ADVANCES IN HYDROFORMING 1
TABLE OF CONTENTS
1. INTRODUCTION...... 3
2. HYDROFORMING...... 4
3. CLASSIFICATION OF HYDOFORMING TECHNIQUES...... 5
4. BENEFITS OF HYDRO FORMING...... 7 4.1 Better degree of deformation of the formed part...... 7 4.2 Good Surface Finish...... 8 4.3 Use of Various Engineering Materials...... 8 4.4 Savings in tooling costs up to 80%...... 8 4.5 Reduction in weight...... 9 4.6 Nearly unlimited wall Thickness variations...... 10
5. FORMING LIMIT DIAGRAM...... 12
6.HYDROFORMING PROCESS CONTROL...... 13
7. APPLICATIONS...... 15
8. ADVANCES IN HYDROFORMING...... 16 8.1 Variform process or Pressure Sequencing...... 17 8.2 Hammering...... 20 8.3 Pre-pressurizing...... 25 8.4 Manufacturing of Clad pipes...... 28
9. CONCLUSION...... 30
10.REFRENCES...... 32
1 ADVANCES IN HYDROFORMING 2
LIST OF FIGURES
Fig.1 Hydro formed handle bar …………………………………………..4 Fig.2 Hydro formed T-junction …….………………………...... …..….4
Fig.3 Sheet hydro forming ………………………………………………5
Fig.4 Tube hydro forming ……………………………………...... …..6
Fig.5 Stresses in Hydoformed component ……………………………..7
Fig.6 Benefits of Hydroforming …………………………………...…..11
Fig.7 Forming Limit Diagram ………………………………………....12
Fig.8 Schematic Diagram of Tube Hydro forming & Process Control 14
Fig.9 Applications of Hydroforming ………………………………….15
Fig.10 Part made using Variform Process …………………………….19
Fig.11 Setup for Hammering ……………………………………….….21
Fig.12 Hammering Cycle ……………………………………….………22
Fig.13 Part made by Hammering ……………………………………....24
Fig.14 Conventional Method of Hydroforming …………………...….26
Fig.15 Pre-Pressurizing Method of Hydroforming …………………....27
2 ADVANCES IN HYDROFORMING 3
1. INTRODUCTION
Hydro forming is a high-pressure deformation process that shapes metal sheets or tubes into a predefined geometry by using a fluid under high pressure. Hydro forming is similar to the conventional deep- drawing technique with a counter-mould. The specific difference from the conventional method is that a fluid is used instead of a die to forming into final shape. This deformation process requires application of fluid pressures up to 4000 bars depending on the size of the component. As the automobile industry strives to make car lighter, stronger and more fuel efficient, it will continue to drive hydro forming applications. Some automobile parts such as structural chassis, instrument panel beam, engine cradles and radiator closures are becoming standard hydro formed parts. Recently hydro forming was used for manufacturing of clad pipe used in oil and chemical industry. The capability of hydro forming can be more fully used to create complicated parts. Using a single hydro formed item to replace several individual parts eliminate welding, holes, punching etc... Hydro forming simplifies assembly and reduce inventory. The process is quite simple - a blank with a closed-form, such as a cylinder, is internally pressurized using fluid. The fluid is frequently water. The applied pressure is usually in the range 80-450 MPa. Its resultant plastic expansion is confined in a die of the desired shape.
3 ADVANCES IN HYDROFORMING 4
2. HYDROFORMING
Hydroforming is a cost-effective way of shaping malleable metals such as aluminum or brass into structurally stiff and strong pieces. One of the largest applications of hydro forming is the automotive industry, which makes use of the complex shapes possible by hydro forming to produce stronger, lighter, and more rigid body structures for vehicles. This technique is particularly popular with the high-end sports car industry and is also frequently employed in the shaping of aluminum tubes for bicycle frames.
Hydro forming allows complex shapes with concavities to be formed, which would be difficult standard solid die stamping. Hydro formed parts can often be made with a higher stiffness to weight ratio and at a lower per unit cost.
This process is based on the 1950s patent for hydra molding by Fred Leuthesser. It was originally used in producing kitchen spouts. This was done because in addition to the strengthening of the metal, hydramolding also produced less "grainy" parts, allowing for easier metal finishing.
