Enhancing Formability of High-Inclination Thin-Walled and Arch Bridge Structures via Tilted Laser Wire Additive Manufacturing

Abstract

Laser wire additive manufacturing (LWAM) offers high deposition efficiency and excellent material utilization. However, manufacturing thin-walled structures with large inclination angles and no support remains a challenge. In this study, the influence of laser tilt angle on the formability of multi-layer inclined parts was systematically investigated. Results reveal that tilting the laser redistributes energy input along the inclination direction, stabilizing the melt pool and reducing angular deviation. Under a 20° tilt condition, thin-walled structures with inclination up to 70° were successfully fabricated, overcoming the limitation of conventional vertical deposition. Furthermore, a multi-inclination arch bridge structure was fabricated under optimized conditions, demonstrating good morphological appearance, dimensional accuracy (deviation within ±0.3 mm), and surface waviness (W < 0.12 mm). The findings provide new insights into the mechanism of energy redistribution in tilted LWAM and establish a promising strategy for manufacturing complex overhanging structures in aerospace and automotive industries.

1. Introduction

Additive manufacturing (AM) has emerged as a transformative technology for fabricating complex metallic components with high design freedom, high material efficiency, and reduced production time. Among various AM techniques, laser wire additive manufacturing (LWAM) has received growing attention owing to its advantages of high deposition efficiency, low feedstock cost, and excellent environmental compatibility compared with powder-based systems [1,2,3]. LWAM is particularly suited for the production of large metallic structures, such as aerospace and energy components, where dimensional accuracy and structural integrity are both critical [4,5].

Recent studies have explored different strategies to improve the process stability and build quality of LWAM. Investigations on parameter control and melt pool dynamics have demonstrated that optimized wire–laser interaction can enhance bead uniformity and reduce porosity [6]. Comparative analyses between wire- and powder-based directed energy deposition processes have shown that wire feeding ensures superior material utilization, but geometric control and dimensional precision remain major challenges [7]. Multi-axis and robotic deposition strategies have been proposed to enable variable overhangs and complex geometries [8], while experimental trials in wire-arc additive manufacturing (WAAM) have further indicated that maintaining stable layer formation at large inclination angles is still difficult [9].

Despite these advances, the fabrication of unsupported thin-walled structures with large inclination angles remains a major technical challenge [10,11,12]. When the inclination exceeds approximately 45°, melt pool instability, layer collapse, and dimensional deviation frequently occur, severely restricting the geometric freedom of LWAM [13,14,15]. Existing optimization approaches, such as parameter tuning, adaptive wire feeding, or the introduction of support structures, either lack general applicability or increase process complexity and cost [16]. Therefore, a more fundamental approach that directly stabilizes the melt pool during high-inclination deposition is still required [17]. Tilting the laser beam offers a promising solution by redistributing the heat input within the molten pool and improving the wetting behavior along inclined surfaces. While such strategies have been reported for WAAM [18,19], systematic investigations in LWAM are still limited [20]. Furthermore, the quantitative relationship between laser tilt angle and the resulting formability limit has not yet been clarified [21].

To address these gaps, this study systematically investigates the influence of laser tilt angle on the formation of high-inclination thin-walled and multi-inclination structures using 316L stainless steel. The effects of tilt angle on melt pool morphology, dimensional accuracy, and surface quality are analyzed. Moreover, the feasibility of fabricating a multi- inclination arch bridge structure under optimized conditions is demonstrated. The outcomes provide both mechanistic insights and process guidelines for extending LWAM to unsupported, high-inclination geometries.

2. Experimental Procedure

2.1. Materials and Equipment

In this study, 316 stainless steel [22] was used as the substrate material, while ER-316L stainless steel [23] wire with a diameter of 0.8 mm served as the filler material. The chemical compositions of the substrate and welding wire materials are given in

Table 1. Chemical composition of 316 stainless steel for substrate.

Substrate	C	Si	Mn	P	S	Ni	Cr	N	Mo	Cu
316	0.043	0.46	1.12	0.027	0.003	10.01	18.15	0.031	2.1	Allowance

and

Table 2. Chemical components of ER-316L stainless steel for welding wire.

