However, the strength and stiffness is still higher than machining or casting as strain hardening occurs [ 81 ]. Grain flow of different manufacturing methods; redrawn from [ 5 , 81 ].
While tensile tests are traditionally used to characterize materials, more advanced techniques have proven to yield different and often superior information. Examples of these tests are the Nakajima and Marciniak tests described earlier in section 3.
The hydraulic bulge test is similar to the Nakajima test except instead of a punch, fluid pressure is used to bulge a sheet metal sample Fig. The fluid pressure is increased until the specimen fractures in the middle of the bulge while the strain levels on the top are monitored. This allows for the determination of stress strain curves in biaxial stress state [ 82 ]. It is now recognized that for tube hydroforming a tube bulging test Fig.
The main challenge in industry is the lack of availability of measurement hardware, so while the data is superior, according to Vitu et al. The test works in a similar fashion to the hydraulic bulge test increasing pressure until a rupture at the middle of the tube while measuring strain except the stock is a tube and axial feeding may or may not be used depending on the setup.
A corner fill test pushes metal into a square corner to see how far into the corner the material will form before the material breaks to give an idea of the minimum formable radius possible in a tube hydroforming operation. Other tests for measuring friction in metal forming applications include devices based on stretching of a strip around a pin, or apparatuses that use strain measurements to infer friction forces [ 85 ].
A corner fill test uses a tube in a die with a square cross section and gauges how easily or how well the tube conforms to the square corners of the die when the interior fluid pressure is increased. Additionally, tube-drift-expanding tests Fig. Eventually the cone will force itself into the tube far enough to cause a split to form on the exterior.
The value of the circumference of the tube at the onset of fracture as compared to the original material gives an indication of formability. Examples of some of these tests can be seen in Fig. There are certain features that make a hydroforming operation difficult or impossible and these features should be avoided during the design phase of a component if at all possible. These limits are general limits for the hydroforming process, but are also dependent on materials to a certain extent.
Features to design out are shown in Fig. Features that limit hydroformability; 24c redrawn from [ 43 ]. An illustration of a figure with bends that would inhibit axial feeding can be seen in Fig.
Severe bends in this case are 90 degrees or more. Furthermore, pre-bending a tube before hydroforming consumes the formability and can greatly reduce the amount of deformation possible during the hydroforming process. The extent to which axial feeding assists hydroforming is quantified in section 5. With both sheet and tube hydroforming, sharp bends as shown in Fig. With a sheet hydroforming operation, a sharp bend may eliminate the possibility of using a punch.
Furthermore, when using a cavity die, the material will have difficulty feeding inwards from the flange if there is a sharp bend.
With a tube hydroforming operation, sharp bends will require a large pre-bending operation prior to hydroforming which will consume formability and limit axial flow [ 6 ]. Draws which are exceptionally deep are difficult to create and may require many steps or stress relieving annealing stages. Also special equipment with large draw depths or multiple sets of dies could be necessary.
This adds considerable cost in areas such as: development, trials, cycle times, labor, and equipment costs. One of the benefits of sheet hydroforming is that it allows for more formability which is expressed in terms of an increased draw ratio or aspect ratio. Larger LDRs allow for larger blanks to be used and for more material to be drawn in to the working area from the flange.
This means a deeper draw made with less material thinning is possible. For normal cold sheet forming operations the limit draw ratio is around 2, but for hydroforming the value can reach 2. While this is a generalization because the limit drawing ratio is dependent on material characteristics as well as geometry the underlying point is that a component can be drawn more in a hydroforming process than a conventional deep drawing process.
This is valuable because if more material draws in from the flange, there is less material thinning in the final component. The LDR calculation is a quick calculation that is particularly useful for a designer that has a specific geometry in mind and has to source equipment or vice versa. The LDR calculation is shown schematically in Fig.
