Laminated Object Manufacturing Process Research Articles

Mechanical property characterizations of woven natural fiber-reinforced polymers 3D printed through a laminated object manufacturing process

ABSTRACT The mechanical properties of woven natural fiber reinforced polymers additively manufactured through Laminated Object Manufacturing (LOM) technology are investigated in this paper. The benefits of both the material and manufacturing process were combined into a sustainable practice, as a potential alternative to traditional synthetic composite materials made from nonrenewable crude oil with limited end-of-life alternatives. Woven jute fiber reinforcements are used to strengthen both synthetic and bio- thermoplastic polymers in creating highly biodegradable composite structures. Such materials, as one of the prospective alternatives for synthetic composites, can be used in many engineering fields such as automobile panels, construction materials, and commodity and recreational products including sports and musical instruments. A LOM 3D printer prototype was designed and built by the authors. All woven jute/polymer biocomposite test specimens made using the built prototype in this study had their mechanical (both tensile and flexural) properties assessed using ASTM test standards and then compared to similar values measured from pure polymer specimens. Improved mechanical characteristics were identified and analyzed. Finally, SEM imaging was performed to identify the polymer infusion and fiber-matrix bonding conditions.

3D printing of gun propellants based on laminated object manufacturing

ABSTRACT The preparation of complex geometry gun propellant to improve combustion progressivity by conventional extrusion processes has been a challenge. An efficient and scalable 3D printing approach based on laminated object manufacturing (LOM) for gun propellant was proposed. A demonstration of the rosette-shaped 61-perf double-base gun propellant using conventional sheet double-base gun propellant and volatile solvent ethyl acetate was printed by a self-developed printer. The printed gun propellants were characterized in terms of printing qualities, mechanical properties, and combustion performances. The standard deviations of inner diameter and web thickness were 0.031 mm and 0.023 mm respectively. Moreover, its density (1.623 g·cm−3) was comparable to that of conventional double-based gun propellants. The tensile strength, compression strength, and impact strength were 10.37 MPa, 74.13 MPa, and 5.60 kJ·m−2, respectively. Importantly, the dynamic vivacity curve tested by the closed vessel matched the theoretical curve well, with a dynamic vivacity increment of 0.23 MPa−1·s−1. This indicated that printed grain has the highest progressive combustion (35% improvement) of the multi-perforated gun propellants to date. Hence, the gun propellant LOM process offers an attractive route to prepare complex geometry gun propellants with higher progressive combustion, breaking the technological bottleneck in the field of gun propellant manufacturing.

Organic mesh template-based laminated object manufacturing to fabricate ceramics with regular micron scaled pore structures

A new aqueous slurry-based laminated object manufacturing process for porous ceramics is proposed: firstly, an organic mesh sheet is pre-paved as a pore-forming template before slurry layer scraping; secondly, the 2D pattern is built with laser outline cutting of the dried mesh–ceramic composite layer; finally, the pore structure is formed after degreasing and sintering. Alumina parts with porosities of 51.5 %, round hole diameters of 80 ± 5 μm were fabricated using 70 wt. % solid content slurry and 100 mesh nylon net. Using an organic mesh as the framework and template not only reduces the risk of damage of the green body but also ensures the regularity, uniformity and connectivity of the micron scaled pore network. The layer-by-layer drying method avoids the delamination phenomenon and improves the paving density. The new method can realize the flexible design of the pore structure by using various organic mesh templates.

Laminated Object Manufacturing of Ceramic‐Based Materials

Since their inception, additive manufacturing (AM) techniques have been the go‐to methods for obtaining highly complex‐shaped rapid prototypes (RPs) and specialized parts, which were produced in small lot sizes. The AM technique of laminated object manufacturing (LOM) is an immensely convenient and cost‐effective method for quickly producing millimeter‐sized to meter‐sized parts, while incorporating micrometer‐sized constructive features. LOM machines offer an open work space, within which nontoxic and highly filled sheet materials can be processed at a high production velocity. The unique property profile of ceramic‐based materials from LOM may be indispensable for applications calling for materials that unite high temperature resistance, mechanical strength, and light weight. Optionally, local material functionalization may engender the electrical conductivity, chemical stability, ferroelectricity, radiation shielding, or filter membrane stability of a limited portion of the material. Herein, a detailed evaluation of the applicability of LOM in the near net shaping ceramic‐based materials is presented. Optional technical adjustments for the LOM process and extensions of the LOM machine configuration can improve the economic feasibility its operation. Previously successful LOM‐printed ceramic‐based materials are showcased within a comprehensive overview on the state of the art and potential novel composite materials are presented.

