Page 24 - MetalForming September 2009

Tooling Technology The
Die-Spring Evolution
Die springs play a critical role in determining the quality of metal stampings, and die-spring manufacturers continue to improve spring shape, tensile properties, coatings and tolerances
to keep up with increase demands from metalformers.
No stamping tool or die would work as designed without good-quality, dependable and durable die springs. In the case of wire die springs, these helical compressive-type springs resist applied compression forces, or store energy in a push mode. While the
Jack W. Adoline is technical and customer service manager, and Olivier Kunckler is marketing and e-commerce manager, Associated Spring, Raymond, Maumee, OH: 419/891-9292, www.asraymond.com.
earliest die springs were of a straight cylindrical shape made from round wire, producers soon introduced rectangular- shaped wire—increasing energy-stor- age capacity, decreasing height, and improving space efficiency.
Spring characteristics such as hole and rod fit, free length and squareness affect overall tooling performance. Now, as advances in spring materials, spring- manufacturing equipment and coat- ings allow stampers to realize dramatic quality improvements.
Key Parameters:Tensile Strength, Wire Shape
The tensile strength of the spring wire determines the spring’s energy- storage capacity and its relaxation. The ideal spring material has a high tensile strength and high elastic limit.
Initially, die springs were typically fabricated using music wire or hard- drawn round wire. Then, in the late 1980s, some manufacturers transitioned to chrome-vanadium steel wire and chrome-silicon wire, which delivered increased tensile strengths and elastic limits to increase energy-storage capac- ity and reduce spring relaxation. The next generation of enhanced spring materials—chrome-vanadium and chrome-silicon combinations—further improved mechanical properties. How- ever, metalformers considering imple- menting these advanced-material springs should carefully consider the cost-benefit equation, since die springs often outlast the life of the tools.
Over the last 20 years, metalforming companies have transitioned from using die springs coiled from round wire to springs constructed with shaped wire— a rectangular or keystoned crosssec- tion. Most die springs manufactured
BY JACK W. ADOLINE AND OLIVIER KUNCKLER
Spring manufacturers continue to implement more reliable and capable in- process SPC controls and advanced CNC coiling equipment to supply consistent- quality-level springs to metalformers, with zero defects.
22 METALFORMING / SEPTEMBER 2009
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