Thin-walled Metal Parts Research Articles

Non-Planar Helical Path Generation Method for Laser Metal Deposition of Overhanging Thin-Walled Structures

Laser metal deposition is a branch of additive manufacturing that offers advantages over traditional manufacturing techniques for forming overhanging thin-walled metal parts. Previously, helical paths that were suitable for manufacturing such parts were not only limited to stacking material on a flat surface but were also fixed to the model boundaries. In order to solve these two problems to meet more complex process requirements, a non-planar helical path generation method is proposed for laser metal deposition. The method is based on the characteristics of the additive manufacturing process planning flow, which first slices the model using curved surfaces, then offsets the contours on the sliced layering, and finally generates continuous helical paths according to the contracted or expanded contours. In order to verify the feasibility of the method, hollow blades are formed on cylindrical surfaces following the planned paths. The results show that the proposed method is not only capable of assisting the laser metal deposition process to fabricate thin-walled structures on non-planar surfaces but also capable of freely adjusting the contour dimension.

A novel micro-rolling & incremental sheet forming hybrid process: Deformation behavior and microstructure evolution

Thin-walled metal parts with functional micro-featured surface have broad application prospects in the fields of resistance reduction, noise reduction, etc. In this study, a novel micro-rolling & incremental sheet forming hybrid process (μR-ISF) is proposed to fabricate thin-walled metal parts with microgroove arrays. An analytical model which relates the rolling force and microgroove depth in the micro-rolling stage was first established. Then, the formation mechanism of microgroove morphology during both micro-rolling stage and macro-shape forming stage are investigated. After the micro-grooved sheet being incrementally formed, a significant reduction (between 21% to nearly 60%) is occurred in the depth of both transverse and longitudinal grooves compared to the flat sheet. Meanwhile, the width of transverse grooves decreases slightly by about 10% on average, while the width of longitudinal microgrooves increases significantly by more than 30% on average. After micro-rolling, 85°{101¯2} tensile twins appear on the micro-grooved sheet and the percentage of 65°{112¯2} compressive twins increases. After incremental forming, the percentage of low-angle grain boundaries and the density of geometrically necessary dislocations in the formed part increase significantly, and the grain size distribution becomes more uniform. The present work provides a new strategy for the fabrication of 3D metal thin-walled components with surface micro-features.

Ratcheting characterization and its effect on low cycle fatigue behavior of DP600 steel sheet under cyclic shear path

For thin-walled metal parts, the effects of shear deformation must be considered. In this study, a device for cyclic shear tests was designed, and a DP600 sheet was used to study the fatigue behavior under a shear path without buckling. Ultimately, based on the results, the ratchet behavior, effect of ratchet deformation on fatigue, and law of ratchet inhibition were analyzed and discussed. The local strain concentration and high dislocation density caused by ratcheting loading led to local grain refinement during strain-controlled fatigue loading, improving the cyclic strength and fatigue life.

Fused plus wire arc additive manufacturing materials and energy saving in variable-width thin-walled

Wire arc additive manufacturing (WAAM) has the potential to become a method to production large and complex metal components, but there is a lot of material waste and energy consumption in the forming of thin-walled metal parts with variable-size. To solve this problem, this paper proposes a method for forming thin-walled parts with variable width and height is proposed, where metal samples are prepared by Variable Polarity (VP) TIG & Fused-deposition Additive Manufacturing (FDAM). This method adopts multi node subsection control strategy. Under the real-time acquisition system of composite dual-vision sensors, through the on-line control of deposition layer size is realized by matching each piece with different process parameters of thin-walled parts. The thin-wall parts with controllable range of 5.5–10 mm and the heights controllable range of 6.5–13 mm. The results show that the multi-node piecewise strategy achieves a stable and convergent control. Compared to the conventional method, the material utilization increases by 51.4%. With a 128% shortening of producing time. The proposed control method can remarkably reduce the frequencies of arc initiation and extinction, improve the production efficiency, and save materials and energy.

