Aluminum is a popular metal used for many applications, from vehicle bodies and airplane parts to consumer products. It’s lightweight, corrosion resistant, and easy to form into complex shapes. This makes aluminum an ideal material for projects where weight savings or intricate forms are needed. However, aluminum’s properties also make it more challenging to bend and shape than other metals like steel. So can you actually bend aluminum using a standard brake or bending machine? Let’s take a closer look at how aluminum behaves when bent and what’s required to successfully form it without cracking.
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The Challenges of Bending Aluminum
There are a few key challenges that need to be addressed when bending aluminum:
Aluminum Work Hardens Rapidly
When aluminum is bent, the metal on the outside of the bend is stretched while the inside layer is compressed. This distorts the aluminum’s crystalline structure, causing it to rapidly work harden. The more the aluminum is shaped, the stiffer and more brittle it gets. Work hardened aluminum can develop small cracks or fractures if bent too far, making it more likely to fail down the road.
Aluminum Springs Back Easily
Due to its low modulus of elasticity, aluminum springs back towards its original shape after bending more than other metals like steel. The higher the degree of the bend, the more aluminum will try to spring back straight once released from the brake. This makes it difficult to achieve accurate bend angles.
Aluminum Has a Large Grain Structure
The crystalline structure of aluminum has a larger grain size than other alloys. The boundaries between these grains are weak points that can cause cracking when bent. Fine cracks also reduce the strength and fatigue life of the aluminum.
Aluminum Conducts Heat Rapidly
Heat is generated when aluminum is shaped at the point where the work piece contacts the brake dies. Aluminum conducts this heat away from the bend location much more quickly than other metals. Localized overheating at the bend can be an issue, resulting in a loss of temper and reduced strength.
Bending Aluminum Safely
Taking the above challenges into account, here are some tips on how to successfully bend aluminum in a brake:
Use a Roller Bending Machine
A standard brake press generates high stresses at the bend point that can fracture the aluminum work piece. Using a roller bending machine is a better option for shaping aluminum. The rollers apply gradual pressure across a wider section of the aluminum, resulting in less concentrated stress. This allows the aluminum to be formed without cracking or fracturing.
Employ Proper Tooling and Dies
The brake tooling must be shaped correctly to avoid deforming the soft aluminum during the bend. Die inserts help prevent deformation but must have the appropriate radius at the bend point. Using too small of a radius will concentrate the forces and weaken the aluminum. The proper size radius for aluminum is typically 2-3 times the material thickness.
Use the Right Aluminum Alloy
Certain aluminum alloys are more formable and less prone to cracking. Alloys like 5052 or 3003 are excellent choices for bending and shaping. The aluminum should also be the proper temper with optimal ductility. Full hard aluminum alloys may be too brittle for extensive bending.
Pre-Stretch the Aluminum
Pre-stretching the aluminum sheet across the grain up to 1% before bending can help prevent failure at the bend location. This counteracts work hardening and allows the material to bend further before reaching its maximum elasticity.
Use a Heating Source
Warming the aluminum sheet to 250-650°F prior to bending can help improve its pliability during forming. This reduces the force required to bend the aluminum and provides more flexibility when setting the bend angle. Use care not to overheat a localized area which can reduce strength.
Start With a Gentle Bend and Re-strike
Trying to achieve the full bend angle in one shot can fracture the aluminum. Make gentle bends in multiple pressing steps, releasing the material between bends. This allows the aluminum to soften before the next bend iteration. Re-striking the material several times is key to successfully bending aluminum without failure.
Factor in Springback
The tendency for aluminum to spring back after bending requires compensating for this elastic recovery. Increase the bend angle slightly past the desired amount to account for springback. The thicker the aluminum gauge, the more spring back you’ll experience. You may need to over-bend the material several degrees more than the target angle.
Use Alignment Stops
Proper metal alignment in the brake is critical to avoid deformation along the bend line. Inserting stops at the correct width before bending provides better control over the aluminum’s positioning in the brake. Keeping the material aligned prevents uneven or concentrated stresses.
Bending Aluminum Tubes, Rods and Bars
In addition to sheet aluminum, bent aluminum tube and rod can enable complex shapes for hand railings, frames, mechanical parts and more. Here are some tips for bending structural aluminum successfully:
Use a Mandrel for Round Tubing
Trying to bend round aluminum tubing without support will often crimp or flatten the tube rather than create a uniform bend. Using an internal mandrel provides even support of the tubing walls during the bend. Mandrels are tapered and lubricated to easily slide through as the aluminum tube is shaped around the die.
Fill the Tubing with Fine Sand for Tighter Bends
An alternative to using a solid mandrel is filling the aluminum tubing with fine sand before bending. Packing the tubing with sand supports the tubing walls evenly when bent to a tight radius. Make sure to fully seal the ends of the tubing to contain the sand.
Heat Round Stock Evenly
When bending aluminum rods or bars, it’s important to heat the full material first to improve ductility. Uneven heating can cause an unpredictable bend location or create weak spots in the aluminum. Heating round stock creates uniform thermal expansion for a controlled bend.
Wrap Bars and Rods to Prevent Flattening
To help retain the round cross section when bending, wrap ductile steel, copper or other soft wire around aluminum rods and bars prior to bending. The wrap metal will stretch on the outer portion of the bend while supporting the inner radius to resist flattening or distortion. Use multiple layers for thicker stock.
