Irradiation System Calibration for Powder Bed Fusion
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Solution Overview
Problem
Existing irradiation systems for producing three-dimensional work pieces by powder bed fusion face challenges in accurately calibrating the focus of the radiation beam due to focus offset issues caused by the curved focal plane of the scanner mirror, which can lead to inadequate compensation and reduced accuracy in the manufacturing process.
Innovation Solution
A method for calibrating the irradiation system involves setting specific distances between a calibration plane and the optical unit, irradiating calibration patterns at different angular positions of the scanner mirror, and evaluating these patterns to determine focus positions. This method allows for precise optimization of the radiation beam's focus in the irradiation plane, considering both z-direction and x-y plane variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If focus offset compensation is performed using conventional means, then the focus position can be adjusted, but the accuracy of focus offset compensation deteriorates due to incorrect or insufficient compensation and optical elements not considered
Solution Approach 1:
The patent performs preliminary characterization of the optical system by measuring the actual focus position at multiple x-y positions across the irradiation plane before production use. These measurements are stored in a lookup table that is later referenced during production to compensate for focus offset, rather than attempting real-time calculation or adjustment
Solution Approach 2:
The system uses measured focus position data from preliminary characterization to create a feedback mechanism. The actual focus positions measured during calibration feed into a lookup table that provides correction values, which are then applied during production irradiation to compensate for focus offset errors
2Measurement precision
If focus position adjustment is performed using scanner optic, then the focus position can be modified, but the accuracy of focus offset compensation deteriorates due to the adjustment process itself
Solution Approach 1:
The patent performs preliminary measurements of focus position at multiple x-y locations across the irradiation plane using the scanner optic in its natural, unadjusted state. These baseline measurements are stored and used to create a lookup table for compensation, avoiding the need to repeatedly adjust the scanner optic during production
Solution Approach 2:
The system creates a digital copy or model of the actual focus positions through preliminary measurements and stores this information in a lookup table. During production, this digital model is referenced to determine compensation values, eliminating the need for physical adjustment of the scanner optic and preserving measurement accuracy
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The calibration method significantly improves the accuracy of the radiation beam's focus, enhancing the precision and quality of three-dimensional work pieces produced by powder bed fusion, while also accounting for temperature-induced thermal focus shifts.
Implementation Method 1
The radiation penetrating into the powder layer causes heating and consequently melting or sintering of the raw material powder particles
Implementation Method 2
subjected to electromagnetic or particle radiation in a site selective manner
Implementation Method 3
causes heating and consequently melting or sintering of the raw material powder particles
Implementation Method 4
causes heating and consequently melting or sintering of the raw material powder particles
Data Source
AI summary
A method for calibrating an irradiation system (10) for use in an apparatus (100) for producing a three-dimensional work piece is described. The method comprising the step of i) setting a distance between a calibration plane (30) and an optical unit (16) of the irradiation system (10) in a z-direction perpendicular to the calibration plane (30) to a first distance (z1). In a step ii), while maintaining the distance between the calibration plane (30) and the optical unit (16) at the first distance (z1), a first calibration pattern (p1,1) is irradiated in a first x-y region (a1) within the calibration plane (30) with a scanner mirror (22) of the optical unit (16) being arranged in a first angular basic position. A second calibration pattern (p2,1) is irradiated in a second x-y region within the calibration plane (30) with the scanner mirror (22) of the optical unit (16) being arranged at a second angular basic position in which the scanner mirror (22) is pivoted relative to the first angular basic position by at least ±1°. In a step iii) the distance between the calibration plane (30) and the optical unit (16) in the z-direction is set to a second distance (z2) different from the first distance (z1). In a step iv), while maintaining the distance between the calibration plane (30) and the optical unit (16) at the second distance (22), a third calibration pattern (p1,2) is irradiated in the first x-y region (a1) with the scanner mirror (22) of the optical unit (16) being arranged in the first angular basic position, and a fourth calibration pattern (p2,2) is irradiated in the second x-y region (a2) with the scanner mirror (22) of the optical unit (16) being arranged in the second angular basic position. In a step v) the first, the second, the third and the fourth calibration pattern (p1,1, p2,1, p1,2, p2,2) are evaluated so as to determine focus positions of the radiation beam (14) in the z-direction in dependence on an x-y position within the calibration plane (30). In a step vi) the irradiation system (10) is calibrated based on the determined focus positions of the radiation beam (14).