Wave washers, also referred to as wave springs, are wavy metal washers designed to provide a compensating spring force or absorb shock when under load. Many design variations have evolved to best serve these basic functions.

SolidWorks: Wave Spring Washer Video Credit: This is Mylife / CC BY 3.0

Wave washers are one of several types of spring washers. They are defined by their wave-like appearance and their ability to bear a load as they are deflected in a linear range.

Operation / Mechanics

Wave washers are a load bearing device distinguished by the load that they can bear and their deflection range. They possess an operational limit described by a load rating or yield point. The load is a force that exhibits stress on the washer. In response to the imposed stress the washer undergoes some amount of strain. Axial strain, referred to as deflection, is a function of the load and described by a spring rate.

Spring Rate

The spring rate is the capacity of the wave washer. It describes a relationship between the load applied and the deflection of the washer. The spring rate is directly proportional to the fourth power of the number of waves on the washer. Hence, higher capacity wave washers will have more waves. It is also controlled by the thickness of the wave. Increasing the thickness of the washer will increase the load capacity and decrease the spring rate, or the amount of deflection per pound of force applied.

Hooke's Law

F = -kx

Where:

F = Load

x = Deflection "Displacement"

k = Spring Rate "Spring Constant"

Yield Point

The yield point is a value describing the maximum force that the spring may absorb. This marks the end of the elastic range, breaching this point will cause the wave washer to experience permanent deformation.

Image Credit: WCL Company

Load / Deflection Equations

The following formulas give a rough estimation of the expected load and deflection of single and multiple wave washers. 

Single Wave Washers

Load equation:

P= S(D - d) t^2t / D 6

Deflection equation:

f= S D^2 / 6 E t

Multiple Wave Washers

Load equation:

P = S N^2 t^2 (D - d) / .75 (D + d)

Deflection equation:

f = S 2 D^2 / 12 E t N^2

Where:

N = Number of waves
P = Load (lbf)
E = Modulus of elasticity of material (30,000,000 P.S.I. for steel)
t = Material thickness (in.)
f = Deflection (in.)
d = Inside diameter (in.)
D = Outside diameter (in.)
S = Maximum allowable stress (200,000 psi for steel)

 Equation Credit: WCL Company

Applications

Wave washers provide a compensating spring force and sustain a load or absorb shock. This characteristic can be used to pre-load shafts or bearings, absorb shock, or compensate for dimensional variations.

Pre-loading Bearings

Wave washers can increase bearing life and performance by applying a load on the face of the bearing. The axial force applied helps reduce bearing noise and eliminate vibrations by ensuring positive contact between the ball bearings and inner / outer collars. 

Image Credit: Smalley Steel Ring Company

Compensation for Dimensional Variations

Wave washers can compensate for dimensional variations in mechanical assemblies. Any amount of gap or misalignment that would allow unwanted movement or vibrations to occur can be secured by the use of a wave washer. Bolts or screws can also use wave washers in order to prevent the loss of friction that would allow the fastener to back out.

Image Credit: Mountain Tamer

Shock Absorption

Wave washers can be designed to operate as a compression spring. They have a linear load - deflection range and can absorb impulses or other non-linear forces. They can be the compression spring of choice when dealing with space limitations as they generally have a smaller deflection range when compared to other types of compression springs.

Compression Wave Spring | Image Credit: STON Springs

Types

There are several basic types of wave washers with distinguishing features including: single turn, crest-to-crest, nested, and interlaced wave springs.

Single turn wave springs are the simplest form of a wave washer. They consisted of a flat washer that has been formed or pressed into a wave form. They are most commonly used in static applications.

Single Turn Wave Spring

Image Credit: SDP/SI

Crest-to-crest wave springs are a series of pre-stacked waves, where each crest is in contact with the trough of the adjoining level. This design increases the deflection range, allowing them to function as a compression spring in dynamic or static applications.

Crest-to-Crest Wave Spring

Image Credit: Smalley Steel Ring Company

Nested wave springs are a series of pre-stacked waves where each wave is superimposed parallel to the adjoining level. They are formed from a single continuous filament of flat wire. This design increases the load rating of the spring while maintaining a low profile with minimal deflection.

Nested Wave Spring

Image Credit: TECH SPRING MANUFACTURING CORP.

Interlaced wave springs are a hybrid of crest-to-crest and nested configurations. They are formed with two or more filaments nested together where adjoining waves are stacked crest-to-crest. This design has an improved fatigue resistance and capacity with a moderate deflection range.

Interlaced Wave Spring

Image Credit: Smalley Steel Ring Company

Selection Criteria

Important parameters to consider when specifying wave washers dimensions, material, number of waves and load rating.

Dimensions

Important dimensions to consider when specifying the size of wave washers include inside diameter, outside diameter, thickness and overall height.

• The inner diameter "ID" is a nominal dimension describing the bore of the washer and is often used to describe the size of a bolt or cylinder that can fit inside the washer when it is compressed and not the actual measurement of the unloaded washer.
• The outer diameter "OD" is a nominal dimension describing the circumference of the washer when it is compressed and is not equal to the diameter of the unloaded washer.
• Thickness is the shortest measured cross-section of a wave in the washer. This is also the thickness of the wire filament used to make the washer or a multiple of that dimension for nested and interlaced wave washers.
• The overall height refers to the axial width of the unloaded washers. This is an axial dimension measured from the crest on one side of the washer to the trough of the wave on the other side of the washer. 

Image Credit: HK METALCRAFT

Materials of Construction

Common materials of construction for wave washers include spring steel, stainless steel, nickel base alloy, and copper base alloy or bronze. 

• Spring steel is any of a variety of steels that are normally of the high-carbon or alloy type. They are used in the manufacture of springs because of their high tensile properties. The type of spring steel used depends on the application and type of spring. They range from plain carbon grades in the range 0.5% to 1.00% C., to chromium, chromium-vanadium, nickel-chromium-molybdenum, silicon-manganese and silicon-manganese-chromium-molybdenum types. 
• Stainless steel is chemical and corrosion resistant and can have relatively high pressure ratings. 
• A nickel base alloy is a metal alloy composed of nickel and one or more other metals, such as copper. 
• A copper base alloy is metal composed of copper as the main alloying metal and one or more other metals, such as tin, zinc, or phosphorus. 
• Sintered bronze is a porous material, which can be impregnated with oil, graphite or PTFE. Sintered bronze is not suitable for heavily loaded applications but is useful where lubrication is inconvenient.

Number of Waves

A wave washer is comprised of two or more waves where the load rating of the washer is directly proportional to the fourth order of the number of waves in the washer.

Load Rating

The rated or working load is the maximum or optimal working load for the product.  Wave washers are often rated at 50% compression.

Resources

WCL - Spring Washers: Descriptions & Design Considerations

Smalley Steel Ring Company - About Smalley Wave Springs

BORRELLY - Wave Spring Washer

Image Credit: Smalley Steel Ring | Unified Supply | Tech Spring Manufacturing Corp.