How to Specify a Sigma Profile (Complete Structural Guide)

Learn how to specify a Sigma profile including section geometry, thickness, steel grade, punch layout, coil width and machine requirements.

Complete Engineering & Procurement Guide

A Sigma profile is a:

• Cold-formed structural section

• Advanced purlin alternative

• High-strength, high-efficiency member

It is commonly used in:

• Long-span industrial buildings

• Heavy roof structures

• Mezzanines

• Solar mounting frames

• Structural steel systems

Sigma sections provide greater bending resistance than standard Z or C profiles due to their complex flange geometry.

1️⃣ What Defines a Sigma Profile?

A Sigma section includes:

✔ Web depth
✔ Primary flange
✔ Secondary return flange
✔ Stiffening lips
✔ Offset geometry
✔ Thickness
✔ Steel grade
✔ Punch pattern

The cross-section resembles the Greek letter “Σ” (Sigma), hence the name.

Because of its multiple bends, full dimensional specification is mandatory.

2️⃣ Standard Section Sizes

Common web depths:

150 mm
200 mm
250 mm
300 mm
350 mm
400 mm

Flange widths vary significantly:

60–100 mm common

Lip sizes:

15–30 mm

Sigma profiles typically have:

More bends than Z or C.

More bends = more forming load.

Never specify only “Sigma 250” — provide full geometry.

3️⃣ Thickness Range

Sigma sections are often heavier than standard purlins.

Typical thickness:

1.8 mm
2.0 mm
2.5 mm
3.0 mm
3.5 mm
4.0 mm

Heavier structural versions may exceed 4 mm.

Machine must be designed for:

Maximum thickness + maximum yield strength.

4️⃣ Material Grade

Common grades:

G350
G450
G550

Sigma profiles frequently use G550 to maximize strength-to-weight ratio.

Higher grade increases:

Forming force
Springback
Roll wear
Punch tonnage

Grade must be declared before tooling design.

5️⃣ Coating Specification

Common coatings:

Z275
Z350
Z450

Industrial or coastal zones may require heavier coating.

Coating affects:

Roll surface wear
Punch wear
Corrosion life

Always specify coating mass.

6️⃣ Typical Coil Width

Coil width is calculated from:

Web + multiple flange elements + lips + bend allowance.

Example (simplified):

Web 250 mm
Primary flange 75 mm ×2
Secondary return 25 mm ×2

250 + 150 + 50 = 450 mm
Add bend allowance → approx. 470–500 mm

Exact developed width must include:

Bend radii
Thickness compensation
Springback correction

Sigma sections have more bends, so developed width calculation is critical.

7️⃣ Structural Load Requirements

Before selecting Sigma size, define:

✔ Span length
✔ Wind load
✔ Snow load
✔ Deflection limit
✔ Load combination

Sigma is often chosen when:

Z purlin cannot meet deflection limits.

Section size must be structurally calculated.

8️⃣ Punch Pattern Specification

Sigma profiles often require:

✔ Bolt holes
✔ Cleat holes
✔ Service holes
✔ Slotted holes

Define:

Hole diameter
Hole spacing
Edge distance
Tolerance

Because Sigma has multiple flanges, punch positioning must be very precise.

Punch misalignment causes installation failure.

9️⃣ Length Specification

Common lengths:

6 m
9 m
12 m
Custom

Length tolerance typically:

±2 mm

Long sections require straightness control.

Sigma twist must be minimized.

🔟 Machine Engineering Requirements

Sigma profile machines are heavier than C/Z lines.

Typical configuration:

• 18–26 forming stands

• 90–110 mm shafts

• 37–75 kW motor

• Heavy-duty frame

• Servo punching system

• Hydraulic or flying cut

Because Sigma has more bends:

Forming load is significantly higher.

Frame rigidity is critical.

1️⃣1️⃣ Production Speed

Typical speeds:

10–20 m/min

Thicker and higher grade reduce speed.

Punch cycle often limits production rate.

1️⃣2️⃣ Tolerance Requirements

Typical tolerances:

Web depth ±1–2 mm
Flange width ±1 mm
Twist control critical
Straightness tolerance defined
Length ±2 mm

Sigma asymmetry increases risk of twist.

Roll alignment must be precise.

1️⃣3️⃣ Sigma vs Z Comparison

Sigma provides improved structural performance but requires stronger equipment.

1️⃣4️⃣ Export Market Considerations

Sigma sections are common in:

Middle East industrial buildings
European long-span structures
Solar mounting systems

Always confirm local structural code:

EN
AS
ASTM

Section geometry must align with structural engineer calculations.

1️⃣5️⃣ Common Specification Mistakes

❌ Not defining full geometry
❌ Not specifying thickness
❌ Ignoring steel grade
❌ Underestimating coil width
❌ Not controlling twist
❌ Selecting Sigma without structural calculation

Sigma mistakes are expensive due to tooling complexity.

1️⃣6️⃣ Developed Width Reminder

Developed width must include:

✔ Web
✔ Primary flanges
✔ Secondary returns
✔ Lips
✔ Bend allowance
✔ Thickness compensation
✔ Springback correction

Multiple bends amplify calculation error risk.

Never approximate.

1️⃣7️⃣ Frame Rigidity Importance

Sigma forming generates:

Higher torque
Higher roll separating force

Machine frame must resist deflection.

Insufficient rigidity causes:

Dimension drift
Twist
Punch misalignment

Machine engineering must match structural requirement.

1️⃣8️⃣ Final Sigma Specification Checklist

Before tooling or machine approval:

✔ Confirm web depth
✔ Confirm flange widths
✔ Confirm lip size
✔ Confirm thickness range
✔ Confirm steel grade
✔ Confirm coating
✔ Calculate developed width
✔ Confirm coil availability
✔ Define punch layout
✔ Define length tolerance
✔ Confirm structural load requirement
✔ Confirm production speed target

Only then proceed.

FAQ Section

Why use Sigma instead of Z?

Higher structural efficiency and longer span capability.

Is G550 common for Sigma?

Yes — often preferred for strength.

Is Sigma harder to form?

Yes — more bends increase forming load.

Does machine need to be stronger?

Yes — heavier shafts and frame required.

Is twist a major issue?

Yes — asymmetric geometry increases twist risk.

Can one machine run Sigma and Z?

Possible with adjustable tooling, but machine must be designed for Sigma load.