HABEEB HATTAB HABEEB Office: BN-Block, Level-3, Room-088 Email: [email protected] Ext. No.: 7292 H/P No.: 0126610058 University Tenaga National Lecturer: Habeeb Al-Ani.
Download ReportTranscript HABEEB HATTAB HABEEB Office: BN-Block, Level-3, Room-088 Email: [email protected] Ext. No.: 7292 H/P No.: 0126610058 University Tenaga National Lecturer: Habeeb Al-Ani.
HABEEB HATTAB HABEEB Office: BN-Block, Level-3, Room-088 Email: [email protected] Ext. No.: 7292 H/P No.: 0126610058 University Tenaga National Lecturer: Habeeb Al-Ani Contemporary (Modern) Casting Processes University Tenaga National Lecturer: Habeeb Al-Ani Metal Moulds: Made of special metals that withstand high temperatures of the molten materials. Used to produce large numbers of castings. Used to produce small-and medium size University Tenaga National Lecturer: Habeeb Al-Ani Dies: - Dies for hot and cold-chamber machine are similar in construction. - Dies are made in to halves to allow Casting removal. - Metal enters the stationary half when the die is closed. - When the die opens ejector-pins for the casting to fall from the die University Tenaga National Lecturer: Habeeb Al-Ani Cont… Dies - Die life depends on the metal cast ( Range from 10,000 filling for brass to several million for zinc). - Vents should be considered to allow the gases to escape -Dies are provided with water channels to cool the die after injection to metal (For rapid production) University Tenaga National Lecturer: Habeeb Al-Ani Die casting: Die – Is a metal mould into which a molten material is forced to fill the cavity of the mould. Die-casting is accomplished using either of the following methods: 1- Hot chamber 2- Cold chamber University Tenaga National Lecturer: Habeeb Al-Ani Hot chamber method: The molten pot is included within the machine. An injection cylinder in Immersed in the molten material all times. The injection cylinder, which is actuated by air or hydraulic pressure, forces the molten metal into the mould Cavity. University Tenaga National Lecturer: Habeeb Al-Ani University Tenaga National Lecturer: Habeeb Al-Ani University Tenaga National Lecturer: Habeeb Al-Ani University Tenaga National Lecturer: Habeeb Al-Ani University Tenaga National Lecturer: Habeeb Al-Ani University Tenaga National Lecturer: Habeeb Al-Ani Cont… Hot chamber method (Die casting) This method is used to cast low-melting point alloys (Zinc, tin, and lead). Relatively high-melting temperature metals are not cast using this method because high temperatures cause damage to hot chamber machines. University Tenaga National Lecturer: Habeeb Al-Ani Cont… Hot chamber method (Die casting) Principle Metal is injected into the mould by an cylinder (plunger). The plunger maintains the pressure required during solidification (this also can be performed using compressed air). At this time the mould is closed by another cylinder. University Tenaga National Lecturer: Habeeb Al-Ani University Tenaga National Lecturer: Habeeb Al-Ani Cont… Hot chamber method (Die casting) After the metal solidification the pressure is relieved, the opens and the casting is ejected by knockout pins (ejector-pins). University Tenaga National Lecturer: Habeeb Al-Ani Cont… University Tenaga National Hot chamber method (Die casting) Lecturer: Habeeb Al-Ani Cold chamber method: The molten material is poured into the Injection cylinder by mechanical means or hand. The molten material is taken from a separate container (Furnace). This method is used to cast alloys with relatively high-melting temperatures and pressures. University Tenaga National Lecturer: Habeeb Al-Ani Cont… Cold chamber method (Die casting) Principle The metals are not molten in a selfcontained pot ladle the molten metal is poured in a cavity before the plunger. Cold chamber machines are designed to withstand high temperatures of the Poured metals and to provide pressure During the solidification process. University Tenaga National Lecturer: Habeeb Al-Ani Cont… University Tenaga National Cold chamber method (Die casting) Lecturer: Habeeb Al-Ani Cont… Cold chamber method (Die casting) A- The mould is closed with cores and the metal is ready to be poured by a ladle. B- The plunger forces the metal into the cavity. c- After the metal solidifies, the cores are withdrawn. D- Die opens and the casting is ejected University Tenaga National Lecturer: Habeeb Al-Ani Cont… University Tenaga National Cold chamber method (Die casting) Lecturer: Habeeb Al-Ani Cont… University Tenaga National Cold chamber method (Die casting) Lecturer: Habeeb Al-Ani Cont… University Tenaga National Cold chamber method (Die casting) Lecturer: Habeeb Al-Ani Cont… University Tenaga National Cold chamber method (Die casting) Lecturer: Habeeb Al-Ani Advantage of Die casting: 1- Rapid Process 2- The core and die are permanent 3- Smooth surfaces of casting 4- Minimizes machining and cutting processes (less waste material than in sand castings) University Tenaga National Lecturer: Habeeb Al-Ani Cont… Advantage of Die casting 5- The wall thickness is more uniform than in sand castings. 