Fig 1 Hydro formed handle bar Fig 2 Hydro formed T-junction
4 ADVANCES IN HYDROFORMING 5
3. CLASSIFICATION OF HYDOFORMING TECHNIQUES
Hydroforming is broadly classified into sheet and tube hydroforming. Sheet hydroforming is further classified into sheet hydroforming with a punch (SHF-P) and sheet hydroforming with a die (SHF-D), depending on whether a male (punch) or a female (die) tool will be used to form the part. SHF-D is further classified into hydroforming of single blanks and double blanks, depending on the number of blanks being used in the
5 ADVANCES IN HYDROFORMING 6 forming process
Fig.3 Sheet hydro forming (Source: [6])
6 ADVANCES IN HYDROFORMING 7 In tube hydroforming tube is loaded into hydoroforming dies and the press closes. The sealing rod engages the part sealing the ends and fills the tube with water. Pressure inside the tube increases, now the sealing rod is pushes the tube into the die and the internal pressure is ramped to maximum value. The hydroformed tube takes the shape of the mould. Final part is removed from the mould.
Fig.4 Tube hydro forming (Source: [6])
7 ADVANCES IN HYDROFORMING 8 4. BENEFITS OF HYDRO FORMING
4.1 Better degree of deformation of the formed part
By applying a uniform force to the metal sheet, the fluid shapes it into the form of the tool. In this process, a uniform distribution of sheet thicknesses is achieved, which allows for maximum degrees of deformation. Abrupt changes in stress are avoided – a factor that ensures high dimensional accuracy and reduces the tendency of the material to return to its original size and shape when the applied load is removed. Conventional deep-drawing Hydroformed with the FB25
strong local thinning of the less internal stress and less tendency material to return to its original shape inhomogeneous distribution of homogeneous strength and less material thicknesses amount of waste less internal stress of the formed high dimensional accuracy part
Fig.5 Stresses in Hydoformed component
8 ADVANCES IN HYDROFORMING 9 4.2 Good Surface Finish Since the metal sheet is deformed using a pressurized fluid instead of a conventional deep-drawing die, the surface is not in direct contact with any tool that may lead to surface damage. In the hydroforming process, the metal sheet only comes into contact with the tool when the maximum required forming pressure is reached. This results in excellent surface finish of the formed parts.
4.3 Use of Various Engineering Materials The hydroforming process allows you to use the complete spectrum of all ductile and malleable materials. No matter if you are using steel sheets, stainless steel, special alloys, aluminum, copper, brass or titan: for all of them, optimum degrees of deformation can be achieved. Metal sheet thicknesses range from 0.05 to 6 mm. Specifically for very thin metal sheets, the possibilities of hydroforming are far superior to those of conventional forming techniques
4.4 Savings in tooling costs up to 80% Low tooling costs are a great advantage of the hydroforming process using the Form Balancer. Tooling costs are reduced to 50% by the fact alone that only the negative molding tool is needed. Further savings are generated by no longer needing hold-down devices and guide way systems. Due to the possibilities of forming complex geometries with only one tool, upstream machining operations can often be omitted, which in most cases reduces tooling costs to only 20% compared to those of conventional deep- drawing tools.
9 ADVANCES IN HYDROFORMING 10 4.5 Reduction in weight Automakers continuously strive to reduce motor vehicle mass, mainly for efficiency and environmental reasons such as improving fuel efficiency and reducing emissions. However, as they reduce vehicle weight, they must try to avoid compromising other important criteria, such as strength and energy management. They look for technologies, techniques, and processes that satisfy these various needs, to which hydroforming is the answer. Also the process and functional characteristics need to be maintained. If a design engineer changes a part, he has to think about how will the manufacturing engineers make the new part? How will the line workers join the various parts to make assemblies? When finished, will everything work as intended? Answers to all this questions in Hydroforming.
Hydoformed versus Stamped Components 10 ADVANCES IN HYDROFORMING 11 Much of a vehicle's weight is in the structural frame, and most frames are made from steel. The exception is aluminum,which is used in some automobiles.
Mass Weld LengthPerformance Fore/Aft Concept (kg) (mm) Loading Red scale set to 1.0 x Stamped 23.0 4,915 material strength Red scale set to 1.0 x Hydroformed 20.9 3,975 material strength Change -2.1 -940 Compared to a traditional stamped automotive part, a similar tubular component has less mass and requires less welding. In this case, the reductions were more than 9 percent mass and 19 percent in weld length.
