Injection moulding - handle production waste

Question

Hi all!

I am using the injection moulding process from Ecoinvent in SimaPro.

In the database information they state that 1kg of the process results to 0,994kg of injection moulded plastic. To simulate 1kg of injection moulded plastic I add therefore 1,006 kg of injection moulding. Since the process will create 0,006 kg of production waste, should I edit anything in the process to account for the waste management of this mass? I assume that the production waste is not reused internally, but sent to waste instead.

Thank you!

Answer 1

Hi,

interesting question. The ecoinvent process you describe is a 'service' process. As stated in openLCA, you can see the documentation "This process contains the auxillaries and energy demand for the mentioned conversion process of plastics. The converted amount of plastics is NOT included into the dataset." So, you add this to a process where you model 1 kg of input plastic. In the documentation of ecoinvent 2, you will find the original details. To my understanding, you add this service process to your respective injection-moulded plastic (in the same amount as the input materials) and also add your own scrap (and not scale to 0,994). This is also the way ecoinvent themselves do it (see, for instance, the "heat pump production, diffusion absorption, 4kW, future" process).
Edit: It seems like the EoL for the packaging is not considered, but the plastic scrap is.

Hope this helps

Answer 2

As Jonas wrote, it is a service process, so you add the service with the same amount as your input products for the plastics (for example 2.0 kg of a certain type of plastics and 2.0 kg of the injection moulding service).

What most do not know and what you can only see with unit processes:

Services in ecoinvent already contain the losses from production / the residuals / the waste left overs. You can see in the example above that the service has 0.006 kg (rounded here) of waste plastic mixtures in the output. This is the "surplus" that is also in the input of the service process with 0.0036 kg polypropylene, granulate and 0.0017 kg polyethylene, low density, granulate and masses from fillers. So the services will already "take care" of losses and surplus material, so that modeling is easier and only the material+service has to be added both with the same amounts and with the amounts that are actually transformed / output of the service. Feel free to add additional losses to your processes if needed.

In other services it is more obvious that the surplus/waste is already included. For example in "metal working, average for copper product manufacturing" you will find in the service 227g of copper (22.7%) coming in and 227g getting out as a recyclable, to model the surplus/waste in the service.

Comments

Hi and thank you both for your responses!

I of course understand that I have to combine the injection moulding service with the respective amount of raw material. What confuses me is that this service says that 1k of the service delivers 0,994kg of injection moulded plastic. In case I want to model for 1kg of injection moulded plastic, shouldn't I adjust the input for the plastic material and the injection moulding service? Also, what if I want to model for, say, 10% of material losses during injection moulding? Shouldn't I in that case adjust my input values?