Have you considered setting up two operations one for each item? Of course you will have other issues when you do that as you will now have to ensure that the utilization of the operation is not double counted.
I work with a Plastic Injection Molding company in India that uses plastic injection molding machines to churn out plastic parts and I am curious to know what’s the business need you are trying to achieve by attempting to factor in such cost models?
I mean you need to track utilization of your machines and operators and you need to ensure that you load the set of products you need to make for a given shift, day or week optimally, but at the organization level it really does not matter much whether you load Product A on Machine X and Product B on Machine Y or the other way round - Product B on Machine X and Product A on Machine Y because whatever you save/lose on one of those combinations will be compensated for by a loss/saving on the other combination.
For a plastic injection molding operation (indeed for any business), I think the following principles apply:
- Focus on demand driven manufacturing, as against capacity driven manufacturing - The costs of non-optimally making a product that you can sell is far less than making perfectly optimally a product you cannot sell
- Map the products to the machines and machines to operators. So some products can be made on multiple machines, some machines can make multiple products and some operators can work on multiple machines
- Now decide on the mix of products that you are going to manufacture for a particular period (the mix of products is driven by demand. Not by capacity). If you want to ensure efficiencies, pick 120% (or 110% or 125%) of your capacity so that you only prioritize on the optimal mix of 100% for a given period. The balance 20% then slips over to the next period. Once this mix of products is chosen, your revenue for the period and the costs for the period are fixed, and how you load products onto machines or assign operators onto machines, does not have a large enough impact on your cost structure for the period. And you can assume that the products you manufacture convert into revenue as your mix of products to manufacture has been dictated by demand.
- Now from the mapping of Products to Machines and Operators to Machines, assign the Products to Machines and Operators to Machines in order of priority - least flexible to most flexible. So, let’s say in your Product Mix for the day, you have a few Products that can only be made on one machine. And a few operators that can only work on one machine. Assign these products to those machines and those operators to those machines. Now move on to the next set of products that can be loaded on to two machines. Now you need to run an iterative process that assigns one of the Products on a machine. As you do that, maybe another machine becomes inflexible as that machine has only one Product that can be loaded onto it. similarly for operators. Any programmer can try out various combinations and report a number and that number should ideally be the revenue potential of that Product Mix. Since you are working with 120% of your capacity, you will be able to get the most optimal mix of 100% for that production period. Plus if you are working at 100% capacity, the overall cost impact (cost to make the mix of products for the period) of loading one product on one machine is almost the same as loading that product on another machine). Now you will have multiple combination of revenue potentials and you pick the one that has the maximum revenue potential. The one’s that couldn’t be loaded on this production period, get a must-schedule flag for the next production period
I think it is important to focus on business outcomes before you decide to implement an ERP system. If you agree with this, it is obvious that you need to invest significantly in customizing ERPNext before it can actually make a strategic impact on your business. You may still want to implement ERPNext for the Purchase to Pay and the Order to Cash cycles and for arriving at data to build your models, but if you want to transform digitally your plastic parts manufacturing business that uses plastic injection molding machines, you need focus on building these models.
Not sure if this is helpful, but I thought I’d tap this out anyway.