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Fibre-delivered Laser Cutting Optimisation

Final Report Summary - FILCO (Fibre-delivered Laser Cutting Optimisation)

Executive Summary:
The laser cutting market is currently dominated by systems that use 10 micron wavelength CO2 lasers, and the performance of these systems is the benchmark by which the new generation of 1μm wavelength fibre and disk laser systems is being measured. In recent years, high brightness high power fibre-delivered 1 micron wavelength lasers have increased their market share. The 1 micron wavelength laser cutting market now accounts for 30% of the market, compared with 10% four years ago, and 4% seven years ago. Globally, in 2010, there were approximately twenty four 1 micron laser cutting system suppliers; it is now estimated there could be more than a hundred: most new system suppliers are now emerging from Far Eastern competitors.

This surge in uptake of 1 micron laser sources for cutting applications is based on many anticipated advantages, such as higher wall plug efficiency, reduced equipment footprint and more flexible processing, with lower maintenance requirements. Furthermore, potential increases in cutting speed, combined with a 30% reduction in electricity consumption, offers significant operational savings, in terms of running costs. Nevertheless, fibre-delivered laser cutting systems are currently disadvantaged in that they produce poor cut quality on stainless steel and non-ferrous metals (i.e. aluminium, nickel, titanium, etc.), for material thicknesses greater than 3mm.

A critical component of any laser cutting system is the cutting head. The FILCO project has created a novel fibre-delivered laser beam cutting head, specific to 1 micron wavelength lasers, which has proven capable of cutting up to 12mm thickness stainless steel, with higher cutting speeds, and a cut quality at least as good as, if not better, than that available from conventional fibre-delivered beam cutting systems. This new head has also significantly increased the cutting speeds possible when compared with those of CO2 laser cutting systems. These achievements have been realised through the development of new laser beam forming optics and supersonic assist gas nozzles.

The FILCO project has met the following objectives in its delivery:
• The design of a prototype FILCO cutting head with adaptive beam forming optics and supersonic assist gas cutting jets.
• The development of optimised laser cutting parameters for stainless steel up to 12mm in thickness.
• A demonstration of the capability of the FILCO cutting head to SMEs from the laser cutting industry.

The results from optical validation of both the adaptive beam forming optics and Schlieren imaging of free stream gas jets corresponded well with the results predicted from simulations of both.

The FILCO cutting trails on 6 and 12mm thickness 304 stainless steel has managed to achieve higher maximum cutting speed compared to a 4kW conventional fibre delivered cutting system. Using the FILCO system, this could potentially lead to an increase in productivity by 8 and 15% respectively.

To find out more about the project, a website ( has been set up that contains publically disseminated information. A video about the project has also been put together, and can be accessed via YouTube

Project Context and Objectives:
Project Context
Laser sheet metal cutting systems offer a method to cut metal sheet both rapidly and precisely, and this technology is well-established within the metal fabrication industry. Since 1980 (when figures first became available), more than 50,000 units have been installed worldwide, based primarily on high-power CO2 laser sources. The annual production of laser cutting systems is in the 3,500 – 4,000 unit range, with a corresponding sales value of ~€1.6 bn.

Recent developments using high power fibre-delivered laser (from either disc or fibre laser sources emitting laser radiation at a 1µm wavelength), have started to revolutionise this market. For example, these systems now offer two to three times the productivity, in terms of cutting speed, in material less than 3mm in thickness, combined with a 30% reduction in electricity consumption, when compared with CO2 laser systems (Table 1). Whilst fibre-delivered laser cutting systems clearly offer significant operational savings in terms of running costs, they are currently disadvantaged in that they produce poor cut quality on stainless steel and non-ferrous metals (i.e. aluminium, nickel, titanium, etc.), for thicknesses greater than 3mm, as illustrated in Figure 2.

Over 60% of the worlds estimated laser cutting operations are performed on materials with thicknesses between 3 and 15mm. Thus, any organisation who wishes to cut material at appreciable thicknesses greater than 3mm, still needs to use, or purchase, a less efficient CO2 laser cutting system.

A critical component of any laser cutting system is the cutting head used. The head contains optics which focus the laser light to a high intensity spot, of high power density. This focused beam melts the material being cut, and a high pressure gas jet then fired at this melt removes the molten material from the cut kerf, to sever the material. Consequently, cut quality is a critical combination of both the interaction of the laser beam and the gas jet with the material being cut.