4.6 Nearly unlimited wall Thickness variations
11 ADVANCES IN HYDROFORMING 12 The wall thickness can be adjusted anywhere along the part between some predetermined minimum and maximum thickness, allowing a nearly infinite combination of thickness zones. This level of design freedom enables design engineers to fine-tune the part to achieve a desired load response. Variable-wall technology is not limited to round cross sections— it can be used to manufacture most symmetric shapes without any postforming operations. Heat treatment adds even more versatility to these structures, imparting properties that range from those of strip to fully cold- worked steel. Finally, it can be beneficial in many nonautomotive applications as well.
Fig.6 Benefits of Hydroforming
5. FORMING LIMIT DIAGRAM 12 ADVANCES IN HYDROFORMING 13
During hydro forming process failure occurs due to thinning, this is due to the excessive deformation in a given region. A quick and economical analysis of deformation in a forged part is analyzed from forming limit diagram. The sheet is deformed, converting circles in to ellipse, and the distorted pattern is then measured and evaluated. Regions where the area has expanded are locations of sheet thinning Regions where area has contracted have undergone sheet thickening. Using the ellipse on the deformed grid, the major (Strains in the direction of larger radius) and associated minor strains (Strains perpendicular to the major) can be determined for variety of locations and values can be plotted on the forming limit diagram. If both major and minor strains are positive deformation is known as stretching, and thinning will possible.
Fig.7 Forming Limit Diagram
13 ADVANCES IN HYDROFORMING 14 6. HYDROFORMING PROCESS CONTROL
A typical hydro forming system would include a press capable of developing necessary forces to clamp the die valves together when internal pressure acts on fluid; a high pressure water system to intensify water pressure for forming component, looking including aerial cylinder and punches, depending on component and a control system for process monitoring. Since the entire process of operation takes place inside a closed die, one cannot see what actually happens during forming. Therefore the controller plays a vital role in displaying, monitoring and controlling the different parameters.
14 ADVANCES IN HYDROFORMING 15
Fig.8 Schematic Diagram of Tube Hydro forming and Process Control
15 ADVANCES IN HYDROFORMING 16 7. APPLICATIONS
Almost any industry can benefit from the advantages of the hydroforming process. Again and again companies are faced with the challenge of simultaneously achieving both lower operating costs and innovative solutions for evolutionary advances of their products. Our high- pressure forming technology offers attractive possibilities in terms of price- performance ratio and manufacturing time. Hydroforming finds its application in following industries:
Automotive industry Aerospace industry Medicine technology Electronic appliances Heating & air conditioning Agriculture industry
(a) (b) (c)
Fig.9 Applications of Hydroforming
16 ADVANCES IN HYDROFORMING 17 8. ADVANCES IN HYDROFORMING
In recent years hydroforming has become a commonly used method of tube expansion for many applications, such as automotive chassis frames, exhaust manifold piping connectors, and air-conditioning system components. Because hydroforming uses water under high pressure to expand the tube or pipe from the inside, and water can take any shape, it’s a versatile process and is suitable for forming complex, single-piece components.
During the last decade, industry has seen dawn of hydroforming as an alternative for stamping and various forming the reason for this are its advantages and the unprecedented research work done in improving the techniques of hydroforming. Some of the new techniques are:
Variform process or Pressure sequencing
Hammering
Pre-Pressurizing
Manufacturing of Clad Pipes
17 ADVANCES IN HYDROFORMING 18 8.1 Variform process or Pressure Sequencing
Pressure Sequence Hydroforming (PSH) is a patented tube hydroforming process that utilizes low internal fluid pressure to support the tube while the die closes. Once closed the majority of the part profile has been formed. At this point the internal pressure is increased to lock in the form and provide backup for punching holes. Hole size can range from as small as 2 times material thickness to as large as 50 mm X 200 mm. Holes can be extruded or clean pierced, and practically any shape including round, slot, square, hexagon, or rectangular. The resulting material slug is typically pushed back out of the way and left attached inside the tube, though there are techniques available to remove them when required. Pressure Sequence Hydroforming (PSH) is compatible with most metals, if it can be made into a tube PSH can form it. The process that normally establishes the required material elongation is the prebending operation. PSH has proven process compatibility with High Strength steel up to 960 MPa UTS, Dual Phase, and TRIP steels. In addition to carbon steel the PSH process has been used to form both 5000 and 6000 series aluminum, and numerous grades of stainless steel.
