Occupational Safety Safety in Laser Beam Melting: Hazards & Recommendations for Action
The increasing use of innovative additive manufacturing technologies and materials in industrial production is leading to an increase in the importance of occupational safety. Only a holistic view can ensure that laser beam melting processes can be carried out as safely as possible.
Every additive manufacturing process requires attention to the inherent material and process-specific hazards. The starting materials for laser beam melting (LBM) are metal powders which, due to their particle size distribution, are classified as inhalable and lung or alveolar (E fraction or A fraction). This applies in particular to metal powders with a particle size below the usual particle size distribution between 15 µm and 60 µm. These metal powders are subject to specific limits of maximum acceptance and dust concentration. In addition, common low-density metal powders such as titanium, aluminum and their alloys are reactive.
Other metal powders, such as steels or other nickel-containing alloys, are classified as carcinogenic, mutagenic and toxic for reproduction (CMR).
In the manufacturing process of laser beam melting, hazards occur not only in the layer-by-layer construction of components, but also in the upstream and downstream processes. A typical LBM process chain has material-specific hazards: highly flammable, carcinogenic and hazardous to the aquatic environment. The specific risk of these hazards must be individually assessed according to the equipment and materials used and the process infrastructure.
On the basis of the hazards along the process chain and during cleaning work, VDI 3405 6.1 makes recommendations for a user-friendly process design. Furthermore, design approaches for cleaning, servicing, conversion and maintenance are recommended.
Holistic Assessment of Hazards Along the LBM Process Chain
Based on a holistic evaluation of the LBM process chain, plant- and material-specific concepts for powder handling were developed and evaluated by the University of Bayreuth. The focus is on the safe handling of the reactive material Ti6AlV4. The order of priority of the protective measures to minimize the hazards is determined by the STOP-Principle: Substitution, Technical, Organizational, Personal protective measures. The implementation strategy is based on the key areas of process, location and employee protection.
Thus, the exposure space of the material and hazards can be limited by spatial separation or encapsulation of the LBM plant and its periphery. The risk of dust explosions is minimized by installing a ventilation system with an individually determined air exchange rate and by carrying out all process steps under equipotential bonding. Furthermore, handling of metal powder must be carried out with the greatest care and with low dust levels and - if possible - in a protective gas atmosphere. As part of fire and explosion protection, the laboratory was equipped with automatic temperature-sensitive sensors. In addition, a gas sensor system was installed to detect escaping protective gas and other process gases. If the residual risk is rising, appropriate personal protective equipment (PPE) must be worn.
Occupational Safety Must Keep Pace with Technological Innovation
The VDI guideline 3405 6.1 describes the hazards of the LBM process chain and offers recommendations for handling them. These recommendations must be adapted to the existing infrastructural, production-technical and structural framework conditions. For this reason, the University of Bayreuth, in cooperation with the Fraunhofer IPA, is striving to apply the guideline to other technological and structural challenges and to establish their findings as an industrial standard. By designing the workplaces and processes in accordance with the 5S methodology of lean management, safety, cleanliness and order are to be further improved. In order to ensure a safe process design, in particular for sporadic processes such as the replacement of recirculation filters, these processes are to be standardized by so-called work sequence cards. Furthermore, these processes are to be recorded by video technology and made accessible via smart devices.
The protective measures should be regularly reviewed to determine their relevance and feasibility. In this way, the standard of occupational safety can always keep pace with the technological innovation of additive manufacturing.
User Safety during Operation of AM Plants: Laser Beam Melting of Metal Powders
Because of the variety of hazards and the lack of long-term studies examining the exposure to the human body, users of laser beam melting equipment are often unsure about the relevance and applicability of existing regulations and guidelines. “The FA 105.6 Additive Manufacturing Technical Committee - Safety in the Operation of Additive Manufacturing Equipment” deals with a uniform procedure to ensure the safe operation of additive manufacturing plants. Experts from manufacturers of additive manufacturing plants, industrial users of this technology and representatives of service providers, universities and research institutes will discuss the hazards involved in the operation of additive manufacturing plants and derive practical recommendations from them. In cooperation with the University of Bayreuth, VDI 3405 Sheet 6.1 “Additive manufacturing processes; user safety in the operation of production facilities; laser beam melting of metal powders” was developed and will be published at the end of 2019. Guideline VDI 3405 6.2 “Additive manufacturing processes; user safety during operation of additive manufacturing plants; laser-sintering of plastics” will be published as a draft at the end of 2019.
This article was first published by Mission Additive.
Original by Joscha Riemann / Translation by Alexander Stark