Lubricate the Bending Area
Just as with sheet aluminum, lubrication is critical when bending aluminum tubes, rods and bars. Generous lubrication of both the material and die contact areas reduces galling and allows the aluminum to flow smoothly around the radius. Use soap, oil, wax or specialty bending lubricants.
Bending Aluminum Extrusions
Aluminum extrusions create unique profiles that are popular for structural frames, machine guards, railings and custom trim. Here are some key tips when bending extruded aluminum:
Know the Extrusion’s Alloy and Temper
Extrusions are produced from various aluminum alloys, with 6061, 6063 and 6060 being most common. Ensure the alloy has adequate formability and ductility to avoid cracking. The temper should also have optimal strength and toughness for bending. Contact the extrusion supplier if you have questions.
Pre-Stretch and Pre-Bend to Relieve Stresses
Due to how the extrusion process work hardens the aluminum, some stress may be locked into straight sections. Gently stretching and reverse bending a small amount before the major bend can help relieve these stresses. This reduces the risk of failure or uncontrolled deformation during the bend.
Support Internally With Fillers or Mandrels
Inserting filler materials or mandrels into hollow sections provides internal support. This prevents collapsing and controls deformation when bending extrusions with open profiles. Cork, polymer foam, sand and low melt alloys make good internal supports.
Use a Step Bending Process
Due to their unique shapes and locked in stresses, extruded profiles should be bent incrementally in multiple steps. Make progressive small bends rather than the full bend at once. This allows the aluminum to gradually deform while minimizing surface marring, crimping or flattening of sections.
Clamp Multiple Points for Complex Bends
Longer extrusions or those with off-center bends may require clamping at various points to isolate the bend area. Prevent uncontrolled movement of unclamped sections by securing strategically along the length. Use soft clamping materials to avoid surface marking.
Choosing the Right Aluminum for Bending Applications
When working with aluminum, choosing the optimal alloy and temper for bending is critical to avoid cracking or fracturing. Here are the most popular options:
3003 Aluminum
3003 aluminum is an excellent general purpose alloy due to its good formability, weldability and corrosion resistance. It can be bent to tighter radii than other alloys while still maintaining its strengths. 3003 aluminum sheet is commonly used for chemical tanks, truck and trailer bodies, architectural paneling, etc.
5052 Aluminum
Known for exceptional ductility, 5052 aluminum can undergo extensive bending operations while retaining uniformity across complex forms. Bend testing has shown virtually no cracking occurs with the proper 5052 temper. This bendable aluminum is found in electronic chassis, solar panel frames, pneumatic cylinders, etc.
6061 Aluminum
The 6061 aluminum alloy has better strength than 3003 and 5052 while still remaining fairly bendable if the proper T4 or T6 temper is used. Care needs to be taken to control cracking, but it can be used for moderate bending requirements. 6061 aluminum sees use in truck and marine frames, pipelines, aerospace applications, etc.
6063 Aluminum
Commonly used for architectural profiles, 6063 aluminum extrusions can achieve successfully bent components with controlled deformation. Good extrusion quality and proper filler support provides reliable performance in bent railing, framing and trim components.
Bending Aluminum Safely
When working with any metal material, proper safety precautions need to be followed. Here are key tips for safely bending aluminum:
Wear Eye Protection
Use safety glasses or a face shield when bending aluminum. Fractured work pieces can generate flying debris or sharp burrs that could cause eye injuries. Make sure nearby personnel also wear eye protection.
Use Proper Gloves
Wearing tight fitting gloves provides grip while handling aluminum stock and protects if sharp edges are encountered. Leather or mechanics gloves are ideal choices. Avoid loose gloves that could get pulled into moving machinery.
Clean Up Oil or Grease Spills
Lubricants are commonly used during aluminum bending to prevent galling and aid forming. Be sure to immediately clean up any slippery oil or grease spills from machinery and work areas to prevent slip and fall hazards.
Prevent Muscle Strain
Bending aluminum stock can require extensive force when maneuvering sheet and working machinery. Use proper lifting techniques and get assistance moving heavy materials. Take breaks as needed. This helps avoid muscle strains or back injuries.
Secure Long Work Pieces
Long aluminum bars, rods or extrusions should rest on proper supports when working on them. Use extra care when bending longer stock to prevent uncontrolled whipping action if slipped out of position. Secure the material and control the bend progression.
Remove Burrs and Sharp Edges
Freshly sheared or bent aluminum can have very sharp edges. Removing these burrs and honing edges helps prevent painful cuts. Be sure to deburr aluminum before handling extensively or installing bent assemblies.
Conclusion
Bending aluminum with a standard brake press is possible but presents some unique challenges compared to other metals. The rapid work hardening, spring back and cracking tendencies of aluminum means special tooling and processes should be used. A roller bending machine with the proper diameter rollers, along with additional steps like pre-stretching, heating and progressive bending, allows aluminum to be shaped without failure. Proper part support and controlled deformation are key when bending aluminum tubes, rods, bars and extrusions. With attention to alloy selection and temper, correct tool geometry, and supporting the work piece, aluminum can be successfully bent to meet most applications. Using the right safety precautions provides protection when working with aluminum material. Understanding the properties of aluminum and following the proper procedures allows for repeatable bending results.
| Alloy | Key Properties |
|---|---|
| 3003 | Good formability and corrosion resistance |
| 5052 | Excellent ductility, bendable |
| 6061 | Medium strength, moderate bendability |
| 6063 | Used for architectural extrusions |