The Cutoff Machine
Fig. 15: 4 Post Mechanical Cutoff Press
To realize the maximum production capabilities of a roll forming machine, including continuous operation and the improved product consistency available by feeding coiled stock, a cutoff machine becomes an important part of the complete roll forming system. The machine in most general use is similar to the 4-post model on Figure #15 and might be pictured as an under-driven press with rails fastened to the bolster plate and to the ram. The flying cutoff die is free to slide on the rails from right to left. These machines function to cut the formed section to length as it exits the roll forming machine without stopping the forward progress of the section.
The section passes through the die and travels along a runout table until the desired length is measured, either via a rotary encoder, photo-eye, limit switch or a positive (mechanical) stop. This target initiates the cutting cycle, and during the period of cutting, the die moves from right to left on its slide rails. Once the cut is completed, it returns automatically to its starting position. This is the most simple form of operation. However, the cut length tolerance can be very broad, depending on line speed, the type of cutoff press, and method of length control employed.
Other methods of actuation for a cutoff operation include:
- Open Loop Measuring System with rotary Encoder
- Closed Loop Measuring System with rotary Encoder
- Mechanical piloting or pickup on a prenotched area triggered by a limit switch.
Line Speed vs Length Tolerance graph
Machine Base Mount Hydraulic Cutoff
A general illustration of the length tolerance as a function of line speed and method of length control is shown in the above figure. Diving into greater detail on the subject would call for a larger discussion, but there are a few considerations to note off-hand. Cutoff performance, die design, triggering method, die acceleration, and material handling all influence rolling machine speeds, the lengths that can be cut, the length tolerance that can be maintained and the investment dollars involved. Be sure to realistically evaluate the available budget and potential the end-use requirements to make a proper decision for long-term investment.