Analysis of the Accuracy and the Surface Roughness of FDM/FFF Technology and Optimisation of Process Parameters

The work deals with the influence of process parameters on the quality and accuracy of parts produced by FDM (Fused Deposition Modelling)/FFF (Fused filament fabrication) technologies. The experiments were carried out on the 3D Ultimaker printer, PLA (Polylactid Acid) thermoplastics were used as the test materials. The practical part is divided into 3 experiments. First, the optimum temperature was set. In the next part, the parameters of retraction rate, retraction length and crossing speed were determined. In the last part, the impact of 13 parameters on the printing time, material consumption, surface quality and accuracy were determined. In this part of the experiment, the effect of the factors on the quality indicators was determined using the DoE Taguchi methodology. Subsequently, the influential parameters were determined by Paret\u27s rule. The results showed how layer height and print speed are the most important factor for the print time. The parameters-percent filling, number of walls, and the height of the layer were marked as essential parameters affecting the material\u27s consumption. The surface roughness and dimensional accuracy are most influenced by the height of the layer

Areal texture and angle measurements of tilted surfaces using focus variation methods

Optical instruments for areal surface topography measurement have seen significant commercial development in the last five years, along with the ISO 25178 areal standard. Providing the user with confidence in new instruments depends on understanding instrument behavior and sources of error. Focus variation techniques rely on the inherent micro- or nano-scale roughness of a surface to allow acquisition of topography data. The work reported here has been examining the sensitivity of the focus variation technique to surface slope, using areal parameters to characterize surface roughness at extended slope values. The results illustrate links between instrument variables and slope characterization

Osseointegration of a 3D Printed Stemmed Titanium Dental Implant: A Pilot Study

In this pilot study, a 3D printed Grade V titanium dental implant with a novel dual-stemmed design was investigated for its biocompatibility in vivo. Both dual-stemmed (n = 12) and conventional stainless steel conical (n = 4) implants were inserted into the tibial metaphysis of New Zealand white rabbits for 3 and 12 weeks and then retrieved with the surrounding bone, fixed, dehydrated, and embedded into epoxy resin. The implants were analyzed using correlative histology, microcomputed tomography, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The histological presence of multinucleated osteoclasts and cuboidal osteoblasts revealed active bone remodeling in the stemmed implant starting at 3 weeks and by 12 weeks in the conventional implant. Bone-implant contact values indicated that the stemmed implants supported bone growth along the implant from the coronal crest at both 3- and 12-week time periods and showed bone growth into microporosities of the 3D printed surface after 12 weeks. In some cases, new bone formation was noted in between the stems of the device. Conventional implants showed mechanical interlocking but did have indications of stress cracking and bone debris. This study demonstrates the comparable biocompatibility of these 3D printed stemmed implants in rabbits up to 12 weeks

Audio-based Roughness Sensing and Tactile Feedback for Haptic Perception in Telepresence

Haptic perception is highly important for immersive teleoperation of robots, especially for accomplishing manipulation tasks. We propose a low-cost haptic sensing and rendering system, which is capable of detecting and displaying surface roughness. As the robot fingertip moves across a surface of interest, two microphones capture sound coupled directly through the fingertip and through the air, respectively. A learning-based detector system analyzes the data in real time and gives roughness estimates with both high temporal resolution and low latency. Finally, an audio-based vibrational actuator displays the result to the human operator. We demonstrate the effectiveness of our system through lab experiments and our winning entry in the ANA Avatar XPRIZE competition finals, where briefly trained judges solved a roughness-based selection task even without additional vision feedback. We publish our dataset used for training and evaluation together with our trained models to enable reproducibility of results.Comment: IEEE International Conference on Systems, Man, and Cybernetics (SMC), Honolulu, Hawaii, USA, October 202

Wear analysis of hip explants, dual mobility concept: Comparison of quantitative and qualitative analyses

International audienceTotal hip replacement (THR) fails mainly because of wear. It is of interest to analyze wear to be able to increase the longevity of the hip implants. One way to achieve it is to use instruments on explants but the most suitable depends on the application. This paper aims at comparing several methods of surface analysis in the particular application of wear determination in a series of dual mobility explants. Wear measurement could help understand the wear mechanism only partially known. A CMM, Coordinate Measuring Machine, is used to get 3D points representing the explants, then Pro/Engineer ® and Matlab ® are used to calculate wear. A mechanical (SOMICRONIC®) and an optical profilometer (Bruker nanoscope Wyko® NT 9100, ex. Veeco) are used to access roughness parameters. The comparisons of the two software showed similar results for wear calculation except in a few cases where differences are due to the theoretical volumes calculation. The comparison of the two profiling techniques resulted in similar results particularly for Sa and Sdr. The comparison of the results showed that wear is present for four explants; it is relevant with the observed characteristics. The mechanical profilometer showed better accuracy than the optical one which enable to conclude that it must not be neglected for that particular application, even if measurements need more time

Failure characteristics of all polyethylene cemented glenoid implants in total shoulder arthroplasty

