Thursday, July 22, 2010

Degrees of Perfection, Part 3

Part 3 of a series

Let's talk about exergy (or available energy and useful work).

With, again, apologies that Wikipedia is not a scholarly resource, the definition of exergy from Wikipedia goes like this: "the exergy of a system is the maximum useful work possible during a process." So, a measure of energy is a measure of our ability to achieve the most with what we have - sort of a thermodynamic "buy to fly" ratio!

The paper by Gutowski I referenced at the start of this series on July 2  gives an excellent discussion of the fundamentals of applying this to manufacturing. Gutowski explains that exergy "represents the maximum amount of work that could be extracted from a system as it is reversibly brought to equilibrium with a well-defined environmental reference state." This is usually comprised of physical energy (the portion of the system that can be removed from the system while bringing it's state to a "dead state" at a reference temperature and pressure, and chemical energy. Chemical energy refers to additional available energy potential by bringing the chemical potentials of a compound to equilibrium with its surroundings. Gutowski explains where these reference state data come from. And there are a lot of equations.

Ultimately, you can derive an expression that represents the work rate of a system derived from the explicit terms representing the physical and chemical exergy of the system.

To illustrate exergy flows, an excellent graphical image of the global energy flow, accumulation and destruction starting with sources of energy (solar primarily) to the eventual natural and anthropogenic destruction (that is, due to human activities, as opposed to that occurring in the biophysical environments without human influence) is presented by the Stanford Global Climate and Energy Project. The site also shows the global carbon flow and accumulation. Fascinating stuff.

Now comes applying this to manufacturing systems.

We defined some time ago the characteristics of a "typical" manufacturing system represented by a series of "boxes and arrows" connected serially and representing the individual processes and the connecting material transport between processes. (See the posting of November 12, 2009 for a refresher).

We can replace (or augment) these arrows between boxes (or going into the box as in the process box discussion in the posting referenced above) with the systems mass, energy and entropy interactions. Recall that entropy is a measure of "disorder" in a system and it increases over time. A typical example of entropy increasing is ice melting. This from the work of the person most credited with putting forth the idea of entropy, Rudolf Clausius in 1862. There is a change from solid, molecularly ordered ice, to "disordered" water as the water increases in temperature over time. Temperature is usually a conjugate variable of entropy in thermodynamics.

So, each stage of a process can have material flows or interactions as well as work and heat interactions. And, with each step and its associated interactions, there will be losses. These are the materials wasted (and accounting for the buy-to-fly ratio) as well as energy losses. Gutowski's paper goes into this analysis in great detail.

First we need to identify all of these "losses" so we can determine the system performance. Then, we can look at how the losses can be avoided, reduced, or "recovered" to improve the performance of the system.

That is, we then have another "metric" for manufacturing system design, operation and optimization.

More to come on this next time. But, I have some small items of (potential) interest to conclude with this time.

I don't "tweet" and don't follow those who do … but if I did … I would have been madly tweeting away the 13th of July from San Francisco. I was invited to a very splashy event hosted by General Electric touting the successes of their "ecomagination" initiative and announcing a new $200 million "Power Grid Challenge" to spur innovation and entrepreneurship in the electrical grid. The show included the GE Chairman and CEO Jeff Immelt, assorted venture capitalist who are helping with the program (like Emerald Technology Ventures, Foundation Capital, Kleiner Perkins Caufield & Byer, and RockPort Capital), Dr. Arun Majumdar, head of ARPA-E (DOE's advanced research agency for energy technology), the President of PG&E, our local utility, among others. One of two panels was chaired by the editor in chaired of Wired magazine and they have a short writeup on the funding part.

You can also check up on this at a GE website which gives the details and a link to the "challenge" website. The site includes a "tracker" listing the latest statistics on ideas submitted, comments and votes on ideas. They even have an app for an iPhone so you can track this on the road.

The comments of the panelists, including Mr. Immelt, were very interesting. Much was said about the potential for "low hanging fruit" - for example, the use of monitoring technology so the consumer can see their energy use (sometimes called "smart meters) is claimed to drive an immediate 10% reduction in consumption. If you see how much you are using, you use less of it! This relates to energy dashboards for manufacturing we've discussed.

Immelt's comments about the business aspects of conservation and sustainability were exceptionally noteworthy. There was a lot of discussion about the inevitability of the jump to eco-consciousness and clean energy. No one can tell when it will happen but it will. The Wired article referenced above quotes Immelt as saying, with respect to companies like GE that want to stay ahead of the curve in terms of investing to maintain competitiveness and profitability,  "…it’s going to change in like, 15 minutes one day.”  “I guarantee that’s going to happen.” He followed on commenting that since no one can predict when this will happen - you have to plan for this in your business strategy.

Wow! I felt like he was speaking to me (or maybe that he'd read the blog!)

To top it all off, during a Q&A session the inevitable question came up about all this potential regulation and conservation (specially pricing to encourage reducing consumption) and the impact it will have on business. Immelt stated "you can have a complete industrial base, and it can grow, while reducing green house gas" emission. This has been GE's experience based on information presented as part of their Ecomagination initative. Granted, this is not your small or medium enterprise but a Fortune 100 company (actually a Fortune 6 company!) But that really makes the case for getting on with it!

