Your goal as a designer is to come up with the design that best meets the requirements of the project. Here is a quick guide with the four key points you need to consider when designing with aluminium extrusions.
Whether you are designing a frame for a bicycle, a roof reinforcement for a car or solar panels, the aluminium profile will take shape on the drawing board. It is therefore essential that you understand the &#;basics&#; for the design of aluminium profiles and components.
Understanding these basics will help you identify ways to reduce weight, add functionalities, simplify assembly, and minimize costs.
Finding the right wall thickness depends on the strength requirements of the profile and your cost-efficiency target. Profiles with uniform wall thickness are the easiest to produce, but if changes are needed, you can easily alter wall thicknesses within an aluminium profile.
The most important factors that influence wall thickness are:
It is not possible to achieve razor-sharp corners with the extrusion process, so take this into account in your design. Corners should be rounded. A radius of 0.5-1 mm is usually sufficient.
Designs that require sharp internal corners can be solved with a hole radius.
You should avoid designing sharp projections in the profile. These can bend quickly and become uneven.
A final aspect is to always ensure rounded transitions. A profile with large variations in wall thickness cools unevenly after extrusion. This creates structural differences, and these become visible, especially after anodizing.
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Decoration can help you achieve the best design. You may not think that it has anything to do with functionality or cost efficiency, but it really does. We recommend that you use decoration to:
Here is an example: If your profile has arms or screw ports, then process-related shadowing (heat zones) can appear on the opposite side. With help of decoration, you can make these zones invisible.
Finally, well-designed decoration also helps protect the profile from damage during handling or storage.
Cost-efficient production is another point that requires your attention during the design process.
Profiles that are easy to extrude have the following properties:
These are the main points to consider when designing aluminium profiles and components. Other factors such as surface treatment and material properties are also influential in the design process. Don&#;t be afraid to ask your supplier for support.
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Shape is a determining factor in the part's cost and ease with which it can be extruded. In extrusion a wide variety of shapes can be extruded, but there are limiting factors to be considered. These include size, shape, alloy, extrusion ratio, tongue ratio, tolerance, finish, factor, and scrap ratio. If a part is beyond the limits of these factors, it cannot be extruded successfully.
The size, shape, alloy, extrusion ratio, tongue ratio, tolerance, finish, and scrap ratio are interrelated in the extrusion process as are extrusion speed, temperature of the billet, extrusion pressure and the alloy being extruded.
In general, extrusion speed varies directly with metal temperature and pressure developed within the container. Temperature and pressure are limited by the alloy used and the shape being extruded. For example, lower extrusion temperatures will usually produce shapes with better quality surfaces and more accurate dimensions. Lower temperatures require higher pressures. Sometimes, because of pressure limitations, a point is reached where it is impossible to extrude a shape through a given press.
The preferred billet temperature is that which provides acceptable surface and tolerance conditions and, at the same time, allows the shortest possible cycle time. The ideal is billet extrusion at the lowest temperature which the process will permit. An exception to this is the so-called press-quench alloys, most of which are in the series. With these alloys, solution heat-treat temperatures within a range of 930°-980° F must be attained at the die exit to develop optimum mechanical properties.
At excessively high billet temperatures and extrusion speeds, metal flow becomes more fluid. The metal, seeking the path of least resistance, tends to fill the larger voids in the die face, and resists entry into constricted areas. Under those conditions, shape dimensions tend to fall below allowable tolerances, particularly those of thin projections or ribs.
Another result of excessive extrusion temperatures and speeds is tearing of metal at thin edges or sharp corners. This results from the metal's decrease in tensile strength at excessively high-generated temperatures. At such speeds and temperatures, contact between the metal and the die bearing surfaces is likely to be incomplete and uneven, and any tendency toward waves and twists in the shape is intensified.
As a rule, an alloy's higher mechanical properties means a lower extrusion rate. Greater friction between the billet and the liner wall results in a longer time required to start the billet extruding. The extrusion ratio of a shape is a clear indication of the amount of mechanical working that will occur as the shape is extruded.
Extrusion Ratio = area of billet/area of shape.
When the extrusion ratio of a section is low, portions of the shape involving the largest mass of metal will have little mechanical work performed on it. This is particularly true on approximately the first ten feet of extruded metal. Its metallurgical structure will approach the as-cast (coarse grain) condition. This structure is mechanically weak and shapes with an extrusion ratio of less than 10:1 may not be guaranteed as to mechanical properties.
As might be expected, the situation is opposite when the extrusion ratio is high. Greater pressure is required to force metal through the smaller openings in the die and extreme mechanical working will occur. Normally acceptable extrusion ratios for hard alloys are limited to 35:1 and for soft alloys, it is 100:1. The normal extrusion ratio range for hard alloys is from 10:1 to 35:1, and for soft alloys is 10:1 to 100:1. These limits should not be considered absolute since the actual shape of the extrusion can affect results. The higher the extrusion ratio, the harder the part is to extrude which is the result of the increased resistance to metal flow. Hard alloys require maximum pressure for extrusion and are even more difficult because of their poor surface characteristics which demand the lowest possible billet temperature.
Difficulty factor is also used to determine a part's extrusion performance.
Factor = Perimeter of Shape/ Weight per Foot.
Weight per foot is of primary importance because of the consideration for profitable press operation. As might seem obvious, a lighter section normally requires a smaller press to extrude it. However, other factors may demand a press of greater capacity such as a large, thin wall hollow shape. Though it has low weight per foot it may take more press tonnage to extrude it. The same reasoning applies to the factor as with the extrusion ratio. A higher factor makes the part more difficult to extrude consequently affecting press production.
The tongue ratio also plays an important role in determining a part's extrusion performance. The tongue ratio of an extrusion is determined as follows: square the smallest opening to the void, calculate the total area of the shape, and then divide the opening squared by the area.. The higher the ratio, the more difficult the part will be to extrude.
In order to help us understand your needs and requirements and service you better, the following is a check list of things to consider when submitting items to an extruder for quoting or new business:
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