What are Snap Fits Joints?
Snap fits are a type of mechanical fastener for joining two parts together (without the need for additional fasteners) that can be used in a variety of applications. Find out how they work and why they are a popular choice in this informative article.
Simply put forward, A snap fit joint is a type of mechanical fastening method used to join two parts together without the use of screws, bolts, or adhesives.
The joint is designed to be quickly and easily assembled and disassembled, making it a popular choice for consumer goods, electronics, medical devices, and automotive applications, among others.
Snap fit joints consist of two main parts:
- the protrusion, also known as the male part, and
- the receptacle, also known as the female part.
The protrusion is designed to fit snugly into the receptacle, creating a secure mechanical connection.
When the parts are pressed together, the protrusion snaps into the receptacle, and the joint is secure.
To disassemble the joint, the parts are separated by applying an opposing force to the protrusion, which releases it from the receptacle.
Snap Fits Joint Design
Snap fit design is the process of designing and creating a joint that can be quickly and easily assembled and disassembled without the need for fasteners or adhesives.
Snap fits are designed to work under a specific set of conditions, such as material properties and environmental factors.
The design process takes into account various factors, such as material properties, environmental conditions, and the required force to assemble and disassemble the joint.
The first step in designing a snap fit joint is to determine the proper fit between the two parts. The fit can be loose, where the parts can be easily assembled and disassembled, or tight, where the parts require more force to assemble and disassemble. The desired fit will depend on the specific application and the requirements of the product.
The next step is to calculate the required force to assemble and disassemble the joint. This is known as the assembly and disassembly force.
The required force is based on the material properties and environmental factors such as temperature and humidity. The assembly force should be high enough to keep the joint securely assembled, but not so high that it is difficult to assemble.
The disassembly force should be high enough to keep the joint securely assembled, but not so high that it is difficult to disassemble.
The allowable deflection of the parts must also be taken into account during the design process. Allowable deflection is the amount of movement or deformation that the parts can undergo before the joint becomes unstable.
This is important because it affects the performance and reliability of the joint.
Proper clearance between the parts is also crucial in snap fit design. The clearance is the gap between the parts when they are assembled and disassembled.
Proper clearance ensures that the parts can snap together properly and that the joint is stable and secure.
Finally, snap fit design includes the consideration of the snap fit’s manufacturing and assembly process, for example, injection molding, sheet metal or thermoforming.
This is important to ensure that the design is compatible with the manufacturing process and can be produced efficiently and cost-effectively.
Types of Snap Fits Joints
There are several types of snap fits, each with their own unique set of advantages and disadvantages.
The most common types of snap fits include:
- Cantilevel Snap Fit Joint,
- Annular Snap Fit Joint,
- Ball and socket Snap Fit Joint,
- Torsional Snap Fit Joint.
Other interesting Snap Fit Joint are explained below:
- Living hinge snap fit: This type of snap fit uses a flexible hinge to allow the two pieces to snap together. This type of snap fit is typically used in lightweight applications and is easy to assemble and disassemble.
- Cantilever snap fit: This type of snap fit uses a protruding tab that snaps into a matching receptacle. This type of snap fit is typically used in applications where a secure connection is required.
- Flexible tang snap fit: This type of snap fit uses a flexible tang that snaps into a matching receptacle. This type of snap fit is typically used in applications where a tight fit is required.
- Ultrasonic snap fit: This type of snap fit uses ultrasonic energy to melt the plastic, welding the parts together, typically it’s used for assembling plastic parts that can’t withstand high assembly forces. This method is suitable for assembling small parts with complex geometry or for assembling parts that are hard to access by hand.
- Magnetic snap fit: This type of snap fit uses magnets to hold the parts together. It doesn’t require any mechanical interference, it is easy to assemble and disassemble, and can be suitable for parts that needs to be demounted frequently.
- Friction snap fit: This type of snap fit relies on friction between the parts to hold them together. It doesn’t require any mechanical interference and is easy to assemble and disassemble, but it can be less secure than other types of snap fits.
Snap Fits Design Calculations
Snap fit design calculations are used to determine the required properties of a snap fit joint such as the required force to assemble and disassemble the joint, the allowable deflection of the parts, and the proper clearance between the parts.
These calculations are crucial in ensuring that the snap fit joint is secure, stable, and reliable.
- Assembly and disassembly force calculation: This calculation determines the amount of force required to assemble and disassemble the snap fit joint. The required force is based on the material properties and environmental factors such as temperature and humidity. The assembly force should be high enough to keep the joint securely assembled, but not so high that it is difficult to assemble. The disassembly force should be high enough to keep the joint securely assembled, but not so high that it is difficult to disassemble.
- Allowable deflection calculation: Allowable deflection is the amount of movement or deformation that the parts can undergo before the joint becomes unstable. This calculation is based on the desired fit and the material properties. The allowable deflection must be taken into account to ensure that the joint remains stable and secure under the expected loads and environmental conditions.
- Clearance calculation: Proper clearance between the parts is important in snap fit design. The clearance is the gap between the parts when they are assembled and disassembled. This calculation is based on the required fit and the material properties. Proper clearance ensures that the parts can snap together properly.
Snap Fit Symbols
There are several symbols that are commonly used to represent snap fits in engineering drawings. These symbols are used to indicate the location and size of the snap fit, as well as the direction of assembly and disassembly.
The most common symbols used for snap fits include arrows to indicate the direction of assembly and disassembly, circles to indicate the location of the snap fit, and lines to indicate the size and shape of the snap fit.
Snap Fit Design Common Issues
Snap fit design can also present some common issues that the designers need to be aware of such as:
- Overstress: this happen when the snap fit is exposed to higher forces than its intended use, which can cause the snap fit to fail.
- Fatigue: this happen when the snap fit is exposed to repetitive loading, which can cause the snap fit to fail over time.
- Wear: this happen when the snap fit is exposed to wear and tear over time, which can cause the snap fit to fail.
- Misalignment: Misalignment can cause the snap fit to fail, as the parts may not be able to snap together properly.
- Resilience: snap fits need to be designed with adequate resilience to prevent them from breaking during assembly or disassembly.
Conclusion
In conclusion, snap fits are an efficient, cost-effective, and versatile method for joining two parts together, They are widely used across different industry and due to the different types available they can be designed to suit various requirements.
However, the designers should be aware of the potential issues that may arise and take the necessary precautions to avoid them.
This includes making accurate calculations, using proper symbols, and thoroughly testing the design before mass production.
