Cast-it: casting solutions for cost and lead time reduction.
Reducing manufacturing cost and lead time are two key components in sustaining a company's livelihood - helping it achieve higher profitability, acquire business and ensure continued customer satisfaction. Manufacturing cost and lead time are inherent to the design of a part, and by using a proven design process along with technological tools, prototype iterations can be reduced, and parts can be optimized prior to production.
In an effort to provide companies and government design agencies with an optimized process, the U.S. Defense Logistics Agency (DLA) has partnered with the American Metalcasting Consortium (AMC) in a cost-shared contract known as the Metalcasting Lead Time and Cost Reduction Program. AMC seeks to achieve two purposes: for industry, to promote the use of castings and the necessary research to improve casting capability; and for the U.S. Dept. of Defense (DOD), to provide lead time and cost reduction and quality improvement for castings used by all branches of the military. Every military organization relies on DLA supply centers for components to support weapon system readiness, repair and maintenance requirements.
The CAST-IT Team
The Casting Advanced Systems Technology-Integration Team (CAST-IT) was formed to showcase castings as complex shapes that meet or exceed the performance of fabrications, forgings or weldments.
The multi-disciplinary team of engineers, foundries and machine shops participate collectively to respond to DOD customer requests involving a wide range of casting design, manufacturing and acquisition-related issues. Engineers working within integrated customer teams have designed, prototyped and tested numerous finished cast components and assemblies, demonstrating the value and efficiency of near net-shape manufacturing. Several components and assemblies that have been redesigned by the team now are available to be procured as castings, typically as an alternate manufacturing process. A few examples of these products are shown in Fig. 1.
The CAST-IT Process
CAST-IT is an established and documented methodology that builds upon the existing knowledge base of experienced team members as well as the various AMC member's collective strengths and core capabilities. The process was developed to effectively design or redesign castings into functional components and, to date, it has provided a $6.75-million cost savings available annually to the DOD. Every redesign process is as unique as the product geometry, field application and associated design team that ultimately conducts the design, prototype and test requirements for complete acceptance. However, every redesign follows the same central process AMC employs to design and acquire cast prototypes for the government. It is a customer-driven process that invokes the latest quality, design and teaming tools, and the use of concurrent engineering and integrated teaming is critical to its success. Seven discrete steps make up the process.
Using a specific casting example, this article illustrates the key steps in the conversion process followed by CAST-IT.
CASE HISTORY: THE M1 ABRAMS ICE CLEAT
The ice cleat CAST-IT process (see sidebar, p. 32-33) was initiated by a requirement for a "should-cost review" by the Defense Supply Center Columbus (DSCC), which identified the part as a potential casting conversion. At the time of the review, a requirement existed for 58 sets of cleats, with 64 cleats/set, for Bosnia and Korea winter operations in 1998-99. Quotes for forged parts required production lead times exceeding 300 days. The team reviewed the part for castability, and after an initial assessment and communication with DSCC-Land Systems Group, it was determined that the cleat could be manufactured as a casting within the required lead time. A team was created with members from Program Management Office Abrams (PM Abrams), Tank-automotive & Armaments COMmand (TACOM), DSCC and AMC.
1 Identify Component
The team partners with the DOD and prime contractor organizations to identify problematic metal components. The team begins building a business case to determine the cast design's impact on acquisition costs and/or production lead time. Identified components may be subcomponents of currently fielded weapon systems, or they may be associated with design development activities for new weapon systems. The team assesses a component regarding its geometry, material requirements and overall application. This initial assessment is conducted quickly with little investment of time and resources.
For the ice cleat, its field application and technical, engineering and test requirements were collected. Ice cleats are used on many tracked vehicles with replaceable track pads, like the M1 Abrams Main Battle Tank, increasing their mobility on snow and ice. The cleat for the M1 was designed and specified to be forged, although other ice cleats are designed as both castings and forgings. The current design configuration of the cleat lent itself to being cast without major design changes.
2 Define Customer Requirements
Critical activities in this second step include identifying team members, building the integrated team and defining all customer requirements, which include all design, manufacture, test, quality, assembly and acceptance criteria.
The traditional lines between design, manufacturing and procurement are becoming blurred as organizations realize the importance of integrated product design and manufacture. Engineers seek out team members relevant to all aspects of the designing, casting, testing, machining, assembling and acceptance of components and assemblies. Customer interface in all aspects of these disciplines is critical for success.
