Grantee Research Project Results
Final Report: Novel Metal Shaping Process Using Nontoxic Working Fluids
EPA Contract Number: EPD05010Title: Novel Metal Shaping Process Using Nontoxic Working Fluids
Investigators: Bonifas, Alan
Small Business: Faraday Technology, Inc.
EPA Contact: Richards, April
Phase: I
Project Period: March 1, 2005 through August 31, 2005
Project Amount: $69,882
RFA: Small Business Innovation Research (SBIR) - Phase I (2005) RFA Text | Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , Hazardous Waste/Remediation , SBIR - Waste
Description:
In this research projct, Faraday Technology Inc. developed an advanced electrochemical metal shaping process to eliminate the use of toxic cutting fluids. Traditional machining operations, such as milling, turning and drilling, require adequate cooling at the point of contact, removal of metal chips, and lubricity between the workpiece and tool to achieve acceptable tool life and process performance. The chemical composition of some cutting fluids presents both worker and environmental safety concerns. For example, water-soluble emulsions are widely used due to their enhanced heat removal capability, as compared to traditional oil formulations; however, bacteria and fungi can infest these solutions, creating a health risk to the worker. Biocides, such as triazine or oxazolidene, are used to control colonization of bacteria and fungi. Although these chemicals control one health issue, their very nature creates another risk. A fact sheet published by the Ohio Environmental Protection Agency identifies three approaches to reducing the use of toxic chemicals: 1) the development of new nontoxic cutting fluids, 2) the development of cutting fluid management programs to reduce waste, and 3) the introduction of “low-waste technology” processes — such as electrochemical machining (ECM) and electrical discharge machining (EDM) — to new industries and new materials. This project focuses on the third approach, by introducing a novel metal shaping process that merges conventional ECM with an advanced, electrochemical edge and surface finishing technique to create a hybrid process with enhanced process control that is capable of relatively high metal removal rates in the presence of pH neutral, water-based salt electrolytes. These electrolytes do not foster the growth of bacteria, thereby eliminating the need for biocides.
The main advantages of this technology, in terms of total value added are described below.
Burr-Free Machining
Complete burr removal is crucial in many applications, especially those in closed fluid loops — such as anti-lock brake manifolds on commercial vehicles, and hydrostatic steer units on military amphibious vehicles. Approaches to burr removal, such as manual deburring and thermal deburring, can add a significant amount of cost and variability in the final product. This technology can be coupled with Faraday’s edge and surface finishing technology—which is already fielded in production—to provide a finished component with the desired edge radius and surface finish, in a way that is safe for both the worker and the environment.
Surface Finishes That Meet or Exceed Those Currently Being Achieved Through Conventional Machining Techniques
Through the proper selection of process parameters, the surface finish achieved using similar electrochemical processes has met or exceeded industrial requirements.
Non-Contact Machining
Since this technique is non-contact, delicate geometries can be machined. Furthermore, residual stresses are not induced.
Summary/Accomplishments (Outputs/Outcomes):
In this project, Faraday has defined an advanced electrochemical metal shaping process that utilizes nontoxic working fluids. The primary material in the investigation is 1018 carbon steel, although there was a preliminary investigation into 300 series stainless steel as well. Based on the experimentation conducted in the Phase I effort, the removal rate for 1018 carbon steel is based on a feed rate of approximately 1.0 to 1.25 mm/min. The volumetric removal rate is a function of the surface area being machined. In typical electrochemical processes, the feed rate is neither limited nor improved by an increase or decrease in machining area. Of course, this assumes that there is not a limitation due to ineffective flushing of the machining gap (which can happen for large surface areas). Similar feed rates are expected in other materials of interest to the program, such as aluminum and stainless steel. The experimentation showed that the surface roughness increased slightly with increasing feed rates; however, the range of surface roughness measurements taken on a single surface (a total of eight scans) increased significantly for feed rates exceeding 1.25 mm/min.
To determine the effects of a pulsed electric field, a design of experiments was executed and analyzed. A total of three variables, with two levels for each, were investigated. The surface finish achieved for 1018 carbon steel was slightly better than 15 µinch Ra. The overall conclusions of this study are: (1) a forward-only pulse delivers a more uniform surface than one with a reverse pulse for 1018 carbon steel; (2) a lower duty cycle results in better surface properties; and (3) an increased on time favors better surface conditions. A similar study for 300 series stainless steel was also conducted. In that case, the surface finish achieved was below 10 µinch Ra. While the results of this experimentation were less clear than for carbon steel, two important trends did emerge. First, the overall ranges were significantly less than for carbon steel, indicating that this process is more robust for processing stainless steel. Second, the addition of a reverse pulse enhanced the uniformity of the metal dissolution. This is an expected result since the reverse pulse is used to control the passive layer that readily forms on stainless steel. Carbon steel does not exhibit the same tenacious oxide film present on stainless steel; therefore, a reverse pulse plays a much smaller role.