Welding Wire	C	Si	Mn	P	S	Ni	Cr	Mo	Cu
316L	0.03	0.3~0.65	1~2.5	0.03	003	11~14	18~20	2~3	0.75

, respectively. The 316 stainless steel substrate contains relatively high levels of Cr and Ni, which provide corrosion resistance and mechanical strength. The ER-316L wire, with its reduced C content, improves resistance to intergranular corrosion in the deposited material.

The experiments were conducted using a HY-PTBZGQ-1000 fiber laser additive manufacturing system (as shown in Figure 1), which is equipped with an MFSC-1000X laser (maximum power 1 kW, wavelength 1.08 μm), a DI-2000L tiltable laser emitter, and a QL-100 numerically controlled wire feeder. High-purity argon shielding gas was continuously applied to prevent oxidation of the molten pool and deposited layers. This configuration ensured stable energy input and reliable process conditions for fabricating specimens under different laser tilt angles.

2.2. Laser Tilt Angle Setup

The laser tilt angle was the primary variable investigated in this study. As shown in Figure 2, laser tilt angles (α) of 0°, 10°, 20°, 30° and 40° were applied relative to the vertical axis to examine their effects on energy distribution, melt pool stability, and part formability.

At α = 0° (conventional vertical incidence), the energy input is concentrated at the upper part of the melt pool, which often leads to instability and poor deposition quality, particularly for high-inclination parts [24]. At α = 10°, energy distribution becomes more balanced, stabilizing the molten pool and reducing heat accumulation, which is suitable for moderate inclinations [25]. At α = 20°, melt pool stability is significantly enhanced, fluctuations are reduced, and deposition quality is improved, enabling the successful fabrication of thin-walled parts with inclination angles (${\theta }_a$) up to 70°. At α = 30°, the energy distribution extends further down the deposition layer, yet the increased tilt begins to alter the interaction between the laser beam and the wire feedstock, potentially affecting deposition consistency. At α = 40°, the significant tilt angle may lead to an over-elongation of the molten pool and a less favorable energy coupling efficiency, which could challenge the stability of the process, especially for structures with extreme geometrical demands.

Table 3. Parameters of single-channel multilayer inclined deposition tests under different laser tilt angles.

Laser Tilt Angle, $\mathit{\alpha }$ (°)	Laser Power, $\mathit{P}$ (W)	Scanning Speed, ${\mathit{v}}_{\mathit{s}}$ (mm/s)	Wire Feeding Speed, ${\mathit{v}}_{\mathit{f}}$ (mm/s)	Shielding GAS flow Rate, ${\mathit{Q}}_{\mathit{g}}$ (L/min)	Linear Energy Density, ${\mathit{E}}_{\mathit{L}}$ (J/mm)
0	540	3.0	10.0	15	180
10	540	3.0	10.0	15	180
20	540	3.0	10.0	15	180
30	540	3.0	10.0	15	180
40	540	3.0	10.0	15	180

illustrates the parameters of single-channel multilayer inclined deposition tests under different laser tilt angles. To ensure process repeatability and isolate the influence of laser tilt angle, all deposition parameters were maintained constant during the tests, except for the laser tilt itself. The detailed process parameters are summarized in Table 3. The laser power ($P$), scanning speed ($v_s$), and wire feed speed ($v_f$) were fixed at 540 W, 3.0 mm/s, and 10.0 mm/s, respectively, corresponding to a constant linear energy density ($E_L$) of 180 J/mm. High-purity argon was employed as the shielding gas at a flow rate ($Q_g$) of 15 L/min to prevent oxidation. The tilt angle ($\alpha$) was varied from 0° to 40° to evaluate its effect on layer formation and wall formability. For each condition, three replicate samples were fabricated to obtain statistically reliable results.

2.3. Fabrication Strategy and Characterization

To ensure stable deposition of thin-walled and high-inclination structures, a single tracking path multi-layer approach was employed. As shown in Figure 3a, each inclined wall was designed to consist of ten layers with a target length of 45 mm. To mitigate thermal accumulation and improve structural stability, the first five layers were deposited vertically before gradually transitioning to the inclined section [26].

The laser tilt angle was introduced as the primary variable in the process. Laser tilt angles of a = 0°, 10°, 20°, 30°, and 40° were tested to investigate their influence on melt pool stability and formability. For each tilt angle condition, three replicate samples were fabricated to ensure statistical reliability. The averaged values and corresponding standard deviations are presented in the quantitative plots in the Results section.