Experimental Study on Inert Gas-assisted Laser Cut Veneer Based on LOM

Based on the LOM (Laminated Object Manufacturing) process, an inert gas-assisted laser method for wood cutting was proposed. The carbonization degree of wood surface was improved by the introduction of helium (He) gas, and the influence of process parameters on the carbonization layer of wood surface was solved, it was significance to reduce the post-processing of LOM and improve the quality of forming workpiece. The cherry wood veneer was used as the experimental material, under the condition of the same process parameters, the wood was cut with or without inert gas-assisted, and the influence factors of kerf quality were studied by variance analysis. The results showed that under the same condition, compared with traditional laser processing, the kerf width was obviously reduced in the inert gas-assisted cutting. Because the He gas had oxygen-isolation and flame retardant effect, which prevented heat accumulation and conduction. The micro morphology of the kerf surface showed that the flatness was better in the inert gas-assisted cutting. As the excess heat was blown out by the cooling and purging of the gas, the phenomenon of oxidation and burning was reduced, the range of HAZ (heat affected zone) was reduced, and the carbonization phenomenon was obviously improved. The surface quality of kerf was improved effectively. According to the analysis of variance, in addition to the effect of laser power, cutting speed and inert gas flow on the cutting width, the interaction between inert gas flow and laser power, laser power and cutting speed were also the main factors which affected the cutting width. The feasibility of the combined inert gas and laser processing to improve wood cutting quality has been verified through experimental research, which provided a certain reference for the followup research on improving the wood processing quality

Research on micro-electric resistance slip welding of copper electrode during the fabrication of 3D metal micro-mold

3D micro-mold fabricated by the micro double-staged laminated object manufacturing process (micro-DLOM) is formed via stacking and fitting of multi-layer 2D micro-structures. The connection of 2D micro-structures is related to forming accuracy and mechanical properties of 3D micro-mold. In this research, micro-electric resistance slip welding of copper electrodes was proposed to connect multi-layer 2D micro-structures. Firstly, the proper process parameters of slip welding were obtained through the welding experiment, and the temperature field of micro-electric resistance slip welding under such process parameters was simulated. Secondly, deposition effect of the copper bar electrode produced during slip welding was studied and the study results show that the copper element deposited in the slip welding area decreases as the surface roughness of copper electrode decreases. Finally, based on the above research, a square micro-cavity mold with micro-channel, a circular micro-cavity mold with cross keyway and micro gear cavity mold with two-stage steps were welded by the micro-electric resistance slip welding.

Error Analysis of 3D Metal Micromold Fabricated by Femtosecond Laser Cutting and Microelectric Resistance Slip Welding

We used micro-double-staged laminated object manufacturing process (micro-DLOM) to fabricate 3D micromold. Moreover, the error of the micro-DLOM was also studied. Firstly, we got the principle error of the micro-DLOM. Based on the mathematical expression, it can be deduced that the smaller the opening angle α and the steel foil thickness h are, the smaller the principle error δ is. Secondly, we studied the error of femtosecond laser cutting. Through the experimental results, we know that the error of femtosecond laser cutting is 0.5 μm under 110 mW femtosecond laser power, 100 μm/s cutting speed, and 0.75 μm dimension compensation. Finally, we researched the error of microelectric resistance slip welding. Based on the research results, we can know that the minimum error of microcavity mold in the height direction is only 0.22 μm when welding voltage is 0.21 V and the number of slip welding discharge is 160.

Study on tungsten electrode deposition effect of 3D metal micro-mold during laminated slip welding

3D metal micro-mold fabricated through the micro double-staged laminated object manufacturing process is formed via stacking and fitting of multi-layer 2D micro structures. In this paper, it is suggested that micro-electric resistance slip welding technology be adopted to optimize the connection of micro structures in 3D metal micro-mold. Moreover, the deposition effect of tungsten electrode which was formed on the micro-mold surface and produced during micro-electric resistance slip welding is also studied. Firstly, the temperature field of electric resistance slip welding was simulated by ANSYS software and the maximum temperature in the slip welding area is 1,219 °C when the number of slip welding discharge is 160, which is far lower than the melting point of tungsten electrode material (3,410 °C). Hence, bulk tungsten will not shed during slip welding; however, the wear of the tungsten electrode will be deposited on the surface of the micro-mold in micro-particle shape. Secondly, the influence of slip welding discharge and surface roughness of tungsten electrode on tungsten deposition effect is studied and the study shows that: the content of tungsten within the slip welding area increases gradually as the number of slip welding discharge increases, and decreases gradually as surface roughness of tungsten electrodes increases. Finally, under 160 time’s slip welding discharge and using tungsten electrodes (0.5-mm diameter and 0.12-μm surface roughness), the 3D metal micro-molds which contains 0.4 % tungsten in slip welding area and has a good quality surface was obtained.

