Engine Inlet Inner Barrel Perforation With Femtosecond Laser Ablation

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Solution Overview

Problem

Conventional methods for forming perforations in acoustic structures, such as the inner barrel of a gas turbine engine, are complex, inefficient, and can cause damage due to mechanical drilling or high thermal conduction from laser drilling.

Innovation Solution

A method using a femtosecond laser to drill perforations in a face sheet attached to an acoustic core, emitting laser pulses at high frequencies and short durations to prevent thermal conduction and achieve precise, uniform perforations without burning the material.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If conventional laser drilling methods are used to form perforations, then the perforations can be formed without mechanical contact, but the material surrounding the perforations is melted and/or burned due to high thermal conduction from the laser beams

Engineering Contradiction:

Improveperforation formation processVSAvoidmaterial burning and melting

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The patent employs pulsed laser drilling instead of continuous laser drilling, where the laser beam is delivered in periodic pulses with controlled duration and intervals. This periodic action allows heat to dissipate between pulses, preventing thermal conduction that causes material burning and melting around the perforations.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The patent changes the parameters of laser delivery by using ultrashort pulse durations in the femtosecond range (10^-15 seconds). This extreme reduction in pulse duration, combined with high repetition rates, fundamentally alters the thermal interaction between the laser and material, enabling precise perforation without surrounding material damage.

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If mechanical drilling methods are used to form perforations, then the process can be relatively simple, but it is time consuming and imprecise

Engineering Contradiction:

Improvedrilling processVSAvoidperforation uniformity and accuracy

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The patent replaces mechanical drilling systems with a laser-based system that delivers ultrashort pulses. This substitution eliminates mechanical contact, tool wear, and positioning errors associated with mechanical drills, while achieving superior perforation precision, uniformity, and faster processing speeds.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Productivity

If conventional laser drilling is used to form perforations, then the perforations can be formed quickly, but the process is relatively energy intensive and causes material damage

Engineering Contradiction:

Improveperforation formation speedVSAvoidlaser energy consumption

Core Design Contradiction:

ProductivityVSUse of energy by moving object

Solution Approach 1:

By using pulsed laser delivery with ultrashort durations and high repetition rates, the system achieves high productivity while controlling energy consumption. The periodic pulsing allows efficient energy coupling into the material without excessive thermal conduction, forming perforations quickly without the energy waste and material damage associated with conventional continuous or long-pulse laser drilling.

Inventive Principle:

Principle #19Periodic action

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

This method provides a timely, energy-efficient, and cost-effective process for forming perforations, enhancing noise attenuation in gas turbine engines by preventing material damage and improving the accuracy and effectiveness of noise absorption.

Implementation Method 1

controlling a femtosecond laser to laser drill a plurality of perforations in the face sheet without burning portions of the face sheet or the acoustic core surrounding the perforations. The method comprises controlling the femtosecond laser to emit laser pulses on the face sheet at a frequency of over 100,000 Hz and to emit laser pulses on the face sheet at pulse durations between about 100 femtoseconds and about 10,000 femtoseconds

Methodology Applied

Scientific EffectLaser ablation: Laser Ablation

Data Source

PatentEP3578288B1Method of forming an inner barrel of an engine inlet with laser-machined acoustic perforations

Publication Date: 2022.06.08 THE BOEING CO

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AI summary

A forming system includes a femtosecond laser and a control unit that includes one or more processors operatively connected to the femtosecond laser. The femtosecond laser is configured to emit laser pulses (302) onto an inner surface (218) of a face sheet (134) of an acoustic inner barrel (120). The acoustic inner barrel (120) includes an acoustic core (128) comprising an array of hexagonal cells attached to an outer surface of the face sheet (134) that is opposite the inner surface (128). The control unit is configured to control the femtosecond laser to laser drill a plurality of perforations (150) in the face sheet (134) via emitting laser pulses (302) at pulse durations between about 100 femtoseconds and about 10,000 femtoseconds and at frequencies over 100,000 Hz such that the perforations (150) are formed without burning portions of the face sheet (134) or the acoustic core (128) surrounding the perforations (150).