25 November 2014
25 November 2014
The High-Load, High-Shear Geared Axial Polymer Thrust Washer (HLHS GAP Thrust Washer), used by General Motors in its 2014 Hydra-Matic 8L90 8-speed transmission, was a finalist in the powertrain category.
The Automotive Division of SPE promotes scientific and engineering knowledge relating to plastics developments in the global transportation industry. Its competition annually draws 60-80 project entries from vehicle manufacturers, suppliers, and polymer producers.
According to Solvay, its Torlon 4275 PAI, an unreinforced, friction/wear grade, was selected because of its capabilities including friction and wear performance at elevated pressures and velocities. Torlon PAI, which was introduced to the automotive transmission market in 2008, is a high-strength plastic with strength and stiffness up to 275°C (525°F). It has resistance to wear, creep and chemicals – including strong acids and most organics – and is ideally suited for severe service environments. The thrust washer is attached to the sun gear of an automotive transmission and pushes with the sun gear against the needle bearing. The material was able to withstand the load applied by the planetary gear set. This allows the needle bearing to operate with high efficiency.
“The HLHS GAP Thrust Washer program provides both a template and benchmark for future component program success and opens opportunities for continued metal replacement in powertrain applications,” said Brian Baleno, Global Automotive Business Manager for Solvay.
Solvay and Freudenberg-NOK worked in close collaboration to collect a broad range of performance data through specialised testing of Torlon 4275. Solvay explains it used a six-lot resin testing system to gather vital information relating to tensile strength, resistance to transmission fluid and heat aging. In addition, Solvay demonstrated the material’s capability in lubricated friction and wear environments via their proprietary ASTM D3702-based friction and wear test rig.
Solvay says a collaborative team approach between themselves (resin supplier), Freudenberg-NOK (moulder/manufacturer), and GM was critical to the success of the project.
“OEM vehicle manufacturers seeking to replace traditional metal components with new thermoplastic designs must have assurances that new materials can be designed, validated, and produced to meet weight and extended performance requirements while also addressing fundamental issues such as cost, quality, delivery and manufacturability,” explained Rory Pawl, Sales Director, Process Seals, and former Director, Future Technology, Freudenberg-NOK.
Solvay explains, the original thrust washer design composed of sintered metal was found to be heavy and costly. A switch to aluminium appeared to solve OEM concerns; however, the aluminium components began to fail critical durability testing. Compressive creep of the aluminium was associated with the high stress on the part while the fretting was associated with cyclic shear and torque.
Freudenberg-NOK says it utilised proprietary equipment to test the Torlon PAI thrust washers under extreme conditions to provide assurance that the new component resolved performance challenges. Freudenberg-NOK’s proprietary thrust washer test machine was used to conduct a multitude of performance analyses on Torlon 4275 thrust washers. This machine uses air pressure to apply upwards of 3000 lb of pressure on the washer, and has the capability of spinning at 10,000 rpm. The machine also regulates oil temperature, oil flow rate and runs components at an angular offset thanks to a unique leveling platen. Data generated by Freudenberg-NOK’s thrust washer test machine, in combination with material data supplied by Solvay, was critical in successfully validating the replacement of metallic components with an advanced thermoplastic design. This test capability opens new avenues for further use of the material and the manufacturing process to replace other transmission components, thus enabling OEMs to achieve fuel and weight savings and superior powertrain durability.
Freudenberg–NOK also implemented an innovative manufacturing process, producing the HLHS GAP Thrust Washer using its Single Cavity Net Shape Moulding process. This lean process uses compact, custom-engineered one-cavity injection moulding machines rather than multi-cavity machines to produce high-performance thermoplastic parts. The process improves part quality and reduces scrap and waste. In fact, the approach has reduced the plant’s rejected parts per million (ppm) by a factor of 20 since its implementation. It is faster, more flexible, and results in consistent high-quality parts, eliminating engineered waste and reducing cost. The process also eliminates additional prototyping requirements, supplemental production steps and unpredictable manufacturing variables.
The HLHS GAP Thrust Washer is being manufactured at Freudenberg-NOK’s Findlay, Ohio, US facility. As GM and other industry players evolve and become increasingly comfortable with high-performance thermoplastics, there are opportunities outside of thrust washers for replacement of metallic components with plastics, according to the companies. As thermoplastic performance is proven, replacement of traditional needle bearings can also be realised.
Photo provided by Solvay.
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