Ytterbium fibre laser cutting of wood

Abstract

This Ph.D. project provides for the first time the basic characteristics of fibre laser interaction with pine wood in dry and wet state. Wood cutting using the CO2 laser has been well documented. Fibre laser has gained importance in the laser material processing market as it presents an advanced technology. It is compact, reliable and more efficient than CO2 and Nd:YAG lasers. The high quality laser beam generated is currently in the kilowatt power level suitable for cutting operations. Furthermore, this laser system needs low maintenance and it has very long working life. It also presents the flexibility of fibre delivery, up to 200 meters from the laser source. Wood is broadly employed in construction, packing, furniture, flooring and panelling industries. It is a natural and renewable material which is readily available and with plenty of variety. Wood is also an anisotropic and hydroscopic material, i.e. it has different properties in relation to the direction of use and it is prone to absorb moisture from the surrounding environment. Cutting wood with lasers provides certain advantages over cutting with conventional methods. Lasers are particularly useful in high precision cutting and when it is necessary to cut thin pieces with complicated patterns (curved sections and end cuts). Additional advantages of lasers include the absence of mechanical stress in the work piece, low noise emission, narrow kerf widths, reduced amount of sawdust, and smooth surfaces The high variability of the material and the multifactor characteristic of the Ytterbium fibre laser cutting of wood required the use of designed experiments to analyse the process. The responses investigated included those related to the yield (i.e. kerf depth, mass loss and energy consumption) and the quality of the process (i.e. kerf width, heat affected zone - HAZ, roughness and perpendicularity). A literature review was carried out to identify the state of the art in laser cutting of wood. Three major experiments were performed in this project. The first multifactor experiment deals with laser cutting of dry pine wood with multiple passes of the laser beam. The second experiment studied the laser cutting of wet and dry pine wood. Here, an energy balance model was employed to analyse the effect of moisture content in the fibre laser cutting process. The third experiment assessed the effect of single and dual assisting gas jet(s) in the fibre laser cutting of wood. In each experiment, the main process parameters and their interactions affecting the process were discussed. Furthermore, the application of a desirability equation provided the optimal combination of the parameters involved (within the experimental window tested) to maximise the yield and the quality of the laser cutting operation. The effect of the assistant gas jet(s) was further analysed with a computational fluid dynamic (CFD) model; this clarified gas function in ejecting fumes and combusted materials in the process. An application study of Ytterbium fibre laser cutting of hardwood branches was performed for the first time; the results obtained were compared with CO2 laser cutting results reported in the literature. The trends observed in the results followed those predicted with an energy balance model; which was complemented with information obtained by the CFD model. The conclusions reached in this project and recommendations for future work are given.

Date of Award	3 Jan 2011
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Lin Li (Supervisor)