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

138 Metal Forming – Process, Tools, Design

**2.1. Data collection** 

2010).

was also the strategy here adopted.

control unit (Oliveira et al, 2010).

**2.2. Accounting and LCA methodologies** 

has been neglected on the common LCI databases.

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

Manufacturing processes analysed were metal bending and Laser-cutting. In both cases, no other process- or operation-related resources, apart from electricity, were consumed, but the influence of the hydraulic oil needs during the equipment's lifetime was considered in the LCA analysis of a conventional press-brake used for bending. In the case of the Laser cutting machine, with individualised sub-systems, power consumption measurements were followed in parallel for the 3 main sub-systems, namely the Laser source, the chiller and the

The energy consumption data were acquired with a Janitza Power Analyzer, model UMG 604, a measuring system able to measure and calculate multiple electrical variables on 3-phase AC systems. The system was configured to record current, voltage, and power factor per line every 1 s, installed in the machine-tool's electrical cabinet; accounts over 24 h for each test have been followed. In the used configuration, the system is capable to measure low-voltage systems up to 300 V conductor to earth and currents up to 60 A, with maximum measuring uncertainties of ±0.50 V and ±0.15 A, respectively, over long periods of time (Santos et al, 2011). The yearly consumption of hydraulic oil was taken from the Preventive Maintenance Plan provided by the machine-tools local manufacturer involved in the time-studies (Adira S.A.,

As advanced, there are still no specific tools and methodologies for the characterization of the environmental profile of a manufacturing process. This is being taken by research groups and associations, such as the CO2PE initiative previously referred, but still much as to be done on the standardization of methods and quality of the inventory data currently available. As referred, the particular system technology being used for the process, i.e., the type of machine-tool available, as well as the utilization mode during production, also plays an important role on the accounting of energy consumption during process, although this

All environmental analysis generated in this framework was followed by application of the Eco-Indicator 99 (H,A) method, using SimaPro 7.0 with Ecoinvent 2.0 unit processes as LCI database (Pré-consultants, 2010a,b). LCI datasets of secondary metals have been used whenever applicable on the equipment-related resources. The main inputs related to the use phase, electricity and hydraulic oil, were distinguished as different use phases, to assist their individual impact during the analysis. The LCA outcome results from Single Score analysis.

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 capacity and production scenario have been proposed.

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 patent on the following case-studies analysed.