Finally, I was interviewed on a very interesting radio program the other day. The program, hosted by Colonel Mason, is called "The Promise of Tomorrow" and deals with the business of emerging science and nanotechnology. We spoke about green manufacturing for quite some time. You can listen to the broadcast at his website - it is program #114 broadcast on July 19th (see archives). He also mentions our upcoming book titled Green Manufacturing: Fundamentals and Applications  from Springer due out late this fall. More to come on this of course. It is already listed on Amazon if you want to "pre-order" a copy!

Tuesday, July 13, 2010

Degrees of Perfection, Part 2

Part 2 of a series

The degree of perfection discussion in the last posting was centered on the term "buy to fly" ratio popular in the aerospace industry to indicate material utilization. I stated that we need to consider all the peripheral "stuff" associated with a product like electronics, appliances, clothing, food, etc. which usually comes packaged so we might want to consider a sort of "buy to fly" ratio for conventional products.

I am aiming in this series to get to a more engineering discussion of exergy (or available energy and useful work) to address this. But, I want to play with this  more fascinating buy to fly concept for manufacturing a bit more.

In fact, based on a number of comments I've received on this, others also are intrigued by the extension of buy to fly to more general manufacturing applications and processes. Ralph Resnick, an old friend from my early days of chasing burrs, now at NCDMM, suggested something along the lines of "energy to manufacturing" for tracking the useful output of the process for the energy input. So, let's explore some other ways to implement this idea.

Last week I attended a research review conference held at a machine tool builder's product design and development facility in Northern California (DTL/Mori Seiki). We toured the facility and I noticed a machine, the Mori Seiki NT1000 mill turn center, that touted it's abilty to provide the same functionality in a 95 x 106 inch (or 2.4 x 2.7 meter) footprint that other machines requiring twice the size deliver. That is, more output per unit of floor space occupied. This measure is traditionally emphasized in the semiconductor industry where space in high tech clean rooms is very expensive.

You might recall that some time ago (last December to be exact), as part of a discussion about ways to green machines and processes I did a virtual comparison of a set of individual machines versus a multi-function machine. This NT1000 machine is one of those. So, in addition to the efficiencies of eliminating the other standalone machines, the reduction in floor space gives extra benefit that can be measured in terms of plant environment, lighting, construction costs and materials, etc.

But, let's push this a little further. The NT1000 and similar machines by other manufacturers has an approximate volume of 15.5 meters cubed and a work volume of approximately 0.06 meters cubed - a ratio of almost 260 to 1. I was curious how this compared to machine tools in general meaning - do we always need that big of a machine to make small parts? (The NT1000 is designed for precision machining for medical devices, automotive hardware, watches, instrumentation, etc.)

A few years back I had a visitor in my laboratory from Doshisha University in Japan. Professor Hirogaki was working on "downsizing" machine tools and presented some interesting data on what is "typical" in the machine tool industry - but he measured the relationship between the weight ratio (machine weight to removal weight) as a function of removal weight (or mass actually). The figure below, from Professor Hiragaki, shows some typical results (again you'll need to click on this for details).

Here, the "target" is a weight ratio of 1 which we approach as the machine size increases. So this would suggest that bigger machines are closer to "perfection."

Interestingly, if we plot the similar ratio for the multi-function machine we've been discussing, the data fits this graph nicely (down in the lower left of the x-axis). The machine mass is given as 8000 kg and the equivalent steel workpiece volume (removal volume) is about 470 kg for a ratio of machine mass to work volume mass of 17. But, and this is a big but, the multi-function machine replaces about 3 equivalently sized machine tools. So, by this "buy to fly" comparison - it looks quite good.

Others are working in micro-sized machines to make micro-sized parts to address this "why do we need a big machine for small parts?" issue. I was curious about how they match up. One leading company, Microlution sells a machine (the 363S CNC 3 axis horizontal mill) with a working volume 2x2x2 in (or 5x5x5 cm - roughly) in a machine volume of 24x24x54 in (or 61x61x137 cm). Volumetrically, this yields a ratio of machine volume to work volume of, gulp, almost 3900.  I did not do the mass ratio to see where this fits into Professor Hirogaki's curve.

Recall that the "conventional" multi-function machine tool above had a volume ratio of 260 to 1.

So, there are limits to using these type of calculations perhaps. Trying to make machines the size of the work volume (the "target" ratio of 1 in Hirogaki's figure) may not be feasible for small footprint machines. The trick is ... how to make larger parts with small features on the small machines?

Finally, lest we beat up on ourselves in the machining business too much, let's look again at microelectronics. In 2002, researchers Eric Williams and colleagues published a paper in Environmental Science and Technology on the "1.7kg microchip: energy and material use in the production of semiconductor devices" The chip, a 32MB DRAM chip with a mass of about 2 grams, requires a total weight of secondary fossil fuel and chemical inputs to produce it and use it  estimated to be 1600 g and 72 g, respectively. This is a buy to fly ratio coming of 835.  They also consider the use of water and elemental gases (mainly N2) in the fabrication stage which are 32000 and 700 g per chip, respectively. Using only those water and gas fabrication numbers gives us a buy to fly ratio of 8175 - a new high!

