Universal Ductile Iron Tensile Bar Part II Design Proposal. Prepared By: Joyworks, LLC. Jeremy Lipshaw Shawn Van Dyke

Transcription

1 Universal Ductile Iron Tensile Bar Part II Design Proposal Prepared By: Joyworks, LLC Jeremy Lipshaw Shawn Van Dyke Prepared For: Ductile Iron Society (DIS) Date Submitted April 2017

2 1 INTRODUCTION Tensile bars are a very important testing apparatus used during the production and analysis of castings. They are tools that can predict how a casting will perform within their application by providing information on the casting s material properties including ultimate tensile strength, yield strength, elastic modulus, etc. Many industries prefer to cut a tensile bar from their casting, however, not all castings can accommodate such a feature. Previously, Joyworks and the University of Michigan researched a design iteration of representative ductile iron test bars that would consist of a universal, in-mold tensile bar pattern for efficient use. This report will discuss possible improvements on this model such as optimizing the bar for as little metal use as possible, adding cast-in round grips that can be easily chucked for machining, and creating methods to bring the design to large-scale manufacturing. The purpose of this report is to present the designs that the authors wish to pursue and test in a Ductile Iron Society research project that needs funding. 2 BACKGROUND Currently, the cast iron industry standard is to use the bottom 1, A bars found within Y-blocks and keel blocks as presented in Figure 1. This practice is inefficient for multiple reasons including the fact that the A bars must be sawed from the blocks, have no centers, and require the chucking and turning of square bars. Additionally, extra steps within the manufacturing process will be encountered to accommodate for the free molding of the block. a) b) Figure 1: Schematic cross-sections of a a) Y-block and a b) keel-block 1 These simple shapes were originally chosen so that the metal found within the A bars will be sound while the rest of the casting can act as a riser, counteracting the effects of contraction or shrink that occurs at the last-to-freeze area. Even though cast irons liberate graphite during solidification, and as such, do not exhibit a high contraction in volume as compared to other nonferrous alloys 2, risers are still recommended. The design of the blocks, specifically the y-like Page 2

3 cross area, helps provide progressive solidification in which castings sections most distant from the point of casting will solidify first and the point closest will solidify last. Since relative cooling rate is proportional to section size, the last point to solidify will be the heaviest or thickest section. Due to these risers, a 7 Y-block weighs lbs and yields one test bar and a 7 keel block weights lbs and yields two test bars (10.88 lbs/bar). In response to these design specifications, Joyworks and the University of Michigan created the first iteration of the Universal Tensile Bar. This bar, as illustrated in Figure 2, has a cooling rate and thus, mechanical properties in between those of a Y-block and a keel block, a round cross-section for easier machining, and the potential to equally represent both horizontally and vertically-parted molds due to its 45 degree angle. In contrast, the mass, excluding the gating, increased to lbs. Figure 2: The universal tensile bar attached to its gating system 3 Although this research project made considerable progress, there are still necessary improvements before this design will be accepted within industry. Thus, the investigators will propose a follow-up design and a more thorough analysis. 3 DETAILS These upcoming sections will describe the ultimate goals, planned process, and proposed budget to accomplish this project. 3.1 Objectives To further the advancement of this design, the investigators must account for the following design considerations: retain representative mechanical properties, reduce mass and cost, allow for minimal and easy machining, and provide methodologies for industrial adoption. A major physical change to the original design will be adding cylinders to both ends of the tensile bar which can serve as centered grips for machining. Subsequently, a machinist would not Page 3

