Today, sustainability becomes one of the biggest challenges. It represents a key issue in every production activity. To face this issue, a possible solution is to enhance knowledge usage in manufacturing and sustainability domains. In this paper, we extend the ONTO-PDM ontology for formalizing sustainable manufacturing knowledge. An industrial case is presented for instantiating the extension. Moreover we design a knowledge-based system, which exploits sustainable manufacturing knowledge for supporting design and process planning with sustainability proposals, generating machine code starting from product specifications.