18 ADVANCES IN HYDROFORMING 19 Pressure Sequence Hydroforming (PSH) reshapes the tube cross section into the required profile without stretching the material. The tube material thickness distribution found after hydroforming is the same as that present in the bent tube. Pressure Sequence Hydroforming (PSH) reshapes the tube while the die closes. Once the die is completely closed the tube has been forced to take the shape of the die cavity without requiring the material to expand. High Pressure Hydroforming first closes the die on an undersized tube and then utilizes high internal fluid pressure to expand the tube to fill the die cavity. The part to part or floor to floor cycle time for Pressure Sequence Hydroforming is in the range of 17 seconds for a small part such as an Instrument Panel Beam to 24 seconds for a large part such as a roof rail or structural member. The Pressure Sequence Hydroform (PSH) process uses a completely different mechanism than HPH to form the corners. In the PSH process, the tool stops before it is completely closed on the tube, this is referred to as the prefill height. The tool dwells at this point as the tube is then filled with fluid and lightly pressurized. The die is then fully closed while the tube is supported by the prepressure. Using this support PSH forms the cross section corners while the die is closing under prepressure. Pressure Sequence Hydroforming is a dimensionally stable and robust process. Product features that are produced in the hydroform tool are typically very stable as the entire part profile and all piercing is completed in a single cavity.
19 ADVANCES IN HYDROFORMING 20 Sequencing the pressure prevents pinching the material in the die. As part complexity continues to increase, in order to minimize part, containing the tubular blank inside the die cavity becomes more difficult. An improperly contained blank can easily become pinched between the die halves, leading to an improper fill and perhaps rupture. It also eliminates the need for posthydroforming processes such as annealing and washing. Using the PSH process, tube corner radii are formed in the bending mode beyond the yield limit of the base material, rather than in the tensile mode reached during conventional high-pressure hydroforming.
Fig.10 Part made using Variform Process
20 ADVANCES IN HYDROFORMING 21 8.2 Hammering
Hammering uses two alternating pressures. It reduces the drag force, which is the friction that develops between the work piece and the die. As the internal pressure increases, the work expansion force increases the drag force, or friction, between the work piece and the die. Also, the internal pressure becomes a force that pushes back against the hydraulic system. The combination of work expansion force and internal pressure is the reaction force.
As the reaction force increases, it becomes difficult to force the material to flow into all of the contours and recesses of the die. The hammering method cycles between a high and low pressure. The repeated pressure drops reduce the drag force, allowing the material to flow further in the die. It also prevents thinning at the expansion areas and improves the process capability.
The hammering process is driven by a pump that varies the pressure it develops, such as a direct drive volume (DDV) control pump, a high- pressure generator that uses a hydraulic servo pump. The DDV is a hybrid of an AC servomotor and reversible-piston pump. The pulsations are generated by controlling the forward and reverse rotation of the AC servomotor at high speed.
21 ADVANCES IN HYDROFORMING 22 The time from start-up time to shutdown time (including hold time) is one cycle. The frequency is the number of cycles that elapse in one second and is measured in hertz (Hz). Results from hydroforming trials have shown that the optimal hammering frequency range is between 1 and 3 Hz. Frequencies higher than 3 Hz make it physically impossible for the pressure to reach the intended high and low points. In other words, reversing the pressure more than 3 times per second doesn’t give the hydraulic system enough time to achieve the programmed pressures. The optimal pressure range is between 725 and 4,350 pounds per square inch (PSI), or 5 to 30 MPa.
Fig.11 Setup for Hammering (Source: [7])
22 ADVANCES IN HYDROFORMING 23 Above figure shows the actual setup used for Hammering. The complete system uses three DDV pumps. One generates the pulsating pressure that forms the tube; the others are multipurpose pumps used to raise and lower the press’s upper die at high speed. When the upper die is completely closed, the DDV seals and presses in both ends of the tube work piece. The DDV’s AC servomotor is regulated by a CNC. This controls the hammering frequency and pressure increase rate.
