Das hängt von dem ab, was Du erreichen möchtest. Es gibt verschiedene Möglichkeiten:
Mit rotate=90, transform shape
\documentclass{article}
\usepackage[latin1]{inputenc}
\usepackage{tikz}
\usetikzlibrary{shapes,arrows}
\usepackage{blindtext}% nur für Fülltext
\begin{document}
\pagestyle{empty}
\blindtext
\begin{center}
\begin{tikzpicture}
[
rotate=90,transform shape,%<-
auto,
block/.style ={rectangle, draw, thick, fill=gray!10, text width=12em, text centered, rounded corners, minimum height=3em, node distance = 1.5cm},
coor/.style ={ draw, thick, },
line/.style ={draw, thick, -latex',shorten >=0pt},
cloud/.style ={draw=red, thick, ellipse, fill=red!20, minimum height=4em}]
\node [block] (1) {\textbf{Bauteil}};
\node [block, right of=1, node distance=7cm] (1-1) {Form / Geometrie};
%\node [block, below of=1-1,] (1-2) {Große (Lange/Breite/Hohe)};
\node [block, below of=1-1,] (2-1) {Warmeausdehnungs- koeffizient $\alpha_T$};
\node [block, left of=2-1, node distance= 7cm] (2) {\textbf{Material}};
\node [block, below of=2,] (2--) {Verarbeitungstemperatur};
\node [block, below of=2-1,] (2-2) {Druckbetttemperatur};
\node [block, below of=2-2,] (2-3) {Druckgeschwindigkeit};
\path [line] (1) -- (1-1);
%\path [line] (1) -- (1-2);
\path [line] (2) -- (2--);
\path [line] (2) -- (2-1);
\path [line] (2) -- (2-2);
\path [line] (2--) -- (2-3);
\end{tikzpicture}
\end{center}
\blindtext
\end{document}
mit \rotatebox{90}
\documentclass{article}
\usepackage[latin1]{inputenc}
\usepackage{tikz}
\usetikzlibrary{shapes,arrows}
\usepackage{blindtext}% nur für Fülltext
\begin{document}
\pagestyle{empty}
\blindtext
\begin{center}
\rotatebox{90}{\begin{tikzpicture}
[
auto,
block/.style ={rectangle, draw, thick, fill=gray!10, text width=12em, text centered, rounded corners, minimum height=3em, node distance = 1.5cm},
coor/.style ={ draw, thick, },
line/.style ={draw, thick, -latex',shorten >=0pt},
cloud/.style ={draw=red, thick, ellipse, fill=red!20, minimum height=4em}]
\node [block] (1) {\textbf{Bauteil}};
\node [block, right of=1, node distance=7cm] (1-1) {Form / Geometrie};
%\node [block, below of=1-1,] (1-2) {Große (Lange/Breite/Hohe)};
\node [block, below of=1-1,] (2-1) {Warmeausdehnungs- koeffizient $\alpha_T$};
\node [block, left of=2-1, node distance= 7cm] (2) {\textbf{Material}};
\node [block, below of=2,] (2--) {Verarbeitungstemperatur};
\node [block, below of=2-1,] (2-2) {Druckbetttemperatur};
\node [block, below of=2-2,] (2-3) {Druckgeschwindigkeit};
\path [line] (1) -- (1-1);
%\path [line] (1) -- (1-2);
\path [line] (2) -- (2--);
\path [line] (2) -- (2-1);
\path [line] (2) -- (2-2);
\path [line] (2--) -- (2-3);
\end{tikzpicture}}
\end{center}
\blindtext
\end{document}
oder auf einer Extraseite mit dem Paket pdflscape
\documentclass{article}
\usepackage{pdflscape}
\usepackage[latin1]{inputenc}
\usepackage{tikz}
\usetikzlibrary{shapes,arrows}
\usepackage{blindtext}% nur für Fülltext
\begin{document}
\pagestyle{empty}
\blindtext
\begin{landscape}
\begin{center}
\begin{tikzpicture}
[
auto,
block/.style ={rectangle, draw, thick, fill=gray!10, text width=12em, text centered, rounded corners, minimum height=3em, node distance = 1.5cm},
coor/.style ={ draw, thick, },
line/.style ={draw, thick, -latex',shorten >=0pt},
cloud/.style ={draw=red, thick, ellipse, fill=red!20, minimum height=4em}]
\node [block] (1) {\textbf{Bauteil}};
\node [block, right of=1, node distance=7cm] (1-1) {Form / Geometrie};
%\node [block, below of=1-1,] (1-2) {Große (Lange/Breite/Hohe)};
\node [block, below of=1-1,] (2-1) {Warmeausdehnungs- koeffizient $\alpha_T$};
\node [block, left of=2-1, node distance= 7cm] (2) {\textbf{Material}};
\node [block, below of=2,] (2--) {Verarbeitungstemperatur};
\node [block, below of=2-1,] (2-2) {Druckbetttemperatur};
\node [block, below of=2-2,] (2-3) {Druckgeschwindigkeit};
\path [line] (1) -- (1-1);
%\path [line] (1) -- (1-2);
\path [line] (2) -- (2--);
\path [line] (2) -- (2-1);
\path [line] (2) -- (2-2);
\path [line] (2--) -- (2-3);
\end{tikzpicture}
\end{center}
\end{landscape}
\blindtext
\end{document}
und vermutlich gibt es noch weiter Möglichkeiten.