6- Waste material is low because the sprue, runners and gates are re-melted. 7- Tolerances are less than in sand Castings. University Tenaga National Lecturer: Habeeb Al-Ani Disadvantage of Die casting: 1- High cost of equipment and dies (so die casting is used in mass production) 2- Undesirable chilling of the casting (The solution: High temperature must be sustained before removing the casting) University Tenaga National Lecturer: Habeeb Al-Ani Cont… Disadvantage of Die casting 3- Metal with high coefficient of contraction should be removed from the mould immediately because of the inability of the mould to contract with the casting. 4- Used mainly for low melting point materials. University Tenaga National Lecturer: Habeeb Al-Ani Features of die casting of Brass and high melting point metals: The difficulty faced in die casting of brass is the damage and rapid oxidation of steel dies because of the high melting temperature. This problem has been overcome by performing the die casting at low a temperature as possible. University Tenaga National Lecturer: Habeeb Al-Ani Cont… Features of D. cas. of Brass and high melt. point metals So metal is can be injected in a semiliquid or plastic state to perform casting operations at lower temperature. There are two variations of die casting Process for BRASS: NEXT SLIDE University Tenaga National Lecturer: Habeeb Al-Ani Cont… Features of D. cas. of Brass and high melt. point metals University Tenaga National Lecturer: Habeeb Al-Ani Cont… Features of D. cas. of Brass and high melt. point metals a- Compression chamber is built in the Die . b- Compression chamber is separate from the die . University Tenaga National Lecturer: Habeeb Al-Ani Lower pressure permanent moulds: - A mould is mounted over a furnace. - The furnace is sealed through a stalk into the cavity. Advantage: Dense, clean and Accurate Casting, less secondary machining and Cutting operations. University Tenaga National Lecturer: Habeeb Al-Ani Cont… Lower pressure permanent moulds University Tenaga National Lecturer: Habeeb Al-Ani Gravity or permanent-Mould Casting : No pressure is used (only gravity). It Is used for ferrous and non-ferrous metals. University Tenaga National Lecturer: Habeeb Al-Ani Cont… Gravity or permanent-mould casting Principle The die is closed using a cylinder and the molten metal is simply poured into the mould cavity by hand or mechanical means. The metal fills the cavity because of the pressure created by the head of the metal poured (no plunger) is used to keep the casting under pressure). University Tenaga National Lecturer: Habeeb Al-Ani Cont… Gravity or permanent-mould casting Casting cycle: Pouring, cooling, ejecting, and setting the cores Advantage: Good finish and surface of the castings, capability of maintaining small tolerances. Disadvantage: Good High cost of equipment and dies. University Tenaga National Lecturer: Habeeb Al-Ani Centrifugal Casting: Principle 1- The mould rotates while the metal solidifies. University Tenaga National Lecturer: Habeeb Al-Ani Centrifugal Casting: 1- High cost of equipment and dies (so die casting is used in mass production) 2- Undesirable chilling of the casting (The solution: High temperature must be sustained before removing the casting) University Tenaga National Lecturer: Habeeb Al-Ani Cont… centrifugal casting Advantage: 1- No need of cores for cylindrical castings. 2- Good dense of the metal. 3- Thin walled castings can be produced. University Tenaga National Lecturer: Habeeb Al-Ani Cont… centrifugal casting Methods of centrifugal casting 1- True Centrifugal Casting This method is used to produce pipes, bars, cylinders and other symmetric objects. The mould rotates about its horizontal or vertical axis. THREE or TWO types: University Tenaga National Lecturer: Habeeb Al-Ani Cont… centrifugal casting a- Using a massive thick metal mould with a thick refractory coating. As a result of this design, the solidification will proceed from the mould wall toward the casting centre. b- Using a thick, highly insulated sand interface between the mould wall and the casting. In this case, the solidification will start from the casting center and from the wall at the same time. University Tenaga National Lecturer: Habeeb Al-Ani Cont… centrifugal casting Finding the centrifugal force CF: The centrifugal force is created by the mould rotation about its axis. If too low A centrifugal force is applied, the metal will slide, slip or rain. mv CF = r University Tenaga National 2 Lecturer: Habeeb Al-Ani Cont… University Tenaga National centrifugal casting Horizontal Lecturer: Habeeb Al-Ani Cont… centrifugal casting Vertical University Tenaga National Lecturer: Habeeb Al-Ani Cont… centrifugal casting / Methods of centrifugal casting 2- Simicentrifugal Casting The mould is completely full of metal. The centre of the casting is solid but with less density then it is in the surface of the casting. Usually, the centre of the casting will be removed using machining processes. Advantage: Good dense