While most extruders don’t require packaging specifications. If you pick your own packaging, you have the most control ensuring perfect parts at your door. For just-in-time manufacturing, sometimes you can’t afford to have losses due to shipment damage so it’s better to pay more for packaging than to put a sale on backorder and risk losing the sale. This is an example of NSM-13, A Northern States Metals provided packaging specification.
Extrusion Packaging
Posted by Matthew Brown on July 15th, 2010 Post a comment »What to Put on a Drawing
Posted by Matthew Brown on July 15th, 2010 Post a comment »
I see a lot of aluminum extrusion drawings and am never surprised at how little information engineers put on their prints. The notations on the left however are fantastic. This gives the extruder enough information (the drawing is not shown to protect the company’s IP) to quote and build the job.
The key information spelled out here is:
- Cut length
- Alloy
- Finish
- Flatness
- Straightness
- Twist
- Surface defect tolerances
- Packaging
Indirect vs. Direct Extrusion
Posted by Matthew Brown on June 15th, 2010 Post a comment »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.
Extrusion Angularity
Posted by Matthew Brown on June 15th, 2010 Post a comment »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.
Aluminum Extrusion Quicktips
Posted by Matthew Brown on June 15th, 2010 Post a comment »When you start designing a new extruded aluminum part there are several things you should keep in mind. Here is a quick list of design tips to get you started:
1. Know your vendor’s circle size. If you don’t know the extruder’s limitations you’ll likely design a part they can’t produce and end up redesigning the part or shopping it around to find a fit. Additionally, the greater the circle size the more tolerance becomes an issue. Start working with an extruder early on. Some offer engineering support and some don’t.
2. Evaluate your tolerance requirements to that which your extruder can support. You can look to aluminum.org for design guidance in addition to your extruder. Aluminum.org’s information is somewhat technical however. So, for quick answers call/email your extruder or you can use Qualified Vendor’s quote service to find suppliers.
3. Critical tolerances: angularity, flatness, roundness and eccentricity.
3. If your parts require secondary machining, make sure you design in indexing features. This can be as simple as an extruded groove in which the machinist can use to take a hole dimension off of.
4. Wall thickness – design them as uniformly as possible. This will prevent voids in the extrusion.
5. Designate critical and cosmetic surfaces. This will prevent unintended marring of critical surfaces.
6. Heat sinks – as a rule of thumb, fins should not exceed 10:1 length to thickness.
7. Screw bosses – keep a 60 degree opening otherwise the die will require a torpedo which will significantly affect the cost and life of the die. Use your machinery’s handbook for McMaster Carr for screw hole guidance. I recommend self cutting/starting thread forming screws. They’re inexpensive and yield a great strength, so much so that you need to be careful when inserting them so you don’t shear off the heads – use a driver with a clutch.
8. Make transition areas smooth with gentle radii.
9. Select the proper alloy for your application and make sure your extruder can use this alloy. Many only work with one or two series of aluminum – 2XXX or 6XXX are most common.
10. Lastly, consider your finish. Design with appearance and performance in mind. Don’t forget that the parts have to have secondary operations, packaged and shipped. Many finishes like anodizing will change your tolerances. Keep this in mind. Likewise, if you’re going to powder or wet paint your finished parts make sure you designate which features (holes, grooves, etc.) need to be masked off to prevent paint contamination. This may affect your final assembly.