advanced design options for custom springs

Advanced Design Options for

Custom Springs.

q  This webinar will be available afterwards at www.designworldonline.com & email

q  Q&A at the end of the presentation q  Hashtag for this webinar: #DWwebinar

Before We Start

Moderator Presenter

Paul Heney Design World

Alex Ek Helical Products

Company

A Webinar based upon the Helical Products White Paper

Wire Springs Versus

Machined Springs A Comparison

•  Founded in 1958 •  Invented Beam Style

Couplings Shown here

Wire-Wound Springs

Wire-Wound Springs

 Machined 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

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

Feature Section Wire Wound Springs

Machined Springs

Coils

Round yes no Square yes yes Rectangular, radial yes yes Rectangular, radial with high ratio no yes

Rectangular, longitudinal yes yes Rectangular, longitudinal with high ratio yes 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

•  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.

Wire-Wound Springs

Parts per minute

Wire-Wound Springs  Machined Springs

Minutes per part

Wire-Wound Springs

Parts per dollar

Wire-Wound Springs  Machined Springs

Dollars per part

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 Plating Wire Springs with materials such as zinc and nickel for corrosion protection is common practice.

Plating Machined Springs is less common because obtaining complete coverage over the edge corners is more difficult. The use of CRES, Inconel, and Titanium materials provides excellent corrosion protection for most Machined Spring applications. Machined Springs made from aluminum are typically anodized or coated to prevent corrosion.

Production time is the major influence in cost. Cost wise, Wire Wound Spring cost benefits 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 $5 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 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 working. Machined springs can be made from any material that can be machined.

Corrosion Resistant Steels moderate to high strength 17-4PH Stainless Steel 15-5PH Stainless Steel Carpenter Custom 455 X750 Inconel MP35N High Strength Maraging Steel C-250 C-300 C-350  

High strength alloy steel 4340 4340M Non-Steels 7075-T6 Aluminum (high strength) 7068-T6511 Aluminum (very high strength) 38644 Beta C Titanium (very high strength and corrosion resistant) Delrin 100 Ultem 2300

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

Flexure configurations for Compression and Extension Springs that resist rotation given axial deformation.

These techniques are

difficult, but not exclusively unavailable for wire springs.

Triple Available only in

Machined Springs

Double Available only in

Machined Springs

Single Available in both

Wire and

Machined Springs

Single Start Multiple Start

Some of the many Machined Spring

Attachments available for

Torsion Springs

Attachment Type

Wire Spring

Machined Spring

Tang (Radial) External and Internal

yes* yes*

Dual Tang (Radial) External and Internal

no yes**

Tang (Axial) External and Internal

yes* yes*

Dual Tang (Axial) External and Internal

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.

Questions? Paul Heney Design World pheney@wtwhmedia.com Twitter: @DW_Editor

Alex Ek Helical Products Company machinedsprings@heli-cal.com

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