One of the strengths of the developed technology is the ability to generate non-circular cavities in one pass. Furthermore, the process can fabricate intersecting geometries without the generation of burrs. This is significant because in some applications (e.g., anti-lock brake manifolds for consumer vehicles and hydrostatic steer units for military amphibious vehicles), complete burr removal is required to prevent, at a minimum, the burr from disrupting a complex flow path and, worst-case scenario, have the burr separate from the substrate, leading to a system failure. To address this requirement, a simple experiment was set up in the Phase I effort where a square cavity was machined into a steel coupon that had an existing hole running perpendicular to the feed of the tool. This experiment demonstrated the capability of the process by creating the intersecting geometry, without generating a burr on the intersection edge. In fact, the edge has a radius, which is desirable for many applications.
The electrolyte utilized in this project is a neutral, water-based salt solution, which, when properly filtered, can last for an indefinite amount of time. Based on the experimentation in the Phase I effort, the pH of the solution remained in the range of 7.5 to 8.5. In addition, the concentration of the total ionic species (including both Fe2+ and Fe3+) remained below 0.1 ppm. The suspended solids in the electrolyte remained around 20 ppm. There were no observable adverse effects due to this level of waste products in the electrolyte. Additional monitoring still needs to be gathered, however, to verify the point at which these effects would be seen. Based on the information gathered in the Phase I effort, reasonable worker protection equipment would be necessary (i.e., gloves, safety glasses, etc.), but extensive protective equipment and ventilation would not be required.
To address the reclamation of metal waste from the electrolyte, Faraday spoke with Innovative Waste Management Inc. This firm has implemented a successful program called Beneficial Reuse that pairs up a waste generator (i.e., the company utilizing the technology developed in this program) and a raw material processing facility. The waste being generated in this technology is primarily iron hydroxide, along with residual salts from the electrolyte. Innovative Waste informed Faraday that the salt content of the waste sludge would not affect the metal reclamation process. Typically, the materials Innovative Waste wishes to avoid are sulfur and phosphorous—neither of these materials will be present in the metal waste. In addition, the pH level of the electrolyte would not require special handling. Therefore, the metal waste will not need to be treated prior to shipping, keeping costs low and eliminating the need for additional processing chemicals.
Conclusions:
In this project, Faraday has started to define an advanced electrochemical metal shaping process that utilizes nontoxic working fluids. The primary material in the investigation is 1018 carbon steel, although there was a preliminary investigation into 300 series stainless steel. The surface finishes achieved in the program exceed the surface finish requirements one would expect for mass-produced steel and non-ferrous components. It was shown that the surface finish is strongly coupled with the shape of the electric field (e.g., on time, duty cycle and reverse pulse peak voltage). The maximum feed rates achieved are smaller than those expected for conventional machining techniques; however, Faraday believes that the developed technology does have merit in specific high value-added components where conventional machining fails to deliver. One example of a high value-added machining operation is in the production of noncircular blind holes. In this project, a square hole was created in a single pass using a shaped tool. A portion of this hole intersected an existing hole, without the formation of a burr along the intersecting edge. This is significant because it eliminates the need for costly post-processing steps.
Supplemental Keywords:
electrochemical machining, electrical discharge machining, pulsed electrolysis, burr removal, surface finish, metal shaping, non-toxic working fluids, noncircular blind holes, pH, electrolytes, carbon steel, stainless steel, metal waste, metal reclamation, EPA, small business, SBIR,, RFA, Scientific Discipline, TREATMENT/CONTROL, Sustainable Industry/Business, POLLUTION PREVENTION, Chemical Engineering, Sustainable Environment, waste reduction, Environmental Chemistry, Technology, Technology for Sustainable Environment, Environmental Engineering, industrial design for environment, metal surface engineering, clean technologies, environmentally benign coating, environmentally conscious manufacturing, green design, waste minimization, environmental sustainability, alternative materials, clean manufacturing, surface finishing technology, metal finishing, pulsed electric field, coating processes, engineering, innovative technology, industrial innovations, clean manufacturing designsThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.