Torsion Spring Design Type

The Torsion Spring design type is a full-featured mathematical model enabling the engineering design of round wire helical coil torsion springs.

This section presents material unique to the Torsion Spring design type. The more general material available at Spring Design Topics provides important supplemental information.

Torsion spring moment-deflection diagram

             |                / 
     M_2 ----|---------------/  
             |              /:
       M     |             / :
             |            /  :        ODOP:Spring
       O     |           /   :          Names
             |          /    :  
       M     |         /     :          Torsion
             |        /      :          spring
       E     |       /       :  
             |      /        :  
    M_1 -----|-----/         :  
             |    /:         :  
       N     |   / :<------->:------- Stroke
             |  /  :         :  
       T     | /   :         :  
             |/____:_________:_________
        L_Free     :         :  
                  L_1       L_2
             Deflect_1     Deflect_2
 
             D E F L E C T I O N

Torsion spring moment-deflection point names

The torsion spring moment-deflection points and associated names are:

	moment (torque)	deflection	length	outside diameter	inside diameter
free:			L_Body	OD_Free	ID_Free
point 1:	M_1	Deflect_1	L_1
point 2:	M_2	Deflect_2	L_2
max safe:

	stress	factor of safety
free:
point 1:	Stress_1
point 2:	Stress_2	FS_2
max safe:

point 1 = minimum operating load point 2 = maximum operating load

Torsion spring dimensions

The following diagram may be of some assistance in interpreting the names associated with various dimensions of a torsion spring.

Torsion Spring Names

Independent Variable names:

Name		Description
Wire_Dia		wire diameter
OD_Free		outside diameter in the free condition
Coils_T		total number of coils, including inactive coils
M_1		load (moment) at point 1 (minimum operating load)
M_2		load (moment) at point 2 (maximum operating load)
Coil_Spacing		extra space between each coil

Dependent Variable names:

Name		Description
Mean_Dia		mean diameter of spring coil in free condition; (OD_free + ID_Free)/2
ID_Free		inside diameter in free condition
Coils_A		number of active coils (turns; includes arm deflection)
Rate		spring constant - moment per unit deflection
Deflect_1		deflection caused by M_1
Deflect_2		deflection caused by M_2
L_Body		length of body in free condition (without ends)
L_1		spring body length at minimum operating load (M_1)
L_2		spring body length at maximum operating load (M_2)
End_Angle_Free		relative angle between arms in free condition
Stroke		angular displacement from point 1 to point 2
Weight		weight of spring; wire density * wire volume
Spring_Index		spring index; the ratio: Mean_Dia/Wire_Dia
End_Deflect_All		End deflection allowance (equivalent coils); calculated from L_End_1 + L_End_2
Stress_1		bending stress at point 1
Stress_2		bending stress at point 2
FS_2		static factor of safety at point 2; The ratio of allowable stress at point 2 to the calculated stress induced by the load at point 2 (Stress_Lim_Bnd_Stat/Stress_2).
FS_Cycle_Life		factor of safety based on the Soderberg endurance limit calculation. This figure uses the allowable endurance stress (Stress_Lim_Bnd_Endur) to include fatigue considerations. Refer to additional discussion in the Cycle_Life topic.
Cycle_Life		expected cycle life based on a calculation using the "modified Goodman method". This value is approximate. Refer to additional discussion in the Cycle_Life topic.
%_Safe_Deflect		the percentage of available deflection consumed at load point 2
Force_Arm_2		Force produced at distance of Arm_2; See: Torsion spring dimensions
Energy		change in elastic potential energy between point 1 and point 2

For additional information: Cycle_Life

Calculation Input names

Name		Description
Spring_Type		character string used only as a label
Prop_Calc_Method		Property Calculation Method controls how material properties and allowable stresses are determined. See also: Materials.
		1 - indicates values come from materials table; allowable stresses will be calculated as a function of Wire_Dia.
		2 - indicates tensile and allowable % are supplied by the user; allowable stresses are calculated.
		3 - indicates allowable stresses are supplied directly by the user.
Material_Type		selects an entry in the material table. Is used to determine allowable stresses when Prop_Calc_Method is 1. Otherwise is ignored.
ASTM/Fed-Spec		character string used only as a label to further identify the origin of material property data
Process		character string used to identify the manufacturing process. It is normally controlled by the material selected from the material table. Values are usually Cold_Coiled or Hot_Wound. See also: Hot_Factor_Kh (below).
Heat_Treat		Selects heat treatment process. Controls use of Kb - stress correction factor
Life_Category		This value reflects the user's input about shot peening and required cycle life. It is input to the calculation of FS_CycleLife. See also: Cycle_Life
Density		wire density; weight per unit volume
Elastic_Modulus		Modulus of Elasticity modulus (E) (a.k.a. Young's Modulus)
Hot_Factor_Kh		empirical correction factor applied to hot wound modulus
Tensile		tensile strength
%_Ten_Bnd_Endur		allowable fraction of tensile strength for bending endurance (cyclic load); See also: Cycle_Life
%_Ten_Bnd_Stat		allowable fraction of tensile strength for bending static load
Stress_Lim_Bnd_Endur		allowable stress limit; cyclic application (bending)
Stress_Lim_Bnd_Stat		allowable stress limit; static application (bending)
End_Type		This selection indicates end configuration: Tangent ends versus User Specified ends.. See also: Torsion spring end types
Arm_1, etc.		See: Torsion spring end types

For additional information:

Values in reports

Other values calculated and displayed in the Reports include:

Name		Description
Wire Length		total length of wire required to manufacture the spring, not including any waste
Safe Load		The load supported by the spring at maximum allowable stress (Stress_Lim_Bnd_Stat).
Pitch		distance between the wire centers of adjacent coils, measured in the free state (Wire_Dia + Coil_Spacing)
Weight/1000		weight of 1,000 springs
Stress Ratio		ratio of minimum stress to maximum stress (Stress_1/Stress_2)
Kb		stress correction factor; (see: Heat_Treat above)
Helix Angle		angle, in degrees, of the spring helix relative to a perpendicular to the spring axis

End Types

For torsion springs, the Calculation Input End_Type has the following possible values:

     Torsion   
     
1    Tangent
2    User_Specified

In the current version of ODOP:Spring, no calculations depend on these End_Type settings. They are for display only.

Separately, the values of Arm_1, Arm_2, L_End_1, L_End_2, XLen_1 and XLen_2 are available to describe end conditions. This diagram may be helpful.