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In the present study, a new automatic laser-processing strategy allowing standardized irradiation of natural tooth areas was investigated. The objective was to find a combination of laser parameters that could cause over a 600°C temperature increase at the enamel surface while not damaging enamel, avoiding temperature change above 5.5°C in the pulp and increasing enamel erosion resistance. Seventy-seven bovine enamel samples were randomly divided into 6 laser groups and 1 negative control (C/no treatment/ n = 11). A scanning strategy (7 × 3 mm) was used for the CO laser treatment (λ = 10.6 µm, 0.1-18 J/cm) with different pulse durations-namely, 20 µs (G20), 30 µs (G30), 55 µs (G55), and 490 µs (G490), as well as 2 modified pulse distances (G33d, G40d). Measurements of temperature change were performed at the surface (thermal camera/50 Hz), at the underside (thermocouples), and at the pulp chamber using a thermobath and human molars ( n = 10). In addition, histology and X-ray diffraction (XRD/ n = 10) were performed. Erosion was tested using an erosive cycling over 6 d, including immersion in citric acid (2 min/0.05 M/pH = 2.3) 6 times daily. Surface loss was measured using a profilometer and statistical analysis with a 2-way repeated-measures analysis of variance (α = 0.05). Only G20 fulfilled the temperature requirements at the surface (619 ± 21.8°C), at the underside (5.3 ± 1.4°C), and at the pulp (2.0 ± 1.0°C), and it caused no mineral phase change and significant reduction of enamel surface loss (-13.2 ± 4.0 µm) compared to C (-37.0 ± 10.1 µm, P < 0.05). A laser-scanning strategy (20 µs/2 kHz/1.25 J/cm, 3.4 mm/s) has been established that fulfilled the criteria for biological safety and significantly increased enamel erosion resistance (64%) in vitro.

Today, manufacturers in the automotive industry have to find a compromise between ensuring maximum safety for passengers, which is achieved by the use of high stiffness materials, and a minimum CO2 footprint. These aims are achieved primarily by the usage of lightweight designs. With respect to the car body, high-strength steels—such as the manganese boron steel MBW® 1500 (22MnB5)—fulfil these requirements. Workpieces made of 22MnB5 have a high tensile strength of about 1500 MPa, respectively, enabling reduction of the sheet thickness. However, this high strength is not favorable in all sections of a part, especially those which are relevant for safety. In order to locally adjust the mechanical properties of MBW 1500, a laser-based heat treatment process has been developed to meet the requirements of high ductility in the deformation zones for better crash performance and in joining areas. By means of laser radiation, the brittle martensitic microstructure of MBW 1500 is either tempered or transformed into a ferrite/perlite-dominated microstructure. While the feasibility of the laser softening of high-strength steels with diode laser systems using a tophat intensity profile at a maximum feed rate of 1.0 m/min has already been shown, the present work focuses on the increase in the feed rate of laser softening using an adapted intensity distribution. This distribution is generated using a free-form optics and is designed in such a way that a homogeneous temperature profile on the workpiece's surface is induced. As a result, the feed rate can be increased maintaining homogeneous softening across the sheet thickness.

The additive production of sensors on massive mechanical components for structural health monitoring (e.g., temperature, strain, and body-sound) using printing and laser technology shows great potential since the sensor structures are applied directly onto the component's surface without using adhesives or leads. The required multilayer stack of different materials can be added consecutively to build up the sensor layer by layer. Digital additive production techniques like printing and laser-induced heat treatment processes enable the manufacturing of highly individualized sensor structures down to batch size one. In this work, the principle of laser treatment of printed layers for temperature and strain sensors (Fig. 1) is introduced and first results are discussed. For the manufacturing process of insulator (glass) and conductor/resistor (silver-based) layers, microparticulate materials are deposited onto steel substrates and laser sintered. For better chemical and mechanical adhesion, the substrate surfaces are also pretreated (oxidized and roughened) using laser radiation. Combining the additive, digital and inline-capable printing, and laser sintering methods, functional layers for sensor applications on massive steel components can be realized