Design and validation of integrated clamping interfaces for post-processing and robotic handling in additive manufacturing

Additive manufacturing (AM), particularly laser-based powder bed fusion of metals (LPBF), enables the fabrication of complex and customized metallic parts. However, 20–40% of the total manufacturing costs are usually attributed to post-processing steps. To reduce the costs of extensive post-processing, the process chain for AM parts has to be automated. Accordingly, robotic gripping and handling processes, as well as an efficient clamping for subtractive machining of AM parts, are key challenges. This study introduces and validates integrated bolts acting as a handling and clamping interface of AM parts. The bolts are integrated into the part design and manufactured in the same LPBF process. The bolts can be easily removed after the machining process using a wrench. This feasibility study investigates different bolt elements. The experiments and simulations conducted in the study show that a force of 250 N resulted in a maximum displacement of 12.5 µm. The milling results of the LPBF parts reveal a maximum roughness value, Ra, of 1.42 µm, which is comparable to that of a standard clamping system. After the bolt removal, a maximum residual height of 0.067 mm remains. Two case studies are conducted to analyze the form deviation, the effect of bolts on build time, and material volume and to demonstrate the application of the bolts. Thus, the major contribution of this study is the design and the validation of standardized interfaces for robotic handling and clamping of complex AM parts. The novelties are a simple and clean interface removal, less material consumption, less support structure required, and finally an achievement of a five-side tool accessibility by combining the interfaces with a three-jaw chuck.

Design and Validation of Integrated Clamping Interfaces for Post-Processing and Robotic Handling in Additive Manufacturing

Additive manufacturing (AM), particularly laser-based powder bed fusion of metals (LPBF), enables the fabrication of complex and customized metallic parts. However, 20–40% of the total manufacturing costs are usually attributed to post-processing steps. To reduce the costs of extensive post-processing, the process chain for AM parts has to be automated. Accordingly, robotic gripping and handling processes, as well as an efficient clamping for subtractive machining of AM parts, are key challenges. This study introduces and validates integrated bolts acting as a handling and clamping interface of AM parts. The bolts are integrated into the part design and manufactured in the same LPBF process. The bolts can be easily removed after the machining process using a wrench. This feasibility study investigates different bolt elements. The experiments and simulations conducted in the study show that a force of 250 N resulted in a maximum displacement of 12.5 µm. The milling results of the LPBF parts reveal a maximum roughness value, Ra, of 1.42 µm, which is comparable to that of a standard clamping system. After the bolt removal, a maximum residual height of 0.067 mm remains. Two case studies are conducted to analyze the form deviation, the effect of bolts on build time and material volume and to demonstrate the application of the bolts. Thus, the major contribution of this study is the design and the validation of standardized interfaces for robotic handling and clamping of complex AM parts. The novelties are a simple and clean interface removal, less material consumption, less support structure required and finally an achievement of a five-side tool accessibility by combining the interfaces with a three-jaw chuck.

FUNDAMENTALS OF THE DESIGN OF FUNDAL MANDRELS FOR THE INSTALLATION OF THIN-WALLED WORKPIECES. PART 1

There are a number of problems in mechanical engineering technology. One of them is related to the installation on the machine and the previous processing of thin-walled rings, which are widely used in mechanical engineering. Due to the low bending stiffness of thin-walled rings after processing there are a large magnitude of rigidity of the form (deviation from roundness). As production experience has shown, in the conditions of mass production, it is advisable to use fungal mandrels and adjustments to reduce shape errors. They allow for a small radial gap between the holes of the ring and the fungal cam to have extended contact rings with cams along the angular coordinate. However, there are no methods for calculating the parameters of contact interaction with cams, considering a number of factors, primarily the radial clearance. Hence, it is impossible to calculate more accurately the error of the form after processing. In this paper (it is supposed to be continued), based on methods for calculating flat rings of construction mechanics of machines, a method for determining the stress-strain state of a thin-walled state is proposed, considering the contact pressure. In this case, the semiangle of contact of the ring with the fungal cam and the shape of the contact pressure plot are determined. This allows you to calculate the stress state of the thin-walled ring and the shape error when processing more accurately in a fungal mandrel, as well as reasonably assign the dimensions of the mandrel parts. Due to the exceptionally large number of calculations in the calculations according to the proposed method, it can only be implemented using a computer program, which creates great difficulties in analyzing different source data. Therefore, it is planned to rework the completed developments into an engineering calculation method with graphs in dimensionless form.

