Axiomatic Grinding Process Model Life Cycle and Sustainability of Abrasive Tools

Section 7.1 described different methods for evaluating sustainability and Sect. 7.2 derived the life cycle inventory for grinding to implement these methods. Data for the analysis is either measured empirically, estimated or obtained from databases. Ideally, fundamental process knowledge would allow calculating all input and output streams from physical and analytical models. The following study uses axiomatic design principles to display how sustainability characteristics are con­nected with physical process principles. This new approach is still in development but creates a holistic model and points out where further research and quantitative equations are needed.

7.3.1 Methodology

Axiomatic design is a way to describe systems and products systematically and was laid out by Suh [SUH01, COCH01]. The idea of axiomatic design is to generalize the principles of the investigated system by axioms. This design method has been used for environmental considerations of manufacturing systems and product ser­vices [STIA07]. However, grinding processes have too many interdependencies between their process components and, therefore, some axiomatic design rules cannot be fulfilled completely, such as the interdependence axiom [LINK12c].

The axiomatic design process works within four domains, which are shown in Fig. 7.9 for the abrasive process including process setup, tool, and cooling lubri­cant. The customer domain is characterized by the customer attributes {CAs} of the grinding application at a defined workpiece. For example, we are aim at a certain surface integrity, roughness or dimensional tolerance. In the functional domain, the functional requirements {FRs}, such as “take away heat from the workpiece”, “control chemical reactions on the work surface”, etc., and constraints {Cs}, such as maximum dimensions of the components, are defined.

The design parameters {DPs} in the physical domain satisfy the FRs. Here, DPs are cooling lubricant properties (heat capacity, supply system, etc.), process setup (thermal conductivity, kinematics, etc.) and tool characteristics (grit type, wheel hardness, etc.).

Finally, in the process domain the procedure to generate the specific DP is char­acterized by process variables {PVs} [SUH01]. Here, PVs describe machine tool components or the production procedures of grinding tool and cooling lubricant. In concurrent engineering the last three design phases interact constantly with each other.

The relation between FR and DP can be expressed by vectors, see example in Eq. 7.7. This way of describing an abrasive tool system offers the possibility to implement qualitative connections or quantitative equations, which then can be used for energy and resource calculations. Additionally, we are able to separate the objectives (here FR) from the means (DP), evaluate necessity of all items and get a holistic overview [COCH01].

Fig. 7.9 Axiomatic description of a grinding process after [SUH01], reprinted from [LINK12c] with permission from Elsevier




Axiomatic design demands that the functional requirements should be inde­pendent from each other (Independence Axiom) [SUH01]. This is not fulfilled in grinding processes because many components serve multiple functions, e. g. cooling lubricant or grits [LINK12c]. Additionally, in axiomatic design the information content should be minimal, i. e. the design with highest probability for success should be chosen (Information Axiom) [SUH01]. This axiom is not satisfied within most common discrete processes because the high process complexity does not allow for optimizing all variables simultaneously. For example, if oil is chosen as cooling lubricant instead of water-based emulsion, the heat from friction will be reduced, but chip formation will be less effective and less heat will be removed from the grinding zone [LINK12c].

In conclusion, representing grinding by axioms is one way to visualize the process mechanisms and aims at understanding the technology. Figure 7.10 explains how the axiomatic grinding process model is visualized in the following. Every functional requirement is met by a design parameter and the according boxes are connected by a line (Fig. 7.10). In axiomatic design, the model has to be decomposed until only one DP appears for one FR [BROW11]. DPs can be pri­oritized and additional DP create an alternative tree. In this study, this decompo­sition was not completely possible because the real grinding process has overlaying DPs. In addition, each DP should have more than one FRs [BROW11]. Final design

parameters, which cannot be broken down to smaller variables, are indicated by the letters (S), (T), or (C) (Fig. 7.10). A dashed line indicates a functional requirement or design parameter that is repeated elsewhere in the axiomatic model on the same or earlier level.

Axiomatic Grinding Process Model
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