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Die springs are a robust type of helical compression springs consisting of rectangular wire. For the same value deflection, die springs carry 30% more load. These springs are designed to carry very high compression loads in hostile environments. Made mainly for punch presses to provide consistent and reliable resistance, die springs also find use in other industries.
Die Spring Operation
Utilizing rectangular wire with a rounded profile, die springs take advantage of the pitch between coils, allowing more wire per spring, reducing stress and enhancing working loads. Die springs work similarly to compression springs, where energy is stored when a load is applied and the spring tries to keep two components separate. Tighter threads directly indicate a stronger spring; chrome alloy wire also contributes to their high-load capability.
Die Spring Composition
Oil-tempered steel is a common material for die springs. Chrome alloys are also common die spring materials, with a chrome layer adding wear and corrosion resistance. Less common, but also much stronger, is chrome silicon or chrome vanadium, which improves dimension accuracy, minimizes individual stress points, and can operate in higher temperatures. These metals allow a pliable layer of colored vinyl to be applied to the spring, indicating a spring's working load.
Die Spring Configurations
Types of Die Springs
The most prominent difference in die springs is their color, which indicates working load. Unfortunately manufacturers do not agree to a uniform color code, so a manufacturer's reference chart should be utilized. Colors indicate a working range of light-load to extra heavy-load, depending on manufacturer. For example, below is a table of some die spring manufacturers and the color codes they use. Note that Century Spring Corp. further delineates their coding by spring material.
Die springs are wound in either a clockwise or counter-clockwise direction. Since the load is applied laterally, wind direction is usually unimportant.
Die Spring Ends
Die springs have two basic configurations for coil ends, closed and open-end.
Both closed-end die springs and open-ended die springs can be ground to create a flattened, perpendicular, reliable load-bearing surface. Below are examples of both open and closed-end die springs with grounded ends.
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Die Spring Specifications
Free length is the length of the die spring before it is subject to a load or preload.
Hole diameter is the outer diameter of the spring, or the overall width of the spring which will increase under compression.
Rod diameter is the inner diameter of a die spring, which is intended to slide over the guide rod in die machinery.
Wire diameter is the width of the wire used to make the coil.
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Die Spring Performance
Elastic limit is maximum compression a die spring can handle before deformity.
Preload is the distance of free length reduced by a consistent load on the spring.
Operating travel is the distance subtracted from the spring length after operating load has been applied.
Compressed length is the overall length of the spring after the preload and operating travel has been accounted.
Solid height is the length of the die spring when all adjacent coils are resting on each other under load.
Spring rate is the amount of load needed to compress a spring a measure distance. In die springs, this can be measure in thousands of pounds/kilograms.
Die Spring Safety
Die spring production is closely monitored to ensure quality springs under heavy duress, so die springs should not be altered in any way by a consumer. Corrosive elements like lubricants and chemicals may shorten a spring's lifespan, as will misaligned or mismanaged spring rods/guides. Die springs should be routinely cleaned, and all springs in a set should be replaced at the same time to maintain a uniformed yield.
Die Spring Applications
Die springs earn their name from their use in punch press die sets, where die sets provide pressure to hold the target material in place while the press perforates the substrate. If the die set were to provide no yield to the punch, the punch could be damaged; if it were to provide too much yield, the material would not be perforated. Die springs occasionally find use in transportation and agricultural industries.
Image credit: The Fabricator