Manufacturing Process
Laboratory # 6
Aluminum Sand Casting

Gold Team

Candace Berry

Rhoda Wilson

Monique Burgess

Time of Presentation 2:00pm 12/11/98

Final product was turned in to Dr.Salimian


Introduction:

Sand casting, and indeed metal casting I one of the worlds oldest form of manufacturing, it dates as far back as 4000 BC . Sand molds are good examples of expendable mold, they generally provides an economical or cost effective means of producing most parts because the sand can be broken up and reused. Apart from being cost effective, sand casting enables the manufacture of products with intricate parts. There is no limit to size , shape or weight of the products manufactured By sand casting. " Typical cast products are engine blocks, crankshaft, piston, valves , railroad wheels And ornamental artifacts." ( Kalpakijain 262) Also, in spite of the impacting manufacturing processes today. Kalpakijian identified two trends that are presently having a large impact on the casting Industry. One is the fact that the casting industry is continuously undergoing mechanization and automation of the casting process. This trend has resulted in the use of advance machinery and automated process control to replace the traditional methods of casting. The second trend affecting The industry is the continuous improvement of the quality of casting resulting in product with Very close tolerance. For this laboratory project, we are required to cast on aluminum dog using a sand mold ( Sand casting). To achieve the desired result, we made an impression in the sand using the pattern with Similar shape and dimension of the required product. After the making of the mold, the aluminum Was melted and poured into the mold via the sprue. The molten metal was left to sodifiy and the product removed by breaking the sand mold. This is the typical procedure that is adhered to in all metal casting process.

DESIGN APPROACH

The design philosophy for this lab takes into consideration that the design should not only serve the function, but must also have the ability to facilitate or favor the casting process. This is especially important due to the fact that the castings have work hardened surface and cause significant tool wear in post cast machining. After selecting a pattern (the dog), it must be evaluated; noting the size and shape, the contours, and overall appearance of the metal piece. These observations play a critical role in deciding where to create sprues, runners, and in-gates. The size of the drag and cope was not big enough to allow much room to "play" with. Therefore, we decided to place the pattern in a slanted orientation. This is to ensure that the molten metal has more room to flow evenly into the cavity. We decided to create the sprue at the bottom, flat base of our pattern. This is a good starting position for the molten metal to be poured. We noticed that the chosen pattern had a great deal of detailed lines. So, the sand must be firmly rammed. We also noticed that the pattern did not come in two halves, but had a small depression shape at the bottom. So when the drag is turned upside down, there is no match for the lower half. We also knew when filling the cope with sand, we must not ram too firmly otherwise the pattern on the bottom will be destroyed.

THEORY AND CALCULATIONS

Sand casting is an art form. It is a form of expression that is simple and effective in itself. It is the casting of material into molds made in sand, with the intention of having the casting itself pick up a layer of sand on the surface. In sand casting, one achieves an object, when viewed from different angles to reflect many different things. Practically anything can be used to make an impression. Ordinary kitchen tools, objects around the house, even rocks can be used in some kind of casting. The objects made by this process are used in various manners. Wall plaques are the most popular, but there is no reason why other things of more useful purposes are not possible. .

Procedure:

As stated earlier, the project involved a sand mold to make an aluminum product. 1. First task was the making of the sand mold required for the casting process. 2. To accomplish this sand mold making process, synthetic sands were used to make the drag and the Cope. The process of making the drag part of the mold involved the use of a wooden plane board, a flask and a parting powder. 3. The parting powder is uniformly distributed over plane board, 4. The half part of the pattern is placed on top of the board and the uniform distribution of the parting powder over the wooden plane is repeated. 5. After the board is uniformly sprayed with the parting powder, the synthetic sand is in like manner Distributed over the surface of the board and half of the pattern 6. The Sand is about half of inch high up the drag, the sand is compacted by pressing on it with a flat wooden material. The uniform sand spraying then continue with the repetition of the compacting process at every half or one inch increment of the sand height. 7. The Process continues until the entire drag flask is filled with sand. 8. After the drag is made, it is turned upside down and the second half of the pattern is placed on top of the drag half. 9. The sprue and open riser pattern are pushed about one quarter of an inch inside the drag to ensure rigidity of the pattern. 10. After positioning the sprue and the open riser, the flask for the cope is placed on top of the drag and parting powder once again sprayed uniformly over the pattern and the inserts for the sprue and open riser. 11. The cope is then sand filled the same way as the drag, After sand filling cope, an area around the top of the sprue and open riser inserts were caved out ot facilitate the removal of these inserts. 12. After the removal of the sprue and open riser inserts, the plane wooden board is used to cover the Exposed surface, then the cope is turned upside down to expose the side with the pattern 13. The two channels are made one from the sprue position to the pattern and the other from the open Riser position to the pattern.This will enable the flow of molten metal from the sprue to the mold and out through the open riser. 14. With the aid of the screw, the patterns are removed both from the drag and the cope leaving behind the mold cavity. 14. The cope is placed on top of the drag such that the two cavities are in contact with each other. 15. Now the mold is ready for pouring of the molten aluminum metal. 16. The molten aluminum which has been in the furnace prior to this time is now poured down the basin in the mold cavity. 17. About three to five minutes after the pouring, the sand mold is broken and the casting removed. 18. The casting was cooled for 5 min in water. 19. The sprue and the open riser were hatched sawing off and edges were smoothed with a file.

