Methods and systems for characterizing laser machining properties by measuring keyhole dynamics using interferometry

Inventors

WEBSTER, Paul J. L.

Assignees

IPG Photonics Corp

Abstract

A method, apparatus, and system are provided to monitor and characterize the dynamics of a phase change region (PCR) created during laser welding, specifically keyhole welding, and other material modification processes, using low-coherence interferometry. By directing a measurement beam to multiple locations within and overlapping with the PCR, the system, apparatus, and method are used to determine, in real time, spatial and temporal characteristics of the weld such as keyhole depth, length, width, shape and whether the keyhole is unstable, closes or collapses. This information is important in determining the quality and material properties of a completed finished weld. It can also be used with feedback to modify the material modification process in real time.

Core Innovation

The invention relates to low-coherence interferometry for monitoring keyhole-related phase change regions during laser welding or material modification. Imaging beams are directed to multiple positions associated with the phase change region, including positions ahead of, aligned with, and trailing the processing laser beam, and also positions across or within the phase change region. Interferometry at each imaging position determines phase change region characteristics in real time from interferometry output based on optical path length differences.

The measured characteristics include keyhole depth, including a location of maximum keyhole depth, average keyhole depth, keyhole length and keyhole width, keyhole surface shape and subsurface keyhole length and width, and keyhole profile information. The techniques also determine wall slope or sidewall angle and characterize collapse and instability of the keyhole, including dynamics of the liquid region and the interface between liquid and solid regions.

An interferometry system is described that includes an optical combiner producing interferometry output from optical path length differences and an interferometry output processor. Optical access is provided via an optical access port and input-output port for delivering imaging light to the phase change region positions, and active deflection is used to create imaging offsets for depth measurement across the phase change region. The signal processing and reference handling include reference arm delay line concepts and techniques that manage top surface reference points and interface localization using interferometry output, including intensity-, phase-, and fringe-based approaches.

Claims Coverage

The claims coverage identifies the use of low-coherence interferometry to monitor phase change region/keyhole characteristics at multiple imaging positions and to derive real-time measurements from interferometry output. The inventive features are the multiple imaging positions, interferometry-based characterization of keyhole geometry and instability, and reference handling for localization and measurement.

The claims collectively cover low-coherence interferometric monitoring of keyhole-related phase change regions using multiple imaging positions, with real-time characterization of geometry, instability, and reference-localized measurement.

Stated Advantages

Documented Applications