Written by Jeff Greenwood Product Sales Engineer
SPIROL International Corporation
Fasteners are some of the most important parts of an assembly as they hold all of the parts together and facilitate any interaction between the components. Ideally, the selected fasteners are simple to install, provide a quality product for the lifetime of the assembly, and yield the overall lowest cost given the entire manufacturing process.
Press-fit pins are one of the most common types of pins used in modern manufacturing. The fasteners are typically easy to install and let manufacturers avoid soldering, such as when assembling electronics.
There are two general categories of press-fit pins: solid and spring pins.
Solid pins either have a smooth, uninterrupted surface (such as dowels) or are designed with retention features (such as knurls, grooves, and barbs). All solid pins are retained by displacing the host material. Conversely, spring pins are self- retained by exerting a radial force (tension) against the hole wall after installation.
There are two different types of spring pins: slotted spring and coiled spring pins.
Slotted spring pins are general-purpose fasteners typically recommended for non- critical assemblies. Oftentimes, these pins are used in applications where they’re manually installed into mild or hardened steel components. They have a gap designed for the pin to flex during installation, which lets it absorb the varying hole tolerance.
Coiled spring pins are available in light, standard, and heavy-duty options, so a designer can choose the optimum combination of strength, flexibility, and diameter suited for varying host materials and performance requirements. These pins have two, 1/4-coils of material, allowing them to flex during and after installation. The flex supports varying hole tolerances, helps dampen shock and vibration, and prevents hole damage.
Although there are several ways to use pins, the most common are shown in the Typical pin functions table below. These guidelines apply the majority of the time, but each application should be evaluated for which pin type is most appropriate.
These are some of the many considerations when determining the proper pin for an application:
• What’s the pin’s function?
• What are the strength requirements of the pin?
• What is the material of the component in which the pin will be used?
• What environment will the pin be exposed to?
• What’s the intended product lifetime or the number of cycles?
• How will the pin be installed?
Spring pins are typically preferred over solid pins because of their flexibility, lower insertion forces, and ability to accommodate wider hole tolerances. However, there are exceptions.
Solid pins are the ideal choice when precise hole locations must be maintained, it’s necessary to manually align several clearance holes, a hollow pin is unsuitable, or increased bending or shear strength is required. Solid pins are also favored when a smooth, uninterrupted surface is preferred (such as when used in conjunction with an angular component) or the head is required for a positive stop or to retain a thinner part to a thicker section of an assembly.
Coiled spring pins are superior for assemblies that are subject to dynamic loading. This is because these pins offer a unique combination of strength and flexibility, which allows them to dampen forces and vibration, preventing hole damage and prolonging the assembly life. Each type of press-fit pin serves a purpose for manufacturers.
The Features and benefits table compares the common features, advantages, and benefits for each type of pin.
Designers can optimize the performance and total manufactured cost of an assembly by selecting the proper pin for an application. To do so, the fastener options must be considered early in the design stage of a project.
One of the most important steps in selecting the ideal pin is to fully evaluate and establish the performance requirements of the intended applications. The design team should also test and validate the fasteners in prototype assemblies before a final decision is made.
To learn more about selecting the proper pin for an application, please click here to read SPIROL’s full white paper.