Advancing Binder Jet Printing for Automotive Applications

In the evolving field of additive manufacturing, binder jet printing has emerged as a promising technology, especially in the production of complex, high-performance metal components. Among the recent breakthroughs in this area is the development of FSLA (free-sintering low-alloy) steel. This material is specifically designed for the binder jet process due to its ability to reach a high density during sintering without the need for high sintering temperatures and long times at temperature. This post dives into the findings of a research study that examines the microstructure and mechanical properties of FSLA steel, highlighting its potential for revolutionizing automotive applications.

Steel Strength Ductility Diagram, illustrating the range of properties available from today’s AHSS grades. World Steel Auto

Understanding Dual Phase Steel

Dual phase (DP) steel is a class of advanced high-strength steel (AHSS) that features a microstructure consisting of both ferrite and martensite. This combination provides an excellent balance of strength and ductility, making DP steel an ideal candidate for automotive structural components. The ferrite phase contributes to good formability, while the martensite phase enhances the steel's overall strength. FSLA steel, through its tailored heat treatments, can achieve similar advantages allowing for versatile applications where high strength and ductility are required.

The Unique Properties of FSLA Steel

FSLA steel represents a significant advancement in material science tailored for binder jet printing. Its formulation is designed to optimize performance post-sintering through heat treatments, which enables a broad range of mechanical properties. These properties make FSLA steel a versatile candidate for demanding applications in the automotive industry.

Key Characteristics

• The microstructure of FSLA steel can be adjusted after sintering through heat treatments, allowing engineers to tailor its properties to specific application needs.
• High Hardenability: By employing inter-critical annealing followed by air cooling, FSLA steel can achieve ultimate tensile strengths exceeding 1000 MPa using gas quenching, liquid media quenching and furnace cooling.
• Heat Treatment Flexibility: A variety of heat treatments can be applied to produce the desired balance of strength, ductility, and toughness.
• Inter-critical Annealing: This process involves heating the steel to a temperature range where both ferrite and austenite phases coexist, followed by air cooling the austenite transforms. This results in a refined microstructure that significantly boosts tensile strength.

The Role of Heat Treatments

FSLA steel stands out for its ability to de-bind and reach full density under standard sintering conditions while offering a wide range of mechanical properties through post-printing heat treatments, reducing the need for extensive printer parameter development. The study reviewed several approaches to achieving mechanical properties that align with the performance requirements of automotive components. For instance, careful control of cooling rates from the sintering temperature facilitates phase transformations that enhance the alloy's mechanical attributes.

Why FSLA Steel Matters for Automotive Applications

The automotive industry continually seeks materials that can balance strength, lightweight properties, and cost-efficiency. FSLA steel addresses these needs by offering:

• High Strength-to-Weight Ratio: The alloy’s high tensile strength ensures durability while maintaining a low overall weight.
• Design Flexibility: Binder jet printing combined with FSLA steel allows for complex geometries that are difficult to achieve through traditional manufacturing methods.
• Cost-Effectiveness: The free-sintering nature of the alloy reduces processing steps, lowering production costs without compromising quality
  

In a recent development project GKN partnered with HP Metal Jet and Volkswagen using FSLA material to redesign the conventional A-pillar reinforcement for the T-Roc cabriolet car.

The goal was to qualify the material to ensure strict safety standards and light-weighting potential with the use of metal binder jetting technology. The challenges included achieving required material properties, automation of depowdering, and conforming to the tight tolerances after printing and sintering. The project was a success, achieving a 40% weight reduction using one material, less parts and out performing the crash requirements. This was all possible due to the flexibility of FSLA material properties using heat treatments and achieving full density under standard sintering conditions.

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Future Implications

The adaptability of FSLA steel, combined with the scalability of binder jet printing, positions this innovation as a game-changer in the production of high-performance components. Beyond automotive applications, the ability to tailor microstructures and properties could pave the way for advancements in aerospace, industrial machinery, and beyond.

As the demand for sustainable, efficient manufacturing grows, materials like FSLA steel demonstrate how targeted research and innovation can unlock new possibilities. This research not only highlights the potential of binder jet printing but also sets a benchmark for how additive manufacturing can meet the complex needs of modern engineering.

Read the full technical paper here:

Microstructure and Mechanical Properties of FSLA Steel Produced by the Binder Jet Process

Stay tuned for more updates on cutting-edge materials and processes shaping the future of manufacturing!