Numerical investigation of the clinched joint loadings considering the initial pre-strain in the joining area

The components of a body in white consist of many individual thin-walled sheet metal parts, which usually are manufactured in deep-drawing processes. In general, the conditions in a deep-drawing process change due to changing tribology conditions, varying degrees of spring back, or scattering material properties in the sheet blanks, which affects the resulting pre-strain. Mechanical joining processes, especially clinching, are influenced by these process-related pre-strains. The final geometric shape of a clinched joint is affected to a significant level by the prior material deformation when joining with constant process parameters. That leads to a change in the stiffness and force transmission in the clinched joint due to the different geometric dimensions, such as interlock, neck thickness and bottom thickness, which directly affect the load bearing capacity. Here, the influence of the pre-straining in the deep drawing process on the force distribution in clinch points in an automotive assembly is investigated by finite-element models numerically. In further studies, the results are implemented in an optimization tool for designing clinched components. The methodology starts with a pre-straining of metal sheets. This step is followed by 2D rotationally symmetric forming simulations of the joining process. The resulting mesh of each forming simulation is rotated and 3D models are obtained. The clinched joint solid model with pre-strains is used further to determine the joint stiffnesses. With the simulation of the same test set-up with an equivalent point-connector model, the equivalent stiffness for each pre-strain combination is determined. Simulations are performed on a clinched component to assess the influence of pre-strain and sheet thinning on the clinched joint loadings by using the equivalent stiffnesses. The investigations clearly show that for the selected component, the loadings at the clinch points are dependent on the sheet thinning and the stiffnesses due to pre-strain. The magnitude of the influence varies depending on the quantity considered. For example, the shear force is more sensitive to the joint stiffness than to the sheet thinning.

Analysis and compensation of shrinkage and distortion in wire-arc additive manufacturing of thin-walled curved hollow sections

Curved hollow sections are used in numerous applications from lightweight space frames to pipings in process engineering. In conventional manufacturing, such structures are produced mainly by metal forming or casting. Despite ongoing efforts in rapid tooling technologies for casting and flexible forming processes, there is a demand for dieless manufacturing of curved hollow structures, as this would allow to produce parts with greatly reduced lead-times, e.g., as on-demand spare parts and on construction sites using mobile equipment. Wire-arc additive manufacturing (WAAM) processes with multi-axis deposition can be used in this case. This process typically draws upon the gas metal arc welding (GMAW) process with cold metal transfer (CMT) technology. Thin-walled metal parts produced by WAAM may show deviations to the target geometry due to material shrinkage and distortion, which may entail tedious trial-and-error compensation. This study analyses shrinkage and distortion in curved hollow sections with different cross sections and curvature radii both experimentally and with a thermo-mechanical finite element model. Based on these findings, a novel method for the compensation of shrinkage and distortion for thin-walled hollow parts is put forward and validated. The correction method draws upon the geometrical deviations that occur when the part is produced based on the CAD geometry, and computes a correction to the CAD geometry, which is used to define the welding path for a part with improved accuracy. The results show that the geometry of the manufactured part can be corrected to tolerances in the range of the waviness of the surface by applying the proposed correction.

Effects of Pillar-Based Substrate on the Wire Arc Additive Manufacturing Process

The Wire arc additive manufacturing (WAAM) process uses a metal plate as a substrate for part deposition. The presented work uses small pillars of cuboidal shapes arranged together to form the required deposition surface instead of a single large substrate. The post-processing of WAAM is arduous due to the need for the part removal from the substrate. The pillar-based substrate made this part removal process simpler and reduced the machining requirement. A WAAM setup was designed and developed in-house by integrating the gas metal arc welding (GMAW) with a three-dimensional gantry. The setup was utilised to deposit thin-walled metal parts over the pillar-based substrate. The online recorded temperature at the base using thermocouples confirmed adequate cooling between subsequent layers. The temperature of the pillar-based substrate was compared with the conventional substrate, which ensured proper heat dissipation. The microstructural study and hardness measurement of the deposited parts also confirmed that the pillar-based substrate has little effect on the part quality. The applications of the pillar-based substrate were further extended to demonstrate the deposition of multiple parts on a single substrate and part containing non-planar layers (overhanging features).

Hyperplasticity effect under magnetic pulse straightening of dual phase steel

An investigation of the behaviour of dual phase steel parts during straightening operations, by means of magnetic pulse treatment, is presented. The mechanical analysis of magnetic-pulse treatment for the straightening of thin-walled sheet metal parts produced from dual phase steel was performed, taking into account the effect of hyperplasticity under the influence of the magnetic field. Taking account of the causes of the hyperplasticity and thus the increase of material plasticity, it has been shown that the magnetic impulse gravity can be adjusted by controlling the operation modes. The dependence of the generated magnetic impulse gravity force on the electrical current strength inducted in this part was explored and used for analysis of the magnetic pulse straightening of dual phase steel part. Experimental results were obtained for thin-walled sheet metal part produced from dual phase steel DP 780. The results are used to demonstrate the material deformation under the influence of magnetic impulse gravity force considering the increase of material plasticity. The dependence of relative material deformation on the generated magnetic impulse gravity as well as on the current strength induced in this material was obtained and analyzed

