## 2 Background
### Including Manufacturing Knowledge in Product Design  
In addition to, e.g., functional requirements, manufacturing processes determine the shape of a product and its components. Therefore, it is advantageous to consider this early in the design process [21]. From a methodological point of view, design guidelines for various manufacturing techniques have been discussed for decades. These are available, e.g., as generalized collections of allowed and disallowed design snippets for a large set of single manufacturing processes, such as sloped surfaces that have never been drilled on or material accumulation in the casting [22]. However, the exploration and limitation of the solution space for the product to be designed is dependent of the designer's experience in instantiating these snippets on the current design task [23]. Additionally, these snippets do not necessarily contain information about feasible geometric parameters as, e.g., traveling distances and achievable tolerances are machine specific data. Although individual development processes, such as axiomatic design [24; 25; 26], integrate the process domain into their methodological framework, the developer is usually still forced to gather relevant information and negotiate the design in reviews with the manufacturing department [8; 27]. Furthermore, especially in variant design, the question arises as to what changes are necessary to the existing production equipment in order to manufacture the new variant and, ideally, to minimize the effects of a new design on machining parameter changes and new CNC programs [28]. In addition to methodological support, knowledge-based assistance systems can take into account concrete manufacturing resources and specific constraints, such as the above mentioned traveling distance of a NC axis [29]. Because today's computer-aided engineering environments offer plenty of capabilities to work with parametric designs and knowledge modeling, both analysis, i.e., checking a design for violations of manufacturing constraints, and synthesis, i.e., completing a design according to manufacturing constraints, are possible [30; 31]. However, the manufacturing knowledge to be implemented must be made explicit and machine-readable [23]. In general, there are many approaches to formalizing individual manufacturing processes and manufacturing process chains in the literature. Beside modeling single constraints, e.g., as value limits for dimensions in a CAD model, holistic approaches often use semantic information models, which are mainly based on the concept created by [PERSON] [32], which understands manufacturing as the sum of product, process, and resource. The process describes the sequences and procedures required to manufacture a specific product shape. The process thus describes the transformations of an operant during production. The product describes the component to be manufactured along a process chain. Since this is subject to different shape changes from process to process, an adaptive modeling is necessary here. The resources describe the production aids, tools, and machines that are used during production and thus determine the production capabilities and restrictions. Figure 1: Tailored forming process chain (reproduced with the permission of Ref. [20]). Within the manufacturing domain, many knowledge-based approaches can be used to formalize entire process chains explicitly and in a machine-readable manner. In doing so, they are able to derive inferences with respect to a process and process chain specification [33; 34; 35; 36; 37]. However, these approaches are generally not suitable for design synthesis, where there is no feedback of analysis results into product design. Approaches from product development can map this feedback by investigating product designs using formalized manufacturing knowledge. Thereby, these models are able to show manufacturing conflicts and support their resolution by hints or direct product model adaptation [38; 39; 40; 41].