Designing with T-Slot Aluminum Extrusions - Vention

T-slot aluminum extrusions generally enable quick design and manufacturing of structural frames, but their design can have a huge effect on overall structural integrity. Below are our three top design tips for creating reliable, rigid, and industrial-grade t-slot aluminum extrusion structures.

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1. Choosing the right extrusion profile

Not all extrusion profiles are created equal. Two profiles might have the same outer dimensions—45 x 45 mm, for example—but very different rigidity, depending on their area moment of inertia.

Another key aspect to consider is the cross-sectional area, which affects the overall weight of the assembly. Since the best profiles are highly rigid and lightweight, the best performance indicator is the area moment of inertia to surface area ratio. The table below lists some key parameters for five well-known extrusion models.

Vention currently offers six extrusion sizes. Our 45 mm series of extrusions suit many applications, from industrial furniture to robot range extenders. There are three sizes of extrusions using 45 mm increments—45 x 45 mm, 45 x 90 mm, 90 x 90 mm and 180 x 22.5 mm—all share the same mounting hardware.

Our light-duty extrusion profile, 22.5 x 22.5 mm, is useful for applications with low loads and low weight limits. See the following table for a detailed breakdown of each profile’s properties.

45 x 45 mm Light Duty Extrusion

The new 45 x 45 mm Light-duty (ST-EXT-101-XXXX) is Vention’s newest offering extrusion profile, allowing for an alternative 45 x 45 profile that is perfect for applications with lower loads and weight limits. With a profile area reduction, and in turn weight per 45mm length, of 31% the 45 x 45 Light-duty offers a best in class balance between the lightweight nature of the profile and the structural rigidity based on weight. 45 x 45 Light duty extrusions are identified with a Light Duty informative label.

Tabletop Extrusion

The 22.5 x 180 mm tabletop aluminum extrusion is perfect for workstation table tops, CNC worksurfaces, machine-tending workstations, and more. It provides a large mounting surface with evenly spaced t-slots, which are ideal for modular jigs and fixtures.

The tabletop extrusion t-nut profile, v-grooves, and spacing follow Vention standards, making it compatible with all gussets, assembly plates, and frame accessories.

Although only 22.5 mm thick, this extrusion is still capable of supporting robots that produce Nm of e-stop torque (Yaskawa HC10 for instance). That is, as long as support extrusions are installed running perpendicular to the tabletop. For maximum strength, these joists should be placed a maximum of 315 mm apart (distance L) and attached firmly attached to the machine frame.

When simply supported a table top extrusion of mm length can support a load of 100 kg. For increased load capacity add supports at consistent intervals.

To mount the tabletop extrusion flush with 45 mm extrusions, use the 67.5 mm gusset (ST-HP-003-). In order to achieve the proper spacing, a 45 x 90 mm or 90 x 90 mm extrusion is required.

Tabletop extrusions have a total of nine t-slots, which allow many different mounting options.

Calculate the safety factor

You must always add an adequate safety factor (SF) for your situation. For instance, if a structure will theoretically fail at N of force, a safety factor of two would establish an allowable load limit of 500 N. Safety factor is a measure of how confident you are of your calculations.

Safety factors should be based on (but not limited to) the following variables:

• Calculation accuracy and thoroughness.

• Environmental conditions.

• Consequences of failure.

• Cost of overbuilding.

Important :

Determine safety factors according to your industry’s standards. Always increase the safety factor if there is any risk of injury occurring due to system failure.

Calculate bending stresses

To evaluate whether a profile meets your design requirements, use free body diagrams and basic static calculations to estimate the applied load on the structure. Do the same for each individual extrusion.

Once determined, use the formulas below to calculate the maximum deflection and bending stress for each of your application-critical extrusions.

Where:

Compare the max bending stress with the material’s yield strength to estimate your extrusion’s capacity to withstand the required load. For Vention’s V2 -T5 aluminum extrusions, for example, a calculated bending stress of 65 N/mm2 is well below the material’s 240 N/mm2 yield strength.

