Number

441-EN

Section

General Section

Use

Abstract

Chromic acid was added to the REACH authorisation list in 2013 and its use requires authorisation in the EU since 2017. Extreme high-speed laser material deposition (German: EHLA) can provide a technical alternative to hard chromium plating, which is particularly suitable for rotationally symmetrical components. The process offers an alternative for applications where increased requirements are made, e.g. on the adhesion of the coating as well as the prevention of corrosion of the coated surface and protection against wear of the treated metal.

Substituted substances

Reliability of information

Evidence of implementation: there is evidence that the solution was implemented and in use at time of publication

Reason substitution

CMR
skin/respiratory sensitizing
other toxic effects
ecotoxicity
physical hazards

Hazard Assessment

a) Human health:
The process uses no chemicals or solvents other than the applied metal alloys. Many harmful and toxic substances to human health used in electroplating with chromium such as chromic acid, boric acid or per- and polyfluorinated surfactants can be substituted with the process. However, the resulting welding fumes, which contain inhalable dusts and toxic substances, must be taken into account. The composition of the welding fume corresponds approximately to the chemical com-ponents of the filler material. For nickel-based alloys, which contain more than ten percent cobalt at the same time - depending on their respective content in the weld-ing fume - nickel oxide or cobalt oxide are considered to be the leading component in welding fumes. With chromium-containing alloys, the formation of Cr (VI) com-pounds can not be excluded [Arbeitsschutz Schweißen 2019] . It is therefore state of the art to suck off the welding fume produced close to the process or close to the release point of the emission. Compared to other deposition welding processes, EHLA produces significantly less welding fumes based on optical assessment and compared to laser welding processes for cutting or joining, significantly lower beam intensities are used. Arbeitsschutz Schweißen 2019: https://arbeitsschutz-schweissen.de/laserschweissen-automatisiert-aber-trotzdem-gefaehrlich-fuer-mitarbeiter

b) Environment:
The process uses no chemicals or solvents other than the applied metal alloys. Many environmentally harmful or toxic substances used in electroplating with chromium such as chromic acid, or per- and polyfluorinated surfactants can be substituted with the process. Arbeitsschutz Schweißen 2019: https://arbeitsschutz-schweissen.de/laserschweissen-automatisiert-aber-trotzdem-gefaehrlich-fuer-mitarbeiter

Description of Substitution

a) Description of procedure or technology (including pre-/post-processing):
EHLA is a variant of laser material deposition (LMD) which uses powdered filler materials with a particle size of approx. 20 to 50 µm. The EHLA process makes it possible to apply metallurgically bonded (very strong bonding) and dense coatings of a broad variety of materials (e.g. corrosion or wear resistant Fe-, Ni- or Co-based alloys) with high productivity and a layer thickness of 50 µm to 350 µm onto rotationally symmetric parts. In addition, EHLA allows building up dense volumes by the application of consecutive layers. EHLA is characterized by elevated welding speed of 20 to more than 200 m/min, which is by a factor of 10 to 100 faster compared to conventional LMD. In addition, the energy of the laser beam is coupled primarily into the powder on its way to the substrate. Most important is a fine powder focus and a longer interaction time on the particles’ trajectories through the laser beam. Therefore, heat input into the substrate can be reduced resulting into layers with a small dilution zone, as well as a small heat affected zone (HAZ) between layer and substrate and consequently low distortion of the part. Due to the high welding speeds, coating rates of 0.5 to 3 m² are realized and metallurgically bonded dense coatings, can be manufactured in an economical way. The process can be used locally and it works continuously. The broad variety of materials that can be processed using EHLA allows the creation of volumes or coatings of graded materials. Thus, graded chemical or mechanical properties can be achieved by applying consecutive layers with filler materials of varying chemical composition and by adaption of process parameters. Layers that are manufactured using an EHLA process exhibit a surface roughness that is typically in the range of Rz = 10 -20 µm. Depending on the required surface quality of the coating, the part has to be post-processed, e.g. by grinding. The high welding speeds of the EHLA process are often realized by rotation of the part. The EHLA process is thus especially suitable for rotationally symmetrical components. The size and weight of the component is limited by the machine or handling system (e.g. crane). Due to technological differences (e.g. surface quality of the manufactured layer), EHLA cannot be re-garded as a one-to-one replacement for Cr(VI)-based coating technologies. However, EHLA presents an alternative for applications where elevated specifications regarding bonding strength of the coating or protection against wear and corrosion are required.

b) Way of application: e.g. spraying, dipping, open/closed system etc:
The filler material is applied in form of powder with a particle size of approximately 20 to 50 μm and, ideally, spherical morphology. The powder is melted by laser radiation on the way from the powder nozzle to the substrate, before it is deposited on the substrate where a metallurgical bonding is created. The process requires a local shielding gas atmosphere, which is typically assured by injecting Argon through the nozzle. Dust and fume extraction are advisable in the proximity of the process.

c) Risk management measures (technical, organizational and personal):
Radiation protection (laser) and dust generation during powder handling and surface finishing (grinding) are the main issues regarding occupational safety and health. In order to avoid exposure of workers to laser radiation, protective housing with inspection windows is required. Alternatively, specific goggles need to be worn during the process. Furthermore, welding specialists operating the systems and involved with powder handling also need to wear respiratory protective masks, workwear and gloves. Access to the site should be restricted to eligible personnel. Dust, residual powder and vapor have to be extracted from the system. After welding, any residual powder is removed from the component. During this procedure, personal protective measures have to be applied as well. Aerosol measurements show higher particle concentrations during post-processing by grinding than during the coating process. The system works CNC-controlled. The process is visually monitored by inspection windows or cameras. Several automated monitoring systems are currently being developed and tested.