A Design for Additive Manufacturing Strategy for Dimensional and Geometrical Quality Improvement of PolyJet-Manufactured Glossy Cylindrical Features

The dimensional and geometrical quality of additively manufactured parts must be increased to match industrial requirements before they can be incorporated to mass production. Such an objective has a great relevance in the case of features of linear size that are affected by dimensional or geometrical tolerances. This work proposes a design for additive manufacturing strategy that uses the re-parameterization of part design to minimize shape deviations from cylindrical geometries. An analysis of shape deviations in the frequency domain is used to define a re-parameterization strategy, imposing a bi-univocal correspondence between verification parameters and design parameters. Then, the significance of variations in the process and design factors upon part quality is analyzed using design of experiments to determine the appropriate extension for modelling form deviation. Finally, local deviations are mapped for design parameters, and a new part design including local compensations is obtained. This strategy has been evaluated upon glossy surfaces manufactured in a Vero™ material by polymer jetting. The results of the proposed example showed a relevant improvement in dimensional quality, as well as a reduction of geometrical deviations, outperforming the results obtained with a conventional scaling compensation.

A Unique Model to Estimate Geometric Deviations in Drilling and Milling Due to Two Uncertainty Sources

Industry 4.0 involves the use of information and communication technologies to transform industry by intelligent networking machines and processes. The availability of big data sets from manufacturing and inspection allow for developing new and more accurate simulation models. This involves the development of new machining simulation models to consider the geometrical deviations of the workpiece due to the machine tool, the part datum surfaces and the fixturing equipment. This work presents a model that kinematically correlates the locator uncertainty, the form deviation on the part datum surface in contact with the locators and the volumetric uncertainty of the machine tool, with the geometric deviations of a surface due to a drilling or milling process. An analytical model was developed in a Matlab® file to simulate the surface geometrical deviations from nominal during drilling or milling. It is new as regards the state of the art because it takes into account two sources of uncertainty. This numerical approach allows for avoiding experimental tests, with a resultant saving of time, energy and material. It was applied to drilling, face milling and contouring processes. It was proved that machine tool volumetric uncertainty influences the form deviation of the machined surface, while the locator configuration and the datum form deviation affect the orientation of the machined surface, as should be in reality. The proposed model allows us to take into account geometrical deviations of the part datum surfaces of 0.001 mm, location deviations in the locators of ± 0.03 mm and machine tool positional and rotational uncertainties of 0.01 mm and σd=0.01∗π180 mm, respectively.

Comparisons of national standards of the unit of length in the field of measurement of parameters of form deviation the flatness of optical surfaces COOMET.L-S15

Precision interference measurement of parameters of form optical surfaces are one of the most important type of the measurement in the field of the geometrical values. In countries-participants of this comparisons the special primary standards in this field of measurements take part in reproduction and transmission the unit of length in this field of measurements ensuring high measuring and calibrating capabilities countries in this type of measurement. In this article presents the result of supplementary comparisons COOMET 570/UA-a/12. The result of comparisons allowed to declare to Belarus and Russia, and to confirm to Ukraine their measuring and calibrating capability in database CIPM MRA.

Numerical Simulation and Experimentation of Additive Manufacturing Processes with Polyurethane Foams

Foam Additive Manufacturing (FAM) is the additive manufacturing process allowing parts to be obtained by depositing layers of polyurethane foam using a high-pressure machine. This inexpensive technology allows large parts to be produced in a reduced time. However, the quality of the parts produced by the FAM technique is greatly affected by the various thermal phenomena present during manufacturing and by the geometrical deviations of the layers due to the expansion of the PU foam. Numerical simulation remains an effective analytical tool for studying these phenomena. The aim of this work is to build a geometric and thermal model predictive of the FAM process by the finite element method, the final objective of which is to provide temperature maps throughout the manufacturing process and also to choose the best 3D printing strategy to have a model with constant cords and the smallest possible form deviation. The proposed model and the various simulation techniques used are detailed in this article. This model is developed under the finite element code Rem3D, and validated by experimental tests carried out on a FAM machinery or a robot, an example of which is detailed in this article.

Realization of a Dental Framework by 3D Printing in Material Cobalt-Chromium with Superior Precision and Fitting Accuracy

We report on the generation of a cobalt-chromium dental framework with superior precision and fitting accuracy using selective laser melting. The objective of this study is the reduction of surface roughness and the possibility to manufacture a dental framework with high precision for passive fit with attachments, in particular a round tack. After selective laser melting, the dental framework is thermally post processed at 750 °C, shot-blasted with glass and highly polished. Nominal to actual 3D form deviation is analyzed by stripe light projection, revealing deviations being less than 250 μm, i.e., warpage is as low as to permit dental application and accurate passive fit. In particular, the critical area of the dental framework, the fixture to the implant (overdenture) shows negligible deviations. This superior fitting accuracy is confirmed by joining the bar with a testing stylus.