Exp. No. 2-Metal Casting Processes.docx

شعار التكنو Jordan University of Science and Technology Faculty of Engineering Department of Industrial Engineering **IE 469: Manufacturing Processes Lab** **Exp. No. 2: Metal Casting Processes** By **Prof. Mohammed Hayajneh** Updated by. Eng. Maysa Al-shraideh **Introduction** Casting is...

شعار التكنو Jordan University of Science and Technology Faculty of Engineering Department of Industrial Engineering **IE 469: Manufacturing Processes Lab** **Exp. No. 2: Metal Casting Processes** By **Prof. Mohammed Hayajneh** Updated by. Eng. Maysa Al-shraideh **Introduction** Casting is the process of metal shaping in which the molten metal is poured into the mold cavity and forms the final part upon solidification. The mold is made from different expandable or permanent metals. Sand resin (which makes the mold in the sand, shell mold and the investment casting processes), ceramic (which makes the mold in the ceramic mold casting) and gypsum (which makes the mold in the plaster mold casting) is the expandable metals. Permanent metals such as grey cast iron, steel, bronze and graphite are used to make the mold in the permanent mold casting processes such as in the die and pressure casting. Where in the composite molds, both expandable and permanent metals can be used to achieve greater flexibility of the two processes. In the expandable casting processes, a piece known as the pattern can be used to make the mold cavities where they are made of different materials like metals, wax, and polystyrene. Cores can be inserted into the mold cavity to make parts with internal holes where it is made of sand mixed with binder materials. **Three types of casting processes** will be covered in this experiment that is: sand, shell mold and centrifuging casting. In sand casting, the mold is made of sand and the pattern is used to make the internal die cavities and cores used to form the internal holes in the final castings. The die is divided into two portions, the upper one is known as the cope and the lower one is known as the drag. The pattern is also divided into two portions one is used to make the cavity in the cope section where the other half is used to form the cavity in the drag portion. Re-usable sand can be used to build the die that minimizes the overall process cost. 1. **Sand casting process** can be used to cast almost any metal type with no limitations on the part size and with low tooling cost. Surface finish and dimensional accuracy of the final parts are low where some finishing operations are needed, the surface finish can be enhanced by the use of small sand particles to form the die but in this case, the die permeability will be reduced and the gasses may confine in the die cavity-forming casting defects such as blow holes. 2. **Shell mold casting** is also an expendable mold casting process in which the molten metal is poured into a heat-cured mold that is non-reusable and in the form of a shell made from silica sand with a resin binder. Two shells are held together and brokered when the final part is solidified. Superior surface finish and good dimensional accuracy are advantages of this process over the sand casting and it can be used for a wider range of alloys with greater die design flexibility than that in die-casting and with lower cost than that in the investment casting process. Secondary machining operations are often not required and the casting cracks are minimized by the mold collapsibility, the process also can be mechanized for mass production. High equipment and pattern cost, low part size, the formation of noxious fumes that must be extracted are the major limitations of this process. **Shell mold casting process is generally characterized by the following advantages:** - Low capital outlay on the sand preparation plant - Good space utilization - Low sand-metal ratio is used - Unnecessary mold coatings - Lightweight molds can be produced which have good storage characteristics - Labor skills are not required - Lower cleaning costs - Surface finish and dimensional accuracy is higher than that in green sand mold castings 3. **Centrifuging Casting** or known as spin casting is a permanent mold casting process that utilizes the inertial forces resulting from the die rotation to force the molten metal to be distributed into the internal cavity of the mold. It can be used to produce relatively thin parts and the die can be designed to form an identical part at one time where each part has a mold cavity that is equally spaced around the rubber disk mold. Low melting point materials like Zinc-Aluminum (ZA) alloys, LEAD-and-TIN-based alloy are the common metals used in this process because of the low melting point silicon rubber mold is used. Large tubular or cylindrical parts, cylinder liners, Pipes and similarly shaped parts can be obtained by this process with good quality and at a high production rate. The tooling cost is high and there are some limitations on the part shape. **Objectives** 1. Get acquainted with different casting processes mainly sand, shell mold and centrifuging casting. 2. Identify the advantages and limitations of these casting processes and their applications. 3. Identify the reason behind different defect types and how they can be avoided. 