There are a number of key differences between fibre or disc lasers, and CO2 lasers, which contribute to the problem of thick section cutting:

• CO2 lasers produce light at 10.6μm, whereas fibre lasers produce light at 1μm.
• Fibre-delivered laser beams are generally of high quality, which do not degrade with increases in laser power. In the CO2 laser, the lasing gas tends to get hotter with an increase in laser power. This can result in changes in refractive index within the laser resonator, and subsequently affects the output beam quality.
• The combination of high laser beam quality and smaller wavelength in the fibre laser results in a much smaller focussed spot than available with the CO2 laser systems.

These differences change the way the laser energy is absorbed in the material being cut, and leads to a much thinner ‘kerf’ (cutting channel) for fibre and disc lasers. At a critical material thickness, this narrow kerf then disrupts the dynamics of the gas flow from the nozzle, this flow being essential to remove the molten material from the kerf efficiently and achieve high cut qualities. Consequently, as the thickness of the material being cut increases, this problem becomes more severe.

Conversely, in fibre and disk laser cutting of thin material the ratio between the material thickness and beam diameter is smaller. This means most of the material is exposed to laser radiation from its most intense and narrow part resulting in much higher absorption when this is coupled with a high gas pressure gradient across the material thickness, this results in a narrow kerf width with clean cut edges. This narrow kerf also explains why fibre and disk lasers are able to cut thinner material faster than CO2 lasers, as overall a lot less material is being melted in the cutting process for a given thickness.

Currently, the high beam quality and absorption offered by 1µm wavelength cutting are not being used effectively in thicker material cutting. The intrinsic advantages of higher absorption, in being able to produce a larger volume of molten material for a given cutting speed, are then offset by the fundamental challenge of ejecting that molten material from the cut kerf. It is the correct combination of these two factors which greatly influences both the maximum cutting speeds achievable and the quality of the resulting cut edges.

In order to overcome the effects of beam absorption and gas dynamics that are experienced in 1µm laser cutting, two key innovations were proposed to be combined in the development of the FILCO cutting head. The proposed innovations were:
• The development of new ‘supersonic’ cutting nozzles;
o Capable of achieving supersonic gas speeds within the kerf, to significantly improve the efficiency of material ejection, leading to higher cut quality.
• Development of a new beam forming unit;
o Capable of adjusting the beam focus to maximise and homogenise the absorption of 1 micron laser light throughout the material thickness, to ensure that material is equally melted/vaporised through the work piece thickness during cutting. Adjustments to the optical configuration being possible, the performance over a range of materials and thicknesses can be optimised.

Furthermore, the FILCO cutting head needed to be flexible enough to be retro-fitted to existing systems or included in any new laser cutting system. As part of this work, the combined developments in the FILCO head were then used to optimise cutting parameters giving the highest possible cutting speeds and most regular cut qualities over a range of material types and thicknesses up to 12mm.

Project Objectives
In order to execute the project effectively, the FILCO SME partners agreed the following technical objectives to be delivered during the technical work program (primarily by the RTD performers). These were split into scientific, technical and demonstration objectives:

Scientific Objectives:
1. Modelling of the laser cut kerf response to incident 1 micron wavelength laser light, to optimise absorption, including multiple reflections, along the cut front.
2. Modelling of gas dynamic effects of current and new designs of laser cutting nozzles, with emphasis on achieving higher shear stress, reduced flow separation and minimised dynamic instabilities in the gas stream incident on the part being cut.

Technical Objectives:
3. Using modelling and simulation, production and demonstration of new optical beam focusing designs, capable of producing a range of different laser beam focus diameters and divergences.
4. Using the results of this simulation, production of a beam forming unit, which can change the parameters of the focussed beam for different material thicknesses, hence optimising laser beam absorption.
5. Using the results of the gas flow simulations, production and testing of prototype nozzle designs to increase cut quality, in terms of reducing surface roughness and minimising adhering dross, at cutting speeds at least as high as those currently achievable using CO2 laser sources.
6. Development of an experimental implementation plan, to allow comparison of cutting results between fibre-delivered laser and CO2 laser sources.

