This article takes an in depth look at Tube Fabricating Machinery.
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Tube fabricating machinery refers to equipment used to permanently bend, cut, or shape tubes and pipes into various configurations. These machines typically handle tubes made from ductile and malleable materials such as stainless steel, aluminum, bronze, brass, and titanium. Most techniques used in tube forming involve metal coldworking processes.
Different types of machinery are employed to transform blank straight tubes into more functional forms. Each machine alters the geometry of a straight tube in its own way, usually by deforming the material. Formed tubes have numerous applications, many of which will be discussed in subsequent chapters.
Tube bending is the process of making an angular bend with the tube by inducing deformation The tube encounters a combination of tensile and compressive forces during this process. The outer side of the bend is stretched and elongated due to tensile forces, while the inner side is thickened due to compressive forces.
Tube bending has several notable applications. It is used to fabricate pipe elbows, allowing the diversion of flowing media in piping systems. Bent tubes are also integral to structural pieces and furniture, and they are commonly found in air conditioning equipment, musical instruments, and automotive parts.
Tube bending techniques are categorized into two main types. In form-bound tube bending, the bend produced is determined by the geometry of the tooling. On the other hand, in freeform tube bending, the tube is shaped by moving through dies, and the resulting bend is not influenced by its geometry.
The following are the types of tube benders. Tube benders can be either semi-automatic or CNC-controlled.
Rotary draw benders are equipped with a set of interlocking dies used in computer numeric control (CNC) tube bending. This tooling ensures that the tube is protected from collapsing, wrinkling, ovality, and wall thinning during the bending process. The dies involved in rotary draw bending include the following:
A mandrel bender has the same set-up as the rotary draw bender. This tube bending machinery uses additional tooling called a mandrel. The mandrel is inserted into the tube and offers internal support to prevent wrinkling and collapsing and to reduce ovalization. It helps achieve quality bend for thin-walled tubes, especially if a sharp bend is to be formed.
Mandrel types include the plug mandrel, formed end plug mandrel, standard mandrel, thin-wall mandrel, and ultra-thin wall mandrel. The selection of a mandrel is based on the tube’s wall thickness and the sharpness of the bend radius.
A hairpin bender is a type of rotary draw bender designed to create a 180° bend (hairpin bend) from coiled bundles of copper and aluminum tubes. Multiple coils of tubes are uncoiled in the unwinding system of the hairpin bender and fed into its tracks. The unbent tubes are transported to the bending section via a conveyor belt, with guides in the conveying system to align and straighten the tubes before bending. Upon reaching the bending section, the tubes are clamped, and mandrels are inserted into them. The clamping die, housed in a robotic arm, rotates 180° from the axis to bend the tube over a bending die, forming the hairpin bend. After the bend is made, the mandrels are withdrawn from the tubes. The bent tubes are then cut to the desired length and collected.
Hairpin benders are high-speed, highly automated machines capable of producing multiple hairpin tubes per cycle. Some models feature a chip-less cutting mechanism, which minimizes material scrap.
Return benders operate similarly to hairpin benders but are designed to produce "return bends," U-tube-shaped fittings that change the direction of fluid flow by 180°. The spooled tubes are uncoiled and fed into the multiple tracks of the return bender. Like hairpin benders, return benders limit the bending to 180°, and the tube is internally supported by a mandrel during the process.
Crossover benders operate with a mechanism similar to that of hairpin benders and return benders but are not restricted to producing 180° bends. They can create a wide variety of bend angles through tooling changes and setup adjustments, making them more versatile. Crossover benders are used to manufacture products such as crossover bends, return bends, elbow bends, and short straight tubes. The following equipment is used to modify the dimensions of these products:
Press benders consist of two dies that secure and support the tube during the bending process, along with a ram that descends to apply the bending force. The ram serves as the bend die and features the contour of the bend to be made. Press benders are efficient at producing symmetrical bends and typically do not require lubrication.
Angle rollers, also known as roll benders, feature three rollers arranged in a pyramid-like configuration. An adjustable working roller is positioned between the two bottom rollers, and its position determines the bend radius. The working roller rotates in the opposite direction of the two bottom rollers. As the tube passes through the slow-rotating rollers, it is compressed, and the process is repeated multiple times until the desired bend is achieved. The tube can be adjusted arbitrarily after each repetition, allowing for gradual formation of the bend angle.
Angle rollers are freeform rollers that produce bends with a large centerline radius. They can also shape tubes with various cross-sectional forms and create spirals from tubes.
Tube spinning is a flow forming process used to elongate tubing and modify wall thicknesses. During the process, the tube is mounted and clamped onto a mandrel, and then drawn along its length by a set of rollers spaced equidistant around the tube. The axial flow follows the direction of the roller movement.
