Aluminum Extrusion Flatness & Tolerances

Views:46 Author:Site Editor Publish Time:2023-10-17 10:07:29 Orgin:Site

Aluminum is used all across the world in diverse industries. Its applications range from vehicle parts to electronics and spacecraft components. Aluminum extrusion is an essential process that prepares the metal for use in these kinds of applications.


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What is Aluminum Extrusion?

The extrusion process is used to create various shapes out of aluminum metal. This molding process changes aluminum, making it usable in many products.

The process starts at the raw material stage. Aluminum is prepared as billets, which are cylindrical-shaped metal pieces. These are then transformed into a malleable molten through heating in a furnace.

The billet heating process requires a temperature of more than 1000 degrees Fahrenheit. The hot molten is then squeezed through a die, which then shapes it into the required dimensions.


Cooling and Cutting

Once the shaped aluminum flows out on the other end, it has to be cooled. It may also be necessary to stretch it to achieve the right characteristics based on the intended applications. Cooling and stretching are done in a manner that allows the extruded aluminum to maintain its properties and structural composition.

The recurring step during the extrusion, as well as processing of aluminum, is cutting. In simple terms, this means sawing or slashing long extruded aluminum pieces into the desired lengths.


Surface Finishing

This is the last process in aluminum extrusion and involves powder coating, painting, and anodizing. This is done for beautification and protection from the elements. Surface finishing may also improve the functionality of the pieces in their various applications.


Shapes Extruded

It is possible to come up with so many different shapes in the aluminum extrusion process. Some of the shapes to expect include:

● Solid beams

● Hollow beams

● Rectangular solids

● Square solids

● C channel or semi-hollow beams



Following aluminum extrusion, you may want to further tinker with the dimensions. This is where you will employ diverse methods such as drilling, punching, and machining to get aluminum that matches your desired specs.


Aluminum Extrusion Tolerances: The Marker of Quality

Tolerance refers to the defining rules for defining the dimensions. For instance, in Aluminum extrusion, set tolerances dictate how long, how heavy, or how flat you want the end product to be. There are precise manufacturer-specific tolerances, and then there are industry standard tolerances.


General Tolerance Guidelines

● To achieve the perfect wall thickness, use ± 10% for dimension specification.

● To achieve the best cross-sectional dimensions, use ± 0.008" for tolerance specifications.

● Use ½ degree tolerance per foot in length for twist in length.

● Use 0.0125" tolerance per foot in length for straightness.

● Wall thickness and surface size determine angularity, but you can use tolerances that vary between ±1 degrees and ±2 degrees.

It is important to use tolerances with agility of thought. The dimensions should help you achieve precision without escalating costs.

Keep in mind that tighter tolerances may require more expensive and precise equipment in extrusion and machining. This can lead to an overall costly production process.


Adjusting Tolerances

You can recalibrate tolerances based on specific project needs. If you need high precision in your final products for aerospace or vehicular construction applications, you can use tighter tolerances.

The same can also be highly beneficial in the electronics and cabling industry. You can use looser tolerances in applications that don't have strict dimensional requirements.



Flatness tolerance is the safest deviation you can work with for a flat aluminum extrusion. You can measure the deviation as the distance in inches from the topmost to the bottom point of the extruded surface.

Tracking this difference in flatness is essential because it affects the quality of the applications. Ensure flatness tolerance aligns with the specific dimensional requirements of the desired application.


Considerations for Flatness Tolerance

When tracking flatness tolerance in Aluminum extrusion, be aware that the factors below will affect the outcome.

The shape of the die. Put simply, die design is instrumental in the final flatness of the extruded aluminum. Ensure to work with a die that's designed to reduce distortion, valleys, and bumps.

The alloy. The true flatness of the final piece will depend on the types of Aluminum alloy you are working with. Choose an alloy whose properties allow for extensive flatness after extrusion.