Total shoulder arthroplasty (TSA) still suffers today from mid-term and long-term complications such as glenoid implant loosening, wear, humeral head subluxation/dislocation and implant fracture. Unlike the hip and knee joint replacements, the artificial shoulder joint has yet to offer a long-term satisfactory solution to shoulder replacement. With loosening being the number one reason for TSA revision, investigating methods of monitoring the glenoid implant loosening and investigate the effects of various design parameters on the loosening behaviour of the glenoid fixation is necessary to explore the problem. Several studies were carried out using in-vitro cyclic testing and FEA to; investigate failure progression and its correlation to quantitative measures in a 2D study (n = 60), investigating key glenoid design features in a 2D (n = 60) and 3D study (n = 20), investigating the validity of using bone substitute foam for studying glenoid fixation in a cadaveric study and investigating any correlation between failure and CT or in-vitro quantitative measures (n = 10). Visible failure was observed, for the first time, correlating to inferior rim displacement and vertical head displacement measures. CT failure was detected in 70% of specimens before visible failure was observed. Out of the design pairs tested; smooth-back/rough-back (range of roughnesses), peg/keel, curved-back/flat-back and conforming/non-conforming, roughening the back-surface to 3.4 μm or more improved fixation performance (p < 0.05). Roughening the back-surface changed the mode of failure from implant/cement failure inferiorly due to tensile/shear stresses, to cement/bone failure superiorly due to compressive/shear loading. Differences in the other design pairs were marked showing peg to perform better than keel, conforming over non-conforming and no difference in curved-back over flat-back, although these differences are marginal. Improvements in the standard testing method have also been suggested

Tribological and Structural Characterisation of Ceramic on Metal Hip Replacements

A tribological investigation of ceramic on metal hip replacements was carried out using in vitro wear testing methods. Two ceramic materials, pure alumina and an alumina matrix compound (zirconia toughened alumina (ZTA)), were articulated against as-cast CoCrMo alloy cups. The diameter was changed from 38 mm to 60 mm to explore the effect of diameter on the tribological performance. Three distinct wear tests were undertaken to allow a direct comparison between materials and sizes. These were; wear testing using standard loading and motion profiles, microseparation (edge loading) in which the loading and motion profiles were modified to allow medial-lateral and inferior-superior displacement of the head, and third body particle tests which incorporated 0.5 g of <1 μm alumina particle in the lubricant. The Durham Mark I Hip Wear Simulator was used to simulate the standard walking cycle, and was further modified to incorporate microseparation during the swing phase of the walking cycle. All simulator tests were gravimetrically analysed and linear regression analysis was used to determine running in and steady state wear rates. In addition, surface analytical techniques including non contacting profilometery, atomic force, scanning electron and optical microscopy were used to identify changes in surface topography throughout the wear tests. Parameters such as the root mean squared roughness and skewness were monitored to provide quantitative changes in the surface features. The roughness was also used to calculate the ratio of minimum film thickness to equivalent roughness known as the lambda ratio. This provided an theoretical indication of the lubrication regime. Dynamic friction measurements were undertaken on the Durham Friction Simulator, using water based bovine serum based lubricants, which allowed the lubrication mechanism to be identified through the generation of a Stribeck Curve. The results showed low wear rates for all materials and sizes tested, compared with standard metal on polyethylene and metal on metal components. The wear of the ceramic heads was unmeasurable using the gravimetric method, as the volume change of the heads fluctuated with a similar trend and magnitude to the control head which did not experience wear. Wear was detected for the softer metallic cups in all tests. The standard wear test produced the lowest cup wear rates, compared with microseparation and third body tests which showed increased wear rates through extensive abrasive and adhesive wear mechanisms. After microseparation testing, characteristic stripe wear patterns were found on the ceramic heads and a flattened lip on the metallic cups. Metal transfer was also identified, which was thought to be due to impact during dislocation of the head during the swing phase of the walking cycle. Third body tests resulted in significant grain loss from the ceramic components compared with both standard or microseparation testing. Low friction factors were recorded for all ceramic on metal components, generally showing the joints to be working close to full fluid film lubrication during the high load stance phase of the walking cycle

Compact microscopy systems with non-conventional optical techniques

This work has been motivated by global efforts to decentralize high performance imaging systems through frugal engineering and expansion of 3D fabrication technologies. Typically, high resolution imaging systems are confined in clinical or laboratory environment due to the limited means of producing optical lenses on the demand. The use of lenses is an essential mean to achieve high resolution imaging, but conventional optical lenses are made using either polished glass or molded plastics. Both are suited for highly skilled craftsmen or factory level production. In the first part of this work, alternative low-cost lens-making process for generating high quality optical lenses with minimal operator training have been discussed. We evoked the use of liquid droplets to make lenses. This unconventional method relies on interfacial forces to generate curved droplets that if solidified can become convex-shaped lenses. To achieve this, we studied the droplet behaviour (Rayleigh-Plateau phenomenon) before creating a set of 3D printed tools to generate droplets. We measured and characterized the fabrication techniques to ensure reliability in lens fabrication on- demand at high throughput. Compact imaging requires a compact optical system and computing unit. So, in the next part of this work, we engineered a deconstructed microscope system for field-portable imaging. Still a core limitation of all optical lenses is the physical size of lens aperture – which limits their resolution performance, and optical aberrations – that limit their imaging quality performance. In the next part of this work, we investigated use of computational optics-based optimization approaches to conduct in situ characterization of aberrations that can be digitally removed. The computational approach we have used in this work is known as Fourier Ptychography (FP). It is an emerging computational microscopic technique that combines the use of synthetic aperture and iterative optimization algorithms, offering increased resolution, at full field-of-view (FOV) and aberration-removal. In using FP techniques, we have shown measurements of optical distortions from different lenses made from droplets only. We also, investigated the limitations of FP in aberration recovery on moldless lenses. In conclusion, this work presents new opportunities to engineer high resolution imaging system using modern 3D printing approaches. Our successful demonstration of FP techniques on moldless lenses will usher new additional applications in digital pathology or low-cost mobile health