Purpose The purpose of this paper is to investigate the factors governing bond strength in fused deposition modeling (FDM) compared to strength in the fiber direction. Design/methodology/approach Acrylonitrile butadiene styrene (ABS) boxes with the thickness of a single fiber were made at different platform and nozzle temperatures, print speeds, fiber widths and layer heights to produce multiple specimens for measuring the strength. Findings Specimens produced with the fibers oriented in the tensile direction had 95 per cent of the strength of the constitutive filament. Bond strengths ranged from 40 to 85 per cent of the filament strength dependent on the FDM processing conditions. Diffusion, wetting and intimate contact all separately affect bond strength. Practical implications This study provides processing recommendations for producing the strongest FDM parts. The needs for higher nozzle temperatures and more robust feed motors are described; these recommendations can be useful for companies producing FDM products as well as companies designing FDM printers. Originality/value This is the first study that discusses wetting and intimate contact separately in FDM, and the results suggest that a fundamental, non-empirical model for predicting FDM bond strength can be developed based on healing models. Additionally, the role of equilibration time at the start of extrusion as well as a motor torque limitation while trying to print at high speeds are described.

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Purpose The purpose of this paper is to present a diffusion-controlled healing model for predicting fused deposition modeling (FDM) bond strength between layers (z-axis strength). Design/methodology/approach Diffusion across layers of an FDM part was predicted based on a one-dimensional transient heat analysis of the interlayer interface using a temperature-dependent diffusion model determined from rheological data. Integrating the diffusion coefficient across the temperature history with respect to time provided the total diffusion used to predict the bond strength, which was compared to the measured bond strength of hollow acrylonitrile butadiene styr (ABS) boxes printed at various processing conditions. Findings The simulated bond strengths predicted the measured bond strengths with a coefficient of determination of 0.795. The total diffusion between FDM layers was shown to be a strong determinant of bond strength and can be similarly applied for other materials. Research limitations/implications Results and analysis from this paper should be used to accurately model and predict bond strength. Such models are useful for FDM part design and process control. Originality/value This paper is the first work that has predicted the amount of polymer diffusion that occurs across FDM layers during the printing process, using only rheological material properties and processing parameters.

An in-line rheometer has been incorporated into a fused deposition modeling printer for the first time by designing a modified nozzle with a custom pressure transducer and a thermocouple for measuring the processed melt temperature. Additionally, volumetric flow rates and shear rates were monitored by counting the stepper motor pulses as well as the pulses from a custom filament encoder to account for filament slippage and skipped motor steps. The incorporation of the sensors and the design and development of the in-line rheometer are described; and pressures, temperatures, and viscosities within the 3D printing nozzle are presented. The in-line rheometer was validated against traditional, off-line rotational rheology and capillary rheology measurements by analyzing two polymeric materials: polycarbonate and high-impact polystyrene. A variety of rheological corrections were considered for the in-line rheometer, including entrance effects, non-Newtonian corrections, shear heating, pressure effects, and temperature fluctuations/inaccuracies. Excellent agreement was obtained between the in-line and off-line rheometers after applying the most critical corrections, which were found to be entrance effects, non-Newtonian corrections, and temperature inaccuracies. After applying the appropriate corrections, the in-line rheometer provides an accurate viscosity measurement that can be used for real-time monitoring and process control.

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The College of Engineering at the University of Massachusetts Lowell (UML) has integrated service-learning (S-L) into many of its core required undergraduate courses over the last three years. Projects that meet real community needs and that help students achieve academic objectives in these core courses are percieved to be difficult to create, but, in this paper, projects for 35 different undergraduate required courses are summarized to help faculty, staff, and students develop S-L projects for their own courses. Faculty at UML were encouraged to “start small rather than not at all.” Courses and projects include, for example, a first-year introduction to engineering course in which 340 students, divided into teams, designed and built moving displays illustrating various technologies for 60,000 middle school students that every year visit a history center that is part of a national park. Another example is a sophomore kinematics course in which student teams visited local playgrounds to assess their safety using deceleration, force, and impact equations learned from the course. Junior heat transfer courses focused in analyzing heat loss and making suggestions for heating system savings for a local food pantry, a city hall building, and a community mental health center, as well as for the university itself; these analyses were developed and presented to the stakeholders. Sophomore student teams from the materials course presented findings to the staff of a local textile history museum to help it begin updating its displays on recent developments in materials. Junior fluids, junior circuits, senior microprocessor, senior design of machine elements, and senior capstone design are having students design and build various parts of an automated canal lock opener for a local national park. Many of the projects are low-cost and can be implemented by individual faculty members without the requirement of a formal institutional program. These S-L projects are integrated into a wide variety of core courses (and not just design courses) and represent typically from 10 to 20 percent of the grade.