Modeling and predicting of aeronautical thin-walled sheet metal parts riveting deformation

Purpose Riveting deformation is inevitable because of local relatively large material flows and typical compliant parts assembly, which affect the final product dimensional quality and fatigue durability. However, traditional approaches are concentrated on elastic assembly variation simulation and do not consider the impact of local plastic deformation. This paper aims to present a successive calculation model to study the riveting deformation where local deformation is taken into consideration. Design/methodology/approach Based on the material constitutive model and friction coefficient obtained by experiments, an accurate three-dimensional finite element model was built primarily using ABAQUS and was verified by experiments. A successive calculation model of predicting riveting deformation was implemented by the Python and Matlab and was solved by the ABAQUS. Finally, three configuration experiments were conducted to evaluate the effectiveness of the model. Findings The model predicting results, obtained from two simple coupons and a wing panel, showed that it was a good compliant with the experimental results, and the riveting sequences had a significant effect on the distribution and magnitude of deformation. Practical implications The proposed model of predicting the deformation from riveting process was available in the early design stages, and some efficient suggestions for controlling deformation could be obtained. Originality/value A new predicting model of thin-walled sheet metal parts riveting deformation was presented to help the engineers to predict and control the assembly deformation more exactly.

Development of a Laser-Based Geometric Imperfection Measurement Platform with Application to Cold-Formed Steel Construction

Geometric imperfections play an important role in the strength and behavior of thinwalled metal parts such as those commonly used in cold-formed steel construction. The objective of this paper is to detail a newly developed imperfection measurement platform, where the full-three dimensional (3D) imperfect geometry of a cold-formed steel member can be measured and reconstructed with reasonably high throughput and sufficient accuracy to explore all relevant imperfections. The measurement platform is composed of a two-dimensional laser sensor mounted on rotary and linear stages. Specimens are placed within a rotary ring and along a reference beam. The linear stage provides a means to scan the length of the specimen and the rotary stage a means to scan from any angle. Control of the custom linear and rotary stages are detailed in the paper, and corresponding control accuracies are studied. A procedure for registering the individual scans into the complete 3D model reconstruction (point cloud) is provided by specific calibration tests, from which rotation and translation quantities can be found to transform surfaces measured in local coordinates to a universal global coordinate system. A variety of different imperfection quantities, from basic dimensions and out-of-plane deviations to more advanced spectral and modalbased imperfection magnitudes may be rapidly processed from the 3D model. Accurate understanding of geometric imperfections is critical to the long-term success of analysis-based design paradigms for cold-formed steel constructions. The apparatus detailed herein will be used to provide a broad suite of imperfection information to assist in these new efforts.

Calculation Method for Interference Value in Metal Joining Structure

Interference-fit joining is one of the important jointing methods to permanently fasten two thin-walled sheet metal parts. In joining process the interference amount is an important factor, which affects ultimate strength and fatigue life of the mechanical structure. In this article, analytical solution for interference value is studied, and the elastic and plastic deformation area near the hole is discussed. The calculation formula for the hole walls displacement and the boundary between elastic and plastic deformation is obtained.

A novel methodology of design for Additive Manufacturing applied to Additive Laser Manufacturing process

Nowadays, due to rapid prototyping processes improvements, a functional metal part can be built directly by Additive Manufacturing. It is now accepted that these new processes can increase productivity while enabling a mass and cost reduction and an increase of the parts functionality. However, the physical phenomena that occur during these processes have a strong impact on the quality of the produced parts. Especially, because the manufacturing paths used to produce the parts lead these physical phenomena, it is essential to considerate them right from the parts design stage. In this context, a new numerical chain based on a new design for Additive Manufacturing (DFAM) methodology is proposed in this paper, the new DFAM methodology being detailed; both design requirements and manufacturing specificities are taken into account. The corresponding numerical tools are detailed in the particular case of thin-walled metal parts manufactured by an Additive Laser Manufacturing (ALM) process.