The hydroforming process is generally limited to a LDR of 2 to 3 [ 1 ], and the draw depth is generally set to be roughly twice as deep as the punch diameter [ 21 ]. If the geometry calls for a larger draw ratio than is possible with the hydroforming process, an alternate manufacturing process must be pursued or multiple drawing stages considered. In certain cases multiple hydroformed components could be drawn to an acceptable draw ratio and welded together.
In a recent study involving the calculation of limit drawing ratio for AZ31B magnesium alloy sheet in a warm deep drawing process Wang et al. This would be visually represented as a shift of points on the surface of the material to the right in Fig. The balance with hydroforming is that the larger the blank size is, the larger the force on the surface of the blank will be as the more area the fluid will be exerting force over.
Too large of a blank size leads to too high of a force which inhibits material draw in and causes the punch to pierce the material. Too small of a blank size leads to the material being formed without hitting the correct draw depth. Experimental Assessment of Draw Ratios [ 88 ]. It is very difficult to bulge or draw material into a tight internal radius or around a tight external radius the latter shown in Fig.
While some companies solve this by using more advanced forming techniques, it still adds cost and complexity. Depending on the source there are different rules about how sharp a radius can be. Subsequent operations, annealing or pressure intensifiers can help tighten up the radii after the forming operation, but as a general rule keeping radii at least 3 to 5 times larger than the material thickness is advisable whenever possible for high pressure hydroforming operations, [ 12 ] and 10 times larger for low pressure operations [ 4 ].
That said, more recent work has shown that in certain circumstances the edging technique [ 89 ] or a subsequent coining operation can produce radii as small as 2 times the material thickness in certain circumstances explained in detail in " Advanced hydroforming techniques "section.
There is also a difference between interior and exterior corners of a component and what happens with insufficient material pressures in each of these locations.
These corners are shown schematically below in a cavity hydroforming operation in Fig. Interior corners are governed by pressure and insufficient pressure will mean the corner is improperly filled and has a larger radius than desired [ 6 ] or more fatally will cause wrinkling [ 4 ]. If an interior corner is formed with insufficient pressure for the radius, then there is a problem with the material properly filling the corner [ 6 ].
If an exterior corner has a sharp radius then it can be difficult for material to pull in from the flange causing excessive thinning and tearing. There is only a certain amount that a tube is physically capable of expanding and this expansion is governed by the material properties, the initial blank size, and the final geometry. This equation determines the expansion that a tube undergoes during an operation and compares it to a calculated theoretical limit. If the tube expands less than this limit then it will most likely form successfully, if it expands more than the limit it will most likely fail.
It is important to realize that this is a heuristic value so it is imperfect and failures can possibly be overcome by geometry changes or stress relieving heat treatments. Also this equation was likely developed for automotive applications using grades of steel and aluminum. The equation uses the maximum possible cross sectional perimeter Pcs max which is shown in Fig.
This equation quantifies the benefits of axial feeding by using the stain hardening coefficient to predict formability. For example, if a strain hardening coefficient is assumed to be 0. The reason for this is that the additional material forced in during the axial feeding replaces material which was thinned during the process.
For a visual understanding of this, the strain path taken is further to the right of the forming limit curve shown back in Fig. The compressive minor strains allow for a higher acceptable level of major tensile strains. Thicker and thinner sections are an unintentional by-product of any cold forming process which must be managed. For interior corners wall thinning should be expected in proportion to the sharpness of the corner and the depth of the draw, i.
This is due to the increased friction that results in stretching material into a tight corner and the additional material required for a deep draw.
Counter-intuitively, the material has been reported to actually thicken in certain points during the operation. Generally, this thickening is most pronounced in a tube hydroforming operation although has been reported in sheet hydroforming as well [ 90 ] where axial feeding is used and is seen on the opposite side of a bulge [ 91 ].
Two examples of tube hydroforming thickness distribution can be seen in Figs. In these examples the thinning is most pronounced in the areas that are stretched the most and the thickening occurs most in areas where material feeding is present but local material expansion is not. An example of achievable tolerances during a sheet hydroforming operation with a cavity die was given by Wesselmann et al.
