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In order to decrease mass, and thus fulfil the targets for airplane traffic emission reduction, the amount of titanium alloys used for structural components is rising. With the conventional milling process, low material utilization and short tool life lead to high manufacturing costs. Therefore, a process chain consisting of wire and arc additive m...
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... the deviations D 3 and D 4 , corresponding to the surface roughness and the waviness respectively, the maximum profile heights R z and W z were measured according to DIN EN ISO 4287 [25]. The maximum profile height was chosen, because for the minimum machining allowance the maximum deviations need to be determined. In Fig. 3 the method to characterize the surfaces is shown. In Y-direction a total of eleven profiles with a distance of 40 px was measured, whereas in Z-direction 21 profiles with a distance of 80 px were ...
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A novel, environmentally friendly, fast, and flexible polishing process for Nitinol parts is presented in this study. Nitinol samples with both superelastic and shape memory properties at room temperature were investigated. The chemical contamination and surface roughness of superelastic Nitinol plates were examined before and after plasma electrol...
Citations
... For milling, on the other hand, the parameters of interest include cutting velocity, feed rate, and axial depth of cut. In an investigation conducted by Fuchs et al. (2020), they modelled the essential machining allowance for post-processed WAAM-manufactured parts. Their study evaluated the alterations to surface roughness due to peripheral milling of such parts. ...
Wire arc additively manufactured components fabricated with the use of titanium and its alloys have extensively gained awareness in biomedical, marine, and aerospace industries owing to their mechanical properties, biocompatibility, and excellent corrosion resistance properties. Post-processing is an essential technique used for fine-tuning microstructure and material properties, correcting incurred errors, and improving surface properties of wire arc additive manufacturing (WAAM)–processed Ti-6Al-4V alloy to enhance the quality of metallic parts. In recent times, several post-processing manufacturing techniques have been fully developed to mitigate the effect of internal flaws formed during the printing of additive manufacturing parts. In this chapter, the significant influence of hot isostatic pressing, heat treatment techniques, machining process, and surface modification techniques as they enhance the structural integrity performance of WAAM-processed Ti-6Al-4V components are fully documented. This chapter systematically reviews the recent progress in post-processing techniques as they improve the material properties of Ti-6Al-4V components produced by the WAAM process.
... This process is characterized by high metal deposition capacity and reduced material waste, part cost, and iteration time compared with standard processes [2][3][4]. The method consists of depositing molten metal through an electric arc between the nozzle and the already-deposited material in a sequence of two-dimensional (2D) layers using a robot to perform the movements [5]. The quality of the weld bead depends on various parameters, such as the quality of the wire, the wire feed speed (WFS), the travel speed (TS), and the heat input [1]. ...
... To limit high residual stresses, internal defects, porosities, and lack of fusion between adjacent weld beads, it is possible to control the deposition parameters or tilt the nozzle along the trajectory [8][9][10]. The mechanical quality of the final part depends on the combination of all the manufacturing input parameters [5]. ...
The WAAM additive manufacturing process is considered one of the most efficient and productive processes. Its implementation is based on the use of a Cold Metal Transfert (CMT) device by a robot. The geometrical quality and the mechanical behavior of the manufactured parts depend on the uniformity of the material deposition rate and the uniformity of the energy input, throughout the realization of the part. This paper discusses the interactions between the CMT device and the robot during the manufacturing process. The reaction times between the two systems are not the same, and depending on a specific parameterization, the real trajectory is disturbed by the start or stop of the electric arc. An experimental study on 8 trajectories and 3 parameters allows us to analyze the behavior of the robot, the accuracy of the trajectory, and the acceleration and deceleration phases. As a general conclusion, compromises must be found in terms of continuous/discontinuous deposition and deposition outside the nominal deposition area or not. Based on the tests performed in this study, the semi-circular strategy appears to be the most relevant in the case of continuous deposition over the whole toolpath. Finally, a model has been proposed to compute the manufacturing time of any area of the layer based on a preliminary identification for a single area.
... Fuchs et al. [15] analyzed the surface waviness of WAAM parts as a function of the welding strategy, which was then used to determine the machininig allowance. It was found that removing 125% of the maximum peak-to-valley results in a high surface quality. ...
Wire arc additive manufacturing is a process with great potential and in full expansion for structural, maintenance, and large-scale product development. It is gaining interest due to its low buy-to-fly ratio. Nevertheless, its major flaw is the low geometric accuracy and the wavy surfaces of the printed parts. To ensure that the requirements of the final part are respected, the dimensions and the minimum quantity of material to be machined have to be specified. Thus, machining allowance and part dimensions are elements that were quantified based on a design of experiments (DOE) and thermal analysis. It was used to determine the effects of cold metal transfer (CMT) parameters on them. For instance, it was found that travel speed and interpass time have a major influence on height, width, and machining allowance. Specific way to achieve the desired requirements is discussed.