Investigation into the failure of Inconel exhaust collector produced by laser consolidation

Among layer manufacturing techniques, Laser Consolidation (LC) finds its ideal application in the production of thin-walled metal parts for industrial niches characterised by high innovation and product complexity. To fully exploit the technological potential, developments must be made to assess LC’s repeatability and reliability. Previous studies proved that high strength parts of fine microstructure are obtained if appropriate build strategies are used. The aim of this research is to analyse a racecar exhaust collector, built in Inconel by LC, relating the failure modes and microstructure to the construction plan.The exhaust collector component was built using a custom strategy and was run on a dynamometer before failing after approximately 1200km. An investigation of the failure mechanism was carried out by a primary macroscopic analysis, aided by an X-ray control and dye penetrant test. Metallographic sections were then sampled from the critical areas to study the microstructure and relate it to the manufacturing process.Results proved that the distribution of primary microcracks associated with internal residual stresses caused by the build strategy and aggravated by differential shrinkage during the test thermocycles was responsible for ultimate failure. This issue was a result of build strategy and the non-coaxial laser head, therefore, alternative pathways could be developed capable of removing most, if not all, of the contributory factors. The analysed case suggests that LC build strategy selection is as critical to ensure low cycle fatigue resistance as component design and confirms that LC is effective in the production of advanced technological parts with high geometrical complexity given the correct build strategy.

Manufacturing of micro thin-walled metal parts by micro-droplet deposition

Metal micro-droplet deposition manufacturing technique is a novel direct metal rapid prototyping for building the miniaturized parts. In this paper, the novel direct metal rapid prototyping was proposed to fabricate micro thin-walled metal parts. A direct droplet fabrication experimental system was developed based on the forming principle of micro-droplet deposition manufacture. Several deposition experiments were conducted to investigate the influences of process parameters on the formed wall thickness and deposition accuracy of droplets. The experimental results show that the proper deposition distance Hs for obtaining high deposition accuracy of droplet ranges from 1 mm to 20 mm; the formed wall thickness W can be controlled by selecting different nozzle diameters D and formed angle of deposited droplet θ. According to the experiment results, a micro thin-walled structure with wall thickness of 400 μm was fabricated by adjusting the process parameters. The above research works show that it is feasible to fabricate the micro thin-walled metal parts by micro-droplet deposition manufacturing technique.

Offsetting operations on non-manifold topological models

This paper describes non-manifold offsetting operations that add or remove a uniform thickness from a given non-manifold topological model. The mathematical definitions and properties of the non-manifold offsetting operations are investigated first, and then an offset algorithm based on the definitions is proposed and implemented using the non-manifold Euler operators proposed in this paper. In this algorithm, the offset elements of minimal size for the vertices, edges and faces of a given non-manifold model are generated first. Then, they are united into a single body using the non-manifold Boolean operations. In order to reduce computation time and numerical errors, the intersections between the offset elements are calculated considering the origins of the topological entities during union. Finally, all topological entities that are within the offset distance are detected and removed in turn. In addition to the original offset algorithm based on mathematical definitions, some variant offset algorithms, called sheet thickening and solid shelling, are proposed and implemented for more practical and efficient solid modeling of thin-walled plastic or sheet metal parts. In virtue of the proposed non-manifold offset operation and its variations, different offsetting operations for wireframes, sheets and solids can be integrated into one and applied to a wide range of applications with a great potential usefulness.

Direct laser fabrication of thin-walled metal parts under open-loop control

Direct laser fabrication (DLF) is an advanced manufacturing technology, which can build full density metal parts directly from CAD files without using any modules or tools. The investigation on the fabrication of thin-walled parts of nickel alloy using open-loop DLF process is introduced in this paper. The experimental setup consisted of a CO 2 laser, a 3-axis CNC table, a coaxial powder nozzle and a powder recycler. The 3D-CAD file of a thin-walled metal part was converted into the STL file format and imported into software HUST-RP to generate ‘pseudo-random’ scanning paths of laser beam. The influence of process parameters on the build height of thin-walled metal parts was studied by 1–10 layered single-bead stacks of nickel alloy. The result shows that the interference factors which affect the build height of thin-walled metal parts occur randomly during the process. For open-loop DLF process, thin-walled metal parts can achieve much better shape quality if the process parameters are suitable. Multilayer single-bead walls were built up with different scanning velocity to obtain the optimal process parameters of thin-walled parts of nickel alloy. It shows that thin walls of nickel alloy with uniform height can be built up layer by layer in a certain range of specific energy. However, it is difficult to control the build height of complex thin-walled metal parts in an accurate manner just using optimal parameters. A special coaxial powder nozzle was designed in this paper. In a certain range, the deposition thickness of the nozzle is nearly linearly increased with increase in the standoff distance between the powder focusing point of the nozzle and the deposition substrate. By means of the nozzle, a novel method to control the build height of thin-walled metal parts using open-loop DLF process was introduced. The difference in build height of a thin-walled part can be compensated automatically in one or several layers during the process. It is proved that the build height of a thin-walled metal part can be accurately controlled in theory using the nozzle. A complex single-bead part of nickel alloy whose geometry was designed to be the well-known Chinese ‘FU’ was fabricated and explained in this paper. The result shows that the shape quality of the sample is quite good, and actual build height of the sample is 53.54 mm while the designed value is 54 mm.

