufacturing are explained. 3.1. The impact of bioinspired design on product life cycle Bioinspired design introduces an interface between the disciplines technology, biology, and sustainability, and aims to balance inputs from all three. Biology provides principles and structures that can be employed in technical applications and sustainability provides the assessment of impact. The impact of product design goes through the entire product life cycle from material (feedstock) processing to end of life. With the change of product design for additive manufacturing, reconfiguration of product supply chain is needed based on the requirement of raw materials, new manufacturing processes, and end of life strategies. Powder processing industry plays an essential role in the supply chain as it is a key raw material for AM made products. Because of simplicity of AM products (e.g. simplified assemblies), the difficulty of recycling is reduced. It is estimated that 95-98% of metal powders can be recycled [50].

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Bioinspired Product design

Process parameters

Feedstock processing Material Extraction

Recycle

Use

Library of bioinspired geometries

Design for AM

Bio-inspired design

AM

Design Remanufacturing Reuse Maintain

Dispose

Feedstock quality

Distribute

Sustainability Life cycle costing

Life cycle assessment

Social life cycle assessment

Fig. 1. A conceptual model for bioinspired sustainable product design for additive manufacturing

3.2. A library of bioinspired geometries for additive manufacturing product design As bioinspired design has great potential in additive manufacturing, standardized bioinspired geometries (e.g. light weight geometries) shall be developed for mass production of future products. These geometries are to assist product designers achieve different product functionality such as light weight, ductility, durability, high strength, etc. The finished parts functionality will be affected by factors including size, feedstock quality, and process parameters. However, the library (Fig. 2) could provide a guide for product designers to identify appropriate geometries to achieve product functions. AM design

Bioinspired Geometry

Examples: Honey comb Lattice Bone Cartilages etc.

A library of geometries shall be first established based on scattered work from 3D design, materials science, and engineering design. So far, some common material structures have been identified and used in composite materials and nanostructures. However, a larger scale of material or product design especially studies on mechanical properties such as stiffness, strength, hardness, ductility and toughness are still needed [10]. Second, these collected structures need to be further characterized by their functions and mechanical properties. An example of collected geometries (Fig. 3) include cellular, bone, nacre, wood, shrimp, dactyl club, teeth, bamboo and palm.

Functional objective

Examples: Size Working environment Yield strength Fatigue strength Crack resistance etc.

A library of bioinspired geometries for additive manufacturing

Fig. 2. Structure of the library of bioinspired geometries for additive manufacturing 2351-9789 © 2018 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the scientific committee of NAMRI/SME.

(a)

(b)

(c) Fig 3. Examples of bioinspired structures. (a): bone structure (adapted from [10]); (b) bamboo structure (adapted from [10]); (c): diatom (from [51])

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Hao Zhang et al. / Procedia Manufacturing 26 (2018) 880–891 Author name / Procedia Manufacturing 00 (2018) 000–000

For example, honey comb structure is a light weight structure that can be used for replacing traditional solid blocks. This structure can be tested in a specific size, material, working temperature, and process parameters. The resulted unit structure can be tested to get yield strength, fatigue strength, and crack resistance. With this bioinspired geometry library, product designers will be able to identify appropriate structures for the product. 3.3. Sustainability of bioinspired geometries product design Cost and environmental impact are affected by the complexity of the geometries. Complex geometries require longer process time compared to simple geometries, and thereby resulting into higher energy consumption and environmental impact during processing. Environmental impact is also affected by the product material use. Documented geometries will show a direct comparison of material use for the same product design. The following are the methods for assessing cost and environmental impact. Life cycle costing (LCC) is used for assessing manufacturing cost for unit geometries. LCC take account into raw material, equipment, energy, and labor costs associate with processing the products. Energy and labor costs are depended on the processing time (set up time and build time). Build time is affected by part volume, support volume, z-height, surface finish, support height and base area [52–54]. A simplified time estimation equation for part main dimensions less than 10 inches is shown below: Estimated Build Time= (0.0341) + (2.0 * Z) + (2.17 * VOL) + (0.018 * SA) Where z is height, VOL is volume, and SA is surface area. Life cycle assessment is used for assessing environmental impact. The same unit structure (functional unit) with different bioinspired geometries are considered as alternatives of design. Therefore, environmental impact is affected by energy consumption during build time and material use in the geometry. The LCA shall be a closed loop cradle to cradle analysis which includes material extraction, material processing, and manufacturing, distribution, use, and end of life stages of product life cycle. Typical environmental impact includes global warming potential, resource depletion, acidification, eutrophication, ozone depletion, fossil fuel depletion,

