Why is lubrication critical in the drawing process, and what types are commonly used?
Lubrication reduces friction and wear. Steels are typically pre-treated with phosphating before lubrication, and common lubricants include oils, soaps, and greases.
What is the process temperature distribution for a precipitation hardening process?
What materials are used for drawing dies?
Drawing dies are made from tool steels, hard metals (such as tungsten carbide with 3–10% cobalt), and diamond dies for high‐precision applications.
What distinguishes dry drawing from wet drawing?
Dry Drawing: Used for diameters >1 mm with solid soap powder as a lubricant.
Wet Drawing: Used for diameters <1 mm where the wire is submerged in a liquid lubricant.
What is tube drawing and what is unique about it?
Tube drawing reduces the cross-sectional area of tubes and can be performed with or without the use of a mandrel.
Name the key equipment components used in the drawing process.
The main equipment includes:
Payoff Reel: Feeds the material.
Lubricating Box: Applies lubrication.
Die: Reduces the cross-sectional area.
Draw Block (Capstan): Controls speed.
Motor & Drive: Provides the pulling force.
How is the true strain in drawing calculated?
What is the formula for the drawing force?
How is the redundant work factor (Φ1) determined experimentally?
How does the die angle influence the drawing process?
What is the drawability limit in drawing, and how is the maximum reduction per pass defined?
What metallurgical benefits does patenting (heat treatment) provide for drawn spring wires?
Patenting creates a fine pearlite microstructure, removes undesirable phases (cementite, ferrite, decarburization, inclusions), and can yield an ultimate tensile strength (UTS) up to 3500 MPa.
What microstructural changes occur during drawing?
Drawing aligns cementite in the drawing direction and forms dislocation cells in ferritic areas, which contribute to higher strength
How are true stress and ultimate tensile strength (UTS) expressed post-drawing?
What are some common surface defects encountered in drawing?
Cracks in martensite (often due to poor lubrication),
Holes and cavities from surface inclusions, and
Decarburization, which reduces surface hardness.
What are chevron cracks and when do they occur?
Chevron cracks are internal defects that occur when the die angle exceeds approximately 2.6–3°, resulting in high tensile stresses at the center and leading to internal failure.
What is the meaning of the factor f in the the calculation of the hardness?
The factor f presents a correction factor to determine how much strain was put into the strain hardening of the wire.
How is the tensile strength of a drawn wire calculated?
if fe<n:
if fe>n (necking):
How is die wear measured in the drawing process?
Die lifetime is measured by the length of wire drawn (in km) until the wires diameter increases by 1 μm. Typical lifetimes vary—for example, about 10 km for patented steels in WC–Co dies and up to 2000 km for polycrystalline diamond (PCD) dies.
What friction coefficients are typical under different lubrication conditions in drawing?
Under boundary lubrication (at low speeds) μ≈0.15; under mixed lubrication (around 1 m/s), μ is in the range of 0.02–0.04.
What are the main types of extrusion?
irect Extrusion: A ram forces metal through a die.
Impact Extrusion: Used for making short hollow tubes (e.g., toothpaste tubes).
Tube Extrusion: Involves a mandrel to produce hollow sections.
How is true strain defined in extrusion?
How does friction affect the extrusion pressure in the die?
Under what stress conditions does extrusion occur?
Extrusion occurs under triaxial compression, where friction in both the container and the die plays a significant role.
What metallurgical phenomenon is observed during extrusion in low–stacking fault energy (SFE) metals?
Dynamic recrystallization (DRX) occurs, leading to microstructure refinement—as seen in alloys like AZ31 (a magnesium alloy).
What surface defects can occur during extrusion?
Internal defects can include chevron cracks (especially at low reductions and large die angles) and surface cracks in thin sections.
What are the primary wear mechanisms for extrusion dies?
The dies primarily suffer from sliding wear (due to friction) and thermal fatigue (especially in hot extrusion).
Which die materials and coatings are used to extend die life in extrusion?
Commonly used die materials include nitrided H11 and H13 tool steels, with coatings such as AlTiN and CrN applied to enhance die longevity.
How can P0 in extrusion be calculated?
How is the average process temperature in extrusion calculated?
How is the temperature in extrusion calculated?
Which parameters influence the sliding wear of extrusion dies?
material properties
extrusion speed
extrusion ratio
matrix hardness
die temperature
lubrication
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