4 have to worry about centering the tensile bar and could quickly begin turning it down to proper dimensions directly from the as-cast bar. However, this design change will affect the solidification properties of the original universal tensile bar. Therefore, a new length and taper for the tensile bar will be necessary. To increase casting representation, an independent and less turbulent gating system may be explored. Since the universal tensile bar is designed to be cast in-mold, it will have to be gated to the same system as the main casting. This may increase the amount of work for the manufacturer as well as causing variation between other universal tensile bars due to different gating designs. Thus, the investigators plan to devise a gating system that will control for these factors and allow for easy attachment to the main gating system. Additionally, it is planned that the inner gate will be notched to simplify removing the gating system. The current universal tensile bar can only be used as a rider within vertically-parted molds. The investigators will be experimenting with creating a core, containing the previously discussed independent gating system, that would primarily be used for horizontally-parted molds. Additionally, the core could also be used as a standalone mold. This would allow the manufacturer to have the option to continue using their current tensile bar molding process, while having the possible effect of standardizing the industry. Throughout this investigation, the mechanical properties must remain representative to the casting and match properties seen within modern standards. The investigators plan to create a statistically significant analysis of the mechanical properties comparing the universal tensile bar to keel blocks. Additionally, the universal tensile bar must also be optimized for less mass. Decreasing the mass and increasing the ease of machining will reduce the cost for the manufacturer. 3.2 Process The investigation process will be structured similar to the previous research project such as starting with gathering a larger baseline; however, this baseline will consist of just keel blocks as they are more mass efficient than Y-blocks. Since one of the goals is to prepare a more significant statistical analysis, Joyworks plans to pour two heats for a total of 13 keel blocks and 26 tensile bars. Further, the investigators will research the process used to pour tensile bars within large-scale foundries. This will include the types of machining and molding equipment and interviewing machinists and pourers. Thus, the investigators can factor these opinions and processes into the design while simultaneously learning about industry. Iterating through Solidworks and Magmasoft and accounting for the design objectives, the universal tensile bar will run through multiple combinations of tapers and lengths. Using similar procedures from the previous report, the investigators will be able to design toward moving the shrink away from the gauge length of the bar and matching the cooling rates of the standards while attempting to optimize the mass. Moreover, Joyworks will 3D print the universal tensile bar pattern. Tensile bars will be machined and tested at Element Materials Technology. Page 4

5 Simultaneously, the less turbulent and independent gating system can be developed and tested with Magmasoft. There will be both a statistical and cost analysis for this investigation. Using the large quantities of tensile bar data from the standards and pouring an additional two heats to yield ~25 universal tensile bars, a statistical correlation can be acquired. Using the industrial research, a cost analysis can be created to discover the savings that may be found by switching over to the universal tensile bar. Additionally, the University of Michigan SEM and Applied Process microscopy equipment could be used for metallography. If time permits, the horizontally-parted mold/standalone core can be developed and tested. 3.3 Budget Unlike the previous project, this is not a University of Michigan sponsored project. Thus, the budget will have to account for the additional costs of Joyworks employees and metallography equipment. Fortunately, Magma once again generously chose to donate their time to this DIS project. Below, in Table 1, is an estimate of the budget. Table 1: The Budget for this Project is $10,500 Joyworks 3D Machining and Metallography Calculation Total Pours Printing Tensile Tests and Reporting Cost ($) 4,000 1,000 3,500 1,000 1,000 10,500 Assuming that Joyworks will be contributing four pours, two for the keel blocks baseline and two for the universal tensile bar iteration, the cost can be approximated to $4,000 at an average of $1,000 per pour. This includes the cost of the employees, the raw material, and the energy imbibed. Furthermore, the pattern for the universal tensile bar will be 3D printed. Since the gating system will most likely be printed along with the actual tensile bar pattern, the cost can be estimated to $1,000. Element Materials Technology will machine and pull all of the tensile bars at a compromised price of $50 per tensile bar. Additionally, Element Materials Technology will also send us the chemistry for each pour. Factoring in these services provides a conservative approximation of $3,500. Finally, metallography and calculation/reporting will each be $1,000. This includes the Joyworks labor involved in microscopy, iterating designs with Magma, and renting metallography equipment. 4 CONCLUSION Further improvement for ductile iron tensile bars have the potential to be a great benefit for the industry within a reasonable budget (Table 1). In comparison to the current standards, the next iteration of the universal tensile bar could increase machining and casting efficiency while reducing costs. Thus, the investigators propose a follow-up research project to bring the universal tensile bar to industrial standards. Using statistical and cost analyses, as well as collaborating with Magma, the universal tensile bar has the potential to revolutionize the way ductile iron can be characterized. Page 5

6 5 REFERENCES 1. A Standard Specifications for Ductile Iron Castings 2. Cast Metals Handbook. Chicago: American Foundrymen's Association, Print. 3. Universal Ductile Iron Tensile Bar. Ductile Iron Society, Research Project No. 55-S, December 2016 Page 6