The pulse frequency and pressure on the secondary side is controlled by the reversible AC servomotor of the DDV pump and pulsing the primary side of the oil and water boosting cylinder at a ratio of 1-to-10. The shape that can be formed in one cycle of tube expansion is determined by the maximum water capacity in the high-pressure cylinder.
Fig.12 Hammering Cycle
23 ADVANCES IN HYDROFORMING 24 The Hammering method cycles between a high and low pressure, so Hammering has more variables than in conventional hydroforming. Instead of one pressure, hammering uses two alternating pressures. Also, in this case, the last two cycles as can be seen in above figure have a brief hold time of 0.2 second at the points of minimum and maximum pressure. Hammering allows the user to vary the difference between the high and low pressure (10MPa in this case), the cycle time and also the hold time.
The two main problems faced while forming are rupturing and buckling. Rupturing is usually the result of setting the internal pressure too high or the expansion force too low. This causes the material to stretch and become too thin in the expansion area, ultimately causing a rupture. This is why it is critical to balance the internal pressure and initial expansion force. Using an initial pressure that is too high also can cause the pipe to expand too quickly, causing the material at the axis sealing area to pull away. This, in turn, causes the fluid to leak, so the pressure does not rise to the set value and the processing can’t start.
Buckling usually is caused by setting the internal pressure too low or the expansion force too high. Using a processing time that is too fast also may contribute to buckling.
Hammering eliminates these problems as it uses two alternating pressures which balances initial pressure & expansion force. As we can see the part made by conventional hydroforming process shown in the diagram below is ruptured, whereas the part at the bottom made by Hammering did not get ruptured.
24 ADVANCES IN HYDROFORMING 25
Fig.13 Part made by Hammering
8.3 Pre-pressurizing 25 ADVANCES IN HYDROFORMING 26 In pre-pressurizing method a metal tube is placed in lower mold with the ends sticking out from it and injects a pressurizing fluid into the metal tube through the inside of a seal punch and gradually presses the seal punches against the tube ends, in the state with internal pressure and pressing force applied the upper mold is lowered so as to deform the tube and end the processing with the tube ends sticking out from the mold and further boosting the internal pressure in metal tube after closing the mold and ending the forming operation and a hydroformed product having a flange across the entire length in longitudinal section is formed.
As shown in Fig.14 the conventional hydroforming method relates to placing a metal tube shorter in length than the mold in a mold so that the tube ends of the metal tube are positioned inside the end faces of mold, then upper mold is lowered to close the mold and clamp the tube between upper and lower molds. After that seal punches advance and water is inserted as a pressurizing fluid from one of the seals, the pressure inside the tube is raised to obtain predetermined shape.
In this new technique of pre-pressurization a metal tube is placed in the lower mold with its tube ends sticking out of the mold, injecting pressurized fluid into the metal tube through an inside of a seal punch while pressing seal punches against the tube ends, filling the inside of metal tube with a pressurized fluid to apply internal pressure, then the upper mold is lowered so as to close the mold, deforming the tube to the predetermined shape with the tube ends sticking out of the mold. The process is shown in Fig.15.
26 ADVANCES IN HYDROFORMING 27
Fig.14 Conventional Method of Hydroforming
27 ADVANCES IN HYDROFORMING 28
Fig.15 Pre-Pressurizing Method of Hydroforming (Source: [3]) 28 ADVANCES IN HYDROFORMING 29
8.4 Manufacturing of Clad pipes
The energy sector is hot right now, and so is pipe production. Pipe for transporting crude oil and crude gas must meet several criteria. The material must have sufficient durability, corrosion resistance, and strength, and the size must be large enough to transport the desired volume. Corrosion resistance is necessary to prevent erosion damage from pollutants in the oil or gas, which include hydrogen sulfide, chlorides, and water. Finding the optimum material for making pipe for this industry is tricky. Low-alloy carbon steels tend to be strong, but lack corrosion resistance. Stainless steels resist corrosion but lack strength. Cladding low-alloy carbon steel with a thin layer of a corrosion-resistant alloy is a suitable process.
