The multi-station end forming machine completes its cycle to form a closed weld at the end of the copper pipe.
Imagine a value stream where pipes are cut and bent. In another area of the plant, the rings and other machined parts are machined and then sent off to be assembled for soldering or otherwise fitting at the ends of the tubes. Now imagine the same value stream, this time finalized. In this case, shaping the ends not only increases or decreases the diameter of the end of the pipe, but also creates a variety of other shapes, from complex grooves to whorls that replicate the rings that were previously soldered into place.
In the field of pipe production, end forming technology has gradually developed, and production technologies have introduced two levels of automation into the process. Firstly, operations can combine several steps of precision end forming within the same work area – in fact, one finished installation. Secondly, this complex end forming has been integrated with other pipe manufacturing processes such as cutting and bending.
Most of the applications associated with this type of automated end forming are in the manufacture of precision tubes (often copper, aluminum or stainless steel) in industries such as automotive and HVAC. Here, the molding of the ends eliminates mechanical connections designed to provide leak-tight connections for air or fluid flow. This tube typically has an outside diameter of 1.5 inches or less.
Some of the most advanced automated cells start with small diameter tubes supplied in coils. It first passes through a straightening machine and then cut to length. The robot or mechanical device then transports the workpiece for final shaping and bending. The order of appearance depends on the requirements of the application, including the distance between the bend and the final shape itself. Sometimes a robot can move a single workpiece from end-to-bending and back to end-form if the application requires a pipe end-formed at both ends.
The number of production steps, which may include some high quality pipe end forming systems, makes this cell type more productive. In some systems, the pipe passes through eight end forming stations. Designing such a plant starts with understanding what can be achieved with modern end molding.
There are several types of precision end forming tools. Punches Punches are “hard tools” that form the end of a pipe, which reduce or expand the end of the pipe to the desired diameter. Rotating tools chamfer or protrude from the pipe to ensure a burr-free surface and a consistent finish. Other rotating tools perform the rolling process to create grooves, notches and other geometries (see Figure 1).
The end shaping sequence can begin with chamfering, which provides a clean surface and a consistent protrusion length between the clamp and the end of the pipe. The punching die then performs the crimping process (see Figure 2) by expanding and contracting the pipe, causing the excess material to form a ring around the outside diameter (OD). Depending on the geometry, other stamping punches may insert barbs along the outer diameter of the tube (this helps secure the hose to the tube). The rotary tool can cut through part of the outer diameter, and then the tool that cuts the thread on the surface.
The exact sequence of tools and procedures used depends on the application. With eight stations in the working area of an end former, the sequence can be quite extensive. For example, a series of strokes gradually forms a ridge at the end of the tube, one stroke expands the end of the tube, and then two more strokes compress the end to form a ridge. Performing the operation in three stages in many cases allows you to get beads of higher quality, and the multi-position end forming system makes this sequential operation possible.
The end shaping program sequences operations for optimal accuracy and repeatability. The latest all-electric end formers can precisely control the position of their dies. But besides chamfering and threading, most face machining steps are forming. How metal forms depend on the type and quality of the material.
Consider the beading process again (see Figure 3). Like a closed edge in sheet metal, a closed edge has no gaps when forming ends. This allows the punch to shape the beads in the exact spot. In fact, the punch “pierces” a bead of a certain shape. What about an open bead that resembles an exposed sheet metal edge? The gap in the middle of the bead can create some reproducibility problems in some applications – at least if it is shaped the same way as the closed bead. Die punches can form open beads, but since there is nothing to support the bead from the inner diameter (ID) of the pipe, one bead may have a slightly different geometry than the next, this difference in tolerance may or may not be acceptable.
In most cases, multi-station end frames can take a different approach. The punch punch first expands the inner diameter of the pipe, creating a wave-like blank in the material. A three-roller end forming tool designed with the desired negative bead shape is then clamped around the outer diameter of the pipe and the bead rolled.
Precision end formers can create a variety of shapes, including asymmetrical ones. However, end molding has its limitations, most of which are related to the molding of the material. Materials can only withstand a certain percentage of deformation.
The heat treatment of the punch surface depends on the type of material from which the structure is made. Their design and surface treatment take into account the varying degrees of friction and other final forming parameters that depend on the material. Punches designed for processing the ends of stainless steel pipes have different characteristics than punches designed for processing the ends of aluminum pipes.
Different materials also require different types of lubricant. For harder materials such as stainless steel, a thicker mineral oil may be used, and for aluminum or copper, a non-toxic oil may be used. Lubrication methods also vary. Rotary cutting and rolling processes typically use oil mist, while stamping may use jet or oil mist lubricants. In some punches, oil flows directly from the punch into the inner diameter of the pipe.
