- 1.0Understanding Shear Capacity Based on Mild Steel Standards
- 2.0Key Factors That Influence Shearing Force
- 3.0The Role of Rake Angle in Metal Shearing
- 4.0How Material Properties Impact Shear Performance
- 5.0Shearing Force and Metal Thickness: What’s the Relationship?
- 6.0Minimum Shearable Thickness by Machine Type
- 7.0Why Knife Clearance Matters in Sheet Metal Shearing
- 8.0Types of Shear Knives and Their Applications
- 9.0Knife Wear, Inspection, and Maintenance Essentials
- 10.0Understanding Work Hardening in Metal Shearing
- 11.0Effects of Work Hardening
- 12.0Practices to Avoid
- 13.0Shear Capacity vs. Knife Capacity: What’s the Difference?
- 14.0General Shear Capacity Reference Table (Excerpt)
- 15.0Steel Shear Capacity Reference Table
- 16.0Optional Shear Features That Improve Cutting Accuracy
- 17.0Final Summary: Best Practices for Safe & Efficient Shearing
Industrial Sheet Shearing Machines are essential for the precision cutting of sheet metal and plate materials. To ensure optimal performance and safe operation, it is critical to understand how shear capacity is rated and what factors influence cutting efficiency. This guide provides a comprehensive overview of shear force fundamentals, rake angle, knife selection, material properties, and maintenance best practices.
1.0Understanding Shear Capacity Based on Mild Steel Standards
Shear ratings are typically based on the maximum cutting thickness of mild steel under a specified rake angle. The standard mechanical properties of mild steel include:
| Property | Value |
| Maximum Shear Strength | 50,000 psi |
| Ultimate Tensile Strength (UTS) | 55,000–70,000 psi |
| Yield Strength (YS) | 35,000–50,000 psi |
| Elongation (in 2″) | 20–35% |
Note: Ratings include allowances for common thickness over-tolerances. For example, a 0.250″ plate may actually be up to 0.030″ thicker and still fall within rated capacity.
2.0Key Factors That Influence Shearing Force
Shearing force must exceed the force required to cut the intended material. Primary influencing factors include:
- Material shear strength
- Rake angle and material thickness
- Ductility and work hardening
- Knife condition and clearance
- Back piece depth and support systems
3.0The Role of Rake Angle in Metal Shearing
Rake angle is the inclination between the upper and lower knife blades. It greatly affects cutting force and material behavior during shearing:
- A larger rake angle reduces the required force
- Excess rake may lead to part distortion or longer knife stroke
3.1Rake Angle in Practice: Force Reduction and Quality Impact:
If R₂ = 2R₁ → then Force₂ = ½ Force₁
Best practice: Use the minimum rake angle that delivers acceptable cut quality without exceeding machine limits. Higher rake angles are especially beneficial for stainless steel and high-ductility materials.
4.0How Material Properties Impact Shear Performance
4.1Material Strength and Its Effect on Shear Capacity
Materials stronger than mild steel (higher UTS/YS) require derated capacity.
4.2Ductility and Knife Penetration in Sheet Metal Cutting
Materials with elongation above 35% reduce shear performance due to deeper knife penetration.
Examples include:
- 1006, 1008, and sometimes 1010/1012 carbon steels
- ASTM A283 Grade A, A285 Grade A, A570 Grade 30 (when elongation exceeds 35%)
5.0Shearing Force and Metal Thickness: What’s the Relationship?
Shearing force increases quadratically with thickness:
Force ∝ Thickness²
→ If T₂ = 2T₁ → Force₂ = 4 × Force₁
6.0Minimum Shearable Thickness by Machine Type
Minimum limits depend on knife clearance and sharpness. Examples:
| Model | Gauge | Inch | mm |
| 375 HS | 26 GA | 0.018″ | 0.45 |
| 500 HS | 22 GA | 0.030″ | 0.76 |
| 750 HS | 20 GA | 0.036″ | 0.91 |
| SE Series | 16 GA | 0.060″ | 1.52 |
7.0Why Knife Clearance Matters in Sheet Metal Shearing
Proper knife clearance ensures clean, consistent cuts.
- Too little: Double shear, burrs, rapid wear
- Too much: Inaccurate cuts, folding
7.1Recommended Knife Clearance Settings by Shear Type:
- Mechanical shears: 7%of material thickness
- Hydraulic shears: 7–15%, adjustable with table shims
For stainless steel, maintain minimum clearance to prevent burrs and work hardening.
8.0Types of Shear Knives and Their Applications
Choosing the right knife material balances wear resistance y shock resistance.
| Type | Wear Resistance | Shock Resistance | Ideal Use |
| A | Highest | Lowest | Thin mild/stainless steel |
| B | High | Low | Light stainless or aluminum |
| C | Medium | Medium | General-purpose cutting |
| D | Low | High | High-shock applications |
| E | Lowest | Highest | Abrasive, brittle, or high-impact materials |
| S | Moderate | Very High | Stainless, Inconel, Hastelloy, ductile alloys |
For frequent stainless steel cutting (especially >50% usage), Type S is recommended.
For light-gauge stainless steel (≤10 GA), Type A may suffice.
9.0Knife Wear, Inspection, and Maintenance Essentials
Dull or damaged knives increase cutting force and can damage machines.