An alternative is to produce clad pipe that makes the best use of corrosion-resistant alloys and low-alloy steels. Such pipe typically is made from strong, low-alloy carbon steel and lined with a sleeve made from a corrosion-resistant material approximately 0.19 inch thick. The simplest mechanically clad pipe consists of a corrosion-resistant liner inserted into a low-alloy external carbon steel pipe. A more sophisticated mechanically clad pipe is produced by shrinking the external pipe or rolling one pipe inside the other. The nature of the mechanical bond depends on the process. Regardless of the method, the bond is purely mechanical. The two distinct materials remain two distinct materials they do not fuse together to become a single mass as metallurgically bonded pipes do.
29 ADVANCES IN HYDROFORMING 30 A process was devised which used hydraulic pressure on the inner pipe and induction heating on the outer pipe. The hydraulic pressure caused the inner pipe to expand; removing the heat caused the outer pipe to shrink as it cooled.
A modern improvement to this process uses a hydraulic pipe calibration and lining machine equipped with an additional water system as well as sophisticated controls. It uses a process similar to automotive parts hydroforming machines to attain a high degree of compressive contact between the two pipes. The corrosion-resistant pipe is inserted into the outer low-alloy carbon steel pipe in a semi automated operation and is then placed into the calibration machine's open tool form. The tool closes and axial cylinders seal each of the pipe ends. Hydraulic fluid under high pressure expands the inner tube. A firm compressive contact is achieved by the elastic and plastic behaviors of the outer pipe and the inner pipe. The elastic spring back of the outer pipe is greater than the plastic expansion of the inner pipe; the resulting residual pressure stress of the inner pipe is in the region of 7,250 to 14,500 pounds per square inch (PSI).
This provides a homogenous contact along the pipe's entire length.
One of the chief advantages of using a hydroforming process to manufacture mechanically clad pipe is simple economics. Compared to producing a non-clad or a metallurgically clad pipe, manufacturing clad pipe with this method represents a significant cost reduction. Potential cost reduction is in welding, because clad pipe has thinner walls than homogenous pipe, and so requires less welding time. In this scenario, the clad pipes are 0.39 in. thick, whereas the homogenous pipe is 0.59 in. thick, a 13 percent difference.
30 ADVANCES IN HYDROFORMING 31
9. CONCLUSION
In this seminar report recent developments in hydroforming are discussed systematically. After discussing these we conclude that:
1. Hydroforming has wide application in many industries like automobile, aerospace, electronic goods, sanitary fittings, etc. Many benefits offered – Good surface finish, Use of almost all ductile and malleable material, Better deformation, High dimensional accuracy, Savings up to 80% in post forming processes (Refer page 8). Because of so many benefits offered Hydroforming is considered as an effective method to meet the demands of ever evolving manufacturing sector.
2. Due to introduction of hydroforming it is now possible to use light weight aluminum structural frame instead of the conventional heavy weight steel frame in automobiles. Resulting in reduction of weight by more than 9 percent and weld length by 19% (Refer page 10).
31 ADVANCES IN HYDROFORMING 32
3. Hydroforming facilitates manufacturing of a single large complex component instead of many small components, reducing the tooling costs by 50%. For example: operations like piercing can be done during hydroforming itself. There is no need of finishing the surface after hydroforming as hydrofomred component has a high grade of surface finish.
4. Of the above discussed recent techniques Pressure sequencing and Hammering are the most useful methods. Using these methods we can hydroform any malleable metal ranging from copper to high grade stainless steel. By reducing the drag force Hammering eliminates the two major problems faced in forming namely rupturing and buckling.
Thus adopting these new techniques there is better utilization of material. The day will not be far away when hydroforming will completely replace the conventional stamping and forming processes.
32 ADVANCES IN HYDROFORMING 33
10. REFERENCES
1) Research paper: “Developments in Hydroforming” – S.H.Zang 2) U.S. Patent 2,713,314 3) U.S. Patent 2010-0186473 4) Book: “Hydroforming for advanced manufacturing”, By M, Koç, 2009 Woodhead Publishing Limited. 5) Book: “Hydroforming technology: Advanced Materials & Processes” (Refereed): May, 1997: ASM International. 6) Book: “Fundamentals of Hydroforming” by Harjinder Singh. 7) http://www.thefabricator.com/techcell/hydroforming 8) http://www.americanhydroformers.com 9) http://www.sciencedirect.com
33