In addition to tilt adjustment, several auxiliary strategies were applied to enhance process stability. A rear-wire feeding configuration was adopted to improve filler transfer into the molten pool, thereby ensuring more uniform deposition at high inclinations [27,28]. High-purity argon shielding gas was supplied at a controlled flow rate to prevent oxidation and further stabilize the molten pool [10]. Moreover, short cooling intervals were introduced between successive layers to dissipate accumulated heat, which reduced interlayer thermal stress and improved bonding quality as well as dimensional accuracy [29].

The fabricated specimens were systematically characterized to evaluate their formability, dimensional accuracy, and surface waviness. A laser scanning system (LJ-X8000A laser profilometer equipped with LJ-X Navigator software (Version 1.02.00), Keyence Corporation, Osaka, Japan) [30] (Figure 4a) was employed to acquire high-resolution surface profiles and measure key geometrical features, including layer height, wall thickness, and surface waviness (W). The corresponding measurement interface is shown in Figure 4b, which provides a top-view measurement of the deposited structure. Five measurement tracking paths were defined across the fabricated arch bridge: paths 1 and 5 correspond to the 0° inclination regions, paths 2 and 4 to the 45° inclination regions, and path 3 to the 70° inclination region.

Non-contact 3D scanning was also performed using the same system to obtain topography data for determining dimensional deviation and inclination error. For microstructural evaluation, cross-sectional samples with surfaces perpendicular to the scan direction were extracted from the deposited parts by wire electrical discharge machining (WEDM). These samples were ground and etched using aqua regia to reveal the fusion boundaries. The etched sections were observed using an SRL-7045 optical microscope (Shangrao Optical Instrument Factory, Shangrao, China) to examine the layer stacking morphology and fusion quality. Geometric measurements such as layer thickness, fluctuation, and wall inclination were further quantified using LJ-X Observer software (Version 1.02.00) (Keyence Corporation, Osaka, Japan), enabling correlation of structural geometry with melt pool behavior and deposition stability.

To further validate the applicability of the optimized process parameters, a multi- inclination arch bridge structure will be fabricated under the most suitable laser tilt condition. As shown in Figure 5, the arch geometry was selected as a demonstrator because it represents a typical unsupported structure with varying inclination angles, making it a stringent test of process stability and formability.

Based on the schematic in Figure 3b, metallographic analysis was performed on cross-sections from workpieces fabricated at each tilt angle to evaluate post-build structural stability. The analyzed cross-sectional surfaces were obtained by electrical discharge machining along the central plane indicated in Figure 3b. The samples then underwent standard metallographic preparation, which included sample mounting, buff polishing (0.25 μm polycrystalline diamond abrasive), and metallographic etching for 15 s in a FeCl₃:HCl:H₂O solution (5 g:20 mL:75 mL). Finally, for rigorous comparison, specific corresponding locations on both the inclined sections and initial five vertically deposited layers were examined across workpieces produced at laser tilt angles of 0°, 10°, 30°, and 40° using optical microscope.

3. Results

3.1. Effect of Laser Tilt Angles on Deposition Geometry

Table 4. Cross-sectional topography of deposited layers at different laser title angles.

$\mathit{a}$ (°)	0	10	20	30	40
Section contour

shows cross-sectional morphology of deposited layers at different laser title angles. It can be observed that the layer-by-layer contour curves, which indicate the welding line, are uneven. The forming process is unstable at laser title angles of 0°, 10°, and 40°. In contrast, the forming process is relatively stable at laser title angles of 20° and 30°. Among these conditions, $\alpha$ = 20° proved most effective, enabling the fabrication of thin-walled parts with inclination angles up to ${\theta }_a$ = 70°.

The laser tilt angle also had a significant influence on the geometrical characteristics of the deposited walls, particularly the layer height ($h$), wall thickness ($\delta$), and their dimensional stability, which is quantified as the layer height fluctuation (${\sigma }_h$) and wall thickness fluctuation by the standard deviations, serve as critical indicators of process stability. Figure 6 shows the effects of laser tilt angles α = 0°, 10°, 20°, 30° and 40° on the formation of 70° inclined walls, the variation trends of the following geometric parameters can be clearly observed:

As shown in Figure 6a, the average layer height ($h_a$) gradually decreased while the layer height fluctuation (${\sigma }_h$) has a significant variation as the laser tilt angle α increased from 0° to 20°. At α = 0° (vertical incidence), the laser energy concentrated in the upper region of the molten pool, causing unstable flow behavior that resulted in excessive layer height and severe fluctuations in the deposited walls. When α increased to 10°, the energy distribution along with the inclination direction became more uniform, improving molten pool stability and leading to reduced $h_a$, lower ${\sigma }_h$, and better alignment with the designed inclination angle.

