Movimiento de tierras

In this research, practical inquiry identified that several factors contributed to the amount of laser power/energy used to process fibres, outlined in Table 9. In stages one and two of experimental sampling – ‘Confirming previous work’ and in the early ‘Exploratory’ phase, perceptions were made about laser technology as a tool. It was assumed that by selecting the power (%) value in the computer program (for all three laser machines) in relation to the

operational power assigned to a particular machine, this would determine the exact amount of laser power output/energy density processing the fabric. However, this ‘face-value’ approach was not rigorous, nor was it reliable. Table 10 shows the values for the 60 Watt Synrad laser marker machine. ‘Selected power (%)’ obtained via computer software is shown against

‘Actual power output (W)’ gained by using a laser power meter. By acquiring this data, an informed and reliable method for processing fabric with accurate and repeatable laser energies was attained.

Laser power parameters

Operational power Energy (in Watts) assigned to a particular machine by the manufacturer.

Computer power selection

Processing power controlled by a computer software power function to specify a power percentage value e.g. 1-100% of a 10 Watt laser machine.

Actual power output

The known amount of actual energy exiting the nozzle of the machine via laser beam output, measured using a laser power meter.

Energy density The amount of energy used over a space per unit volume which is the power + dwelling time e.g. Joules per centimetre squared (J/cm²) applied to the fabric surface dependent on the mark/design/size, laser beam diameter and scanning velocity in relation to contributing factors described above.

Table 9: Laser power parameters observed in this study

Selected Power (%) Actual Power Output (W)

5 0.2

Table 10: Data for the 60W Synrad laser marker showing selected power (%) via computer software against actual power output (W) measured using a laser power meter

Further understanding of the technology regarding characteristics of the laser and the validity and/or transferability of computer software functions was gained through practical study.

Regarding laser aspects, knowledge obtained related to ‘power drop-off’ which occurs over time associated with the age of the machine, and that which occurs between the point of switching on the machine and subsequent use; and ‘inertia’ which refers to the tendency of a laser machine to change speed during processing causing varying levels of modification and so inconsistent surface effects. In terms of the computer software, factors included ‘functions’

which differed between laser systems. In some instances, specific features were attributed to a particular machine so experimental results were not a characteristic of the technology.

Instead, these results were a function of the software; ‘data input’ enabled the user to specify processing values such as power, for example. However, the accuracy of some features was unreliable, hence the need to measure actual power output with a laser power meter, independently of the laser machine(s); and ‘software versions’ such as updates which impacted aspects of this research in the initial exploratory stages of the work. As such, irreversible settings during installation altered previous software parameters.

First-hand experience revealed the importance of knowing and being able to control these issues rather than relying on ‘given’ data containing unknown anomalies. Such aspects were relevant to the creative and repeatability objectives of the project. The ability to determine and reproduce specific effects with specific fabrics whilst retaining fibre stability with subtle fibre modification levels and minimal fibre damage, was essential in establishing the laser-dye process for textile patterning and coloration. ‘Know-how’ (further discussed in Chapter 2:

Methodology) was attained by identifying optimum processing parameters through methodical experimental practice directly related to individual laser machines, fibre type, fabric construction, dyes and dyeing methods.

Experimental practice carried out in terms of laser processing power required a systematic approach to obtaining data during sampling based on multiple parameters that influenced laser energy such as machine/software features, selected power and speed/velocity.

Table 11 is an example of one type of data collection table matrix created within this study to facilitate focused structured experimentation with the CO2 10W Synrad laser marker. All laser parameters associated with the laser computer software for the machine are listed in the first column – 1, (rows a-s). Columns 2-6 identify five experimental samples studied, numbered 1-5, in relation to the laser parameters in the first column. The next 5 columns (7-11) state the different numerical values of an ‘individual parameter observed’ for each of the five samples, which was either selected power or speed (velocity).

Table 11: Data collection table matrix for the 10W Synrad laser marker showing laser and experimental parameters investigated

Figure 40 visualises one configuration of multiple velocity parameters (mm/sec) explored in relation to a ‘laser-fibre’ treated woven polyester textile sample, using the 10W Synrad laser marker. A constant power value of 35% was selected via computer software to process all 10 test squares with variable speed parameters of 550.00 mm/sec – 1000.00 mm/sec (increasing by 50.00 per square). The resulting laser modified fabric indicates some form of treatment has taken place due to tension differences across the fabric. However, incremental subtleties between each parameter generated little distinction overall, prior to the dyeing stage. The benefit of this result was the ability to understand that the fabric was not processed with too much power due to the lack of obvious fibre deterioration or significant visual damage to the

Column 1 Columns 2-6 Columns 7-11

All parameters 5 Samples Individual parameter observed

Sample No. 1

Structured Experimentation Power and speed variables Sample No. 2

textile structure. The effect of these variables led to a range of dye uptake levels as a result of differential energy across the fabric, influenced by different processing speeds.

Figure 40: Configuration of laser parameters explored using the CO2 10W Synrad laser marker (left);

and the resulting woven polyester woven fabric sample (right)