Keeping Costs in Check: Designing Aluminum Extrusions with Proper Tolerances

aluminum extrusion tolerancesDesigners must keep an eye on the bottom line in every project. Finding creative and practical solutions to accomplish cost control while also maintaining the integrity of the design is important, but it can consume engineering resources. One often overlooked way to keep costs down is to examine tolerance requirements. With unnecessarily tight tolerances parts become more expensive to produce. In fact, customers sometimes ask us why a part is so expensive, not realizing that extending tolerances out just one more decimal point can increase the cost by a factor of two or three. That is because tighter tolerances require greater care in fabricating and inspecting in order to ensure accuracy.

Some simple steps in the planning process can help prevent over-tolerancing without compromising design or function.

Have Your Aluminum Extruder Review the Design

First perform a comprehensive tolerance review at the concept stage of the design process. Although tolerance is typically one of the topics addressed, reducing tolerances is an area of concern for most design engineers. A simple and effective solution for this concern is to improve communication between design teams working on different aspects of the project.

You should also include your aluminum extruder in the conversation to get expert advice from the manufacturing side of the project. Most best-in-class aluminum extruders, such as Vitex Extrusion, provide Design for Manufacturing support.

By working with designers early in the design process, we ensure a product is designed to take full advantage of all aluminum extrusion manufacturing functions. We review a design’s profile and tolerances and determine process capabilities to meet dimensional limits. Our manufacturing team also identifies any issues and alerts the designer if additional machining or fabrication will be needed to meet the desired requirements, and in some cases, identify opportunities to avoid additional machining.

Be Realistic About What Tolerances Are Needed

Next, determine the actual required tolerances; this is most effectively done by understanding a part’s application and interaction with other parts. Assess tolerances overall – not just of a single component – and determine if there will be any inconsistencies with outside components.

Sometimes, if there is a rush to get a design to the manufacturer, a designer may over tolerance a part just to be sure. Or, a designer may accept the software’s default tolerances without understanding whether or not they’re truly necessary, or simply not noticing them at all. Both of these actions can unnecessarily drive up cost.

Here are just a few typical examples:

  • An extra decimal of tolerance is specified not for a technical reason — that is, not because the particular part needs that level of precision — but because that is “the way it has always been done.”
  • In a project with several components requiring a tolerance of ±0.001 because of the way they must fit together, a separate part is automatically specified using the same tolerances, even though the part does not interact with the others and may or may not need the same tight tolerance.
  • In an effort to keep mechanical drawing labels consistent to the same decimal point, a zero is accidentally misplaced, labeling a tolerance ±0.001 instead of ±0.010.
  • Two parts that failed to fit together correctly are re-specified at tighter tolerances — but the original failure was due to the parts being cut at two different loose tolerances.

Understand the Cost Tolerance Equation

Ensuring designers are aware of exactly how tolerancing affects cost is another key to successfully keeping costs down. Tighter tolerances lead to higher costs. Over-toleranced parts are more costly, harder to manufacture, take longer to produce, and may be entirely unnecessary. Choose a sample project and calculate how much each tenth of tolerance costs in dollars, then multiply it by features. This knowledge will help the team be more conscious of the total cost.

Have a new design project? Vitex aluminum extrusion experts can help you determine the proper tolerances for your design and help you keep an eye on the bottom line. For more information on how Vitex can help your design team contact us.

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