Opel COST WEIGHT OPTIMIZATION (CWO) DIAGRAM, STARTING EARLY, C = m • Cs, BIG ENLIGHTENMENT, BLUE, GREEN, RED

techniques. The reasons are as varied as the spectrum of alternative materials available: the often biased expertise of concept engineers regarding the potential, maturity and cost of alternative materials, semi-finished products and techniques, the expensive procedures before they are released as suitable for use, and insufficient importance being attributed to the learning curve in cost models. Often dimensional concepts designed for use with steel are used for lightweight materials; when transposed at a ratio of 1:1, they generally result in greatly inadequate weight reduc- tions. In practice, cost-optimized lightweight construction fails not least because of a tendency to ignore the designers’ old rule of

COST WEIGHT OPTIMIZATION (CWO) DIAGRAM

													5,0		30
	14
															25
	12												4,0
	10														20
													3,0
		8
															15
/kg)(€		6											2,0
															10
Specifiiccosts		4												Weight(kg)		costTotal(€)
													1,0
															5
	2			hells	conventional			hot shaped		IHPF	new process
			Sheet steels-			Aluminum,	Magnesium,		Aluminum,			Aluminum,

thumb that design costs should already be fixed during the concept phase.

STARTING EARLY

Enter CWO (Cost Weight Optimization) – a method developed by IVM Automotive that allows simple calculation of production costs for lightweight concepts very early on and a positive impact on the whole process. CWO enables the marketability of new materials or semi-finished products to be assessed, new techniques to be compared, and aims for their development to be defined. Entire car bodies, not to mention individual modules or compo- nents, may be cost-optimized for each size of production run. By the end of the development process you have a vehicle that strikes the right balance between cost, weight and other required properties in production, too.

At the heart of the CWO method lies the simple cost equation

C = m • Cs

Where C is the cost of the component in euros, m its mass in kilos, and Cs the specific cost in €/kg of the ready-to-fit component: this includes material and production costs, tooling cost depreciation and extra charges.

Specific costs are generally determined by only a handful of cost factors. In a CWO pro- ject, the designer receives a table of possible materials matching the project concerned and the scale of production; the contents of the table vary considerably depending on the latter (diagram left).

The aim of the concept phase must be to achieve the weight targets while maintaining sufficient rigidity and meeting the cost tar- gets. In the past, however, the calculation of production costs has frequently been postponed into subsequent project phases. If it is assumed that automobile designers can optimize and control the mass and other properties of a vehicle or component using finite element (FE) methods, CWO represents an opportunity to optimize costs at the earliest possible stage while taking account of other target values (diagram above).

BIG ENLIGHTENMENT

Having developed it between 1996 and 2001, IVM Automotive has so far applied the CWO method to various customer projects. The results are persuasive: in each individual case, whether involving small or large components, in small or large production runs, the early transparency in production costs for lightweight construction effectively helped optimize costs. In several cases where a maximum weight saving was achieved, the costs even matched those of conventional construc- tion. In one project, for instance, it proved possible to design the production of a light- metal car cross member in such a way that its cost matched that of the reference model while achieving a 50 percent reduction in

weight. Ralf Anderseck

BLUE, GREEN, RED

The blue bars represent the specific costs of the material. The bottom end marks the cost-optimized solution for the material in question. The blue ball represents the targeted concept status. The designer can thus ascertain the cost of a particular design.

The green bars stand for weight. Once again, the ends of the bars should be regarded as positive and negative benchmarks. The green ball represents the target weight. The designer can thus ascertain how lightweight a particular design is.

The absolute costs are shown in red. Multiplying the above values produces the range. The designer can ascertain whether the cost targets have been met.

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