Wednesday, November 18, 2009

Is green lean? (Part II of a III part series)


(Or ... is lean green?)

In the last posting we started the discussion about lean and green. Lean has for sure been a hot topic for some time and now it is being closely connected to green manufacturing by a number of solution providers and others - usually with good reason.

Oh, and you might notice that I have inserted another part to the series! We need more time on this one so it is now a 3 part series.

We started by looking more closely at a manufacturing system comprised of discrete processes (represented as boxes) assembled into a system (connecting a number of boxes). each process box had certain characteristics of inputs and outputs and was responsible for adding some value to the product moving through the system. It was apparent that some boxes don't "add value" for various reasons but are still included in the process.

This was the preamble to a discussion about using the cycle time as "productively as possible."  In other words - have as little or no waste as possible. Not surprisingly, this is the main objective of green manufacturing. But the definitions for "waste" may be a bit broader than those usually associated with lean manufacturing.

I  referred to a definition of "lean manufacturing" by Wikipedia as a production practice that "considers the expenditure of resources for any goal other than the creation of value for the end customer to be wasteful, and thus a target for elimination." Further to this, we know that there are a number of approaches to "lean."  First approach is nominally the elimination of waste and the tools that assist in uncovering waste in the process and system and getting rid of it. A second approach is more aligned with the Toyota Production System (TPS), which focuses on the the "smoothness" of production and constructing a process with the capability to produce the required results by designing out process inconsistency (or "muri"). This is to be done while trying to maintain as much flexibility as possible since excessive constraints or rigidity often induce waste (as in excessive set up/change over time, high minimum run lot sizes requiring extra inventory or inducing poor response to customer needs, i.e. poor response to "pull.") I listed the seven types of wastes used in TPS in the October 7th posting as part of an initial discussion of TPS.

As an example of the second type of lean manufacturing, Comau recently introduced a "smart assembly" cell focused on the production of high precision complex assemblies as in valve trains for auto engines (for all the details see http://WardsAuto.com/ar/comau_smart_assembly_091109/index.html). Citing the large number of individual machines and process steps used in traditional valve train assembly (some 72 parts in one case at a cycle time of from 25-30 seconds per machine) and several minutes per assembly in total along with a large capital investment), Comau's smart machine replaces the entire line by four operations and a total cycle time of 54 seconds. And, the cell, designed for 325,000 cylinder head annually, requires only 223 sq. meters of floor space compared to 753 sq. meters. And the machine can be reconfigured quickly according to the report.

Although I doubt that Comau was motivated by green manufacturing concerns in its cell design, the cell will have an impact on energy consumption by nature of the reduced number of stand alone processes and, importantly, the tremendous reduction in floor space. (Unless, of course, there is some requirement for "pre-processing" of components to feed into the cell and their accompanying energy and floor space requirements! But, that's why we need to do a careful analysis.)

One of the main tools for the "first type of lean" is the value stream map - charting exactly the material and information flow in the system (and, of course, this can be applied to a wide range of manufacturing and services - it is not restricted to mechanical parts manufacture.) One popular reference on this is the book "Learning to See" by Mike Rother and John Shook (see http://www.amazon.com/Learning-See-Stream-Mapping-Eliminate/dp/0966784308), a practical hands on implementation guide to value stream mapping (VSM). They define a value stream as "all the actions (both value added and non-value added) currently required to bring a product through the main flows essential to every product: (1) the production flow from raw material into the arms of the customer, and (2) the design flow from concept to launch."

Sounds like a promising approach for introducing green manufacturing concepts to the enterprise. It starts with a very careful (and often tedious) assessment of the present state of your production system. This means outlining the process boxes (as illustrated in the last post) with the key interconnections and relationships, and collecting process data for each box. Rother and Shook give examples of this data as: cycle time, changeover time, uptime (on demand machine availability), production batch sizes, number of operators, number of product variations, pack size, working time (minus breaks), and scrap rate.

Many of these characteristics have green implications (meaning they are predictors of energy or resource consumption - like cycle time which can help define process energy. Or scrap rate which is an indication of efficiency of conversion of resources into product.

The procedures for VSM are well established. The use of VSM on green manufacturing analyses is not so well defined, although there are a number of good starts on the market. The best approach is to use the concepts of VSM and lean to compliment the development and operation of efficient manufacturing operations with the requirements of reduced energy and resource utilization - leading towards green and sustainable manufacturing. This will not always be a slam dunk analysis. There will be many aspects of lean (which requires or encourages exceptional levels of process flexibility) which will conflict directly with aspects of green. We can define some of these tradeoffs. Ultimately, the specifics will determine which wins out. But, importantly, this is an attempt to make the analysis more inclusive and systematic.

What we'll cover next time is a brief review of some of the approaches of "using lean to get green" as well as areas that may not be well covered by extending lean concepts to greening manufacturing. And these are usually related to the level of detail needed for tradeoff analysis and process design.

Stay tuned for part 3!


2 comments:

  1. Six sigma is one of the best concepts in improving the quality of the product and eliminate the problem. However, it has less concern on the cost involved. Therefore, now more and more company going to lean six sigma rather than only six sigma lean manufacturing

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