Cold Drawn Tube Deformation Theory

The main way to force state drawing cold drawn tube when the tube or without mandrel pull system, short mandrel drawing system, drawing and swimming long mandrel mandrel pull system and so on. Extubation process, the metal is always pulling and two compressive stress state. When the force is pulling and pulling and deformation of the metal, which is always both compressive stress state and extubation basic mechanical characteristics of the deformation process. Always pull the two compressive stress state deformation resistance of metals lower, due to the tensile stress also makes metal plasticity is reduced. It is more difficult to pull out the plastic made of metal or severe low metal hardening. Because the force is exerted on the rear portion of the hammer pull the tube leaving the tube deformation zone is the role of the pull system extubation tensile stress, called pull system stresses. When the system without actually pulling mandrel, prior to the start of the deformation of the tube in contact with the die wall, and when the tubing exits the die orifice into the inlet hole with the sizing, may continue to have a certain degree of deformation. Before the general came into contact with the mold wall tube has been slightly reduced in diameter, wall thickness has been a slight increase in the diameter of the pipe leaving the deformation continues to have some of the reduced wall thickness also some thinning. As the die wall at the entrance pressure generated first bend. Bending the result that some of the metal in contact with the mold wall began before deformation, deformation zones front does not contact form. When the process of leaving the narrow entrance cone into the unit body with sizing moves in the original direction , due to the die wall pressure disappears, narrow cell body in the drawing force action will produce the opposite direction of the previous one another bend. Before the end of the bending process, the pipe continues to have some distortion, resulting in pulling the tube with a diameter smaller than the diameter of the sizing die holes.
Sometimes you can reach a lot of value, which is caused by pulling the main reason for the waste pipe burst. Metal more brittle deformation excessive ambient temperature is low, and the work hardening is not completely eliminated by the impact when a large hardening or annealing and other factors exist before pulling the tube will generate increased air burst extubation. Burst main measures to prevent the production of reasonably determine the amount of deformation is pulling empty, annealing time according to need, beginning with the quality of attention, and so avoid the formation of horseshoe tail pipe.
Short conical mandrel extubation generally use cylindrical mandrel constitute the outer mold and deformation zones, but also the use of curved and tapered mandrel outer mold, or both, with the use in production. Establish short mandrel drawing process is critical and whether the mandrel into the deformation zone. The mandrel tip end shape of the mandrel into the main factors affecting the condition. The front end of the chamfer shape of the mandrel to ensure the tube wall should be in contact with the mandrel, the mandrel being applied to the pressure body and the horizontal component of the friction force r system toward the direction of pull. To this end, the distal end of the mandrel is tapered down to prevent back into the arc. Pull system in a stable phase, the deformation process is to reduce the tube diameter, followed by reducing the wall, the final sizing. Thus short pull mandrel deformation zone system by reducing the time zone, reducing the wall area and sizing zone three parts. When short mandrel pull system, wall to thinning, while the inner and outer surfaces of the tube are present friction, resulting in non-uniform deformation of the metal in the air pull factors, in the short mandrel pull system is weakened, thus representing an empty metal deformation when pulling evenly, additional stress and residual stress generated is also small. (When is the use of a cylindrical mandrel) in the short mandrel pull system, under certain conditions, a mandrel rod system generates jitter. Jitter causes the pipe surface alternating light and dark rings, mold damage and loud noise. The basic reason for this is that the pull system jitter mandrel-way system is a flexible rod vibration system. Reaction force equilibrium the total friction force on the mandrel and pull the lever system in the elastic stretching process. If the positive pressure acting on the mandrel and the friction coefficient in the drawing process is frequently changing, the balance of the above conditions are constantly changing, the elastic deformation and the position of the mandrel rod is subsequently changing, causing a lever system to force the mandrel vibration and produce jitter. The main factors that prompted the production of jitter are: pull before annealing, poor quality pickling, cleaning and lubrication; rod diameter is too small and too big, and the length of pull system when excessive deformation. When pulling speed system is also prone to excessive jitter. Long long mandrel mandrel deformation process extubation extubation mandrel moves together with the tube, which can reduce the drawing force and increase the pass deformation, deformation is more uniform and because the movement of the mandrel, the inner surface of good quality. The disadvantage is the long mandrel pull system: the more difficult long mandrel manufacturing needs after pulling off the stick.