Laser Welding of Micro-VLE-Measurement Device and its Practical Application

By: Marika Hirvimäki, Heidi Piili, Arttu Jussila, Tuomas Purtonen, Matti Manninen, Petri
Uusi-Kyyny, Aarne Sundberg, Ville Alopaeus, Antti Salminen

Lappeenranta University of Technology, Finland
Aalto University, Department of Biotechnology and Chemical Technology, Finland
Machine Technology Centre Turku Ltd, Finland

The knowledge of phase equilibrium is critical for the modeling and operation of reactors and separation units. Vapor-liquid equilibrium (VLE) is defined as a state in which the component flux between the phases is equal in both directions. In the VLE-measurement the temperature, pressure and composition of both phases are determined for a range of concentrations. Typical volume of chemicals used in a VLE- measurement is 100 cm3 or above. When studying components that are either very expensive or hazardous the amount of chemicals used is preferably minimized. The other advantages of micro-VLE devices are e.g. small equipment size, surface area-to-volume ratio increases, which allows the unit to reach the temperature of the water faster and reduction of inside dimensions reduces the time required to reach equilibrium. In this study the volume of the measurement cell of micro-VLE was approximately 2.5 cm3.

The laser micro/fine processing is one of the fastest spreading and developing areas of all laser processes in the world. The welding of micro/milli scale devices would not have been possible with conventional methods because components of devices cannot tolerate high heat input, especially if there are heat sensitive elements in presence. Also the dimensions of parts and welds are very small.

Aim and purpose of this study was to utilize the potential of laser welding in manufacturing of micro-VLE-equipment (welding of two valves and sensor) and do a practical application with this equipment. The design of micro-VLE-device is shown in Figure 1. The laser equipment used in this study was a 5 kW IPG YLR-5000 S fiber laser with a standard Precitec welding head. The used material was SS316L because it´s corrosive resistance and weldability.

The optimal welding parameters were clarified with preliminary tests where the test pieces for valves and sensor were used. These test showed that it is possible to get the welds for valves and sensor with a good quality. With the right parameters there was no microcracs, welds were narrow (under 0.8 mm) and following the shape of air gap.

The practical tests showed that the measured vapor pressures of 2-methylpropane and n-butane agreed well with the pressures calculated from the literature correlations. This confirms that laser machining can be a valuable tool for manufacturing chemical micro/milli scale devices.