Tube spinning can be performed externally or internally on the mandrel. In external tube spinning, the tube is stretched over the outer surface of the mandrel, while internal tube spinning involves spinning and stretching the tubing within a hollow mandrel.
Tube spinning is employed to fabricate tubes with varying diameters when wall thickness is not a concern. It requires precise tooling design and enhances the mechanical properties of the tube.
Shear spinning applies downward force on the tubing while stretching it over the contour of the mandrel. This process results in finished tubing with a reduced thickness compared to its original form, while maintaining the same diameter. The compressive forces exerted on the tubing enhance its mechanical properties as its depth increases.
Shear spinning demands a more robust tooling design and precise machine control, as it impacts the dimensional accuracy and surface finish of the tubing. Increased friction on the tubing and greater wear on the mandrel necessitate the use of coolant to manage the heat generated during the process.
There are four distinct deep drawing processes: tube sinking, floating mandrel, fixed mandrel, and moving mandrel. In all these processes, the tubing is drawn or pulled through a die. However, the positioning and shape of the mandrel vary among the processes, affecting how the tubing is formed.
In tube sinking, also known as tube drawing, the tube is pulled through the die, with the outer diameter (OD) of the tubing being defined by the diameter of the die. The process does not regulate the inner diameter or tube thickness. Instead, tube sinking modifies the thickness of the tube walls.
In the floating mandrel deep drawing process, the mandrel is drawn into the die by frictional forces, while normal forces attempt to push it out. The mandrel settles in a position where these forces are balanced. As frictional forces vary, the mandrel adjusts its position, leading to changes in the tube thickness.
In fixed mandrel deep drawing, the mandrel is drawn into the die along with the tubing, which helps change the tubing's thickness. On the entry side, the tubing's cross-sectional area increases while its speed decreases. At the exit side, the mandrel moves at the same speed as the tubing, but the deformation zone of the mandrel moves faster than the tubing. Frictional forces pull the tubing into the die during this process.
In moving mandrel deep drawing, the mandrel is a cylinder that is drawn along with the tubing through the die. This process is used to reduce the thickness of the tubing. As the tubing enters the die, its cross-sectional area increases, causing its speed to decrease. At the exit side, the mandrel moves at the same speed as the tubing, while the mandrel's deformation zone moves faster than the tubing.
The pilgering process is used to reduce both the diameter and wall thickness of tubing, achieving cross-sectional reductions of over 90% in a single cycle. Pilgering employs a pair of ring dies and a mandrel. The mandrel is fixed inside the tubing, similar to tube drawing with a moving mandrel.
In the rolling section of pilgering, the mandrel is tapered, and the dies feature matching grooves around their circumferences. The pilgering machine moves the tubing forward and backward to allow the dies to reduce its outer diameter (OD). The grooves in the dies decrease in size along their circumference, forming a semi-circular shape. During the process, the dies disengage at the center position, causing the tube to advance and rotate. This disengaging and rotation ensure consistent wall thicknesses throughout the tubing.
Autofrettage aims to enhance the durability of tubing and increase its resistance to stress corrosion cracking by applying intense pressure. This pressure causes the tubing to expand and stretch its inner layers beyond their elastic limits, so the tubing cannot return to its original shape.
In autofrettage, the outer layers of the tubing are not stretched beyond their elastic limit because the stress distribution is uneven. Although these external layers try to return to their original shape, they are prevented from doing so by the inner layers, which remain stretched.
Additionally, during the autofrettage process, the inner layers are subjected to a low-temperature heat treatment that further promotes expansion beyond the elastic limits.
Tube end formers, or end formers, are machines used in shaping the tube typically on or near its end. End formers create an installation port on the tube for other media (e.g., hoses, blocks, or another tube). Formed ends enable tubes to fit with other mechanical parts. For fluid conveying applications, it ensures that no fluid will leak from the connection. It also changes the fluid velocity by increasing or decreasing the flow area.
The axis of the tube remains unchanged after the process. End formers can alter the geometry of the tube end in various ways:
Reduction and expansion refer to the decrease and increase of the tube end’s cross-sectional area, respectively.
Beading is the process of creating protruded "beads" near the end of the tube. These beads serve multiple purposes: they act as mechanical stoppers when the tube is fitted with other parts, enhance the effectiveness of seals, facilitate the connection of a tube to a hose, and strengthen the tube's end. Additionally, they help dampen vibration in solid lines.
