PSI - Issue 13

Peter Monka et al. / Procedia Structural Integrity 13 (2018) 959–964 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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4. Results and discussions

A minimum 5 pieces of every type of tap were used within the experiments at every cutting speed. The results were statistically processed, while the data were evaluated by means of the Grubs´ tests and a statistical significance along with a quality of regression function were evaluated by Fisher-Snedecor testing criterion. (Petru et al., 2013) Achieved results of tool durability are organized in Table 2. It is clear from the table below that tool life decreases with the cutting speed increasing, what corresponds to the expectation.

Table 2. Tool durability (m) Helix angle

Cutting speed vc

ω

10

20

30

40

0°

7,1

4,555

3,385

1,875

15° 35°

7,7667 8,4933

4,9133 5,0867

3,5267

1,7667 1,6533

3,28

An example of typical signal record in time domain (in this case relating to the worn tool with helix angle ω = 35° and cutting speed 20 mmin -1 ) is presented in Fig. 5, where three time periods are identified. They are: 1 – period of threading, 2 – period of spindle stops and 3 – period of tool run out from threaded hole.

Fig. 5. Typical signal record in time domain with detailed view within the first time period

The most important and corresponding results for evaluation were obtained from the channel 1 (accelerometer number 1 attached to the tool spindle). It could be probably caused due to the fact that accelerometers 2 and 3 (channels 2 and 3) were attached to the workpiece, which wasn´t sufficiently rigidly clamped. Time data have been processed and transformed into the frequency domain by means of Fast Fourier Transformation (FFT). (Vasina, 2016); (Lapcik et al., 2016) The data obtained for both tools (new and worn), that have had the same geometry and worked at the same cutting speed, were compared each other and they are shown in Fig. 6.

Fig. 6. Data comparison in frequency domain obtained for new and worn taps