This research aimed to optimize the process parameters of small copper parts printed with binder jetting. The optimisation was distinguished by dividing the parameters in print and post-process parameters. Binder jetting is an additive manufacturing technique that combines layers of the material in powder form with a binder. After the printing process the printed samples need curing, debinding and sintering. The binder acts as a temporary glue to hold the shape and is later removed during the debinding. The sintering fuses the powder particles together, below the melting temperature. With binder jetting it is the aim to achieve the high density parts, as there is no compression of powder during the printing process. This often leads to low density parts with binder jetting. The two problems that needed to be solved, were: how can the bleeding issues be stopped and at what temperature, time and environment can the printed copper be sintered. Multiple print sessions were done to: first test the known print parameters, second optimize the print parameters and third, print with optimized print parameters. ThermoGravimetric Analysis (TGA) was conducted to determine the correct debinding and sintering temperature of the copper samples. The bleeding issues could be solved by adjusting the saturation level. The saturation level was reduced from 104 % to 72 %. The lower percentage gave 0.5 mm dimensional accurate samples and no bleeding issues. Compression testing was done to compare the mechanical behaviour to that of conventionally manufactured copper. However the discs used for compression testing needed to be bigger in size than the cubes used for optimizing the sintering process. This lead to not fully sintered discs used for the compression testing. Meaning the achieved compressive strength and elasticity modulus were 1 % of conventionally manufactured copper. Three working sinter sessions were compared to see which gave the highest achieved density. Sintering 10 hours in argon at 1093 ℃ or in vacuum at 1080 ℃ both achieved the same high densities. Shell printed cubes performed better with an average density of 73 ± 8 % in argon and 74 ± 7 in vacuum. The samples placed on the top level inside the sintering oven achieved higher densities than in lower levels. Two shell printed cubes in argon achieved a density of 83 ± 0.5 % with a volumetric shrinkage of 40 ± 1 % and two shell printed cubes in vacuum achieved a density of 82 % with a volumetric shrinkage of 40 %. Solid cubes reached lower densities, with 67 ± 10 % in argon and 71 ± 7 % in vacuum. As with the shell printed cubes, the solid cubes have a high deviation due to the placement of the samples on different levels. The solid cubes had less volumetric shrinkage and rather high deviation due to the same reason, with 25 ± 16 % in argon and 35 ± 11 % in vacuum. The density is measured with a caliper and with Archimedes which gave quite different results. Densities measured with Archimedes were up to 22 % higher due to the porosity of the samples. All the measurements done by other copper binder jetted parts are done with Archimedes. Thus it seems the 74 % and 82 % is low when compared to 91 % density achieved in literature, but it is not known how accurate these measurements are.

Shoulder exoskeleton is a popular solution to work-related shoulder disorders and muscle fatigue. With a wide range of exoskeletons designed, a comprehensive report on how the use of shoulder exoskeletons changes shoulder biomechanics is still missing. In this project, the impact of exoskeletons on shoulder biomechanics was investigated with the musculoskeletal simulation OpenSim. This study proposed a "human-in-the-loop" optimization-based design tool for shoulder exoskeletons. This design tool incorporates the predicted biomechanical effects of a shoulder exoskeleton from musculoskeletal simulations into design considerations. This design tool was validated with a case study designing a shoulder exoskeleton based on a compliant beam and testing the design in the musculoskeletal simulation and experiments.

The exoskeleton design tool is a coupling of finite element analysis and OpenSim. OpenSim calculates the deformation of the exoskeleton with human motion, and the finite element analysis calculates the force exerted from the exoskeleton upon deformation. Then OpenSim computes muscle activities under the external force from the exoskeleton. By merging muscle activities and the resultant glenohumeral joint reaction force to an objective function, the optimization-based design loop is closed by looking for the best objective value iteratively.

Several exoskeletons were designed by the new design tool to assist different types of tasks. The design tool exhibited good ability in finding optimal solutions for a range of design choices and design requirements. Simulated tests of designed exoskeletons showed significant effects on reducing muscle activities and good robustness in resisting the influence of perturbed motions in arm-elevated tasks. An exoskeleton was selected to be tested with an experiment set up in the same way as the simulated test. Experiment results supported the performance of the exoskeleton predicted in the simulated test.

This project established a method to comprehensively predict the effect of an exoskeleton on shoulder biomechanics and provided a more comprehensive understanding of biomechanical effects of shoulder exoskeletons. This facilitated the “human-in-the-loop” design process of shoulder exoskeletons which could greatly save money and time investments into prototyping, testing, and validation.