Thursday, February 4, 2010

Paper or plastic?


We aren't really going to delve into this question at this time (although in the LMAS we are working on sustainable packaging and how to add some clearer data on benefits/costs/tradeoffs in packaging choices - more on this in a later posting) but it is phrase that we are confronted by more often these days. I've seen hard core environmentalists stumble when asked this in the grocery store line. The truth is, not surprisingly, the answer is not simple. Depending on what you consider in your analysis, the answer may be different.

The phrase "paper or plastic" does point out, however, the often confusing choices we are faced with when trying to do the right thing.  We'll talk about this in this posting (and have a bit more casual conversation than the past few blogs.) The topic is really comparisons between comparable technologies and how they stack up in terms of green manufacturing.

At a recent conference in Europe on manufacturing engineering there was a growing presence of green and sustainable topics of discussion - ranging from the folks like myself who are looking a systematic ways to address, assess and act on green technology for manufacturing to others who are simply trying to figure out what is best. That is, paper or plastic?

A good friend and colleague from Brazil and a grinding expert, Dr. Joao Oliveira, gave an interesting paper on "Sustainability performance assessment of Grinding and Turning applications." Meaning, in a face off between grinding and turning - which is more "sustainable?" Logical question, right?

For those of you who are not manufacturing processing folks, grinding uses abrasives fixed on a wheel or other shape, rotated against a workpiece to remove small amounts of the workpiece with each engagement of the abrasive grain (the piece of abrasive) with the work. It is able to remove a lot of material of different types and create a very nice surface finish. So, many components in your automobile (like crank shaft, valves, etc.) or in jet engines are ground. Turning uses a single point tool made of a hard wear resistant material to remove metal in chips by engaging the workpiece (which in this case is turning, or rotating, hence the name) along the length of the material to be removed. Usually this has a higher material removal rate and can handle some more complex shapes but doesn't yield a fine a surface finish.

Both processes can use liquid for chip handling and temperature control, or not. Both require energy to drive the process and both are widely used in industry.

My friend Joao reviewed what the industry and researchers normally consider as the basis for  assessment of grinding vs turning:
- minimum setup time
- process flexibility
- material removal rate
- low residual stress
- process reliability
- quality of surface roughness
- dimension and shape accuracy
- low sub-surface damage, and
- environmental compatability

These are all production characteristics that are important to manufacturing productivity as well as quality. Things like residual stress (the tendency for a part to deform after processing due to an imbalance in the stress state from machining - like distortion or warping) and subsurface damage (excessive destruction of the basic material condition below the surface, and not visible, that can limit the life of the product in fatigue situations) as well as the others need to be controlled in any fair comparison or else the processes are not interchangeable.

It is important to note that one cannot generally simply replace grinding with turning (or the reverse) but there are many situations where they can be interchangeably used. For a fair analysis one needs to try to start with those situations.

Now, on to the "comparison." Dr. Oliveira put forward a set of "core sustainability performance aspects" that could be used as a basis of evaluation of these two process choices (assuming the results of the processes, according to the items above, are as close to the same as possible.) The figure below, from Dr. Oliveira, summarizes these aspects.


As you see, these aspects address the three pillars of sustainability- finances, environment, and social.

It is interesting to see the elements chosen for evaluating the sustainability of the processes. Certainly, cost is one piece. But we also see ROI considerations, energy, emissions/waste and effluents, labor relations, training, health and safety, and so on.

Some of these are easier to characterize than others. Labor relations was measured by average salaries of machine operators for the two cases. Health and safety was measured by job related accident data, noise levels and risk data. Apprentice training data was used to assess training differences as a social element. ROI info can come from investment calculations for comparable (in capability) machine tool costs of purchase, maintenance and disposal. End-of-life information was based on retrofit costs to return a used machine to productive use (a typical end use scenario for machine tools).

The study then used three "business" scenarios as a basis for decision making (The question to be answered was - Which of the sustainability dimensions is more relevant in this scenario?) :

Scenario 1: Economic return and environmental laws and standards followed
Scenario 2: Cleaner production strategy
Scenario 3: Sustainable production strategy

It is hard to give all the details of the analysis ... but, to summarize:

- When the environmental and social dimensions grow in relevance, turning has the larger advantage. This is likely influenced by the energy/unit of material processed, the size and nature of the "swarf" (or chips) which, for grinding, are very fine and often considered to be more hazardous, and, grinding has a potential for more severe accidents due to wheel problems, etc.

