Manufacturing Processes UTA026 PDF

Thapar Institute of Engineering & Technology – Patiala Manufacturing Processes UES102 1 Manufacturing Processes UTA026 MOLD & GATING SYSTEM Lecture - 20 2  The Mold in...

Thapar Institute of Engineering & Technology – Patiala Manufacturing Processes UES102 1 Manufacturing Processes UTA026 MOLD & GATING SYSTEM Lecture - 20 2  The Mold in Casting The Mold contains a cavity whose geometry determines the shape of the cast part. Mold is a hollow container (cavity) used to give shape to molten or hot liquid material (such as wax or metal) when it cools and hardens. 3 *https://www.youtube.com/watch?v=vovhaSxjIzU4  Open Molds and Closed Molds Two forms of mold: (a) open mold, simply a container in the shape of the desired part; and (b) closed mold, in which the mold geometry is more complex and requires a gating system (passageway) leading into the cavity. 5 Sand Casting Mold (Closed) 6  Sand Casting Mold (Closed) Actual size and shape of cavity must be slightly oversized to allow shrinkage of metal during solidification and cooling. Molds are made of a variety of materials, including- o Sand, o Plaster, o Ceramic, o Metals 7  Mold Terms Mold consists of two halves: – Cope = upper half of mold – Drag = bottom half – Cheek = intermediate molding flask (optional for bigger molds) The rigid metal or wood frame that holds the moulding sand together is called as flask. The two halves separate at the parting line. 8  Desirable Mold Properties Strength - to maintain shape and resist erosion Permeability - to allow hot air and gases to pass through voids in sand Thermal stability - non reactive with hot molten metal Collapsibility - allow casting to shrink without cracking the casting or mold Reusability - sand of broken mold can be reused to make other molds 9  Gating System The gating system in a casting mold is the channel, or network of channels, through which molten metal flows into cavity from outside of mold. 10  Gating System The pouring cup (or pouring basin) is the portion of the gating system that receives the molten metal from the pouring vessel and delivers it to the rest of the mold. Pouring cup is often used to minimize splash and turbulence as the metal flows into downsprue Splash Pouring Cup Turbulence https://makeagif.com/gif/slow-motion-dropping-a-big-rock-into-water-_c8rnH 11  Gating System From the pouring cup, the metal travels down a downsprue also called simply the sprue (the vertical portion of the gating system). Downsprue 12  Gating System Then liquid metal flow along horizontal channels, called runners. Runner 13  Gating System Finally liquid metal through controlled entrances (i.e. gates) reaches into the mold cavity. Gate 14  Gating System The gates are usually attached to the 1. thickest or heaviest sections of a casting to control SHRINKAGE 2. to the bottom of the casting to minimize TURBULENCE AND SPLASHING. For large castings, multiple gates and runners is used to introduce metal at more than one point in the mold cavity. 15  Gating System Turbulent flow is generated while pouring the molten metal into the mold which causes the following problems: – absorption of gases, – oxidation of the metal, and – erosion of the mold. Turbulent flow Therefore gating systems should be designed to minimize turbulent flow. 16 https://www.tumblr.com/tagged/dynamics  Gating System Short sprues are desirable, since they minimize the distance that metal falls when entering to the mold and kinetic energy acquires during that fall. 17 https://www.youtube.com/watch?v=vovhaSxjIzU  Gating System Rectangular pouring cups prevent the formation of a vortex or spiralling funnel, which tends to suck gas and oxides into the sprue. Spiralling funnel 18 https://forum.freecadweb.org/viewtopic.php?t=8468  Gating System Tapered sprues also prevent vortex formation. Vortex formation Spiralling funnel19 https://mscharrer.net/povray/whirlpool/  Gating System A large sprue well can be used to dissipate the kinetic energy of the falling stream and prevent splashing and turbulence as the metal makes the turn into the runner. The choke , or smallest cross-sectional area in the gating system, serves to control the rate of metal flow. 20  Gating System Gating systems can also be designed to trap dross (slag) and sand particles and keep them from entering the mold cavity. 21  Gating System Since the first metal to enter the mold is most likely to contain the foreign matter (dross from the top of the pouring ladle and loose particles washed from the walls of the gating system), RUNNER EXTENSIONS and RUNNER WELLS can be used to catch and trap this first metal and keep it from entering the mold cavity. 22  Gating System Sprue well Runner well Gate 23 Sprue well Runner well 24 Sprue well Runner well 25 Sprue well Runner well 26 Sprue well Runner well 27 Sprue well Runner well 28 Sprue well Runner well 29 Sprue well Runner well 30  Riser A Riser is an additional void in the mold that also fills with molten metal. 31  Riser  Riser is a reservoir of additional molten metal that can flow into the mold to compensate for shrinkage of the part during solidification.  The riser must be designed to freeze after the main casting in order to satisfy its function i.e. it should have a larger volume-to-area ratio so that the main casting solidifies first. 32  Riser Dead (or cold) risers fill with metal which already flowed through the mold cavity. As shown in Figure, top risers are almost always dead risers. Dead Riser 33  Riser Live risers (also known as hot risers) receive the last hot metal that enters the mold. Risers that are part of the gating system generally live risers. Live Riser 34  Riser Dead Dead Live 35  Riser Location A riser should be located in such a way that directional solidification is obtained. Since the heaviest section of the casting solidifies last, the riser should be located to feed this section. The heaviest section will now act as a riser for other sections which are not so heavy or thick. For small castings, a single riser can feed the entire casting, but more than one riser is required for large castings. 36  Riser Location The number of risers and their locations depend on the casting configuration. The risers are generally located at a short distance from the casting since they are ultimate separated from the final casting. The connecting channel between the casting and the riser should be large enough (Diameter) to ensure that this link does not freeze before the casting. 37  Vent holes As the metal flows into the mould, the air that previously occupied the cavity, as well as hot gases formed by reactions of the molten metal, must be evacuated so that the metal will completely fill the empty space. In sand casting, for example, the natural porosity of the sand mould permits the air and gases to escape through the walls of the cavity. In permanent-metal mould, small vent holes are drilled into the mould or machined into the parting line to permit removal of air and gases. 38  Vent holes *https://www.the-warren.org/GCSERevision/engineering/casting.htm  References: M. P. Groover, Fundamentals Of Modern Manufacturing: Materials, Processes, and Systems, Wiley (2016), 5th edition. Degarmo, E. P., Kohser, Ronald A. and Black, J. T., Materials and Processes in Manufacturing, Prentice Hall of India (2008) 8th ed. Kalpakjian, S. and Schmid, S. R., Manufacturing Processes for Engineering Materials, Dorling Kingsley (2006) 4th ed. https://www.youtube.com/watch?v=vovhaSxjIzU https://makeagif.com/gif/slow-motion-dropping-a-big-rock-into-water-_c8rnH https://www.the-warren.org/GCSERevision/engineering/casting.htm https://forum.freecadweb.org/viewtopic.php?t=8468 https://www.tumblr.com/tagged/dynamics https://mscharrer.net/povray/whirlpool/ 40 Video disclaimer “The information contained in this multimedia content (‘Video Content’) posted by Thapar Institute of Engineering & Technology is purely for education (class teaching) and informational purpose only and not for any commercial use”. 41 Thanks!! 42 1 4 2 3 43