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carcinogenic, respiratory effects, noncarcinogenic, and smog etc. Social life cycle assessment considers social impact from additive manufacturing process itself and the impact from bioinspired designs. Within the AM process, safety is a key factor in social impact assessment. In the product life cycle, the social impact can be extended to many aspects such as supply chain configuration, business model change, design innovation revolution, technical training of new labor force on design and AM process control. 3.4. Application of the conceptual model Product designers could use this model to guide their material structure selection and analysis in the early design stage. First, according to the purpose of the product, designers can select appropriate candidate structures to meet the function needs. Then 3D models are created to evaluate product stress, strain and fatigue. Second, additive manufacturing design considerations (e.g., feedstock size, shape, regularity, and processing parameters (e.g., power, scan speed) need to be evaluated to achieve targeted product quality. Third, sustainability assessment including life cycle costing, life cycle assessment, and social impact assessment can be conducted to study the potential sustainability outcomes from design alternatives. In the end, decision making methods such as multicriteria decision making can be used to find the best solution by concurrently comparing functionality, economic, environmental, and social performances from selected designs. In the application, however, there exists several challenges from design to manufacturing such as accuracy, repeatability, resolution, predictability of mechanical properties, and consistency of feedstock [55–58]. Designers need to select preferences of features (e.g. resolution) when they must compromise other factors (e.g. accuracy). For example, to produce repeatable parts, Selective Laser Sintering (SLS) process can be selected over Fused Deposition Modelling or Stereolithography (SLA) [57,59]. 4. Case study To demonstrate the conceptual model, three-unit parts with the same dimension (1″ × 1″ × 0.5″) were created. The structures for the units are diamond, honeycomb and bone. The three structures that were

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selected for this study were: diamond, honeycomb, and lattice. The diamond structure is a face-centred cubic structure and it was selected based on its current numerous applications in industry; such as aerospace, aviation, automotive, and healthcare. The advantage that the diamond structure offers is its ability to reduce material consumption without sacrificing product strength and reliability. Honeycomb structures can vary widely. The honeycomb structure is this study is an array of hollow cells formed between think vertical walls. The honeycomb structure was selected for similar reasons to the diamond structure; such as its current use in aviation and the advantages that it offers. However, the honeycomb structure supported the team in reaching their goal of selecting biological inspired structures so that they may be integrated into product design functionality. In product design, practitioners have used different bone structures, for example bone network structure and a scaffold composed of compacted single bone structures. In this case study, scaffold with single bone structures is selected to further utilize biological inspired structures. The advantage of the bone structure echoes that of both the diamond and honeycomb structures, that is the ability to reduce material consumption while maintaining product strength. Differences of structure details are shown in Figure 4. A functionality analysis and a sustainability assessment were conducted based on the material (Commercially Pure Titanium Grade 2), size, with two example forces (10lb and 50lb) applied on the top and side of the parts. The result is to provide functionality and sustainability (economic & environmental) support for small product design (e.g., implant).

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honeycomb) in the long side of the structure. This size is determined by the machine minimum feature size which is 100 μm [60]. Part mass, volume, density, weight, and surface areas are calculated with Solidworks 2017. It is shown that bone structure has the highest mass value and volume value, however, its surface area is smaller than diamond and honeycomb structures. Therefore, bone structure part also has more material use compared to diamond structure and honeycomb structure. Table 1. Physical properties of the three structures Physical Analysis Structure Measure Mass: Diamond Volume: Density: Weight: Surface area Mass: Bone Volume: Density: Weight: Surface area Honeycomb Mass: Volume: Density: Weight: Surface area

Results 0.0104195 2.31 4510 0.102111 303.6 0.0131234 2.91 4510 0.128609 140.5 0.0110225 2.44 4510 0.108021

kg mm3 kg/m3 N cm2 kg mm3 kg/m3 N mm2 kg mm3 kg/m3 N

249.2

mm2

The processing parameters are based on 3D Systems ProX DMP300 [60]. Processing times are estimated based on the built time equation demonstrated in section 3.3. Because of the surface area for bone structure is smaller than diamond and honeycomb structure, its processing time is also smaller. The detailed feedstock properties, process parameters, and estimated processing times are shown in Table 2. Table 2. Part Feedstock Properties, Process Parameters, and Estimated Processing Times

Fig. 4. Diamond structure, honeycomb structure, and bone structure products

Physical properties of the three parts are shown in Table 1. The length of each diamond in the structure is 0.762 mm (0.03inch) and the length of each unit honeycomb is 0.508 mm (0.02 inch). There are nine units (diamond and honeycomb) in the short side of the structure, and there are 19 units (diamond and

