Assembly January2011 : Page 65DFM analysis provides guidance on the most economical method of creating each part of the assembly. There are clear differences between lean and DFMA. First, a huge issue with lean is sustainability. Lean efforts often run out of steam because lean cannot correct latent design inefficiencies. But, a design change will. With a well-run DFA analysis, design changes should be unnecessary. The inefficiency will be identified and fixed before the design is released. Second, lean organizes how parts are ordered, fabricated, purchased and delivered. Material shortages will inevitably occur due to delayed delivery, discrepancies, handling damage and misplaced parts. By reducing part count, DFMA can eliminate many of these problems. Third, inefficient designs include parts that are hard to handle and difficult to insert. DFA analysis will highlight these problems, enabling engineers to do something about them before the production release. The message is clear: It’s vital to remove inefficiencies before the design is released. I learned this lesson early in my career, and I will never forget it. In the mid-80s, I was a member of the producibility group at a company that manufactured radar systems. One of my responsibilities was a small piece of a large system known as “The Grid Pulser.” If it sounds ominous, it was. It was about 2 cubic feet of electromechanical, high-voltage nightmare. The design was the most difficult to manufacture and assemble I have ever seen. After weeks of battling with design engineers, I relented and approved the design for production release, figuring I would fix whatever needed fixing after we commenced building the first unit. But, the problems were many, includ-ing excessive soldering, sheet metal misalignments, springs, tiny screws and dimensional discrepancies. When we finally reached the point where we could get one built in a week, the leader of the assembly team scowled at me. “What The original design for this ball valve called for 33 parts, some of which needed to be aligned in a fixture prior to assembly. was I thinking when I approved the release for manufacturing?” she asked. I was speechless and embarrassed. All I could say was “sorry.” Hindsight being 20/20, DFA analysis would have made all the difference. The design-related manufacturing waste needed to be removed before the parts were purchased or fabricated. A Case in Point To see how waste can be removed ahead of the design release, let’s look at a simple example involving a ball-valve assembly. The product consists of a valve body, fittings, seals and a valve ball. It’s designed to be operated with a separate actuation mechanism. The original design had 33 parts, and the assembly process required some parts to be aligned with a fixture. DFA analysis indicated that the valve would require 8.02 minutes to assemble. Labor costs were estimated at $4.29 per unit, material costs were $1,179.13 per unit, and fixture costs were $0.13 per unit, for a total of $1,183.55 per unit. The DFMA software suggested the following design improvements: Ⅵ integrate two mounting brackets into the valve body. Ⅵ integrate one of two fittings into the valve body. Ⅵ eliminate five washers. Ⅵ eliminate four threaded inserts. Ⅵ eliminate two O-rings. Ⅵ eliminate four hex nuts. Ⅵ reduce length of hex bolts to 0.5 inch. DFMA analysis suggested a number of improvements to the ball valve, including integrating a pair of mounting brackets into the valve body, eliminating five washers, and reducing the length of the hex bolts to 0.5 inch. www.assemblymag.com January 2011 / ASSE M B LY 65 Publication List Using a screen reader? Click Here |
