Hydroforming Sheet Metal: The Complete Guide
Hydroforming sheet metal is a versatile fabrication process. In this guide, you will find all information about the hydroforming process. From techniques, features, and applications – this guide will make you an expert in hydroforming sheet metal.
What Is Sheet Meal Hydroforming?
Hydroforming is a metal forming method that involves exerting high pressure on a metal sheet to alter its shape. Typically, a pressurized fluid force of about 10,000psi is exerted on the metal, creating structurally complex and strong metal sheets. Notably, hydroforming is an alternative to the conventional draw forming processes that require tooling blocks, i.e., die or punch.
Advantages Of Hydroforming Sheet Metal
Cost-effective – Hydroforming is considered fairly affordable.
Usable – Hydroforming allows for the easy formation of irregular contours and shapes. You do not need matching dies to form such complex machines with a hydroforming machine.
Condensation of operations – The hydroforming process condenses the many metal forming operations into one operation.
No thinning prerequisite – Hydroforming does not necessarily require the initial thinning of the metal sheet before it is shaped.
Durability of metal sheets – Metal sheets manufactured through hydroforming are durable since they are manufactured from high-strength metal alloys.
Minimal setup time – You can easily mount the hydroforming tools. What’s more, these tools are self-aligning and self-cantering.
Fluid Cell Forming Sheet Metal
Fluid cell forming uses either a bag press or a fluid-cell press to form metal sheets having complex shapes. Fluid cell forming is widely used in the aerospace industry.
Fluid cell forming occurs in two major steps:
- First, the bag press or fluid-cell press exerts high pressure of up to 1600 psi onto a flexible rubber diaphragm.
- Consequently, the pressure exerted on the diaphragm shapes the metal sheet into the desired shape.
The major advantages of fluid cell forming includes faster prototyping, lower tooling cost, great design flexibility and production of thinner but stronger metal sheets.
Sheet Metal Materials For Hydroforming
Hydroforming aluminum sheet metal – Aluminum and its alloys are used in hydroforming in manufacturing parts such as oil filter pans, gyroscope cases, and lens retainers.
Hydroforming nickel alloy sheet metal – Hydroformed nickel alloy parts include components in the aerospace industry, such as nose cones and nozzle systems.
Hydroforming stainless steel sheet metal – Stainless steel is used in hydroforming parts of jet engines
Hydroforming titanium sheet metal – Titanium is an ideal material when hydroforming parts such as potable water tanks.
Sheet Metal Hydroforming Tolerances
According to the American Society of Mechanical Engineers, tolerance is the total amount that a design’s dimension can vary. Dimensions tolerance are written using the symbol ±, which precedes the actual range, for example, ± 0.5. A high range implies the sheet metal has a loose tolerance and vice versa.
Hydroforming is a preferred metal forming method since it can produce metal sheet parts with a high tolerance of about 0.76mm – which is the standard aircraft tolerance. The tolerance may vary due to the below factors such as age of the material, impurities in the material and heat-related changes.
Micro Hydromechanical Deep Drawing Sheet Metal
Micro hydromechanical deep drawing (MHDD) is a sheet micro forming process that uses hydraulic force. MHDD involves the application of a counter pressure which enhances fluid flow and enables uniform deformation by controlling the thinning and thickening behavior.
One major application of MHDD is in forming long and complex-shaped micro-products that require high shape accuracy.
MHDD occurs in four major stages:
- Generation of counter pressure – This occurs when the die cavity is sealed following the downward movement of the upper die parts.
- Blanking stage – Occurs when the upper die moves further down while the blank holder remains fixed.
- Drawing – A constant gap between the drawing die and the blank holder is maintained as the drawing punch moves downwards.
- Knock-out stage – As the stroke reaches the bottom dead point, the upper die moves back up, and the drawn cup is removed.
Sheet Metal Hydroforming Process
The sheet metal hydroforming process has universal procedures which might be slightly altered depending on the shape of the metal being formed.
Before delving into the die-forming process, we need to understand the various parts of the hydroforming equipment. The primary parts are:
- The female or upper die element – This part comprises the hydroforming press comprising a rubber diaphragm, a chamber of oil, and a wear pad.
- The male or the lower die element – Consists of a punch (attached to a hydraulic piston) and a ring (or blank holder) that surrounds the punch.
- Forming Chamber – Where the actual formation of the metal part occurs.
The standard steps for the sheet metal hydroforming process include:
- Fixation of a metal blank to the placeholder ring.
- Next, the forming chamber is pressurized with oil as the upper part of the press is lowered.
- The male die element (in this case, the hydraulic die punch) is raised.
- Consequently, a metal bank is formed around the rising punch. The metal blank will assume the shape of the punch.
- On completion of the hydroforming cycle, pressure is released, and the punch is retracted, leaving the finished part.
Note: In hydroforming, the rubber diaphragm supports the entire blank during the formation process. Hence the end product will have no scratches, unlike in traditional stamping.
Deep Draw Hydroforming Sheet Metal
Deep draw hydroforming involves stretching and bending a metal sheet into the desired shape. The main components in the deep draw hydroforming process include:
- A die – Has a cavity of the desired shape.
- A blank holder
- A blank or metal sheet
- A punch
The deep draw hydroforming process is as below:
- First, the metal sheet or blank is placed in the blank holder above the die.
- Next, the punch tool moves downwards onto the metal sheet.
- The punch tool stretches the sheet into the cavity resulting in the desired shape.
