Design & Process Guidelines

When designing a casting, active participation should take place between the Design Engineer, the casting producer and the machining source. Meloon Foundries Inc. does this through direct contact with the casting buyer or with the Sales Representative.

Tolerances and Wall Section Considerations | Pattern or Tooling | Aluminum Alloys | Copper Base Alloys | Casting Design
Process Guidelines | Rapid Prototyping

Tolerances and Wall Section Considerations

The chart establishes general guidelines, the type of metal and other variables that will affect the casting cost directly linked to the process.

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Pattern or Tooling

A significant variable in the construction of a pattern is the determination of the shrink factor. The shrink factors vary for different metals and also the configuration of the part. The number of impressions, the gating system, the process or methodology will affect the casting cost. This is better left to the foundry and pattern maker to determine.

Aluminum Alloys

The chart provides typical mechanical properties for aluminum alloys and copper base alloys commonly cast by Meloon Foundries.

Aluminum Alloys

1. Mechanical properties are dependent on the casting process
2. Other and special alloys are available on request

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Copper Base Alloys

1. Mechanical properties are dependent on casting process
2. Other and special alloys are available on request
3. Bismuth is substituted for lead in above alloys - Alloys are lead free.

Additional information may be obtained by contacting Meloon Foundries or The Non-Ferrous Founders Society.

Casting Design

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A Between two points in same part of mold not affected by parting plane or core

B Across parting plane. A-type dimension plus following:

C Affected by core. A-type dimension plus following:

D Dimension: Draft

Normally, a drawing does not show draft. Standard foundry practice is to "add" draft to the part. For the amount of draft required depends on design and type pattern.

E Allowance for finish

Process Guidelines

It is important that the foundry and the casting purchaser establish a good relationship in order for the casting producer to make an acceptable cost effective part. Producing a casting for the first time creates a certain amount of trial and error. It is a development phase and experimental. The expertise and past experience with similar casting configurations provide a guideline for the initial production. Usually the more intricate the casting design and the more drastic the change in section thickness the less predictable the casting soundness. This is why it is important to consider location of isolated heavy sections, uniform wall thicknesses and correct placement or ribs and junction design. Visual casting soundness many times is not sufficient to verify acceptability and machining the sample casting prior to production release is important.

Specifications

Over specifying can increase the cost of a casting appreciable. For example the selection of an alloy that is more difficult to melt. The selection of an alloy that is susceptible to cracking during the solidification process, permission to weld repair, choosing the right chemistry and heat-treatment requirements and finally improper quality requirements adding substantially to the casting cost such as enforcement of radiographic standards in non critical applications.

Under specifying leads in many cases to miss-understanding between the casting producer and the casting supplier. Castings that are designed for critical applications require specific quality criteria. Selection of material that does not meet environmental or mechanical properties frequently leads to poor casting performance.

New Jobs

What are the requirements of first run or sample castings?

1. Is written sample approval requested?
2. Is 100% casting layout required?
3. What inspection standards are required: x-ray or liquid particle inspection?
4. Tolerances and dimensions must be clearly legible on the raw casting and machined casting drawings?
5. What received casting condition is specified? Is shot blasting, surface finish, packaging or shipping requirements specified?
6. Price, delivery and production quantities should be clearly defined.
7. Casting certification critical to casting performance must be agreed to in the quotation. Mechanical and physical test must be specified.

Rapid Prototyping

Rapid Prototyping is the developing of a temporary pattern or tooling from a 3-D computer design. This temporary tooling reduces casting time from months to days. The computer model is used as the blue-print and its dimensions to produce a model. Any rapid prototype pattern that is durable enough to withstand green sand or no bake molding can be used. There are several rapid prototyping processes and the selection depends on the application.

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