The casting design

In the casting design, factors to consider are:

1. The function of the casting,

2. The ability of the casting,

3. Strength casting,

4. Ease of production,

5. Considerations for safety

6. Economies in production.

In order to meet this requirement, we must have a thorough knowledge of production methods including pattern making, molding, core making, melting and flow, etc.

The best design will be achieved only when one is able to make the right choice from a variety of methods available. However, some rules for designing castings are given below to serve as a guide:

1. Sharp corners and often use the fillet should be avoided to avoid stress concentrations.

2. All parts must be designed in a casting of uniform thickness, as far as possible. If, however, the variation is unavoidable, it should be done gradually.

3. A sudden change from the very thick to very thin sections should always be avoided.

4. Casting should be designed as simple as possible, but with a good appearance.

5. Large flat surface on the casting should be avoided because it is difficult to obtain the correct surface on large castings.

6. In designing the casting, various allowances should be provided in making the pattern.

7. The ability to withstand pressure of casting contraction of some members can be enhanced by providing for example a curved shape, arms, pulleys and wheels.

8. The rigid members such as webs and ribs are used in the casting must be at least possible amount, because it can cause various defects such as hot water and shrinkage, etc.

9. Casting should be designed in such a way that would require a simple pattern and the mold easier.

10. In order to design cores for casting, consideration should be given to provide them adequate support in the mold.

11. Deep and narrow pockets in the casting should always be avoided to reduce cleanup costs.

12. The use of metal inserts in the casting must be kept at a minimum.

13. Signs such as names or numbers, etc., should not be given on vertical surfaces because they provide a barrier in the withdrawal pattern.

14. A tolerance of ± 1.6 mm in the casting of small (under 300 mm) must be provided. In terms of accuracy over the desired dimensions, tolerance ± 0.8 mm can be given.

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Classes and Characteristics of Composite Materials

There is no universally accepted definition of a composite material. For the purpose of this work, we consider a composite to be a material consisting of two or more distinct phases, bonded together.

Solid materials can be divided into four categories: polymers, metals, ceramics, and carbon, which we consider as a separate class because of its unique characteristics. We find both reinforcements and matrix  materials in all four categories. This gives us the ability to create a limitless number of new material systems with unique properties that cannot be obtained with any single monolithic material. Table 1 shows the types of material combinations now in use.

Composites are usually classified by the type of material used for the matrix. The four primary categories of composites are polymer matrix composites (PMCs), metal matrix composites (MMCs), ceramic matrix composites (CMCs), and carbon/carbon composites (CCCs). At this time, PMCs are the most widely used class of composites. However, there are important applications of the other types, which are indicative of their great potential in mechanical engineering applications.

Figure 1 shows the main types of reinforcements used in composite materials: aligned continuous fibers, discontinuous fibers, whiskers (elongated single crystals), particles, and numerous forms of fibrous  architectures produced by textile technology, such as fabrics and braids. Increasingly, designers are using hybrid composites that combine different types of reinforcements to achieve more efficiency and to reduce cost.

A common way to represent fiber-reinforced composites is to show the fiber and matrix separated by a slash. For example, carbon fiber-reinforced epoxy is typically written ‘‘carbon/ epoxy,’’ or, ‘‘C/Ep.’’ We represent particle reinforcements by enclosing them in parentheses followed by ‘‘p’’; thus, silicon carbide (SiC) particle-reinforced aluminum appears as ‘‘(SiC)p/ Al.’’

Composites are strongly heterogeneous materials; that is, the properties of a composite vary considerably from point to point in the material, depending on which material phase the point is located in. Monolithic ceramics and metallic alloys are usually considered to be homogeneous materials, to a first approximation.

Many artificial composites, especially those reinforced with fibers, are anisotropic, which means their properties vary with direction (the properties of isotropic materials are the same in every direction). This is a characteristic they share with a widely used natural fibrous composite, wood. As for wood, when structures made from artificial fibrous composites are required to carry load in more than one direction, they are used in laminated form. 

Many fiber-reinforced composites, especially PMCs, MMCs, and CCCs, do not display plastic behavior as metals do, which makes them more sensitive to stress concentrations.  However, the absence of plastic deformation does not mean that composites are brittle materials like monolithic ceramics. The heterogeneous nature of composites results in complex failure mechanisms that impart toughness. Fiber-reinforced materials have been found to produce durable, reliable structural components in countless applications. The unique characteristics of composite materials, especially anisotropy, require the use of special design methods.

Mechanical Engineers’ Handbook: Materials and Mechanical Design, Volume 1, Third Edition.

Edited by Myer Kutz

Copyright  2006 by John Wiley & Sons, Inc.

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Metal Casting Processes

Casting is making components in a way pour the melted material into the mold. Material herein may the form of metal and non-metal. To melt the ingredients necessary furnace (cupola kitchen). Furnace is a kitchen or a place equipped with a heater (heating). The solid material melted until temperature melting point and can be added to the mixture of materials such as chrome, silicon, titanium, aluminum and other materials in order to become more good. Materials that are liquid can be poured into molds. Molds for casting can be made with sand or

metal. For components that are complex and numerous usually use sand mold, while the components that form simple and can use any mass-produced metal molds. In making molds that need to be considered is the porosity and tolerance for sringkage (depreciation) after casting. porosity the higher the better mold to release the gases trapped inside the mold.

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What Are Superalloys?

For purposes of this chapter superalloys are those nickel-, iron–nickel-, and cobalt-base corrosion-resistant alloys generally used above a nominal temperature of 540 C (1000 F).

The iron–nickel-base superalloys are an extension of stainless steel technology and generally are melted and cast to electrode / ingot shapes for subsequent fabrication to components. The iron–nickel-base superalloys usually are wrought, i.e., formed to shape or mostly to shape by hot rolling, forging, etc. On the other hand, after primary production by melting and ingot casting, the cobalt-base and nickel-base superalloys may be used either in wrought or cast form depending on the application or the alloy composition involved. The stainless steels, nickel–chromium alloys, and cobalt dental alloys which evolved into the superalloys

used chromium to provide elevated-temperature corrosion resistance. A Cr2O3 layer on the surface proved very effective in protection against oxidation. Eventually, cast superalloys for the highest temperatures were protected against oxidation by chromium and aluminum. In our opinion, superalloys must contain chromium, probably at the level of 5% (some would argue 8%) or higher for reasonable corrosion resistance.

Mechanical Engineers’ Handbook: Materials and Mechanical Design, Volume 1, Third Edition.
Edited by Myer Kutz
Copyright  2006 by John Wiley & Sons, Inc.

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