One-touch connections are one of the most common mechanical connection mechanisms found in products around us. The action of “taking something” usually refers to a background snap. Tupperware lids, bottle caps, and pen caps are common examples of snap-fit products.
This text discusses instant connections in detail. We'll cover different types of instant connections, the advantages and disadvantages of instant connections, and some cool tips and tricks for instant connection design.
What is instant closing?
Let's start with a formal definition of instant closure. A snap lock is a mechanical arrangement that connects flexible components. The mating components, usually made of plastic, have flexible features designed to block each other's movement when placed in a specific relative position. To create the lock, one component is pressed against another, deforming the flexible features until they “snap” into their locking positions.
Instant Connections
One-touch connections are a type of mechanical connection mechanism that takes advantage of the advantages of an instant connection. They are created by components that can be interconnected. Additionally, snap-together components do not require additional fasteners to hold them together.
However, their most striking feature is that they are reusable. This means that users can assemble and disassemble plug-in connections thousands of times without the mechanism losing quality. This is generally not the case with other types of fasteners. For example, experts recommend discarding threaded fasteners after repeated use.
Flexibility is an important material property for snap-lock components because they temporarily deform when they are snapped in and out. Once locked, the components return to their original shape without permanent deformation. Therefore, plastics are often used to make plug-in connections because of their flexibility and durability.
Types of instant connections
There are different types of instant connections with specific applications, advantages and limitations. This section explains the most important types.
1. Cantilever snap closure
Cantilever fittings are probably the most common of the different types of fittings. They consist of a cantilever arm with a locking feature at the free end. For assembly, the component is inserted with the arm into a recess in the other component, which deforms the arm. Finally, the locking feature snaps into place at the end of the recess and the arm returns to its original shape.
It is a durable mechanical joint available in temporary and permanent versions. A common problem is permanent deformation of the boom arm. Excessive stretching can result in the arm not being able to return to its original shape or even breaking.
2. Ring-shaped instant connection
Annular snap fittings consist of a circular ring that expands when slid into a rigid, mating groove. The expansion creates tension in the annular ring, creating enough frictional force to hold it in the groove structure.
This snap lock is suitable for heavy-duty applications due to uniform tension distribution in ring-shaped shapes. However, there is a risk of overstretching and excessive use can also cause the snap lock to loosen over time.
3. Twist snap closure
Twist fittings are very similar to cantilever fittings in that they have cantilever arms with clip-like locking features. However, the arm remains in position due to a torsional force (usually from a spring and bearing).
To assemble/disassemble it is necessary to work against the spring force and release the locking clip. It is a simple connection, with a lower risk of failure and a long service life.
4. U-shaped snap closure
U-shaped socket fittings, as the name suggests, have a U-shaped locking element. The easiest way to imagine this is to think of a cantilevered socket joint with the arm folded halfway in on itself. . It works in a similar way. The arm flexes during assembly/disassembly and the clip locks the components.
It is a useful and durable snap lock design. However, it is more prone to overstretching due to multiple areas of stress concentration. Furthermore, it is not easy to manufacture due to its geometry.
Advantages of instant connections
One-touch connections are used in many areas due to their numerous advantages in product design. A brief summary of its main benefits is as follows:
Easy assembly/disassembly
In contrast to most mechanical connections, snap fasteners are very practical to use. They can be attached and removed in seconds and require no special tools (like screwdrivers for screws).
No additional hardware
Snap connections are enough to create mechanical connections. No additional fasteners such as nuts, washers, screws, etc. are required to connect the components.
Reliable and durable
When used correctly, snap fasteners can last a lifetime. They have a useful life of several years and generally do not contribute to making a product unusable.
aesthetics
Generally, mechanical fasteners are visible and can make the product unsightly. For example, in the aerospace industry there are thousands of fasteners. Snap fasteners are generally not visible from the outside, preserving the aesthetic design of the products.
Limitations on using instant connections
Of course, a product like snap fasteners, with its numerous advantages, also has some limitations. We will discuss this now.
Complex production process
Interlocking features and stress concentration areas make producing instant connections a challenge. Features like locking clips require cuts to the mold design, increasing complexity and cost. Furthermore, because there is a risk of the joints becoming excessively stretched when ejected from the mold, special care and time are required.
