In 1871, Carl Eberhard Weiss founded a small forging business with three employees in Siegen. This marked the birth of SMS group, now a world leader in the metallurgical machine and plant engineering sector. The company produced all kinds of pushcarts, special carts for brickyards and quarries, and sack trucks. Around the turn of the century, customers of Maschinenfabrik und Dampfschmiede Karl Weiss included Rheinische Stahlwerke, Mannesmann, Buderus, Stumm, Krupp, and Thyssen.

Between 1914 and 1916, Maschinenfabrik Karl Weiss acquired Siegen-based machine factories Hoffmann and Oechelhäuser. In 1918, the three machine factories Weiss, Oechelhäuser and Hoffmann merged to form Siegener Maschinenbau AG. Mining and iron/steelmaking machinery, such as steam and blowing engines, metallurgical equipment, bicycles, and transmission and conveyor chains, were among the products manufactured by the company.

In 1927, with the takeover of Dahlbrucher Maschinenbau-Actiengesellschaft vormals Gebr. Klein, Siegener Maschinenbau AG expanded its product range to include rolling mill construction.

Siegener Maschinenbau AG was renamed Siemag Siegener Maschinenbau AG in 1939. Two years later, Bernhard Weiss acquired all shares in the company.