In metal coil processing lines, the cutting system is a critical component that determines production speed, cut accuracy, and material utilization. Two primary cutting technologies are used in modern cut to length and roll forming lines: the flying shear and the stop start shear. Understanding the differences between these systems helps you choose the right solution for your production requirements.
What Is a Flying Shear
A flying shear, also known as a rotary shear or continuous shear, cuts the material while it is continuously moving through the line. The shear blade or cutting head travels along with the material at the same speed during the cut, then returns to its starting position for the next cut. This allows the line to run continuously without stopping for each cut, resulting in much higher production rates.
Flying shears use either a rotary drum with blades that rotate through the material, or a reciprocating blade that accelerates to match line speed. The cutting action is synchronized with the material feed using encoders and servo drives, ensuring precise cut lengths even at high speed.
What Is a Stop Start Shear
A stop start shear, also known as a stationary shear or batch shear, requires the material to stop moving before each cut. The material is fed to the required length, the line stops, the shear makes the cut, and then the line restarts. This cycle repeats for each sheet or part.
Stop start shears are typically hydraulic or mechanical presses with a fixed blade arrangement. They offer very high cutting force and can handle thick and high strength materials. However, the stop start cycle limits production speed and can cause wear on the drive system due to frequent acceleration and deceleration.
Key Differences Compared
The following table summarizes the main differences between flying shears and stop start shears.
| Feature | Flying Shear | Stop Start Shear |
|---|---|---|
| Material movement during cut | Continuous (moving) | Stopped (stationary) |
| Production speed | High (60 to 200 cuts/min) | Low to medium (10 to 60 cuts/min) |
| Cut length accuracy | Very good with servo control | Excellent (fixed position) |
| Maximum material thickness | Typically up to 6 to 8 mm | Up to 20 mm or more |
| Material strength | Medium to high | Very high |
| Equipment cost | Higher (complex servo system) | Lower (simpler design) |
| Energy consumption | Lower (no frequent acceleration) | Higher (stop start cycles) |
| Maintenance complexity | Higher (servo drives, encoders) | Lower (hydraulic or mechanical) |
| Footprint | Larger (requires travel space) | Smaller (stationary) |
Advantages of Flying Shears
The primary advantage of a flying shear is high production speed. Because the material does not need to stop for each cut, the line can run at maximum speed continuously. This makes flying shears ideal for high volume production of short to medium length parts.
Flying shears also produce less wear on the line drive system because there is no frequent acceleration and deceleration. This reduces energy consumption and extends the life of drive components. The continuous motion also results in more consistent material feeding and less chance of feed errors caused by slip during restart.
Advantages of Stop Start Shears
Stop start shears offer superior cutting force and can handle much thicker and higher strength materials than flying shears. The stationary blade arrangement provides a clean, square cut with minimal distortion, even for heavy gauge material.
Stop start shears are also simpler and less expensive to build and maintain. They do not require complex servo synchronization systems, and the hydraulic or mechanical drive is well understood and reliable. For low to medium volume production, a stop start shear offers excellent value.
How to Choose the Right System
The choice between a flying shear and a stop start shear depends on several factors.
First, consider your production volume. If you need to produce more than 50 to 60 cuts per minute, a flying shear is essentially required. For lower volumes, a stop start shear may be sufficient and more economical.
Second, consider your material specifications. If you process material thicker than 6 to 8 mm, or very high strength steel, a stop start shear is likely necessary because flying shears have limited cutting force. For thinner material at high speed, a flying shear is the better choice.
Third, consider your cut length requirements. Flying shears are excellent for short to medium length cuts where high speed is important. For very long sheets, the difference in production speed diminishes because the material feed time dominates the cycle.
Fourth, consider your budget and maintenance capability. Flying shears are more expensive and require more sophisticated maintenance. Stop start shears are simpler and more robust.
Integration with Your Processing Line
Both types of shears must be properly integrated with the rest of your processing line. For a flying shear, the key integration points are the feed encoder, the servo drive synchronization, and the material tension control. The shear must be able to accelerate to line speed, make the cut, and return to position without disturbing the material feed.
For a stop start shear, the key integration points are the feed stop accuracy, the clamping system that holds the material during cutting, and the restart sequence. The line must be able to stop quickly and accurately, hold the material steady during the cut, and restart without causing feed errors.
Frequently Asked Questions
- Can a flying shear cut thick material? Flying shears are generally limited to material up to 6 to 8 mm thick, depending on width and strength. For thicker material, a stop start shear is recommended.
- How accurate is a flying shear? Modern flying shears with servo control can achieve cut length accuracy of plus or minus 0.2 mm or better, comparable to stop start shears for most applications.
- What maintenance does a flying shear require? Flying shears require regular inspection of servo drives, encoders, belts, and bearings. The blade should be checked and sharpened periodically. Lubrication of the drive mechanism is also important.
- Can I upgrade from a stop start shear to a flying shear? In some cases, yes, but it requires significant modifications to the line control system and drive. It is often more cost effective to purchase a new line designed for flying shear operation.
- Which system is better for roll forming lines? For high speed roll forming of short parts, a flying shear or rotary cut off is preferred. For longer parts or thicker material, a stop start cut off may be more appropriate.
Conclusion
Flying shears and stop start shears each have their strengths and are suited to different production requirements. Flying shears offer high speed and continuous production for thinner materials, while stop start shears provide high cutting force and simplicity for thicker materials and lower volumes. By evaluating your production volume, material specifications, cut length requirements, and budget, you can choose the cutting system that best meets your needs. Work with an experienced equipment supplier to ensure the shear is properly integrated with your processing line for optimal performance.