Castings produced with green sand molds, however, will require more draft than usual. Less draft is required for machine-molded castings. Several factors will affect how much draft is required for each casting: the manufacturing process, the casting size, and whether the molding is performed by hand or machine will all change the required degree of draft. Ignoring the limitations of these angles will cause the mold to tear when it is removed from the casting. A draft is necessary to extract the pattern from the mold without disturbing the mold walls. The term "draft" refers to the taper on the vertical faces of a pattern. Investment casting allows for a greater level of freedom and wall thickness can drop to as low as to 0.030 in (0.76 mm). As a rule, designs should not have areas that are thinner than 0.25 in (6 mm) when conventional processes are used. It may cool too quickly to enter thin sections that are far away from the mold’s gate. Liquefied (molten) metal cools at an exceptionally fast rate. To be successful, a casting’s design must allow liquefied metal to fill the mold in the thinner sections. Designs thinner than the specifications may make the project un-castable. Minimum section thickness Pouring cups are highlighted in white on green sand molds in preparation for casting.Įvery casting has a minimum thickness determined by its strength and rigidity. There are several key components of design where an understanding of foundry processes and/or communications with supplier foundries will help determine the most cost-effective designs from a foundry’s point of view. For efficient and cost-sensitive production, casting design should select for the simplest production methods that will result in the desired physical properties, net shape demands, and cosmetic appearance.ĭrawings detailing the exact dimensions of the part required should be included with any request for quote. There are at least nine important considerations to be addressed when requesting metal casting pricing from a supplier foundry:Ī cast metal part should be designed to take full advantage of the casting process. Other factors, such as reduced machine work, improved delivery terms, and supplier foundry experience and reliability, are particularly important to determine the actual cost versus value of the casting. While it may be tempting to automatically select the lowest price quoted, doing so can lead to delayed delivery or a lower quality casting-both of which can be more expensive in the long term.Ī savvy customer must weigh all the provisions of the quotation received, including tooling requirements, tolerances, and finish allowances, as well as any exceptions taken to drawings, specifications, and processing requirements. The purpose of requesting a quotation for a casting is to establish the optimal balance of purchased casting cost, quality, and delivery time. Clear and thorough communication with the supplier foundry will result in a well-designed and economical final product. Costly blunders can be avoided by understanding the quotation and casting process. Qualifying a supplier foundry and ordering metal castings can be a time-consuming ordeal, but it doesn’t have to be. Cast metal products offer exceptional strength and durability, making them useful for heavy machine applications in industries related to farming, automobiles, railroads, home appliances, building architecture, ship building, oil and gas extraction, water processing, forestry and mining-to name a few. Metal casting is a process that produces shapes (castings) by filling voids in molds with liquid metal. 9 important considerations to ensure the success of your custom metal casting projects Molten metal being tapped out of a furnace and into a pouring ladle prior to casting.
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