9.1Common Knife Wear Indicators
- Cupping
- Bright zones (indicate double shear)
- Poor edge finish
9.2Factors That Accelerate Knife Wear:
- Flame-cut or hardened materials
- Patterned sheets (e.g., tread plate)
- Improper clearance
- Cutting materials >300 BHN
9.3The Impact of Back Piece Depth on Shearing Force:
- Regularly rotate and sharpen knives
- Monitor wear near the squared arms
- Avoid cutting AR plates >360 BHN
10.0Understanding Work Hardening in Metal Shearing
Back piece depth is the distance from the blade to the material’s trailing edge:
- Greater depth → higher required force
- Use pneumatic tables or corner arms for heavy or ductile material support
11.0Effects of Work Hardening
Work-hardening materials like stainless steel and nickel alloys require more force to shear due to increased surface hardness. Use knives with high shock resistance and appropriate rake settings to mitigate this.
12.0Practices to Avoid
| Practice | Risk |
| Trim cuts < 0.125″ | Increased load, material trapping |
| Large knife clearance on thin sheets | Wiping instead of clean cuts |
| Multi-layer cutting | Poor cut quality, machine overload |
| Angle cuts < 20° | Slivers, shear failure |
13.0Shear Capacity vs. Knife Capacity: What’s the Difference?
Understanding this distinction prevents premature failure:
| Parameter | Governs | Depends On |
| Shear Capacity | Machine | Thickness² × Shear Strength × Rake Angle |
| Knife Capacity | Knife Material | Thickness × Shear Strength (independent of rake) |
Hydraulic models often have overload protection. However, stalling increases knife wear.
14.0General Shear Capacity Reference Table (Excerpt)
| ASTM Grade | Tensile Strength (ksi) | Yield Strength (ksi) | Min Elongation (% in 2″) | Rated Mild Steel Thickness | Equivalent Max Capacity (inches) |
|---|---|---|---|---|---|
| A36 | 58–80 | 36–51 | 23 | 0.188″ (approx. 7 GA) | 0.250 / 0.375 / 0.500 / 0.625 / 0.750 |
| A514 | 110–130 | ≥110 | 18 | 0.188″ (approx. 7 GA) | 0.281 / 0.375 / 0.500 / 0.625 / 0.750 |
| A572 Grade 50 | ≥65 | ≥50 | 21 | 0.188″ (approx. 5 GA) | 0.344 / 0.438 / 0.562 / 0.688 / 0.875 |
Usage Notes:
This chart is intended for estimating maximum shearable thickness for various ASTM steel grades on metal shearing machines, including hydraulic shears, mechanical shears, and CNC-controlled shearing systems.
“Equivalent Max Capacity” reflects the typical shear rating based on mild steel as the baseline material.
14.1Example:
- 250″ A572 Grade 65→ Requires shear rated for 0.375″ mild steel
- T-1 (ASTM A514)on a 750″ shear → Max capacity: 0.625″
15.0Steel Shear Capacity Reference Table
| Steel Grade | Tensile Strength (ksi) | Yield Strength (ksi) | Min. Elongation (%) | 12 GA (0.1046″) | 10 GA (0.1345″) | 0.188″ | 0.250″ | 0.281″ | 0.375″ | 0.500″ | 0.625″ | 0.750″ | 1.000″ | 1.250″ |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| A1008 CS Type A/B/C | N.S. | 20–40 | 30 | 12 GA | 10 GA | 7 GA | 0.250 | – | – | – | – | – | – | – |
| A1008 DDS | N.S. | 17–29 | 38 | 14 GA | 12 GA | 10 GA | 0.250 | – | – | – | – | – | – | – |
| A1008 SS Grade 40 | 52 MIN | 40 MIN | 20 | 12 GA | 10 GA | 7 GA | 0.250 | – | – | – | – | – | – | – |
| A1008 HSLAS Grade 50 Cl. 1 | 65 MIN | 50 MIN | 20 | 13 GA | 11 GA | 8 GA | 5 GA | – | – | – | – | – | – | – |
| A1011 SS Grade 36 Type 2 | 58–80 | 36–51 | 21 | 12 GA | 10 GA | 7 GA | 0.250 | – | – | – | – | – | – | – |
| A1011 HSLAS Grade 70 Cl. 1 | 85 MIN | 70 MIN | 14 | 14 GA | 12 GA | 9 GA | 7 GA | – | – | – | – | – | – | – |
| A1011 HSLAS-F Grade 80 | 90 MIN | 80 MIN | 18 | 14 GA | 12 GA | 10 GA | 7 GA | 0.281 | 0.375 | 0.500 | – | – | – | – |
Notes:
This table provides general guidelines for estimated shearable thickness based on material mechanical properties.
Values are nominal and should be verified against the specific cutting machine’s capacity and blade configuration.
GA (gauge) references are approximate and may vary by standard (e.g., U.S. Steel Gauge vs. Manufacturer Spec).
Shearing performance is affected by rake angle, blade clearance, blade condition, and material hardness.
16.0Optional Shear Features That Improve Cutting Accuracy
- Captive table shims for fast knife clearance adjustment
- Power knife clearance(automated models)
- Pneumatic sheet supports for handling large or flexible materials
- Rear corner supports to prevent distortion on thick or ductile stock
17.0Final Summary: Best Practices for Safe & Efficient Shearing
- Start with maximum rake angle, then reduce based on cut quality
- Always match knife type to material and thickness
- Monitor wear, maintain clearance, and rotate knives regularly
- Never exceed rated shear or knife capacity
By applying these principles and understanding the physics behind shearing, operators can ensure safe, precise, and long-lasting performance of their cutting equipment.
