Six questions for an effective snap-fit joint
A common way of saving production costs is to eliminate time and thus cost-intensive joints between multiple components, such as screws, gluing or welding. Snap-fit joints are an alternative.
Snap-fit joints use the elasticity of aluminium profiles and form a quick fit between two or more extruded profiles. I’ve put together some questions to help you in your work to find an effective snap-fit joint.
1. Do we need a permanent or detachable snap-fit joint?
A snap-fit joint that can be opened usually has an angle B that varies from 45° to 60°. For permanent connections B = 0° or is even negative.
2. How much space is available?
The “snap-fit arm” needs a certain length to be able to spring. This means a spring of sufficient length must be constructed, and it must remain within the material’s range of elasticity in the event of deformation.
Rule of thumb: The length of the snap-fit arm should be at least 12 times the wall thickness. The longer, the better.
If there is not enough space for the desired length of the snap-fit arm, then an alternative is to create more elasticity with thinner wall thicknesses and/or recesses at the beginning of the snap-fit arm. This is the position where the most torque is found.
The downside is that the extrudability and the productivity of the profile is reduced because extrusion speed falls dramatically. This has an adverse effect on the cost of the aluminium profile. Another way of creating more elasticity when a very small amount of space is available is to increase it by adding an extra part made of another material, such as rubber or plastic.
3. Can the connection be created with a hinged movement or must the click be pressed straight in?
The advantage of a hinged connection is that the deformation of both arms is absorbed and the click height needs to be overcome only on one side, so that the profile falls more easily into place. Given the choice, a hinged connection is preferable.
4. Is the click connection manual or by machine?
In many cases, it is preferable for a click connector to be engaged and disengaged by hand. But in others, such as for applications in public areas where click connectors are exposed to vandalism, it is only possible to disengage the connector mechanically. In that case, a solid connector is required, on which greater forces can be exerted when disengaging by mechanical means. In addition, if greater forces are exerted on the snap-fit joint for functional reasons, then it must be made more solid and operated mechanically to make it stronger.
5. What types of surface treatment are the profiles given?
This is important, since during the anodizing process +/- 0.025 mm of thickness is lost per surface and in the case of powder coating +/- 0.05–0.1 mm of coating thickness is added per surface. This should be taken into account in the dimensions of the structure. You must also pay special attention to structures where the profiles are both anodized and powder coated. I don’t recommend using untreated surfaces. If untreated aluminium parts are rubbed together under pressure, scratching can occur and this may block the clips. It is therefore advisable to anodize one of the two profiles for protection purposes, or to use a suitable lubricating oil.
6. What will be the shortest/longest length of the connection?
Snap connectors can also be used on long sections of six meters or more. Longer parts require less pre-stressing because the forces are divided better. To position, we start by snapping on the one side and then continuing lengthwise. More pre-stressing is required for short sections to ensure that the profiles cannot easily slide away from each other lengthwise.