Pre-cut vs. Post-cut

When it comes to producing length-specific formed parts, there are two roll forming line options

YOU CAN ALSO LISTEN TO THIS ARTICLE

A common question many fabricators face when choosing a roll forming process is if a pre-cut or post-cut roll forming line might be best for business. While shop needs vary in terms of roll forming layout, there are several aspects that affect the decision between a pre-cut and post-cut system to create length-specific formed parts.

Pre-cutting involves cutting the steel coil with a shear before it enters the roll former, whereas post-cutting is where a profiled shear cuts the sheet after it is formed. Both methods have their advantages, so the choice comes down to production requirements.

Bradbury developed the Boss high-speed, closed-loop flying shear with a variety of state-of-the-art features for high-production rates with close tolerance shearing.

Pre-cut advantages

The advantages of a pre-cut roll forming line include the fact that cutting in the flat allows the shear to seamlessly feed roll formers with various profiles, eliminating the need for blade changes. This makes pre-cut roll forming lines perfect for running multiple profiles on the same line. This includes Cee and Zee purlin lines; double-high, rafted roll forming lines; or standing seam lines with multiple width variations.

Also, a pre-cut shear allows for higher production lines. Whether the machine accumulates steel in a pit for continuous shearing or utilizes a rotary shear, production rates are significantly increased. For instance, a Boss pre-cut rotary shear can run metal building panels at impressive rates of 300 ft./min. While a post-cut flying shear can achieve similar results, it often requires a higher investment.

With a pre-cut shear, the flat blades are reversible and can be used on all four sides before requiring sharpening.

For situations where flat sheets must be produced by a secondary operation, a conveyor can be incorporated after the shear, so blanks can be easily removed before entering the roll former, streamlining the process.

Finally, a pre-cut shear is specifically designed to shear a flat pattern, allowing for seamless integration of various features in the end profile, such as notching, holes or tabs.

Shown here, a punched and notched piece of metal enters the equipment to be sheared. 

Post-cut advantages

One advantage of a post-cut roll forming line is that post-cutting doesn’t require minimum length requirements because the roll former is always filled with material, which is beneficial with short sheets for soffit, wainscot or panels for press-formed ridge caps. Additionally, there is no need to invest in a separate cut-back shear, reducing the need for additional part handling.

Post-cut machines typically have a smaller footprint compared to other equipment. They eliminate the need for an entry conveyor as the infeed table is directly mounted on the entry of the roll former, making them more space efficient and streamlined.

Alignment concerns are greatly reduced as the roll former remains consistently filled with material and enclosed within the tooling during production.

Tooling wear is minimized in post-cut machines for a couple reasons. Because it doesn’t require powered upper tooling passes to drive the sheet, the tooling can rotate freely. This simplifies the control of mismatched speeds in the roll tooling during part formation and reduces tooling wear. And, because the machine is filled with steel after thread-up, there is no leading edge of steel entering each pass, further reducing tooling wear and ensuring long-lasting performance.

Finally, another benefit is the reduction in end flare on the part, as the profile is formed first and then sheared.

Technical advancements

With advancements in technology, pre-cut and post-cut roll forming lines have become effective and efficient configurations. Servos and closed-loop controls have revolutionized post-cut flying shears, providing them with increased speed and accuracy. Moreover, anti-flare fixtures can now be controlled by servos, allowing a pre-cut line to achieve comparable flare tolerances to a post-cut line.

In fact, some roll forming lines are equipped with both pre-cut and post-cut shears, and with advanced control features, the entry shear can make the final cut of the order, eliminating the scrap traditionally associated with post-cut lines. This technological progress has truly transformed the process, making it more efficient and sustainable than ever.

The Bradbury Group

Get industry news first
Subscribe to our magazines
Your favorite
magazines
under one roof