Seminar On Hydro Forming Processes report Download
Hydroforming is a cost-effective way of shaping ductile metals such as aluminium, brass, low alloy steel, and stainless steel into lightweight, structurally stiff and strong pieces. One of the largest applications of hydroforming is the automotive industry, which makes use of the complex shapes made possible by hydroforming to produce stronger, lighter, and more rigid uni-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 aluminium tubes for bicycle frames.
Hydroforming uses fluid pressure applied to a tubular or sheet metal blank to form it into the desired component shape. The most commonly used materials in hydro-forming include the various grades of steel.
These grades of steel are used extensively because they exhibit good fatigue properties, high energy absorption, and reasonable resistance to corrosion. Other metals used for hydro-forming include:
• Stainless Steels
• Copper Alloys
The Hydroforming System
All hydroforming systems include:
• Tooling and dies
• A hydraulic press
• A fluid-pressure intensification system
Hydro-forming dies vary dramatically with regards to sheet metal hydro-forming and tubular hydro-forming operations. Dies may be single or multi-cavity.
Hydro-forming utilizes hydraulic, rather than mechanical, presses for many reasons. Hydraulic presses are able to deliver full tonnage at any point in the stroke, not just at the bottom as is the case with mechanical presses. The hydraulic press can be adjusted to provide optimal part clearance. Also, hydraulic presses can be stopped in mid-stroke which is advantageous to some hydro-forming operations.
The fluid-pressure intensification pressure system consists of a low-pressure, high flow rate filling system, along with a high-pressure intensifier to raise the fluid pressure to forming levels. The forming fluid is water based and contains additives such as lubricants, drying agents, rust preventatives, and bactericides.
Working Of Hydro Forming Process:
In a typical hydroforming operating cycle, a blank is placed on the lower die tooling, and the press is closed. Fluid is then introduced to either one side of the sheet metal blank, or within the tubular blank. As fluid pressure is intensified the blank deforms, taking the shape of the tooling. Lubrication is especially important in hydroforming. Lubricants assist in reducing the friction and stresses as the metal flows into its final shape.
Tubular hydroforming begins with the placement of either straight tubes, or more commonly preformed tubes, into the die. Sealing punches within the die close off the tube ends as fluid pressurization begins. The three surfaces of a tube that can act as sealing surfaces, include:
• The outside diameter of the tube
• The inside diameter of the tube
• The end surface of the tube
During forming, a combination of increasing internal fluid pressure and a simultaneous axial pressing on the tube ends by the sealing punches cause the tubular material to flow into the contours of the die.
Tubular hydro-forming cycles also include ‘hydro-piercing’ to create holes and slots in the part. The piercing tool is incorporated into the hydro-forming die and activated during the forming cycle by hydraulic cylinders.
The piercing action is usually inward against the pressurized fluid. Piercing can also be performed outwardly by retracting a plunger, or backup punch. The fluid pressure within the tube causes the surface material to fail, creating a hole in the unreinforced portion of the tube wall.
Sheet Metal Hydroforming
In sheet metal hydroforming, controlled metal flow during the operation minimizes localized stress concentrations that may cause workpiece buckling or wrinkling. Sheet metal hydroforming is slower than traditional stamping, thus its use is limited to short runs of more highly specialized parts.
Hydroforming is capable of producing parts within tight tolerances including aircraft tolerances where a common tolerance for sheet metal parts is within 0.76 mm (1/30th of an inch). Metal hydroforming also allows for a smoother finish as draw marks produced by the traditional method of pressing a male and female die together are eliminated.
While springback has long been a topic of discussion for sheet metal forming operations it has been far less of a topic of research for tube hydroforming. This may in part be a result of the relatively low levels of springback naturally occurring when deforming the tubes into their closed section geometries. Tube Hydroformed sections by the nature of their closed sections are very rigid and do not display high degrees of elastic deformation under load. For this reason it is likely that negative residual stress induced during tube hydroforming might be insufficient to deform the part elastically after the completion of forming. However, as more and more tubular parts are being manufactured using high strength steel and advanced high strength steel parts, springback must be accounted for in the design and manufacture of closed section tube hydroformed parts.