Assembly Feature

Assembly feature is a specialized class of the generic concept feature. The Oxford dictionary defines feature as “a distinctive attribute or aspect of something”. However most definitions of feature, found in the literature review, relate it with product lifecycle domain especially the design and manufacture.

For example, Pratt and Wilson (1985) define feature as “a region of interest on the surface of a part”. Rosen (1993) describes feature as “meaningful abstractions of geometry that engineers use to reason about components, products, and processes”. Lenau and Mu (1993) believe that “features are information sets that refers to aspects of form or other attributes of a part”. It is obvious from the above discussion that a feature is a physical constituent of a component in context of design and manufacture but still it should not be constrained to a particular domain as it has been considered a generic concept in this research.

A more specialized class “FormFeature” can be introduced to replace feature.

Form features are the “features producing volumes” (Rosen, 1993) or the

“features that relate to the shape or form of the part” (Roller, 1989). However form features can carry design information and/or the manufacturing information (Hounsell, 1998) as well as other such domains. Hence form features may not

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be applicable to any particular product lifecycle domain and can be declared as a generic concept.

Form features can relate to products and resources therefore they can specialized into product feature and resource feature (the term resource feature is further explained in section 4.3.19). A product feature can have further implications in the design and manufacturing domains and could represent different aspects of these domains. For instance, a product feature for the design domain may be described as “a parameterised geometrical entity used for building the CAD model” (Molloy, et al., 1998) and may have the functional information as well. While product feature in context of the manufacturing domain can be described as the “interpretation and, most importantly, the combination of form features from the viewpoint of manufacturing, assembly and inspection” (Krause, et al., 1993) or “a parameterised entity linked with one or several alternative manufacturing methods” (Molloy, et al., 1998).

The concept product feature which carries design and manufacturing information can be further specialized into single piece part feature and assembly feature. The single-piece-part-feature concept deals with the design and manufacture of single piece parts and therefore it is not in the scope of this research. The concept assembly feature which carries assembly design and assembly process planning information is explored further in this research for the representation and sharing of assembly knowledge.

The assembly feature has different implications for assembly design and assembly process planning domains as it is evident from the definitions of assembly feature found in the literature as well. For example, Deneux (1999) defines assembly feature from design perspective as “a generic solution referring to two groups of parts that need to be related by a relationship so as to solve a design problem”. Molloy, et al. (1998) describe assembly feature from assembly planning point of view as “a parameterised entity linked with one or several assembly methods”. Comaa et al. (2003) define assembly feature from

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various viewpoints as “any topological, geometrical, technological or functional information assigned to a face, a part or a sub-assembly, whose presence is inherent to the assembly process”.

In this research assembly feature has been specialized into various classes which can support the capture and sharing of assembly knowledge across the assembly design and assembly process planning domains. Hole and shaft assembly features provide basis for limits and fits, and are commonly found in literature. Hole assembly feature represents the female assembly feature and whereas shaft assembly feature represents the male assembly features. Hole and shaft assembly features have been explored in details in chapter 5 and 6.

Other subsumptions of assembly feature class include the plane mate assembly feature (Holland, 200) and alignment assembly feature (Shah, 2001).

Plane mate assembly features represent those assembly features which have plane to plane mating relations as shown in figure 4.12a. The alignment feature represents the assembly features where the latter have their axis aligned with each other as shown in figure 4.12b.

Figure 4.12: Examples of plane mate and alignment assembly features

Other specializations of assembly features are handling assembly features (Holland, 1997) and tooling assembly features. Holland (1997) proposed that assembly feature could potentially be specialized into handling feature and connection feature. The handling feature represents the handling information while connection feature represents mating or connection information. Figure

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4.13 shows two assembly components which have handling and connection features. However in this research, the concept connection feature has not been used and instead various instances of connection feature e.g. hole, shaft, plane mate feature, and alignment feature have been directly subsumed under the assembly feature concept.

Figure 4.13: Handling and connection features

The concept tooling assembly feature has been used to represent those assembly features which actually interact with assembly resource features to accomplish the assembly task. An example of tooling assembly feature is shown in figure 4.14.

Figure 4.14: Examples of tooling features on the butterfly valve assembly

The nut runner (assembly resource) shown in figure 4.14 interacts with the tooling features to perform the fastening process. The concepts of handling and

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tooling features could be useful in the scenarios where products interact with assembly resources.

A complete concept specialization of assembly feature is shown in figure 4.15 where the assembly feature has been specialized into hole, shaft, plane mate, alignment, handling and tooling assembly features.

Figure 4.15: Concept specialization of assembly feature

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