Quantification of surface roughness of parts processed by laminated object manufacturing

Additive manufacturing (AM) technology is essentially performed using a layered manufacturing (LM) process. Because more complex 3D physical models can be efficiently fabricated without geometric limitation by the technology, a remarkable reduction in production life cycle has been achieved. However, due to the LM process, a deterioration of the surface quality of the parts processed by AM may occasionally occur, which is the primary reason that the surface problem has been a key issue in AM. In this paper, a methodology is proposed to quantify the surface roughness of the parts processed by laminated object manufacturing (LOM), which is a typical technology in AM. The surface profiles of the parts were investigated, a schematic was constructed by considering the LOM process factor geometrically, and a theoretical approach to quantify average surface roughness according to surface angle variation is presented. The expressions required for numerical computation were deduced and defined. By comparing the measured data and computed values, the proposed approach was verified. Additionally, the effects of the process variables related to surface quality were evaluated and analyzed.

A neural network solution for LOM process performance

A neural network (NN) modeling approach is presented for the prediction of laminated object manufacturing (LOM) process performance. A NN was developed using experimental data which were conducted on a LOM 1015 machine according to the principles of Taguchi design of experiments (DoE) method. The process parameters considered in the experiment to investigate LOM process performance were nominal layer thickness (NLT), heater temperature (HT), platform retract (PR), heater speed (HS), laser speed (LS), feeder speed (FS), and platform speed (PS). LOM process performance is divided in dimensional errors in X and Y directions (Ex and Ey), actual layer thickness (ALT), average surface roughness of vertical supporting frame (VSF-Ra), and tensile strength in X direction (TSx). It was found that NN approach can be applied in an easy way on designed experiments and predictions can be achieved, fast and quite accurate. The developed NN is constrained by the experimental region in which the designed experiment is conducted. Thus, it is very important to select parameters’ levels as well as the limits of the experimental region and the structure of the orthogonal experiment. The above analysis is useful for LOM users when prediction of process performance is needed. This methodology could be easily applied to different materials and initial conditions for optimization of other Rapid Prototyping (RP) processes.

A benchmark study on rapid prototyping processes and machines: Quantitative comparisons of mechanical properties, accuracy, roughness, speed, and material cost

Various kinds of layer manufacturing process are available, such as stereo lithography (SL), fused deposition modelling (FDM), Poly-jet, selective laser sintering (SLS), three-dimensional printing (3DP), laminated object manufacturing (LOM), etc. The object of the current study is the quantifications and comparisons of the processes' characteristics using representative apparatus and various materials. Through the tests, mechanical properties, such as tensile and compressive strengths, hardness, impact strength, and heat resistance, and surface roughness, geometric and dimensional accuracy, manufacturing speed, and material costs were compared for each process and machine. It was verified that the SL process is advantageous in hardness, accuracy, and surface roughness and the Poly-jet process in tensile strength at room temperature. The SLS process was advantageous in compressive strength and manufacturing speed, the 3DP process in speed and material costs, and the LOM process in heat resistance. The FDM and LOM processes were superior in impact strength in the scanning direction, but the change of building direction significantly reduced the tensile and impact strengths.

