The Extension Spring Component Generator is designed to calculate plain extension with a correction for additional bending. It uses four basic spring states:

Free	The spring is not loaded (index 0).
Preloaded	Applies the smallest working load to the spring index (index 1).
Fully loaded	Applies the maximum working load to the spring (index 8).
Limit	The spring is deflected to the solid length (index 9).

The Calculation tab has two modes: design and check. During spring design, the wire diameter, number of coils, and spring free length L0 are designed for a specific load, assembly dimensions (L1, L8, H) or for the spring diameter and material. In the check mode, assembly dimensions or spring loads are calculated for the specific spring.

In the Extension Spring Component Generator:

On the Design tab, set parameters for an extension spring design such as the spring length or hook types.
On the Calculation tab, set parameters for calculation of an extension spring, loads or spring materials for example.

TipThe calculation procedure is described in the Engineer's Handbook for both modes and for the calculation in metric and English units. There are other instructions for designing extension springs there.

Procedures

Design extension springs

Insert extension springs

On the ribbon, click Design tab Spring panel Extension.
In the Design tab, select the options for designed extension spring. For example, select the type of load or hook types.
Switch to the Calculation tab and enter the calculation values. For example, select the type of strength calculation and set the loads and spring material.
Note: Click More in the right lower corner to display additional options for spring calculation.
Click Calculate to perform the Calculation.
Calculation results are displayed in the Results area. The inputs that fail the calculation are displayed in red (their value does not correspond with other inserted values or calculation criteria). The description of calculation results is displayed in the Summary of Messages area which is displayed after clicking the chevron in the right lower part of the Design and Calculation tabs.
Click OK to insert a spring to the Autodesk Inventor assembly.

TipClick

Results to display the HTML report.

Edit springs using Extension Spring Generator

Open the Autodesk Inventor assembly with the already inserted Design Accelerator extension spring.
Select the extension spring, right-click to display the context menu and select the Edit Using Design Accelerator command.
Edit the extension spring. You can change the type of the load, change the spring material, or change the size of the spring. If you changed calculation values, click Calculate to see if strength check was OK. Calculation results are displayed in the Results area. The inputs that fail the calculation are displayed in red (their value doesn't correspond with other inserted values or calculation criteria). Reports of the calculation are displayed in the Summary of Messages area.
Click OK.

References

Extension Spring Component Generator - Design tab

Sets parameters for design of an extension spring.

Access:

Ribbon: Design tab

Spring panel

Extension

Spring Reference Image

Click to display an image with the basic spring dimensions.

The image updates when the spring diameter is changed to Inner, Median, or Outer.

The image does not update for changes in length, hook type, hook length, spring diameter value or wire diameter.

Model

Use this section to specify a placement options, and the type of spring loaded state.

NoteWhen the full placement is specified, the graphical preview with appropriate dimensions, and spring type is created.

Installed Length	Min. Load angle between arms is set based on the minimum deflection of working arm.
	Work Load angle between arms is set based on the maximum deflection of working arm.
	Max. Load angle between arms is calculated based on working force.
	Custom angle between arms is set by a user.
Min., Work, Max. Custom Load Length	This edit field changes according to the load selected in the previous drop-down menu. Enter or measure the spring length.
Coil Direction	Select the direction of the coil, left or right.

Spring Wire

Enter or measure the wire diameter value.

Spring Diameter

Use the drop-down list to specify which spring dimensions are the inputs for the calculation, and which dimension is calculated.

Outer - Mean and inner spring diameters are calculated for the specified wire diameter and outside spring diameter.

Median - Inner and outside spring diameters are calculated for the specified wire diameter and mean spring diameter.

Inner - Mean and outside spring diameters are calculated for the specified wire diameter and inside spring diameter.

NoteAccording to this selection the name of the following edit field changes to Inside Diameter, Mean Diameter, or Outside Diameter.

Start

The spring ends are typically the same on both ends. This is especially true for stock springs. However, you can select different start and end types for compression springs.

Hook Type	Use the drop-down menu to select type of start hook. See the Hooks of extension springs chapter in the Engineer's Handbook for hooks calculation formulas.
Hook Length	Enter the length of the hook. For Non-specified Hook Type, if you enter 0, the coil end is natural (no bend).

End

The spring ends are typically the same on both ends. This is especially true for stock springs. However, you can select different start and end types for compression springs.

Hook Type	Use the drop-down menu to select type of end hook. See the Hooks of extension springs chapter in the Engineer's Handbook for hooks calculation formulas.
Hook Length	Enter the length of the hook. For Non-specified Hook Type, if you enter 0, the coil end is natural (no bend).

Spring Length

Use this section to define which parameters are entered and which are calculated.

