Do you know the challenges of building an Expeditionary Fighting Vehicle?
Engineers tasked with the design of the US Marine Corps’ Expeditionary Fighting Vehicle faced a challenge on the materials that they have to use in the construction of the combat craft which should be of lightweight aluminum alloy in order for it to meet its mission objectives. But aluminum is a relatively soft material and as such requires a special type of fastener. The fastener used to attach components to the aluminum frame has to satisfy a number of requirements.
It’s not easy to fasten a soft material and not destroy the material. In the case of aluminum, the fasteners need to solidly lock in place, be lightweight, resistant to extreme shocks and vibrations, create watertight seals and endure extended saltwater exposure. An additional requirement of the Marines is for them to be able to remove and replace the fasteners in the field.
Searching For The Right Fastener
The engineer design team had planned on using threaded inserts which is a common practice when using bolts on soft materials like aluminum and magnesium. Inserts are usually made of a tough metal like stainless steel. They are installed into pre-tapped holes and locked in place permanently. The inner threads provide a strong, wear-resistant interface to install bolts into.
Special Requirement By The US Marines
The task could have been easier if not for the special requirement of the Marines – which was having the ability to remove the fastener in the field. For a conventional insert to be removed for whatever reason, a drill is needed to take it out, thereby damaging the hole in the parent material. Moreover, drilling can be difficult if the insert is not really that accessible.
For this particular application, inserts may not be the best fastening hardware to use because they cannot create seals that are airtight and watertight without using a thread-locking compound although the compound still doesn’t guarantee air or water tightness, leaving a leak path.
Developing A New Insert
Challenged by the limitations of the conventional and commercially sold inserts, the design team developed a new type of insert that would satisfy the requirements of the US Marine Corps without any additional cost. The engineers called the newly-developed inserts, “Fredserts”.
Advantages Of The New Inserts
This new insert combines a tapered thread profile, 100% thread engagement, and a flanged-head that will allow the creation of friction that fits the material compression that would lock it in place. The external threads on the other hand are over-sized compared to other inserts and tapered in some areas to create a friction-fit when installed with the parent material which is aluminum. The threads are engaged with the material very similar to the way taps interface with the threaded holes. Other inserts utilize standard bolt threads that end up with less contact with the parent material in terms of the surface area.
Complying With The US Marine Requirement
The new inserts are designed to exceed that tensile strength of bolts installed in them. Actual tests showed that bolts break much earlier than the Fredserts ever budges from the aluminum material. And most importantly, the soldiers or technicians can quickly remove and replace bolts and inserts in the field.
Do you know of other fasteners that can be used with aluminum or other soft metals?