Reducing Costs and SKU with Casting Conversions B. Flegl, D. Palmer and K. Wright AerWay Advanced Aeration Systems, Norwich, Ontario, Canada

K. O’Bannon, Urick Foundry, Erie, PA, USA

S. Sumner and V. Popovski Applied Process Inc., Livonia, Michigan, USA

ABSTRACT Manufacturers face multiple challenges in bringing equipment to market. Reducing cost is always important, but not at the sacrifice of performance. Additional considerations like manufacturability and availability of resources can be a challenge regardless of pricing. Converting to a new material or manufacturing process can be an uphill battle for design engineers. There is often resistance to change if a component functions without performance issues. Ultimately, cost reductions can serve as the driving force for a conversion process providing that the performance of the redesigned component is at least equivalent to the prior design. Successful conversions require a team effort between manufacturers and their suppliers. This article summarizes the joint efforts between an agricultural component manufacturer, metal casting facility, and a heat treater to develop a new design for a trunnion bracket assembly that resulted in a dramatic cost savings and improved component performance. INTRODUCTION Agricultural equipment is typically produced with a large numbers of welded components or weldments. To make such equipment requires skilled welders and machinists, and they are in short supply. As stated by Matthew Philips in Bloomberg Businessweek,1 “Manufacturing has grown faster than the rest of the U.S. economy since the recession ended in June 2009. For the first time since the early 1960s, manufacturers have added jobs four years in a row. Couple that with the oil and gas boom and the thousands of miles of new pipeline being built, and the demand for skilled welders has risen sharply.” As a result, it is easy to see that manufacturing companies can face long lead times and high prices for welded and machined components. Iron castings offer an alternative method and material for many components that would otherwise be welded. Ductile iron produced in modern foundries can allow the designer to put material where it is wanted and to remove material from where it is not needed. Ductile iron also offers a wide variety of properties in the as-cast and heat treated conditions to further optimize price and performance on such new designs. The near-net-shape advantages of using ductile iron casting were applied to redesigning a welded trunnion bracket assembly. In addition, the austempering heat treat process was used to produce Austempered Ductile Iron (ADI) which further increased the properties achievable from ductile iron. This ultimately resulted in both cost and part number reductions.

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CASE STUDY The original trunnion bracket, shown in Figures 1(a) and (b), was machined entirely from carbon steel (CSA G40.2144 W) barstock. The mating part, a trunnion bracket guard, consisted of bent steel with two steel ears welded on as shown in Figures 2(a) and (b). Two trunnion brackets and a guard were assembled as shown in the drawing in Figure 3 (a). This assembly protected a bearing as shown in Figure 3(b).

(a)

(b)

Figure 1. A photo of the original trunnion bracket (a) and a sketch of the component (b) are shown. It was completely machined from carbon steel barstock.

(a)

(b)

Figure 2. A photo of the original trunnion bracket guard weldment (a) and a sketch of the component (b) are shown.

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(a)

(b)

Figure 3. A drawing of the trunnion bracket assembly showing how two trunnion brackets and one trunnion bracket guard are fastened together (a) along with a photo showing the assembly and the bearing that is protected inside (b).

One of the early considerations was to design one of the brackets as a GR 80-55-06 ductile iron. Eventually, the mating trunnion bracket and accompanying guard were conceived as a one-piece ADI casting. Austempering is a specialized form of heat treatment that imparts combinations of wear resistance and impact toughness to ductile iron that cannot be achieved in the as-cast state or by the use of other heat treat processes. The ADI piece was specified in GR 230-180-01 for improved wear resistance in the field, as the part is often subjected to severe abrasion and impact damage from rocks and debris. Additional benefits of the new trunnion bracket with guard design were reductions in SKUs and assembly time, thereby further reducing overall cost. The initial draft of the ductile iron and ADI design would have been an effective one and had achieved a cost reduction, but it was not fully optimized. More work was done to take advantage of the design flexibility of the near-net shape technology that is unique to the metal casting process. The natural flowability of ductile iron was used to minimize section sizes which consequently reduced the need for expensive alloying in advance of heat treatment. ADI production requires some discussion between the designer, the foundry, and the heat treater to assure sufficient, but not excess, use of alloying elements like copper and nickel. This further design work reduced part weight, which alone was a cost reduction, but it, also, reduced manufacturing costs at the casting site because the foundry would not have to maintain separate (segregated) stock of heavily-alloyed returns. Lastly, the team conceived a plan for all steps in the manufacturing process, including a critical machining detail; the part would be machined before heat treatment. Machining in the soft state further reduced machining costs compared to machining after austempering.

