Fastening Points

The subtle trade-offs that changed one automotive team’s fastening material decision

Sometimes, shaving off a few grams just isn’t worth the downstream cost.

When lightweighting is a constant pressure, aluminium might seem like an ideal fastening material. Especially in automotive design, where every gram counts.

But changing one small detail can introduce unforeseen challenges. Challenges that can easily go unnoticed until you take a system-level view.

That’s what happened when a customer recently asked us: Could they replace their current steel bigHead fasteners with aluminium versions to save weight on an interior composite frame?

It was a logical question. But it opened up a wider conversation about material compatibility, assembly practicalities, and how fastening works as a system.

An AI example of the type of EV discussed in this article

Overview

• Component: Composite frame for interior feature in EV
• Initial setup: Steel bigHead fasteners used in R&D
• Goal: Weight reduction
• Consideration: Switch to aluminium fasteners
• Risks: Corrosion, torque value deviations
• Outcome: Retained original steel fasteners

A simple question with system-level implications

This customer was deep into the development of a new composite frame for an interior feature in their vehicle. During early trials, they’d been using a steel bigHead fastener with success. But with lightweighting front of mind, they began exploring alternatives.

Aluminium naturally came up. Their thinking was sound: it’s light and widely used in vehicle components. Could swapping fastener materials help them achieve their weight targets?

From a materials standpoint, yes.

But from a system standpoint, we saw two main concerns.

When aluminium fasteners aren’t the best fit

1. Mixed material compatibility

The team intended to keep using their existing carbon steel screws and washers. But pairing aluminium and steel in the same fastening stack can trigger galvanic corrosion, particularly in environments with fluctuating humidity or temperature.

In a vehicle, that kind of degradation may go unseen until an end user or technician removes a panel and finds corroded and weakened fixings, or that the assembly has seized.

2. Tightening torque deviations

Torque settings in automotive assembly are tightly controlled. Changing just one component – like the fastener base material – would invalidate the known torque profile for that connection.

Introducing a single aluminium fastener into an otherwise steel-based system would have required new torque validation and re-documentation for a single part.

For a complex, global production line, that’s a logistical headache. And it’s exactly the kind of challenge that tends to appear late in the process, when it’s harder (and costlier) to resolve.

A diagram of a standoff fastening

Looking beyond the fastener

A standoff fastening

The customer was focused – understandably – on the component design and composite integration. Assembly and service considerations are easy to overlook during the early-phase dialogue.

That’s where we can help. At bigHead, we don’t just see fasteners as a single component. We see fastening as a system that needs to work across design, manufacture and assembly.

Our role is to support teams to make those cross-functional connections, and spot unintended consequences early, when changes are easiest and least costly to make.

Decision and outcome

As we talked through the trade-offs, the customer quickly decided that the corrosion risk and torque value changes outweighed the benefits. The added complexity just wasn’t worth saving a couple of grams.

The customer’s response:

“These points mean the potential risks outweigh the benefits in weight reduction. Many thanks for the time and effort in investigating the concept, but we will stick with the original steel fixings.”

So, they chose to retain the original steel bigHead fastener, which had already proven effective during R&D. Their timeline stayed on track, and the solution continued to meet their performance and reliability goals.

An AI example of the type of EV discussed in this article, from another angle

Fastening guidance with integrity

Could we have said yes to the switch? Taken the development request and sold the aluminium fastener?

Yes. But we didn’t think it was the right solution.

Our job isn’t to sell components. It’s to support robust, system-wide decisions. We love helping teams to weigh the trade-offs and keep their projects moving smoothly. Each time we help a customer avoid a problem before it arises, that’s a success in our book.

Sometimes, that means saying no to a quick win, and yes to a more reliable outcome.

Learn more about how we can partner with you to simplify your journey to great outcomes.

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