Wire Drawing and Deep Drawing Metal Forming Processes

Introduction to Wire Drawing and Stretching

The wire drawing (trefilado) and stretching processes are two procedures for the formation of ductile materials. These methods are performed by stretching the material through calibrated holes known as spinnerets.

Differences Between Stretching and Wire Drawing

Although the working procedure is the same, there are three main aspects to consider:

• Material Type: Stretching applies to bars 4-6 meters in length with diameters greater than 10 mm and pipes. In contrast, wire drawing is applied to circular rolling materials with diameters between 5-8 mm.
• Purpose of the Operation: The object of stretching is mainly calibration, work hardening, or giving shape to the bar. In this procedure, the thinning of the material is the means to achieve the set purposes rather than the end itself. However, in wire drawing, the goal is to thin the material almost exclusively, with hardening and calibration being secondary objectives.
• Execution: In stretching, the operation is performed in a single pass, whereas wire drawing thins the material through several passes.

The Wire Drawing Practice

Preparatory Operations

1. Sharpening: You must sharpen the end of the round in order to introduce it into the line at about 20 or 25 mm.
2. Stripping: You must clean the surface perfectly because metal oxides are very hard and lack plasticity.

Wire Drawing and Finishing

The drawing itself is performed in wire-drawing machines. Afterward, the following finishing operations are conducted:

• Shearing: This is done using shears or scissors.
• Annealing: As drawn wire is hardened by deformation, it is generally subjected to annealing to relieve work hardening.
• Polishing or Coating: These treatments are often applied to the finished wires.

Deep Drawing Processes

Deep drawing is an operation that aims to convert a flat sheet into a hollow body. The operation is performed using a setup composed of three main parts:

• Die (Matrix): The gap that the plate must adapt to.
• Punch: The component that pushes the plate to adapt to the hollow of the die.
• Blank Holder (Pisador): This presses the sheet at the edge of the die. Its mission is to prevent wrinkles without fixing the sheet so firmly that it can flow as it is pushed by the punch.

Development of a Drawn Component

One of the fundamental problems encountered in designing technical drawings for a piece is the a priori determination of the shape and dimensions of the panel to be employed. For bodies with a circular cross-section and simple geometric shapes, these can be determined through the development of specific formulas.