Metrics are established to determine the key measures of success for the process. Examples of key measures of success include a cost savings, lead time reduction, part count reduction in a complex assembly or the availability of alternate sources resulting from a sole source supply chain. The team must work together to establish design requirements and a test plan, which when successfully followed will allow component or assembly acceptance as a viable, manufacturing alternative, signed off by the design authority. Often the team documents all customer and team expectations in a written memorandum of agreement that formally details the roles and expectations of each team member.
For the ice cleat process, DSCC requirements were obtained to ensure that the investment in redesigning and prototyping would be returned to them by way of reduced cost, lead time or improved value. Defining requirements ensured that all teammates become involved at the initial stage of the process. During this step, business and technical data for the part were compiled with the assistance of DSCC and TACOM. Although the quoted costs for the orders were reasonable, the shortest lead time was 300 days. Given this lead time, troops would not receive parts until after the winter. By working with TACOM and PM Abrams, it was determined that a deviation for casting the cleats would allow a lead time reduction for the next order, following successful testing.
3 Casting Design
Metalcasting processes offer the most flexibility and design freedom of any metalforming process. Applying this design freedom to complex metal shapes requires knowledge of metalcasting processes and casting design. In addition, building a design that takes advantage of this flexibility often requires changing the way people think about a component's shape and function. To develop the most efficient design, the team analyzes a design feature's shape, size, complexity and system/assembly integration. As the ability to form near net shape into complex geometry is exploited, the conceptual design emerges and then establishes a geometric footprint, basic functionality requirements and general material properties. The team also considers combining multiple parts and functions to create a more efficient assembly. Formal design reviews with the customer are conducted for both the preliminary and detailed designs. These key milestones maintain focus on the customer requirements as the design progresses.
Computer Aided Design (CAD) tools are used to create a solid model, and this geometric model becomes the origin for all subsequent design work and prototype building. The CAD model provides the vehicle for design changes and iterations as the conceptual design moves to the detailed design. Functional performance simulations are conducted at this step and may include stress analysis or other required simulation tools. Flow and solidification simulation software tools are used for analytical means of calculating initial gating and risering parameters. Rigging parameters then are fed into the design model for the pattern or tool. The various options for patternmaking and foundry processes are considered and selected here. Source selection criteria are determined for identifying potential manufacturing sources, including: a combination of previous foundry experience with similar alloy, size, complexity, tooling/pattern and foundry process; delivery; quality constraints; cost; and teaming aptitude and attitude.
One of the most important factors in developing a successfully detailed design is including foundry process considerations. The team then is able to deliver all customer requirements in a complete design package that incorporates production capabilities and greatly improves the chances for prototype success.
During the design phase of the ice cleat, the latest tools were used in conjunction with input from the team to design a part that not only met the functional requirements but also was economical to manufacture. Several tools were deployed to design the ice cleat, and a conceptual solid model was created and transmitted electronically for review through the use of model-viewing software. This enabled the team to manipulate and review the overall geometry for castability. Through the use of AFSolid (solidification analysis software), gating and riser locations were optimized. Mold fill and solidification parameters for the design were verified, and design changes were made to the part geometry to make the part more castable. One such change was to extend the pad where the stud is mounted to the edge of the profile of the part. This modification was made to allow gating of the part through the edge section, which reduced post-processing. Industry teammates (foundry, pattern shop and machine shop) contributed to a producable design. The team recommended an alloy change from 4340 to 8630 steel to reduce hot tearing and material expense. TACOM reviewed and approved the detailed design.
4 Develop Tooling
Customer approval of the detailed design moves the process to the prototype tooling step. A pattern or tool is produced from the solid model that is created by the detailed part design. The team commonly uses rapid tooling techniques such as Laminated Object Manufacturing (LOM), Stereolithography (SLA) or CNC machining for the first pattern. Rapid tooling exploits current technology advances and is typically the team's choice to compress prototype delivery time.
To meet the aggressive deadline for parts for the ice cleat, the mold pattern had to be produced quickly. Once again, industry innovation was put to use as patterns of the cleat were produced by CNC machining blocks of aluminum, which was selected for its moderate cost and good wear properties. Using the solid model to derive the machining code for the CNC machine, the parts were quickly machined to be exact replicas. The patterns were mounted on a mahogany board with the required rigging. Wood was used for mounting and other features to minimize cost. The foundry tooling was completed in less than 2 weeks. In addition, LOM rapid prototyping was used to create a mock part. The LOM part also was used to facilitate the machining fixture set points, allowing concurrency with building both foundry and machine tooling. The LOM part also was used to fit-check the casting design on a T158 track shoe.