Easy to break
Flexible parts can break easily. The same applies to snap fasteners. Although they are durable, they are prone to breaking under slight overload.
Connections that are weaker than lasting
Instant connections are non-permanent connections whose strength is not comparable to that of screws, nuts and bolts. While this comparison isn't fair given the specific applications of instant connections, we believe it's still worth mentioning.
Common Snap-Fit Design Issues
Although instant connections are durable and efficient, they have some common problems that sometimes lead to failures. These are things you should keep in mind when designing and using instant connections to avoid problems.
Stress concentration : Stress concentration refers to the condition in which a small part of the mating connection is under much greater tension than other parts. If stresses in these areas exceed the strength limits of the material, the structure will fail. Stress concentrations are common in plug-in connections because they are flexible and have curves/turns in their geometry that are susceptible to high stresses.
Dragging : Creep is a phenomenon in which a material weakens under load over a long period of time. As plug-in connections remain loaded for long periods of time, creep occurs, which can compromise their structural integrity.
Fatigue : Fatigue refers to the weakening of a structure due to cyclic/repetitive loading. Plug-in connections may suffer from fatigue failure due to frequent assembly/disassembly.
Environmental conditions : The performance of plug-in connections can be affected by conditions such as high temperatures, exposure to chemicals, and humidity.
Best Tips for Designing Lasting Instant Connections
The development of snap fasteners is a challenging field. Engineers need to consider several factors when designing pressure fasteners and keep the practicalities mentioned above in mind. Design decisions largely depend on factors such as application, material availability, manufacturing capacity and budget.
In this section, we share some expert tips on snap-together design best practices.
Reasonable tolerance
Most problems arise because the mechanical fit between interconnected components is too great or too small. Tight fits result in high stress concentrations and loose fits do not have sufficient engagement force at the connection point. A general rule of thumb is to design the connection with a tolerance between interference fits and sliding fits.
Skirting on cantilever arm
A common method for reducing stress concentrations is to eliminate the geometric features that cause them. For cantilever joints, these are the sharp corners at the base of the arm. Rounding these corners increases their resistance to stress concentrations.
Wide clip
The clip is an important component of plug-in connections and carries a large part of the load. A wider clip is more stable. Therefore, it is able to withstand stress better.
Stops and eyelets
These are design features that prevent excessive nesting of interconnected components, which would lead to stress concentrations and excessive stretching. Furthermore, they are also useful for aligning corresponding components and distributing their load.
Tapered design
Adding a slight taper to the snap lock design reduces stress concentrations and material consumption.
Application areas of instant connections
Snap connections have countless uses due to their ease of use and convenience. We will highlight some of the most common uses.
Snaps : Snaps are incredibly useful for attaching great-looking, durable pieces, they remain invisible and create a strong connection.
Pen caps : Pen caps often have ring-shaped snap closures. Users press them on the top of the pen, causing them to open a little and close the pen tightly.
Bag closures : The small snap closures on trekking backpacks are useful when they are full and difficult to handle. These strong snap connections are cantilever connections that provide enough strength to hold the backpack's contents in place.
Tupperware lid : We all use Tupperware to pack our food. Lids often feature snap locks that last for years without breaking and are strong enough to create airtight connections.
Concluding
Snap connections are undoubtedly an important part of the product design industry as they provide an efficient and practical method of creating long-lasting mechanical connections. They are ubiquitous in our environment and are definitely important for designers.
Common questions
What are instant connections?
Snap connections are a type of mechanical connection in which interlocking elements hold two parts together without additional fasteners or adhesives.
What processes are commonly used to produce instant connections?
The most commonly used process to produce plug-in connections is injection molding. CNC machining and 3D printing are also occasionally used.
What materials can be used for instant connections?
The most common materials for push-in connections are plastics such as ABS, PETG, nylon, and PLA because they are flexible and easy to mold.
What are the proper tolerances for snap lock design?
There are no hard and fast rules for the design tolerance of plug-in connections, but it is recommended that they be neither too tight nor too loose. A typical range for gap width is 0.2–0.5 mm, depending on the type of connection and material used.
