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Getting More for Less with Castings

Edward Vinarcik

Keeping down costs is a never-ending challenge in business. Figuring out how to do more with less is always challenging whether you are in purchasing, manufacturing, design, or any other function within an organization. When working to launch a new product, many facets of the company become tasked to deliver on time, under budget, and without any unexpected quality issues.  

During design, the best way to minimize cost is to keep the design simple by first minimizing the number of unique components and then assuring the remaining components are easy to manufacture and assemble. Engineers and designers must be aware that every time a part is integrated into another, at least one manufacturing operation or process is eliminated. In most cases, several operations are reduced along with the support activities associated with each component. For every part removed from a bill of material, purchasing has one less component to tool and buy, shipping has one less product to receive, incoming quality has one fewer part to qualify, warehouses have one fewer part to store, operations have one fewer part to manage. Every component has a direct cost associated with it. Often, the cost is quantified by looking at the price of the raw material, but this quantification is over simplistic and leaves out hidden financial burdens.

From a quality standpoint, every component adds risk. Fewer parts means fewer things can go wrong during manufacturing, and fewer opportunities for failure once the product is the field. Every quality issue or problem carries a financial burden no matter whether it is fixed.

Developing Designs & Analyzing Integration Potential
During the initial stages of product development, it is not uncommon to build functional prototypes by laser cutting sheet metal, stacking components, and using threaded fasteners or welding to hold them together. Although this might be an effective and easy way to prove out an initial concept, the design can be matured quickly and simply. Analysis methods have been developed to assist engineers and designers in the evaluation of products to determine if components may be integrated. The application of these methods is commonly referred to as Design for Assembly (DFA) or Integrated Design.

Presented in Figure 1 is a flow chart summarizing the main DFA principles as defined by Boothroyd and Dewhurst. The flow chart addresses three key areas, which affect component integration:
•   Movement for function.
•   Material type for function.
•   Service needs.

A designer or product engineer can utilize this flow chart as a guide in analyzing an assembly to determine if component integration is possible.

Figure 1
Figure 1

Component Integration Through Cast Metal Technology
Choosing a manufacturing process often is the next hurdle to component integration. Many manufacturing processes are limited in their ability to produce complex geometries while being competitive. Some processes require the use of many individual parts, which must be assembled into the final component. Other processes require costly secondary operations. Subtractive processes such as machining may be able to produce an integrated design with the very low yield when comparing the amount of raw material at the start to the amount of material in the finished product. To realize the benefits of integration, a flexible and cost-effective additive process is needed.

Few manufacturing methods offer the flexibility obtained from cast metal technologies. All casting processes produce components which are near net shape and offer engineers the ability to go to a finished component in sometimes as little as one step. Extremely complex component geometries can be cast in one piece.

As a result, secondary operations, such as machining, may be minimized or eliminated entirely.

Putting All Your Eggs in One Basket
Some may argue combining sub-components into a single part is like putting all your eggs in one basket, but this is a misconception. If you are missing one sub-component for an assembly, you cannot build. Too many times, manufacturing lines have been shut down because of a missing one-cent fastener. Regardless of the number of sub-components, there is only one basket. Integration reduces the number of eggs in your basket, making it easier to carry. 

Click here to see this story as it appears in the March/April 2019 issue of MCDP.

Numerous case studies can be found to illustrate the power of integration. Pictured in Figure A is single piece cast sub-frame. This casting replaced 79 components and 136 fasteners while simultaneously reducing overall weight by 28%. In addition to eliminating the need to order, track, and manager these sub-components, over four hours of assembly time was saved.

Shown in Figure B are two planter row unit assembly units for the agricultural industry. The initial fabricated assembly was composed of 30 stampings held together with fasteners and welding. The improved integrated design is composed of six assembled ductile iron castings. The new planter with ductile iron row units has less slop, more stability, and improved dimensional accuracy, and vertical travel. By eliminating the distortion and warpage associated with the welded fabrication, seed placement accuracy was improved to 99%.

Magna International, the U.S. Department of Energy, and Ford Motor Company collaborated to develop an integrated vehicle front kick down rail (Figure C). This structural casting reinforces the chassis front structure and adds stiffness, torque load capacity, and torsional rigidity to the body structure. Cast in aluminum, this vacuum diecasting integrates five steel stampings with a 25% reduction in weight. 

This single-piece sub-frame replaced 79 components and 136 fasteners while reducing weight by 28%.
















Figure b
This planter row unit assembly was originally a 30-piece stamped fabrication (left) but converted to an assembly of six ductile iron castings.

















Figure c
A vehicle front kick down rail integrated five steel stampings into a single aluminum diecasting, reducing weight by 25%.