Chloe Zhang
Snap-fit joints are a cost-effective way to assemble plastic parts without the need for welding or screws. This method involves applying force to a flexible plastic wall with a protrusion, which then fits into a groove in the mating part. However, there are some disadvantages to this method, such as the requirement of undercuts, which can increase costs, and the fact that snaps are not as strong as screws. Additionally, creating a waterproof enclosure design with snap joints can be challenging. When designing snap-fit joints, it is important to consider the type of joint, such as cantilever or annular, and the problems that may arise, including snap deflection and high strain in the snap section.
| Characteristics | Values |
|---|---|
| Type of joint | Snap-fit joints, cantilever snap joints, annular snap joints |
| Advantages | Simple and reliable, improved aesthetics, reduced number of parts, reduced product assembly cost |
| Disadvantages | Requires undercuts, which increase injection mould tool cost, not as strong as screws, challenging for waterproof enclosures |
| Assembly process | Apply force to flex part, causing cantilever snap protrusion to go inside the mating part groove |
| Design considerations | Snap deflection or overlap, strain in snap section, plastic material and length, snap cross-section thickness |
| Tools | Snap setting tool, pliers |
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What You'll Learn
Design the inner ring as a tube and split it in half
When designing a plastic armature that snaps together, one approach is to design the inner ring as a tube and split it in half. This method can be used to create a snap-fit connection, similar to how plastic Easter eggs snap together.
To implement this design, start by creating a cylinder and then cutting it in half lengthwise. This will give you two identical semi-circular halves that will form the inner ring. The next step is to modify these halves to facilitate the snap-fit mechanism. This involves extruding a smaller diameter along the curved surface of each half, creating a slightly narrower profile along the edge that will first make contact during the insertion process.
The objective of this design is to have these two circular halves deflect toward each other as they are pushed together and then snap into place, forming a secure coupling. To achieve this, it is crucial to introduce a flare or a thicker region at the distal end of each half, ensuring that it has a flat back surface. This flared section will act as a locking mechanism, providing the necessary coupling strength to hold the pieces together.
However, one challenge with this design is ensuring that the halves can be easily separated without damaging the connectors. To address this, experiment with sloping the back face that holds the halves together. By making small adjustments to the slope angle, you can find a balance between coupling force and ease of manual separation. Adjustments to the slope will allow you to fine-tune the mechanism, either increasing the coupling force for a more secure hold or making it easier to pull the pieces apart.
Additionally, consider the material properties of the plastic used for the armature. Companies often employ specialized plastics that are harder, smoother, and more resistant to wear. These characteristics can improve the performance and durability of the snap-fit connection, reducing friction during insertion and prolonging the lifespan of the connectors.
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Use embedded hardware, like magnets, for releasable couplings
Designing snap-fit connectors can be challenging, as they require some degree of flex and the range of dimensions between "too loose" and "too tight" is very small. This often leads to a lot of trial and error. To avoid this, one can use embedded hardware such as magnets for releasable couplings.
Magnetic couplings employ magnetic forces to transfer rotational motion and torque from one shaft to another, without any physical contact. This is achieved by using two magnet assemblies, where the rotation of the driver magnet causes the driven magnet to rotate in sync through magnetic attraction and repulsion. This results in a seamless transfer of power without a physical connection.
Magnetic couplings offer several advantages over traditional mechanical couplings. Firstly, they provide a non-contact design that minimises the transmission of vibrations, resulting in quieter and smoother operation. Secondly, they are highly durable as they lack physical wear components, making them well-suited for harsh environments. Thirdly, they improve energy efficiency by eliminating friction associated with mechanical couplings, reducing energy losses. Finally, magnetic couplings enhance safety by reducing the risk of mechanical failure due to the absence of direct mechanical connections.
When using magnets for releasable couplings, it is important to consider the torque limitations, as the amount of torque that can be transferred is dependent on the strength of the magnets. Additionally, the design should ensure that the magnets do not come into direct contact, as this can lead to an axial load as the magnets pull on each other.
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Use a snap setting tool to press down on the plastic pieces
When using a snap setting tool to press down on plastic pieces, it is important to follow a few key steps to ensure a secure and accurate snap. Firstly, mark the placement of the snap with a water-soluble marking tool to ensure no permanent marks are left on the project. The centre position of the snap is critical and can be marked with an "x", with each line being the diameter of the snap. This allows for precise registration of the snap.
