Hot Bending vs Cold Bending

 In custom metal forging, manufacturing capability, metal manufacturing

Bending is fundamental to modern manufacturing. Creating curves and twists in metalwork may seem simple, but complex bending processes demand a great deal of expertise from metalworkers. These processes divide into two types: hot bending and cold bending. Choosing between these types of bending is a hugely important step in the manufacturing process. Understanding the hot bending vs cold bending question can make or break your work, which is why we’ve created a guide explaining the two.

Hot bending basics

Hot bending, also known as induction bending and incremental bending, this technique relies on high heat to create bends. An induction bending machine induces local electrical heating on bars or pipes via an induction coil. The coil quickly and accurately heats the piece, allowing for specific bend angles to be efficiently produced. Though incremental bending typically creates standard bend angles, the heating process can also create bespoke structural shapes.

Within the scope of Greg Sewell Forgings, most of the bending operations are performed on solid round bars of steel. This may entail the bending of U-Bolts or the bending of J-Bolts and L-Bolts.

L-Bolts are usually used in concrete foundations and the L-portion of the bolt serves as a “lock” into the concrete. 

In achieving the above hot bends, the solid bar is usually locally heated within a specific temperature range, depending on the steel grade used. The heated portion of the steel becomes more pliable and a bending load is applied around some type of forming die or forming wheel/disc.

When to choose hot bending

If you’re bending fragile or high-tensile material, then hot bending vs cold bending is an easy decision. The size of a steel bar as well as its condition and grade are important determinants. The larger the diameter of the steel, the greater the bending loads. By heating the material, the bending loads are reduced considerably and therefore the size of equipment required is reduced.

However, one of the most important determinants for hot bending is whether the product is to undergo some form of surface treatment, such as hot dip galvanising. If the products are to be hot dip galvanised, then hot bending is definitely the choice of operation. The reason for this is to mitigate the possibility of hydrogen embrittlement due to the cold working (if cold bending is employed) or acid cleaning before galvanising. Hydrogen embrittlement can cause cracking and therefore result in catastrophic failure if not considered into the equation.

Radius or diameter of bend is also an important determinant and this is primarily dependent on the grade of the steel used. 

Cold bending basics

Cold bending creates curves without heating the materials you’re using. The process relies on physical force: you place the metal in a machine bed, wrap the piece around a set shape and apply a bending force. Once the bend reaches the required radius, cold bending is complete. Without heat, cold bending machines often result in a lower bending radius than hot bending counterparts, as the metal pieces are less pliable. Cold bending methods have distinct advantages. They create gentle curves, which can extend to 360-degree coils and 90-degree corners. Unlike hot alternatives, bending at room temperature strengthens metals.

There is a wide range of cold bending methods. Mainly, they refer to different machine beds, not different bending radii. Rotary Draw Bending is one of the most common techniques. In Rotary Draw Bending, steel pieces are drawn through rotating components in a purpose-built machine, bending as they go forward. Roll bending, another method, achieves comparatively larger bends and curves. The piece of metal is passed through three rollers in a pyramid shape, allowing metalworkers to surpass standard bend angles.

When to choose cold bending

Cold bending has multiple benefits. Speed is a simple advantage: as you work at room temperature, there’s no wait for materials to cool down. Another win in the hot-bending vs cold-bending matchup is cost. Cold bending processes are simple and require little fuel. These factors mean cold-bending is often the cost-effective option. Metalworkers also favour products of cold bending for their glossy finish. Cold techniques result in a smooth metal surface, often considered more aesthetically pleasing than hot bending works.

If the metal is in the form of mild steel and the bend radii are gentle, cold bending is a consideration. Also, the most important consideration in this field is that the final products do not require subsequent corrosion protection, such as galvanising, making cold bending the more economical option.

What we offer at Greg Sewell Forgings

Hot bending vs cold bending is an important question, so it’s crucial to have experts on your side. At Greg Sewell Forgings we offer a range of metalworking capabilities that we’ve built up working across Australia’s industries. We can tackle any job that requires hot bending and advise you on which technique best suits your requirements and material type. As one of Australia’s oldest forging operations, we’re partners you can trust.

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