This points out the need for considering some additional ways to measure our "degree of perfection." That is the perfect transition to our discussion of exergy next time in part 3 of this series!

By the way, this posting is our one year anniversary of the blog. Happy Anniversary! We started this blog last July 15th and, thanks to your reading and feedback, it has been a great year. Thanks for following!

Friday, July 2, 2010

Degrees of Perfection

Part I of a series

Enough with the personal life analysis and reflections on sustainability - let's get back to techy stuff!

I know I said in the last posting that this time we'll look at how some industries are doing and guidelines/strategies they are using to move up on the "sustain-o-meter." Well, let's start this process by another type of  self examination - dealing with the "degree of perfection" for manufacturing.

This discussion is going to take a few postings so we'll do this as a series starting, today, with one way to look at performance and some examples.

This term "degree of perfection" comes, originally, from a 1988 book by Jan Szargut and colleagues (Exergy Analysis of Thermal Chemical and Metallurgical Processes, Springer-Verlag, New York, 1988 - Amazon has it!). We'll get to exergy later. But, first, perfection!

The term "degree of perfection" is a ratio of useful products to inputs. The most recent discussion I read that referred to this was a paper by a clever person I've referred to before, Tim Gutowski at MIT, and others, in Env. Sci. Technology on "Thermodynamic Analysis of Resources used in Manufacturing Processes."

This term is used in a variety of ways and sort of represents a manufacturing "bang for the buck" measure. But before we delve into the thermodynamic aspects of this, let's look at conventional measures.

One of the more novel uses is in the aerospace industry where it is called "buy to fly ratio." Boeing, for example,  has a long history of tracking this value. Due to the peculiar requirements of aircraft components (demanding precision, unique shapes, incredible strength and fatigue requirements, etc.) many structural components (from wing spars to ribs) and many other parts, like landing gear, are machined out of large blocks of material. This results in most of the material going to waste. Buy to fly ratios in the 30's are common. This means, only a bit over 3% of the material purchased actually ends up on the plane. This waste for machined components is usually in the form of chips - which are recycled of course but discarded never-the-less.

In fact, some postings ago I referred to the role of precision in sustainable manufacturing under the topic of "Little things matter". I stated that if the machining process used in aircraft production is under control and precision manufacturing principles applied, a reduction in machining tolerances from +/- 0.006 inches to +/- 0.004 inches on the features of the airframe can account for a weight reduction of 10,000 pounds/aircraft and substantial fuel savings (8%). This allows an increase of 10% in passengers (engines don't need to carry as much plane), and substantial reduction in manufacturing cost of the aircraft (less material and improved assembly). That reduces the need for the original material (one can spec the rough material tighter if the machining tolerances are better controlled) but that will only reduce the waste slightly.

Recent trends in material costs, production time (even if you throw the chips  away you have to machine them in the first place) and performance have allowed aerospace companies to focus on this more. Switching to other materials, like high strength titanium, allows reduced part size with similar strength or other performance.

Switching to other production methods (beside machining away most of the material) such as laser welding of complex rib components can make huge savings. Using laser welding to produce a rib component that had previously been machined resulted in a reduction in the buy-to-fly ratio from 30:1 to 3:1 (see article).

Ditto for use of carbon fibers. But in this case, the concern is how to better reuse the fibers or replace processes that generate so much scrap. A recent article in Plastics Today discusses Boeing's recent efforts to find secondary outlets for carbon fibers reclaimed from aircraft production. The article states "For its purposes, Boeing is buying the highest grades of carbon fibers available: AS4, IM7, T8005, which can cost anywhere from $5-$50/lb as virgin materials. Of the amount it buys however, much of it ends up as scrap ... the buy-to-fly ratio for materials is less than 33%, meaning that 2/3 end up as production waste."

And to make matters worse, the fibers are usually encased in an epoxy matrix which requires processing to remove them.

So, what would you do if you were paying $50/pound for raw materials and then threw away 2/3's in your manufacturing process? Just so we don't forget that this is an not easy task, recall that a typical Boeing 737 has about 367,000 parts and even an average car as about 15,000 parts. So, we are not talking about toothpick production here.

And, we need to consider all the peripheral "stuff" associated with a product. Planes are delivered "au natural" if you will. But electronics, appliances, clothing, food, etc. is usually packaged (and sometimes several times for transport to distribution centers before it gets to the shelf) and that is part of the "buy to fly" ratio for conventional products.

Point made on the need to measure and track degree of perfection and manufacturing performance!

But, the original concept of degree of perfection does not speak specifically to material use ratios but useful output in terms of energy compared to input energy. The term used is exergy - a term you should have heard if you went to engineering school and took a thermodynamics course and may remember or - if you had a good physics course in high school.

Next time we will dive deeper into exergy and the concept of available energy and useful work. This forms an interesting basis for measuring the performance of manufacturing processes and material conversion/transformation and could allow us to look at the potential for greening and process improvement in a new way. This could be a better way to evaluate alternate technology.