5 Produce Prototypes
Foundry setup activities include gating, risering and mold production. First, a sample pour verifies rigging, shrink, quality and all other critical features. Few surprises are anticipated at this step since foundry engineers have been integrated team members since the design step. Following sample approval, prototype castings are poured.
Castings then undergo post-processing operations such as cleanup, heat treat, nondestructive testing and evaluation, and all other required processing. Final machining, protective finishes, component subassembly and finish assembly then are performed. These machining features (datum, tolerances, fixturing, surface finish) and other required post-processing requirements were established in the detailed design step. Integrating post-casting finishing operation capabilities into the casting design features compresses prototype delivery times by eliminating redesign iterations.
To validate the fill process parameters for the ice cleat, a sample pour of two molds was made. Validation was successful and the prototype order of parts was cast, finished and heat treated at Varicast, Portland, Oregon. The parts passed several nondestructive evaluation tests for conformance, including visual, dimensional, hardness and magnetic particle. The cast cleats then were machined and assembled with the fastening stud. Several issues such as a proprietary stud design and phosphate coating were identified prior to manufacturing and were resolved by the team. In the case of the stud, the design was modified for assembly with Loctite adhesive to reduce the cost and lead time that would have been associated with the original design. Since the phosphate coating was determined to be solely for the purpose of shelf life, the design team opted for deviation from this requirement to again minimize the lead time. The prototype order of 80 cleats was taken from design to complete assembly in only 6 weeks, and the parts were successfully inspected to print.
6 Test Prototypes
Finished prototype castings or assemblies are laboratory and/or field-tested on weapon systems per specified customer requirements. Team members and customers witness these tests to verify acceptable functional performance. Many times CAST-IT prototypes are considered first article samples, which, when successfully field-tested, provide engineering data to verify the casting performance. Field test data then is used to initiate an engineering waiver document by the military that allows castings for future acquisitions.
PM Abrams specified and funded functional field tests of the ice cleat at Yuma Proving Grounds in Arizona. The field tests were intended to ensure that no catastrophic failures of cast ice cleats would occur. The cleats successfully passed all course requirements. Before submitting a request for engineering change proposal to add a casting option to the drawing, TACOM requested a second test to be performed. The cleats performed equally well in colder conditions at the Aberdeen Test Center in Maryland.
7 Produce Technical Data Package
The team delivers a commercially compliant TDP in the CAD file format specified by customer requirements for both the casting and finished assembly designs. Additionally, engineering prints are provided to all team customers. The TDP includes all required Quality Assurance Provisions (QAP) and detailed processing specifications as needed. The final technical document is reviewed by all industry team members for manufacturability. The final products of every CAST-IT process are customer-accepted prototype castings and full technical data packages that enable the customer efficient future casting acquisitions.
The solid model of the ice cleat was used to create 2-D drawings with applicable geometric dimensioning and tolerancing (GD&T) to ensure proper design intent for manufacturing. Drawings were created for both the cast and machined part that allow inspection to print after each manufacturing process. In addition to incorporating GD&T, the prints were updated to the most recent specifications. The team and the manufacturers of the prototypes reviewed the technical package for any final modifications, and electronic and printed drawings of the TDP then were delivered to TACOM. The final TDP assists in efficient procurement of future orders for production parts.
The team delivered a final TDP to support current and future ice cleat orders in a fraction of the time required for forgings. Shorter production lead times have been demonstrated for future buys (300 to 90 days), increasing weapon system readiness. The design package allows two options for manufacturing methods - forging and casting, and the availability of alternate sources provides the Army with the lowest cost and lead time for delivery. Finally, through the process, a team consisting of the procurement offices, engineering support authority, casting expertise and industry effectively partnered to support the soldier in the field.
Upon conclusion of the process, the team documents and shares its findings and results with its partners so that in the future, these team partners can operate on their own or with little assistance from AMC.
A Proven Process
The team continues to demonstrate the benefits gained by taking advantage of castings as the primary manufacturing method for complex metal shapes. Through this demonstration, the team has investigated, developed and deployed the process - a robust design and acquisition process using the latest technological and teaming tools. The process is continually being improved by adaptations invoked by its engineers and as the process is applied and lessons are learned. Process steps are added, modified and refined as integrated design teams seek and implement new tools for compressing design and manufacturing lead times and cost. The process has proven that open communication between integrated members of manufacturing, design, test and procurement makes for a winning partnership.
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|Comment:||Cast-it: casting solutions for cost and lead time reduction.|
|Date:||Sep 1, 1999|
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