MD-8 Spring design

1 1 August 15, 2007 August 15, 2007118. 8. Spring designSpring designObjectivesObjectives Identify, describe, and understand principles of several types oIdentify, describe, and understand principles of several types of springs f springs including helical compression springs, helical extension springsincluding helical compression springs, helical extension springs, torsion , torsion tubes, and leaf Spring , and leaf Spring systems. design and analyze helical compression springs, including design and analyze helical compression springs, including compatibility with allowable with allowable stresses.

2 Develop necessary analytical tools for Spring design . Develop necessary analytical tools for Spring design . Understand the principles of operation of springs and how to anaUnderstand the principles of operation of springs and how to analyze lyze the energy being absorbed by springs. the energy being absorbed by springs. Review principles of design for other types of springs, such as Review principles of design for other types of springs, such as extension extension springs and leaf and leaf springs.

3 Select Select predesignedpredesignedsprings from manufacturerssprings from manufacturers catalogs and catalogs and incorporate them in appropriate them in appropriate 15, 2007 August 15, 200722 IntroductionIntroduction Springs give a relatively large elastic Springs give a relatively large elastic Application of springsApplication of springs Control of motion in machinesControl of motion in machines Reduction of transmitted forces as a result of Reduction of transmitted forces as a result of impact or shock loadingimpact or shock loading Storage of energyStorage of energy Measurement of forceMeasurement of forceAugust 15, 2007 August 15.

4 200733 Fig Common Types of SpringsFig Common Types of SpringsAugust 15, 2007 August 15, 200744 Fig Common Types of SpringsFig Common Types of SpringsAugust 15, 2007 August 15, 200755 Helical Compression springsHelical Compression springs Made from round wire and wrapped in Made from round wire and wrapped in cylindrical form with a fixed pitchcylindrical form with a fixed pitch Plain end Plain end Least expensiveLeast expensive Tends to bow sideways under loadTends to bow sideways under load Plain and ground endPlain and ground end Better mating conditions being flatBetter mating conditions being flat Likely to get entangled in storageLikely to get entangled in storage

5 Squared end Squared end SSquaredquaredand ground endand ground endAugust 15, 2007 August 15, 200766 Fig. Types of compression springsFig. Types of compression springs2 August 15, 2007 August 15, 200777 Types of compression springsTypes of compression springsPlain end Plain and ground Squared Squaredand ground August 15, 2007 August 15, 200788 Helical Extension springsHelical Extension springs Similar to compression springsSimilar to compression springs Manufactured with each winding touching the Manufactured with each winding touching the adjacent winding with a preset residual loadadjacent winding with a preset residual loadAugust 15, 2007 August 15, 200799 Fig.

6 Helical Extension springs Types of end hooksFig. Helical Extension springs Types of end hooksAugust 15, 2007 August 15, 20071010 Helical Extension springs Types of end hooksHelical Extension springs Types of end hooksAugust 15, 2007 August 15, 20071111 Torsion springsTorsion springs To resist turning motionTo resist turning motion Left or right hand motionLeft or right hand motionAugust 15, 2007 August 15, 20071212 Helical Compression Spring DesignHelical Compression Spring design Outside diameter, ODOutside diameter, OD Inside diameter.

7 IDInside diameter, ID Mean diameter, DMean diameter, Dmm Wire diameter, DWire diameter, DWW3 August 15, 2007 August 15, 20071313 Fig. Helical Compression Spring DesignFig. Helical Compression Spring design Free length, LfFree length, Lf Solid length, LSolid length, LSS Deflection, Deflection, August 15, 2007 August 15, 20071414 Spring RateSpring Rate Spring rate (k) is ratio of change in force to the Spring rate (k) is ratio of change in force to the change in lengthchange in length Force (F) exerted by the Spring isForce (F) exerted by the Spring is F = k (LF = k (Lff LLoo))

8 Appendix 12 Standard Spring selectionAppendix 12 Standard Spring selectionLFk =Eq 15, 2007 August 15, 20071515 Spring Spring animationanimationAugust 15, 2007 August 15, 20071616 Spring indexSpring index Ratio of mean diameter of a Spring to the wire from Ratio of mean diameter of a Spring to the wire from which the Spring is constructedwhich the Spring is constructed Spring index, CSpring index, C See Appendix 10 for wire sizes usedSee Appendix 10 for wire sizes usedWmDDC=Eq 15, 2007 August 15, 20071717 Spring indexSpring index Low indices result in difficulty with Spring Low indices result in difficulty with Spring manufacture and in stress concentrations manufacture and in stress concentrations induced by curvature.

9 Induced by curvature. Springs in the range 5 Springs in the range 5 C C 12 are preferred, 12 are preferred, while indices less than 3 are generally while indices less than 3 are generally 15, 2007 August 15, 20071818 Number of coils (Tab )Number of coils (Tab )DDWWNNaa+2D+2 DWWNNa a + 2+ 2 PNPNaa+2D+2 DWWS quared and Squared and groundgroundDDWWNNaa+3D+3 DWWNNa a + 2+ 2 PNPNaa+3D+3 DWWS quaredSquaredDDWWNNaaNNaaPNPNaaPlain groundPlain groundDDWWNNaa+D+DWWNNaaPNPNaa+D+DWWP lainPlainSolid heightSolid heightTotal Total coilscoilsFree lengthFree lengthType of Type of endsendsNa= Number of active coils; P = Pitch of coils.

10 DW= diameter of wire4 August 15, 2007 August 15, 20071919 PitchPitch Number of coils per Number of coils per inch of lengthinch of lengthm1D Ptan =August 15, 2007 August 15, 20072020 Spring materialsSpring materials SteelSteel Most commonMost common Phosphor bronzePhosphor bronze Cold wound for small size (<5/16 in)Cold wound for small size (<5/16 in) Wound from hot rolled barWound from hot rolled barAugust 15, 2007 August 15, 20072121 Types of MaterialsTypes of Materials Hard drawn high carbon steelHard drawn high carbon steel Oil tempered high carbon steelOil tempered high carbon steel Stainless steelStainless steel LightLight--duty springs duty springs Copper or nickel based alloysCopper or nickel based alloysAugust 15, 2007 August 15.