DYNAMIC MODELLING OF FLEXIBLE PAYLOADS MANIPULATED BY A SMART GRIPPER IN ROBOTIC ASSEMBLY

During robotic assembly of flexible payloads, gravity and inertial forces acting on these payloads may induce both static shape deformation and vibration of the thin-walled payloads. Static deformations, which arise from deformation of the part due to its own weight under the influence of gravity, lead to misalignment of mating points of the part. Unwanted vibrations, arising from inertial forces acting on the part as it is positioned for assembly, must be damped out before it can be mated with other parts. This paper investigates the development of dynamic models of arbitrarily shaped flexible thin-walled payloads grasped by a smart gripper, comprised of multiple linearly actuated fingers with non-contact proximity sensors. Such an actuated gripper allows both part-reshaping and active damping of unwanted vibrations of the part. Finite element modelling techniques are used to generate dynamic models of these arbitrarily shaped parts. Component mode synthesis methods are used to combine the dynamics of the actuated gripper with the dynamics of the thin-walled parts. The resultant dynamic model, developed with finite element modelling, is of high order, and hence model order reduction methods are employed to reduce the model order but retain the essential dynamics of the thin-walled payload gripper system. Using a two time-scale modelling technique, an integrated closed-loop modal truncation and control design procedure is used to design a shape and vibration controller for thin-walled payload. Simulation results modelling thin-walled sheet metal parts manipulated by an industrial robot confirm the validity of the proposed modelling approach.

Springback Analysis of Sheet Metals Regarding Material Hardening

The phenomenon of springback of thin-walled sheet metal parts after forming is a well known problem of forming technology in general, but particularly since the finite element simulation offers the opportunity to predict geometrical and material properties after forming. Irrespective of the intensive efforts in the previous years, a reliable and accurate prediction of springback deviations by use of the finite element simulation is still not possible. This paper deals with the numerical and experimental analysis of the springback effect itself, which dependents on the final stress states of a part after the forming process. Experimental investigations have been carried out to analyze geometrical accuracy in loaded and unloaded conditions to isolate the springback effect. Additional finite element simulations have been conducted in order to compare the experimental and numerical results and to determine the geometrical differences and their reasons. Two experimental set-ups are being discussed: Air bending on the one hand, which offers good access to the specimen in the testing equipment, and draw bending on the other hand, which is characterized by a simple strain state, but also by strain reversal within the tests. Both experiments were carried out using DP600 and X5CrNi18.10 with three different sheet thicknesses and bend radii and were compared with according FE-models. An additional shear test experiment has been developed to characterize the material behavior of the tested sheet metals for strain reversal. Furthermore, the importance of the Bauschinger effect and usable hardening models were analyzed. This study intended to investigate reasons for insufficient form and dimensional accuracy between simulations and experiments after springback and to propose modeling methods to improve the accuracy.

Three‐dimensional localization of thin‐walled sheet metal parts for robotic assembly

AbstractThis article presents a technical demonstration of a system for determining the three‐dimensional spatial location of complexly shaped, thin‐walled sheet metal parts grasped by robots during assembly. For successful part assembly, the precise location of grasped parts (essential for successful mating of parts) must be achieved. A localization system is implemented to determine the accurate position and orientation of a sheet metal part that has been picked up by a robot from an arbitrary location. The proposed localization system employs a novel sensing method, utilizing laser‐based proximity and edge detectors, to extract the part feature data in real time. These geometrical feature data are incorporated into an existing localization algorithm, which is based on the singular value decomposition formulation of the part localization problem. The sensing method is particularly effective in measuring 3‐D feature geometry (i.e., thin edges) of sheet metal parts. An experimental single‐robot test bed has been developed to demonstrate the feasibility of the part localization concept for a single sheet metal part. The experimental results obtained from the test bed demonstrate that the system can be effectively used for the localization of thin‐walled sheet metal parts. © 2002 Wiley Periodicals, Inc.