Summary
Tube and sheet hydroforming start with different blanks and use fluid pressure differently. Both can produce hollow parts, so the finished shape alone cannot identify the process. Choosing between them also depends on the material, hole and connection requirements, and the required finished-part quality.
On this page
Start with the blank, not the finished shape
A welded tube may originally have been made from strip. By the time it reaches hydroforming, however, it is a tube blank. Making that tube and reshaping it with internal pressure are two separate operations; the second is tube hydroforming.
A finished assembly may contain a formed body and components attached later. To understand how it was made, distinguish the shape formed in one operation from the parts added afterwards. A hollow finished shape alone does not tell you what blank was used.
| Difference | Tube hydroforming | Sheet hydroforming |
|---|---|---|
| Starting material | A straight or preformed tube blank | Sheet metal; some methods use two blanks |
| Use of fluid pressure | Pushes the tube wall outward from inside | Shapes the sheet; how pressure is applied varies by method |
| Possible shapes | Tubular parts with curves or noncircular cross sections | Shells and other parts, including hollow parts formed from two sheets |
| Holes, ports, and attachments | Not necessarily completed during body forming; other operations may be needed | Not necessarily completed during body forming; other operations may be needed |
Tube hydroforming reshapes an existing tube
Fluid pressure inside the tube pushes its wall outward to form the required contour. The tube may be straight or preformed before this operation. The finished part can have bends and noncircular cross sections; it does not have to retain the appearance of a straight, round tube. Schuler’s tube hydroforming description
A part formed from a tube can resemble a shell formed from sheet. The distinction is what the operation starts with, not whether the finished parts look alike.
Sheet hydroforming includes several methods
Sheet hydroforming is not a single method. Hydromechanical deep drawing combines mechanical drawing with fluid pressure, whereas hydraulic deep drawing uses pressurized fluid to shape the sheet blank. Both work with sheet, but fluid pressure serves a different purpose in each. Hydromechanical deep drawing; hydraulic deep drawing
Quintus Flexform fluid cell forming is another sheet-forming method. It uses a flexible diaphragm to shape the blank. This diaphragm arrangement is specific to the method, not a common feature of all sheet hydroforming. Quintus Flexform Fluid Cell Presses
These methods differ in how fluid pressure acts on the sheet and whether mechanical drawing is involved. The choice depends on the sheet blank, the part's shape, and its quality requirements.
Sheet blanks can also form hollow parts
A hollow part need not start as a tube. In two-blank forming, fluid pressure is applied between two sheets to shape them into a hollow part. Schuler’s description of two-blank forming
Holes, ports, and attached components are not necessarily made in the operation that forms the body. Other work may be needed to complete them. See hydropiercing, post-form holes, and joining for the different approaches.
A hydraulic press can perform conventional sheet deep drawing as well. Here, “hydraulic” describes the machine's drive, not a hydroforming process. The distinction is whether fluid pressure drives the press or helps shape the tube or sheet blank. Schuler’s overview of deep-drawing presses
Choosing a process for a specific part
The manufacturing plan for a complete assembly may involve more than forming its body. Holes, ports, and connections can require additional operations. When choosing between tube and sheet, consider how these features will be made as well as the main contour.
Parts with similar outlines may need different processes because of their material or quality requirements. Cost comparisons should include the work needed to complete the holes and connections, not just to form the body.
Discuss a custom tubing project
ShuiYiYuan provides custom tube hydroforming. To discuss a tubing component, send its drawing, material, and finished-part requirements through the tube hydroforming services page.
Frequently asked questions
Is it sheet hydroforming if the tube was made from strip?
Can a complex contour identify the right hydroforming method?
References
Schuler describes tube forming, hydromechanical and hydraulic deep drawing, and press drive types. Quintus explains Flexform sheet forming. The linked Insights article discusses holes, ports, and joining.