Demonstration Objectives:
7. The integration of the beam forming unit and cutting nozzle advancements, to demonstrate cutting of 304 stainless steel in the thickness range from 3 to 15mm using nitrogen as the assist gas, giving a comparable cut quality and a doubling in cutting speed, when compared with CO2 laser cutting.

Project Results:
In order to deliver the FILCO project effectively, the project time line was separated into three phases, consisting of design/development, integration/experimentation and optimisation/demonstration, as described below.

Phase 1: Simulations pertinent to the two key project innovations, the beam forming optics and the supersonic gas-jet nozzles, were performed, to establish the two key component designs. Two main work packages were involved, each assigned to a designated innovation produced by the two RTDs in the project, and activities in these work packages were streamlined to address inter-related simulation requirements and future hardware developments.

Phase 2: The results of the two sets of simulations from Phase 1 were used to design the beam forming unit and the supersonic nozzles, respectively. Each were manufactured and initially validated as separate operational units. Once validated, these were then integrated, together with a Precitec focussing module, to form the FILCO prototype cutting head. The FILCO head was integrated with a CNC platform and subsequently used to perform a variety of cutting experiments. In addition, and for comparison purposes, access to state-of-the-art fibre laser and CO2 laser cutting systems was provided by the SME End-Users in the FILCO consortium. This access was used to generate comparative cutting result data when using conventional optics and conventional cutting nozzles. In particular, a Design of Experiments (DOE) approach was used to predict the optimum cutting parameters, from a statistical analysis output responses, in terms of measured cut edge roughness and dross adherence as a function of cutting parameters (cutting speed, laser beam power, laser beam focus position etc). The cutting performance of the FILCO system was then compared with that of the conventional fibre laser and CO2 laser systems.

Phase 3: The optimised results from the FILCO laser cutting trials were demonstrated to an invited audience from the laser cutting industry, and the comparison of those results to conventional fibre-delivered and CO2 laser cutting systems disseminated. Throughout the project duration, market information and innovations in fibre-delivered cutting technology, as well as CO2 laser cutting technology, were monitored, in particular reports of laser cut quality, and how they compared with the results from the FILCO system.

FILCO cutting head design and development
Beam forming optics design consideration
Using the CALCut software developed by Fraunhofer ILT, optimised beam focus parameters were determined for the cutting of 6mm thickness 304 stainless steel with the current state-of-the-art 1μm laser wavelength laser sources. According to the objectives of the FILCO project, the optimisation targets were to maximise the cutting speed and at the same time improve the cut quality that could be achieved. A highly detailed optimisation strategy using the CALCut sofware was based on the following criteria:

• The selection of a base parameter set, taking into account technical, economical and other market-relevant arguments, collected with the support of Q-Sys and Laser Expertise, and SMEs representative of laser cutting industry.
• A matrix of simulations of maximum cutting speed, in the parameter field [focal length x focal position], using CALCut SR-solutions, resulting in a regime of highest process efficiency.
• A matrix of simulations of gas jet penetration depth at maximum cutting speed, in the parameter field [focal length x focal position], using CALCut SR-solutions, resulting in a regime of highest cutting gas effectiveness, and a trade-off between efficiency and quality.
• The selection of a reference speed for the subsequent CALCut MR-simulations, taking into account multiple reflections in the cutting kerf.
• The evaluation of matrices of CALCut MR-simulations of gas jet penetration depths regarding:
o The value of gas jet penetration depth.
o The smoothness of cutting front geometry.
o The regularity of the absorbed power density distribution.
o The robustness of the cutting front response to incremental speed variations at the optimum cutting speed, as well as at stepwise increased speeds, in order to provide a parameter regime of highest efficiency, quality and robustness.

The compiled optimisation strategy using the CALCut simulation produced optical properties for the cutting of 6mm thickness 304 stainless steel. The CALCut predicted base optical parameters were then used by Eksma Optics to initiate Zemax optical modelling, to specify high quality theoretical and practical design specifications of the beam forming unit, providing the range of different F-numbers and laser power densities predicted to be needed to meet the objectives of the FILCO project.

Laser cutting nozzle design consideration
Using Computational Fluid Dynamics (CFD), simulations of combinations of conventional laser cutting nozzle diameters and gas pressures through simplified kerf geometries in 6 and 12mm thickness 304 stainless steel substrates were performed, covering the operating range currently used by the laser cutting job-shop industry. The results of compressible flow from each simulation were analysed and used as a benchmark, to design FILCO nozzles to suit a particular thickness of material.