Feedstock (Commercial Pure Titanium Grade 2) Property Value Unit Powder size 20 μm Shape Spherical Yield strength 540 MPa Young's Modulus 105 GPa Process parameters (Selective Laser Sintering) Property Value Unit Scan speed 400 mm/second Layer thickness 40 μm Laser power 500 W Laser wavelength 1070 nm Equipment cost 850000 $ Life span 15 years Labour cost 60000 $/year/operator

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Equipment power Processing time Structure Diamond Honeycomb Bone

15

KVA

Value 3.18 3.05 2.82

Unit hr hr hr

Table 6. Stress, strain, and displacement from 50 lb side force

By conducting finite element analysis on the three parts, stress, strain, and displacement measures are analysed. Each force (10 lb and 50 lb) is tested on the two sides (1”×0.5” and 1”×1”) of the part. The forces are evenly distributed on one surface of the part and have the opposite side fixed. The results are shown in Table 3-6. Table 3. Stress, strain, and displacement from 10 lb top force Structure

Measure

Diamond

Stress (N/m )

Honeycomb Bone

2

Strain Displacement (μm) Stress (N/m2) Strain Displacement (μm) Stress (N/m2) Strain Displacement (μm)

Result Min. Max 13488 5.26E+06

6.53E-08 0 4478.35 4.44E-08 0 5107.65 2.71E-08 0

3.69E-05 0.81 5.46E+07 1.11E-04 1.02 2.25E+06 1.55E-05 0.32

Table 4. Stress, strain, and displacement from 10 lb side force Structure

Measure

Diamond

Stress (N/m2)

Honeycomb Bone

Strain Displacement (μm) Stress (N/m2) Strain Displacement (μm) Stress (N/m2) Strain Displacement (μm)

Result Min. Max 1315.99 8.47E+06

5.44E-08 0 1135.93 1.09E-08 0 762.12 2.71E-08 0

6.26E-05 1 2.45E+07 1.36E-04 0.3 1.06E+07 1.55E-05 3.7

Table 5. Stress, strain, and displacement from 50 lb top force Structure

Measure

Diamond

Stress (N/m2) Strain Displacement (μm) Stress (N/m2) Strain Displacement (μm) Stress (N/m2) Strain Displacement (μm)

Honeycomb Bone

887

Result Min. Max 63403.9 2.65E+07 5.18E-07 1.80E-04 0 4.03 18732.1 4.25E+08 2.55E-07 1.11E-03 0 5.24 25582.1 1.13E+07 1.35E-07 7.74E-05 0 1.6

Structure

Measure

Diamond

Stress (N/m2) Strain Displacement (μm) Stress (N/m2) Strain Displacement (μm) Stress (N/m2) Strain Displacement (μm)

Honeycomb Bone

Result Min. Max 21239 4.24E+07 5.18E-07 1.80E-04 0 6.84 9237.99 1.07E+08 1.32E-07 3.98E-04 0 1.53 1547.61 5.28E+07 1.35E-07 7.74E-05 0 18

The bone structure has the smallest max stress, strain, and displacement. For the min stress, however, honeycomb structure has the smallest value. To study the supply chain effects of the design, a hypothetical scenario is used to demonstrate economic and environmental impact. The products are produced in Harrisonburg Virginia and will be shipped to New York. The distance is 353 miles between the two places. With current product volume (668 units/year for honeycomb, 640 units/year for Diamond, and 724 units/year for Bone structure), the products are shipped twelve times every year. The mileage rate for transportation is 0.545 $/mile [61]. During the use stages, there is no additional consumables or costs caused by the product. At the end of the product life, all products are assumed to be recycled with current steel recycling price. Parameter for transportation and end of life stages are shown in Table 7. Table 7. Transportation and End of Life Parameters Transportation Parameters Distance Mileage rate Frequency

Value 353 0.545 12

Unit miles $/mile Times/year

End of Life Recycling price

0.032

$/kg

Cost assessment is conducted with life cycle costing method and is based on 15 years life span. The case study gives an assumption of production with two eight-hour shifts per day and 255 working days per day. The inflation rate is 2.2%. The industrial rate for electricity is $0.0667/KWh [62]. Two operators with annual salary of $60,000 are hired for the two shifts. The cost assessment results are shown in Table 8 and Fig. 5).