The satellite dish as well as the tolerance which was measured at multiple locations is seen in Fig. Example of sheet hydroforming tolerances achieved on a Satellite dish mm [ 94 ].
Like all engineering tolerances, tighter tolerances become increasingly difficult to achieve with larger part sizes. This section reviews some of the more advanced techniques used currently in the hydroforming industry.
Many different forming techniques have been discovered which aid in the creation of complicated geometries, or add in additional features. Some of the most popular are listed with descriptions, schematics, and governing principles. In cases of insufficient available pressure, pressure intensifiers can be used for finishing operations. They are used as a second step in the hydroforming process [ 95 ] and work by enhancing pressure in a given area particularly when a piece of equipment does not have sufficient pressure capacity to create a tight enough radius on its own.
A simple example of a pressure intensifier is that of a coining ring which is a large disc that sits on top of the component during a secondary forming operation although technically the operation bears more resemblance to ironing than coining. A hydroforming operation which produces a part with a large flange radius can be seen in Fig. A pressure intensifier works by converting the fluid pressure to an acting force concentrated in a corner which is greater than what fluid pressure can achieve alone.
This is done by converting the pressure of the fluid exerted on the ring to mechanical pressure which is concentrated into the radius. There are also other kinds of intensifiers that can be used including interior intensifiers that work with cavities and rubber intensifiers.
If the example given in Fig. Pressure intensifier as described in [ 95 ]. For a radius on the top of the geometry, restriking operations have been suggested in the literature for forming a tighter radius.
Also, in a new study Wang et al. In cases of deep drawing or the creation of finer details in a drawn component, hydroforming operations can use multiple sets of dies which change size.
In the case of multiple stage deep drawing, shown schematically in Fig. Then the flange is trimmed off of the part, and it is set over a tube shaped ring. Then the punch is changed to a narrower punch which can make use of the material generated in the first operation and draw it further [ 21 ].
Hydroforming using a holding ring and multiple stages [ 21 ]. This means that hydropiercing is not a secondary operation as it takes place in situ after the forming operations have completed and while the component is still inside the die. Tube hydroformed components used in automotive applications often make use of holes through which fastening devices are inserted and in such cases hydropiercing can be a cost effective alternative to drilling, milling, cutting or mechanical punching [ 6 ].
When hydropiercing care should be given as to what happens to the punched material and how it is removed or bent. While this technology may theoretically be possible with a bladderless sheet hydroforming process, the examples in the literature are limited to hydropiercing of tube hydroformed components. Various types of hydropiercing; redrawn from [ 6 ].
In a cavity sheet hydroforming process, dies can be designed in such a way as to shear components after the forming operation has completed which removes the need for subsequent cutting or shearing operations [ 20 ].
A sharp edge is created in the die whereby when the forming operation completes, the pressure builds around a sharp edge, and the formed metal is forced over which shears the component in situ as shown in the industrial example from Quintus Technologies Fig.
In process trimming; republished with permission from [ 20 ]. There are a few different ways in which drilling holes in the blank prior to the forming operation can be beneficial to creating more complicated geometries or enhancing physical characteristics such as stiffness. If a hole is drilled into a component before a pressing or hydroforming operation, then the material can be pulled into the hole to create a circular protrusion [ 21 ].
Also, predrilling a hole prior to a forming operation is a punch hydroforming and deep drawing technique that can allow for less material thinning in a wall by allowing material to flow into the wall from both the top and flange sections. However, it is generally only useful when the thickness in the walls is important and the top of the geometry is to be removed after the operation.
Lastly, this process is only viable in deep drawing or with hydroforming equipment that has a bladder. If there is fluid acting directly on the blank, the fluid will likely find a path through the hole.