Length Inputs	n, o L₀	Calculates the loose spring length for the specified wire diameter, number of spring coils and shape and size of spring hook.
	L₀, o n	Calculates the number of spring coils for the specified wire diameter, length of unloaded spring and shape and size of spring hook.
	L₀, n o	Calculates the size of a spring hook for the specified wire diameter, number of coils and length of unloaded spring.
Loose Spring Length	Enter or measure the loose spring length value. NoteThis option is available only if L₀, t n is selected in the Length Inputs drop-down list.
Total Hook Length	A sum of hook lengths o₁ and o₂. If you select the same hook type of both spring ends their lengths are the same (o₁ = o₂)
Active Coils Number	Specify the spring number of active coils.
Coil Pitch	Specify the coil pitch. NoteThe edit filed is enabled if you select Without Pre-stress in the spring Pre-stress drop-down menu in the Calculation tab. Click next to the edit field to open the Pitch between Spring Coils dialog box where you can specify the value of the pitch between spring coils. Selected value transfers to the Design tab when you click OK. When the edit field is enabled, the value is calculated when you click Calculate.

Results

To display the Results area on the right side of the Calculation and Design tabs, double-click the double line on the right or click the chevron.

Results area displays appropriate results which need to be calculated to get all proper dimensions of spring. Click Calculate to display the values. The units of the results values can be changed. Double-click the specified value you want to change.

Following output parameters are displayed in the Results pane:

Spring Index (c)
Mean Spring Diameter (D)
Outside Spring Diameter (D₁)
Inside Spring Diameter (D₂)

NoteFor further description of the calculated parameters in metric or English units, see Engineer's Handbook.

Summary of Messages

Displays the reports about calculation. To open the Summary of Messages area at the bottom of the Calculation and Design tabs, double-click the double line at the bottom of tabs or click the chevron at the bottom of the tabs.

Toolbar commands

Extension Spring Component Generator - Calculation tab

Sets parameters for calculation of an extension spring.

Access:

Ribbon: Design tab

Spring panel

Extension and click the Calculation tab.

Type of Strength Calculation

Extension Spring Design	Designs dimensions of the extension spring for the specified spring load.
Spring Check Calculation	Calculates assembly dimensions and an extension spring strength check for the specified load and spring dimensions.
Work Forces Calculation	Calculates the forces induced by the extension spring of the specified dimensions.

Calculation Options

Select the options for spring calculation.

Design Type	NoteThis option is available only if you select Extension Spring Design in the Type of Strength Calculation area.
	F, Assembly Dimensions d, L₀, n, D, Hook	Designs suitable wire diameter, number of coils, spring diameter, and hook size for the specified load F₁, F₈ and assembly dimensions L₁, L₈, H of the extension spring.
	F, Assembly Dimensions, Hook d, L₀, n, D	Designs suitable wire diameter, number of coils and spring length and diameter for the specified load F₁, F₈, assembly dimensions L, L₈, H, and hook shape of the extension spring.
	F, D d, L₀, n, Assembly Dimensions, Hook	Designs suitable wire diameter, number of coils, length, assembly dimensions L₁, L₈, H of the spring and hook size for the specified load F₁, F₈, and the extension spring diameter.
	F, D, Hook d, L₀, n, Assembly Dimensions	Designs suitable wire diameter, number of coils, length and assembly dimensions L₁, L₈, H of the spring for the specified load F₁, F₈, extension spring diameter and hook shape.
	F₈, D, Assembly Dimensions, Hook d, L₀, n, F₁	Designs suitable wire diameter, number of coils, spring length and required force F₁ in the pre loaded state for the specified working force F₈, diameter, assembly dimensions L₁, L₈, H and hook shape of the extension spring.
Method of Stress curvature correction	Use the drop-down list to select the method of stress curvature correction.
	With helical springs, the stress appearing in the spring coils at the given loading is calculated for simple torsion. Additional bending stress appears in the coil due to its rounding. Therefore, the stress is corrected in the calculation using a correction coefficient. As several different coefficients are commonly used, choose from the list the correction coefficient which meets your local usage or recommendations of standards.
	NoteFrom the view of strength check of a spring exposed to static loading, using the correction coefficient from Gahner gives the best results.
	Hint: With springs exposed to static loading, corrections are not executed.

Loads

The edit fields are enabled if you select Work Forces Calculation in the Spring Strength Calculation area.

Dimensions

Enter or measure the spring dimensions.

NoteThe availability of the edit fields depend on the selected option in the Type of Strength Calculation area.

Spring Prestress

Cold formed extension springs are preferably produced with pre-stressing, with close-coiled active coils. The spring pre-stressing has a considerable effect on increasing the loading capacity of the spring. For deformation of the spring to the appropriate length, use a higher loading than with springs without pre-stressing. Pre-stressing appears in coils of the spring in the course of coiling of the spring wire, and its size depends on the used material, spring index and the manner of coiling. Pre-stressing of the spring is significantly lower with springs coiled on automatic spring coiling machines.

