How Conflux Achieves Ultra-Thin, Gas-Tight Walls in AM Heat Exchangers

For high-performance heat exchangers, gas tightness is a fundamental requirement. In sectors such as aerospace, automotive and advanced energy, heat exchangers must reliably separate fluids under pressure while maximizing thermal transfer efficiency. Conflux sets a benchmark within the AM heat exchanger sector by achieving gas-tight ultra-thin walls, as thin as 300 microns.  
 
While traditional manufacturing can produce even thinner walls through intensive metal forming, shaping these forms into complex geometries is prohibitively difficult and costly. This is where AM and Conflux excel. We realise highly complex geometries with relative ease. The challenge, and our ongoing frontier, is to continue pushing minimum wall thicknesses even lower. 

What does “Gas Tight” mean in Additive Manufacturing?

In the context of AM, “gas-tight” describes a wall’s ability to prevent any leakage between internal domains, whether that’s gas-to-gas, gas-to-liquid or liquid-to-liquid. The industry standard for assessing gas tightness is compressed air submersion testing; any observable air leakage constitutes failure. While this methodology is effective for most fluids, certain applications introduce additional complexity.

For example, gases like hydrogen and helium can permeate through metal at the molecular level, even without detectable defects. This molecular permeation makes material selection, design optimization and testing methodology even more critical. In applications such as rocket engine cooling or advanced energy systems involving helium, close collaboration with customers becomes essential to develop appropriate testing protocols and acceptance criteria when it comes to defining gas-tightness.

Where is Gas used in AM Heat Exchangers?

Gases play a prominent role in both the final applications and the manufacturing processes of AM heat exchangers. On the application side, AM heat exchangers are used in systems where air, exhaust gases, hydrogen, helium (and many other fluids) must be thermally managed. Examples include turbocharged engines, rocket propulsion systems and compact thermal control units for industrial machinery.

Within the metal additive manufacturing (AM) process, inert gases, such as argon, are crucial for maintaining a stable and contamination-free build environment. During laser powder bed fusion, argon is used to displace oxygen and moisture, preventing oxidation of the molten metal and reducing the risk of defects such as inclusions or surface degradation. The thermal and flow characteristics of the shielding gas must be tightly controlled, as variations can lead to spatter, inconsistent melt pools, or reduced part integrity. To address these challenges in large-format systems, AM machine manufacturer AMCM collaborated with Conflux to engineer a compact, high-efficiency argon gas heat exchanger for the M 4K platform. This solution stabilises gas temperature and supports consistent thermal conditions across extended build durations, safeguarding part quality in demanding production environments.

What are the Main Technical Challenges in Achieving Gas Tightness?

Ensuring gas tightness begins long before printing starts, requiring careful consideration of multiple interconnected factors.

1. Design and Geometry

AM enables the production of heat exchangers with highly complex geometries, and with this design freedom comes specific manufacturing challenges:

• • Build orientation: refers to the direction in which a part is constructed layer by layer during the AM process, and it significantly affects manufacturability by influencing surface quality, support requirements and build time.
  • Downskin surfaces: Downward-facing surfaces are prone to rough finishes due to layer-stepping process of the AM build; smoother finishes can be achieved with thinner layers (e.g., 20 microns), albeit at higher build times and costs.
  • Internal overhangs: Often cannot be post-processed, so designs must be inherently self-supporting.

Part attached to a build platform showing upskin side, downskin side. In this part orientation, there is an overhang feature.

2. Porosity and Micro-Defects

Porosity arises when gas bubbles are trapped in the melt pool during solidification. While minor porosity may be tolerable in thick-walled parts, in thin-walled, high-precision components, even microscopic pores can compromise gas tightness. At Conflux, we have developed a core capability to print gas-tight, defect-free walls down to 300 microns.

The physics of the process defines these limits; specifically, the laser spot size (typically 80 microns) and powder particle diameter (25–90 microns). These parameters place fundamental constraints on minimum feature size and finish resolution.

