Design for Wire + Arc Additive Manufacture: design rules and build orientation selection

Wire + Arc Additive Manufacture (WAAM) is an additive manufacturing technology that can produce near net-shape parts layer by layer in an automated manner using welding technology controlled by a robot or CNC machine. WAAM has been shown to produce parts with good structural integrity in a range of materials including titanium, steel and aluminium and has the potential to produce high value structural parts at lower cost with much less waste material and shorter lead times that conventional manufacturing processes. This paper provides an initial set of design rules for WAAM and presents a methodology for build orientation selection for WAAM parts. The paper begins with a comparison between the design requirements and capabilities of WAAM and other additive manufacturing technologies, design guidelines for WAAM are then presented based on experimental work. A methodology to select the most appropriate build orientation for WAAM parts is then presented using a multi attribute decision matrix approach to compare different design alternatives. Two aerospace case study parts are provided to illustrate the methodology

Assessing the effect of TIG alternating current time cycle on aluminium wire + arc additive manufacture

The effect of electrode positive time cycle (% EP) of the alternating current TIG process has been investigated for aluminium wire + arc additive manufacture of linear walls. The study considered the effect on oxide removal, linear wall dimensions, microstructure, mechanical properties as well as the effect on electrode wear. The results showed that the effective wall width was minimum at 20%EP with a corresponding maximum in layer height. It was also observed that increasing the% EP increased the electrode wear rate, which in turn affected the arc stability. Microstructure analysis showed a noticeable increase in the grain size for higher% EP. The study also showed that% EP had no significant effect on mechanical properties. From a heat input analysis, a direct correlation was observed between the arc voltage and the% EP. The study also indicated that there could be other contributing factors to wall dimensions. For aluminium wire + arc additive manufacture of linear walls, minimum cleaning ranged between 10%EP and 20%EP

Properties of wire+ arc additively manufactured 2024 aluminum alloy with different solution treatment temperature

2024 aluminum alloy deposits were produced with wire + arc additive manufacturing procedure. Solution treatment + natural aging processes with different solution treatment temperature were conducted to improve the properties. The microstructure and mechanical properties were investigated. After heat treatment the distributing characteristic of the second phase changed to be dispersive from continuous in as-deposited condition. Solution treatment + natural aging process can significantly improve the properties of WAAM 2024 aluminum alloy. With higher solution treatment temperature, the micro hardness, tensile properties and elongation presented an increasing trend. After 503 °C solution treatment + natural aging process, the micro hardness, ultimate tensile strength, yield strength and elongation were 143HV, 497 MPa, 330 MPa and 16%, respectively, which can nearly meet the applying requirement

Criticality of porosity defects on the fatigue performance of wire + arc additive manufactured titanium alloy

This study was aimed at investigating the effect of internal porosity on the fatigue strength of wire + arc additive manufactured titanium alloy (WAAM Ti-6Al-4V). Unlike similar titanium alloys built by the powder bed fusion processes, WAAM Ti-6Al-4V seldom contains gas pores. However, feedstock may get contaminated that may cause pores of considerable size in the built materials. Two types of specimens were tested: (1) control group without porosity referred to as reference specimens; (2) designed porosity group using contaminated wires to build the specimen gauge section, referred to as porosity specimens. Test results have shown that static strength of the two groups was comparable, but the elongation in porosity group was reduced by 60% and its fatigue strength was 33% lower than the control group. The stress intensity factor range of the crack initiating pore calculated by Murakami’s approach has provided good correlation with the fatigue life. The kink point on the data fitting curve corresponds well with the threshold value of the stress intensity factor range found in the literature. For predicting the fatigue limit, a modified Kitagawa-Takahashi diagram was proposed consisting of three regions depending on porosity size. Critical pore diameter was found to be about 100 µm

Design study for wire and arc additive manufacture

Additive Manufacture (AM) is a technique whereby freeform structures are produced by building up material in a layer by layer fashion. Among the different AM processes, Wire and Arc Additive Manufacture (WAAM) has the ability to manufacture large custom-made metal workpiece with high efficiency. A design study has been performed to explore the process capabilities of fabricating complicated geometries using WAAM. Features such as enclosed structures, crossing structures, and balanced building structures have been investigated in this study. Finite Element (FE) models are employed to take the thermo-mechanical performance into account. Robot tool path design has been performed to transfer the WAAM component designs into real components efficiently. This paper covers these essential design steps from a technical as well as practical point of view

A wire deflection detection method based on image processing in wire + arc additive manufacturing

