DFMA 2010 Forum on Design for Manufacture and Assembly, Day Two

June 16, 2010
Nick Dewhurst, one of the co-founders of Boothroyd Dewhurst Inc., spoke on why companies tend to shove designing costs out of the product to the back burner. Design for Manufacture and Assembly (DFMA) software should be part of lean manufacturing, at the ...

Nick Dewhurst, one of the co-founders of Boothroyd Dewhurst Inc., spoke on why companies tend to shove designing costs out of the product to the back burner. Design for Manufacture and Assembly (DFMA) software should be part of lean manufacturing, at the design phase. DFA -- take out the number of parts; DFM -- an early cost-estimating tool. He says that a typical product cost breakdown shows piece parts cost is usually around 72%; overhead about 24%; and labor only 4%.

Reducing piece-part cost has a big impact on taking costs out of the final product, he says. The software works in supplier costing (what should individual parts cost?); product costing (what can I do to influence cost in minor things such as changing a draft angle?); and product simplification (what can we do to simplify the product structure?).

Influence of design on supply chain: Example part with screws, end plates, motor. Many companies don't have a standardized BOM, they contain different sets of data. What is missing is a column that says what an item should cost. Filling a column like that in would be a basis for a powerful analysis.

On product costing: Consider a sand casting design. What if we changed the process? Let's have a data-driven discussion on the effects of offshoring a design to India, for instance. One company found out it can die cast a part in the U.S. for the same cost as doing so in India.

For product simplification: Go through an analysis and slash the number of parts, remove suppliers for the supply chain; cut assembly time; and cut labor costs. Average reductions in DFMA cases is 50% (for assemblies).

What exactly is "lean," says Dewhurst? Lean is a production process tool. However, good design practices are a way to get more.

Basic definitions: product - a thing produced by labor; process - a series of actions directed to some end.

Consider an example component: A sheetmetal assembly consists of part A and part B. Have to take both parts, move them to another area of the factory, then workers put rivets in them to attach the parts. To produce this product requires two turret press setups, two brake press setups, and several workers. Employing lean techniques might cut about 2% of these costs to get a part for around $1.93. Companies should apply DFMA first, then lean, says Dewhurst. This can slash total part cost.

Next speaker: David Vranson, ITT Aerospace Controls His mantra: "There is nothing so useless as doing eficiently that which should not be done at all" (Peter Drucker). He says the father of the Toyota production system wanted to preserve value with less work and learn how to find out where waste comes from. Vranson says he doesn't like the way lean is used today: Companies just like to tell their customers they are lean as an excuse to transfer costs.

Traditional waste categories in lean are: defects; over-production; transportation -- people, equipment, or products waiting for process; over-processing; hunting for parts; and inventory. The idea is to prevent waste from being introduced into the manufacturing enterprise in the first place. He was working as a design engineer for a defense contractor years ago making an assembly with numerous amounts of fasteners, all sizes and shapes, different types of soldering, etc. He had to cave in and let it go to production, thinking he would fix anything wrong then. Big mistake. It was too hard to make the changes.

Current example: He performed a DFMA analysis on a ball valve assembly with 33 parts including mounting brackets, shaft, valve body, bolts, nuts & washers, ball, and seals. 33 finished parts cost $1,183.55. Analysis showed that taking the body, two brackets, and one fitting and then casting and machining it would eliminate four nuts, five washers, and two O rings, for a total of 15 parts. The 33 parts now cost $980.00.

DFMA provides an indicator of what manufacturing costs should look like. Here is how it can affect waste:

Defects - fewer parts, fewer defects; simplifies assembly.

Overproduction - eliminates piece parts; eliminates batching.

Transportation - fewer parts, less movement.

Waiting - single axis part construction.

Overprocessing - assembly is easier to build.

Motion - need fewer tools to put things together.

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