Types of Casting And manufacturing process

Types of  Casting  And manufacturing process

    Precision CNC machining parts Casting is a manufacturing process in which molten metal is poured or injected and allowed to solidify in a suitably  shaped mold cavity. During or after  cooling, the cast part is removed from the mold and then processed for delivery.

    Casting processes and cast-material technologies vary from simple to highly complex. Material and process selection  depends on the part’s complexity and function, the product’s quality specifications, and the projected cost  level.

     Castings are parts that are made close to their final dimensions by a casting process. With a history dating back 6,000  years, the various casting processes are  in a state of continuous refinement and evolution as technological advances are being made.

A:Sand Casting  

    Sand casting is used to make large parts (typically iron, but also bronze, brass, aluminum). Molten metal is poured into a mold cavity formed out of sand (natural or synthetic).

    The processes of sand casting are discussed in this section, including patterns, sprues and runners, design considerations, and casting allowance.

    The cavity in the sand is formed by using a pattern (an approximate duplicate of the real part), which are typically made out of wood, sometimes metal. The cavity is contained in an aggregate housed in a box called the flask.

    Core is a sand shape inserted into the mold to produce the internal features of the part such as holes or internal passages. Cores are placed in the cavity to form holes of the desired shapes. Core print is the region added to the pattern, core, or mold that is used to locate and support the core within the mold.

  Precision CNC machining parts  A riser is an extra void created in the mold to contain excessive molten material. The purpose of this is to feed the molten metal to the mold cavity as the molten metal solidifies and shrinks, and thereby  prevents voids in the main casting.

    In a two-part mold, which is typical of sand  castings, the upper half, including the top half of the pattern, flask, and core is called cope and  the lower half is called drag,  The parting line or the parting surface is line or surface that separates the cope and drag.

    The drag is first filled partially with sand, and the core  print, the cores, and the gating system are  placed near the parting line. The cope is then assembled to the drag, and the sand is poured on the cope half, covering the pattern, core and the gating system.

    The sand is compacted by vibration and mechanical means. Next, the cope is removed from the drag, and the pattern is carefully removed. The object is to remove the pattern without breaking the mold cavity.

    This is facilitated by designing a draft, a slight angular offset from the vertical to the vertical surfaces of the pattern. This is usually a minimum of 1.5mm(0.060in.), whichever is greater. The rougher the surface of the pattern, the more the draft to be provided.

    The molten material is poured into the pouring cup, which is part of the gating system that supplies the molten material to the mold cavity.

    Precision CNC machining partsThe vertical part of the gating system connected to the pouring cup is the sprue, and the horizontal portion is called the runners and finally to the multiple points where it is introduced to the mold cavity called the gates.