Roll Forming Hydraulic & Cutting Engineering (Part 7): Flying Shear Physics, Blade Metallurgy & Dynamic Load Control

That transition is where most instability is introduced.

How a Roll Forming Machine Is Made — Part 7

Hydraulic System & Cutting Technology Engineering

(Flying Shear Physics, Blade Metallurgy & Dynamic Load Control)

Introduction — Where Continuous Motion Meets Instantaneous Force

Roll forming is continuous.

Cutting is instantaneous.

That transition is where most instability is introduced.

At the moment of cut:

• • Strip tension changes
• • Drive torque spikes
• • Frame experiences shock load
• • Hydraulic pressure peaks
• • Torsional oscillation increases

Poorly engineered cutting systems cause:

• • Length inaccuracy
• • Profile deformation
• • Gear wear
• • Bearing fatigue
• • Frame micro-movement
• • Noise spikes

This section explains the physics and control behind cutting systems.

1. Hydraulic System Engineering Fundamentals

Hydraulic systems in roll forming power:

• • Flying shears
• • Stop-cut shears
• • Punch presses
• • Notching systems

A hydraulic system must provide:

• • Adequate force
• • Controlled speed
• • Repeatable stroke
• • Pressure stability
• • Thermal control

1.1 Hydraulic Power Equation

Hydraulic power:

P=p×QP = p × QP=p×Q

Where:

• p = pressure (Pa)
• Q = flow rate (m³/s)

Power in kW:

P(kW)=p(bar)×Q(L/min)600P(kW) = \frac{p(bar) × Q(L/min)}{600}P(kW)=600p(bar)×Q(L/min)

Example:

Pressure = 180 bar
Flow = 40 L/min

P=180×40600=12kWP = \frac{180 × 40}{600} = 12 kWP=600180×40=12kW

Hydraulic motor must exceed this requirement.

2. Shear Force Calculation

Cutting force estimation:

F=τ×AF = \tau × AF=τ×A

Where:

• τ\tauτ = shear strength
• A = shear area

For mild steel:

Shear strength ≈ 0.8 × yield strength

Example PBR:

Yield = 350 MPa
Shear strength ≈ 280 MPa

Material thickness = 0.75 mm
Profile width = 914 mm

Shear area:

A=0.00075×0.914=0.0006855m2A = 0.00075 × 0.914 = 0.0006855 m²A=0.00075×0.914=0.0006855m2

Force:

F=280,000,000×0.0006855F = 280,000,000 × 0.0006855F=280,000,000×0.0006855

F≈191,940N≈192kNF ≈ 191,940 N ≈ 192 kNF≈191,940N≈192kN

Hydraulic cylinder must exceed 200 kN with safety margin.

3. Stop-Cut vs Flying Shear Engineering

Stop-Cut System

Process:

• • Line stops
• • Shear actuates
• • Line restarts

• Advantages:
• • Simpler
• • Lower cost

• Disadvantages:
• • Speed limitation
• • Profile distortion at restart
• • Production inefficiency

Flying Shear System

Process:

• • Shear moves with strip
• • Synchronizes speed
• • Cuts while moving
• • Returns

• Advantages:
• • Continuous production
• • Higher speed
• • No stop marks

• Disadvantages:
• • Complex motion control
• • Higher cost
• • Servo synchronization required

4. Flying Shear Motion Physics

Flying shear must:

1. Accelerate to strip speed

2. Match velocity

3. Perform cut

4. Decelerate

5. Return

Motion equation:

v(t)=atv(t) = a tv(t)=at

If strip speed = 40 m/min = 0.666 m/s

If shear acceleration = 2 m/s²

Time to reach speed:

t=0.6662=0.333st = \frac{0.666}{2} = 0.333 st=20.666=0.333s

Total cut window often < 1 second.

Control must be extremely precise.

5. Dynamic Load Transfer During Cutting

Cutting introduces shock load into frame.

Dynamic load multiplier:

Fdynamic=Fstatic×KdF_{dynamic} = F_{static} × K_dFdynamic=Fstatic×Kd

Where KdK_dKd often 1.3–1.8 depending on blade geometry.

For 192 kN static:

Worst case dynamic:

192×1.5≈288kN192 × 1.5 ≈ 288 kN192×1.5≈288kN

Frame and shafts must absorb this.

