CAD software is an essential tool for today’s industrial designers to explore both form and function of their design ideas. In addition to better visualization of product designs, CAD software is being used to analyze strength and dynamic assemblies helping lower product development costs and greatly shortened the design cycle.
While we still get a few designs on napkins, most designers send us their aluminum extrusion profiles as CAD files. Unfortunately, these drawings sometimes lack important details or have issues that create a lot of back and forth between our manufacturing team and a designer to produce a production quote.
To save yourself time and cost, here are four things to always include in your CAD file when sending an aluminum extrusion profile to your manufacturer.
Make Sure Your Drawings are Readable
Precise measurements are necessary to understand the component’s dimensions and shape and determine the proper container size needed for producing the extrusion die. While CAD drawings are ideal, if your dimensions aren’t readable, can’t be traced to the feature, or the drawing is too cluttered it’s going to create problems.
Do not use too many dimensions on drawings and details. Use only the dimensions that are needed to properly illustrate drawings and details. If two dimension lines show up close together, either put a note on one dimension to clarify what feature it refers to or apply dimensions in a logical flow.
Use clear, standard (simple) Geometric Dimensioning and Tolerancing (GDT) call outs with standard Datum call outs. Do not reinvent the GDT handbook. And remember, the more datums you use for fabrication, the more costly the component.
If the shape is complicated, such as requiring compound miter cuts, cutout shape locations in relation to extrusion walls, etc. include the following file types .DXF and/or AutoCAD .DWG / Solid Works .STP file. Also, indicate “exposed surfaces” on your design drawing so the extruder can give them special attention and protect the finish during both extrusion and post-extrusion handling.
Lastly, verify your drawings show the proper scaling and measurement units English/Imperial or Metric units. Double checking that you start out with the correct scaling and units will save time in the end.
Be Consistent with Your Tolerances
Consistency in tolerancing methods is every bit as important as consistency in dimensioning. As a reminder, tolerance is used to control the amount of variation inherent in all manufactured parts, in particular for mating parts in an assembly. The use of plus/minus (+/-) dimensioning provides the allowable positive and negative variance from the dimension specified.
Most designer use plus/minus (+/-) dimensioning, but some may opt to express dimensional data with double minus or positive tolerances, which is also an acceptable style. Regardless of which style you prefer, it is important you maintain consistency throughout your drawing to make it easier for the extruder to interpret, saving time and reducing errors. Also, use tolerance extrusion dimensions that can be easily checked with calipers and other handheld inspection tools.
If you have custom specific tolerance specifications, and you have a document that calls that out, be certain to supply that document. If it is not sent, your manufacturer will either have to request it from you or have to provide a quote and note that your custom tolerances were not used.
Check Your Tolerance Settings
While standard industry tolerances usually provide adequate precision for most applications (these tolerances are published in the Aluminum Association’s Aluminum Standards and Data Guide), more complex components may call for greater geometric dimensioning and tolerancing in order to achieve the shape-related intricacies of the design. When requested, very precise tolerances of 1/2 or 1/3 of the specified tolerance may be feasible. For example, if the tolerance calls for + or – .010, a tighter tolerance of perhaps + or – .005 could be held, when requested and deemed feasible.
However, to achieve these tighter tolerances may require more involved die corrections, slower extrusion rates, and sometimes a higher rejection rate. All that special care adds up to higher costs. Therefore, carefully consider the application of your part or product when setting tolerances.
A good rule of thumb is NOT TOLERANCE ANYTHING that doesn’t absolutely have to have a tolerance. Aluminum Association standard tolerances will be applied wherever tolerances are not specified. But do ensure you always identify your Critical to Function (CTF) tolerances, such as areas where you are mating hardware.
Pay close attention to the default settings in your CAD programs. Using the default numbers on your drawing program when the decimal setting is three or four places out means every dimension shown appears to require the highest precision.
Calculate Your Tolerance Stack Up
If you are designing parts that assemble, also be aware of tolerance stack up. Tolerance stack-up calculations represent the cumulative effect of part tolerance with respect to an assembly requirement. By adding tolerances to find total part tolerance, then comparing that to the available gap or performance limits, you can determine the probability that a part will have a poor or impossible fit with a mating part.
Most CAD software programs include a tolerance analysis tool. Use these tools to automatically check the effects of tolerances on parts and assemblies to ensure the consistent fit of components and to verify tolerancing schemes before sending a profile to your manufacturer. If your program doesn’t include an analysis tool, there are a variety of analysis methods you can choose from and can calculate using a spreadsheet.
Don’t Be Afraid to Ask Your Extrusion Provider for Help
Whether you’re new to aluminum extrusions or a seasoned extrusion designer, your aluminum extrusion manufacturer can help you figure out proper tolerances and stack up, saving you time and frustration. Best-in-class extruders like Vitex work directly with designers to ensure their designs take full advantage of all aluminum extrusion manufacturing functions.