Remember, however, that this is only an estimate, since it does not account for other important factors like the extrusion’s own weight and shear stress.

Calculate buckling strength

When calculating the strength of a structure it is important to consider buckling. Buckling occurs when a long vertical beam is compressed by a force. The beam tends to bend outwards, which further reduces its structural integrity, leading to sudden failure. This failure is most likely to happen with vertical beams, because the load due to gravity is larger than the other forces acting on the structure.

Calculate the max allowable buckling load using Euler’s critical load formula. First, determine which end conditions match your scenario based on the joint types. Then use your chosen extrusion profile’s column length factor and area moment of inertia to calculate maximum load capacity.

Third, compare the max load capacity to your expected force from a free body diagram, and determine the safety factor. Your safety factor should exceed standards for your industry.

2. Choose the right joint configuration

Selecting the right extrusion profile is only part of an effective structure. The assembly joint configuration can also substantially change the rigidity and structural integrity of a design.

Avoid relying on friction-based joints to support the load. Instead, position one extrusion on top of another, as shown below. Force is transmitted directly from the horizontal extrusion to the vertical extrusion increasing strength.

❌ Friction joint (not recommended): Lower strength; force transmitted through friction between plate and extrusion.

✔️ Reaction force-based joint (recommended): High strength; force transmitted directly to the frame via contact with vertical extrusions.

When friction-only joints are unavoidable, the strength of the joint is dependent on the number of fasteners multiplied by each fastener’s friction force. Each Vention M8 fastener (the type used in extrusions) can support N in friction.

In the friction joint example above, each fastener can generate 2,100 N of friction when tightened to 13 Nm, the horizontal beam can support a maximum load of 12,600 N (that is, 2,100 N per fastener x 6 fasteners). Consider the total amount of force needed to support your desired load, and divide it by N to find the number of fasteners you will need. This number will tell you which size assembly plate to choose, from one-fastener plates to eight-fastener plates.

Calculating the necessary assembly plate size is a great way to optimize the cost of your design. You might be tempted to choose the strongest assembly plate available, but you can save costs by going with one that only fits the amount of fasteners you need (and no more). Our application engineers routinely reduce costs by up to 15% just by replacing six-, seven-, or eight-fastener assembly plates for ones with fewer fasteners.

If possible, transform a friction-only joint into a stronger three-way joint by threading one of the fasteners directly into the extrusion’s end. By uniting three different extrusions in such a configuration (i.e., one vertical and two horizontal), none of the plates depend on friction alone.

✔️ Strong three-way joint: one bolt threads directly into the end of the extrusion.

❌ Weak friction-only joint, bolt does not thread into the extrusion end. (These are sometimes unavoidable.)

In some cases, joints may undergo a force that pulls the bolt and t-nut out of the extrusion. The extrusion’s resistance to this force is what we call “pull-out strength.” This “ultimate strength”—the point at which complete failure occurs—is given on a per-fastener basis.

For Vention V2 extrusions, the ultimate strength is 16.7 kN. However, designs should not be based on this value, because even much lower values can permanently damage the extrusion.

We recommend a design value of 7.2 kN per fastener. This value is lower than the material’s yield point, so no permanent deformation will occur. As with all design values, remember to apply a safety factor.

Ultimate strength is also affected by the direction of load. Whereas bolted connections under tension will fail when the pull-out strength is exceeded, compressed connections can withstand much higher loads, because the force is directly supported by the extrusion. As shown below, placing the assembly plate correctly with respect to the load will maximize strength.

Max load is 2 x 7.2 kN, because two bolts are sharing the tensile load.

Max load is just 1 x 7.2 kN, because one bolt is supporting the entire tensile load.

3. Use high-strength extrusion systems for demanding applications

Combining effective assembly joints with the appropriate extrusion profile can improve the structural integrity of your assemblies. For heavy-duty or precise applications, Vention’s high-precision assembly plates (part numbers ST-HP-XXX-XXXX) feature a patented V-shaped boss (protrusion) on the plate underside.