Specifically, at $\alpha$ = 20° laser tilt, ${\sigma }_h$ reached its minimum value, demonstrating optimal layer height uniformity. However, when the laser tilt angle ($\alpha$) was further increased to 30° and 40°, the layer height uniformity began to deteriorate. The excessive tilt caused energy dispersion and reduced deposition efficiency, leading to increased ${\sigma }_h$ values of 0.1 mm and 0.12 mm respectively, compared to 0.06 mm at $\alpha$ = 20°.

Figure 6b further demonstrates the strong dependence of wall thickness ($\delta$) and its fluctuation (${\sigma }_{\delta }$) on laser tilt angle ($\alpha$). At $\alpha$ = 0° tilt, irregular average wall thickness (${\delta }_a$) and large ${\sigma }_{\delta }$ = 0.33 mm were observed. When α increased to 10°, ${\sigma }_{\delta }$ decreased to 0.30 mm, indicating improved wall thickness uniformity. The optimal performance was achieved at $\alpha$ = 20° with ${\sigma }_{\delta }$ of 0.06 mm. However, at $\alpha$ = 30° and 40° tilt angles, ${\sigma }_{\delta }$ increased to 0.15 mm and 0.22 mm respectively, as the excessive tilt angles caused uneven material distribution and reduced dimensional control.

Specifically, at $\alpha$ = 20° laser tilt, both ${\delta }_a$ and ${\sigma }_{\delta }$ reached their minimum values, and the deposited structures exhibited the most uniform geometry and highest dimensional accuracy, closely matching the designed profile. Under this optimal condition, thin-walled structures with inclination angles up to 70° were successfully fabricated, an achievement unattainable with vertical laser incidence or excessive laser tilt angles beyond 20°.

3.2. Maximum Achievable Inclination Angle

The maximum inclination angle that could be achieved without structural collapse was strongly dependent on the applied laser tilt, as shown in Figure 7. Under vertical incidence ($\alpha$ = 0°), stable deposition was limited to tilt angles below 45°. Beyond this value, the molten pool became unstable, leading to collapse of the deposited layers and severe deviation from the designed geometry.

When $\alpha$ increased to 10°, the maximum inclination angle ${\theta }_a$ reached about 69°. The energy distribution became more uniform, which improved molten pool stability. This allowed deposition on steeper slopes. However, some collapse and irregular bead shapes still appeared near the top of the walls.

At $\alpha$ = 20° laser tilt angle, the process became much more stable. Thin-walled structures with ${\theta }_a$ up to 70° were successfully made without collapse, as shown in Figure 7b. The tilted laser helped spread energy better and elongated the molten pool. This improved metal flow along the slope, which maintained shape accuracy and prevented collapse.

When $\alpha$ increased further to 30° and 40°, the maximum inclination angle continuously increased. Namely, ${\theta }_a$ increased to about 72° at $\alpha$ = 30°, and it became to around 73° at $\alpha$ = 40°. However, these higher tilt angles caused the energy to spread too widely. Melt pool stability suffered, leading to more irregular beads and weaker structures near the top (e.g., a partial collapse occurred on the top layers of $\alpha$ = 30° in Figure 7b).

Above results show that tilting the laser can greatly improve the formability of unsupported structures. However, the best results occur near $\alpha$ = 20°. Going beyond this angle reduces performance and limits the maximum slope that can be built.

3.3. Multi-Inclination Arch Bridge Fabrication

To validate the capability of the optimized process for fabricating complex unsupported structures, a multi-inclination arch bridge was manufactured using the determined optimal laser tilt angle ($\alpha$) of 20°. This structure, integrating ${\theta }_a$ = 0°, 45°, and 70° inclination angles, serves as a demanding test for evaluating the stability and formability of the tilted LWAM process.