... The schematic of the manufacturing strategy for the WAAM-parts based on[22] ...
The capability of wire and arc additive manufacturing (WAAM) to produce large, near-net-shaped parts with inexpensive equipment has led to the process being considered as one of the options to significantly decrease the buy-to-fly ratio in aircraft manufacture. Even so, there are several challenges associated with the process: achieving mechanical properties and microstructure similar to wrought material, as well as the low surface quality of the parts. The low surface quality is usually improved by milling. As with the microstructure, here too the question arises as to whether the process is comparable to milling wrought material. A significant factor influencing the microstructure according to literature is the interlayer temperature during the WAAM process. Therefore, the objective of this research was to study the influence of the interlayer temperature on the machinability and the microstructure of wire and arc additively manufactured Ti-6Al-4V. Consequently, the machinability was first determined for Ti-Al6-V4-parts manufactured with three different interlayer temperatures. Then, the macro- and microstructures were analyzed and, finally, the mechanical properties were determined. Contrary to expectations based on the state of the art, the machinability was not influenced by the interlayer temperature. This aligns with the mechanical properties and the macro- and microstructures, which are only slightly affected by the interlayer temperature.
... Fig. 21. Influence of heat treatment and intentionally generated porosity on cutting forces [120] With regard to the removal of inhomogeneous surface layers on AM components, the compensation of component distortion resulting from AM processes as well as the renewed deformation of the components during mechanical post-processing due to residual stress effects, stock allowances on AM components must be provided from which the desired component geometry can be precisely worked out [195]. However, since the causal chain of effects is not fully understood and describable, oversized stock allowances are usually implemented. ...
... In order to manufacture high-performance components by LMD, the technology has to be combined with a subsequent subtractive finishing process to be considered as a process chain. In this case, an additional allowance for the subtractive manufacturing process is necessary to ensure that the process chain is both economical and resource-efficient [8]. When producing high-aspect-ratio structures from individual tracks, it is crucial to map a minimum allowance as accurately as possible over the entire geometry, since imperfections with undersize cannot be compensated by an additional deposit. ...
Powder-based laser metal deposition (LMD) represents a future-oriented additive manufacturing process given the large
number of available materials as well as the high degree of geometric freedom. These potentials are further enhanced by
high build rates and a better material utilization compared to turning or milling. However, the LMD process is very complex
as a result of the large number of machine and process parameters.
Different thermal conditions occur during layer-by-layer buildup. Newly supplied energy due to the laser-material
interaction with the newest layer is supplemented by the heat energy still stored in the solidified component, which is
distributed inhomogeneously depending on material and part geometry. In order to avoid dimensional deviations and
microstructural defects, the machining parameters have to be adjusted during the LMD process.
The following paper presents a strategy for the efficient and process-safe buildup of thin-walled VDM Alloy 780
geometries on 316L substrates using powder-based LMD. Adaptive adjustment of parameters and monitoring of cooling
times improve the dimensional accuracy of the geometry while avoiding defects. The fabricated specimens are then
analyzed using optical microscopy, SEM and EDX. Porosity analysis is performed by various methods. In addition,
mechanical properties are determined by tensile tests in perpendicular and parallel directions as well as by macrohardness
tests.
... However, titanium alloys are expensive and challenging to extract [23], machine and form [5,24,25]. As such, WAAM technology allows for a reduction in waste and simplification of manufacture when compared to production by machining or forging [26,27]. ...
Additive manufacturing (AM) offers advantages in many aspects over conventional manufacturing techniques. These include reduced lead times and material waste. A recent topic of interest is the environmental impact of manufacturing techniques. However, there is a lack of literature detailing the impact of titanium manufacturing processes. In addition, there is also a gap in knowledge comparing AM to conventional manufacturing methods with the aim of investigating the reduced environmental impact as a further advantage of AM.
In this research, an environmental impact analysis is used to compare wire + arc additive manufacturing (WAAM) against conventional forging in the production of a Ti6Al4V component. This is achieved by comparing the material waste, energy consumption and carbon emissions of each production method. WAAM shows a 50% reduction in carbon emission and 40% reduction in energy consumption over forging. The largest difference is in the material waste, with a 55% reduction in discarded material. The comparison metrics of specific energy consumption (SEC) and specific carbon emissions are presented for evaluating the sustainability of processes, with the WAAM produced component in this study presenting a SEC of 574.9 MJ/kg compared to 958 MJ/kg for conventional forging.
