1. SUBJECT:DESIGN OF MACHINE ELEMENTS TOPIC:DESIGN OF HELICAL SPRING SUMITTED TO:Mr. DHAVAL DARJI
MADE BY:
YASH SHAH( )
SHIVANG PATEL( )
SHIVANI SISODIA( )
RAKESH SODHIA( ) A.D.PATEL
JAYDEEP SOLANKI( ) INSTITUTE OF
TECHNOLOGY

2. A coil spring, also known as a helical spring, is a mechanical device, which is typically used to store energy due to resilience and subsequently release it, to absorb shock, or to maintain a force between contacting surfaces.

3. Outline Spring Functions & Types Helical Springs Compression Extension
Torsional

4. The Function(s) of Springs
Most fundamentally: to STORE ENERGY
Many springs can also: push
pull
twist

5. Some Review Parallel Series linear springs: k=F/y F k
nonlinear springs:
Parallel
ktotal=k1+k2+k3 y

6. Types of Springs
Helical:
Compression
Extension
Torsion

7. More Springs
Washer Springs:
                                           
Power springs:
Beams:

8. Helical Compression Springs
d diameter of wire
D mean coil diameter
Lf free length
p pitch
Nt Total coils

9. Length Terminology Lf La Lm Ls Free Length Assembled Length
minimum of 10-15%
clash allowance
Free Length
Assembled
Length
Max Working
Load
Bottomed
Out Lf La Lm Ls

10. End Conditions Na= Active Coils Plain Plain Ground Square Ground

11. Stresses in Helical SpringsF F
Spring Index C=D/d T F

12. Curvature Stress
Inner part of spring is a stress concentration
(see Chapter 4)
Kw includes both the direct shear factor and the stress concentration factor
under static loading, local yielding eliminates stress concentration, so use Ks
under dynamic loading, failure happens below Sy: use Ks for mean, Kw for alternating

13. Spring Deflection

14. Spring Rate
k=F/y

15. From the free body diagram, we have found out the direction of the internal torsion T and internal shear force F at the section due to the external load F acting at the centre of the coil.
The cut sections of the spring, subjected to tensile and compressive loads respectively, are shown separately in the Fig.1 and 2.

16. The broken arrows show the shear stresses ( τT ) arising due to the torsion T and solid arrows show the shear stresses ( τF )due to the force F. It is observed that for both tensile load as well as compressive load on the spring, maximum shear stress (τT + τF) always occurs at the inner side of the spring. Hence, failure of the spring, in the form of crake, is always initiated from the inner radius of the spring.

17. fig fig.2
The radius of the spring is given by D/2. Note that D is the mean diameter of the spring.

18. The torque T acting on the spring is
If d is the diameter of the coil wire and polar moment of inertia , the shear
stress in the spring wire due to torsion is

19. Average shear stress in the spring wire due to force F is

20. where, C=D/d, is called the spring

21. The above equation gives maximum shear stress occurring in a spring
The above equation gives maximum shear stress occurring in a spring. Ks is the shear stress correction factor.
To take care of the curvature effect, the earlier equation for maximum shear stress in the spring wire is modified as,

22. Where, KW is Wahl correction factor, which takes care of both curvature effect and shear stress correction factor and is expressed as,

23. From simple geometry we will see that the deflection, δ, in a helical spring is given by the formula,

24. THANK YOU