Dual NURBS Curve-Based Impeller Blade Industrial Robot GMAW Additive Manufacturing

Overview and Motivation

Additive manufacturing (AM) of impeller blades using GMAW (Gas Metal Arc Welding) has emerged as a promising technology for producing complex geometries in aerospace, energy, and chemical processing industries. The paper under study introduces a path planning method based on dual NURBS (Non-Uniform Rational B-Spline) curves for robotic GMAW additive manufacturing of impeller blades. From a pressure vessel engineering perspective, this technology has potential applications in fabricating impeller components for pumps, compressors, and agitators used in pressure vessel systems.

Core Technical Framework

The dual NURBS curve approach addresses the challenge of generating continuous, smooth deposition paths for complex three-dimensional geometries. Traditional path planning methods often produce discontinuous or jagged paths that lead to surface roughness, dimensional inaccuracies, and poor mechanical properties.

Parameter	Description	Typical Values
Blade thickness	Wall thickness of impeller blade	3–8 mm
Deposition layer height	Height of each deposited layer	0.5–1.5 mm
Deposition width	Width of each deposited bead	3–6 mm
Robot joint accuracy	Positional accuracy of robot joints	±0.05 mm
Surface roughness Ra	Arithmetic mean roughness of as-deposited surface	10–50 μm
Dimensional accuracy	Deviation from nominal geometry	±0.5 mm
Deposition rate	Volume of material deposited per unit time	50–200 cm³/h

The dual NURBS curve method uses one set of NURBS curves to define the blade surface geometry and another set to define the deposition path, ensuring that the path follows the surface contour while maintaining continuous, smooth motion.

Process Parameters for GMAW Additive Manufacturing

Parameter	Range	Effect on Quality
Welding current	150–250 A	Higher current increases deposition rate but may cause spatter
Welding voltage	20–28 V	Affects arc stability and bead width
Wire feed rate	4–8 m/min	Controls deposition rate and bead geometry
Travel speed	200–500 mm/min	Affects bead height and width
Shielding gas flow	15–25 L/min	Prevents oxidation and porosity
Preheating temperature	100–200°C	Reduces residual stress and cracking
Interlayer temperature	150–300°C	Controls solidification rate and microstructure

Engineering Practice Considerations

For pressure vessel applications, the following factors are critical when considering GMAW additive manufacturing of impeller components:

Material selection — The choice of filler wire must be compatible with the base material and service conditions. For stainless steel impellers, ER308L or ER316L wires are commonly used.
Build orientation — The orientation of the impeller during deposition affects support requirements, surface quality, and mechanical properties.
Post-processing — As-deposited components typically require machining to achieve final dimensions and surface finish. Allowances must be planned in the initial path design.
Inspection and qualification — Additive manufactured components require comprehensive inspection, including UT for internal defects, MT/PT for surface defects, and mechanical testing for property verification.

Defect Analysis in GMAW Additive Manufacturing

Defect Type	Root Cause	Detection Method	Prevention Strategy
Porosity	Gas entrapment, wire contamination	UT, RT	Clean wire, adequate shielding gas
Lack of fusion	Insufficient heat input, high travel speed	UT, MT	Optimize current and speed
Cracking	High residual stress, material incompatibility	MT, PT	Preheating, controlled cooling
Dimensional inaccuracy	Path deviation, robot calibration	CMM, laser scanning	Regular robot calibration
Surface roughness	Oscillation amplitude, wire diameter	Surface profilometry	Optimize oscillation parameters

Key Insights and Reflections

The dual NURBS curve approach represents a significant advancement in path planning for robotic AM. In my experience with traditional welding processes, the quality of the deposited material is highly dependent on the consistency and smoothness of the welding path. The NURBS-based method ensures that the robot follows a mathematically defined, continuous path, which should translate to more uniform bead geometry and improved mechanical properties.

The research also highlights the importance of integrating computational geometry with process control. The ability to define complex geometries using NURBS curves and automatically generate deposition paths reduces the reliance on manual path programming, which is time-consuming and prone to errors.

Reference Value and Outlook

This technology has potential applications in pressure vessel fabrication, particularly for custom impeller components where traditional manufacturing methods are impractical or uneconomical. Future development should focus on expanding the range of materials that can be additively manufactured, including nickel-based alloys and titanium, which are commonly used in high-performance pressure vessel applications. The integration of real-time process monitoring with path planning would enable adaptive control, improving quality and consistency.