Development and Evaluation of Environmentally Friendly Cold-Forging Lubricants Based on an Emulsion Polymerization System
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Date
2006-05-08
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Abstract
Cold forging applications are used in the manufacturing of machine parts, this is due to the conservation of material and high geometric tolerances achieved. The cold forging industry currently uses a zinc phosphate system combined with soap which involves many different chemical baths that produce some toxic wastes. This research covers the development and testing of a new environmentally friendly cold forging lubricant based on an emulsion polymerization system as an alternative to the zinc-phosphate lubrication system. The developed lubricants were compared to the zinc phosphate and a second lubricant, MEC HOMAT.
The lubricants developed under this study were all based on an emulsion polymerization process in which polymer sub-systems were investigated. Iterative testing resulted in a Steryl Methacrylate and 2 Ethyl Hexyl Acrylate system. These polymers have a high glass transition temperature, Tg, and low molecular weight which enhances lubricity during forming.
A total of 29 variants of lubricant were formulated. Out of these, five lubricants were selected for comprehensive testing and comparison with the zinc phosphate system. In order to evaluate the lubricants with respect to their tribological performance, four different lubricant tests were used in conjunction to evaluate the developed lubricant. These tests included the ring compression test, the spike test, double-cup backward extrusion test, and the ball penetration test. The tooling was designed and built to conduct all the tribological tests. In order to size the tooling and properly select material for the tooling and the dies, Finite Element Analysis was used. To investigate the lubricants at an elevated temperature level, a heated set of dies was also designed and constructed. The heated dies designed were used to conduct compression tests at temperatures of 360°F which gave trends indicating friction at higher temperatures.
The ring compression test, a medium severity test, resulted in a friction factor, m, of 0.158, 0.153, 0.142, 0.125, and 0.123 for Poly Lubes 1-5, respectively, compared with 0.124 and 0.157 for HOMAT and Zinc Phosphate respectively. The spike test, a medium severity test, Poly Lubes 1-3 had friction factors of 0.035, 0.055, and 0.050 respectively. The zinc phosphate samples exhibited a friction factor of 0.045. The double-cup backward extrusion test was used to compared the performance of HOMAT and Poly Lube 3. The friction factor for HOMAT on AISI-6061 aluminum was 0.05 compared to 0.04 with Poly Lube 3. Cold forging process temperatures can approach 600°C locally, thus lubricants need to withstand this temperature rise.
To evaluate the lubricants for warmer conditions, dies were heated to 360°F in order to simulate hot dies in an actual forging production process. The elevated temperature testing revealed that the polymer lubricants perform the same or slightly worse at elevated temperatures. The friction decreased 1.0% for Poly Lube 4 and increased 8.2% for Poly Lube 5. The lubricity of zinc phosphate system increased with temperature, having a friction reduction of 31.9%. The performance of HOMAT lubricant was also improved by 17.2% at higher temperatures.
Based on the test results, the developed polymeric lubricants are expected to function well in light to medium severity forging applications.
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Keywords
cold forging, forging, lubrication, tribology, metal forming, metal working, emulsion polymerization,
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Degree
MS
Discipline
Mechanical Engineering