... In all cases, the ultimate tensile strength of their samples was a little below 300 MPa, with maximum strains in the range 22-29% depending on the sample orientation. Fuchs et al. [ 2 ] studied the machining allowance of Ti6Al4V nearnet shaped WAAM parts in the frame of aeronautic industry. Rodrigues et al. [ 3 ] compared conventional GMAW WAAM and UC-WAAM in which the electric arc is established between the wire feedstock material and a non-consumable tungsten electrode. ...
This work is devoted to Wire Arc Additive Manufacturing processing. The question of automatic generation of robot trajectories is mainly addressed. An in-house slicer was first developed. Once the part to be manufactured has been designed and converted into STL format, the slicer allows automatic generation of successive vertices defining the part contours and corresponding robot trajectories. Automatic generation of the robot program is then performed including displacement instructions written in KRL language (case of KUKA robots), as well as commands related to the CMT welding device. The different steps in the offline programming pre-treatment process are first described. In a second step, two distinct parts with increasing degrees of complexity were printed using the corresponding offline programming tool. Finally, the question of the scanning strategy is discussed, the manufactured parts are shown, and required further improvements are explained.
... In addition to geometric part defects, thermal gradients encountered during deposition can cause residual stresses and variable microstructure resulting in distortion and potentially undesirable material properties [16][17][18]. Failure to account for these variances in additive depositions can lead to finished parts with under-deposition, high surface roughness, and less compressive surface stress due to improper machining allowances and cutting parameters [18,19]. Consequentially, both the additive and subtractive parameters need to be considered when designing a hybrid part. ...
... Machining allowance is usually set using a single error or combination of errors found in a particular process [20,21]. For WAAM, Fuchs et al. [19] proposed a model that set the minimum machining allowance to the sum of all machining errors and the maximum part surface error. In their analysis, surface waviness was identified as the dominating source of error and was used to inform machining allowance. ...
... For the robot-CNC hybrid system, part positioning error may be a dominating factor, so a more intricate model for machining allowance that addresses multiple factors may be needed. In addition to setting the machining allowance, several studies have looked at the effects of WAAM parameters, WAAM part geometry, and machining allowance on cutting conditions and the resulting surface roughness [19,[21][22][23]. General trends show that chip thickness, spindle speed, and deposition temperature are key factors in determining the surface roughness of a hybrid part. ...
Wire and arc additive manufacturing (WAAM) has shown promise in recent years for producing large-scale parts with higher deposition rates than other additive processes. WAAM is often combined with subtractive machining to form a hybrid manufacturing process. This hybrid process can be realized by retrofitting computer numerical control (CNC) machines with deposition heads, adding spindles and deposition heads to robots, or developing part localization methods to transfer parts from an additive cell to a CNC machine. Here, a novel, robot-CNC hybrid configuration is introduced where a maneuverable robot is placed in front of a CNC machine to deposit material within the machine envelop. This method removes the need for part localization and the extensive machine modifications required for retrofitting; however, the problem of robot localization is also added. In this work, the effects of error in vision-based, contactless robot localization on machining parameters in a robot-machine hybrid process were studied. Performance was characterized on an implementation of this system using classical computer vision techniques. In addition, machining simulations were conducted to evaluate the effects of image-induced error on chip thickness, material removal rate, and machining allowance. Initial tests show that computer vision could adequately locate a robot for the hybrid WAAM process within .5 mm.
... Weld seams are deposited layer-by-layer using a solid wire as feedstock material, resulting in three-dimensional parts. The WAAM part must reach geometrical accuracies in order to be properly machined consecutively to the final shape [5]. ...
Wire and Arc Additive Manufacturing (WAAM) of Ti-6Al-4V is becoming increasingly important in the aerospace industry for the production of large parts. Due to the high welding requirements of the material, high quality demands are placed on the process. To meet these high demands, quality assurance measures are applied to maintain mechanical and geometrical part properties. First, the interlayer temperatures that are applied influence the final geometry. The part must meet geometric accuracies in order to be machined after the WAAM process. Second, Ti-6Al-4V materials have a high affinity to absorb oxygen from the environment at elevated temperatures. This oxygen uptake results in a discoloration of the surface and an embrittlement of the material. Therefore, a defined and monitored oxygen content in the build chamber is crucial. This work presents an approach to determine limitations for the interlayer temperature of the part and the oxygen content in the build chamber. The influence of a temperature deviating from the set interlayer temperature on the layer width was analyzed. By varying the interlayer temperature, the layer width varied by up to 3 mm. It was shown that different restrictions for the oxygen content in the build chamber apply depending on the part size.
