Design of Testing Period for Reliability Assessment of Numerical Control Machine Tools Considering Working Conditions

Table 3

Testing periods of NC machine tools under different covariates.

Covariates		Testing period			Change rate of MTBF interval estimation
Fc	Nh	/MTBF	/h	MTBF difference
(KN)	(n/h)
0.35	2	1.5	1627	645	-0.18
0.43	17	1.6	878	-104	-0.192
0.54	4	1.6	1338	356	-0.185
0.78	10	1.6	837	-145	-0.192
0.81	4	1.5	973	-9	-0.193
0.84	6	1.6	930	-52	-0.187
1.03	14	1.6	563	-419	-0.19
The method in [1]		1.6	982	0 (baseline)	-0.19