Extruder Metrics. These are the parameters that guide the extrusion process. They include settings such as temperature, speed, or pressure. If you control these metrics properly, you can come up with a highly consistent flat piece.

Post Extrusion. At the end of the extrusion process, where you have cooling or machining, it is important to take care not to imperfect the flatness of the piece. Employ best practices for cooling and cutting.


General Flatness Tolerances for Aluminum Extrusions

Let's look at some of the common industry standards that set the pace for aluminum extrusion flatness. The most popular tolerance standards include the following.


AA 6063 Standard (Architectural Components)

Follow these standards for aluminum extrusion processes for architectural parts. The building materials must have a flatness tolerance not exceeding 0.010 inches per foot. This applies to things such as ceiling beams, door frames, and wall curtains.


AA 6061 (Industrial Application)

This standard sets the requirements for aluminum extrusion flatness deviations allowed in industrial fixtures. The best deviation allowable is 0.015 inches per foot. This range applies to aluminum extruded parts for machinery and plant equipment to help with performance and dependability.


ASTM B308 (for 6061-T6 Alloy Shapes)

This standard applies to extrusions for diverse engineering and structural applications. The flatness deviations allowed vary based on extrusion sizes and shapes.


Manufacturer Specifications

Sometimes, different manufacturers in different industries specify unique flatness deviation requirements. You must be prepared to look beyond general standards. Design your extrusions to a flatness that helps them meet their structural, performance, and aesthetic requirements.


ISO 8062-3:1994 (for Aluminum Precision Castings)

If the plan is to use extrusions with cast components, the flatness must be precise enough to allow for the best performance in assemblies.


Heat Sink Profile Standards

Heat sinks are standard in electronic equipment for temperature management. The flatness of the used extrusion part directly impacts the efficiency of heat transfer. The industry standard deviation is 0.005 - 0.010" per ft.


ASTM B241/B241M (Pipes and Extruded Tubes)

The aerospace and vehicle manufacturing industries demand consistent flatness for seamless extruded pipes and tubes. The exact allowable deviations vary depending on the specific use cases.


AA Standard (Automotive Components)

The vehicle manufacturing industry has specific requirements for the flatness of aluminum parts following extrusion. You should keep updated on these standards because they change frequently. They compel strict adherence because they directly impact vehicular safety and performance integrity.


ASTM B666/B666M (Electrical Applications)

ASTM standard is essential for extrusions used in electrical applications. It provides dimensional tolerances, including flatness, for extrusions intended for use in electrical equipment. These tolerances are crucial to ensure proper assembly and electrical performance.



These are the measurement methods used to ascertain the flatness and uniformity of the extruded pieces.


Metric Profiling

This method involves making direct contact with the flat surface to detect deviations. Experts may use micrometers and calipers to measure the metric variations of the extruded aluminum surface. They would take readings at each point and use these measurements to benchmark against the industry standards.


Coordinate Measuring Machine

CMM uses a precision measuring instrument that analyses variations in the flatness of the surface. It makes it possible to obtain highly accurate measurements at specific points of the extruded piece. The CMM methodology is popular in the automotive industry.


Visual Profiling

Beyond the old techniques of measuring, it is possible to determine the flatness deviation of the extruded aluminum via optical means. Optical measuring is popular in the aerospace industry. The methods applied here include confocal microscopy and laser scanning. Using these methods, one can create a 3D image of the extruded surface. With this level of high visibility, it becomes possible to spot and correct even the tiniest deviations that go beyond standard range points.  


Comparative Measurement

This is a method of referencing the actual flatness of the extruded piece with theoretically known flatness measurements. It allows you to find out whether the tolerance meets the desired parameters for function and performance.


How Aluminum Post-Extrusion Impacts Flatness

Flatness deviations can occur following the extrusion process. It is essential to use post-extrusion processes to correct any aberrations and achieve the desired tolerances of flatness.


