WIRE AND BAR DRAWING
Drawing is a process that involves dragging a bar, rod, or wire through a die opening to shrink its cross section.
The procedure is similar to extrusion in terms of broad characteristics. The difference is that in drawing, the work is drawn through the die, but in extrusion, it is pushed through the die.
As a result, indirect compression is occasionally used to describe the distortion that occurs while drawing.
The stock size that is processed is the primary distinction between bar drawing and wire drawing.
Although the mechanics of the operation are the same in both circumstances, the methodology, equipment, and even terminology differ slightly.
The number of dies varies between 4 and 12 in most cases.
Because of the long production runs that can be performed with the wire coils, which can be butt-welded together to make the operation truly continuous, the phrase continuous drawing is used to characteristic this sort of operation.
DRAWING PRACTICE
Drawing is frequently done when the material is still cool.
It is most commonly used to create round cross sections, although it can also be used to draw squares and other shapes.
Wire drawing is a crucial industrial operation that produces commercial products including electrical wire and cable, as well as wire stock for fences, coat hangers, and shopping carts, and rod stock for nails, screws, rivets, springs, and other hardware.
Metal bars are produced through bar drawing for machining, forging, and other procedures.
- Close dimensional control
- Good surface quality
- Improved mechanical qualities such as strength and hardness
- Adaptability to economical batch or mass manufacturing are all advantages of drawing in various applications. For very fine wire, drawing speeds can reach 50 m/s (10,000 ft/min).
When a bar is drawn to create stock for machining, the technique increases the bar’s machinability.
Inventive Tools A draw bench is a machine that consists of an entry table, a die stand (which holds the draw die), a carriage, and an exit rack for drawing bars.
The stock is pulled through the draw die by the carriage.
Hydraulic cylinders or motor-driven chains power it. The die stand is frequently constructed to handle many dies so that several bars can be pulled through their individual dies at the same time.
To draw wire, continuous drawing machines are utilised, which comprise of multiple draw dies separated by accumulating drums between the dies.
Each drum, known as a capstan, is powered by a motor to generate the necessary pull force to pull the wire stock through the upstream die.
As it moves on to the next draw die in the series, it keeps a light tension on the wire.
Each die reduces the wire by a particular amount, allowing the series to accomplish the desired total reduction. Between groups of dies in a series, annealing of the wire may be necessary depending on the metal to be treated and the total reduction. The entry, approach angle, bearing surface (land), and rear relief are the four distinct zones of the die.
In most cases, the entering region is a bell-shaped mouth that does not make contact with the work. Its purpose is to funnel lubricant into the die and prevent work and die surfaces from being scored. The drawing procedure takes place on the approach. It’s cone-shaped, with a half-angle that usually ranges from 6 to 20 degrees.
Depending on the work material, the correct angle changes. The size of the ultimate drawn stock is determined by the bearing surface, or land. Finally, the departure zone is the back relief. It has a back relief angle (half-angle) of roughly 30 degrees.
Tool steels or cemented carbides are used to make draw dies. For the wear surfaces of high-speed wire drawing dies, diamond (both synthetic and natural) inlays are widely used.
TUBE DRAWING
After the initial tubing has been created by another technique such as extrusion, drawing can be used to lower the diameter or wall thickness of seamless tubes and pipes.
Tube drawing can be done with or without the use of a mandrel. The easiest approach, which does not require a mandrel, is used to reduce diameter.
This procedure is sometimes referred to as tube sinking.
The problem with tube drawing without a mandrel is that it is difficult to control the tube’s interior diameter and wall thickness.
This is why numerous types of mandrels are employed.
The first, (a), establishes interior diameter and wall thickness during the process using a fixed mandrel attached to a lengthy support bar.
In this procedure, practical limits on the length of the support bar limit the length of tube that can be drawn.
The second kind, depicted in (b), employs a floating plug with a form that allows it to settle into a ‘‘natural” position in the die’s reduction zone.
The fixed mandrel’s constraints on work length are no longer an issue with this procedure.
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