Note: The stretching action does not reduce the strength of the metal sheet.
Tube Hydroforming Vs. Hydroforming Sheet Metal
The main difference is in the raw/ primary material used. As the names suggest, tube hydroforming uses metal tubes as its primary material while the latter uses metal sheets.
Below we have discussed these two types of hydroforming to bring out the difference.
As earlier mentioned, this method uses metal tubes as the primary material for manufacturing its end products.
The end products are usually tubular parts commonly used in the automotive industry.
With tube hydroforming, it is possible to create pipes and tubing of various shapes, lengths, and weights.
This method involves the inward application of pressure to the metal tube, pushing the metal outward into the die surrounding.
Hydroforming Sheet Metal
Unlike tube hydroforming, the primary material is a metal sheet, otherwise called a blank. Pressure is applied onto the blank, forcing it to assume the shape of the die beneath.
Sheet hydroforming is used in many industries, including healthcare, aerospace, commercial lighting, and defense.
The above industries require parts with complex shapes easily produced through sheet hydroforming. Moreover, sheet hydroforming provides exact surfaces and shapes as stipulated by these industries.
Sheet Metal Stamping Vs. Hydroforming Sheet Metal
Sheet metal stamping was once the conventional metal forming process. However, hydroforming has gained popularity and is considered the future of metal forming.
We will compare the two metal forming processes as per the below subheadings:
Quality Of Final Product
Hydroforming results in the formation of high-quality metal products with impressive structural strength.
Due to stretching, sheet metal stamping will reduce the desired tolerance for the final product.
Hydroforming allows for easy alteration of the designs, unlike sheet metal stamping, which is rigid to some extent.
Cost Of Tooling
Sheet metal stamp tooling is costly and repetitive, depending on the quality of the tooling.
On the other hand, hydroforming tooling has a one-off purchase and installation cost.
Economies Of Scale
Hydroforming defies economies of scale while sheet metal stamping upholds the economies of scale.
Therefore, it implies that hydroforming remains economically feasible in both small and large-scale production. The same does not apply to stamping.
Sheet metal stamping has a longer lead time, extending to several weeks.
Conversely, hydroforming has a shorter lead time regardless of the production level.
Hydroforming reduces material wastage by up to 70 percent. Consequently, it is characterized by minimal metal wastage.
Stamping has a high scrap metal production rate, implying increased metal wastage.
Hydroforming has minimal need for secondary finishing since it creates blemish-free and shiny parts.
However, secondary finishing is necessary for stamping as the finished product usually has a not-so-pleasing look
Traditional Sheet Metal Drawing Vs. Hydroforming Sheet Metal
Hydroforming requires no tooling fit, translating to a lower tooling cost. However, traditional sheet metal drawing has a higher tooling cost.
Hydroforming allows for easy setup of the tooling and self-centers after mounting. It is, however, not the case in traditional sheet metal drawing, which is demanding in the setup process.
Draw marks are common in traditional sheet metal drawing. On the other hand, a flexible diaphragm in hydroforming minimizes or eliminates draw marks.
With hydroforming, you can easily form parts with complex geometry while retaining high tolerance of the material used.
Traditional sheet metal drawing equipment is cheaper than hydroforming equipment.
Compared to traditional forms, hydroforming is more economical even when producing a few parts.
Arguably, hydroforming may have a slower cycle time than traditional forms.
Limitations Of Hydroforming Sheet Metals
Purchasing the tooling for hydroforming sheet metals is expensive and may stretch your budget to the maximum.
Although the cycle time is between 15 seconds to 1 minute, the process is slightly longer since there are several prerequisite conditions before the actual cycle.
Due to the large active blank surface areas, a lot of force must be exerted to deform the metal blank to the desired shape.
Application Of Hydroforming Sheet Metal
Common parts in the aerospace industry manufactured from hydroforming include oil filters, jet engine components, nozzle systems, and potable water tanks.
Hydroforming sheet metal is ideal for making long-lasting commercial food equipment with a high tolerance.
Potable tanks are the main waste storage equipment manufactured through hydroforming sheet metal.
Most satellites are products of hydroforming sheet metal.
For making wheel rims and chassis covers for small motors.
Most parts of HVAC components are manufactured through hydroforming sheet metal to maintain high tolerance levels.
People Also Ask:
Hydroforming is a metal forming technique that uses fluid pressure to form complex metal shape components. Additionally, hydroforming creates complex parts that are precise, scratch free, and have a high tolerance rate. The main types of hydroforming are tube hydroforming and sheet hydroforming.
The main advantages of hydroforming include:
- Produces more complex shapes.
- Hydroformed products are light.
- Reduced tool costs.
- Minimal metal wastage during the formation process
- High precision regardless of the complexity of the part.
- Short formation cycle of between 15 seconds to 1 minute.
- Requires less welding and secondary finishing.
Any metal that qualifies for cold forming is a candidate for hydroforming. Examples of such metals include:
- Stainless steel/Carbon steel
- Clad metals
- Any other high-grade metal alloys
The main parameters put into consideration when carrying out hydroforming include:
- Fluid pressure.
- Axial pressure is simply the seal plug’s displacement.
- Temperature; in some instances
Tubular hydroforming has existed but was specifically used to produce plumbing parts. However, in the recent past, it has also incorporated other applications such as bicycle manufacturing.
In tubular hydroforming, fluid pressure is applied inside a tube held in position by dies. Eventually, the fluid pressure will make the tube conform to the shape of the dies.