Disc Springs Come Through in the Clutch for DeWalt
The custom spring costs just a few pennies more than the original spring.
The DeWalt Industrial Tool Co. is well-known for its high-quality power tools and accessories used in manufacturing, construction and woodworking. Established in 1936, the company has been a subsidiary of Stanley Black and Decker since 2010. Its product line includes corded and lithium-ion drills, impact wrenches and circular saws.
In 2012, DeWalt decided to introduce a right-angle drill (DWD460) that is powerful yet lightweight, compact and portable. Engineers designed the drill with a mechanical clutch that limits maximum torque output to 70 ft-lb. Without the clutch, the drill would produce 175 ft-lbs of lock rotor torque at the spindle and transmit it directly to the operator.
However, the tool’s compact size limits the amount of space available for the clutch. To maximize clutch thrust capacity in a small space, engineers decided to use a disc spring rather than a conventional coil spring. The disc spring also improves reliability, enabling the drill to meet DeWalt’s three-year performance warranty.
A disc spring is a conically shaped, washer-like component designed to be axially loaded. Its deflection for a given load is predictable, making it easy to determine minimum life cycle.
The spring can be statically loaded continuously or intermittently, or dynamically subjected to continuous load cycling. It can also be used individually or in multiples stacked parallel, in series or in a combination thereof.
For the prototype drill, DeWalt used a low-cost disc spring. The drill performed very poorly during testing, achieving less than half the targeted life cycle. Analysis indicated premature fatigue failure of the spring for two reasons. It was made of low-quality material in a flawed manufacturing process, and it was exposed to higher-than-expected stress.
DeWalt’s lead engineer on the project then turned to disc spring manufacturer and supplier Spirol International Corp. for help. After evaluating the drill’s performance objectives and design constraints, Spirol’s application engineering team determined that a low-cost, poor-quality standard disc spring was not sufficient for such a high-performance application.
The team developed a custom disc spring that is made of high-quality material, but costs just a few pennies more than the original spring. The custom spring also requires secondary operations for greater durability.
DeWalt replaced the original spring with the custom one and tested the drill. It exceeded the company’s life cycle requirement, enabling DeWalt to proceed with tool production.
Spirol disc springs meet all DIN 2093 performance, tolerance and quality specifications, as well as DIN 2092 design criteria. The company stocks standard size discs having outside diameters from 8 to 200 millimeters. All springs are available pre-stacked and shrink wrapped with a perforated tab for easy assembly.
For more information on disc springs, call 860-774-8571 or visit www.spirol.com.