The arch bridge was successfully fabricated without collapse or visible defects, as shown in Figure 7b (the case of arch bridge under $\alpha$ = 20° without collapse) and Figure 8b. The structure demonstrates consistent layer stacking and excellent interlayer bonding across all inclination sections, confirming the robustness of the $\alpha$ = 20° tilt angle in managing high-inclination deposition.

Surface waviness (W) was quantitatively measured along five predefined paths (Figure 8), with results summarized in

Table 5. Waviness values at different tracks of arch bridge part.

Tracking path	1	2	3	4	5	Averaged
Waviness (mm)	0.056	0.087	0.113	0.096	0.044	0.079

. The waviness level remains low across all paths, ranging from 0.044 mm to 0.113 mm, with an average of 0.079 mm. Although waviness increases with inclination angle, from the near-vertical regions (Paths 1 and 5) to the steep 70° segment (Path 3), the values are consistently controlled. This trend, while common in additive manufacturing, is effectively mitigated by the tilted laser strategy, which maintains deposition stability and minimizes surface undulation even at high inclinations [31].

The successful fabrication of the multi-inclination arch bridge highlights a principal advantage of the tilted laser approach: its ability to seamlessly fabricate unsupported structures with varying overhang angles in a single process. This is attributed to the energy redistribution mechanism (Section 4.1), which ensures uniform melt pool stability and fusion quality across different inclinations without requiring parameter adjustments or support structures.

In summary, the high geometric fidelity and controlled surface quality of the arch bridge demonstrate the effectiveness of the tilted LWAM strategy. This method provides a promising solution for manufacturing complex, unsupported components with stringent dimensional requirements, showing significant potential for applications in aerospace, automotive, and other industries requiring lightweight, high-integrity structures.

3.4. Stability and Defect Analysis

The metallographic structure was examined to analyze internal defects such as argon bubbles. As shown in Figure 9, sporadic porosity can indeed be observed within initial vertically deposited 5 layers. These pores are primarily caused by the entrapment of shielding gas (argon). In contrast, Figure 10 shows that the inclined region is largely free of such bubbles. For the Inclination layers, this power creates a larger and longer-lasting melt pool, allowing keyhole-induced pores to escape. Moreover, the keyhole position and gravity affect melt pool flow: in the initial vertically deposited 5 layers, the keyhole is central, and bubbles rising from it cannot escape, causing porosity. In the inclination layers, the lack of support underneath causes the melt pool to flow downward, enabling keyhole-induced bubbles to escape upward and toward the upper rear, thus preventing pore formation [32].

The distinct difference in porosity distribution between the vertical and inclined sections underscores the profound impact of laser tilt angle on melt pool dynamics. The elimination of porosity in the unsupported, high-inclination regions provides direct metallurgical evidence for the stabilization of the process and the effectiveness of energy redistribution. A detailed discussion on the underlying mechanism of how laser tilting redistributes energy to stabilize the melt pool and facilitate defect suppression is presented in Section 4.1.

4. Discussion

4.1. Mechanism of Energy Redistribution

Figure 11 illustrates the effect of laser tilt angle on the geometry and energy distribution of the melt pool. The variation in the laser tilt angle significantly affects the shape, depth, and stability of the melt pool, which in turn influences the part formation quality [33].

Under conventional vertical laser incidence (0°), the laser spot primarily targets the highest point of the deposited layer. This concentrates energy input in the upper region of the molten pool [34]. Since the input power is fixed, the melt pool depth remains largely unchanged, while the lower portion receives insufficient energy. Consequently, the material at the bottom remains incompletely melted or only partially fused. This partially fused zone can provide some mechanical support but also restricts the downward flow of the molten metal. The resulting fusion line therefore has a limited inclination, which restricts the maximum achievable overhang angle.

In contrast, tilting the laser beam shifts the spot to a lower position on the deposition layer. This redirects the energy deeper into the melt pool [32], promoting complete melting and improved fusion at the bottom. The redistribution of energy allows the fusion line to achieve a steeper angle. This enables the fabrication of parts with inclination angles (${\theta }_a$) up to 70°, which is not feasible with traditional vertical laser deposition.

