In this paper, we explore that designers can generate more effective interactions and decisions in the design process, when they use knowledge artifacts as design protocols with the following research question-- how designers could generate different types of knowledge artifacts with or without actual users in the design process? To address this, we adopt boundary objects as a theoretical foundation to argue the knowledge artifacts that designers produce. As an empirical approach, this study presents two case studies that represent the multiple knowledge artifacts between designers and users in a user-centered design projects. Based on this, it will provide feasible guidelines for designers to create effective knowledge artifacts with and without users as a design vocabulary in their actual design project settings.