Based on analysis of the results with respect to boundary layer and nitrogen gas purity for a given operating pressure, four FILCO nozzles for three operating gas pressures were designed, aiming to achieve uniform exit gas flow conditions. The results of CFD simulations of both conventional and FILCO laser cutting nozzles were compared for simplified kerf geometries in material thicknesses of 6 and 12mm, by analysing the features of compressible gas flow. In addition, simulations on real kerf geometries obtained from initial fibre laser cutting trials, and predicted CALCut geometries, were also carried out, for comparison purposes.

Beam forming optics development
The combination of the 1μm laser wavelength laser source optimised cutting parameters for 304 stainless steel predicted using the CALCut program, and the optical design specifications obtained from Zemax modelling, were used to develop a final design specification of the beam forming unit. The unit was designed to be retro-fitted with a Precitec focusing module for FILCO cutting, as well as being a stand-alone system which could be retro-fitted to other optical systems, for use in other laser based applications (e.g. welding, cladding etc) to enhance process capabilities.

Furthermore, over the course of the project, the robustness of the FILCO cutting head with respect to bandwidth or dynamic stability during operations, and compactness and ease of use, resulted in the development of new strategy for its design optimisation.

The optimisation strategy and procedure during the development of the beam forming unit took into account the following issues:
• An optimized range of F-numbers for the base parameter set and the intended application range.
• A minimized number of optical components, to reduce any set up sensitivities and costs of the optical system.
• The use of standard lens diameters, to be compatible with conventional optics, enabling an easier provision of replacements or alternatives. This would enhance the flexibility and adaptability of the beam forming unit. Further requirements in this respect included:
o A system aperture sufficient for high power laser beams.
o A sufficient lens edge thickness for appropriate mechanical robustness.
o An adequate optical imaging quality (i.e. a near-diffraction limited image, compatible with multimode laser sources).

The final specification was provided by ILT and the beam forming unit was constructed by Eksma Optics.

TWO beam forming units were manufactured, each integrated and optically validated with fibre lasers emitting 1 micron wavelength beams, with Beam Parameter Products (BPPs) of either 3 or 6mm*mrad, typical of those currently used by fibre laser cutting system integrators.

Laser cutting nozzle development
On establishment of suitable designs for the FILCO laser cutting nozzles, an inexpensive route to their manufacture was identified. Form tools for these nozzles were constructed, and a number of FILCO nozzles machined for validation.

Nozzle design validation was performed by comparing CFD simulation results with an optical gas flow visualisation (Schlieren) technique. CFD results predicted that the gas jet exit from the nozzle was slightly over-expanded: this meant that the expansion or divergent section of the FILCO nozzle designed was approximately 4% longer than theoretical prediction. However, results from Schlieren analysis revealed that the tools and the machining process used for nozzle construction actually produced better results than those predicted by CFD. This difference in the real and simulated flow expansion was further picked up when validating 3mm diameter conventional laser cutting nozzles currently used by industry.

The results of nozzle validation indicated that the conventional laser cutting nozzle had a maximum stable operating distance of 3 nozzle diameters from its exit. Conversely, the FILCO nozzle indicated that this operating distance could be extended to be as long as 10 diameters.

FILCO cutting head integration and validation
FILCO cutting head integration
Two manufactured beam forming units and the Precitec focusing module were integrated by each of the RTD partners at their respective premises. The beam forming was integrated at 90° to the optical path of the Precitec focusing module by ILT, and connected to a fibre laser with a BPP of 3mm*mrad. The second beam forming unit was integrated along (parallel to) the optical axis of the Precitec focusing module by TWI, and connected to a second fibre laser with a BPP of 6mm*mrad. Both systems had motorised focus control, with stroke lengths of 20mm.

Optical validation of FILCO cutting head
The first integrated beam forming unit by ILT was used in combination with beam profilometry to validate its optical characteristics. The results of this profilometry showed that the theoretical prediction reported using the CALCut software and the Zemax model agreed with the experimentally measured laser beam properties with a deviation of <5%.