This process is shown in Fig. This technique utilizes a fluid cell press with a specially made tube die inside. A tube is inserted into the die and rubber is fitted inside the tube. Upon initiation of the pressure cycle, the fluid pressure will push the rubber inside of the tube outwards, expanding it into the die and creating a tube hydroformed component on sheet hydroforming equipment.
The dies used generally have to be split dies which increases labor costs and cycle times and axial feeding is generally not possible but this is a proven way to form tube components on SHF equipment, [ 20 ] Fig. Expansion forming schematic; redrawn from [ 20 ]. An alternate technique to the coining operation described earlier in 5. This technique, as described by Triform presses an equipment vendor is called edging and allows for extra material to stretch in from the flange on the upwards stroke and be pushed into the corner when the punch travels back down.
Bell et al. Edging, unlike a coining operation, does not require extra tooling or an additional forming cycle but it is not quite as accurate or repeatable. If the tolerance on the radius is critical, a coining operation is preferred, but if it not then a punch hydroforming operation with an edging step at the end is likely acceptable [ 21 ] Fig.
In related sheet metal forming processes, equipment manufacturers have invested heavily in automation in order to reduce cycle times.
Schuler, a press manufacturer, have incorporated many servo presses together to accommodate more complicated operations which optimize transfer taking into movement overlaps. This new technology can produce up to car body parts per minute which is nearly twice as fast as conventional lines [ 98 ]. AIDA, another press manufacturer, has also adopted servo drive systems in conjunction with new transfer presses to increase efficiency. Because of the increasing amount of electrification and hybridization of modern vehicles, sheet metal components are increasingly in demand and require increasing levels of complexity.
Therefore AIDA have aimed to combine many presses into one system to ensure that future systems are versatile. Hydroforming operations are also likely to follow the same trend of increasing automation, but because the technology is newer and more complicated it has a more stringent set of challenges. However, there are developments in efficiency aimed at reducing cycle times by increasing machine utilization with press automation. This significantly reduces cycle time and increases output [ 99 ] Fig.
Automated SHF schematic [ 99 ]. Certain sheet hydroforming technologies utilize both traditional pressing and hydroforming actions to form sheet. As seen in Fig. Dual process mechanical pressing with hydroforming; redrawn from [ 38 ]. The use of two blanks during a hybrid hydroforming operation is also possible. This allows for the press to essentially double its productivity, but can usually only be applied to two geometries which can be formed with the same pressure cycle and blank holding force however [ ] looked at using counter pressure on one blank to compensate.
The operation shown would be a hybrid dual sheet hydroforming process and would work by first pressing both sheets and then pumping fluid in between them while the punch backs off. This is depicted schematically in Fig. Double blank sheet hydroforming; redrawn from [ 38 ]. Micro manufacturing is a promising research area with a large amount of commercial potential due to an increasing demand in telecom, electronics and medical device sectors [ 43 ].
In hydroforming, there are many different research areas looking into both sheet and tube hydroforming applications. While the same principles apply, there are challenges which are inherent to micro manufacturing that are not present in similar macro sized applications.
In general, the main challenges to micro manufacturing are cost, accuracy, precision, and standardization. Anisotropy causes variation in material properties depending on orientation which is shown most frequently in the literature as mechanical property changes with regard to rolling direction. At the macro scale this can lead to typical values like a 5. Other technical concerns include: extreme tribological conditions caused by high surface to volume ratios, achieving tolerances [ ], inapplicability of available lubrication products, excessive forces on miniature dies, and handling concerns, [ ].
To address these manufacturing challenges, many streams of research are underway at various academic and private institutions. Some of the research areas are based upon new techniques or hardware, for example, Sato et al. Sato et al. Ngaile and Lowrie [ ] introduced a new hydroforming system with a floating die assembly to improve sealing by decoupling the sealing and material feed requirements and verified the invention on stainless steel tubes.
Nakamori et al. Furthermore, other researchers are performing work that addresses identifying the key process variables in different operations and how they interact with one another. A better understanding of the key process variables Manabe et al.
