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Archive for the ‘Extrusion Terms’ Category

Indirect vs. Direct Extrusion

Tuesday, June 15th, 2010

There are two main types of extrusion processes: Direct extrusion and indirect extrusion. Both methods involve forcing a billet of material through a die, but with indirect extrusion the billet is held stationary.

So direct extrusion a billet is forced through a die. This results in pressure buildup on the billet itself and a range of exit temperatures on the material.

Indirect extrusion forces the die against the billet. Since there is an absence of pressure of the billet against the cylinder walls, indirect extrusion more closely resembles a steady-state process. Indirect extrusion produces greater front to back tolerances, but it does not match the productivity rates of direct extrusion due to the cleanup required at the end of the process – removal of “skin” of the billet from the press. Additionally, indirect extrusion requires more complex tooling since it is the die itself which moves.

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Extrusion Angularity

Tuesday, June 15th, 2010

Aluminum extrusion angularity is defined as the feature angularity – the angle between adjacent extruded features. Many extrusions are >20′ in length. Typical angularity tolerances are +/- one to two degrees. However, many aerospace applications require +/- 0.5 degrees or less.

Higher tolerances can be achieved with indirect extrusion, however this process can not achieve the production rates of direct extrusion. In direct extrusion a billet is force into a die, and for indirect a die is forced against a billet.

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Extruded Thermal Barriers

Thursday, May 6th, 2010

The image to the left taken from a patent filing demonstrates a completely isolated thermal barrier for use in a window casing. What the designers have done is to turn one extrusion into two halves by a process of knocking out thin joining sections in the area of 45 and 47. The two halves are now joined by parts 41 and 49 which are thermally insulators.

Without this arrangement heat from the inside of the building could easily transfer to the outside of the building by the window frame during a cold winter and vice versa during the summer.

If thermodynamics taught me anything, this should cut down on heat transfer. However, a more efficient method would be to employ a series of resistors instead of one. The challenge being not to reduce the structural integrity of your window frame.

It may even be possible to do a co-extrusion process and have the whole assembly extruded right on the line. Of course, this would only be cost-feasible with a very large production run and not for prototyping. If you’re looking for extrusion quotes, keep Qualified Vendor in mind.

Tags: thermal barrier
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Eccentricity

Tuesday, April 13th, 2010

One thing to keep in mind when designing aluminum extruded tubes is the eccentricity of the part. This is of particular importance when you have tapped holes coming in from the sides or are milling groves in the inner wall to accept other parts. I’ve seen bollard lighting fixtures with 1/2″ thick walls that had an eccentricity of 1/8″ an inch. Screws up the mating threads on the bottom and the light fixture portion at the top has a lip on one side and an overhang on the other. With eccentricity, it varies per the diameter of your part and to some extent with each extruder. CHECK FIRST! If you don’t get involved with an extruder early on you’re risking a costly redesign.

The technical definition of eccentricity as it pertains to extrusion is: “Deviation from a common center, as, for example, the inner and outer walls of a round tube.”

This is not to be confused with circularity which we’ll discuss later.

Tags: Drill Pipe Extrusions
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Torpedoes in Dies

Thursday, April 8th, 2010

Torpedoes are used in aluminum extrusion dies to produce hollow shapes. The actual torpedo here (conical shaped insert) is being used to produce a tubular extrusion profile. The arrows indicate the direction of the material flow.

Torpedoes add expense because tooling, which would otherwise be one open profile, now contains the torpedo and its support members. So die complexity increases significantly with the addition of hollow features. This isn’t a bad thing if in your design you can use hollows to eliminate other parts in the assembly. Just keep in mind that use of torpedo will at least double the cost of your design. So for small production runs (less than 1000 pieces or 1000 pounds) you may want to seriously consider not using hollow features.

Torpedoes can be made of any shape, but whatever they are, they must be able to be supported in the mold. The vertical member in the diagram supports the torpedo in this picture. The front of the support member is wedge shaped to allow the aluminum to flow around the member.

As an aside, we also maintain a blog on custom machining if anyone is interested in custom machining tips and die design.

Tags: Design Tips, Torpedoes
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