Tuesday, June 21, 2011
Where did all the material go?
Some time ago (July last year to be specific) we discussed the concept of "buy to fly ratio" used to track the ratio of the amount of material that an aircraft manufacturer starts with to the amount that actually ends up on the airplane. It was part of a discussion on degrees of perfection and was a led in to a series of discussions about how to actually measure the impact of what we are doing in terms of "greening" manufacturing. That is, if we keep track of everything - are we ahead at the end of the day or not?
The buy-to-fly ratio came out of the aerospace industry but has applicability to manufacturing broadly. Unfortunately, numbers for this ratio are not too impressive and I cited some published from aircraft manufacturing that are in the 30's - meaning 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.
And here is the issue. Even with recycling of "wasted" materials in manufacturing we use energy and resources. So, recycled content is not free!
Recall Henry Ford's comments cited in one of the first postings for this blog on "why green manufacturing" two years ago: "… we will not so lightly waste material simply because we can reclaim it — for salvage involves labour. The ideal is to have nothing to salvage." This was published in his book "Today and Tomorrow" (1926).
At that time Henry was probably generating his own electricity from "waste" steam from steel or coke making or wood chips from his wooden frame production so he wasn't even thinking about the cost of energy. And, I don't think the concept of global warming/CO2 was a topic of discussion then.
(Note: Today's Ford Motor Company is fully engaged in energy and resource efficiency in both product and manufacturing. You can find their CSR report online)
So, back to the chips (or the "hole").
The International Society of Industrial Ecology just held their annual meeting in Berkeley. One of the attendees was Professor Julian Allwood from Cambridge University and we had a chance to meet up and talk a bit about his work under the banner of "WellMet 2050." I introduced this project in a blog earlier this year on 'resource dieting.' He is a creative thinker about green manufacturing challenges and firmly grounded in processes and analysis.
One of the big 4 themes of their research is "less metal, same service" and Julian was discussing, basically, the "buy to fly ratio" problem. He focusses specially on metals in his research.
The details are documented in the "Going on a metal diet" report from the study and you can download it from their website.
One focus of the study as part of the "less metal, same service" is on reducing the scrap in manufacturing. There is a common misconception (or, at least, benign neglect) that recycling hits the reset button on inefficient use of material. This is a big mistake!
Inefficient use of materials is usually referred to as yield loss. That is, in the course of normal manufacturing (whether you are making airplanes, automobiles, semiconductors or polo shirts) material gets 'left on the foor.' Shapes are cut out of sheets and the bits around the shape that need to be held in the press, or due to standard size sheets larger than the part being produced, etc. are left over.
At best these leftover pieces are large enough to be used for other pieces (a concept called "nesting" in manufacturing). At some point there is not enough material left to be used productively in the operation and it is discarded and, hopefully, recycled.
Recall that recycled can mean anything from remelting and added to virgin material for making new sheets of material (as used here); mixed with other similar materials to produce lower quality metal; or collected and dumped somewhere (recycled to you - waste to the collection organization).
Take a peak at the Ricoh Comet circle from prior blogs to see the various paths of "down cycling" of materials.
The metal diet report states boldly "Going on a metal diet has much greater potential for CO2 emissions abatement than the pursuit of further efficiency measures in an already efficient liquid metals production process." So Professor Allwood's research team is focussed on the data to prove that statement.
First, let's define what we mean by yield. The figure below, from Allwood's "Going on an energy diet" shows how yield is determined based on the ratio of
metal going on to a downstream process over the sum of all process inputs. That which is not part of yield along the process chain is lost.
Now, how about the connection between the yield losses and the embodied energy of the material? Allwood has used a very novel way to display this that pretty clearly points out the challenge.
In the graph below, also from Allwood's "Going on an energy diet" report, the horizontal, x, axis shows the "yield path" of a material amount during processing through several steps. That is, starting with 1 ton of liquid metal, it plots the mass remaining after each step of the process. This, essentially tracks the buy to fly ratio across several process steps. The vertical, y, axis shows the cumulative increase in embedded energy with each process step. Constant embodied energy contours are shown.
Reading this figure, for a specific product, tracks the consumption of energy and the loss of mass of the product (relative to the original raw material input at the start). You'd start with the liquid metal, cast it into billets or other shapes, rolled/formed into finished raw material stock (like sheet or bar) and then further processed by stamping or cutting, then finishing, etc. to yield the final product. These process steps are the "process AB" and "process BC" shown in the individual lines of product manufacture on the chart. You'd use as many process steps as needed to complete the product.
One interesting thing to note is that if you want to maintain constant embodied energy in the manufacture of the product you need to follow the constant energy contours.
We will see that this is the real manufacturing engineering challenge for green manufacturing!
In the next posting we'll show some examples of real products from this study (like a beverage can or a car door panel) to illustrate the use of this energy yield vs material yield chart.
Once we are comfortable with the metrics for measuring our success (or documenting our failure!) we'll talk about engineering tools to overcome this scenario in product design and manufacture.
Sunday, June 5, 2011
Or, keep your eye on the hole!