In SHF, Liang et al. In order for micro hydroforming to overcome the aforementioned challenges these advances need to continue in conjunction with other supporting manufacturing technologies.
Process parameters need to be further investigated with emphasis on the interactions between key process variables to ascertain a better understanding of the process and how to design for hydroforming operations. New tooling innovations are needed to provide sufficient force to seal while not harming the die [ ]. New lubrication methods need to be developed which work well and repeatably on the micro scale.
The development of supporting technologies could also be crucial in the development of micro hydroforming as they could ensure commercial viability of end products. For example, in T shaped THF operations with axial feeding there is generally an increase in wall thickness on the non-T side [ 91 ].
In macro hydroforming this is usually evenly distributed and not of any major concern, but with micro THF it is more of an issue because of the higher friction due to the close proximity of the fluid to the walls and the relatively large walls as compared to the diameter of the tube. This juxtaposition in wall thickness can be seen in Figs.
Micro machining could help ensure the micro tube is fit for purpose by removing the aforementioned protrusion and possibly skimming the walls to reduce friction, but only if the micro machining technology is compatible. Furthermore, punches used for axial feed often have a hole drilled in the middle for fluid to travel through to pressurize the tube during forming.
This can be an issue if the punch has a small diameter and a comparatively long length [ ]. Thickness of Y shaped automotive exhaust component Redrawn from [ 91 ], as seen in [ 6 ].
Warm, hot and isothermal forming and forging techniques have been used for millennia as a way to increase the formability by increasing the amount of strain a material can undergo before fracture by applying heat.
Even though the potential benefits are significant, it has not been widely incorporated into the hydroforming industry because of the technical challenges, the first of which is forming with warm metal adjacent to fluids, oils, and rubbers [ ] which generally are not able to withstand high temperature applications.
To solve this problem researchers have tried using, oils [ ], gasses [ ] or even steam [ ] can which have a higher operating temperature than water. Additionally, clever placement techniques can be utilized which heat parts of the blank which are not adjacent to the fluids like the flange area in SHF. This technique was found to be optimal by Acar et al. Thermal conductivity for warm operations must also be taken into account.
The thermal conductivity of tool steel is far higher than that of the fluids or rubber used, so it is likely that the blank will more closely align to the temperature of any tooling that it is touching instead of the fluid or rubber. This bears particular significance with punch and cavity hydroforming, as with punch hydroforming the blank will emulate the temperature of the punch, and with cavity hydroforming the temperature will be much closer to the fluid.
Other challenges have to deal with the handling of hot fluid or gas at high pressure, the preheating and handling of specimen at elevated temperature, chemical reactions at high temperatures, and cost constraints such as cycle times, which while higher than cold hydroforming, are still lower than superplastic forming [ 5 ]. Regardless of these difficulties the potential is so great that research on warm hydroforming is being carried out in many areas.
Texts have been written reviewing warm hydroforming challenges and potential such as Landgrebe et al. Gao et al. Aissa et al. Each fluid has different advantages in the hydroforming process.
Water based fluids are cheap but need anti-microbial agents added [ 6 ] and have a low working temperature before turning to steam. This means the forming operation either needs to be modest in heat application or cleverly designed to separate the fluid from hot surfaces as in Fig. Hot gasses must be specifically chosen to not interact chemically with surfaces but as the chemical inertness of a gas increases there is a corresponding price increase e.
In addition, the medium can have wear issues as ceramic beads break down after use. There are many different ways in which hydroforming research is progressing and a lengthy description of some of the more relevant technologies including schematics can be found in texts such as [ 1 ], [ , ] but to quickly summarize some of the main components the following table is presented.
This shows each technology followed by a newly developed hierarchy shown in Fig. Some of the various technologies such as warm hydroforming appear in multiple locations as they are applicable in multiple technological areas. All of the research areas presented below are being explored to either enhance the formability of a hydroforming process or reduce the costs of the process.