The proposed mechanism of energy redistribution and its impact on the fusion boundary, as summarized in the schematic of Figure 11, was derived from meticulous observation and analysis of the deposited layers’ cross-sectional morphologies. As shown in Figure 11, the fusion boundary is represented by a yellow dashed line. With laser tilt, the fusion profile aligns more closely with the designed geometry. This confirms that the energy redistribution mechanism is responsible for the observed enhancements in geometric accuracy and process stability. In summary, the tilted laser strategy enhances molten pool stability by controlling the spatial distribution of absorbed energy, offering a new approach for fabricating complex high-inclination structures.

It is critical to note that the single-track, multi-layer deposition strategy itself provides an inherently low risk of lack-of-fusion [35], as each new layer is deposited onto a pre-heated substrate that facilitates local remelting and ensures metallurgical bonding. This mechanism has been directly confirmed by in-situ observations in additive manufacturing processes [36]. The primary challenge, therefore, is not achieving basic fusion, but controlling the melt pool stability and metal flow to maintain geometric accuracy at high inclination angles, where gravity-induced instability becomes dominant.

The tilted laser strategy is precisely designed to address this challenge by redistributing the energy input, which shifts the laser-material interaction point downward. This fundamental action not only stabilizes the molten pool for precise contour formation but also provides a compelling explanation for the distinct defect characteristics observed between the initial vertically deposited 5 layers and the inclination layers, the concentration of energy input under vertical laser incidence (0°) fosters an unstable, often turbulent keyhole. This instability promotes the entrapment of shielding gas, leading to the sporadic porosity evident in Figure 9.

Conversely, in the inclination layers, the downward energy shift generates a more stable, elongated, and flatter melt pool. This optimized pool geometry, coupled with the reorientation relative to gravity, fundamentally alters the bubble escape dynamics. Instead of being trapped, bubbles generated by the keyhole are afforded a clear escape path towards the upper-rear free surface. Therefore, the energy redistribution mechanism simultaneously enhances geometric formability and suppresses the formation of gas porosity, ensuring superior metallurgical integrity in the challenging unsupported regions.

4.2. Comparison with Conventional Strategies

Traditional approaches to improving the formability of high-inclination structures in LWAM mainly focus on process parameter optimization, advanced wire feeding techniques, or the use of support structures [37,38,39]. While these methods can extend the process window to some extent, they also present limitations. Parameter optimization often requires extensive trial-and-error experiments, wire feeding modifications increase system complexity, and support structures add material waste and post-processing effort. As a result, these strategies either lack universality or compromise manufacturing efficiency.

Compared with traditional strategies such as parameter tuning, modified wire feeding, or support structures, the tilted laser approach offers a hardware-free and efficient means to improve the formability of high-inclination features. By redistributing energy within the melt pool, it enhances deposition stability and enables the fabrication of unsupported structures with inclination angles up to 70°. The successful fabrication of a multi-inclination arch bridge component further demonstrates its potential for application in aerospace and automotive sectors where complex geometries and strict tolerances are required.

Furthermore, when compared with arc-wire additive manufacturing, where tilted torch strategies have been more widely explored [40,41], LWAM with tilted laser incidence offers distinct advantages. Owing to the lower overall heat input of LWAM, the tilted laser approach achieves higher dimensional accuracy, reduced distortion, and improved surface quality. These benefits underline the broader applicability of the method in industries requiring lightweight components with strict tolerance control, such as aerospace and automotive manufacturing.

To further clarify the process capability of the proposed method, a comparison with representative LWAM studies is summarized in

Table 6. Comparative LWAM studies involving laser tilt and wall inclination performance.

No.	Material	Wire Diameter	Wall Width	Laser Tilt Angle	Max Achievable Inclination	Surface Quality	Reference
1	316L Stainless Steel	Ø 1.2 mm	~2–3 mm	0°, 10°, 20°, 30°, and 40°	70°	W ≈ 0.12 mm	This study
2	Ti–6Al–4V	Ø 0.3 mm	~0.6–1.0 mm	0°	69°	Not reported	[42]
3	304 Stainless Steel	Ø 1.2 mm	Not reported	0–40° (Substrate tilt)	40°	Not reported	[43]
4	Ti–6Al–4V	Not reported	Not reported	0°	30°	Not reported	[44]

. While some prior work has achieved wall inclinations up to 69°, these often relied on ultra-fine wires (e.g., Ø 0.3 mm) or narrow beads (≈1 mm), which may limit industrial applicability. In contrast, the present study demonstrates successful fabrication of unsupported 70° inclined structures using standard Ø 1.2 mm wire and wall widths of 2–3 mm, while maintaining surface waviness below 0.12 mm and dimensional accuracy within ±0.3 mm.