4. Get acquainted with the design consideration in casting processes. **Practical application** The castings process can be used to make several parts weighing from a few grams to several tones worldwide where the complexity ranges from simple to complex shapes and from one part to a large number of production. The used process and its control are greatly influenced the final part quality, surface finish and dimensional accuracies. The casting process enables the forming of a single part with the elimination of time and cost consumed by the assembly operations where the cost will be reduced by 50% or more concerning other machined parts. casting processes can be used to produce several parts worldwide such as different components for aerospace, automobiles, railways, mining equipment, farming equipment, machine tool equipment, plant machinery, motors, pumps for electrical machines, joints, fittings and valves. **Equipment and TOOLs** 1. **In the sand casting process**, the mold as mentioned above is divided into the cope and the drag portions that are formed inside a wood or metal case known as the flask as shown in Figure 1. The patterns and cores also are used to form the die cavities and the internal holes in the final castings respectively. Good pattern design is an important consideration to avoid die damage and allow casting to shrink freely. All sand die features, cores and good and poor pattern design are shown in Figure1.  Figure 1. Sand casting die features, cores, good and poor pattern design 2. **In the shell mold casting machine** used in Figure 2 with their processing steps, the resin sand is used to cover the pattern and form a shell in which the molten metal will be poured. At the pouring time, the mold vaporizes to create a hard shell. This machine can be used to produce hollow-symmetrical shape with superior surface finish. Figure 2. Shell casting machine 3. **In the centrifuging casting process**, three machines are used, the first and second ones are the electrically heated press (the machine used to pack and cure the rubber mold) and the Melting furnace (metal melting) shown in Figure 3, and the third one is the spin caster machine shown in Figure 4 in which a silicon rubber mold is clamped between a pressures plates that rotate the mold at high speed forming centrifugal forces that push the molten metal far reaches inside the mold cavities. This machine is designed for casting several thin identical parts at one time where each part cavity has the same distance from the center of the rubber disk. Mold design, the amount of poured metal and the machine speed are important quality considerations in this process.  Figure 3. Electrically heated press & Melting furnace Figure 4. Spin- Caster machine **EXPERIMENT PROCEDURE** 1. **The five basic steps in the Sand Casting process are:** - **Pattern making**: Pattern is a replica of the final casting shape but with some dimensional allocation for metal shrinkage and final part finishing. They are generally made of plastic, wood or metal or combination of these metal types based on the final part complexity, specifications and the number of castings to be obtained. patterns with draft angles shown in figure 1 are the best design that allows the casting to shrink freely and prevent die damage, they are usually covered with powder materials to facilitate their removal from the sand die. - **Core making**: Cores are placed inside the mold cavity to create internal holes in the final casting. They are generally made of sand mixed with water and organic binders that are backed together for the final shape. So, cores tend to be strong yet collapsible and can be removed from the final castings easily. The cores should be fixed with both ends of the die or by the use of chaplets as shown in figure 1 to hold them in their position to avoid any casting defects. - **Molding:** It is a multi-step in which the casting molds shown in figure 5 are created. In horizontal casting, the cope and the drag portions are formed inside a two pieces frame known as the flask. Firstly, the sand is packed around the pattern. then, the pattern is removed, next to that, gating and runner systems are formed in the drag while the sprue is placed in the cope portion, cores also can be inserted in the drag portion for hollow cavities in the final castings. Finally, the cope and the drag portions are closed and clamped together along the parting line. - **Melting and pouring** **the cast metal**: where the metal is converted from solid to liquid State using the melting furnace and then poured into the mold cavity. After the molten metal solidified, the molds vibrate and the sand shacked out to remove the final part - **Cleaning and finishing of the final part**: in which all materials that are not part of the final casting must be removed, gating systems are removed by rough cleaning and any mold residuals or sand cores are removed, superfluous metal is removed by the trimming process. - **And finally, finishing off the final part to improve their appearance**, the part is then inspected for the presence of any defects to promote quality standards by the means of nondestructive testing to determine whether the part will adequately perform the required functions. -  Figure 5. Sand mold features 2. **In the shell mold casting process,** the processing is shown in figure 2 and simply summarized in the following six steps: - Create the pattern - Create the mold - Assemble the pattern sections - Pour the molten metal - Wait upon solidification - Shack the mold and remove the part 3. **In the centrifuging casting process,** the casting process is shown in Figure 6 and the steps of the process can be summarized as: - Prepare the silicon rubber mold - Vulcanizing the mold in an electrically heated vulcanizing press for curing - Provide the gating and runner system and the vent in the rubber mold by using a sharp knife. - Place the mold in the spin caster machine - Pour the molten metal and spin casting - Remove the final casting parts 9 Moldings ideas in 2021 \| molding, it cast, injection moulding Figure 6. Centrifuging casting 4. **Casting defects** - **Misruns**: where the molten metal