In wire and arc additive manufacture (WAAM), the twist of wire during a robot’s movement can result in the sudden changes of the wire-feeding position and thus cause deposition defects and dimensional errors. In the worst case, it may cause wire jamming and damage of the wire-feeding system. Therefore, online monitoring and correction of the wire deflection are very important for WAAM. In this paper, a vision-based measuring method is proposed for detecting the deviations of the wire-feeding position of a plasma welding-based WAAM process. It uses adaptive threshold and Hough transform to extract the wire edges, judges and merges the coincident lines, and applies Radon transform to measure the wire deflection. Software to automatically detect the wire deviation was developed based on the proposed method. The method and the software were verified with experiments

Measurements of wire + arc additive manufacturing layer heights during arc operation using coherent range-resolved interferometry (CO-RRI)

Wire + arc additive manufacture (WAAM)promises high build rates and is well-suited to the manufacture of large structures.In-process measurements of layer height are critical for WAAM process control but are difficult to achieve due to the presence of bright arc light. In this paper, a novel coherent range-resolved interferometric (CO-RRI) technique is successfully applied to the measurement of layer heights during arc operation in a first step towards gaining full in-process control of deposition layer heights

The application of knowledge based engineering to design for Wire+Arc Additive Manufacture (WAAM)

Wire+Arc Additive Manufacture (WAAM) is well suited to Aerospace applications, due to its ability to produce medium to large structural parts with good structural integrity, and lower manufacturing cost/ waste material than conventional manufacturing processes. However, designers of WAAM parts need expert knowledge of WAAM to maximise the benefits, and substantial modelling effort is required to develop the digital models that are needed for design assessment and manufacturing. This paper introduces Knowledge Based Engineering (KBE) as an approach to automate WAAM design assessment and manufacturing planning for aircraft structural parts. A prototype KBE tool for WAAM has been developed that can check adherence to WAAM design guidelines, perform cost estimations and automatically generate the CAD models that are required for design assessment and manufacturing planning. The paper also includes a case study design assessment for an aircraft structural part

Refinement of Ti-6Al-4V prior-β grain structure in the as-deposited condition via process control during wire-direct energy deposition

This study demonstrates that refinement of the prior-β grains generated during the wire-direct energy deposition of Ti‐6Al‐4V is achievable whilst maintaining a stable processing condition in the as-deposited condition, not reliant on penetration of the feedstock to the melt pool. Previous studies on prior-β grain refinement of Ti‐6Al‐4V have been reliant on either post-processing, alloy modification or agitation of the melt pool to achieve refinement. Through process control alone, it was identified that an increase in the deposition rate for a fixed energy input led to a reduction in the specific energy density of deposited material. Utilising pyrometry, it was determined that the reduction in the specific energy density led to a decrease in the thermal gradient, measured using a linear thermal gradient approximation, encouraging apparent homogenous nucleation within the melt pool. Whilst maintaining a stable ‘droplet’ transfer mode, the gradual reduction in specific energy density transformed the grain structure from the typical columnar morphology through a mixed morphology to an equiaxed grain morphology; confirmed via prior-β grain reconstructions and inverse pole figure analysis made possible by electron back scattered diffraction microscopy of the deposited samples. Microhardness measurements demonstrated larger variations in the refined prior-β grain specimens as compared to the columnar as a result of more complex α morphologies generated

Vom Draht zum Bauteil: Entwicklung einer Aluminium-Lithium-Legierung für die additive Fertigung mit Draht und Lichtbogen

The Innovative Aluminium filler Wires for Aircraft Structures (IAWAS) project aimed to demonstrate the potential of Wire Arc Additive Manufacture (WAAM) for the production of aluminium lithium components. Preliminary testing demonstrated the possibility of depositing an 2395 aluminium lithium filler wire using a plasma arc heat source and a local shielding device. The deposit had a low porosity level but also low ductility caused by long, vertical, segregated grain boundaries. Both chemical composition and deposition conditions are known to impact the deposit microstructure. In-situ alloying, an efficient technique to develop new material, was implemented using plasma arc as a heat source on aluminium lithium alloys. The results aligned with the literature review on the impact of copper on crack sensitivity and led to the design of a new alloy. Unfortunately, the composition selected yielded challenges during the drawing process, and the filler material quality was poor, leading to a low WAAM deposit quality. Machine hammer peening was implemented on the AA2395 alloy, resulting in a drastic increase in ductility and yield strength of 480 MPa after solution treatment and ageing. This alloy was used to manufacture an aluminium lithium demonstrator to showcase the potential of WAAM to produce real-life components.The authors would like to acknowledge the European funding allocated to the IAWAS project partners (Grant agreement ID: 821371). This research work was also supported by the Engineering and Physical Sciences Research Council (EPSRC) through the NEwWire Additive