Multi-position end formers have different levels of piercing and clamping force. Other things being equal, stronger stainless steel will require more clamping and punching force than soft aluminum.
Looking at a close-up of the tube end forming, you can see how the machine advances the tube before the clamps hold it in place. Maintaining a constant overhang, that is, the length of metal that extends beyond the fixture, is critical. For straight pipes that can be moved to certain stops, maintaining this ledge is not difficult.
The situation changes when facing a pre-bent pipe (see Fig. 4). The bending process can lengthen the pipe slightly, which adds another dimensional variable. At these settings, orbital cutting and facing tools cut and clean the end of the pipe to make sure it is exactly where it should be, as programmed.
The question arises why, after bending, a tube is obtained? It has to do with tools and jobs. In many cases, the final template is placed so close to the bend itself that there are no straight sections left for the press brake tool to pick up during the bend cycle. In these cases, it is much easier to bend the pipe and pass it to the end forming, where it is held in clamps corresponding to the bend radius. From there, the end shaper cuts off excess material, then creates the desired final shape geometry (again, very close to the bend at the end).
In other cases, shaping the end before bending can complicate the rotary drawing process, especially if the shape of the end interferes with the bending tool. For example, clamping a pipe for a bend can distort the previously made end shape. Creating bend settings that don’t damage the final shape geometry ends up being more trouble than it’s worth. In these cases, it is easier and cheaper to reshape the pipe after bending.
End forming cells can include many other pipe manufacturing processes (see Figure 5). Some systems use both bending and end forming, which is a common combination given how closely related the two processes are. Some operations start by forming the end of a straight pipe, then proceed to bending with a rotary pull to form radii, and then return to the end forming machine to machine the other end of the pipe.
Rice. 2. These end rolls are made on a multi-station edger, where a punching punch expands the inside diameter and another one compresses the material to form a bead.
In this case, the sequence controls the process variable. For example, since the second end forming operation takes place after bending, the rail cutting and end trimming operations on the end forming machine provide a constant overhang and better end shape quality. The more homogeneous the material, the more reproducible the final molding process will be.
Regardless of the combination of processes used in an automated cell—whether it’s bending and shaping the ends, or a setup that starts with twisting the pipe—how the pipe passes through the various stages depends on the requirements of the application. In some systems, the pipe is fed directly from the roll through the alignment system into the grips of the rotary bender. These clamps hold the pipe while the end forming system is moved into position. As soon as the end forming system completes its cycle, the rotary bending machine starts up. After bending, the tool cuts the finished workpiece. The system can be designed to work with different diameters, using special punching dies in the end former and stacked tools in left hand and right hand rotary benders.
However, if the bending application requires the use of a ball stud in the inside diameter of the pipe, the setting will not work because the pipe fed into the bending process comes directly from the spool. This arrangement is also not suitable for pipes where a shape is required at both ends.
In these cases, a device involving some combination of mechanical transmission and robotics may be sufficient. For example, a pipe can be unwound, flattened, cut, and then the robot will place the cut piece into a rotary bender, where ball mandrels can be inserted to prevent deformation of the pipe wall during bending. From there, the robot can move the bent tube into the end shaper. Of course, the order of operations may change depending on the requirements of the job.
Such systems can be used for high-volume production or small-scale processing, for example, 5 parts of one shape, 10 parts of another shape, and 200 parts of another shape. The design of the machine can also vary depending on the sequence of operations, especially when it comes to positioning fixtures and providing the necessary clearances for various workpieces (see Fig. 6). For example, the mounting clips in the end profile that accepts the elbow must have enough clearance to hold the elbow in place at all times.
The correct order allows parallel operations. For example, a robot may place a pipe into an end former, and then when the end former is cycling, the robot may feed another tube into a rotary bender.
For newly installed systems, programmers will install work portfolio templates. For end molding, this may include details such as the feed rate of the punch stroke, the center between the punch and nip, or the number of revolutions for the rolling operation. However, once these templates are in place, programming is quick and easy, with the programmer adjusting the sequence and initially setting the parameters to suit the current application.
Such systems are also configured to connect in an Industry 4.0 environment with predictive maintenance tools that measure engine temperature and other data, as well as equipment monitoring (for example, the number of parts produced in a certain period).
On the horizon, end casting will only become more flexible. Again, the process is limited in terms of percent strain. However, nothing stops creative engineers from developing unique end shaping devices. In some operations, a punching die is inserted into the inner diameter of the pipe and forces the pipe to expand into cavities within the clamp itself. Some tools create end shapes that expand 45 degrees, resulting in an asymmetrical shape.
The basis for all this is the capabilities of the multi-position end shaper. When operations can be performed “in one step”, there are various possibilities for final formation.
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Post time: Jan-08-2023