Case Study: Seatbelt Pillar Adjustable Guide Loop

Process: Metal Additive Manufacturing (AM) 

Density: 97% of Theoretical

Material: Proprietary 17-4 PH stainless steel

Ultimate Tensile Strength: 900 MPa

Elongation: 6%

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End Use and Function

This safety critical seatbelt pillar adjustable guide loop is used in the Cadillac Celestiq electric vehicle. It is the first safety critical metal AM application approved by General Motors. 

Fabrication

The 17-4 PH stainless steel part is binder-jet (BJT) processed to a 97% relative density and is scaled up about 20% to account for shrinkage during sintering.  Expendable sintering setters are printed at the same time as the parts and are designed to hold the bottom face of the parts for isotropic shrinkage and prevent distortion. The BJT parts have a tensile strength of 900 MPa (130,500 psi), a 6% elongation, and an apparent hardness of 25 HRC. Tension testing is conducted on one part from each batch. The surface of the parts is semi-automatically polished prior to a multi-layer bright nickel-chrome plating operation to improve corrosion performance and provide a hard, scratch-resistant surface. The electroplating process contains over 20 different liquid baths to build the multiple layers of plating. The part was designed with AM processing in mind and includes a complex internal channel to reduce mass and material waste and maximize liquid flow out of the parts during the electroplating process. Parts are also tested for cyclic corrosion resistance, copper accelerated acetic acid salt spray resistance, thermal shock resistance, environmental dimensional stability/dimensional variation, perspiration resistance, and resistance to cleaning agents.

Results

Prior to General Motors selecting the AM process for this application, the safety critical cosmetic seatbelt pillar adjustable guide loop was an assembly of four separate parts. Moving to BJT allowed for the opportunity to quickly pivot from prototype to production utilizing the same manufacturing process without the need for tooling or requalification as required in different machinery. Another benefit of BJT is the recovery of excess metal powder that can be repurposed in future prints. This eliminates shipping turnings to a recycling center and is much more sustainable.