CASTING LAB #1 REPORT: INTRODUCTION TO SAND CASTING PROCESSES AND METAL CASTABILITY

Transcription

1 CASTING LAB #1 REPORT: INTRODUCTION TO SAND CASTING PROCESSES AND METAL CASTABILITY Technical Report Submitted to: Dept. of Industrial & Manufacturing Engineering Prof. Edward C. De Meter 310 Leonhard Building The Pennsylvania State University University Park, PA Submitted by: William Delgiorno Erin Farrell Joshua Kukorlo Matt LaMarr Date: April 2, 2014

2 TABLE OF CONTENTS INVESTIGATION RESULTS Green Sand Composition and Properties Green Sand Molds Cores Advantages and Disadvantages of EPC Advantages and Disadvantages of Permanent Mold Casting Advantages and Disadvantages of Investment Casting Research on 6061 Aluminum and 356 Aluminum Analysis of Fluidity Test Results... 5 REFERENCES... 6 APPENDIX

3 INVESTIGATION RESULTS 5.1 Green Sand Composition and Properties Four principle components of green sand and their purposes: [1] 1. Silica Sand inexpensive and resistant to high temperatures, creates higher green strength, more permeability, and greater refractory strength 2. Clay (Bentonite) 3. Water used to plasticize clay and enable molding 4. Combustibles ignites, resultant gases drive out moisture at the mold interface Mullers are used to combine the sand with the additives so that the mixture is uniform. [1] Green strength and permeability are the two most critical properties of green sand composition. A high strength is needed to prevent mold breakage, but a strength that is too high can cause mold interference which will cause hot tears during solidification and shrinkage. A higher permeability allows gases to exit casting, but a lower permeability will make the surface finish better. These properties must be controlled because an extreme of either property could ruin the mold. [2] 5.2 Green Sand Molds Deciding how to position and orient a casting in a mold relative to the cope and drag is important. The height of the casting should be minimalized and the largest portion kept relatively low. Also, porosity should be taken into account. Porosity will form and float upwards due to buoyancy, weakening parts at the top of the mold. Therefore, the more critical component of the casting should be facing down. The location of the parting line should be flat and not contoured. Also, it is better for the parting line to be placed on edges and corners so that the flash will not be as visible. The parting line should be placed as low as possible relative to the casting for less-dense metals and around the middle of the height for denser metals. [1] A parting line is a visible line on a product that results from the sand casting process. Since the mold is composed of two parts (cope and drag) the final product will have extra material at the line where the cope and drag meet. [1] The typical draft relative to the parting line in sand-mold patterns ranges from 5 to 15 mm/m, or the draft angles range from 0.5 to 2. [1] 2

4 5.3 Cores A core is used to create internal cavities. Cores are usually made from sand aggregates. A core print is a recess in the mold. The core print supports the core and provides a way for gases to escape. Cores are created in a core box, which is similar to a pattern. Sand is packed into the core box to create the core. [1] 5.4 Advantages and Disadvantages of EPC In comparison to green mold sand casting, what are the principal advantages and disadvantages of EPC? In answering this question, you are going to need to go on the internet rather than rely on your text. Some of the principal advantages of EPC are: [3] No cores are needed Much more economical, and lower operating costs Closer tolerances can be achieved Can use regular, unclean sand, and its reusable (no additives) Little to no cleaning Some of the principal disadvantages of EPC are: [3] Hard to develop the Styrofoam insert Cant mess up. The mold and metal will be wasted 5.5 Advantages and Disadvantages of Permanent Mold Casting In comparison to green mold sand casting, what are the principal advantages and disadvantages of EPC? In answering this question, you are going to need to go on the internet rather than rely on your text. Some of the principal advantages of EPC are: [3] No cores are needed Much more economical, and lower operating costs Closer tolerances can be achieved Can use regular, unclean sand, and its reusable (no additives) Little to no cleaning Some of the principal disadvantages of EPC are: [3] Hard to develop the Styrofoam insert Cant mess up. The mold and metal will be wasted 3

5 5.6 Advantages and Disadvantages of Investment Casting In comparison to green mold sand casting, what are the principal advantages and disadvantages of investment casting? Is it possible to create internal passageways using this process? If so, how is it done? Some of the principal advantages of investment casting are: [3] Closer tolerances Very fine finish Generally good for large and small quantities of parts Useful for alloys difficult to machine Some of the principal disadvantages of investment casting are: [3] Limited to smaller parts Higher casting costs Internal passageways are possible and are done by using internal ceramic cores that help keep the flowing metal out so a hollow form can be made. [3] 5.7 Research on 6061 Aluminum and 356 Aluminum Parameter Aluminum 606 Aluminum 356 Plastic Deformation or Near Net Shape? Ingot/Plastic Deformation Cast to near-net shape Silicon Content (wt %) Hardening Mechanism Precipitation Hardening Precipitation Hardening Solidus/Liquidus (F) 1080/ /1135 Yield Strength MPa/ksi 276 /40 138/20 Ductility (% Elongation) ~(12-17) ~3 4

6 The reason that Aluminum 356 is more castable relates directly to the aluminum-silicon phase diagram. The transition between phases is dependent on the heat and the silicon content. For low values of silicon, like Aluminum 6061, there is a very quick transition to the solid phase as the temperature decreases. For Aluminum 356, the material stays in the liquid phase longer and doesn t go directly to the solid alpha phase. 5.8 Analysis of Fluidity Test Results Aluminum Alloy Pour Temperature Specimen Fluidity Number ( F) B C D A 20 Liquid metal fluidity is inversely proportional to the freezing temperature range of the metal. Freezing Range = TL TS For 6061 aluminum, freezing range = 1205 F 1080 F = 125 F For 356 aluminum, freezing range = 1135 F 1035 F = 100 F Therefore, since 356 has a smaller freezing range, it has a greater fluidity as compared to Fluidity is directly proportional to pouring temperature. Therefore, the 356 specimen with the higher pouring temperature will have the greatest fluidity. On the other hand, the 6061 specimen with the lower pouring temperature will have the least fluidity, which was specimen B. Specimen C was given as being poured 200 F above its liquidus temperature, at 1470 F. Deducting 200 F from 1470 F yields an approximate value for specimen C s liquidus temperature, around 1270 F, which is closer to liquidus temperature of 6061 than 356. By process of elimination, specimen D must be the 356 aluminum poured at 1200 F. 5

7 REFERENCES 1. Kalpakjian, Serope and Steven Schmid. Manufacturing Processes for Engineering Materials. Upper Saddle River: Prentice Hall, Print

8 APPENDIX Table A1: Fluidity Measurements Specimen Fluidity Number A 20 B 3 C 16 D 10 7