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The final design of the part shown in Figure 4 resulted in both weigh-saving and cost-saving improvements over the initial version. This design fully exploits the ductile iron casting process’ ability to put material where it is needed and to remove material from where it is not necessary. Other manufacturing methods like forging and fabricating are less able to do this cost-effectively by their very nature. That is, solid metal just does not flow like molten metal. In addition, the material choices in the final assembly were optimized for cost control. Specifically, the regular ductile iron trunnion bracket did not incur the cost of heat treatment while the more demanding trunnion bracket with guard was properly austempered. The redesigned final assembly is shown assembled and mounted to a unit in Figures 5 (a) and (b).

Figure 4. A drawing of the final 2-piece casting design to replace the trunnion bracket assembly is shown. The trunnion bracket with guard on the left is an ADI component while the trunnion bracket on the right is an as-cast ductile iron component.

(a) (b) Figure 5. Views of a unit showing the as-cast ductile iron trunnion bracket (a) and the ADI trunnion bracket with guard (b) are shown.

In addition to reducing the number of parts required, the new design has enabled the manufacturer to move the installation of the bracket from final assembly to roller assembly where it is a more seamless installation. This has reduced assembly time and made installation of the rollers easier and quicker for final assembly. The new trunnion bracket with guard can also be retrofitted to previous units for users who want to upgrade the front only and not buy both halves. It provides additional coverage of the bearing housing over the previous model of approximately ¼ inch on either side (½ inch total) for better protection. May 2014

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Ultimately, the new design was made with improved field performance in mind. Better wear resistance means less labor for the farmer in changing parts and more protection for the critical bearing being protected. SUMMARY • • • • • •

The original trunnion bracket was machined from barstock and became an as-cast 80-55-06 ductile iron casting. The original design of the trunnion bracket with guard was an eight-piece assembly (bracket machined from barstock, three-piece weldment, four fasteners). The final design was a onepiece ADI (GR 230-180-01) casting. The creation of the trunnion bracket with guard casting resulted in a 43% cost reduction compared to the original assembly. Assembly time was also reduced. The integrated guard helps the farmer to reduce downtime. The bearing constantly works in the dirt and, depending on soil type; the bearing housing can be subjected to severe abrasion and impact damage. The new integrated guard design acts as a deflector and shield to protect the bearing and bearing housing. This benefit to the farmer is improved longevity to the bearing, fewer work interruptions, and reduced operating costs associated with parts and labor. Then new design also offers the ability for the farmer to retrofit the new design onto older machines.

ACKNOWLEDGMENTS

The authors would like to thank our colleagues at AerWay Advanced Aeration Systems, Applied Process Inc., AP Westshore Inc., and Urick Foundry for their information and assistance in the preparation of this work. AerWay is made by SAFHolland Canada. The authors would especially like to thank Dr. Kathy Hayrynen of Applied Process Inc. who provided the technical support and editing that made this paper possible. Additional thanks go to the worldwide standards organizations for their efforts in codifying ADI to provide designers with a quantified alternative material/process combination. REFERENCES 1.

Philips, Matthew, “Welders, America Needs You”, Bloomberg Businessweek, March 20, 2014. Web. http://www.businessweek.com/articles/2014-03-20/skilled-welder-shortage-looms-in-u-dot-s-dot-with-many-nearretirement

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