solidified before they completely fill the die cavity due to lack of fluidity, low pouring temperature, thin cross-sections or slow poring. - **Cold shut**: Occurs if the molten metal is poured from both sides of the mold but there is an insufficient fusion between them due to premature freezing. - **Cold Shots**: solid globules are formed due to splattering during pouring where the redesign of the gating system or pouring procedure is needed. - **Shrinkage Cavity**: the main reason for this type of defect is the internal void or depression caused by shrinkage during the solidification process. Proper riser design can be used to solve the problem - **Micro-porosity**: where a network of small voids is distributed within the casting resulting from localized shrinkage of the molten metal in the dendritic structure - **Hot Tearing**: occurs if the casting cannot shrink naturally due to high stresses where it can be avoided by removing or collapsing from the die rapidly after freezing. - **Sand blow**: is a cavity inside the casting caused by gases entrapped in the die due to Low die permeability, high moisture content or poor venting. - **Pin holes**: which are small gas cavities. - **Sand wash**: which is an erosion of the sand mold during pouring. - **Scab**: in which the mold surface is flaked off and introduced in the casting upon solidification. - **Penetration** of the poured metal into the sand where hard packing die eliminate this problem - **Mold shift**: Shift of the cope relative to the drag portion. - **Core shift**: Shift of the core from their position. - **Mold crack**: occurs if the mold has low strength. These common casting defects are shown in Figure 7.  Figure 7. Casting Defects 5. **Design considerations:** Die design, strength, permeability, collapsibility and thermal resistance are important considerations to minimize several casting defects, other considerations include: - Shrinkage allowance to avoid cracking of the final casting upon solidification which depends on the casting metal type. Machining allowance, residual stress and tolerance also should be considered. - Sharp angles, corners and fillets cause cracking and tearing as shown in Figure 8 so they should be avoided. Fillet radii also affect proper liquid-metal flow and stress concentration. Figure 8. Hot tears - Hot spots can develop porosities and shrinkage cavities at the largest inscribed circle within a specific area as shown in Figure 9. The problem can be solved by using small cores. Also, the section changes within the part should be smoothly blended into each other.  Figure 9. Porosities and shrinkage cavities developed in the large area of the casting Figure 10 below shows a good design that can be used to eliminate shrinkage cavities in the final casting. Figure 10. Good versus poor casting mold design Large flat areas may warp as a result of temperature gradients during cooling or develop poor surface finish because of the uneven flow of the molten metal however it should be avoided. These flat areas can be broken up with serration and ribs. It is desirable for the parting lines that separate the cope and the drag portions to be along a flat plane rather than contoured. **6. Exercises** Finally, **four experiments** will be carried out using the sand casting process to determine the reasons for some casting defects such as shrinkage cavity and internal cavities and determine how they can be avoided. Also, we will describe how the shrinkage coefficients of metals can be determined. **[The First experiment:]** **Shrinkage cavity** Shrinkage Cavity refers to void defects in shaped metal casting. It is formed during the solidification of the molten metal because of shrinkage. Shrinkage cavities are usually located in the upper portion of an ingot or in those spaces within a casting where the molten metal is last solidified. **The Experiment:** Making a complete mold without using a riser, and the result is a casting that contains a shrinking cavity**.**  **[The Second experiment: ]** **Avoiding Shrinkage cavity** **The Experiment:** Making a complete mold with the use of a riser, and the result is a casting that does not contain a shrinking cavity. A riser, also known as a feeder is a reservoir built into a metal casting mold to prevent cavities due to shrinkage **[The Third experiment:]** **The effect of excess moisture in the sand on the final casting** **The Experiment:** Making a complete mold without drying it, the result is a casting that contains many internal and external cavities  - **[The Fourth Experiment:]** **Measuring the shrinkage coefficient of Aluminum** **The Experiment:** Make a complete mold for a model of known dimensions and then pour the molten metal into it to get the final casting. From the dimensions of the pattern and the casting, the shrinkage rate is calculated by the following equation: Shrinkage coefficient =[\$\\frac{(X - X1)}{X}\*100\\%\$]{.math.inline}= (10-9.82/10)\*100=1.8% **results** At the end of this lab, each student got acquainted with the several casting processes that have been discussed, their uses, their advantages and their limitations, casting defects and their reasons and design consideration to reduce the defects. **~~Report~~** ~~The report type should include the following:~~ 1. ~~A description of the three casting processes discussed in this experiment~~ 2. ~~List the several equipment and machines used~~ 3. ~~A comparison between the three mentioned casting processes shows the advantages of each one over the other and their limitations.~~ 4. ~~Illustrate some different casting defects (important 5 defects), identify the reasons behind them and how they can be avoided.~~ 5. ~~Discuss the results of the four experiments~~