Each technology is briefly summarized in Table 1 alongside a schematic and brief description of each process. Technology readiness levels were developed by NASA as a way to of concisely describing and comparing how mature a technology is based on its ability to be deployed in a commercial application. Now this paper will revisit the main three categories of hydroforming which have been described at length in the literature and are defined in Fig.
To this original structure, all of the aforementioned technologies will be added. The resulting taxonomy will show where all of the technologies fit in one single diagram and point out which ones are currently used commercially as well as which are not yet commercially available due to either technological or economic rationale. Figure 46 contains all of the varieties of hydroforming described in the previous sections, but not the simpler hydroforming tricks such as edging as they do not qualify as independent technological branches.
This diagram represents a current snapshot of the possibilities in hydroforming technology. All of the technologies which are in development can also be ranked by their technology readiness level which allows for a roadmap towards future hydroforming capacity.
This gives a categorization of the relative maturity of the experimental hydroforming technologies discussed above as well as an indication of when they will be commercially viable.
This roadmap of hydroforming technologies defined in Table 1 can be seen in Fig. A few other novel technologies which are either periphery operations or hydroforming adaptions which deserved mentioned as well include the following.
Similarly others are developing other die materials such as Kleiner et al. Numerous hybrid processes are mentioned in the literature including Geiger et al. Werner et al.
Also described by Werner et al. Psyk et al. The pulsed magnetic fields which weld the blanks together are created at lower temperatures than traditional welds would be able to use thus reducing the influence high temperature welding has on the final material properties [ ]. Other sustaining developments which enhance the hydroforming process include: enhanced systems to prevent leakage [ ], better ways to utilize material feeding with moving dies and special axial feeding motion allowing for larger cross sectional expansion [ ].
Halkaci et al. Also Sato et al. Hydroforming has many advantages over competing manufacturing processes as well as a few disadvantages all of which will now be discussed and summarized in Table 2. The first of these is an increased formability which can be most clearly seen in the literature as an increased limit draw ratio from 2. From a manufacturing perspective, this means that more complicated geometries can be created during a hydroforming operations which reduces weld lines, material waste, factors of safety, weight, and rework required in an assembly due to formed parts being closer to the final desired shape.
Also the resulting mechanical properties can be stronger as can be observed by an increase in stiffness and the surface finish can be of higher quality because fluids will not scratch materials during forming. Singh et al. Tooling costs can also be lower than stamping operations as only one tool is required because the other is replaced with fluid pressure. The major disadvantage with the hydroforming process is the increased costs which express themselves in two distinct ways.
Typical cycle times are around 20 to 60 s instead of just a few seconds in a traditional cold forming operation [ 28 ]. This is because it takes more time to flood and increase fluid pressure inside a chamber than it does to mechanically press a set of dies together. The other disadvantages to a hydroforming process are that it is difficult to produce sharp radii without using pressure intensifiers and that the material loses ductility in the forming process.
Required pressure and the smallest radius on a part have an inversely proportional relationship. This means that a radius of 1 mm takes 4 times as much pressure to form as a radius of 4 mm so a pressure intensifier is often required to sharpen radii in a secondary operation.
Lastly, all forming processes work harden materials which has the effect of stiffening them and reducing their ductility, so if a certain amount of flexibility is required in a hydroformed component a heat treatment might be required post forming. A general set of advantages and disadvantages for all of the hydroforming processes is stated in Table 2.
To understand if a hydroforming process is viable to a specific application, the costs and design benefits of the entire manufacturing process including all periphery operations should be weighed against the costs and benefits of the likely alternative manufacturing processes. While this can vary greatly based upon application, the methodology proposed in the text counts the number and characterizes the complexity of the constituent manufacturing operations and uses this information along with the manufacturing cost to compare the potential manufacturing methods.
Enhanced mechanical properties are difficult to realize from a design perspective and come at the cost of decreased ductility. The degree of strain hardening achieved depends on the details of the specific part geometry and the deformation that will be required to create that geometry.
