The Slovene toolmaking industry is forced to follow the trends of world automotive industry demanding increased use of steels with improved mechanical properties like high strengths, high elongations etc. The higher strengths of so-called 'high strength low alloyed' steels and 'advanced high strength' steels cause higher tool pressures and loads during forming, higher springback effects of the products after forming and demand special design of the tools. In the paper, the material properties of H220, H420LA and TRIP700 steels were analysed and the bending tests were performed in order to compare the springback effects of all three materials. Based on the obtained data, first guidelines were prepared for the design of the tools. These guidelines were taken into account when the first forming tools for HSLA and AHSS materials were designed in Gorenje Orodjarna d.o.o. tool factory. The FEA approach was used for the tool design of the part made of H420LA steel.
A sequence $(x_n)_{; ; ; ; ; n \geq 0}; ; ; ; ; $ of positive real numbers is log-convex if the inequality $x_n^2 \leq x_{; ; ; ; ; n-1}; ; ; ; ; x_{; ; ; ; ; n+1}; ; ; ; ; $ is valid for all $n \geq 1$. We show here how the problem of establishing the log-convexity of a given combinatorial sequence can be reduced to examining the ordinary convexity of related sequences. The new method is then used to prove that the sequence of Motzkin numbers is log-convex.
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