Metalworking Processes and Techniques

Posted on Aug 18, 2024 in Geology

Temper

Tempering includes 3 phases:

  1. Heating to a temperature below the critical temperature Ac
  2. Keeping time approx. 1 hour
  3. Cooling of the air

This treatment is given to steels that have undergone treatment. It has 2 functions:

  • Remove tensions
  • Increase toughness

This causes a change in mechanical properties, and increases:

  • The elongation at fracture
  • The necking and density

It also causes a drop in:

  • The tensile strength
  • Yield strength
  • Hardness

Sintering

Sintering involves heating compressed pieces to achieve a complete weld. The sintering temperature must be high enough so that the increased mobility of the surface atoms of each particle produces an increase in their surfaces, until a total recrystallization that does away with the limits of each particle and are encompassed by a total mass. This temperature should not reach the melting point of the metal.

The duration of sintering depends on the temperature at which it is carried out and may be shorter, the closer it is to the melting point. In general, temperatures are chosen in the order of 2/3 – ¾ of the absolute melting temperature. These times should not be too long, to prevent grain growth in the pieces.

Sometimes the sintering takes place in reducing gaseous atmospheres in order to destroy oxide films that are formed on the surface of the particles, which favors the sintering of the tablet. The most commonly used type of furnace is the continuous, controlled atmosphere to prevent oxidation of the powders. We distinguish 3 zones in the sintering furnace:

  1. Warming
  2. Sintering
  3. Cooling

TTT Curves Diagrams

Diagram of isothermal transformation of austenite provides the following information:

  • Time to begin the transformation to a given temperature
  • Time to complete the transformation to the temperature
  • The nature of the product processing at that temperature

Cutting Steel

Cutting steels are used where machinability represents a crucial factor. They are characterized by a good start and chip fracture essentially by the high content of sulfur and other special additions. These elements provide certain inclusions, chip treaceability, and self-lubrication of the tool. The use of classic hardware is manufactured by tearing the chip. To encourage machinability, lead is used.

The ease of machining depends primarily on 3 factors:

  1. Hardness
  2. Grain size
  3. Thickness of inclusions in the steel mass

Although steels often use so-called easy-cutting steels: sulfur, lead, and phosphorus.

Carbon Steel Construction

Carbon steels are those in whose preparation is not the voluntary addition of alloying elements. Therefore, in this composition, manganese and silicon come apart from other waste. These carbons are composed mainly of ferrite and pearlite, and increased carbon decreases ductility and toughness.

The heat treatments applied to these steels are:

  • Manganese: Increased hardness
  • Silicon: Increases the elastic limit
  • Phosphorus: Increases hardness in the cold

Milling

Peripheral Milling

In peripheral milling, also called plane milling, the axis of the tool is parallel to the surface being machined, and the operation is performed by the cutting edges on the outer periphery of the cutter. Peripheral milling can be done in two opposite directions of rotation.

Two forms of peripheral milling are up milling and down milling.

Front Milling

  • Advance perpendicular to the axis of rotation
  • Axial depth produced by peripheral edges
  • Surface finish produced by the edges of the front side

The main differences between peripheral milling and front milling are that in peripheral milling the piece is moving and on the front is the cutter. The other main difference is that peripheral milling is used mainly for roughing, while the front is used for more detailed work.

Steel Mill

A steel mill passes a type of material through rollers in order to reduce its thickness. There are two types of rolling mills: the rolling mill (which has different configurations depending on how many rolls we have), and the tandem rolling mill.

The basic rolling mill consists of two rollers, but may be as mentioned above, with diameters ranging from 0.6 to 1.4 m. The configuration of the rollers may be reversible or not.

In non-reversible rolling mills, the rollers rotate in the same direction and work always goes through the same side. The reversible mill allows rotation of the roller in both directions, this allows a series of reductions.

The tandem rolling mill has several rollers that can carry different reductions in thickness each. Every step of rolling speed is increased step. These mills are frequently used in continuous casting operations.

Molding Sand Mechanic

In mass production, manual methods are replaced by mechanical molding made with specialized machinery. Molding is essentially a box of sand fill and pressing.

There are different types of molding machines:

  • Pressure molding machines
  • Projection molding machines
  • Jerk molding machines
  • Combined procedure molding machines

There is a final type for molding male mechanics.

Molding vs. Casting

Advantages of Molding:

  • Greater accuracy and consistency in the dimensions of parts
  • Optimized surfaces

Disadvantages of Molding:

  • Limited shape and size, especially inside
  • High cooling rate, which can create internal tensions

Jet vs. Plasma Oxyfuel

Advantages of Jet and Plasma Cutting:

  • Cuts all metals and alloys
  • Very small deformation of the pieces

Disadvantages of Jet and Plasma Cutting:

  • The flame cutting short blocks reaches 2500mm thickness
  • The groove is about 50% wider than the oxyfuel
  • Cuts are not always square

Plasma Jet vs. Water Jet Cutting

Disadvantages of Plasma Jet Cutting:

  • The cut is not omnidirectional
  • The cut thickness is limited
  • The cross section is thermally affected

Stitching

Stitching is a deformation process in which a hardened form of a block of steel is pressed on mild steel. It is normally used to make holes for plastic molding and die casting.

Drawing:

A rammer with a hardened steel cutter, with the way we want to do, when low the ram crushes the work material that is in a receptacle, thus leaving the figure marked.

Laser Welding vs. Conventional Welding

Advantages of Laser Welding:

  • Improved accuracy
  • Suitable for small, deep pieces
  • Minimal shrinkage and distortion
  • Ductile and free from porosity

Disadvantages of Laser Welding:

  • Extreme risk to the eyes
  • Solid state lasers are potentially dangerous
  • The cost of equipment is arguably more expensive (€400,000 to €1 million)

Electric Shock

: remove metals through a series of discontinuous discharges, which produce localized temperatures high enough to melt or vaporize the metal in the immediate vicinity of the discharge. Drawing: electrode (-) immersed in a dielectric fluid moves down, leaving a separation with the working material (+) to jump the spark