Investigation of LOM process quality using design of experiments approach

PurposeTo investigate laminated object manufacturing (LOM) process quality, using a design of experiments approach.Design/methodology/approachThe quality characteristics measured were in‐plane dimensional accuracy, actual layer thickness (ALT), and mean time per layer. The process parameters tested were nominal layer thickness (LT), heater temperature (HT), platform retract (PR), heater speed (HS), laser speed (LS), feeder speed (FS) and platform speed (PS). A typical test part has been used, and matrix experiments were carried out based on Taguchi design. Optimal process parameter values were identified and finally, additive and regression models were applied to the experimental results and tested using evaluation experiments.FindingsThe statistical analysis of the experimental results shows that error inXdirection was higher than error inYdirection. Dimensional accuracy inXdirection depends mainly on the HS (89 percent) and HT (5 percent), and inYdirection on HS (50 percent), LT (31 percent), LS (9 percent), PS (6 percent), and HT (3 percent). On the other hand, ALT depends mainly on the nominal ALT (96 percent), HS (2 percent), HT (1 percent), and PR (1 percent). Finally, mean time per layer depends mainly on HS (59 percent), LS (17 percent), FS (17 percent), and PS (4 percent).Research limitations/implicationsFuture work should involve extensive matrix experiments using parameters such as dimensions of test part (Xmax,Ymax,Zmax), hatch spacing inXandYdirections, and delay time between sequential layers.Practical implicationsUsing the extracted models, the quality of LOM parts can be predicted and appropriate process parameter values selected. This means minimization of post processing time, easier disengagement between supporting frame and part, easier decubing, process optimization, less finishing and satisfactory final LOM parts or tools. Also, ALT prediction and mean time per layer analysis could be used to improve LOM build time predictions.Originality/valueThe above analysis is useful for LOM users when predictions of part quality, paper consumption, and build time are needed. This methodology could be easily applied to different materials and initial conditions for optimisation of other LOM‐type processes.

An experimental investigation of the surface roughness of parts produced by LOM process

PurposeTo investigate the influence of different process parameters of the laminated object manufacturing (LOM) process on the roughness of vertical surfaces alongZ‐axis on ZX‐plane of parts produced by LOM.Design/methodology/approachThe process parameters tested were layer thickness, heater temperature, platform retract, heater speed, laser speed, feeder speed and platform speed. A typical test part has been used, and matrix experiments were carried out based on Taguchi design. Optimal process parameter values were identified and finally, a regression model was applied onto the experimental results, and compared with bibliography models, using arbitrary experiments.FindingsThe statistical analysis of the experimental results showed that the surface roughness depends mainly on the heater temperature, layer thickness, and laser speed. Moreover, the regression model gave good predictions when heater temperature values were within the initial experimental area and inaccurate predictions when heater temperature takes the value 200°C.Research limitations/implicationsFuture work should involve extensive matrix experiments using parameters such as dimensions of test part (Xmax,Ymax,Zmax), hatch spacing inXandYdirections, and delay time between sequential layers.Practical implicationsUsing the extracted regression model, vertical surface roughness can be predicted and selected proprietary process parameter values. This means minimization of post processing time, easier disengagement between supporting frame and part, easier decubing, process optimization, and less finishing.Originality/valueThis methodology could be easily applied on different materials and initial conditions for optimisation of LOM processes.

Process build‐time estimator algorithm for laminated object manufacturing

A method for estimating the build‐time required by the laminated object manufacturing (LOM) process is presented in this paper. The proposed algorithm – taking into account the real process parameters and the information included in the part's STL‐file – performs a minimum manipulation of the file, and calculates total volume, total surface area and flat areas involved in fine cross‐hatching. A number of experiments performed verify the applicability of the algorithm in process build‐time estimation. The time prediction estimates are within 7.6 per cent of the real build‐times for the LOM process. It is believed that, through specific minor adjustments, the algorithm could well be employed in process build‐time estimation for similar rapid prototyping processes.

Study of the key technologies of LOM for functional metal parts

To address the problems associated with laminated object manufacturing (LOM) using sheet metal as a modeling material, an approach of cutting the sheet metals by a new LOM process and connecting them by diffusion welding technology is proposed. The conventional LOM process and the new LOM process are compared with reference to the theoretical manufacturing error. A slicing algorithm for the new LOM process has been deduced. The conclusions drawn from the experiments and analysis are shrinkage in the stack direction is small; atom diffusion between two joints occurs clearly and new grains form; the shear strength of the welding zone is above 100 MPa; the micro-hardness of the welding zone is almost the same as that of the substrate. The fabrication of sample part suggests that the new LOM process with diffusion welding could be a useful method for the rapid manufacturing of metal parts.

