Engineering Integrity Society

a unique way for engineers in industry to exchange ideas and experience

60 Second Spotlight on Thomas Llewellyn

60 Second Spotlight on Thomas Llewellyn, Coexlion

Ahead of the Bolted Joints Seminar taking place on 8 February we caught up with Thomas Llewellyn to hear his thoughts on the topic.

Please briefly explain your current role and involvement with bolted joints.

I am Managing Director of an engineering consultancy firm, Coexlion.  We specialise in EV and motorcycle design.  Bolted joints are often a source of challenge / opportunity.  For the past few years, I have been delivering training on the fundamentals of bolted joints in the UK and India, on behalf of Dr Bill Eccles. I have spent many hours discussing bolted joint issues!

What changes have you seen in bolted joint technology over the past 5 years?

In the automotive industry the trend has been adoption of “high tech” plated finishes.  I have seen the level of awareness of Coefficient of friction as a critical parameter increasing, and therefore the tighter controls on friction bands, introduction of friction testing as a quality control step, and development of advanced coatings.  I believe the exclusion of Hexavalent Chromium from coatings acted as a catalyst for changes and drove many companies to understand the details of what was involved in the plated finishes.

What are some common challenges engineers face in your specific area of expertise and how will your presentation address these?

There are 2 areas I feel are misunderstood, that I hope to address in my talk.

  1. Understanding of the impotence of coefficient of friction on torque-preload relationship.
  2. Understand the effect of Relaxation. Even without self-loosening.

What do you see as the key priorities for engineers working with bolted joints?

The paradigm shift:  that torque is almost irrelevant.  It is preload that is critical to us in the performance of the bolted joints.

The presenters at the EIS seminar work in a variety of different sectors. What are the benefits of sharing bolted joint knowledge and approaches across different industries?

I spent my whole working career in automotive. When I began the bolted joint training, it gave me the opportunity to see other industries.  I found it informative to see how best practice differs in different industries and how solutions that were not considered in automotive were implemented in other industries, that actually could have been of benefit to automotive if we had had knowledge outside of the tried and tested solutions.

In light of technological advancements and industry changes, how do you foresee the future of bolted joint technology evolving?

I believe the use of advanced tightening methods, featuring tooling with process data logging will increase as the cost of this tooling comes down, and more companies adopt industry 4.0 methodologies.

What will you be presenting at the EIS seminar and how will this benefit participants?

Dealing with Electric Vehicles we frequently come across traction battery designs.  The bolted electrical connections between busbars are critical for performance and safety of batteries.  But as these are not structural joints, they are sometimes insufficiently analysed.  I aim to put some test data behind the “received wisdom” of the popular materials and tightening methods.

Why is it important for engineers to join this event?

Bolted joints are a critical part of most engineered products.  However, they are often overlooked as bolts are considered low cost components, viewed as “standard” and therefore low risk. I feel that inadequate attention is paid to bolted joint theory in colleges and universities, and therefore it is an area which is often misunderstood.  Hopefully my talk, alongside the others presentation, will help highlight the need for a focus in this area.

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