De-stressing by Heat Treatment

This heat-based post-extrusion process helps to relieve internal pressure in the extruded piece. You heat the surface of the extrusion, then cool it gradually until relaxation. This is the point where it will regain the desired shape without bends and twists.

The typical heating temperature for this process is 300 degrees Celsius. The metal is then cooled over several hours. Heating then cooling straightens the metal and redistributes its unevenness for a flatter surface.


Mechanical Ironing

This is a flattening and straightening of the extruded piece to remove bumps and valleys. The aluminum profile is passed through a mechanical press that shapes it into the desired.

This strategy is time-consuming and requires precision and skill. The pressing machines can be mechanical or hydraulic, and they must be operated carefully to get the desired results.


Surface Machining

This is a sculpting process that refines the straightness of the flat surface. As you would expect, the process uses a grinder to saw valleys and protrusions off specific areas of the aluminum profile. It leads to a finely surfaced flat piece with the desired tolerances.


Roll Forming

The aluminum piece is guided into a series of rollers to fine-tune its flatness. It is like using a rolling pin to flatten dough for cakes. As it passes through each roller, it becomes flatter. Roll forming is the most affordable method for rectifying deviations on a flat aluminum surface.

Roll forming is highly automated. A computer process helps to set the right parameters for modifying the profile's shape. It is kind of an assembly line, with each step in the process advancing the flatness of the extruded profile.


Profile Stretching

Mechanical equipment is used to stretch and tag the aluminum piece until it achieves the desired flatness. You can only use this for aluminum extrusions with a localized bump. It is not effective for correcting aluminum profiles that have too many imperfections.


Communicating Tolerances

Proper communication of flatness tolerances is essential. It can help streamline the manufacturing process and align costs and goals.

In any collaboration setting where engineers and designers work together, there must be a clear tolerance communication protocol that everyone can understand. It helps to avoid errors during the production process.


Accuracy in Production

Understanding flatness tolerance helps define the desired variation based on aluminum's use case. When this is correctly done, it becomes possible to quickly produce precise parts that excel in form and function.


Design Goals

Flatness tolerances are largely guided by the design goals of the project. Engineers and designers must properly communicate deviations and use clear standards to attain desired dimensional accuracy.



Sometimes, aluminum parts need to fit into each other or work together in buildings, machines, or electronics. With a proper flatness deviation measuring and recoding system, it will be possible to achieve parts with matching tolerances for better function.


How to Communicate Flatness Tolerances

In a design engineering or manufacturing setting, the right approach to communicating tolerances is application-specific. It is also guided by industry standards. Here are some of the most common methods.


Geometric Dimensioning and Tolerancing (GDT)

GDT uses geometric symbols, modifiers, and frames to indicate tolerance deviations. This method is advantageous because it leaves no room for ambiguity.


Plus-Minus Tolerancing

In this approach, you must specify the desired dimension and then use the ± symbol to indicate allowable tolerances. Let's say that flatness is specified as 12mm ± 0.2 mm.

This indicates that designers can work with any piece in the range of 11.8 mm to 12.2 mm. It is an easy method, but its efficiency may fall short in complex applications.


Dimensional Limiting

This communication standard sets the upper and lower limits of an extruded flat surface profile using the stroke "/" sign. For instance, if you specify width as 11.2"/11.4", it means that the lower tolerated limit is 11.2" and the upper tolerated limit is 11.4". It is very easy to understand.


Bilateral /Unilateral Tolerances

In this communication standard, you can use bilateral tolerances to indicate negative and positive deviations from the nominal. Use unilateral if you want to indicate only a single direction of deviation – either positive or negative.


Tolerance Tables

Many manufacturers have designed standard deviation tables to communicate allowed tolerance values. The numbers depend on the specific features and areas of applications for the aluminum profile. Such tabulations may not be efficient for custom machining.



Tolerance is a north star for quality in aluminum parts manufacturing. You can use Aluminum extrusion tolerance as a guide for the acceptable variations in flatness and sizes.