Automatic fabrication for bridged laminated object manufacturing (LOM) process

Laminated object manufacturing (LOM) is one of the most popular rapid prototyping (RP) techniques in terms of speed and cost effectiveness. Despite the advantages of the LOM process, some problems are yet to be overcome. One of the major difficulties encountered in the current LOM practice is the metallic part cannot be fabricated. Focusing on the drawback inhered in LOM, a new Bridge-LOM process and its associated building algorithm are proposed in this paper. The process starts with the construction of the bridge structures to link a stack of 2D geometry contours to the outer frame based on the proposed bridge building algorithm. Afterwards, laser is directed to cut along the contours, and then the upper pressing head is pushed down and the layers are bonded. Spraying adhesive on the top of bonded layers follows this. The procedures of cutting, bonding and adhesive spraying are repeated until the complete part is produced. The proposed Bridge-LOM process has overcome two problems, support and position. Regarding the function of position, in order to ensure the proper bonding treatment, as well as holding a precise position between layers, the processes from cutting to bonding in the process should maintain the same X–Y position. Therefore, worries of not having a fixed positioning would then be eliminated. Regarding the function of support, bridge has taken the place of the supporting function of waste material in the current LOM process. The metallic part can be built directly based on the efficiency of on-line waste material removal in the process. From the experiments, it is verified that the proposed Bridge-LOM process and its associated building algorithm not only save laser-cutting time, the time on waste material removal is also reduced significantly. Furthermore, the metallic part and mold can be fabricated and their performances are investigated.

A new approach of online waste removal process for laminated object manufacturing (LOM)

A new online de-cubing laminated object manufacturing process which employs self-adhesive sheet with shielding paper is proposed in this paper. The main idea of this new process is to perform bond-then-cut at the same position, avoiding the accumulated error resulted from reposition, and to de-cube the inner waste material in process by peeling off the shielding paper. By doing so, about 30–80% waste material according to various geometric shapes can be removed during the machining process. The new process not only shortens the time for laser cutting and de-cubing, but also enables the production of hollow and shell-shaped parts. Hence, the proposed process promotes both the performance efficiency of laminated process and the manufacturing ability regardless the geometry of the parts.

Composite Material Based Laminated Object Manufacturing (LOM) Process Simulation

In laminated object manufacturing process (LOM) as a rapid manufacturing technique, the key process parameters for achieving a successful prototype are the roller temperature, the roller speed, the roller indentation and the laser cutting time. In addition to these basic process parameters, the material properties and the configuration of the parts affect the internal stresses, local deformations built during the process and the bonding quality. A finite element method was adopted to simulate the thermal aspects of the bonding process along with the structural deformation of the part. Thermal and stress analysis was carried out to calculate the interlaminar shear strength between layers. Experiments were conducted to verify the simulation result for the internal temperature profiles. The finished prototype was tested mechanically to measure interlaminar shear strength to estimate the bonding quality. The calculated bonding quality was compared with the bonding strength converted from the measured interlaminar shear strength, showing a good agreement between the two. In compliance with the increasing demand for high-strength working prototypes, the developed simulation code can simulate the incorporation of new material for the LOM process.

Warping Analysis in Laminated Object Manufacturing Process

This study presents an analysis of warping that occurs in the laminated object manufacturing process. Based on the study of thermal-mechanical behavior of the adhesive and its effect on the laminated materials, the cause of warping, the relationship between temperature and adhesive viscosity, and the adhesive connecting intensity is investigated. A heat transfer mathematical model and finite difference solution algorithm was developed to calculate the intralaminar thermal force induced by the material addition in the processing of laminated object manufacturing. The results of the model prediction were compared to available experimental data. Simulation of intralaminar thermal force and case studies show that the processing parameters, such as roller temperature, speed, and contact pressure, the mechanical properties of laminated material and adhesive will all contribute to the formability and warping of the laminated prototype. An optimal combination of the processing parameters may reduce the undesired warping effect.

An octree-based algorithm for the optimization of extraneous material removal in laminated object manufacturing (LOM)

Layered Manufacturing (LM) has emerged as the technology of choice for creating prototypes from CAD models. Laminated Object Manufacturing (LOM) is a form of layered manufacturing technology developed by Helisys Inc. Here the solid is built from stacked-up layers of paper (or other laminates) backed with a heat-activated adhesive. A laser is used to cut the profile of the solid and crosshatch the extraneous material on each layer for easy removal. Layered manufacturing has greatly reduced the time required to make models and prototypes. There is, however, great scope for making the processes faster and more accurate by using better algorithms. Experiments have shown that the cross-hatching of the extraneous material contributes between 30 to 50% of the build time in the case of the LOM process. This paper targets the cross-hatching of extraneous material as a means to reduce the build time of the LOM part. In this paper, an octree-based, variable-size cross-hatching algorithm for generating the laser path is presented. Results on test parts have produced up to a 50% reduction in the cross-hatching time of the object as compared to the traditional fixed-size cross-hatching approach. An AutoLISP/AutoCAD environment was used for validation of the laser path generated by the algorithm.