52733149 Hydro Forming Final 14

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ADVANCES IN HYDROFORMING

TABLE OF CONTENTS

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

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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

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.

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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.

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.

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Fig 1 Hydro formed handle bar Fig 2 Hydro formed T-junction

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

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forming process

Fig.3 Sheet hydro forming (Source: [6])

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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])

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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

material

inhomogeneous distribution of

material thicknesses

less internal stress of the formed

part

less internal stress and less tendency

to return to its original shape

homogeneous strength and less

amount of waste

high dimensional accuracy

Fig.5 Stresses in Hydoformed component

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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.

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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

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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.

ConceptMass

(kg)

Weld Length

(mm)

Performance Fore/Aft

Loading

Stamped 23.0 4,915Red scale set to 1.0 x

material strength

Hydroformed 20.9 3,975Red scale set to 1.0 x

material strengthChange -2.1 -940Compared 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

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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

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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

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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.

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Fig.8 Schematic Diagram of Tube Hydro forming and Process Control

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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

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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

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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.

Pressure Sequence Hydroforming (PSH) reshapes the tube cross

section into the required profile without stretching the material. The tube

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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.

Sequencing the pressure prevents pinching the material in the die. As

part complexity continues to increase, in order to minimize part, containing

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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

8.2 Hammering

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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.

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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])

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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

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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.

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Fig.13 Part made by Hammering

8.3 Pre-pressurizing

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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.

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Fig.14 Conventional Method of Hydroforming

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Fig.15 Pre-Pressurizing Method of Hydroforming (Source: [3])

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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.

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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.

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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).

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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.

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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

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http://www.sciencedirect.com/

http://www.americanhydroformers.com/

http://www.thefabricator.com/techcell/hydroforming

http://www.google.com/patents?vid=2713314

http://www.google.com/patents?vid=2713314

Documents

52733149 Hydro Forming Final 14