Types of Tube End Forming
There are a variety of types of tube end forming. Today, in this blog post, we will highlight some of the more popular types of tube end forming type throughout various industries.
One of the most common forms of tube end forming is beading. Beading is universally used throughout many industries as a connection or sealing point between two mating parts. Within the past few decades, beading has seen a drastic change in development as automotive manufacturers push to design tighter tolerance parts to aid in assembly and prevent leaks. Beads can vary in all shapes, sizes, and material being as small as .150” to larger than 16”+. Within the beading family, there are subcategories of beads that are used to fulfill various applications. Let’s take an overview look of the various kinds of beads that are commonplace within multiple industries.
Originally designed in the 1940’s, the Marmon bead has become commonplace throughout the tube and pipe industry. Today, this application can be seen daily from diesel particulate filter canisters (DPF) on heavy trucks to bi-cone exhaust connectors in the automotive industry. The Marmon clamp is a 3-part assembly consisting of a female part, a male part, and the clamp itself. The male connector is typically a 20° flare which seats on the bead of the female connector. The clamp is then used to pull the two together to create a sealing surface between the two mating parts, preventing leaks. Marmon beads can be a high tolerance part as the front bead surface is critical to produce a practical sealing surface with the mating part. Marmon beads can be formed a variety of ways, but the most common and efficient process is through segmented end forming which will be explained later.
SAE beads are beads that were standardized by the Society of Automotive Engineering. The SAE was founded in 1905 to create an organization where engineering developments could be shared with the industry. Many SAE beads are used prominently in automotive applications with many being used as a connection for fuel or fluid transfer systems within a vehicle. These parts are usually smaller in size. Due to their smaller nature many SAE beads are either ram or rotary end formed.
Rather than expanding the diameter of a tube, an inverted bead is one that is recessed within the diameter of the tube. Inverted beads have a variety of applications. Many inverted beads are used as rollers for conveyor systems. Inverted beads are also used as a location to seat an O-ring on the outer diameter of the tube so it can be seated within another part. Most inverted beads are rotary end formed.
The Norma Ball is new exhaust component that was recently developed for the automotive industry. Unlike the Marmon bead and flare, this exhaust connection allows a minor range of movement within exhaust assemblies prior to the addition of the clamp. This movement is obtained due to the shape of the form. The ball form allows a ball flare to seat on top of the outer surface of the ball. This connection is becoming increasingly popular among automotive manufacturers as it is being implemented into more vehicles with 2.5” – 3.0” exhaust systems. The Norma ball is an ideal end form for segmented or rotary end forming.
Flaring is the expansion of the end of the tube with the expansion facing outwards. Flares are commonly used as the counterpart to beads to complete a variety of connections. Flares can vary in all shapes, sizes, and material being as small as .150” to larger than 16”+. Within the flaring family, there are subcategories of flaring that are used to fulfill various applications.
20° flares serve as the mating part for many Marmon beads. The inside of the flare seats on the front bead of the Marmon bead. Once the clamp is applied, those two surfaces are pulled together to create a sealing surface. These surfaces usually have a surface profile GD&T callout to maintain accuracy so the final assembly will not have any exhaust leaks. 20° flares are best suited for rotary or ram end forming.
37° & 45° Flares
37° & 45° flares tend to be smaller diameter end forms that are used for high pressure fluid transfer lines. These transfer lines are often for hydraulic or fuel lines for fluid power and motion control. The mating part has a chamfered edge around the outer diameter which seats inside the flare. This mating fitting also has threads that are found behind the connection point. A nut is often added over a 37° flare, which is used to secure the fitting with the threads to the flare itself creating a sealing point. Due to their smaller nature, 37° & 45° flares are end forms that are best suited for ram end forming.
Similar to a 37° or 45° flare, double flares are end forms where the flare has been folded back in on itself to create a flare with two walls. The double wall strengthens the flare and adds rigidity to the connection. Instead of single flares, these flares are used for extremely high-pressure applications such as brake lines. In most cases, a single flare would crack or leak due to the pressure inflicted by the hydraulic system. Double flares are an end form only suited to ram end forming.
Ball flares serve as the mating part to the Norma ball and standard ball forms. As aforementioned, these flares seat on top of the form where a clamp is added to pull the two parts together to create the connection. These flares are becoming an increasingly popular connection for automotive exhaust applications. Ball flares are best suited for rotary end forming.
Tube cut-off is the process of cutting a tube to length to get a tube ready for another application or process. There are many ways to cut tube and pipe for tube end forming applications. Band saws and cold saws are most used, but they often leave chips, burrs, and other imperfections that could affect tube end forming. For high volume production, rotary end forming equipment using cut-off tooling is a practical option since it mitigates the need for a deburring operation after the tube has been cut. This cut off process also provides a square concise cut, compared to a cold or band saw.
Knurling is an end forming process that adds texture to an area of the tube. This application is used on the outer diameter of a tube to add grip area for a mating part, typically hoses or other flexible mediums for fluid transfer. Real world applications would be coolant and low-pressure fuel lines. Knurling is an application that is used in conjunction with a bead especially when the formed part mates with a hose. Some end forming processes can form the bead and the knurl within the same operation. Knurling is a tube end forming application that is best suited for rotary end forming.
Tube reducing is the process of shrinking the outer diameter of a section of tube to be used with another mating part as part of a full assembly. Reductions are one of the most widely used applications throughout the world. Tube reductions go into many everyday items such as cars, trucks, planes, water lines, and more. The size of the reduction will vary based on its final application. Many reductions are a simple slip fit to be used in exhaust assemblies while others are heavily reduced for tie rods or other applications. Wall thickness and tube diameter play a key role in deciding which tube end forming process will be best for the application at hand. Most heavy wall applications are best suited for ram end forming. Segmented end forming is ideal for average wall tube that does not need a drastic reduction.
Tube expanding is the process of expanding a section of tube to a size larger than its nominal diameter. Similar to its tube reduction counterpart, expansions are widely used for various applications. Wall thickness and tube diameter play a key role in deciding which tube end forming process is best for the decided application. For larger expansions greater than 1-inch, progressive ram end forming is the best suited process. Segmented end forming is ideal for expansion with an expansion range less than 1-inch on diameter and a wall thickness less than .120”.
Offset expansions are a different to a normal expansion in the fact that the expansion is offset from the center of the tube. This type of end form is primarily used in the automotive industry for fuel funnel applications. Offset expands are best formed when using a progressive ram end forming process. Progressive end forming allows the material to be gradually expanded over a series of hits. This gradual expansion does not compromise the material.
Tube coping is the process of cutting tube to fit against another piece of tube. Coping is used to prep the ends of tube that will be mated together to form a final assembly. Real world applications include furniture frames, roll cages, and more. Ram end forming is a practical way to cope tubes for high volume production.