MSE 5090: Case Studies in Material Selection

Arrayed below are the figures presented on Wednesday 10/21/98 in class. They depict the method used by the CMS software to categorize, sort and  plot various materials processed according to attributes of these processes. The key to their use in the selection process involves obtaining a congruence between the component attributes such as size, shape , finish, cost etc. and those of an process. In other words , if a component requires a surface finish of 1 micron and the process under consideration can only yield surface finishes of 10 microns , then the incongruence will move that process out of the selection space in the program.

In this regard , the outcomes of the material selection part of the design process, coupled to the design requirements on the component that were passed through from the customer form the constraints and design requirements for the process . These form the screen from which the choices for acceptable  processes are narrowed.
 

Figure 1 (above) The classification of processes and (below) the breakdown of a component design. The method identifies processes with an attribute-profile which matches that required by the design.
Figure 2(a) The classification of process types. Each process is linked to one or more members of each.
Figure 2(c) The classification of shapes. Each process is linked to one or more members of each.
Figure 3(a) Physical attributes of processes.
Figure 3(b) Economic attributes of processes.

Description: In the CO2/SILICATE process, a mixture of sand and sodium silicate binder is packed around a pattern that has the shape of the desired casting. C02 is introduced to the compacted sand whereupon the sodium silicate gels to produce a rigid mold. The pattern is then removed to leave the cavity in which molten metal is poured. When the metal solidifies, the mold is broken to retrieve the casting. The pattern is made of either wood, plastic or metal. The pattern is made slightly larger than the desired casting to compensate for shrinkage of the metal as it cools, If the casting is to he machined, a machining allowance is also added. The process is not widely used. Major reasons have been the problems of deterioration of molds and cores during storage and thc poor breakdown characteristics associated with the inorganic silicate bond. In addition, close control over process variables such as temperature, CO2 flow rate and gassing time is essential.

Shape notes: Bosses, undercuts, inserts and hollow sections are all practical. Shapes are frequently solid but complex internal shapes can he made using cores.

Environmental notes: Safe and environmentally acceptable, however care is required in handling process chemicals and adequate ventilation required for C02. The binders are odorless, non-toxic, non-flammable and water-rinsable.

Notes: Minimum wall thickness depends on the alloy to be cast and the length of the section involved. Tolerances depend on the dimension - the values given apply to a 25 mm dimension.

Typical uses: Wide range of applications including machine tool castings, large engine blocks and heads. Process is also used for the mass production of cores.

References: G_ENAL001;G _ENBR001;G_ENKA001;G_ ENSC001;G_ENWA001

Figure 4  above .A typical record. It is that for a member of the casting family: C02/Silicate Sand Casting.

Figure 5 (a) The SCREENING stage. The attributes of processes are plotted as selection charts, created by the software. The attributes specified by the designer are plotted as selection boxes on the charts. The software retrieves the subset of processes which meet all the required attributes.

 Last update 10-21-98