Metal Casting, Pressing & Machining Processes

Casting Processes

Casting: The process used to produce useful parts or objects from molten metal. It consists of pouring molten metal into a container (mold) shaped like the part or object being constructed, allowing it to harden as it cools.

Molds (e.g., sand, plaster, cavity wax, plastic) are filled with molten metal to produce parts similar to the mold shape.

Mold Types

• Green sand
• Dry layer
• Dry sand
• Metal
• Clay
• Furans
• CO2 process
• Special types

Foundry Core Characteristics

Cores must possess the following characteristics:

• Permeable
• Heat resistant
• Easy to collapse (after casting)
• Dry strength
• Friability
• Minimum tendency to generate gas

Pattern Types

Disposable Patterns

These are destroyed during the process of preparing the piece. They do not require special tolerances, the finish is uniform, and they last a short time.

Removable Patterns

Used for multiple castings, they last longer, produce more than one piece, and affect costs differently.

Pressworking Operations

Pressing: Sheet metal operations performed using machines called presses.

Operations in Pressing

• Bending
• Swaging
• Forging
• Stamping
• Cutting
• Extrusion
• Ironing
• Coining
• Expanding
• Twisting

Press Types by Energy Source

• Hydraulic
• Mechanical
• Manual

Ram Types

• Vertical single-acting
• Vertical double-acting

Purpose of the Press

Common uses include bending and punching.

Drawing

The transformation of a metal sheet into a hollow or concave shape, like a cup, by drawing the metal.

Shearing

The operation of cutting a sheet of metal along a straight line between two cutting edges.

Bending

The deformation of metal around a straight axis. Two common types are V-bending and edge bending.

Common Drawing Defects

• Puckering
• Wrinkling in the wall
• Tearing
• Earing
• Surface scratches

Material Removal (Machining)

Involves a workpiece, a cutting tool, and the machine tool.

Machining: A process by which material is removed from a basic piece (workpiece) to shape it and make it useful.

Machine Tool: The equipment that processes materials under commercial conditions by cutting, without presenting defects.

Requirements for Machining

• Material (Workpiece)
• Machine Tool
• Energy
• Relative motion (between tool and workpiece)
• Cutting Tool
• Elements of execution (fixtures, etc.)
• Hardness (appropriate relationship between tool and material)

Advantages of Machining

• Better surface finish
• Higher precision
• Accurate internal profiles
• Textures not possible with forging and casting

Disadvantages of Machining

• Time-consuming
• Cost
• Process difficulties
• Material removed becomes waste (chips)
• Requires skilled workmanship

Lathe

A very versatile machine tool, often operated manually, widely used in low and medium production.

Lathe Components

• Bed
• Headstock
• Tailstock
• Carriage (includes saddle, cross-slide, compound rest, tool post)