Advantage or Disadvantage of Alternative

Aspect	Advantage/disadvantage to conventional process
Technical requirements	With the ability to process filler materials providing a wide range of properties, specifications of the coating can be precisely adjusted for a given application. Depending on the chemical composition of the filler material, the corrosion and wear resistance of the coating can be superior to Cr(VI)-coatings, which is required for example in off-shore applica-tions. Increased wear resistance of the coating can be achieved by incorporating ceramic particles into the metal matrix. EHLA can also be used for the repair of damaged components. Additional preparation of the part exceeding cleaning is not necessary. The high welding speeds of 20 to more than 200 m/min are often realized through rotation of the part. The EHLA process is thus especially suitable for rotationally symmetrical components. The size and weight of the component is only limited by the machine or handling system (e.g. crane). It is part of current research activities to adapt the EHLA process and system technology for planar, non-rotationally symmetric surfaces (EHLA 3D). Since the laser power can be controlled precisely, fine ad-justments to the resulting heat affected zone and layer properties are possible. The handling system usually runs stable because no external forces act on the component.
Implementation	The system can be divided into two subsystems: •    Optical and laser components •    Peripherals (powder feeding system, handling system, housing, local shielding gas atmosphere, etc.). The costs for the laser beam source and optical components range from 100.000 to 200.000 €. The peripherals consisting of the powder feeding system, the handling system as well as other peripherals for shielding and protection vary be-tween 300.000 and 1.000.000 €. There are several providers of turnkey solutions for EHLA systems. Other companies act as integrators for various components and offer individual compilations. Investment costs are comparable to those of thermal spraying processes. Since integration of EHLA processes into existing productions lines is easy, the effort for logistics is reduced and independence from coating service providers can be ensured.
Operational expenses	Energetically, the process is highly efficient. The energy yield for laser radiation is about 30 to 50 %. Electricity costs are estimated to be low compared to electroplating (energy saving approx. 80 % to 90 %). The powder yield can reach up to 90 %, depending on the materials and process parameters used. The powder nozzle of the powder feeding system is subject to wear and must be replaced within certain intervals. Powder quality may vary depending on the manufacturer. System lifespan depends on the application. Maintenance of the laser is required yearly, assuring high availability. Cool-ing filters and desiccants are to be exchanged. Costs of protective measures result from personal protective equipment, exhaust devices and wet scrubbers.

Case/substitution evaluation

The case story shows a technical alternative to hard chrome plating for certain applications and does not represent a general replacement. The feasibility and applicability of this alternative technology must be examined in each individual case.

State of implementation

In use

Enterprise using the alternative

TRUMPF Laser- und Systemtechnik GmbH Industrie Mmt Oberfläche+Makro TLD Johann-Maus-Straße 2, 71254 Ditzingen https://www.trumpf.com">https://www.trumpf.com">https://www.trumpf.com

Availability of Alternative

The EHLA process has been developed by Fraunhofer ILT in Aachen and has been in industrial use since 2017. Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e. V. (FHG) and RWTH Aachen University hold a patent for the EHLA process in Germany. The EHLA process is used by companies on a license basis. Fraunhofer ILT runs cooperation projects with companies to implement EHLA for industrial processes, after implemented EHLA already several times in the industry for different applications. Further information on the EHLA process is available on the internet.

Contact

Fraunhofer-Institut für Lasertechnik ILT Laser Material Deposition Steinbachstr. 15, 52074 Aachen, Germany

More information can be found here: https://www.ilt.fraunhofer.de/en/technology-focus/additive-manufacturing/laser-material-deposition.html

TRUMPF Laser- und Systemtechnik GmbH Industry Mmt Surface+Macro TLD Johann-Maus-Straße 2, 71254 Ditzingen, https://www.trumpf.com

Further information

TRUMPF GmbH + Co. KG is a manufacturer of lasers and turnkey systems for EH-LA. The company runs an application center for the EHLA process. The EHLA process has been applied commercially for hydraulic cylinders in the off-shore sector (for example for dredging vessels) by the company IHC Vremac Cylinders B.V. since 2017. These types of hydraulic cylinders are conventionally coated by thermal spraying either with ceramic layers or Ni/Cr layer systems, as the corro-sion protection of hard chrome plating is often not sufficient. In addition, due to the trend towards ever longer and thinner designs, hydraulic cylinders are subject to increased mechanical deformations. The resulting demands on the adhesive strength of the coatings are met by the EHLA process. Further applications are under constant development as part of R&D work in the ar-ea of general engineering, for rollers in the paper and steel industry, in the oil and gas sector, in the aerospace sector, and in the automotive sector (e.g. brake discs of passenger cars).

The factsheet describing the case study is available as a pdf download: to factsheet 441-EN

Publication source: author, company, institute, year

company

Date, reviewed

September 2, 2022