• Eliminates angular misalignment, because it is no longer necessary to locate plates by their screw’s loose clearance holes.

• Increases slippage resistance, by converting friction-bonded joints to structurally bonded joints.

Many plates come in GP (general purpose) and HP (high precision) variants. Your choice depends on whether you want to optimize for lower price (GP) or higher strength and precision (HP).

4. Structural joint design guide

Use the following tables to determine the strength of single sided jointed connections when subjected to moment, torsion and friction forces. The values are valid for the following assumptions:

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1. For moment loading, the load is created by a vertical force applied on a beam mm from the joint.

2. All bolts are assumed to be torqued to 10-13Nm.

3. For friction loading, the load is created by a vertical force directly on the joint, with negligible torsion or moment.

4. Given values are valid for structural extrusions: ST-EXT-001-XXXX, ST-EXT-002-XXXX, and ST-EXT-005-XXXX.

5. Values indicate when permanent slippage or plastic deformation begins to occur. This is the point where permanent damage starts, and should be avoided by using a safety factor.

Important :

Determine safety factors according to your industry’s standards. Always increase the safety factor if there is any risk of injury occurring due to system failureA safety factor of 4-5 is suggested.

*: These configurations assume no contact between the extrusions, which is common in assembled structures.
**: This configuration is more dependent on a buckling failure mode than friction. Use the calculation methods for buckling shown in Section 1 of this .
***: The values for these configurations are for joints fixed by an assembly plate on a single side.

Conclusion

Aluminum t-slot extrusions have become a compelling alternative to welded steel for many applications, but they require a few design considerations. If you need any help with your project, or simply want to confirm some design parameters, you can ask our team of application engineers for free using Vention’s live chat or us at:

Vention V1 extrusion properties

As one of the most established fabrication techniques, it’s not strange to find aluminium extrusion applications all around, from every-day-life to high-end uses.

Releasing an aluminium extrusion part into the market encompasses a multistage development process, typical of mass production manufacturing processes. Therefore, experienced developers strongly recommend prototyping from the early stages to enable a smooth flow between design, tooling, and final production.

For this reason, aluminium extrusion companies are increasingly engaging FDM machines in their prototyping processes to provide more confidence in the design before committing to tooling costs.

This article will point out some of the basic concepts surrounding the development of aluminium extrusions from design throughout mass production. Then, we’ll evaluate why and under what conditions it is worth investing in 3D printing as a prototyping tool.

What is Aluminium Extrusion? Why Use It and Where?

Aluminium extrusion is a forming process where an aluminium billet is pushed past a die mould with immense pressures to shape it into a part with a characteristic cross-sectional profile.

As a material, aluminium has one of the highest weight-to-strength ratios among metals. Its extraordinary ductility makes it an incredibly friendly material to work with in forming, casting and cutting processes. Additionally, aluminium alloys are non-magnetic, and their properties excel at corrosion resistance, high electrical and thermal conductivity and recyclability. For these reasons, aluminium alloys have been one of the favourite options in engineering applications for several decades.

Extrusion processes are highly demanded, given their low costs and fast turnaround times for custom and mass production requirements. The resulting profiles can meet precisions for applications with tolerance requirements as tight as +- 0.1 mm.

Some of the best-known applications for aluminium extrusions are:

• Structural: Widely employed for all kinds of structural frames, common in architectural and industrial settings. Given aluminium’s excellent strength-to-weight ratios, these frames are fundamental in aircraft and land vehicles. It is also worth mentioning that these structures ar common in 3D printer frames!
• Heat sinks: Common in HVAC, electrical and electronic devices
• Highly corrosive environments, namely in the marine and chemical industries

The Aluminium Extrusion Process

Once initial investments are met, this process is relatively low cost and straightforward. Let’s quickly overview its core stages.