4.3. Application Significance

Nevertheless, several limitations must be acknowledged. First, while tilting the laser effectively improves melt-pool stability and enables the formation of large-inclination structures, it also introduces challenges in practical implementation. Precise alignment between the laser head, wire-feeding direction, and deposition path is required, and minor deviations can lead to geometric distortion or inconsistent bead overlap. In addition, although the maximum inclination angle was successfully extended to 70°, further increases may be restricted by heat accumulation, gravity-driven metal flow, and the reduced effectiveness of shielding-gas protection at extreme angles.

Furthermore, this study primarily focused on the processability and geometric formability of high-inclination thin-walled structures, aiming to establish a stable process window and forming strategy for tilted LWAM. Such process-oriented exploration provides the essential foundation for subsequent investigations into microstructural evolution and mechanical performance, which are decisive for evaluating the reliability of additively manufactured components. The local thermal history and solidification behavior induced by different tilt angles are expected to influence grain morphology, hardness distribution, tensile strength, and residual-stress development, thereby affecting the structural integrity and service life of fabricated parts. Recognizing this significance, our ongoing work is extending the present study to correlate tilt-angle-dependent process parameters with microstructure, hardness, and mechanical strength, establishing a quantitative process–structure–property relationship for tilted LWAM.

Future research will therefore focus on integrating microstructural characterization and mechanical testing to validate these correlations and to optimize laser-tilt strategies for various geometries and materials. The combination of experimental and numerical modeling, together with real-time monitoring and closed-loop control, is expected to further enhance process reliability. Extending the tilted LWAM strategy to multi-material and large-scale components will broaden its industrial applicability, particularly in the aerospace and energy sectors.

5. Conclusions

This study proposes a laser tilt strategy to improve the geometric formability of unsupported high-inclination structures in laser wire additive manufacturing (LWAM). By systematically adjusting the laser incidence angle, the method provides intrinsic melt pool stabilization without introducing additional hardware or complex toolpath planning. The findings significantly expand the process window and fabrication flexibility of LWAM for thin-walled and overhanging components. The main conclusions are as follows:

• By introducing laser tilt angles of 0°, 10°, 20°, 30°, and 40°, the process stability and geometric quality of inclined walls were systematically evaluated. The optimal performance was achieved at a tilt angle of 20°, where the maximum achievable inclination angle reached 70° without structural collapse, thereby enabling the direct fabrication of components with steep overhangs, such as lightweight aerospace ducts and integral mounting brackets.
• Under 20° tilt, the fabricated structures exhibited reduced height fluctuation (from ±0.21 mm at 0° to ±0.09 mm at 20°) and improved wall thickness uniformity. These improvements are attributed to the energy redistribution within the melt pool, which lowered the laser-material interaction point and stabilized the molten metal flow, ensuring the dimensional accuracy required for the direct manufacturing of complex, unsupported structural elements in the automotive and energy sectors.
• The feasibility of fabricating unsupported multi-inclination components was demonstrated through the construction of a freeform arch bridge structure. The inclined paths were successfully deposited without collapse or support, validating the proposed method’s effectiveness in complex overhang geometries, and showcasing its direct application potential in creating support-free, weight-critical architectural elements and custom industrial fixtures.
• Compared with conventional formability enhancement strategies—such as parameter tuning, modified wire feeding, and support structures—the tilted laser approach is hardware-free, easier to implement, and provides intrinsic melt pool control. This enables more consistent fabrication of lightweight, geometrically complex parts with reduced trial-and-error and post-processing effort, offering a streamlined and cost-effective solution for building complex prototypes and end-use parts with internal channels or variable cross-sections in small to medium batch production.
• Looking ahead, the proposed tilted laser strategy presents strong potential for enabling the direct fabrication of unsupported, high-inclination structures such as overhangs, lattice struts, internal ducts, and bionic ribbed walls. These capabilities are especially valuable in aerospace, marine, and energy applications where geometric freedom and structural reliability are critical. Future work will focus on correlating tilt-angle-dependent thermal behavior with microstructure and mechanical performance to establish a robust process–structure–property relationship.