## 3 Results and Discussion
### Prediction of WKL, WHAZL versus AR, P  
In this chapter we will deal with prediction of WKL and WHAZL vs. AR, \(P\) at non-measured input parameters which give information about quality of Picea abies cut on lower board. The results we will present as graph of output property vs. AR, \(P\) in categories of laser power at cutting speed 1.2\(\cdot\)10\({}^{-2}\) m\(\cdot\)s\({}^{-1}\).  
In the Figure 3a,b we are showing dependence of WKL and WHAZL vs. AR and \(P\) for a cutting speed of 1.2\(\cdot\)10\({}^{-2}\) m\(\cdot\)s\({}^{-1}\) in this order.  
From Figure 3a,b we can see that AR has an effect on WKL only for a laser power pf 200 W and does not have an effect on WHAZL. WKL however changes on average from 0.6 mm to 0.53 mm which corresponds to 11.7% decrease. During cutting of wood HAZ increases with depth of cut and this is mainly because of local heat sources above the lower board which lead to heat transfer from the \"higher\" parts of the wood to the lower surface. This also leads to enlargement of the width of HAZ together with fact that at a lower board, the heat transfer to the heat affected zone is more significant thus the heat generated in the cutting kerf region is transferred to the heat affected zone. This fact also is in good agreement with Figures 2b and 3b from which it is good to see that the width of heat affected zone at the lower board 0.29 mm is statistically significantly higher than for the upper board of 0.21 mm which correspond to a 39% increase. However, a decrease of WKL vs. AR is on the bounds of measurement error.  
On the other side, similar to the cutting kerf width at the upper board WKU, WKL increases with laser power only for laser powers lower than 300 W at which the cutting kerf width at the lower board reaches stabilization. This describes why the values of WKL have statistically equal values for all laser powers between 300 and 500 W. These results have been recorded in many scientific journal papers such as those by [PERSON] (5), [PERSON] (15), [PERSON] (10), [PERSON] (11) and [PERSON] (7).  
From Figure 3b, it is good to see that P and AR do not have a significant effect on WHAZL. The reason for this lies in the fact that \(P\) and AR are not the main reasons for the width of heat affected zone increasing, which is caused by heat transfer from the upper parts of the wood to the lower parts of wood.  
Comparison of P and AR Effect on Cutting Kerf Width and Width of the Heat Affected Zone for the Upper Board and Lower Board  
From Figures 2 and 3, we can conclude:  
* For all values of \(P\), AR value of WKU is statistically significantly higher than for WKL which is caused by the fact that at lower board heat transfer, it plays a more significant role in the kerf region.  
For all values of \(P\), AR value of WHAZU is statistically significantly lower than for WHAZL which is caused by the fact that at lower board heat transfer, it plays a more significant role in the heat affected zone region.
* The smallest difference between the values of WKU and WKL is at a minimal power of 200 W.
* AR and \(P\) do not play a significant role in both WHAZU and WHAZL.
* WHAZU is significantly lower than WHAZL because of heat transfer from the upper board to the lower board in the HAZ region.