Laser beam

In this research, ‘Fibre-laser’ (FL) interaction refers to the point where contact is made between the textile fibre, i.e. polyester and the laser beam demonstrated in Figure 36, further discussed in Chapter 5 – Experiments and discussion of results. Figure 37 is an image of a

double page log book entry, which roughly illustrates some of the thinking and problem solving, regarding laser beam behaviour and laser scanning when processing fabric in this way.

Figure 36: Fibre-laser interaction

Figure 37: Log book: Problem solving in relation to beam behaviour and laser scanning

Figure 38 shows documented meetings notes generated from supervision minutes. This conversational exchange facilitated further understanding and knowledge acquisition regarding laser beam characteristics such as: beam delivery systems; beam interaction with textile fibres; and beam scanning, for example.

Figure 38: Documented meeting notes generated from supervision minutes: laser beam characteristics

Through this interaction between the fibre and laser, laser irradiation alters the structure of the synthetic PET textile fibre. This energy is delivered via laser the beam by continuous wavelength activity. As such, this interaction can be controlled by computer software to achieve various alterations to the fIbre at the molecular level. Resulting, essentially in a visible change to the textile surface, ranging from a cut to a mark. In this research two laser marking methods, facilitated by CAD were explored – raster and vector:

 Raster fill - a series of closely spaced parallel scanning paths via laser beam mark (etch) to surface fibres creating a filled pattern or shape on the textile in relation to the design, computer software and CAD file.

 Vector line-pattern fill – a pattern, shape or block was pre-filled with a series of repeated vector lines (or paths) with a specified distance between each line to create an all-over laser marked area on the textile.

Essentially, both approaches were investigated in attempt to identify ‘best practice’ for laser-processing textile fibres with graphics in terms of consistent flat colour/dye uptake with even/level laser energy, in relation to laser-dye treated areas of the fabric. Each method induced a physical and chemical change to the textile impacting the appearance and

performance of fibres. However, visual effects differed due to the procedures carried out.

These differences along with results are further discussed in Chapter 5.

Fundamental laser beam characteristics were observed in this study relevant to each laser machine employed. The purpose of such was to identify optimal parameters for effective exploration of the laser-dye process. These are outlined in Table 8.

Laser beam parameters

Spot size Denotes the diameter of the laser beam actually marking the fibre/fabric during fibre-laser interaction. The spot size is determined by Focal distance and influences the Resolution of the graphic marked on to the textile and is also relevant to yarn size/diameter within a textile structure.

Focal distance

Height / distance between beam output and fabric surface which determines the beam focus and optimal focus. This also influences marking Resolution based on the Spot size.

Resolution Based on ‘dots per inch’ (dpi) for marking via the laser beam. This defines the

‘sharpness’ or the ‘blurriness’ of the mark/image. A larger dpi produces a sharper graphic representation.

Scan direction Determines whether the marking of a raster image is performed with horizontal or vertical scanning. The laser beam therefore travels in a specific direction in relation to the fibre axis and orientation of the fabric structure i.e. weave or knit.

Table 8: Laser beam parameters observed relevant to this study

In a laser system, the beam has an optimum field of focus which is the optimal location or focal position for processing (Figure 39) This is where the beam/spot size is at its tiniest and therefore considered most effective in relation to the work piece. In terms of fabric and textile design, this may enable a cut or surface marking with graphics and other creative effects facilitated by CAD technology. By carrying out ‘burn prints’ in this research, detection of the optimal focus area for processing fabrics was enabled. Burn print refers to a test method that involved firing the laser beam multiple times into a material such as acrylic or light sensitive paper in order to measure the beam size and determine the shortest diameter in order to find the optimal focus (Figure 39).

Figure 39: Burn print in a circular piece of acrylic showing the layout of multiple laser spots

In doing so, an understanding of the highest/sharpest resolution (further described in Table 8) processing area was known. This knowledge was beneficial for exploring the laser-dye process in terms of patterning regarding image/surface quality. Two test approaches were used in this study - one for each Synrad laser marking machine (both paper and acrylic methods). The significance of test results related to the fibre-laser interaction between fabric and laser in terms of achieving consistency across the textile surface through even or level laser scanning. Therefore, understanding the impact of laser beam variables was necessary to this investigation to enable satisfactory or exemplary outcomes both technically and creatively. Burn print tests carried out in this research are further discussed in APPENDIX 1 of this thesis.