Flaring is the process of forming joints on two tubes, so they produce a leak-proof seal when fitted to each other. Double-lap flared tubes have thicker material on their inner diameter; this offers additional strength and fatigue resistance and reduced variation in the flow area. Special types of flared joints include Marmon bead flares and spherical ball flares.
Flanging involves flattening the material at the end of the tube to create a flange that is seamlessly integrated with the tube.
End forming machinery comes in various types, including ram formers, segmented end formers, and rotary forming machines:
Ram end formers shape the tube end by applying axial force to induce material deformation. These machines feature vise jaws and a ram nose. The vise jaws clamp and support the tube while one end is being formed. Positioned next to the unsupported end, the ram nose, which contains the final shape of the tube end, strikes the unsupported end to induce deformation. This process is repeated with different ram noses over several strokes, gradually achieving the final shape. Due to the heat and friction generated during each stroke, lubrication and coolant are typically applied.
Ram end formers can produce tube ends in various shapes, both symmetrical and asymmetrical, depending on the tooling geometry. They are particularly useful for applications requiring significant expansion or reduction.
During a beading operation, the tube is positioned in a clamp with a gap between its halves. These clamp halves feature spaces for forming the tube bead. The bead is created as the clamp halves push each side of the tube towards each other in the axial direction. When beading is performed using a ram former, it is referred to as compression beading.
Segmented end formers work by applying radial force to the circumference of the tube to induce material deformation. These machines use a circular die divided into segments that apply the radial force. Unlike ram forming, segmented end forming usually does not require a clamping mechanism.
In the case of compression, a radial force from the outside of the tube squeezes it, reducing its cross-sectional area. Conversely, during expansion, a tensile radial force from the inside stretches the tube, increasing its cross-sectional area. The radial force application is repeated over a specific number of strokes, with the segments rotating slightly to ensure uniform deformation of the workpiece.
The common types of tooling used in segmented end formers are C tooling and inside/outside (I/O) tooling. C tooling can perform either expansion or reduction operations. I/O tooling offers greater flexibility, featuring two concentric circular segmented dies between which the tube is fed, allowing it to carry out both functions.
Rotary end formers use a rotary head to modify the tube’s cross-sectional area by applying either tensile or compressive radial force. The rotary head is equipped with three to four cylinders that move axially through the tube, either on the inside or outside, while applying radial force. Rotary end formers can create flaring with angles ranging from 20° to 90°.
Tube hydroforming and tube swaging machines alter the cross-section of the tube at various points along its length.
Tube hydroforming is a process that uses highly pressurized fluid to expand metal tubes against the inner walls of a mold, altering their cross-sectional shape. This technique is versatile, accommodating tubes and hollow sections of various shapes. Tube hydroforming machines can transform stock tubes into complex and irregularly shaped sections.
To start the tube hydroforming process, the stock tube is placed between the mold halves of the hydroforming machine, which are then closed with sufficient clamping force. The length of the stock tube should be slightly longer than the cavity length. Sealing rods with internal presses are inserted at both ends of the tube, which is then filled with water. The internal press, powered by thrust actuators, compresses the fluid inside the tube. The resulting high internal pressure causes the metal tube to expand into the mold cavities. Finally, the hydroformed tube is ejected from the mold.
Hydroformed tubes offer high stiffness and seamless connections, enhancing their strength. The cost-effectiveness of tube hydroforming increases when used to form large tubes.
Tube swaging is a tube forming process designed to reduce and shape the cross-section of a tube. It can also alter the tube's cross-sectional shape. Essentially a forging process, tube swaging involves forcing the tube through and compressing it with a confining die to achieve the desired shape. The types of tube swagers are as follows:
In rotary swagers, a motorized spindle with reciprocating dies is enclosed within a cage that holds pressure rollers surrounding the spindle. As the spindle rotates, centrifugal force pushes the dies against the pressure rollers, causing the dies to move inward and close. The alternating open and closed positions of the dies compress the tube into the desired shape as it passes through the cavity of the rotating dies. A mandrel can be inserted to support and aid in shaping the tube.
Rotary swagers can be either two-die or four-die machines. Two-die swagers are typically used for smaller parts and offer a better surface finish. Four-die swagers are employed for larger parts, especially when significant initial reductions are required.
Long die swagers, a category of rotary swagers, are designed to create extended, shallow tapers.
In stationary spindle swagers, the dies exhibit a reciprocating action similar to that of rotary swagers. However, in this setup, both the spindle and the forming dies remain stationary while the head rotates and drives the pressure rollers. Because the forming dies are fixed in place, stationary spindle swagers can reshape a tube’s cross-section into different or asymmetrical forms.