surface of the metal, especially near the surface. University Tenaga National Lecturer: Habeeb Al-Ani Cont… University Tenaga National centrifugal casting / Methods of centrifugal casting Lecturer: Habeeb Al-Ani Cont… centrifugal casting / Methods of centrifugal casting 3- Centrifuging Several cavities are located around the mould axis. As the mould is rotated, the CF encourages the metal to fill the cavities through radial gates. Advantage: Not limited to symmetrical objects. University Tenaga National Lecturer: Habeeb Al-Ani Cont… University Tenaga National centrifuging casting / Methods of centrifugal casting Lecturer: Habeeb Al-Ani Precision or investment Casting: This process is used to cast unmachinable alloys and radioactive metals (Poor machinability). Advantage: 1-Intricate and smooth casting. 2-Good for unmachinable metals and it Can replace die-casting. University Tenaga National Lecturer: Habeeb Al-Ani Cont… Precision or investment Casting: Disadvantage: 1- Very expensive. 2- Limited to small parts. 3- some difficulties when cores are used . University Tenaga National Lecturer: Habeeb Al-Ani Type of Precision or investment Casting 1-“Lost Wax” precision casting process. A wax pattern is used to form a cavity In the mould. The Wax pattern is covered with plaster investment. When this plaster becomes hard the plaster mould will be heated. As a result, the Wax pattern will melt away from the mould leaving a cavity having all the details of the Wax pattern. University Tenaga National Lecturer: Habeeb Al-Ani Schematic illustration of investment casting 1. WAX INJECTION : Wax replicas of the desired castings are produced by injection molding. These replicas are called patterns. University Tenaga National Lecturer: Habeeb Al-Ani Schematic illustration of investment casting 2. ASSEMBLY : The patterns are attached to a central wax stick, called a sprue, to form a casting cluster or assembly. University Tenaga National Lecturer: Habeeb Al-Ani Schematic illustration of investment casting 3. SHELL BUILDING : The shell is built by immersing the assembly in a liquid ceramic slurry and then into a bed of extremely fine sand. Up to eight layers may be applied in this manner. Lecturer: Habeeb Al-Ani University Tenaga National Schematic illustration of investment casting 4. DEWAX : Once the ceramic is dry, the wax is melted out, creating a negative impression of the assembly within the shell. University Tenaga National Lecturer: Habeeb Al-Ani 5. CONVENTIONAL CASTING: In the conventional process, the shell is filled with molten metal by gravity pouring. As the metal cools, the parts and gates, sprue and pouring cup become one solid casting. University Tenaga National Lecturer: Habeeb Al-Ani 6. KNOCKOUT: When the metal has cooled and solidified, the ceramic shell is broken off by vibration or water blasting. University Tenaga National Lecturer: Habeeb Al-Ani 7. CUT OFF: The parts are cut away from the central sprue using a high speed friction saw. University Tenaga National Lecturer: Habeeb Al-Ani 8. FINISHED CASTINGS: After minor finishing operations, the metal castings--identical to the original wax patterns--are ready for shipment to the customer. University Tenaga National Lecturer: Habeeb Al-Ani Cont… Type of Precision or investment Casting 2-Plaster Mould Casting. 1- Mold is made of plaster 2- Mixed with water and additives and poured over a pattern 3- After plaster sets, pattern is removed and the mold is dried at 120 C 4- Have low Permeability – gases can not escape 5- Patterns are made of: University Tenaga National Lecturer: Habeeb Al-Ani Cont… Type of Precision or investment Casting -Al alloys, -Thermosetting plastics -Brass or Zinc alloys 6-Have fine details and good surface finish 7-Form of precision casting Plaster moulds are also not permanent because they are destroyed when the casting is removed. University Tenaga National Lecturer: Habeeb Al-Ani Cont… University Tenaga National Type of Precision or investment Casting Lecturer: Habeeb Al-Ani Continuous Castings Continuous casting process consists of continuously poring the molten metal into a mould that has the capability for rapidly chilling the metal to the point of solidification and then withdrawing It from mould. University Tenaga National Lecturer: Habeeb Al-Ani Continuous casting University Tenaga National Lecturer: Habeeb Al-Ani Continuous casting and hot rolling plant University Tenaga National Lecturer: Habeeb Al-Ani Asarco process The mould is built in the furnace. The molten metal is fed by gravity into the mould from furnace. At the mould exit, the metal solidifies and it is withdrawn by rolls. The exit consists of a graphite die that forms the final shape of the withdrawn product. The graphite die is build in a cooling jacket, which uses water to cool the product at the mould exit. The products: Bars, Rods. University Tenaga National Lecturer: Habeeb Al-Ani Next Lecture: Metal Cutting University Tenaga National Lecturer: Habeeb Al-Ani THANK YOU University Tenaga National Lecturer: Habeeb Al-Ani