Development of Additively Manufactured Self-Lubricating Rolling Element Bearings for Warehouse Centric AGVs
Date
2024-12
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Stellenbosch : Stellenbosch University
Abstract
The rolling element bearings market is mature, with a massive range of products available and new ones being developed continuously due to technological advances. Developing self-lubricating bearings using additive manufacturing techniques presents an exciting advancement in this industry, specifically for automated guided vehicles in e-commerce warehouse applications. It is speculated that South Africa’s online retail industry will break the R100 billion retail sales mark by 2026. As a result, one of South Africa’s biggest online retailers, Takealot, has started integrating automated guided vehicles into its operations. In April 2022, Takealot opened a new Cape Town warehouse equipped with state-of-the-art distribution centre technology. Notably, the Weasel automated guided vehicles boosted productivity by ensuring a fully automated collection process, with an average collection time of just 3 minutes. It was important to focus on developing self-lubricating bearings with a reduced wear rate because even though it is cheap to replace a worn-out bearing, it is the loss in productivity and reduction in operational efficiency that are more costly to a company when a bearing fails to meet its expected life.
This study focused on using selective laser melting technology to develop rolling element bearings with a reduced wear rate and coefficient of friction. These rolling element bearings could ultimately improve operational efficiency and reduce the maintenance costs of automated guided vehicles by addressing the limitations of conventional rolling element bearings, such as the need for regular lubrication and susceptibility to wear and tear. The study involved printing porous 304 stainless steel samples by selective laser melting. The targeted porosity range for this exercise was between 15% and 35%, as is typical for self-lubricating bearings produced by conventional powder metallurgy processes. The parameter values of scanning speed, laser power and hatch spacing that obtained porosity values within the targeted range were then used to print samples for compression as well as friction and wear testing after they had been determined to have connected porosity by impregnation. Friction and wear tests were conducted on the porous samples, with a fully dense sample used as a control.
The results demonstrated that SLM can fabricate porous samples with connected porosity, facilitating their impregnation. The tested samples also exhibited the capability to sustain the compressive loads sustained in the intended area of application, as well as superior wear and friction performance. The lowest recorded coefficient of friction was 0.041, corresponding to the lowest tested porosity of 16.8%. The highest recorded coefficient of friction was 0.100. These values were significantly lower than the coefficient of friction for the dense sample, which was 0.650. These findings suggest that selective laser melting can produce high-performance bearings, and its successful implementation could lead to significant cost savings and productivity improvements in automated guided vehicles.
Description
Thesis (MEng)--Stellenbosch University, 2024.