Physical Mechanisms of Laser Oscillation Mode: From Kinematic Characteristics To Energy Distribution

01 Introduction
Modern laser oscillation welding technology is essentially an advanced "path-based energy programming." Its core principle is to first select an oscillation pattern with a specific "energy distribution framework" (e.g., linear Zig-Zag, figure‑eight, spiral) based on the welding goal—such as achieving penetration depth, bridging gaps, or suppressing porosity. Each pattern's kinematic characteristics dictate both instantaneous and cumulative energy distribution. Engineers then fine-tune parameters such as oscillation amplitude, frequency, power, and travel speed to precisely control energy delivery, thus enabling “customized” regulation of molten‑pool fluid dynamics and keyhole stability to achieve optimal weld quality.

02 Kinematic Characteristics & Energy Distribution Mechanisms of Different Oscillation Patterns
From a kinematic standpoint, the essential differences among laser oscillation modes lie in key parameters: instantaneous velocity, acceleration, path curvature, and turning characteristics. Instantaneous velocity determines energy dwell time at a given spot, while acceleration affects the strength of fluid impact. Path curvature governs flow direction in the pool and pressure distribution on keyhole walls.

Figure 1. Weld surface profiles for laser welding using different oscillation modes.

• Zig‑Zag: segmented linear motion with instantaneous reversals, resulting in high constant velocity in straight segments but theoretically infinite acceleration at turning points ("singularities"), causing local energy concentration.

• Sine/Cos: smooth, continuous curves with tangential velocity peaking at centerline and tapering at peaks/troughs, minimizing abrupt acceleration.

• Figure‑eight or Infinity (∞): complex paths combining smooth curvature and crossings, producing low‑velocity zones at loop extremities and high recurrence at the center crossover—creating a stable, high‑energy core beneficial for keyhole depth and stability.

• Spiral: continuously varying curvature with controlled tangential velocity, enabling progressive radial or concentric energy coverage—useful for preheating or post‑heating corrections.

These kinematic differences translate into distinct spatiotemporal energy distributions:

• Spatial: dwell time determines cumulative local energy density—longer dwell yields higher energy.

• Temporal: the sequence and frequency of energy application influence preheating, stirring, and solidification behaviors, shaping final microstructure and performance.

Different modes yield different outcomes: Zig‑Zag concentrates energy at vertices, increasing risk of keyhole overheating and spatter; ∞‑mode creates a stable, dual‑pass high‑energy core ideal for sustaining keyhole stability; spiral mode offers layered coverage, allowing fine control over temperature gradients; Sine/Cos enhances sidewall fusion via edge‑focused energy.

03 Coordinated Control of Process Parameters: Impact of Amplitude and Frequency on Molten‑Pool Dynamics
Oscillation frequency and amplitude are core orthogonal parameters for controlling energy distribution and molten‑pool behavior.

• Frequency: High (>100 Hz) supports rapid, continuous stirring and uniform energy distribution; low frequency emphasizes periodic energy input.

• Amplitude: Larger amplitude broadens coverage (useful for bridging gaps), while smaller amplitude constrains energy centrally, shaping or focusing energy on the weld seam.

  

  Figure 2. Changes in weld energy and velocity during a single cycle at different frequencies. (a) 10 Hz, (b) 20 Hz, (c) 50 Hz, (d) 100 Hz, (e) 150 Hz, (f) 200 Hz

  
  

Figure 3. Weld energy density distribution at different frequencies. (a) 0 Hz, (b) 10 Hz, (c) 20 Hz, (d) 50 Hz, (e) 100 Hz, (f) 150 Hz, (g) 200 Hz

Figure 4. Fluid velocity distribution at different oscillation amplitudes under constant power of 4.5 kW, velocity of 4 m/min, and frequency of 200 Hz. (a) 0.6 mm, (b) 1.2 mm, (c) 1.8 mm, (d) 2.4 mm

These, combined with welding speed, define oscillation overlap, ranging from linear to planar heat source effects.

• In Zig‑Zag, amplitude has dramatic effects: high amplitude enhances sidewall fusion by creating dwell points (“deep‑penetration nails”); low amplitude flattens energy distribution, improving weld morphology in thin‑sheet, high‑speed welding.

• Sine/Cos provides smoother transitions: high amplitude generates edge dwell effects to fully fuse corners, while high frequency yields wide shallow pools to suppress spatter and improve aesthetics.

• Figure‑eight (∞) and spiral modes excel in stirring and homogenization: high frequency cross‑shear induces turbulence to minimize porosity and compositional segregation in aluminum or dissimilar metal welding. Large amplitude 8‑mode drives broad convection; small amplitude focuses energy intensely for deep penetration.

• Spiral mode is ideal for circular seam closure, surface cladding, or arc‑end correction tasks owing to its diameter, pitch, and turn‑rate control.

04 Conclusion
The selection of oscillation mode must align core physical properties with application requirements. High lateral force patterns (wide‑amplitude Zig‑Zag or Sine) suit gap‑bridging and sidewall fusion. For aluminum welding prone to porosity or dissimilar metals requiring grain refinement, high‑frequency 8‑mode/∞‑mode offers exceptional stirring benefits. For circular welds, surface cladding, or problems requiring precise thermal sequencing, spiral mode provides the optimal solution. Modern process development thus becomes strategic: selecting an oscillation mode as an “energy‑distribution template” and tailoring its auxiliary parameters to precisely and custom‑control molten‑pool metallurgy and dynamics.

**--Cite the article published by 高能束加工技术 on August 5, 2025, in the WeChat public account "High-Energy Beam Processing Technology and Applications."