A wave spring is a compression spring made of coiled flat wire with waves added along the coils to give it a spring effect. They can be used in place of conventional round wire compression springs in applications requiring tight load deflection in space critical applications. Generally, they occupy 30 to 50% of the compressed height space of comparable round wire springs offering more deflection with the same load specifications.
Wave springs are typically manufactured from a single filament of flat wire formed in continuous precise coils with uniform diameters and waves. They are manufactured with either plain ends (wavy) or squared-flat ends (shim ends). Generally, 17-7pH is used as the standard material for wave springs.
Some manufacturers offer single, nested, and multi-turn wave style springs. A single-turn wave spring with overlapping ends saves axial space so that more space is given for travel. The spring clings to the bore, which saves more radial space. The overlapping ends prevent radial jamming because a circumferential movement is allowed. The spring ends could move against each other so that the specification load at work height is always given.
Nested wave springs suit applications requiring higher forces to meet safety regulations, such as those in government or military applications. A nested-wave spring provides a higher load than a single-turn wave spring (a stamped wave washer) and uses the same radial space as a single-turn design.
Multiple-turn wave springs do not cling to the bore, because radial jamming affects the specified load at work height. If the design of the multi-turn wave spring results in peripheral movement of the turns against each other, this could render the spring unstable.
Compared to a single-turn design, bigger travel/deflection is possible because the deflection in total is split. Every turn has to tolerate less deflection compared to a single-turn design. Use of a multi-turn wave spring could also save 50% in axial space compared to a traditional coil spring. There is also no concern about torsional movements during the compression to work height as there is with a coil spring; a wave spring always provides its load in an axial direction. Very similar loads without big tolerances are provided at different work heights; in that way, the application could be easily adjusted to meet given requirements.
There are four critical factors when considering a wave spring –
- Constraints of the application: Bore/shaft, ID/OD etc.
- Load
- Working height at which the load is applied
- Material desired
If a spring is designed for a static application, make sure that the percent stress at working height is less than 100%. Springs will take a “set” or length loss in operation due to the high stress condition of the spring, if subjected to a higher stress.
If a spring is designed for a dynamic application, make sure that the percent stress at working height is less than 80%. Springs will take a set if subjected to a higher stress.
If the work height per turn is less than 2X the wire thickness, the spring will operate in a ‘non-linear’ range and actual loads may be higher than calculated.
- Number of turns must be between 2 and 20
- Number of waves per turn (N) must be in ½ increments
- Min. radial wall = (3X Wire Thickness)
- Max. radial Wall = (10X Wire Thickness)
It is not recommended to compress a wave spring to solid OD expansion and OD tolerance must be taken into account while designing a spring to fit in a bore and/or over a shaft.
Formulas:
Operating Stress
S = 3π PDm/4bt2 N2
Where:
S = operating stress
P = load in pounds
Dm = mean diameter in inches
b = radial width of material in inches
t = thickness of material in inches
N = number of waves per turn
Fatigue Stress Ratio
x = s-s1/s-s2
Where:
s = Material tensile strength
s1 = Calculated operating stress at lower working height (must be less than s)
s2 = Calculated operating stress at upper working height
Deflection
f = (PKZDm3/Ebt3n4) * (ID/OD)
Where:
f = deflection in inches
P = load in pounds
K = multiple wave factor
Dm = mean diameter in inches
Z = number of turns
E = modulus of elasticity
b = radial width of material in inches
t = thickness of material in inches
N = number of waves per turn
Spring Rate
R = P/f = (Ebt3n4/KZDm3) * (ID/OD)
Where:
R = Spring rate in pounds/inch
P = load in pounds
f = deflection in inches
E = modulus of elasticity
b = radial width of material in inches
t = thickness of material in inches
N = number of waves per turn
K = multiple wave factor
Dm = mean diameter in inches
Z = number of turns
Filed Under: Motion Control Tips
