BEFORE I discuss the types of Snap Fit Designs and Their Association Design Parameters, I ’D LIKE to Focus on Some Basic Funirements for SNAP LOCKS, Which Are L itds,

　　A Snap Lock Must be designed to work within the stringth limits of the plastic.

A Snap Lock Can Be Designed for Single One-Time Use.

A snap lock can be designed for repeated use.

A Repeatedly Use Snap Lock Should be designed to Limit the deflection with working stress levels.

Ideally, a Snap Lock Should only Internet Two Parts by CONSTRAING THEM in a Single Axis.

A Snap Lock Can Be Designed for on/Off Bidirectional Applications.

A Snap Lock Ideally Should be English with Little to NO Residual Stress.

A Snap Lock Can be designed to apply a constant residual force.

A Snap Lock Should Be Designed to Account for Tool Design.

A Snap Lock Should Be Designed to Compensate for Tolerances.

A Snap Lock Should be designed to withstand opation sections forces.

Although there are three basic types of Snap Locks — Annular, Cantilever and Torsional — the design considations listted above.

　　Annul Snap Lock

　　

　　Torsional Snap Lock

　　

　　CANTILEVER SNAP LOCK

　　

　　DEFLECT Within the Stringth Limits of the Plastic

　　

　　Calculations for Determing.

　　Material Elastic Modulus, Maximum Strain and Stress withIn ITS Elastic Region;

Geometry of the miss to be flexed; and

Amount of deflection determined by the height of the hook propile or the force required to deflect the snap lock.

lock.

　　Annul Snap

　　

　　. Basic Insertion FORCE is Calculated USING The Equation Below:

　　F = y ? d ? ES ? X

　　F = Insertion force (LBS or Newton)

Y = Undercut (in. Or MM)

D = Diameter of the Cylinder or Joint (in. Or MM)

ES = Secant Modulus (PSI or MPA)

X = Geometric Factor

　　If the outer tube is rigid and the inft is elastic, the formula is identical to the one above except v, poisson’s raatio, have a negative vas. Plus as shown above.

　　Retention force.

　　An Fea Example of Annular Snap Applied to a Small Injection Molded Box is Shown Below:

　　of Either Material. These types of class will be much too time consumption and complicated with the aid of fea.

　　Torsion snap

　　as Shown Below:

　　The angle of twist for the torse latch base on the appliced force (f) is Shown Below:

　　Then, then

　　Cantilever Snaps

　　

　　Premature Failure. Determing the Industs at the Base of the Snap Can Be Calculated by:

　　OR, The Maximum Allowable Deflection with the Material ’s Elastic Limit Can Be Calculated by Substitch FORCE FOTH The EQUIVALENT MAXIMUM Stress, As Follows:

　　Examples of I (Area Moment of Inrtia) are shown belW:

　　Figure 1.

Figure 2.

For Added Stiffness, The Neutral Axis Must be Computed Based on the Formulas Given Below for Each Respect Cross section.

　　Figure 3.

FIGURE 4.

Examples of Snap Designs with These Various Cross Sections Are Shown Below.

　　Figure 5.

It should be noted that the calling calculations are base on the footowing assumptions:

　　The deflections are Small, and the material strain is within the elastic region of the stress-strong carve.

The cross-sectional area of the snap is constant. Typically, snap fingers are trapeidal, and the cross section varies throughout the length of the beam.

The base is of the snap is right and will not def on. Typically, the candilevered snaps are attached to a plastic wall, the which will also some extens.

Feature, Which Will Accurately Compute the Area Moment of Inrtia for Shapes Other than Those Discussed in this article.

　　An Example of An Fea Analysis of a Simple Cantilevered Snap Lock is Shown Below.

　　Snap Thickness = 0.090 in. (T)

Snap width = 0.6 in. (B)

Snap length to tip of hook = 1 in. (L)

Horizontal Force Applied at tip to deflect 0.06 in. = Amount of Undercut for Hook = 2.0 LBS (F)

The maximum von mises stress = 2423 PSI at base. USING this equation,

　　WE Can Also Compute The Stresses and Compare The Results to the Fea Study.

　　

　　

　　Figure 6.

Figure 7.

Loads that can be transferred to the snaps are now restricted to tensile and torsional loads, processing a much more secret interlock.

　　Limiting its deflection withIn ITS Elastic Limit.

　　Profile Will Enable the Force Vector to deflect the snap in Either Direction Equity. If the angles on Either Side of the HOOK are equal, the Forces Will Diffeter AcacorDingly.

　　Extra Steel in the Mold Can Easily Be Removed Versus The Costly and Time-Consump Process of Welding and Machine.

　　Draw Must be drafted properly to allow the core and cavity to properly kiss office galling the model.

　　

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