Next, prepare the snap setting tool. For plastic snaps, snap fastener pliers are often used. The specific tool depends on the brand and size of the snap, so compatibility must be ensured. If using pliers, the flat piece of the cap should be placed inside the black tray or divot of the pliers, fitting snugly. The socket should be matched with the other end of the pliers, ensuring the indentation is away from the prong. No part of the button should sit outside the divot.
Then, the fabric should be placed in the jaws of the pliers, with the wrong side facing the open prongs, and the snap should be aligned with the placement markings. The pliers should then be squeezed slowly and firmly until the snap is secure. It is important to note that the correct pressure is crucial. If the snap is loose, more force may be needed.
For painted snaps, a hammer and anvil setting tool is recommended as it is gentler on the painted surface. To protect the painted surface, a small piece of fabric can be placed between the metal cup and the snap cap. A topcoat can also be added for interest and texture, such as a glitter topcoat or a design created with a toothpick.
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Use pliers to snap pointy pieces together
When snapping together pointy plastic pieces, it's important to have the right tools and techniques to ensure a secure connection without damaging the pieces. Here are some detailed instructions to guide you through the process:
First, identify the male and female pieces of the snap. The male piece is the one that pokes out, while the female piece goes in. The pointy part of the male snap is designed to fit into the black side of the pliers, with the point facing up. Place the male snap into the pliers, ensuring it is securely positioned.
Next, use an awl or a sharp tool to poke a hole in the fabric where you want to attach the snap. The hole should be just large enough to accommodate the snap without being too loose. Now, take the pointy backing piece with a prong (this could be a white circle or yellow star) and insert it through the hole you created. The pronged side should be facing up.
Place the female snap piece (often purple) on top of the prong, ensuring the cup side is facing up. You can now use your pliers to firmly press the two pieces together. Squeeze the handles of the pliers tightly so that the clear piece presses down onto the assembled snap. You should see the pointy prong of the backing piece mash down, securing the male and female snaps together.
If you're working with thin fabric, consider adding a stabilizer or a small piece of fabric to ensure the snap holds securely. Additionally, always double-check that the snaps are facing the correct direction before pressing them together. This will ensure they function properly once attached.
When using pliers to snap pointy pieces together, it's important to be cautious. If you need to separate the snaps, use two pliers to carefully grip each side and gently pull and twist until they come apart. This method will likely leave holes in your fabric, so proceed with caution. Alternatively, you can use a flathead screwdriver and sharp scissors to separate the pieces, but this also carries a risk of damage to the fabric.
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Use annular snap joints to join symmetrical round parts
Snap fit joints are a common mechanical joint mechanism found in many products. They are created by interlocking components that can be assembled and disassembled without losing quality. Snap fit joints are useful because they do not require additional tools or fasteners to hold them together. Plastics are a common material used for manufacturing snap joints due to their flexibility and durability.
Annular snap joints are a type of snap fit joint used to join symmetrical round parts. They are suitable for cylindrical-shaped parts and often feature container lids and pen caps. Annular snap joints consist of a circular hoop that extends when pushed onto a rigid, complementing hollow or indentation. One of the components (the male) features a ridge at its circumference, which corresponds to or locks into the groove of the tube-shaped second part (female).
To design an effective annular snap joint, it is important to consider parameters such as bending, deformation, strain, and deflection. The return angle of the joint also affects the robustness of the assembly, with a 90-degree return angle resulting in a permanent assembly for annular joints. Additionally, the amount of force required to assemble and disassemble the joint should be considered to ensure that the connectors are not damaged during use.
When designing annular snap joints, it is important to ensure that the mating components are designed to lock each other's movement when put in a specific relative position. This can be achieved by pressing one component into the other, deforming the flexible features until they snap into their locking positions. The flexibility of the components allows for temporary deformation during assembly and disassembly without permanent deformation.
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Frequently asked questions
Snap-fit joints are a way to join plastic parts without the need for screws or welding. They consist of a protrusion in a flexible plastic wall and a groove in the mating part.
During assembly, force is applied to the flex part, causing the cantilever snap protrusion to go inside the groove of the mating part.
Snap-fit joints are simple and reliable. They improve aesthetics by making the product look clean as fasteners are not visible from the outside. They also reduce the number of parts and assembly costs as additional fasteners are not required.
Undercuts are required to create a snap feature, which increases injection mould tool costs. Snap joints are also not as strong as screws and designing a waterproof enclosure with snap joints is challenging.
The three widely used types of snap-fit joints are cantilever snap joints, annular snap joints, and embedded hardware joints (using magnets, nuts and bolts).
