Technical cost modelling in lightweight engineering

Technical cost modelling in lightweight engineering

Using fibre-reinforced composite materials, a lightweight transport design can be created that lowers fuel costs and emissions. Despite being lightweight, composite raw materials can be expensive, and the fabrication of consecutive components can be challenging and costly. To design weight- and cost-efficient composite structures and find ways to reduce production costs, technical cost modelling must be applied.

Cost modelling strategies

• Qualitative
• Quantitative
• Statistical
• Analogous
• Generative-analytical

There are a number of fundamental methodologies that can be used to estimate production costs using either qualitative or quantitative methods. A comparative method known as qualitative cost modelling rates the cost of a design as either better or worse than an existing design. This approach is suitable for use in later stages of the design development process, where a fixed design is continuously improved. It is not, however, an effective tool for preliminary or general cost studies.

Quantitative strategies can be further divided into statistical, analogous and generative-analytical approaches. Large numbers of data points are used by statistical or parametric cost models to develop statistical criteria for causal relationships between product attributes and costs. Analogous methods make use of previous knowledge by adjusting costs defined on similar products according to existing differences. On the other hand, the generative-analytical (also called bottom-up) approach represents a production-tied methodology. The approach is based upon a detailed analysis of the production process flow in which associated costs are determined for each subprocess in accordance with a user-defined level of detail.

Developed composite technical cost model

The bottom-up sum of each subprocess is used to calculate the estimated production costs of any composite production method taken into consideration. For each defined sub-process step, required relationships to estimate process times as a function of component geometry and complexity are established.

Costing categories

Direct costs

• Material and scrap
• Labour
• Electric consumption
• Consumables (ignore)

Indirect costs

• Facility rent
• Equipment investment
• Tooling
• Fuselage instalment
• Maintenance (ignore)
• Overhead and R&D (ignore)

Developed composite cost models ignore overarching costs associated with overhead and product development in favour of costs that can be directly attributed to the manufacturing of a specific component. Costs included are defined above and are feedstock material costs as well as production process-specific costs such as production-related material and scrap costs, labour costs, equipment investment costs, tooling costs and required facility costs.

Geometric complexity

Manufacturing a more complex component is more difficult and time-consuming than manufacturing a simpler component. A sophisticated component’s entire manufacture will therefore have longer cycle times and cost more money. Subsequently, a production’s entirety is affected. The amount of scrap material produced by increasingly complex components rises as a result of more prepreg and dry fibre reinforcement edge cuts, for example. Actions like layup, cutting, and edge trimming have longer processing times. As its creation and manufacture become more complex, tooling costs rise.

Technical cost model implementation possibilities

The created technical cost model can be utilised both independently as an analytical tool and in conjunction with other essential design tools. Utilising the cost model as part of a larger design optimisation strategy to reduce both cost and weight is particularly intriguing. However, it is not always desirable computationally to drive the optimisation exclusively on the lowest product cost given the difficulties surrounding the combinatorial nature of component production.

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