Cheltenham Tool Company


Sheet Metal Forming
Core Process

Cheltenham Tool Company manufactures precision formed sheet metal components using fluid forming, hydro-mechanical forming and conventional cushion deep draw forming methods. Our varied forming techniques allow us to produce a wide range of formed parts for the aerospace, defence industries and the automotive and industrial metal forming markets.

Our plant list includes 6 hydraulic presses ranging from 150 tonnes to 2500 tonnes and 10 fluid cell systems of 8" 10" 12" 15" and 19" diameter capable of achieving pressures up to 1000 bar.

Picture (Component 1)

Fluid forming employs the use of a single tool on which the blank is placed this is located below a fluid cell with the fluid contained through the use of a rubber diaphragm.

The rubber diaphragm used in the fluid form process allows an even pressure to be exerted on the component blank as it is being formed around the tool. Local stress concentrations are thus minimised reducing the chances crack initiation and wrinkle formation. In addition the entire area of the blank is controlled during the forming operation. As a result complex shapes can be formed while still maintaining accurate control of the finished wall thickness and reducing thinning to typically less than 5%.

The versatility and controllability of the fluid forming process allows almost any kind of sheet metal to be formed, in thicknesses ranging from 0.05mm to 10.0mm.

Picture (Component 2)

Hydro-mechanical forming is a very similar process to fluid forming, like fluid forming it employs both a fluid cell and a one part tool however in hydro-mechanical forming the fluid cell is at the base with the component blank placed on top of it and the tool above that, more importantly it does not employ the use a rubber diaphragm in the forming process.

The lack of a diaphragm means that hydro-mechanical forming is used to produce completely different components to fluid forming. Hydro-mechanical forming produces components that are not as intricate and relatively simple in shape when compared to fluid formed components, however the ability to alter the fluid pressure during the forming process allows very high levels of small detail to be left on the component.

Picture (Component 3)

Conventional cushion deep draw forming uses a two part tool one piece attached to the ram and the other fixed to a hydraulically driven cushion, this cushion provides the resistance to the ram that stops the blank splitting during forming. Because of the metal to metal characteristics of this type of forming it is almost impossible to produce the accuracy found in the other methods we use, consequently it is used as a complementary method to our other forming techniques.

Our forming techniques allow us to produce single part components to replace the multi-component assemblies that are produced using other manufacturing techniques. Typical cost savings over these type assemblies are 50% to 75% for both tooling and production.

The fluid forming process removes the need for adjustment and resizing while still providing repeatability and is a cost effective replacement for processes like, spinning, deep draw, drop hammer, dual form, asea press, hot forming and areas of superplastic forming.

  Picture (Beam Mount)  This part is a good example, previously manufactured from five conventionally formed components and that were riveted together, we fluid formed a one-piece component, saving the customer 75% on production costs. This part won the BEST FLEXFORMED PART award at FLEXAIR '98 sponsored by ABB and Boeing.

The Fluid Form Process

Fluid forming of sheet metals was developed by the Saab company in Sweden during the early 1950's to form aircraft parts. The requirement for cold plastic forming of material into complex shapes, whilst maintaining control over wall thickness without stretching and fracturing led to the development of various processes which use one rigid tool half and an oil-filled fluid cell as the other half of the die.

Picture (Evenly Distributed Pressure)In punch forming the fluid cell is used as a flexible die, drawing the sheet metal blank over a rigid punch. By controlling the counter pressure in the fluid cell against the punch movement rate, great control can be exercised during the forming process. As the punch advances, the blank is wrapped gradually over it by the flexible die, which is in continuous contact with the blank. Because there is no unsupported surface of the blank, fracturing, wrinkling and thinning of already formed sections of the material are controlled.

Picture (3:1 Draw Ratio)Using fluid forming allows the use of much thinner blanks than would be used in conventional drawing and achieves very high draw ratios up to 3:1, this results in fewer forming operation and much simpler tooling.

Containment of the fluid is effected by using a rubber diaphragm, the properties of which enable it to be considered as an extension of the fluid at the high pressures experienced during forming.

In cavity forming, the fluid cell acts as an infinitely plastic and incompressible punch, which serves as a blank holder at the same time.

Punch Forming Cavity Forming
Picture (Punch Forming Legend)
Picture (Punch Forming Step 1)
Picture (Punch Forming Step 2)
Picture (Punch Forming Step 3)
Picture (Punch Forming Step 4)
Picture (Cavity Forming Legend)
Picture (Cavity Forming Step 1)
Picture (Cavity Forming Step 2)
Picture (Cavity Forming Step 3)
Picture (Cavity Forming Step 4)

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