While strain hardening is achievable in a simple one stage process, complications arise with a multi-stage process. Strain hardening occurs in direct proportion to plastic deformation and just like residual stresses, is alleviated with heat treatments. Also strain hardening is not uniform throughout the component and is higher in the places where the most plastic deformation has occurred.
It is also important to note that locations with the greatest amounts of strain hardening are often the places where the material thinning is the highest, this is analogous to a uniaxial tensile test where most of the necking takes place next to the fracture.
With regard to how strain hardening affects the design stage of a component, this yields 3 main points:. Only the plastic deformation that occurs between the final annealing stage and the final part creation matters in terms of the mechanical properties of the final geometry.
A patchwork fabrication is a component that is an assembly of several smaller components all of which are cut, shaped, and welded together to make an assembly. The different hydroforming subcategories all fit into different places in the market based upon the limitations of the individual technologies and the alternate manufacturing methods available.
Tube hydroforming operations are suited for complicated cross-sectional geometries and internal shapes. Tube hydroforming produces high value parts, but unlike sheet hydroforming, it uses two dies. This means the tooling cost savings of sheet hydroforming that benefit low part count do not apply. In specific cases the tube hydroforming process is the only method which can form certain geometries in one piece due to the unique way in which fluid acts from the inside while new material is simultaneously fed in, so the future of hydroforming will undoubtedly utilize this advantage.
Sheet hydroforming operations are suited for high value or low part count operations where traditional stamping operations are ineffective and are especially valuable when high surface finishes are required. Because the two main alternative processes pressing and deep drawing are generally cheaper in large quantities [ 20 ], a clear advantage to hydroforming must present for viability at large volumes. Sheet hydroforming can become advantageous if complicated shapes or high surface quality are required, especially in cases where the removal of weld lines or lowering of part count can be achieved [ 7 ].
Lastly, shell hydroforming is applicable in low part count manufacturing as it is a labor intensive process. It must be used on geometries manufactured with a simple bulging operation and because dies are not used, the addition of any complicated geometries is not possible. The main advantage of shell hydroforming is that large geometries are possible and it consolidates a lot of smaller individual forming operations into one larger operation.
Equally, individually pressing large sheets may necessitate large presses and dies which can be avoided with the shell hydroforming technique. While all of these criteria in each subcategory do not necessarily need to be present to choose hydroforming, they greatly help the economic justification for using the technology. These market areas just discussed can be seen in Fig.
Looking at the history of hydroforming, its current uses, the market niches it currently fills, the current research areas and the trajectory of the current competing manufacturing processes, a projection of the future applications of hydroforming technology can be made.
This section will briefly go over what the current market niches are, how they will change in the future, and what future applications of tube, sheet, and shell hydroforming might look like. Although the excitement around hydroforming has worn off in the past decade as the additional costs, cycle times and limitations of the process have become better understood, high value manufacturing sectors will most likely continue to use sheet hydroforming technology in high value applications instead of conventional pressing technology.
This is because the additional formability allows for less thinning and more precise geometry creation, and the fluid pressure allows for higher quality surface conditions.
The development of technologies like warm hydroforming, impulsive hydroforming, and hydro-rim deep drawing will yield further formability in an operation. This will allow for hydroforming to create geometries with even more elaborate features and deeper draws and possibly manufacture parts currently made by superplastic or creep forming.
In cases of high value components, especially when great benefits can be realized with deeper draws and fewer weld lines, sheet hydroforming operations will provide a distinct advantage over other manufacturing processes and this can be seen with the recent interest in the hot gas hydroforming of automotive components [ 23 ].
In lower value components, parts that are manufactured with a sheet hydroforming operation need an economic justification because of the additional costs and cycle times imposed by the process. However, both conventional pressing and hydroforming are being automated to greater extents and cycle times for both are decreasing.