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Table 8. Unit product cost Processing Cost Material Cost Total Production Cost Transportation cost Recycling cost Material % Production % Transportation % Recycling %

Diamond

Honeycomb

Bone

$143.23 $3.63 $146.86

$137.3 $4.41 $141.71

$126.66 $5.44 $132.1

$3.6 $0.0003 2.36% 95.31% 2.33% 0.0002%

$3.46 $0.0004 2.95% 94.74% 2.31% 0.0003%

$3.19 $0.0004 3.86% 93.87% 2.27% 0.0003%

Costs of the Three Unit Structures

Environmental Impact Results (pt) 2

1.5 1 0.5

0

Diamond

Honeycomb

Lattice

Acidification

Ecotoxicity

Eutrophication

Global Warming

Ozone Depletion

Fossil Fuel depletion

Carinogenics

Non carcinogenics

Respiratory effects

Fig. 6. Environmental impact of the three structures

$160.00 $140.00

Table 9. Environmental Impact from the Three Structures (Functional unit: one unit product)

$120.00 $100.00 $146.86

$141.71

$132.10

Diamond

Honeycomb

Bone

$60.00

$40.00 $20.00

$0.00

time and energy consumption.

Smog

$180.00

$80.00

9

Material Cost

Total Production Cost

Transportation cost

Recycling cost

Fig. 5. Unit cost of the three structures

The cost assessment results show that because of the long processing time for each part, unit cost remains to be high and is sensitive to the production volume which reflects current challenge over additive manufacturing industrialization for mass production. For example, if production is change to one shift per day, the resulted production unit costs will be $191.09 for diamond structure, $184.11 for honeycomb structure, and $171.22 for bone structure, which are about $50 higher than two shifts unit costs. Similarly, cost and environmental impact on transportation and material supply is not only affected by the distance but also by the size and quantity of product in transportation. For example, in this case study, the transportation costs will be doubled if frequency of transportation is 24 times per year. A cradle to cradle LCA is conducted to assess environmental impact of one unit product for each structure. The system boundary includes raw material extraction (Titanium) and processing (powder processing), manufacturing (selective laser sintering), distribution (truck), use, and end of life (recycled). The impact results are shown in Table 9. The environmental impact assessment result (Table 7 and Fig. 6) shows that bone structure has the lowest impact on all categories due to its smaller processing

Impact Category Total Impact (mpt)

Diamond Honeycomb 1.5 1.4 Ecological damage Acidification 0.1017 0.09436 Ecotoxicity 0.0694 0.06538 Eutrophication 0.0162 0.01498 Global Warming 0.5418 0.50232 Ozone Depletion 0.0003 0.00028 Resource Depletion Fossil Fuel depletion 0.1497 0.13888 Human health damage Carcinogenics 0.3405 0.31626 Non carcinogenics 0.15 0.14658 Respiratory effects 0.0693 0.06426 Smog 0.0612 0.0567

Bone 1.3 0.08671 0.06149 0.01378 0.46163 0.00026 0.12766 0.29146 0.14586 0.05915 0.05213

The results from the case study in applications can be sensitive to several factor such as repeatability, process failure rate, feedstock consistency, and manual operations in the process. These will affect the final costs and environmental impact in the case study. However, the case presented in this section is to demonstrate that researchers can conduct functionality analysis and sustainability assessment on various bioinspired structures and the results will be able to assist future industrial product design and enhance the development of additive manufacturing application in industry. 5. Discussion The industrial application of additive manufacturing has great potentials but is hindered by process and design limitations. Bioinspired design provides solutions to various design purposes (e.g., light weight). Developing a framework for researchers and engineers to build a bioinspired structure library is

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desired for additive manufacturing industrialization. This paper aims to develop a conceptual model towards sustainable bioinspired design of additive manufacturing products. The conceptual model aims to assist product design engineers identify bioinspired geometric structures for product applications, assess the functionality, economic, and environmental impacts of the selected structures, and make decisions on design alternatives. The method integrates concurrent considerations of multiple additive manufacturing design and bioinspired design factors including raw material quality (e.g. size, shape, internal porosity), processing parameters (e.g., laser power, roller speed), and functionality of the product (e.g., stress, strain, displacement). Sustainability assessment methods (e.g. life cycle costing, life cycle assessment) have been used for evaluating cost and environmental impact for processing different geometries. Finite element analysis is used for product functionality testing. A case study is conducted on making a unit Titanium product with selective laser sintering process. Three structures were examined: diamond structure, honey comb structure, and bone structure. Cost assessment considered material, labour, energy, and equipment components. A cradle to grave life cycle assessment was conducted to assess environmental impact along life cycle. The results show that bone structure yields lowest cost and environmental impact. This study reveals that the model can be applied in additive manufacturing early product design and it assists researchers and engineers explore new bioinspired geometries that could be used in manufacturing. Future research will be focused on more geometries and conduct static and fatigue analysis at various temperature conditions. Sensitivity analysis and uncertainty analysis can be conducted based on new testing results. Surface finish of the product also needs to be studied with prototypes. Acknowledgements The authors would like to thank James Madison University College of Integrated Science and Engineering for the support of the research. References [1] [2]

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