6. Blade Metallurgy Engineering

Shear blades operate under:

• • High compressive stress
• • Impact loading
• • Abrasion
• • Micro-chipping risk

Common blade materials:

• • D2
• • H13
• • SKD11
• • Tungsten carbide inserts (high production lines)

6.1 Blade Hardness Targets

Roofing:

58–60 HRC

Heavy deck:

60–62 HRC

Too hard:

• Brittle fracture

Too soft:

• Rapid edge rounding

7. Blade Clearance Engineering

Proper blade clearance:

Clearance≈5–10Clearance ≈ 5–10% \text{ of material thickness}Clearance≈5–10

For 0.75 mm:

Clearance = 0.037–0.075 mm

Too tight:

• Burr
• Excess load

Too loose:

• Tearing
• Distorted edge

8. Servo vs Induction Motor Deep Comparison

Induction Motor + VFD

• Advantages:
• • Robust
• • Cost effective
• • Low maintenance

• Disadvantages:
• • Slower torque response
• • Less precise position control
• • Speed drift under rapid load change

• Best for:
• • Medium-speed lines
• • Stop-cut systems

Servo Motor System

• Advantages:
• • Instant torque response
• • High precision speed matching
• • Better flying shear sync
• • Reduced torsional oscillation

• Disadvantages:
• • Higher cost
• • More complex control
• • Requires tuning

• Best for:
• • Flying shear
• • High-speed stud lines
• • Punch integration

Torque Response Comparison

Induction motor torque response delay:

50–150 ms

Servo motor response:

< 10 ms

At 40 m/min:

In 100 ms strip travels:

0.0666 m = 66 mm

That difference directly affects cut accuracy.

9. Harmonic Frequency Modeling

Mechanical systems have natural frequencies.

Natural torsional frequency:

fn=12πKJf_n = \frac{1}{2\pi} \sqrt{\frac{K}{J}}fn=2π1JK

Where:

• K = torsional stiffness
• J = inertia

If motor excitation frequency matches fnf_nfn:

Resonance occurs.

Effects:

• • Gear noise
• • Shaft fatigue
• • Dimensional fluctuation

Increasing shaft diameter increases K → raises natural frequency → reduces resonance risk.

Helical gears reduce harmonic excitation vs spur gears.

10. Harmonic Chart Example (Conceptual)

If natural frequency = 22 Hz
Motor electrical frequency at certain RPM = 22 Hz

Resonance risk occurs.

Engineering solution:

• • Change gear ratio
• • Increase shaft stiffness
• • Add damping
• • Adjust motor ramp profile

11. Hydraulic Lubrication & Oil Viscosity Selection

Hydraulic oil must:

• • Maintain film strength
• • Resist oxidation
• • Dissipate heat
• • Prevent cavitation

11.1 ISO Viscosity Selection Table

Operating Temperature	Recommended ISO Grade
20–40°C	ISO 32
40–60°C	ISO 46
60–80°C	ISO 68
Heavy load / hot climate	ISO 68–100

• Too low viscosity:
• • Film breakdown
• • Wear

• Too high viscosity:
• • Pump inefficiency
• • Heat buildup

12. Hydraulic Cooling Engineering

Heat generated from:

• • Pressure drops
• • Flow restriction
• • Pump inefficiency

Temperature target:

40–55°C oil temperature

Cooling methods:

• Air cooler
• Oil-water heat exchanger

Overheating causes seal degradation.

13. Integrated PBR Cutting System Example

For 36” PBR at 35 m/min:

• • 250 kN hydraulic cylinder
• • ISO 46 oil (moderate climate)
• • Servo-driven flying shear
• • 30 kW main motor
• • 50:1 gearbox
• • Harmonic damping via helical gears
• • Blade clearance 0.05 mm

This configuration ensures:

• • ±1 mm length accuracy
• • Minimal burr
• • Controlled dynamic load
• • Reduced torsional oscillation

Final Engineering Summary

Hydraulic and cutting systems are the highest instantaneous force zones in roll forming.

They determine:

• • Length accuracy
• • Dynamic stability
• • Gearbox lifespan
• • Frame fatigue
• • Profile edge quality

Servo integration, harmonic control, blade metallurgy, and oil selection must be engineered together.

Cutting is not just slicing metal.

It is a controlled energy transfer event inside a synchronized mechanical system.