Mastering hard and soft joint applications: Progressive Pulse

In today’s industries, tightening operations must cope with an increasing level of variability. Assembly lines rarely deal with a single joint type: they combine a mix of hard and soft joints, each with different behaviors and constraints. Managing this diversity while maintaining consistent quality has become a key challenge for manufacturers.

Some tightening methods deliver high speed but struggle to maintain accuracy across varying joint conditions, while others ensure precision at the expense of cycle time. Adapting to multiple applications can therefore require changing tools or adjusting parameters: an inefficient approach for overall productivity.

Manufacturers need adaptability to handle different joint types with a single setup, without sacrificing speed, accuracy, or reliability. This is where new approaches such as Progressive Pulse come into play, enabling tightening strategies that can adjust to joint variability while maintaining consistent performance across applications.

Hard vs. soft joints: What’s the difference?

The distinction between hard and soft joints is essential because it directly impacts how torque is applied during tightening. A hard joint is characterized by minimal deformation of the assembled parts: once the components come into contact, torque rises very quickly with little rotation. This typically results in short tightening times and high repeatability but also increases the risk of torque overshoot if not properly controlled. In contrast, a soft joint involves more elastic deformation (gaskets, plastics, special washers), meaning that torque builds up more gradually over a larger angle of rotation. These joints require longer tightening times and more power to ensure tightening within a short time. In real production environments, many assemblies involve a mix of both behaviors, making it critical to use tightening strategies capable of adapting to varying joint stiffness.

Progressive Pulse: A greater variety of assemblies with the same Pset

Pulse tools are widely recognised as a market benchmark. However, feedback from the field has shown that certain tightening applications could sometimes reach their limits due to one of the key characteristics of fastening operations: joint stiffness.

To address this challenge, a new tightening approach has emerged: the Progressive Pulse. This strategy extends the capabilities of Pulse tools by adapting more effectively to variations in joint stiffness, particularly in softer joints. By dynamically adjusting the tightening process, it enables a single tool - and even a single Pset - to handle a wider range of applications with greater consistency, meeting customer expectations.

With Progressive Pulse, the risk of torque overshoot when moving from a soft joint to a harder one is significantly reduced, while tightening times remain controlled when switching from hard to more elastic assemblies.

Explore more about the Progressive Pulse by Desoutter by discovering BLRTC080 pistol: The new addition to the ePULSE range

How does Progressive Pulse work?

With a conventional Pulse strategy, each pulse is delivered with the same speed and energy level. With Progressive Pulse, Desoutter has developed a strategy in which the first pulse amplitudes are reduced and then progressively increase in intensity.

• For hard joint applications: the operation can be completed within only a few pulses, as the lower initial impacts are sufficient for this type of assembly.  
• For softer or more elastic joints: the pulse amplitude gradually increases, generating impacts powerful enough to complete the tightening process efficiently.

The result?

• Reduced overshoot, as the tool no longer applies excessive force at the beginning of the tightening cycle.
• No significant increase in the number of impacts, since the pulse amplitude automatically ramps up to complete the tightening operation within a controlled cycle time.
• Easier Pset configuration, enabling one single Pset to manage multiple applications.

The diagram below illustrates the Progressive Pulse technology

1. Set the final pulse amplitude, and the first pulse amplitude is automatically initiated at half of this final amplitude.
2. Set the number of pulses (ramp-up) required to reach the final amplitude.

Recommended Pulse settings for optimum performance

For optimal use of the Pulse strategy, Desoutter recommends: 

• Minimum: 8 pulses 
• Maximum: 15 pulses 

This ensures both pulse quality and controlled tightening duration.

Improved operator comfort with Progressive Pulse

Operator comfort is a key factor in modern assembly environments, particularly for repetitive tightening operations or applications requiring high torque. Progressive Pulse enhances ergonomics by delivering smoother and more controlled torque applications. Thanks to the gradual build-up of the impulses, the operator has time to prepare for the reaction torque, making the tightening process smoother and less abrupt.

This results in an improved user experience, making the technology particularly well-suited for demanding industrial applications, where flexibility and ease of handling are essential.

Learn more about the ePulse nutrunners range

Use cases for Progressive Pulse technology

The main applications for this new technology within the Pulse range include off-road vehicles, agriculture, heavy trucks and 2-wheelers, as well as final assembly line in the automotive industry, chassis and rear axle assembly, powertrain & engine applications, and strut mounting. Discover a few use cases based on field experience:

• Seat tightening in the automotive industry

A typical example involves two seat rails, each secured by two screws. Weld nuts and captive nuts coexist on the same production line, resulting in different joint stiffness characteristics. Progressive Pulse allows configurable pulse behaviour that adapts to different joint stiffness levels, helping ensure stable tightening.

• Rear seat rack assembly in vehicle interiors

In this application, the joint stiffness levels can again vary significantly. Progressive Pulse therefore provides an ideal solution by adapting efficiently to these different assembly conditions. 

• General Industry: large assemblies such as circuit breakers for power plants or nuclear facilities

These applications typically involve a ring of bolts used to close and secure the assembly, with a gasket positioned underneath. The tightening sequence generally follows a star pattern - tightening bolts in an alternating and opposite order rather than sequentially around the flange. 

As the assembly progressively clamps into position, the joint stiffness can vary from one bolt to another. This means the Pset behaviour may differ across the same assembly. Progressive Pulse technology is therefore essential to adapt to these variations and ensure safety, performance and long-term asset integrity.

With Progressive Pulse, ePULSE evolves to address a wider range of assembly applications, including a mix of joints. By combining adaptive tightening performance, improved operator comfort and simplified configuration, this technology helps manufacturers increase productivity while maintaining high quality standards across diverse assembly scenarios. 

More broadly, it reflects a shift toward smarter and more flexible tightening strategies, capable of adapting to the growing complexity of modern industrial production while ensuring consistent and reliable results.