The Monel K500 test specimens above illustrate the influence of Laser Powder Bed Fusion (LPBF) parameters on defect formation.

The specimen on the right demonstrates the results of optimised and customised LPBF parameters, producing minimal porosity. The remaining pores are small, spherical, and limited in number, the desired outcome for mechanical performance and material integrity.

In contrast, the left specimen reveals the consequences of unsuitable LPBF parameters, which lead to extensive porosity and associated defects.

3. Material Selection

Material choice is critical for balancing performance, manufacturability, and gas containment (especially for some of the gases we mentioned earlier like helium and hydrogen). Conflux selects alloys tailored to each customer’s performance requirements and undergoes a rigorous process to onboard new materials to our facility.

Commonly used alloys include:

• • AlSi10Mg Aluminium: Lightweight, high thermal conductivity (130–150 W/mK), established AM processing. Limited by corrosion resistance and temperature ceiling.
  • 316L Stainless Steel: Excellent corrosion resistance, stable up to 600°C+, lower thermal conductivity (15–20 W/mK).
  • Monel K500: Superior high-temperature and chemical resistance, requires tight process control to avoid defects.
  • Inconel and Titanium: As emerging AM materials at Conflux, Inconel and titanium open new opportunities for demanding applications. Inconel is widely used across industries, with applications similar to those of Monel.

Conflux selects alloys tailored to each customer’s performance requirements.

How Does Conflux Validate and Qualify Gas-Tight Heat Exchangers?

Qualification requirements vary by customer, industry, and application. Conflux maintains a rigorous internal quality process that includes:

• Technical cleanliness inspection
• Metrology inspection
• Calibrated pressure testing tools
• Video documentation of all gas pressure tests
• Non-destructive inspection methods, including CT Scanning at the Australian Synchrotron for microscopic analysis of internal structures

In many cases, part certification is defined contractually through the Statement of Work. Some customers require full test traceability; others simply need proof that the part works under specified conditions.

“Qualification means different things to different customers,” Ian adds. “For some, it’s just about proof of function. For others, we’re signing off on a process that must hold true for hundreds of future parts. So our internal QA process includes traceable calibration, video documentation and detailed reporting.” Ian Fordyce, Head of R&D, Conflux

How do 150-Micron Fins Enhance Conflux Heat Exchangers?

Conflux has pushed the boundaries of heat exchanger design by producing walls as thin as 150 microns within the fluid domain. These ultra-thin ‘walls’ serve as (to transfer heat from fluid to tube walls) or turbulators (to aid fluid mixing), rather than gas-tight barriers. Such geometries are integral to nearly all heat exchangers, regardless of size. Since both sides of a fin or turbulator wall are exposed to the same fluid, these features do not require gas-tight integrity. By reducing fin thickness, Conflux is able to pack more surface area into a given heat exchanger, thereby maximizing heat transfer efficiency.

Intricate fin geometries enhance heat transfer and reduce pressure drop.

Advancing Capability: Process Integration and Ongoing R&D

Gas tightness in metal AM isn’t achieved through one decision. It results from integrated optimization across design, materials, process control and inspection. Success requires results from integrated optimization across design, materials, process control and inspection. Success requires managing trade-offs at every stage; from initial geometry optimization and build orientation selection, through to material choice, porosity mitigation strategies and post-build testing protocols.

As demand grows for compact, high-efficiency thermal solutions, the requirement for reliable, validated AM components intensifies. Conflux’s continuous R&D advances our capabilities through developing LPBF parameters for new alloys, larger build volumes and process innovations that expand the boundaries of achievable performance.

As part of our improvement program, Conflux is also investigating the use of emerging LPBF machines equipped with smaller laser spot sizes, some as small as 40 microns. These systems offer the potential for even finer resolution and thinner wall capabilities.

Gas tightness represents much more than a test requirement – it’s a fundamental measure of our manufacturing excellence and design capability.