Free State Stress

Enter the free stress value. Click the arrow to open the Initial Extension for Specified Diameters dialog box where you can set the value.

NoteThe edit field is enabled only if you selected Free Pre-stress option from the previous drop-down list.

Spring Material

Select the spring material and its properties. Click to open the Material Database where you can select the appropriate material.

Warning: Strength parameters of material are determined empirically and reflect minimum values applicable for a group of materials. Although these values are close to the values obtained using measurement of particular materials, it is recommended in cases of final calculations to use the parameters of material according to the material sheet or specifications of the producer.

Material	Specifies material values you enter or select from the Material Database.
	If a material is selected from the Material Database, its values are inserted automatically into the following edit fields, and the edit fields are locked. To unlock the field clear the box.
Allowable Torsional Stress	Enter the value.
Modulus of Elasticity in Shear	Enter the modulus of elasticity of the spring material.
Density	Enter the density of the spring material.
Utilization Factor of Material	Enter the utilization factor of the spring material. Click the arrow next to the edit field where you can set the value.
	The coefficient gives a relation between the torsion stress of a spring in the fully loaded state and the allowable torsion stress, such as u_S » t₈ / t_A. If a greater value is selected, less material is needed for spring production, the spring dimensions and the space for mounting are less, but the securing of spring stability during its function is lower, and vice versa. Therefore this coefficient is a reciprocal value of the safety rate. For common operational conditions, the value of the utilization factor of the material is recommended to be within the u_S = 0.85 ... 0.95 range. Lower values can be used for springs working in aggressive surroundings, at high temperatures or loaded with impacts.
	The value of the utilization factor of the material is selected in a dialog box where a range of recommended values is designated.

Assembly Dimensions

H, L₁ L₈	Calculates the length of a fully loaded spring for the specified working deflection and the length of the pre loaded spring.
H, L₈ L₁	Calculates the length of a pre loaded spring for the specified working deflection and the length of the fully loaded spring.
L₁, L₈ H	Calculates the working deflection for the specified lengths of a pre loaded spring and a fully loaded spring.

Spring Coils

Rounding of Coil Number	Set the value for rounding the coil number value.
Active Coils Number	Specify the spring number of active coils.

(More)

Displays additional options for spring design. To display the More Options area, click More in the right lower corner of the Calculation Tab.

Design of Working Deflection
NoteAvailable only if you select Extension Spring Design in the Type of Strength Calculation area, and these options in the Design type drop-down list: F, D d, L₀, n, Assembly Dimensions, Hook or F, D, Hook d, L₀, n, Assembly Dimensions.
Not Specified	Designs suitable spring working deflection for the specified load and spring diameter.
Minimum Working Deflection	Designs suitable spring working deflection that is larger than the minimum allowable value Hmin, for the specified load and spring diameter.
Maximum Working Deflection	Designs suitable spring working deflection that is smaller than the maximum allowable value Hmax, for the specified load and spring diameter.
Deflective Range	Designs suitable spring working deflection that is the nearest to the demanded deflection H', for the specified load and spring diameter.
Design of Spring Diameter
NoteAvailable only if you select Extension Spring Design in the Type of Strength Calculation area, and these options in the Design type drop-down list: F, Assembly Dimensions d, L₀, n, D, Hook or F, Assembly Dimensions, Hook d, L₀, n, D.
Not Specified	The smallest suitable spring diameter is designed for the specified load and spring assembly dimensions.
Minimum Diameter	The smallest suitable spring diameter larger than the minimum allowable value D2min is designed for the specified load and spring assembly dimensions.
Maximum Diameter	Designs suitable spring outside diameter smaller than the maximum allowable value D1max for the specified load and spring assembly dimensions.
Diameter Range	Designs suitable spring diameter nearest to the demanded diameter D' for the specified load and spring assembly dimensions.

Results

To display the Results area on the right side of the Calculation and Design tabs, double-click the double line on the right or click the chevron.

Displays the calculated dimensions values such as Correction Factor or Spring Mass. Values are calculated when the Calculate command is pressed.

Following output parameters are displayed in the Results pane:

Wahl Correction Factor (K_w)
Spring Constant (k)
Length of Coiled Spring Part (L_z)
Theoretic Limit Length of Spring (L₉)
Min. Load Spring Deflection (s₁)
Total Spring Deflection (s₈)
Limit Spring Deflection (s₉)
Limit Test Length of Spring (L_minf)
Initial Extension (F₀)
Spring Limit Force (F₉)
Min. Load Stress (t₁)
Max. Load Stress (t₈)
Natural Frequency of Spring Surge (f)
Deformation Energy (W₈)
Developed Wire Length (l)
Spring Mass (m)

NoteFor further description of the calculated parameters in metric or English units, see Engineer's Handbook.

Summary of Messages

Toolbar Commands

Inventor

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Extension Spring Component Generator

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