DEvelopment of advanced LASer based technologies for the manufacturing of TItanium HLFC structures

Project Information

DELASTI

Grant agreement ID: 687088

DOI

10.3030/687088

Project closed

EC signature date 3 December 2015

Start date 1 January 2016

End date 31 August 2018

Funded under

• SOCIETAL CHALLENGES - Smart, Green And Integrated Transport

Total cost

€ 448 843,75

EU contribution

€ 448 843,75

Coordinated by

LORTEK S COOP
Spain

Periodic Reporting for period 2 - DELASTI (DEvelopment of advanced LASer based technologies for the manufacturing of TItanium HLFC structures)

Reporting period: 2017-07-01 to 2018-08-31

Summary of the context and overall objectives of the project

World air traffic volume is expected to grow per two in the next 15 years and that is the reason why the reduction of air transport contribution to air pollution emissions and climate change is nowadays one of the most challenging objectives for aircraft manufacturers. Hybrid Laminar Flow Control (HLFC) on wings and fins is key to enhance the efficiency of the aircraft and to achieve up to 10% of fuel saving in commercial passenger aircrafts.
DELASTI project aims at developing manufacturing processes and system technology for reproducible laser beam welding (LBW) and laser straightening (LS) of titanium structures for HLFC Technology. A technology demonstrator based on the VTP (vertical tail plane) of Airbus A-350 has been manufactured and the manufacturing technology has been demonstrated up to TRL 6 (industrial relevant environment). Targeted HLFC structures are long (up to 4.5 m) and thin (0.8 mm thickness) components which are based on T-joints between microperforated Ti Gr.2 skin and Ti Gr.5 stringers. LBW leads to distortions and the so-called “Zeppelin effect”. The goal is to reverse and remove these distortions by applying subsequent LS process on the reverse of the samples.
Main technology challenges of the project imply the integrated fabrication on a single assembly system of large welded panels with stringent dimensional tolerances, and full process supervision, relying on vey local heating techniques involving last generation laser sources.
DELASTI project pursuits the following specific objectives:
Development of LBW and LS processes to obtain structures with high quality joints and aerodynamic flatness, in buckling prone large-scale thin structures
Attain the desired quality and reproducibility of Ti LBW joints, by the integration of seam tracking and development of on line process surveillance system including seam penetration control and temperature measurement
Accurate and fast prediction of distortion and residual stress by means of FE based numerical models for the whole process chain involving the welding and straightening processes
Optimize and find useful parametric distortion related correlations for LBW and LS process parameters, based on experimental and validated FE numerical models (which use of efficient local and global modeling techniques)
Development of a new closed loop LS concept based on the physical model equations, and the online feedback from the measured real time angular distortion
To mature and demonstrate the fabrication of lightweight promising flow control technologies in a fully integrated large scale demonstrator up to TRL 6

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

In terms of technical progress, the following main achievements must be highlighted:
System for LBW and LS of HLFC structures has been designed
LBW seam penetration (on-line monitoring) and seam tracking system have been developed
Control system for real time angular distortion measurement and simultaneous straightening of welded aeronautic structures has been developed
LBW and LS process development has been completed (process window and shielding conditions). This was done both for microperforated and non-microperforated skin sample
Metallographic and mechanical characterisation of base materials and welded samples has been performed. Both static and fatigue tests have been carried out at specimen and coupon level
Local FE models for the prediction of temperature field and angular distortion induced by LBW and LS in T-joined structures have been developed. These models were correlated with experimental observations and a good matching with experimental conditions in terms of melt pool size, temperature evolution and angular distortion was obtained
Global FE models were generated to simulate distortion and straightening of large structures composed by several stringers. These global models were based on the so-called inherent strain method. These models were not able to predict non-constant angular distortion in large welded structures whose origin was related to buckling
Optimum LS strategy to reduce as-welded distortion of welded demo panels has been defined
Practical conclusions on the effect of number of stringers, span distance and microperforation of the skin and stringer shape were drawn. These conclusions are useful for future design criteria of HLFC aircraft structures
Four large scale double-curvature structures as shown have been manufactured and subjected to quality control
Dissemination and exploitation rules were included in the final Plan for Dissemination and Exploitation of Results (PDER) which outlines a global Dissemination and Exploitation strategy. 9 exploitable results were identified and described. 4 public dissemination events and 2 scientific publications have been completed during project execution time.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Scope of DELASTI represented a new flanged approach. The progress beyond the state of the art and singularities are resumed herein:
A FE modelling framework has been established integrating LBW and LS simulation based on a local (detailed FEM modelling ) and global (inherent deformation based) integrated approach so that the distortion can be predicted and assessed in a rapid way (minutes)
Joint quality control: The robustness and quality of thin sheet T-joint has been assured by a validated seam penetration system based on a vision system which analyses root geometry
LS of titanium: process development has been carried out and relevant process parameters and strategy have been linked to induced straightened angles. Analysis of relevant parameters has been done through a combination of experimental and FEM modelling
Mechanical performance: static and fatigue strength has been assessed and linked to weld quality
Fully integrated manufacturing system: Full integration has been demonstrated for the whole production chain, relying on the use of a single laser source (disk laser)
DELASTI project aimed at validating a new enabling manufacturing route for large scale perforated thin sheet structures, while achieving the required in service performance and aerodynamics through combined laser welding and straightening. The final aim in the roadmap is to produce innovative wing and tail HLFC structures with reduced aerodynamic drag.
Concerning expected impact, DELASTI focused on large scale demonstration of technologies integrated at aircraft level in Large Passenger Aircraft (LPA) IADP. Within this Demonstration Platform, DELASTI is linked to WP 1.4 focused on the application of Hybrid Laminar Flow Technology (HLFC) for drag reduction on commercial transport aircraft. HLFC area in particular expects to reach the development and manufacturing of an improved HLFC demonstrator for long-term in-service operational use. In parallel to that, the definition of rules and processes required for certification for in-service long term demonstration and deployment of the HLFC technology at major components of the airframe have been discussed.
DELASTI project was based on the specific issue of the manufacturing of leading edge segments with micro perforated outer skins out of titanium, to solve the challenge of reproducibility and consistency of laser-welding process with stringent surface quality requirements.
DELASTI project entails industrial, financial, technical and environmental impacts. Main short-term beneficiaries of these impacts will be European aeronautical industry, laser market, TM, partners (HZG and LORTEK) and the global society.

LBW of double curvature HLFC structures

Scheme of LBW and LS of T-joint based HLFC structures

Metrology analysis of SIDE PANEL 4.

Transverse weld cross section of welded T-joints with microperforated skin

Photos and 3D distortion plots of PANEL DEMO 11 in as-welded and LS

LBW process windown. "a" is the incidence position and "P" laser power

Transverse weld cross section of welded T-joints.

Comparison of a welded and straightened demonstrator

L100 transient thermo-mechanical FE model. Von Misses stresses

Photos of the SIDE PANEL 2 (non-microperforated Ti skin) and 4 (microperforated Ti skin).