The Benefits of In-Line Punching & Cutting in Roll Forming
Ryan Hernden
In this blog, we discuss the process, benefits, and use cases of in-line punching and cutting within a roll forming manufacturing operation.
In this blog, we discuss the process, benefits, and use cases of in-line punching and cutting within a roll forming manufacturing operation.
Roll forming is a continuous process where a profile is put into a strip of raw material. After forming, the strip is cut into lengths for storage and transport. If those lengths need holes or other features, which can add value for the customer, they are best put in before the strip is profiled (called pre-punching) because it’s easier and avoids the cost of a secondary operation.
Punching is a method of removing material from a strip or a sheet. The process is done at an in-line punching station, which sits between the coil or strip straightener and the first of the profiling rollers. The punch station features a punch and die set positioned above and under the strip, respectively. The punch is pushed down through the material held by the die, creating a shearing action that cuts through the strip.
Punching can produce a wide variety of shapes, from circular holes to slots, notches, and tabs. Punching can also be used to apply a deformation without shearing the strip.
Punching needs precise positioning of the punch and die on either side of the strip. This is why it’s easier to do it before profiling while the strip is flat.
Roll forming works best when the strip moves at a constant speed. To avoid the need to stop and start as the punch penetrates the strip, the punching station must move at the speed of the strip as the punch and die go up and down. Accordingly, in-line punching stations incorporate mechanisms that provide this synchronized motion.
In-line punching ensures more accurate feature placement than when attempting to add them after forming. This is because punch movement is synchronized with strip speed, ensuring highly repeatable longitudinal placement. It also eliminates any inconsistency that could result from material springback after forming.
Punches can be given whatever shape is needed. They could be hexagonal, oval, elliptical, or any other form. Multiple punching stations can be combined to remove or deform material as required. Longitudinal spacing can be whatever is needed and can be varied as the strip passes through the station.
Features like slots and tabs can aid assembly operations by helping lock lengths together mechanically or positioning pieces for operations like welding.
Deformation can be used to apply features like date codes, product identification markings, or assembly guides, such as “TOP” or directional arrows.
Lateral indentations or deformation can be applied to increase the stiffness of cut lengths across their width. Adding dimples to the strip can also help improve stiffness.
Positioning features away from the regions of forming strain helps prevent cracking around the bends in service.
In-line punching improves material utilization in two ways:
Reasons for incorporating in-line punching in custom roll forming include:
If you’re designing products made from roll-formed material and want to include punched features, there are some points to be aware of. Strip stretches as it’s bent into a particular profile, which can have unanticipated consequences if feature size and positioning aren’t considered carefully.
More specifically:
Hole diameter must be larger than the thickness of the strip. Holes should not be placed so their edges are less than twice the strip thickness from a bend. Holes near edges should have a boundary of at least three times the strip thickness.
Notches must be wider than the strip thickness. A minimum width is 0.040 inches. Notch depth should be less than five times the width.
The width of a tab should be at least twice the thickness of the material. Its length (the distance it protrudes) should not be longer than five times its width.
Slots can deform when placed near a bend, so placement depends on the thickness of the material, the diameter of the strip, and the bend radius.
Slots should be placed four times the material thickness away from any bend, and the slot width must be greater than the strip’s thickness.
MMC Roll Forming specializes in producing high-quality profiled metal products made by the roll forming process. We have an extensive inventory of roll form tooling and we can produce a wide and varied range of profiles with special features, including holes, cutouts, and notches.
If you already have profiles designed, we can review those for you to identify any cost-saving or improvement options you may have missed. Alternatively, if you are still in the design phase of your project, we can provide engineering recommendations that may help you save money and improve product performance.
Please visit our blog for more roll forming resources or contact us today to learn more about our capabilities or to request a project analysis.