1. Preheating: Around 400 to 500 C, but it can alternatively be a cold process
2. Extrusion: An hydraulic ram pushes the billet throughout the die at extreme pressures until the material achieves enough plasticity to flow throughout the cavities (As toothpaste would from a tube)
3. Quenching, cutting, stretching and ageing: At controlled rates to achieve optimal mechanical strengths, relieve internal stresses and achieve higher temper grades.
4. Inspection: Extrusions commonly undergo inspection processes to verify tolerances
5. Post-processing: Extrusions are friendly to many additional techniques like grinding, polishing, painting, powder coating, anodisation and welding.

Die Tooling

Considering the high pressures and temperatures, plus the numerous cycles die tools must bear, they are naturally made of alloys like H13 steel. These tools consist of a stack of round plates with cavities. There’re two kinds of plate arrangements: Solid profile dies and hollow profile dies.

Solid profile dies consist of a feeder plate to control the flow of aluminium, followed by the die plate containing the profile and a backer and a bolster plate to support and protect the other plates from failure. Alternatively, an additional mandrel-cap die set is necessary to produce hollow profiles. Processes like turning, CNC milling, wire EDM and grinding are commonplace in die plate production.

Aluminium extrusion dies offer favourable fabrication costs, ranging between £400 and £, within a few weeks lead times. In comparison, tooling costs can generally cost above £ and take several months to complete.

An extrusion die receives thousands of tons of pressure, which takes a toll on the die and ultimately leads to failure—having the correct design decisions optimally balances your die’s cost and life.

Design Considerations for Aluminium Extrusion

So, what should you consider in your profile design before submitting it to manufacturing? Thankfully, the range of possibilities for extruded profiles is wide. However, having a clear understanding of design for manufacturing rules is key to a successful and cost-effective product. Before starting an aluminium extrusion production, the following design considerations are essential to know.   

Standard vs Custom

The aluminium extrusion process enables enough versatility to produce many shapes, from the standard profiles (i.e. rod, tube, square, L, T, I, C shapes) to complex custom designs. As designs grow in complexity, developers and manufacturing shops face challenges, escalating risks of failure and increased tooling and extrusion costs.

Solid vs Hollow

As stated before, an additional mandrel-cap plate is necessary to produce hollow features. In terms of costs, solid die costs are around £400-, while a hollow one can cost from £.

Moreover, there’s a third semi-hollow classification. An excellent example of this is the fin features of a heat sink, and the hollow space between each fin is called a tongue. The tongue ratio is the relation between the length and the thickness of that void area. Issues arise as this number increases. Since we must consider the extreme pressures a die must undergo, the higher the tongue ratio, the result becomes prone to:

• Wavy surfaces

• Die breakage, or at least a shorter life
• The extrusion might have to go slower

An ideal tongue ratio must go below 4:1.

Symmetry

Designers must strive for as much symmetry as possible. The more asymmetric the shape, the higher the unbalanced weight distribution, ultimately causing:

• Die breakage at large mass sections
• Pushing the material slower is also necessary
• Difficulties in holding dimensional tolerances
• Runout surfaces can’t hold flatness specifications
• Bowing in the centre

Wall thicknesses

Some considerations regarding wall thickness are:

• Strive to avoid thin walls
• Wall thickness should be +- 10% of nominal thickness
• Look for walls as uniform as possible. Variable wall thicknesses lead to variable velocities as the material flows through the die.
• Sharp corners are not ideal, but, if needed, budget costs might rise

Tolerances

Tolerance specification is needed because no dimension or measurement is exact, and it depends on machinery design and human factors. For this reason, international standards exist to control deviations and potential manufacturing errors.

The following standard guides enable a clear framework regarding design and tolerance decisions for aluminium extrusion:

• The BSI BS EN 755 standard
• Aluminium association’s Aluminum Standards and Data
• AEC’s Aluminium Extrusion Manual

In some cases, custom designs require to achieve precisions beyond the standard tolerances. For instance, profiles intended to fit interlocking features must deal with tighter requirements. Fortunately, this is possible to achieve. However, it comes with additional corrections, costlier and more time-consuming inspection tasks, slower extrusions and increased rejection rates. In other words, as a design’s customisation level increases, not only does a project become costlier, but also your process becomes highly uncertain.

