**2. Methodologies used**

136 Metal Forming – Process, Tools, Design

and thus have significant costs.

information.

�������������� = �� � ��� (1)

�� � � (2)

where *P0* is the fixed part corresponding to the total stand-by power [kW], �� is the rate of

������ <sup>=</sup> ��

typically proportional to the amount of material being processed or to the type of work.

While the constant part is used to insure the active response of sub-systems, such as driving controls, exhaustion or cooling apparatus, and is independent of whether or not a part is being produced, the variable part corresponds to the energy needed to produce a work-piece and is

As demonstrated by Santos (Santos et al, 2011) for pure forming processes with discrete loading, such as bending, the maximum value of the variable part is limited by the machine characteristics, affecting the throughput. On the other hand, this is the theoretically constant value to which the SPE model would tend to, considering the fixed consumption would be shared by an infinite throughput. In real scenarios, the rate between constant and variable contributions associated to a production cycle, as well as their respective values, is mostly dependent on the system technology. However, the full implications of technology to the environmental profile of the machine should be attained in terms of the contributing triangle referred and not only the energy-consumption during use of the machine-tool.

Another point is the guiding for environmental improvement, as the environmental impact assessment requires the application of specific methods and tools. Life-cycle assessment (LCA) is the reference tool for environmental profiling of products and processes, as it is the most effective tool for this purpose and permits the most advanced environmental analysis possible. Every LCA methods use qualitative, quantitative or semi-quantitative analysis, although the quantitative form is considered more suitable for detailed LCA studies (Curran, 1996; Hochschorner, 2003). However, LCA tools can be time and work consuming

In recent years, there has been a trend for the development of simplified methods for LCA. These are quantitative or semi-quantitative methodologies aiming to give quick answers and suggestions. Although these methods tend to be very universal and wide-ranging, given the broad applicability of these methodologies and the strong emergence of its use, they have a strong customization potential. In fact, these simplification techniques can be adapted to provide 'customized' or 'tailor-made' perspectives in studies of specific systems or sectors, enabling to include system-specific principles and practices more relevant and appropriate to the interested LCA end-user, while still producing valid and robust results, and keeping the LCA basic conditions regarding scope and methodology (Bala, 2010; Curran, 1996). In line with this, Hochschorner (Hochschorner et al, 2003) highlighted the importance of the method applicability to the field of application as the most important selection criteria of the proper LCA method to adopt, in order to deliver the required

material processing, typically in cm3/s, and *k* is a constant provided in kJ/cm3.

Additionally, from Eq. (1), the SPE would be built as indicated in Eq. (2):

The strategies for improvement expected from the environmental profile assessment of a process shall be based on the comparative analysis between alternative production scenarios. Relevant technologies and application ranges have been selected, considering the respective technology/application market share. Comparative studies were followed with a pre-defined job and application ranges (material, shape, process quality,…), and under similar utilization modes.

Regarding data collection, particularly on preliminary process evaluations, it seemed realistic to start focusing on energy consumption and any main consumable. The same measuring system and accounting methods were used throughout the comparative studies followed.

Special attention was dedicated to the accounting methods and assessment methodology to use. A wide discussion has been followed about the limitations of the non-standardized methodologies and the impact of the quality of the inventory and main indicators to the reliability and standardization of environmental profile assessment results. As presented in a previous work (Azevedo et al, 2010), for the purpose of the analysis of the environmental profile of a machine-tool, the contribution of the different main inputs to the overall impact shall be analysed relatively to each other. On the other hand, the detailed analysis per environmental impact category should consider absolute values, in order to reveal those categories to which the process is potentially more detrimental to, and which main input contributes most to it, in order to properly inform about the real extent of the impact. This was also the strategy here adopted.

Towards Benign Metal-Forming:

The Assessment of the Environmental Performance of Metal-Sheet Forming Processes 139

**3. Critical factors in the analysis of main environmental impact** 

capacity and production scenario have been proposed.

patent on the following case-studies analysed.

time-dependent power parameter value.

according to Eq. (4):

**3.1. System technology impact: Sheet metal bending** 

Regarding the SPE contribution, the differentiation between metal manufacturing processes involving material removal and deposition from those pure forming operations, understood as discrete loading operations, has been proposed (Santos et al., 2011). In the different studies supporting this work, comparison and modelling of the electricity consumption data during process with systems of different technologies, and the influence of production use scenarios, were discussed based on time studies followed at industrial users. For discrete production cycle operations, such as bending, the definition of a specific exergy reference unit was proposed, since the units typically associated to manufacturing processes, generally described per unit of material processed, were considered not suitable. In this work, direct process categorization criteria such as system technology, maximum loading

On the other hand, in what refers to system technology, overall vs sub-systems (energyconsuming or not) strategies for data collection and accounting were adopted. For bending, the overall approach was used in the analysis of the pess-brakes, while for the laser cutter, parallel analysis of 3 main sub-systems was followed. This later case is in line with the current trend to more efficient power technologies and modular design, with no single dominating consumer sub-system but on a set of sub-systems with comparable energy consumption levels, which justifies the sub-system approach. In what concerns the SPE assessment, this is definitely the approach to adopt targeting the identification of main contributors, even if the total SPE value is the one to be final accounted. This problematic is

When compared to other manufacturing processes, such as chipping, coating or cutting, the effective loading time per production cycle during bending is relatively short and the specific rate at which the load is applied is not a significant process parameter. In turn, the analysis of the energy needs should focus on effective energy values in alternative to the

The scans in Fig. 1 expose the referred discrete loading character inherent to bending, and the influence of machine-tool technology in the temporal evolution of power and energy consumed per operation cycle. In the case of bending, and according to the time scans presented in Fig. 1,

where, P���� is the active power consumed during stand-by mode, being technology-related, and �������� is the active power consumed during loading, here proposed to be modelled

������ � ������ ������ ����������� ����������� ��������� ��������� (3)

�������� ������������ � ��� �������� (4)

the total energy consumption per bending cycle can be modelled according Eq. (3):

**contributors** 
