PERMANENT MOULD CASTING cont… Drawback of sand mold process: A mold need to be prepared for each of the casting produced. Specialty of permanent mold process: a METALLIC MOLD is used in the place of sand mold with which large no. of casting are made. The metallic mold is known as DIE.

 PERMANENT MOULD CASTING PERMANENT MOULD CASTING APPLICATION: This method is suitable for small and medium sized casting such as carburetor bodies, oil pump bodies, connecting rods, pistons etc. It is widely used for non-ferrous casting.

Permanent mold process (die casting) Types of die casting processes 1.Gravity die casting 2.Pressure die casting a.Cold chamber pressure die casting b.Hot chamber pressure die casting

PERMANENT MOULD CASTING Gravity die casting Features:  Uses a metal mold (steel or cast iron) or, a ‘die’  Molten metal is poured into the die and not forcibly injected  Non-ferrous metals are typically used (Al. Mg, Cu alloys)  Irons and steels can be cast using graphite molds STEPS:  Mold pre-heated to °C  Ceramic coating applied to the cavity to facilitate part removal and increase the mold lifetime.  Mold halves and core used to form complex features

 Cycle of operation requires less time.  Economical for mass production.  less floor space required.  Close dimensional tolerance  Good surface finish and surface details  Casting defects observed in sand castings are eliminated.  Fast rate of production can be attained.  The process requires less labor.  Cost is higher than the sand mold. Thus impractical for large castings.  Metals with low melting point  Refractoriness of the high melting point alloys ADVANTAGES LIMITATIONS

Features:  Metal forced into die under pressure  P ressure generally created by compressed air or hydraulic means  Pressure varies from 70 to 5000 kg/cm2  Production of intricate components at low cost  Commonly used in casting of zn, al, and cu, mg, pb and sn PERMANENT MOULD CASTING Or, Pressure die casting

1. Hot chamber die casting: - A die casting machine consists of frame, source of molten metal and molten metal transfer mechanism, casting dies, & metal injection mechanism - The melting unit is an integral part - Can produce several hundred castings weighing a few grams per hour PERMANENT MOULD CASTING ► Video\The Hot Chamber Die Casting Process.mp4

2. Cold chamber die casting: Molten metal generally at higher temperature Pressure much higher (of the order of 200 to 2000 kgf/cm2) than those applied in hot chamber process. this process reduces the contact time between the liquid metal and the shot chamber. PERMANENT MOULD CASTING ► Video\Die Casting Animation.mp4

ADVANTAGES 1. It is very quick process 2. It is used for mass production 3. Improved surface finish 4. Thin section (0.5 mm Zn, 0.8 mm Al and 0.7 mm Mg) can be easily casted 5. Less nos. of rejections 6.Cost of production is comparatively less 7. Process require less space 8. All casting has same size and shape. DISADVANTAGES 1. Cost of die is high. 2. Special skill is required. 3. It is not suitable for low production. APPLICATIONS 1. Carburetor bodies 2. Hydraulic brake cylinders 3. Refrigeration castings 4. Washing machine 5. Connecting rods and automotive pistons 6. Oil pump bodies 7. Gears and gear covers 8. Aircraft and missile castings, and 9. Typewriter segments

CENTRIFUGAL CASTING (video)(video) POINTS TO REMEMBER : TRUE CENTRIFUGAL Applying ceramic slurry to the mold wall, drying and baking. Rotation of the mold at a predetermined speed( rpm) Pouring a molten metal directly into mold(no gating system is employed). The mold is stopped after the casting has solidified. Extraction of the casting from the mold.

SEMI-CENTRIFUGAL CASTING POINTS TO REMEMBER : For more complicated but axi-symmetric shapes Rotating speed is not as high as true centrifugal casting Symmetrical objects like wheel having arms like flywheel, gears

CENTRIFUGING CASTING POINTS TO REMEMBER : For producing non- axisymmetrical small castings having intricate details. Small jobs connected by radial runners and central sprue Centrifugal force aids proper feeding

Advantages… Formation of hollow cavities in cylinders without cores. Non-mettalic and slag inclusions and gas bubbles are forced to the inner surface of the casting by the centrifugal force. No gating system. Hence casting yield is high. Fine outside details can be successfully cast. Casting yield= (WT.OF THE CASTING/WT.OF THE POURED METAL)X100

Disadvantages… Equipments are expensive and thus is suitable or large quantity production. Skilled workers are required for operation. Inaccurate internal diameter.

Fine material is used first to give a smooth surface finish and reproduce fine details INVESTMENT CASTING Known as lost Wax Process or Precision Casting Common pattern material: Wax (others are Frozen mercury,plastic,tin)

INVESTMENT CASTING STEP: ONE Pattern creation: 1.The wax patterns are typically injection molded into a metal die. 2.Several of these patterns are attached to a central wax gating system (sprue, runners, and risers), to form a tree-like assembly. 3.The gating system forms the channels through which the molten metal will flow to the mold cavity.

INVESTMENT CASTING contd…. STEP: TWO Mould creation: 1.The "pattern tree“ dipped into a slurry of fine ceramic particles, coated with more coarse particles, and then dried. 2.This process repeated until the shell is thick enough. 3.The shell then placed into an oven and the wax is melted out leaving a hollow ceramic shell. 4.Also known as "lost wax" casting.

► video\sander_01.wmv Finally, the coating is allowed to harden. These steps are repeated until the investment is the required thickness, which is usually 5 to 15 mm The investment is then allowed to completely dry, which can take 16 to 48 hours

INVESTMENT CASTING contd…. STEP: THREE Pouring and Solidification: The mould is preheated in a furnace to approximately 1000°C to harden it further to remove any moisture and residual wax The molten metal poured from ladle into the gating system of the mold, filling the mold cavity. Pouring achieved manually under the force of gravity, but vacuum or pressure sometimes used. After solidification mould is broken (sometimes by water jet) and cast is taken out VIDEO:LOST WAX

Investment Casting Applications: Small size, complex parts (art pieces, jewelry, dental fixtures), gas turbine blades, pinion gears Advantages:  Shell thickness typically 9 mm is used  Surface of shell mold cavity is smoother than sand mold  Easy flow of molten metal, good surface quality  Finish is of the order of 2.5 micrometer  Can be mechanized for mass production and is very economical Limitations:  Expensive metal pattern  Difficult to justify for small quantities  Possible on small to medium size  Suitable for steel castings<10 kg. Preferred for casting weight less than 5 kg, maximum dimension less than 300 mm, Thickness is usually restricted to 15mm