Analysis:

This experiment used Analytical theory of sand casting is produced when molten metal is poured at atmospheric pressure into a cavity formed in a compacted molding sand. In typical Ferrous casting, the mold would be bonded with 6 to 8 percent western bentonite mulled with 2 to 3 percent water. Patterns would be reusable, but the sand molds would be broken from the casting after the solidified casting had cooled sufficiently. The sand would be returned to the muller for recycling by mulling with some new clay and water to reactivate the old clay. Sand molds define the external geometry of a casting, whereas cores define the interior or undercuts. Sand casting accounts for more than 90 percent of all metal poured, on a tonnage basis. It can be an extremely high production process .The process requires a high investment in plan facilities and sand handling equipment to make such production rates possible ( they hire Morgan state Industrial engineering ) . Sand casting is versatile and is capable of making parts ranging from small knobs to huge radiotelescope bases weighing more than 200,000 lbs.
Discussion of Corrections and Results
After the removal of the aluminum product from the mold, it was analyze for errors and defects . A drawing of the final product is was present in the presentation. Some of the major defects observed on the casting include metallic projections, cavities and incomplete casting. The metallic projections were more prominent at the parting line sections of the casting. They were produced because the drage and the cope were not tightly closed together, therefore some molten metals escaped from the parting line and soldified to form metallic projection on the casting. Example of metallic projections, cavities were also noticed on the casting. Both external and internal cavities such as blowholes and pinholes respectively were observed on the casting. An example of the blowhole is seen on one side of the casting and an example of a pinhole occurred at the bottom or base of the product. These cavities must have resulted form defect in the sand mold. A third type of defect not noticed on the product as incomplete runs which resulted from the premature cooling of the metal before it reached the end of the mold cavity. These misruns are attributed to slow pouring speed and not insufficiency of the molten metals since there was enough molten metal left over after the pouring. Although we encountered some problems in the course of the laboratory project , further Analysis of the aluminum casting showed that it was dimensionally consistent with the required product. Some of the problem encountered included the breaking off of the some tips of the sand Mold during the process of removing the pattern. This problem was corrected by patching the affected area with synthetic sand. The surface finish was excellent. After receiving the final product, there were a few imperfections. Firstly, the surface of the pattern had several small holes. This is known as macroporosity, which may be amplified by the evolution of gas before and during solidification. Ventilation holes should have been made in the cope and drag to allow circulation of airflow. Secondly, much more emphasis was placed on the ramming process instead of creating runners and in-gates which would allow a more continuous, uniform flow of molten metal into the mold cavity without turbulence. Also, ramming excessively (especially in the drag) caused the pattern to stiffen in the sand and made removal difficult; another sprue had to be created near the head of the pattern. Parts of the pattern that was disturbed and did not quite match the original. However, thorough ramming made the detailed lines and shapes appear clearly.

CONCLUSION

The overall process was shown to be effective, yet time consuming. Ramming the sand took the greatest amount of time and effort. Automated process would improve efficiency and quality of castings, and may reduce the amount of defects. Also, the removal of the gates, runners, and risers is better automated to produce high surface quality. By using the hacksaw and file, the surface quality is reduced; its finish is not as smooth as the original. Eventhough, the permeability* of the sand was good, it was not excellent. There was a lot of moisture content present in the sand. Safety factors played an important role in this laboratory exercise. Especially when removing the cast from the sand, the metal is still extremely hot (the instructor performed the actual pouring of the metal into each mold).

CASTING

Disadvantages Advantages Tooling lead time is long Facilitates complex shapes Tooling cost is high Allows hollow parts Design changes are costly and time-consuming Allows use of hard materials Reduces material waste * The ability of the molding sand to allow gases to pass through

WORKS CITED

El Wakil, Sherif. Processes and Design for Manufacturing: Second Edition; PWS Publishing Company, Boston; 1998.