Experimental validation by ILT of this first unit was then performed by cutting 6mm thickness 304 stainless steel, using parameters predicted as optimum from CALCut simulations. The results indicated that the experimental outcome matched the CALCut predicted optimised laser cutting parameters well, with respect to maximum cutting speed and cut edge quality.

At the same time, the optical characteristics of the second beam forming unit were validated by TWI, again using beam profilometry. The optical configuration in the second beam forming unit was then optimised experimentally, to cut 6 and 12mm thickness 304 stainless steel (see below).

FILCO cutting parameter optimisation
The fully integrated and beam focus position optimised FILCO cutting head at TWI was used in the development of optimised FILCO laser parameters, seeking the highest cutting speed and best cut quality. Using both conventional and FILCO cutting nozzles, cutting procedures for 6 and 12mm 304 stainless steel were developed, and processing windows identified experimentally, when using either 3 or 4kW of laser beam power.

The FILCO cutting trails on 6 and 12mm thickness 304 stainless steel has managed to achieve higher maximum cutting speed compared to a 4kW conventional fibre delivered cutting system. Using the FILCO system, this could potentially lead to an increase in productivity by 8 and 15% respectively.

By taking the 4kW optimised FILCO cutting parameters identified for 6mm thickness 304 stainless steel, 6mm thickness Al alloy 5252H22, 5mm thickness Ni alloy 718 and 7.8mm thickness Ti64 alloy could all be cut to high quality, demonstrating the multi-material cutting capability of the FILCO system.

FILCO demonstration and acceptance
The FILCO demonstration was hosted by TWI for attendees from the laser job-shop community, who were invited to witness the FILCO system cutting 1mm, 3mm, 6mm and 12mm thickness 304 stainless steel samples. The attendees were then able to compare the quality of these cuts (in terms of surface roughness, kerf width and dross height) with those produced by state-of-the-art CO2 and conventional fibre-delivered fibre laser cutting systems. A clear increase in the cutting speed compared with the state-of-the-art was demonstrated, as was an improvement in cut edge quality. Further demonstrations have subsequently taken place to targeted individual companies.

A further demonstration is also planned at Fraunhofer ILT in 2015. This demonstration is to be performed outside the scope of the Description of Work, and post project.

Potential Impact:
Potential Impact
As a result of participation in this FILCO project, each SME expects to increase its market share following the completion of the project, by introducing new products in to the highly competitive laser cutting market.

The main features of the FILCO system are:

Simple interfacing with the operator
The operation of the system has to be straightforward for the operator. All the development will be “transparent” to the operator, so that the underlying complexity of the system does not have to be understood. Thus, the operator can set up the cutting process very simply by selecting appropriate material and thickness information. From this, the system will automatically program the configuration of the variable optical path, and will propose parameters for the cutting process (power, speed, cutting nozzle type and diameter etc…).

Compact design that minimize the safety laser requirements of the traditional laser cells
The processing head will have a compact design. This design will meet industry’s current requests for more compact and safer design of laser cutting heads.

Provision to interface with the rest of elements of the laser cell
The system will have to interface both with the Robot/CNC positioning system and the laser source to communicate all parameters related to the cutting process (laser power, robot speed, start/stop signal, etc.).A FILCO prototype system is now available, and testing of the systems by consortium partners will continue after project completion to ensure that systems will be available commercially towards the end of year two after project completion.

Main Dissemination Activities
Project announcements
In order to raise awareness of the project, its aim and objectives, the partners constructed a concise project brief, which has already been used for dissemination purposes via e-mail, partners’ websites, social media, in project flyers etc. The agreed text was distributed by all partners through the channels outlined above. Links to selected dissemination activities via partner websites are detailed below:

Tradeshows and conference attended
An analysis of the various dissemination methods was performed by Precitec, and the consortium agreed that the most beneficial dissemination activity would be through the promotion of the FILCO project activities at tradeshows attended by the consortium partners. The tradeshows attended by the consortium, and at which the FILCO project was disseminated, include:

• ILOPE. Beijing, China. October 16-18, 2013.
• Advanced Solid State Lasers. Paris, France. October 27-31, 2013
• Laser World of Photonics India. Mumbai, India. November 12-14, 2013.
• Expolaser. Piacenza, Italy. November 14-16, 2013.
• Precision Fair. Veldhoven, The Netherlands. November 27-28, 2013.
• Photonics West. San Francisco, CA, USA. February 1-6, 2014.
• Laser World of Photonics China. Shanghai, China. March 18-20, 2014.
• ICALEO, California, USA. October 19-23, 2014.

