Important Considerations When Designing a Custom Spring

Important Considerations to

Consider When Designing a

Custom Spring

This webinar will be available afterwards at

www.designworldonline.com & email

Q&A at the end of the presentation

Hashtag for this webinar: #DWwebinar

Before We Start

http://www.designworldonline.com/

Presenter

Gary L. BoehmHelical Products Co.

Moderator

Mary GannonDesign World

A Webinar based upon the Helical White Paper

Wire Springs versus Machined Springs,

A ComparisonAuthored by

Gary L Boehm PE

Helical Products Co Inc, Santa Maria, CA

© 2014 Helical Products Co, Inc. 4

• Founded in 1958

• Invented Beam Style

Couplings

Shown here


Wire-WoundSprings


Springs

Wire-WoundSprings


Machined Springs

Springs


• Wire Springs existed before the

Industrial Revolution

• First Machined Springs in 1960’s

• Now- New designs created daily

• Both are manufactured with CNC

controlled machines

Wire Wound

Springs

Machined

Springs

Precision

10% yes yes

1% maybe yes

0.1% no maybe


Wire Wound Springs are typically made from medium and high strength steels, nickel alloys, titanium and stainless steels that gain their strength predominately from heat treating and cold reduction.

CRES (Corrosion Resistant Steels), moderate to high strength

a 17-4PH per AMS 5643

b 15-5PH per AMS 5659

c CC455 per AMS5617

d X750 Inconel per AMS 5667 and 5670

Very high strength steel

a C300 per AMS6514

Other materials of interest

a 7075-T6 Aluminum (high strength)

b 7068-T6511 Aluminum (very high strength)

c 38644 Beta C Titanium (very high strength and corrosion resistant)

d Delrin 100 (machinable plastic)

e Ultem 2300 (machinable plastic)


0


1

A long, torsion Machined

Spring using a dime for size

comparison.

Wire Springs can be larger.

A small, compression

Machined Spring.

Wire Springs can be

smaller.

Some of the many

Machined Spring

Attachments

available for

Compression and

Extension Springs


Some of the many

Machined Spring

Attachments

available for Torsion

Springs



Feature SectionWire Wound

Springs

Machined

Springs

Coils

Round yes no

Square yes yes

Rectangular, radial yes yes

Rectangular, radial

with high rationo yes

Rectangular, longitudinal yes yes

Rectangular, longitudinal

with high ratioyes yes

Slots

Zero width yes

yes, with

special

process

Zero width w/prestress yes no

0.100 inch yes yes

Over 0.250 inch yes maybe

Number

of

coils

1 coil minimum yes yes

20 coils yes yes

50 coils yes maybe


Percentage of Compression

based upon Free Length

Wire Wound

Springs

Machined

Springs

10% yes yes

20% yes yes

30% yes yes

40% yes yes

50% yes maybe

60% yes maybe

70% maybe no

80% maybe no

90% no no

In a closed-ground wire compression spring, the active coil (that in which

strain energy can be stored) extends to the very end of the spring.


In a Machined, Compression Spring, the active spring coil stops short of the

spring end relegating at each end one slot width and one structural width

unavailable for storing energy.


Production time is the major influence in cost. Cost wise, Wire Wound Springs benefit greatly from short production times. Machined Springs cannot approach the low cost of wire product. It would be very surprising to find a very simple and inexpensive Machined Spring, produced in high quantities costing less than $1 USD each.

However, these value enhancements related to Machined Springs usage helps to validate their usage:

• Integrated attachments

• Enhanced performance or functionality

• Via Multiple Starts, more uniform elastic reactions, and better control of internal moments

• Higher precision

• Reduced assembly and acquisition efforts

• No sound creation from coil contacts

• No debris created by coil contacts

Without one or more of these benefits being present, there is usually little justification of employing Machined Springs in place of Wire Springs.


Wire Springs Machined Springs

Wire Springs are often shot peened for enhanced fatigue resistance. This process is possible because the gap between the coils is typically wide enough to permit passage of shot that can condition the inside of the opposite coil, as well as the outside of the coils.

Machined Springs typically have coil slots that are too small for the passage of shot. Hence, shot peening is not common. To insure fatigue resistance, features such as stress relief holes and slots can be added to the slot ends. Selecting high strength, fatigue resistant, materials is also a significant benefit.


Wire Springs Machined Springs

It is not uncommon to plate Wire Springs with materials such as zinc and nickel for corrosion protection.

Plating Machined Springs is uncommon because of the existence of sharp edge corners that typically receive insufficient coverage. The use of CRES and titanium materials provides excellent corrosion protection for most Machined Spring applications.

Machined Springs made form aluminum are typically anodized or coated to prevent corrosion.


Flexure configurations for

Compression and

Extension Springs that

resist rotation given axial

deformation.

These techniques are

difficult, but not

exclusively unavailable for

wire springs.



TripleAvailable only in

Machined Springs

DoubleAvailable only in

Machined Springs

SingleAvailable in both

Wire

and

Machined Springs


Single Start Multiple Start

Some of the many

Machined Spring

Attachments

available for Torsion

Springs



AttachmentType

Wire Spring

MachinedSpring

Tang (Radial)

External and Internal

yes* yes*

Dual Tang (Radial)


no yes**

Tang (Axial)


yes* yes*

Dual Tang (Axial)


no yes**

Dual Pin Holes (Axial) no yes**

Geometric ID Shapes

(square, hex, etc)

no yes**

*Force at distance requiring force resolution

**Pure moment drive

Multiple Start Machined Springs have a

history of providing effective Single

Degree of Freedom elastic elements for

such systems.

Double Start Springs set the baseline

for such usage, but Triple Start Springs

are the gold standard because of their

uniform stiffness in all lateral

directions.

© 2014 Helical Products Co, Inc.27

Thank you for sharing your time with us…

And now…

Does anyone have a question?


Questions?

Mary GannonDesign [email protected]

Phone: 440.234.4531

Twitter: @DW_MaryGannon

Gary L. BoehmHelical Products [email protected]

Phone: 877-353-9873

mailto:[email protected]

mailto:[email protected]

Thank You

This webinar will be available at designworldonline.com

& email

Tweet with hashtag #DWwebinar

Connect with Design World

Discuss this on EngineeringExchange.com

http://www.designworldonline.com/

http://www.engineeringexchange.com/

Important Considerations When Designing a Custom Spring

Engineering

Transcript of Important Considerations When Designing a Custom Spring