In die-closing swagers, a segment of the tube to be swaged is inserted through a set of closed reciprocating dies before the swager begins rotating. The wedges then advance to compress the dies. A radial compressive force is applied each time the die strikes the tube for a set duration. After the swaging process is complete, the dies retract, and the swaged part is removed.
Tube cutting machinery is a category of tube forming machines designed to either reduce or divide the length of a tube or remove some of the tubing material through cutting. Tube cutting typically serves as an intermediate step in other fabrication processes.
Some examples of tube cutting machinery include:
Tube threading is the process of creating helical ribs on the end of a tube or pipe to facilitate assembly with other tubes or parts with threaded ends. It does not alter the tube’s cross-section or axis and is not considered an end forming process.
The tube stock is inserted and clamped by the jaws on the center of the tube threader’s wheel. These jaws are locked to prevent the tube from slipping. Prior to threading, burrs on the tube end are removed in a process known as reaming. If the tube threader lacks a reaming tool, this step is performed by a separate deburring machine.
To create the thread, material is cut away from the tube end using a stationary universal die head equipped with sharp teeth. The universal die head is adjusted to match the outer diameter of the tube. Once setup is complete, the wheel rotates the tube while the universal die head is placed on the tube end. Cutting begins as the sharp teeth engage with the tube. Liquid coolant is applied to the cutting area, and the chips generated from cutting are collected on the bed of the tube threader.
Tube and pipe notchers are used to reshape the ends of tubes by removing a portion of the material, enabling them to be mounted on other tubes and mechanical parts. Notched tube ends are often welded to create joints for structural applications. Side-notched pipes, for instance, facilitate the fabrication of tee fittings used in fluid flow branching.
There are several types of tube and pipe notchers, including end mill notchers, punch-type notchers, and plasma notchers. End mill notchers remove material from the tube using a sharp, rotating mill positioned perpendicularly at its end. Punch-type notchers apply a shear force to cut the tube end using a punch. Plasma notchers utilize a jet of ionized gas to melt and cut the tube end, making them more practical for cutting large sections compared to the other types of notchers.
Tube slotters are used to remove a portion of tubing material to create slots. Slots can be formed using a press, where a punch strokes the tube and applies shear force to cut the material. Mandrels are used to support the tube internally during the cutting process. Additionally, slots can be created through machining or laser cutting methods.
Tube deburring removes excess metal from the tube end, polishes it for a smooth finish, and improves the aesthetic quality of the tube.
In a brush deburring machine, the tube end is sanded by a brush with rough and abrasive bristles made from thin metal wires. The brush is attached to a rotating element, such as a rotating disc or cylinder, which scrapes off the unwanted material from the tube end while the tube remains fixed during the process.
Tube cutting is the process of cutting a tube to its desired length. Various types of tube cutting machines are available for this purpose:
A cold saw machine uses a circular toothed blade to cut the tube to a specific length. The blade can be made of solid high-speed steel (HSS) or tungsten carbide-tipped (TCT). It is powered by an electric motor that rotates the blade. A coolant is sprayed on the cutting section of the tube to reduce friction and heat. Cold saw machines generate minimal friction and heat during cutting, resulting in a longer blade life.
In band saw machines, the toothed blade is made from a continuous band of thin, sharp metal. The blade rotates around two wheels and is cycled in one direction. The orientation of the cutting plane, whether horizontal or vertical, is determined by the arrangement of the wheels. The tube is placed on the bed of the band saw machine and fed towards the blade.
Band saw machines are ideal for large-volume production and can cut tubes with various cross-sections. However, they are not suitable for thin-wall tubes.
Supported shear cutting machines use internal punches and external dies to cut the tube. Stationary and movable punches are inserted into the tube to provide internal support during cutting. The tube is clamped between external dies, which include both stationary and movable dies. The movable punch and die apply shear force to cut the portion of the tube between the stationary and movable components.
Dual blade shear cutting machines are designed to cut carbon steel and alloy steel tubes while eliminating the dimple produced by single-blade cutting machines. These machines use a horizontal blade to make an initial scarfing cut on the side of the tube. Following this, a vertical blade continues the cut from the notch created by the horizontal blade. Throughout the process, the tube is clamped tightly by a set of tooling.
In rotary cutting machines, the tube is supported on two backup rollers, while a rotating blade is fed from the top and descends to cut the tube.
In lathe cutting machines, the tube is fed through a chuck-type clamping mechanism that rotates the tube while feeding it to the cutting tools. Alternatively, the setup may involve a stationary tube with rotating cutting tools surrounding and cutting the tube.
Laser cutting machines use high-energy solid-state or CO2 lasers to melt the tubing material, allowing for quick and precise cutting of the tube into the desired length.
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