At the end of the day, communication is vital when it comes to dimensions and tolerances. Unclear communication between designer and workshop leads to costly misunderstandings. Beyond avoiding incomplete drawings and inconsistent dimensioning, it’s highly beneficial to transmit the big picture regarding intended functionality and how the extrusion interacts with other parts so that manufacturers can be on the same page.

Other Considerations

Although alloys are beyond the scope of this article, it’s worth mentioning that alloys composition and temper designations also affect tolerances, extrusion rates, costs and the process in general.

Lastly, the profile size is a crucial factor to take into account. The diameter of a circumscribed circle determines the size of a profile, thus tolerancing and costs.  

How Does a 3D Printer Help?

Knowing the many variables involved throughout the aluminium extrusion development process, it is clear that accuracy is a major concern as the complexity of the design increases.

Investing in prototypes early in the design process enables decision making clarity and smooth bridging into manufacturing. For more information on prototyping, click here.

Prototypes can help you answer the following questions:

• Will my design work the way I thought it would?
• Can I lower my extrusion costs through a design change?

A 3D printed profile is a great way to assess your design and verify whether it’s going to work. Having a physical representation of your design at hand enables you to visualise and quickly identify if any adjustments are necessary before any tooling commitments.

Making assertive changes to the design early on is a great way to prevent tolerancing issues as you go forward. With a 3D printed profile, you can actually feel and test in a real-life setting potential problems that can be unpredictable on paper, such as weight distribution and fits.

Again, communication is of utmost importance. Having a tangible representation of an intended profile is an excellent way of communication between all the parts involved in production.

Recommended Printers for Aluminium Extrusion Prototyping

Thankfully, it’s possible to prototype extrusion profiles with almost any FDM machine. However, investing in a high-quality printer is a must to avoid potential and costly errors. Since tolerances are vital under this context, an ideal printer must excel at dimensional accuracy, repeatability and ease of use.

The following three examples are among the best and most reliable professional 3D printers currently available in the market.

Raise3D Pro 2 Plus

As a larger version of the Raise3D Pro 2 , this machine is designed to run continuously with 24/7 reliability. The Raise3D Pro 2 Plus is equipped with multiple fail-safe systems, such as:

• An integrated battery keeps your print paused and ready to restart after a power brake
• Fast and reliable electronic lifting nozzles
• Best in class 32-bit controller enables fast, smooth and precise movement

Specs:

• Build volume:  305×305×605 mm
• Nozzle: 0.2/ 0.4/ 0.6/ 0.8/ 1.0 mm
• Accuracy: 5 μm repeatability
• Price: £4,499.00 ex. VAT

Bigrep Pro

This machine is all about bulk and size. Equipped with industrial-grade components, the Bigrep Pro can print large parts with outstanding speed and precision. Some of its most notable features are:

• A state-of-the-art Bosch CNC control system
• The Metering Extruder Technology (MXT®) enables further speed and precision
• An enclosed build chamber and temperature-controlled filament chambers

Specs:  

• Build volume:  x 970 x 985 mm
• Nozzle:  0.6 mm, 1.0 mm
• Accuracy:  ±0.2mm or ±0.002mm/mm
• Price: Request quote

BCN3D Epsilon W50

Besides their reliability, BCN3D printers are best known for their IDEX technology, an independent dual extrusion system that enables duplication and mirror mode printing, doubling productivity for the same price. The Epsilon W50 is at the top of BCN3D products. Some of its most notable features are:

• IDEX Technology
• Bondtech Extruder: High-tech dual drive gears
• Hotends optimised and manufactured by E3D

Specs

For more information, please visit aluminium extrusion prototyping(ar,pl,af).

• Build volume: 420mm x 300mm x 400mm
• Nozzle: Brass: 0,4mm/ 0,6mm/ 0,8mm/ 1,0mm
• Resolution: 1,25μm/ 1,25μm/ 1μm
• Price: £6,575.00 ex. VAT