Line feeding decision levels

As the actual assembly line feeding problem has been introduced, we will further delimit the scope by discussing different levels of decision making.

1Standardized VSM symbols are used; as only material flow is taken into account, push arrows are used.

Table 2.3Line feeding decisions on different decision levels

Strategic Tactical Operational

Placement of feeding preparation Feeding policy assignment Product sequencing Facility sizing Supermarket organization Replenishment scheduling Outsourcing degree Vehicle selection Transportation scheduling Standardization degree Automation degree Preparation scheduling

In general planning, strategic, tactical and operational levels are distinguished. Bhatnagar et al. (1993) describe that decisions of different levels affect each other and should be con-sidered in an integrated way regarding the intra-organizational decision levels as well as the inter-organizational hierarchy. Although the regular planning process is a top-down, hierarchical process, it is widely believed that there is an interaction of strategic, tactical and operational management decisions (Armbr¨uster and Kempf, 2012). Transferred to this framework, it can be stated that the assignment of parts to line feeding policies, being a tactical decision, is influenced by decisions made at other planning levels and also affects other planning levels itself.

The tactical decision of assembly line feeding influences the efficiency of the system on an op-erational level, but an improvement of opop-erational efficiency, e.g., by locating parts in a more efficient way, could also have an influence on the tactical decision of line feeding. The same holds true for the relation of tactical and strategic decisions. Hence, tactical decisions can influence operational or strategic decisions and vice versa, though the actual planning process is often done in a hierarchical way. Even within one decision level there might be hierarchical decisions.

E.g., the ALFP determines part feeding policies and possibly the layout of a feeding system if the system has not yet been designed. If the design is determined up front on the other hand, it affects the ALFP.

In order to state the limits of the ALFP on the tactical level and distinguish it from strategic and operational levels, the scope of every level is shortly explained in the following and some examples of decisions on each level are given in Table 2.3.

Strategic line feeding

From a hierarchical point of view, one very long-termed or strategic issue in line feeding is the cooperation with suppliers or logistics providers. This can be described by the outsourcing decision, which deals with the determination of the right amount and consequences of outsourcing logistical handling. It might also include the selection of suitable logistics providers or suppliers.

Another strategic decision is the location of external warehouses, which influences operations and applicability of line feeding policies. This decision level could also be described as a supply chain level. Klingenberg and Boksma (2010) provide a framework to investigate outsourcing of logistics handling activities. They also incorporate the tactical and operational level by applying strategic frameworks, like transaction cost theory, to outsourcing of line feeding aspects. For that, mainly two dimensions are distinguished: the location of the outsourced activities and the type of outsourced activities. Moreover, Mathisson-Ojmertz and Johansson (2000) evaluated five case

studies with a different degree of outsourcing logistical handling. In those cases, material handling operations were stationed at different locations within the supply chain. It was found that systems, where a logistical service provider was integrated, required much more logistical handling overall. On the other hand, no significant difference was found between performing handling at the supplier and in-house. In Figure 2.3, it is schematically depicted how the flow of material could look like, assuming different outsourcing options. This type of strategic considerations are not elaborated in the following, as they are outside of this review’s scope.

Supplier

line

stocking boxed-supply sequencing kitting

Logistics Provider

boxed-supply sequencing kitting

Manufacturer

Inbound Inbound

boxed-supply sequencing kitting

Assembly line

Figure 2.3Effects of external handling on line feeding policies

Tactical line feeding

The tactical level is subordinate to the strategic or supply chain level, and could also be described as assembly system planning. The fundamental and constituting aspect of the tactical ALFP is the assignment of parts to line feeding policies. Additionally, one may include other tactical decisions that impact or are impacted by the decision making of line feeding policies. Those decisions, amongst others, could be the number of storages, the kind of preparation areas or the

types of vehicles used for transportation. All these decisions influence a system’s performance in the medium term and can hence be classified astactical and incorporated in decision models on assembly line feeding. Those decisions do not have to be incorporated necessarily though. This is due to the fact that in preexisting assembly systems those decisions might have been taken in the past and are not desired to be changed.

The scope of decisions to design tactical aspects in an assembly feeding system is quite large, and furthermore, impacts the operational as well as the strategic level. The chosen line feeding policies, e.g., have an influence on the operations that need to be performed and hence on the costs, which in turn may influence the desired degree of outsourcing.

Operational line feeding

Opposite to strategic and tactical, operational issues are more short-dated and can be changed easily. On the operational level, decisions on facility design, products and the number and characteristics of storage are already taken. Typical tasks are e.g. the constellation of load carriers such as kits, transportation of pallets to stations and replacement of empty ones. All these tasks depend on the current demand for parts and have to be planned in real-time whenever the production schedule is altered. The aim of planning within this stage is, consequently, to increase the efficiency of an assembly system while satisfying demand, which is of very high importance since waiting for parts results in very expensive idle times of the entire assembly line. Similar to strategic issues, operational ones are rather out of the scope of this review. They might be classified by a framework similar to Brucker et al. (1999) or Graham et al. (1979) for individual sub-processes.