Material and manufacture calculations

As the mass specified in the bill of materials represents that of the finished component, there is a need to 'correct' its value to account for material that is removed by the secondary machining processes. This influences the environmental footprint of both the material and manufacturing life phases.

To account for this, both the amount of 'starting' material and the waste produced need to be known. These are calculated by applying the following 'correction' factors to the final component mass.

In order to account for the waste produced by the secondary machining processes, the following assumptions are made:

• All waste is collected and sorted at source
• All waste is reclaimed by recycling or, if this is not appropriate, downcycling
• Recovered material is fed directly back into the material supply chain

Note: The manufacturing scrap associated with the primary processes has already been accounted for in data quoted for the primary processes (i.e. these values include typical scrap rates).

Material phase

There are three main contributors to the embodied energy and CO2 footprint of the Material Phase. These are: the embodied energy of the raw material, the energy associated with collecting the manufacturing waste and the 'credit' for recovering the manufacturing waste. This leads to the following calculations:

where:

H_grade, CO2_grade depend on the level of recycled material used in the product (see Recycled content)

H_c, CO2_c = energy and carbon footprint associated with collection of manufacturing waste

H_{recycle(waste)}, CO2_{recycle(waste)} depend on how the waste is recovered

If the material comes from a reused part, then there is no contribution from the material to the embodied energy and CO₂ footprint.

Recycling manufacturing waste

For recycling, which is the default option for reclaiming the manufacturing waste, the credit for recovery is calculated as follows:

Downcycling manufacturing waste

In cases where a material is flagged as not recyclable, it is assumed that it will be downcycled, where it will be either reprocessed:

...or comminuted into aggregate:

Manufacture phase

The manufacturing phase calculations can be split into two groups; primary & secondary processes (which are applied to individual materials/components) and, joining and finishing processes (which are independent of materials/components).

Primary and secondary processes are not applicable for reused parts.

Primary and secondary processes

There are two contributions to the manufacturing phase for an individual component. The energy / CO2 footprint associated with the primary process (based on the initial amount of material used) and the secondary machining process (based on the amount of material removed). These are calculated and summed as follows:

Joining and finishing processes

The joining and finishing processes are specified by a range of different units (length, area, number of units) and, as a result, are not associated with the component mass. The environmental footprint of these processes is calculated as follows:

Values for H_a&f and CO2_a&f are summarized in table 3 (see joining and finishing processes).