My father had an interesting expression he would bring out when my brother and I would be worried about something or, more likely, be interested in a "short term gain" in some venture. And, mind you, he lived through the depression and many years in the Army Air Force during the war in the Pacific so had the authority to use these kinds of expressions.
He'd remind us "as you wander down life's highway, whatever be your goal, keep your eye upon the donut, and not upon the hole."
I always liked that and believed it put a lot of things in perspective as one's career moves along. I've used this from time to time when the situation seems relevant.
But, I found an exception to this wise advice ... or I think I found an exception. We recently spent some time on a vacation trip to the Grand Tetons and Yellowstone National Parks in Wyoming. Along with the impressive scenery (and impressive amount of snow still around at this late date in June) I was also struck by the efforts of the concessionaires (those who run the lodging, shops and restaurants) in these parks to "go green."
One in particular, Xanterra (they are a descendent of The Fred Harvey company), in Yellowstone has taken this very seriously. They even have a sustainability report on their corporate website and state that they are working to reduce their footprint in "energy, carbon emissions, waste, development, foods, transportation, and water."
This is good. There is nothing more troubling, to me at least, than wasting a lot of fuel, water, electricity to see nature while trying to live greener.
So, the hole.
One of the things Xanterra puts in the rooms in their lodges in Yellowstone, Grand Canyon, Zion, Crater Lake, etc. is bath soap with a hole in the center! They call it "waste reducing exfoliating body cleanser" - but it's soap.
The soap is called Green Natura (see the website if you don't believe me) and the package, made of recycled materials and printed with soy inks of course, says that the soap is "ergonomically shaped waste reducing" and has been designed to "eliminate the unused center of traditional soap bars."
So, this is neat. It has the size and shape of a more standard bar of soap without all the material that usually gets wasted/thrown away after a stay in a hotel. I like that. I know I should use the liquid soap dispensers in many bathrooms/showers which leave nothing (except the dispenser, etc.) to be wasted but there is something enjoyable about using a real bar of soap. I must note that there are some "other opinions" about whether or not this is really green (see, for example, the green soap site.) But, for the moment, let's focus on the hole!
Unfortunately my father is not around to see this product … it might cause a ripple in his "don't watch the hole" adage. But, to be fair, he never threw away the center of the soap. In our family there was no wasted soap - you just stick the last bit on top of the new bar and get on with it.
This, of course, does not work in hotels.
In this case, removing unused/un-needed/unwanted material is good. Actually, you might have seen this before in your undergraduate engineering studies (if you are an engineer!) where you learned to design simply supported beams with varying cross-sections to accommodate moments due to loading that cause the moment to be greater at the mid-span than at the ends. Making the beam of uniform shape along its length would add unnecessary weight and waste material.
There are better examples for real products, like automobiles, that tie into our green discussion. According to what I've seen recently, a new GM car, the Cruz ECO, has higher gas mileage due to reduced weight among other improvements.
The Cruz Eco article posted on Motley Fool (and based on an article by Wolfgang Gruener, of Conceivably Tech titled "Chevy Cruze Eco: 58 MPG, No Hybrid Magic") has shown remarkable fuel economy for a "conventional" internal combustion engine vehicle. According to the article the most significant changes implemented in the Eco are:
• Weld flanges reduced 1 mm to 2 mm in length
• Metal gauge thickness reduced by 1 mm
• Lightweight 17-inch wheels
• Low-resistance tires
• Revised gear ratios (particularly first, second, and sixth gears).
• Unique front fascia with deeper front air dam
• Electronically controlled front air shutter that closes at higher speeds to reduce drag
• Metal pans below the car to improve air flow
• No spare tire (!)
• Lowered suspension
• Trunk-lid spoiler
The article states that these changes reduce the vehicle weight by 125 pounds (compared to 3,134 pounds for the Cruze LS) and 214 pounds less than the Cruze 1LT. Also, according to GM, the reductions in things like weld flanges saved several pounds and smaller wheels save 21 pounds compared to the 1LT version. Other improvements dealing with aerodynamics reduced the Eco's drag coefficient by about 10% below the other Cruze models. That means it can move through the air with less resistance - better gas mileage.
The article states that all these changes resulted in a notable improvement in fuel efficiency. In tests run by the author of the article, stop-and-go driving yielded 32.3 MPG, and suburban driving with a mix of streets ended up at 39.8 MPG. Extremely careful cruising on the interstate at exactly 55 MPH resulted in a "stunning" 57.9 MPG.
You might recall the discussion here in the September 2009 posting about precision manufacturing and green. In that posting we discussed a Boeing example of tolerances (posted under the title "Little things matter"). A reduction in machining tolerances from +/- 0.006 inches to +/- 0.004 inches on the features of an airframe accounted for a weight reduction of 10,000 pounds/aircraft and substantial fuel savings (8%). This allowed 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). And less fuel consumption means reduced CO2 impact from operation.
So, we've seen examples of this before.
This clearly shows some nice leveraging of manufacturing but this leads to a follow on set of questions:
- can we do this more generally for manufacturing processes/machinery/tooling as well?
- what kind of analytical or engineering tools can we use to formalize the design of such processes/machinery/tooling?
We'll focus on that in the next posting - part 2 of "keep your eye on the hole!"