In order to increase the likelihood that a successful casting will result, the buyer must give proper attention to design principles, alloy selection and/or specification, the choice of casting method and the type and rigor of inspection procedures. This is especially true when the foundry is an independent job shop, where communication among designer, metallurgist, and foundrymen may not be so close as it might be in an in-house or captive operation. The following sample RFQ is to provide a basic guideline on what information goes into ordering a casting.
ALLOY SELECTION - Identify the alloy unambiguously. This normally involves nothing more than specifying the appropriate UNS designation. Conforming specifications should be cited, where applicable, and special compositional requirements may be added, if needed. Heat treatment and/or annealing conditions should be spelled out. Avoid ordering alloys by common names, as these can be inexact, and that can lead to disagreement. Also, common or descriptive names usually don't satisfy quality assurance requirements.
CASTING DESIGN - Describe the casting's design using appropriate drawings for the product, pattern and mold layout. Ideally, drawings will represent a consensus arrived at among the designer, metallurgist, patternmaker and foundryman. All parties involved should accept the design package before production begins.
PATTERNS - Patterns may be supplied by either the customer or the foundry. Whatever the arrangement, the foundry should be consulted regarding the type, material, layout and coring requirements for the patterns involved.
MOLDING METHOD - The molding method used will generally be based on either the product's quality requirements, the type of alloy and/or the number of castings to be produced. Any special requirements or limitations of the casting method should be carefully addressed by the designer - and understood by both the designer and foundryman - before committing the job to production.
INSPECTION REQUIREMENTS - Quality control requirements are usually spelled out or given as options in conforming specifications, and the designer/customer need only refer to these documents to determine what may be reasonably expected of the foundry. Where conforming specifications are not called out, it becomes very important that all quality requirements are thoroughly agreed upon before any metal is poured. Typical requirements include chemical composition, mechanical properties tests on concurrently cast test bars, radiography and/or other non-destructive examination. Performance qualifications such as pressure tests can also be called for in the case of large production runs or new designs involving safety-related products.
PROTOTYPE PRODUCTION - Unfortunately, many casting mistakes do not become evident until the product has been cast, cleaned, machined and inspected, i.e., until all of the value has been added. It is therefore common practice to make a few trial runs, particularly for complex castings with extensive coring. Costs are involved, but they can be offset in part by reclaiming the metal. Assuming the metal composition is correct, failed prototype castings make ideal corrosion test specimens. It is far less costly to modify the design, change the foundry practice or tweak the alloy composition than it is to repair or reject an entire production lot of faulty products.