Design for Manufacturing and Assembly Basics

Lean is most often associated with production. However, it can also be used in other areas, like design. Bridging the gap between design and production is design for manufacturing or design for manufacturability (DFM) and design for assembly (DFA), often combined into design for manufacturing and assembly (DFMA). Lean can also be combined with lesser-known topics like design for inspection (DFI) or, more recently, design for additive manufacturing (DFA). There are many more. Let me give you an introduction to the reasoning behind design for manufacturing and its “Design for X” variants before going into more details on how to do it in subsequent posts.

The Basic Idea

Piggy BankOne frequent company goal is to minimize the cost of their products. Some companies are even interested in the cost during the product’s actual use or even the disposal cost. Hence, it is of great interest to look at these costs, including material, labor, and overhead, not only where they occur but especially where the cost is determined.

Design for manufacturing and assembly optimizes not only the function of the product, but also the cost of making or assembling it, or even the cost across the entire life cycle of the product. The idea itself is probably quite old, and often combined with general cost reduction through optimizing the product for manufacturing and assembly. The method itself was formalized (and commercialized) by Geoff Boothroyd at MIT around 1977, and together with Peter Dewhurst they developed computer software to support this in 1981. However, most examples of design for manufacturing, etc. that I am aware of are still done manually.

Where Do the Costs Originate?

Happy MoneyWe need to distinguish where the cost is defined and where the cost happens. Product development is usually not so expensive compared to the production, and most expenses happen in production. Yet the product design fixes a lot of the costs that happen later during production, use, and disposal.

You may have seen a graph similar to the one below somewhere before. It shows the total cost (not per part) throughout the product life cycle. To be more precise, it shows when you have how much influence on the total cost, and its inverse, the cost that is committed over time. It also shows the cost that actually happened. While this graph is pretty generic, it does contain a lot of truth. As it turns out, while product design does not cost that much itself, it does fix a lot of the cost later on. Most of the cost happens during production, but production itself has little influence on the costs.

This graph is very generic, and the curve for your product may look slightly different, but the basis remains the same. Changes in the curve depend especially on product complexity and production quantity. If your product is complex, you have more development cost than a simple product. If you produce a large quantity, the production cost will be larger than for a small quantity. More for inspiration than for hard facts is the graph below showing you the total incurred cost for different scenarios.

It is often claimed that 80% (or sometimes 70%) of the total cost is determined by development, albeit a good source is never cited, simply because there is none. Barton et al thoroughly debunked this claim. Ulrich et al actually calculated that design causes 50% of manufacturing cost for coffee makers (all sources below). Yet, even influencing only 50% of the total cost is quite a potential. Also, before you get excited about reducing total cost by 50%, this won’t happen. No matter how good your design is, you still have to produce the goods and have production costs.

Yet, if you can reduce the cost even only by 5%, it will be a huge savings. I participated in a design for manufacturing and assembly workshop where the participants initially were highly skeptical, since they believed that they had a very finished design with no further potential for improvement. After the workshop they were flabbergasted that we were able to find potential for almost €3 per product that retails for €60. They completely reversed their initial view of “a waste of time” to “one of the best workshops we ever did.”

Design for X

Above I mentioned quite a few variants of a general design for excellence, or more generally “Design for X.” But there is more. Here is the result of a brief search for variants of design for X:

  • Design against corrosion damage
  • Design for additive manufacturing
  • Design for assembly
  • Design for cost
  • Design for inspection
  • Design for lean manufacturing
  • Design for logistics
  • Design for manufacturing/manufacturability
  • Design for manufacturing and assembly
  • Design for minimum risk
  • Design for postponement
  • Design for quality
  • Design for reliability
  • Design for safety
  • Design for short time to market
  • Design for six sigma
  • Design for standards
  • Design for test/testing
  • Design for variability

There are probably a lot more. Don’t try to cover them all. Sometimes it is just a fancy name for some sort of optimization, but then, all of them are just methods to optimize the design for one aspect or another besides the product functionality. Please do note that it is quite possible to look at more than one during the same workshop, but you should not overdo it. If you focus on everything, you focus on nothing. The most common workshop is a combination of design for manufacturing and assembly, since they are also thematically very close.

Within this short series of posts I will also focus more on design for manufacturing and assembly. My next post will look at the basic prerequisites for a design for manufacturing and assembly workshop, and subsequent posts go into more details on the different levers and aspects that can be used to improve the design. Until then, stay posted, and go out and organize your industry!

Sources

5 thoughts on “Design for Manufacturing and Assembly Basics”

  1. Thanks for bringing up the importance and value of DFM and DFA. They both are critical and enablers for target costing. The processes worked well in the garment industry as well as hard goods manufacturing. The cost reductions were significant.

  2. Thankyou Prof. Christoph for interesting insights. The Concept of Lean applications in “Design for X” may be highly impactful in Apparel Manufacturing.

    Just a thought, I believe, in the Graphs the Costs are considered for total Quantities. Like Simple Product (High Volumes) shall cost more than Complex Product (Low Volumes). Suppose, if we take Unit Cost then most probably (due to the Economy of Scale) unit production cost for Simple Product (high volumes) may be lesser than Complex Product (Low volume).
    Please enlighten.

  3. Hello Dr. Tiwari, that’s what I meant with the y-axis label “Total Cost”, i.e. the cost for all products, not the unit cost. if it would be the unit cost you would of course be correct.

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