Today I am going to be talking about snap fits in which you will learn a complete overview of snap fits such as their types, design guidelines, common problems during design, and much more.
Snap fits are a very simple, economical, and rapid way of joining two different components.
All types of snap joints have in common the principle that a protruding part of one component, such as a hook, stud, or bead is deflected briefly during the joining operation and catches in a depression (undercut) in the mating component.
After the joining operation, the snap-fit feature should return to a stress-free condition. The joint may be separable or inseparable depending on the shape of the undercut; the force required to separate the components varies greatly according to design.
So without wasting time let's get started.
What is Snap Fit?
A snap fit is a type of mechanical connection commonly used in plastic parts, where one part "snaps" into another part, creating a secure and tight fit. This is typically achieved through the use of flexible tabs or protrusions on one part that "snaps" over or into a corresponding feature on the other part.
Snap fits are the simplest, quickest, and most cost-effective method.
Snap-fits are also the most environmentally friendly form of assembly, easy to recycle.
Some snap-fits can also increase the cost of an injection molding tool due to the need for slides in the mold.
Snap fits are popular in applications where ease of assembly and disassembly is desired and are often used in consumer products such as toys, electronics, appliances, mobile cases, containers, belt buckles, helmet joints, toys, etc.
Types of Snap Fit
Snap-fit can be classified into the following types:
- Cantilever Snap Joints
- L-Shaped Snap Joints
- U-Shaped Snap Joints
- Torsion Snap Joints
- Annular Snap Joint
Show in the figure different types of snap fits is described below in detail.
Cantilever Snap Joints
Most engineering material applications with snap-fits use the cantilever design.
These snap-fits joints mainly carry the flexural load.
When designing a cantilever snap, it is not unusual for the designer to go through several iterations (changing length, thickness, deflection dimensions, etc.) to design a snap fit with a lower allowable strain for a given material.
L-Shaped Snap Joints
It is formed by designing slots in the base wall which effectively increases the beam length and flexibility compared to a standard cantilever beam.
This allows the designer to reduce the strain during assembly below the allowable limit of the selected material.
U-Shaped Snap Joints
The "U" shaped snap is another way to increase the effective beam length within a limited space envelope.
Allowable strain limits such as highly glass-filled materials can be designed to meet assembly requirements.
The "U" shaped design usually incorporates the undercut on the outer edge of the part to eliminate the need for a slide in the mold, unless a slot is acceptable in the wall from which the snap projects.
Torsion Snap Joints
A torsion snap joint is a type of mechanical fastening that utilizes torsional forces to hold components securely together.
These joints mainly carry the shear stress load.
This torsion snap fits basically deflects the beam by rotating the bar.
It typically consists of a projecting tab or tongue on one component that is twisted or rotated to engage a corresponding groove or recess on another component.
The joint relies on the resiliency of the materials and the geometry of the joint to provide a secure connection.
Torsion snap joints are commonly used in applications where quick and easy assembly and disassembly are required, such as in electronic devices, toys, and appliances. They are also used in automotive and aerospace applications where high strength and durability are required.
Annular Snap Joint
An annular snap joint is a type of mechanical fastening that utilizes the deformation of an elliptical, circular, or ring-shaped element to hold components securely together.
These are rotationally symmetrical and involve multi-axial stresses.
It typically consists of a ring-shaped projection on one component that is snapped into a corresponding groove or recess on another component.
The joint relies on the resiliency of the materials and the geometry of the joint to provide a secure connection.
Annular snap joints are commonly used in applications where quick and easy assembly and disassembly are required, such as in electronic devices, toys, and appliances.
They can also be used in automotive, aerospace, and industrial applications where high strength and durability are required.
Snap Fits Design Guideline
Snap-fit is a mechanical feature that allows two parts to snap together, typically used for assembling plastic parts without the need for fasteners or adhesives. When designing with snap fits, there are several guidelines to keep in mind:
- Provide enough clearance between the parts to allow for easy assembly and disassembly.
- Make sure the snap-fit has a positive stop to ensure proper alignment of the parts and prevent over-insertion.
- Make sure the snap-fit has a sufficient retention force to keep the parts securely assembled.
- Avoid sharp corners or edges that can cause stress concentrations and reduce the strength of the snap-fit.
- Reducing snap thickness at the base can also reduce stress concentration. But lowering base thickness also lowers mating force drastically.
- A tapered snap results in lower stress concentration, lower use of materials, and lower mating forces.
- Consider the effects of thermal expansion and contraction on the snap-fit when designing for different temperatures.
- Test the snap-fit design to ensure it meets the required assembly and disassembly forces and has adequate retention strength.
Common Snap Fit Design Problems
Common snap-fit design problems include:
- Insufficient Engagement
- Excessive Engagement Force
- Insufficient Retention Force
- Excessive Deformation
- Fatigue Failure
- Environmental Impact
- Cost
Insufficient Engagement
When the snap-fit features do not engage fully, the connection may be weak and prone to failure.
Excessive Engagement Force
When the engagement force required to assemble the parts is too high, it can make the snap-fit difficult to use and may cause damage to the parts or the snap-fit features.
Insufficient Retention Force
When the retention force, or the force holding the parts together after assembly, is not strong enough, the connection may be prone to separation.
Excessive Deformation
When the snap-fit features are deformed excessively during assembly, it can cause permanent damage to the parts or the snap-fit features, making the connection less reliable.
Fatigue Failure
When the snap fit is subjected to cyclic loading, the snap-fit features may eventually fail due to fatigue.
Environmental Impact
The snap-fit design may be affected by temperature, humidity, chemicals, and other environmental factors.
Cost
The snap-fit design may be affected by cost considerations, such as the cost of the materials and the manufacturing process.
I hope that I have cleared all your doubts related to the snap-fit.
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Thank You.
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