## 4 Conclusions  
Modern analytic methods allow for calculating different values of the friction coefficient in different regions of contact surfaces between the die and the blank--under the blankholder and on the drawing edge. These can be used in FEM modelling of stamping processes. In the paper strip drawing test was performed for uncoated extra deep drawing quality steel DC 05 and austenitic stainless steel AISI 304. The friction coefficients were determined by two methods, the first based on linear regression and the second based on analytical models. Thus, the friction coefficient under the blankholder and on the die drawing edge were calculated. The results were verified by a cup test performed experimentally and numerically.  
Based on the strip drawing test and cup test (experiment and numerical simulation), the following outputs were illustrated:  
1. Applying the linear regression model, the friction coefficient equals half of the slopes of dependence the difference of drawing forces to the difference of blankholding forces. Values of the friction coefficient in the area under the blankholder were f\({}_{1,2}\) = 0.11 for uncoated extra deep drawing quality steel DC05 and f\({}_{1,2}\) = 0.23 for austenitic stainless steel AISI 304.
2. Applying analytical models, the friction coefficients under the blankholder and on the drawing edge were not constant for different loading of the contact surfaces when measured for material DC05. The results obtained indicate that, with increased loading on the contact surfaces, the effectiveness of Anticorit 3802-39 S lubricant with high-pressure EP additives improves. The results obtained show that for the calculation of the friction coefficient the analytical model appears to be more suitable than the linear regression model.  
Figure 9: Comparison of hardening laws for experimental materials.  
3. The unambiguous tendency was not recorded for material AISI 304. It is assumed that lubricant during drawing the strip was not retained well on the contact surfaces because the steel sheet surface was very smooth (Ra = 0.07 \(\pm\) 0.02 \(\upmu\)m). This resulted in cold weld formation between the sheet surface and the roller even for lower pressures and shorter paths of drawing. 4. The applied friction model in the FEM simulation was verified experimentally by a cup test. The difference \(\Delta\)f between friction coefficients \(\mathrm{f_{m}}\) determined from experimentally-measured forces and \(\mathrm{f_{c}}\) determined from calculated forces by FEM simulation was higher for material AISI 304. This is due to the material model definition used in the numerical simulation.  
Conceptualization: E.E. and N.D.; methodology: E.E., N.D., and A.M.; software: E.E. and A.M.; validation: E.E., N.D., and M.T.; formal analysis: M.T. and K.P.; investigation: K.P.; resources: E.E., N.D., A.M., and M.T.; data curation: A.M. and M.T.; writing--original draft preparation: [PERSON] and M.T.; writing--review and editing: K.P. and M.T.; visualization: A.M. and M.T.; supervision: [PERSON]; project administration: [PERSON]; funding acquisition: N.D. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Scientific Grant Agency of the Ministry of Education of the Slovak Republic (projects VEGA 2/0800/19, KEGA 032 EU-4/2020, and APVV-17-0381 a).  
Not applicable.  
The data presented in this study are available on request from the corresponding author.  
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.