1. Design Procedure of Helical Compression Spring

2. Process
Step.1 For the given application, estimate the maximum spring force P and the corresponding required deflection δ of the spring.
Step.2 Select a suitable spring material and find out ultimate shear strength from design data hand book (table no.11.8).Calculate the permissible shear stress for the spring wire by following relationship
τ = .30 to 0.50 τult

3. Process….
Step.3 Assume a suitable value for spring index c from design data book (Fig.11.1).
Step.4 Calculate the Wahl-factor by the following equation
K = 4c ………….11.2b
4c c
Step.5 Determine wire diameter d by equation
τ = K x (8Wc)… a
πd2

4. Process…
Step.6 Determine mean coil diameter D by the following equation
D = cxd ……………………………..11.2c
Step.7 Determine the number of active coils n from axial deflection of the spring by following equation
δ = 8WD3n …………………………11.5a
Gd4
In general modulus of rigidity G for steel wires is N/mm2

5. Process…
Step.8 Decide the style of ends for the spring depending upon the configuration of the application. Determine the number of inactive coils. Adding active na and inactive nina coils, find out the total number of coils nt by the following equation
nina = nt - na
Step.9 Determine the solid length of the spring by the following equation
ls = nt x d
Step.10 Determine the angular deflection of the spring
θ = 16WD2n…………………………….11.4
Gd4

6. Process….
Step.11 Assume a gap of 0.5 to 2mm between two adjacent coils, when the spring is under the action of maximum load. The total axial gap is given by,
Total gap ntgap = (nt -1)x gap between two adjacent coils.
In some cases, the total axial gap is taken as 15% of the maximum deflection.
Step.12 Determine the free length of the spring by the following equation
Free length = solid length + total gap+ max deflection
lf = ls + δmax + ntgap ………………11.20

7. Process…
Step.13 Determine the pitch of the coil by the following equation
p = Free length
(nt -1)
Step.14 Determine the rate of spring by following equation
k = Gd4
8D3 n …………………………11.5c

8. Process.. Step.14 Energy stored in helical springs of circular wire
U= V x τ 2 …………………………….11.4
4GK2
Where V volume of the spring wire
= Length of the spring wire x cross sectional area of wire