Thursday, December 3, 2009

Diving Deeper - Green at the Process Level (Part I of II)


In the last three postings we discussed the potential for combining lean approaches to manufacturing process optimization with green analysis to get a double hit. The basis of this is, of course, that both are seeking to eliminate waste in the process and the system so should have a logical link. I noted that the linkage between lean methodology and green and sustainable production analysis shows great promise and should offer valuable insight to process improvement that is both economically and environmentally sound.

A staple of lean manufacturing is the value stream map. A brief overview was given of that with some references for more details. But there is more to this and we need to bore deeper into the process box to see the full potential (or, make the case for a more detailed value stream analysis than is often done today.)

The posting on November 12 (part of the series on "is lean green" - http://green-manufacturing.blogspot.com/2009/11/is-lean-green-part-i-of-ii-part-series.html) illustrated the process box representing a manufacturing process. There were a number of inputs and outputs identified, including:

Inputs:
 - Process energy
 - Machine/process “tare” energy
 - Process chemicals
 - Other process consumables
 - Machine/process operation consumables
 - Machine/process operation environment
 - Operator consumables
 - Operator operation environment

Outputs:
- Product
- Waste (heat, liquids, other consumables/tooling, etc.)
- Rejected/failed product

Later in that posting I linked several of these boxes together to create a system of production - that was the basis of our discussion on value stream maps. Many of these inputs are included in the value stream map for lean manufacturing analysis. Reviewing the list of inputs, and recalling the "Google earth view" of manufacturing that was presented in one of the earliest postings (see September 15th posting - http://green-manufacturing.blogspot.com/2009/09/green-manufacturing-technology-wedges.html), we know that we can look deeper into the process box than the rather summary data listed above. In fact, we can dig a lot deeper.

Allow me to elaborate! Take just two of the inputs - process energy and tare energy. This refers to the actual consumption of the machine but allocated to that which is associated with the actual production process (process energy) and that which is associated with the peripheral consumption just to keep the machine running (tare energy). This later one is called tare energy consumption from the similar concept of weight determination - the weight of the container holding the contents has to be accounted for when accurately determining the weight of the contents. The two will be dependent upon the process, the machine design, the sophistication of the control, the number of processes on the machine, the precision and accuracy of the machine, etc.

For the sake of simplicity, let's look at a machining process - like milling (but you can do the same for welding, injection molding, chemical vapor deposition, baking a turkey, etc.) We measure these two components by hooking up a power meter to the machine and noting the energy consumption when the machine is "on" but idle - not making any parts or, in the case of milling, cutting metal. We then start up the machine and begin cutting metal and again measure the power consumption during the cycle to create the part (or finish the process).

Interestingly, we can divide the performance up into two large camps - one in which the process energy dominates or, at least, is a significant component of consumption relative to tare energy, and another where the tare power dominates. We can represent these two regimes as in the figures below (and click on the figure to get a larger image).




We see in the figure on the left the circumstance where the tare energy dominates, Et >> Ep and, on the right, the opposite, Ep >> Et, process energy is much greater than tare energy. The strategies we'll want to follow to reduce energy will be entirely different! For the left case, our best interest is served if we try to make the part with the smallest cycle time possible since the process uses very little energy and slowing down only uses more. In this case we should focus on the machine design and operation to try to reduce the idle energy consumption.

In the right case where the process energy dominates, since the tare is much lower than the process energy, it will pay to look more closely into the details of the process to see how we can reduce energy consumption in the process.

There is also a small component labeled "embedded energy" that must be included to be complete. This represents the amortized "cost" of the energy it took to build, transport, and install the machine. We'll get back to this at a later date.

We''ll dig into these two cases in more detail next time. An important question we'll need to answer is - what is the unit of measure? Are we tracking power (or energy)/unit product? or power (or energy)/unit time?

(Blogger's note: I am liberally interchanging energy and power in this discussion. They are not the same of course but, I think, you follow the idea. I don't want to annoy the purists too much!)

Finally, in the last blog I mentioned that one approach to "lean and green" is offered by  Future State Solutions, Inc. (see futurestatesolutions.com). They have invited me to present a webinar on Thursday, December 10, 2009 11:45 PM - 12:45 PM EST. The topic is "Built to Last:  Sustainable Manufacturing" - go to  http://bit.ly/5RY3UC to register or you can register through the Future State Solutions website and see details of the webinar discussion.

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