Metal Forming Operations

Narrator: Today's open-die forging operations combine precision control technology with massive presses or hammers with a variety of processes to choose from. Open-die forging provides the versatility to produce a wide range of shapes from virtually any type of metal stock, including today's specialty micro alloys. And with the component size constrained only by that of the forged stock, open-die operations can handle the production of parts up to 80 feet in length and over 200 tons in weight. When the job calls for short runs and superior performance characteristics, open-die forging is the process of choice.

Narrator: This is a Dalarna University production. Roll forming is a process where a metal sheet passes through a series of roll stands that change the sheet's shape. The sheet undergoes what is called a profile bending. Roll form details are very common in, for instance, the furniture, construction, and car industry. It is possible to create advanced profile shapes in high-strength materials, and many different materials can be used. All materials that can be bent can also be roll formed. Roll forming is gentle on the material and has a minimum of wear on tools.

Today, the roll forming process and the tools are designed in a computer environment before production. Computer simulation is an important tool in order to analyze the roll forming process geometry. Forming forces and residual stress are factors that can be monitored in the material. The roll stands are designed so as to allow the material to undergo a gradual shape alteration. Here, the different steps are illustrated in a so-called flower pattern.

This is a roll forming machine with six roll stands. It does not have an automatic feeder; instead, it is fed manually. More advanced profiles require more roll stands in order to reach a final result. This machine shapes the strip into a simple V profile. Note that the sheet springs back. Spring back is the elastic deformation that appears after shaping. Spring back is compensated for when the roll stands are constructed, thus overbending the sheet and letting it spring back into the correct form.

What the roll forming tool looks like is decided by what kind of profile is needed. The starting point is to draw a cross-section where the required radius, thickness, and dimensions are applied. The minimum radius for bending is decided by the thickness and the properties of the material. Here, it is also decided if the profile will be punched or pre-cut, and if it needs to pass through more preparatory stages before roll forming.

There is a great demand for machines that can complete as many stages as possible in a single production line. If more operations can be incorporated into the production line, large volume processing will be more cost-effective. Roll forming can be a part of a production line producing profiles that do not require further refinement but are ready to be used immediately.

Narrator: The primary type of hot extrusion is direct or forward extrusion. In direct extrusion, the hot billet is loaded into a thick-wall container and forced through an extrusion die secured in a holder. The force for extruding is applied by a ram along with an intermediate reusable dummy block. Metal flow from the die is in the same direction as the forward motion of the ram. Since the surface of the billet length slides along the wall of the container, extrusion force depends on the friction between the billet length and the container and the material. The friction portion of the force can be reduced by using lubrication.

Force increases rapidly as the billet is upset to fill the container, then increases further as breakthrough force before extrusion begins. Upon breakthrough, the force declines as billet length decreases until a minimum force is reached. As the billet thins, the force rapidly rises again to continue metal flow radially toward the die opening. Resistance to deformation or force requirements increase markedly as the thickness of the butt or unused billet portion decreases.

Hot extrusion is most commonly performed on horizontal hydraulic presses. Hot extrusion presses are usually rated in force capacity, which translates to the amount of pressure applied to the billet. That pressure depends on billet material and temper, its cross-section and complexity, length and temperature, extrusion speed, and reduction or extrusion ratio. The extrusion ratio equals the cross-sectional area of the container liner divided by the cross-sectional area of the die openings.