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Hi there,

I'm curious how to use the "CUTOFF injection moulding-RER" flow, specifically, and in what context it's appropriate? I am attempting to do an LCA of a product that has 3 components, each made out of different amounts of different types of plastic (polycarbonate, PA66, TPU), but all using injection molding. I did not want to include the production of the injection molding machine within my system boundaries.

My plan was to use this "CUTOFF injection moulding-RER" flow + a TPU flow (for example) + an electricity flow as the inputs to the respective "product component production" process. 

However, I'm confused what to put as the "amount" of the "CUTOFF injection moulding-RER" flow? it asks for a number of kg...is that the kg of material (TPU in this case) being inputted into the injection molding machine? I'm confused what else it would be, but also not sure. Any help would be greatly appreciated, thanks! 

in openLCA by (260 points)

1 Answer

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by (70k points)
Hi, basically, a cutoff flow is a "remainder" from other LCA softwares which require always processes producing a product to be able to calculate systems (like e.g. SimaPro). In openLCA, we do not have this limitation, if you have products in your life cycle where you exclude the supply chains from your system, because you do not have the information or because of goal and scope system boundaries, you can simply have a product flow as input, without setting a provider, and then create the product system so that only flows with providers are autoconnected.

As result, you will see in your calcuated inventory results the product as input, it is not hidden as it is in other LCA software but will be transparently visible. Of course you should still set the amount of the input product (if this was your question?).

In newer ecoinvent versions, we do not have product fows named "CUTOFF" any more.
by (260 points)
Hi Andreas, thanks for the info! I guess my main question is how to know what amount of "kg" to put when defining the "CUTOFF injection moulding-RER" as an input flow into a process I've created? Since this is a just a machinery flow, what does the kg as the reference unit mean? I'll already be putting the kg of plastic material as a separate input flow into the same process, along with the kWh of energy. But what kg of injection molding?
by (70k points)
Ah I see - if this is just the machinery then you can either skip it (if you do not want the machinery to be considered at all) or you can specify the "mass of machine" you would need per unit service (a bit comparable to ecoinvent's cars which are also measured in mass). If the machine weighs 1000 kg and can be used for 100,000 product units it's 10g machine per product unit).
by (260 points)
Got it, that makes sense. Thanks so much!
by (260 points)
Hi Andreas, a follow up question for you - I tried creating a simple product system with 2 processes, only using the ecoinvent CUTOFF flow for injection moulding (the one mentioned above) and two other CUTOFF flows for the material and energy as inputs ("CUTOFF synthetic rubber - GLO" and "CUTOFF Electricity, low voltage, at grid - CN"). When I the went to the product system and hit "Calculate", I got no impacts whatsoever. The values for each impact category are zero and I tried multiple impact assessment methodologies (TRACI, IMPACT 2002+).

Is that what's supposed to happen? I know the CUTOFF flows don't take into account the impacts of any previous processes used to create that respective flow, but I thought they would still have and include at least some impacts by being used in a product system?

Let me know if the lack of any impacts as a result of using exclusively CUTOFF flows makes sense, or if this sounds like an error. Thank you!
by (70k points)
if you have no elementary flows in your processes then you will not get impacts, so this is not an error.
Best wishes, Andreas