Further Planned Dissemination
Figure 3 highlights the additional dissemination activities planned for the FILCO project, to be performed post project. These dissemination activities include:

• Attendance at further trade-show and conference attendance
• The publication of conference and peer-reviewed papers on the FILCO project, which are in preparation
• A further planned demonstration at Fraunhofer (Aachen, Germany)
• A final project announcement, of which the text is currently being agreed.

Exploitation of Results
Results of the FILCO project

Result 1 - New Nozzle Designs
Innovation in cutting nozzle design was achieved by the development of a ‘Minimum Length Nozzle’ (MLN). This nozzle design creates stable uniform supersonic jets with desirable properties beneath the nozzle exit and inside the cut kerf. The FILCO cutting trials in WP4 have shown that MLNs produce significantly better cut edge qualities (i.e. minimised dross and reduced cut edge roughness) compared with conventional laser cutting nozzles. The new nozzles have been designed to be retro-fitted to an existing Precitec focusing module, as well as other laser cutting heads on the market.

Result 2 - Beam forming unit
Innovation in this area was achieved by the design and development of an adjustable optical ‘beam forming unit’ system, to strike the correct balance between the size and shape of the laser beam, matched to the requirements of the particular material thickness being cut. The beam forming unit for the FILCO head was designed to produce a number of different F-Numbers, tailored to suit a given material thickness, offering increased cutting speeds and improved cut profiles. A unique set of optical configurations for cutting 6 and 12mm 304 stainless steel have been identified, producing these higher cutting speeds and improved cut edge qualities, when compared with conventional CO2 and fibre-delivered beam laser cutting systems.

The beam forming unit has been designed to be a stand-alone optical system capable of producing different F-Numbers, and (as in this project) capable of being retro-fitted to an existing Precitec focusing module. This universal design approach has the potential to be used in combination with other processing heads as well, for laser based applications beside cutting, e.g. welding, hardening, cladding etc.

Result 3 - FILCO Prototype Cutting Head Design
Results 1 and 2 have been combined into a 1m wavelength specific laser cutting head, flexible enough to be retro-fitted to existing cutting systems, or included in any new system being developed. Tailored gas flow inside the kerf from the MLN combine with an optimised laser beam profile for the thickness of material being cut, from the optical beam forming unit, have delivered improved cut qualities and higher processing speeds than are currently available with conventional 1m laser cutting systems (see Result 4 below).

Result 4 - Optimised Cutting Parameters
Using the integrated FILCO cutting head, new parameters developed have resulted in further improvements in cut edge qualities and cutting speed, when cutting 6 and 12mm thickness 304 stainless steel. Project results also indicate that these 304 stainless steel FILCO cutting parameters are directly transferable to the cutting of other non-ferrous alloys, such as Al alloy 5252H22, Ni alloy 718 and Ti64 alloy.

The exploitation of the project results will be made by the SMEs. Initially, each of the SME partners could be involved in the following exploitations:

• MetalMark Limited (United Kingdom) will exploit Result 1.
• Eksma Optics (Lithuania), as manufacturer and global supplier of precision optical components, will exploit Result 2.
• PRECITEC (Germany), as global supplier of laser cutting heads, will manufacture and sell the FILCO cutting head, Result 3.
• Laser Expertise Ltd. (United Kingdom), as the user, will benefit from the advantages of the new FILCO cutting capabilities, Result 4.
• Q-Sys B.V. (Netherlands), as machine builder, will benefit of the advantages of the FILCO system, by providing bespoke laser cutting systems.

List of Websites:
Project Public Website
The FILCO project website has been set up with two areas:
• Public facing area
o Home page
o Project Background
- Project overview
- Project concept and objectives
- Summary of project activities as they arise
o The profiles of the project partners involved
o Project publications, as they arise
o Project news & events of notes
o Related links
o A ‘Contact US’ link
• Private project partner area (with a login required)
o Project notice, e.g. meeting details etc.
o Project Files, e.g. reports, data etc.
o Partner contact details

This website can be accessed via (
A video about the project has been put together and can be accessed on YouTube