- The economic performance of grinding appears to be superior than turning, probably due to the cost/performance in which grinding gives a better surface quality, for example.

- With respect to health and safety, turning shows better performance considering health and worker safety indicators while grinding is superior with respect to salary and training.

- Overall, there was no real difference with respect to the two from a purely "social dimension" but one would conclude that turning was more "sustainable."

Dr. Oliveira was quick to point out that this is not the death knell for grinding! But, it is an interesting example of a sober comparison. And Oliveira's presentation was followed by one from a US company heavily into grinding, specially for very large components as in wind turbines, who showed that, in terms of specific energy (energy per volume of material used), grinding was way ahead!

So ... there you have it. As I stated in the beginning, depending on what you consider in your analysis, the answer may be different! This is not surprising, nor is it a problem. What is encouraging is that one can consider this wide range of elements around a process choice and get answers that are reasonable.

Finally, in the "odds and ends" department, I served as a judge for a recent business plan competition on the Berkeley campus. If you are not familiar with these, some organization or company pledges a reasonable sum of money to the team that has the best business plan for some new product, system, etc. Smart students flock to these like moths to a light.  In this case it was for socially relevant business propositions.

One of the teams represented a new venture in the bay area, BTTR (or Back to the Roots) which was, to me, as clear an example of a sustainable business as you can find (and see  http://www.bttrventures.com/ for more details.)

From their website they state that "BTTR Ventures, formed by two 2009 grads from  UC Berkeley, is turning one of the largest waste streams in America, the tons of coffee ground waste generated daily, into a highly-demanded, nutritious, and valuable food product – gourmet mushrooms. Currently, BTTR Ventures is transforming over 6000 lbs a week of coffee grounds from Peet’s Coffee and Tea into delicious oyster mushrooms, the BTTR Garden (grow-it-at-home mushroom kit), and rich compost (spent mushroom substrate)." So, diverting tons of waste from landfills, taking waste off the hands of companies that otherwise need to pay to get rid of it, growing, locally, a valuable product (specially in the gourmet bay area) - all positive steps.

And, I learned that at the end of the growing cycle, the rich compost can be used for soil to plant more crops ...  maybe even grow coffee! Talk about cradle to cradle.

I know, some of you are saying ... mushrooms?! But, examples of successes are important. Mushrooms today ... machine tools tomorrow!

6 comments:

  1. This is a typical optimization question: how can an output be maximized or minimized given certain inputs/resources and constraints. As described by professor Dornfeld, the difficulty lies in formulating and quantifying all the above. However, it is not an impossible task and, especially for engineers and finance people, it provides the most convincing arguments, by using quantifiable, traceable and comparable criteria.

    One of the most complicated problems is finding the boundaries for the optimization model or for the processes analyzed. For instance, should the sourcing of tools for grinding and turning be included? If the tools are procured locally from an OEM, are emissions from transportation and warehousing lower and the economic and social benefits for the local region higher? How would the substitution of technology be dealt with? Let's assume the conclusion is that grinding is better, but one uses turning at present. Would the disposal of turning machines, tools, re-training of operators, changing of all engineering documents, etc. constitute a waste from an environmental aspect, even if economically it would just be considered a sunk cost in the ROI model of replacement.

    I hope you will spend more time on this topic, which is one of the most difficult, relevant and fascinating in sustainable manufacturing.

    Thank you, Silvia

    P.S. Please allow me to answer the title question: neither. Please use cloth totes. I must admit I have no optimization model to prove it, but I can give an anecdotal proof: my two Fresh Fields totes have been in use for 14 years and the only maintenance required is washing.

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  2. Much work has been done in the area of sustainability in manufacturing in the United States. Virtually everyone agrees that much more needs to be done to improve energy efficiency in manufacturing, reduce waste, improve the development and management of the workforce, and design and manufacture products that use our scarce material and human resources in a more optimal manner.

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