Estimating costs in mechanical production

Companies live in a competitive world where they seek maximum profit and the acquisition of promising markets. In the face of this technical and economic competition, controlling the costs of a project or product is not just an asset, but an obligation.

The first paragraph of this article situates cost estimation in relation to the product life cycle. It also presents the various cost estimation methods currently in use, specifying their field of application in relation to the product life cycle. The following three generic methods are distinguished:

• the analog method ;

• the analytical method ;

• parametric method.

In the second paragraph, we define the technical cost price and explain how difficult it is to know each of its components. This section reminds the reader of the most important elements to be taken into account in the cost of a mechanical part.

In order to master the results of a costing, the next two paragraphs deal with method accuracy and learning curves. These two elements are very important and explain the reasons for different costings for the same part.

Finally, in the last paragraph of the article, there's a detailed presentation of each of the methods mentioned above with, for each :

• definition ;

• implementation ;

• advantages and disadvantages ;

• application to a real-life case.

We show that the parametric method based on Cost Estimating Functions (CEFs) allows us to identify general trends in the evolution of a cost, but does not allow us to solve the cost estimation of a particular case. One of the examples used to illustrate the parametric method is the determination and implementation of a CEF. As for the analogical method, by searching for similar cases, it is able to solve a particular case provided it has already been dealt with. We present an application of the analogical method using a reasoning tool based on past cases. This is a different technique from group technology, involving learning, indexing and similarity measurement techniques. The results obtained today with case-based reasoning tools are very interesting. Finally, the analytical method is widely used for large-scale production, when the aim is to optimize the manufacturing process during the industrialization phase.