The good news from a hydroforming perspective is that there are likely greater opportunities for optimization in hydroforming operations as equipment has generally not been automated to the same extent and therefore there is more to be gained through process automation.
One manufacturer implemented automation techniques on their hydroforming presses by using sheet metal feeding from coiled sheets and this brought hydroforming cycle times down from 20 s to 8 s.
They also formed two components in one forming operation bringing the effective cycle time down to 4 s.
For comparison, several press manufacturers including AIDA [ ] and Schuler [ 98 ] are currently researching better automation methods for sheet metal pressing which use transfer presses that tightly use the same space. While automation makes both conventional and hydroforming processes more efficient, cycle times in hydroforming are longer and more prohibitive, so the impact of automation is more noticeable.
Tube hydroforming press sales have plateaued in the last decade and estimations of another major increase in hydroforming equipment sales [ 18 ] has yet to materialize. There are however many applications for tube hydroforming that look promising, specifically in the manufacture of high value and weight sensitive components.
For example Zhang et al. This has been suggested as a research area in other previous publications [ 10 ] and even patented as far back as [ ], but large scale commercial application has previously been elusive most likely due to problems with achieving industrial part quality for such a technically demanding application.
Now that process capability and simulation have increased demanding applications like rotating components are more likely to become viable. Furthermore, there are many possibilities for the utilization of hydroforming in the aerospace industry as parts are high value, relatively low volume when compared to the automotive industry and weight sensitive [ 7 ].
Specifically, in the manufacture of gas-turbine engine components, various complicated ductwork pieces such as bleed valve ducts, fairings and complex exhausts could potentially be made with a hydroforming process instead of patchwork fabrications. These examples can be seen in Fig. As the capability of hydroforming increases due to the ongoing research by many different groups worldwide as summarized in Table 1 hydroforming will be considered as a manufacturing process for an increasing number of components.
The taxonomy developed in Fig. This allows equipment to be properly sourced where available and identified where still in development. In this way the taxonomy enables hydroforming technology by identifying key current hydroforming technologies which are ready for manufacturing and along with Fig.
These new technologies will enable the manufacture of increasingly complicated components like the ones highlighted in Fig. This paper summarizes and discusses the past, present, and likely future of hydroforming through the use of academic papers, conference proceedings, books, patents, manufacturer websites, and communication with industrial experts.
The first aim of this paper was to provide a comprehensive overview of the state of the art in all forms of hydroforming which was covered in sections 4 and 5 with descriptions of the materials and novel hydroforming techniques. The second aim was to identify emerging hydroforming technologies which was reported in section 6 with a discussion of the recent research and technological developments of hydroforming.
The taxonomy shown in Fig. And finally, the 5th aim was characterizing the position of hydroforming with regard to manufacturing and state the likely future.
Rapid Design and Simulation of Tube Hydroforming. Springback Compensation in Tube Hydroforming. Digital Solutions for Industry 4. News Archive. Home Topics Technologies Tube Hydroforming. Industry 4. By using our site, you agree to our collection of information through the use of cookies.
To learn more, view our Privacy Policy. To browse Academia. Log in with Facebook Log in with Google. Remember me on this computer. Enter the email address you signed up with and we'll email you a reset link. Need an account? Click here to sign up. Download Free PDF. Manufacturing Tubes For Hydroforming Applications. Nhan Le. A short summary of this paper. Download Download PDF. Translate PDF. The metal processing industry is working in this way in research and development for alternative materials and production processes.
Hydroforming provides several advantages versus traditional To compound this benefit, steel is the most recyclable material in the stamped and welded structures, including: world. Hydroforming technology has therefore been called to offer an interesting technical and economic potential. Current applications include suspension frame, body structure, When used with high strength steels hydroforming is able to produce power-train components and exhaust pipes.
The major advantages structurally superior parts with thinner sections at a reduced mass. In the ULSAB Project Tubular hydroforming and its cold working effect produces high dimensional stability and increases effective yield strength in any component.
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