Sheet Metal Work

Creating flat patterns that form into 3D shapes is the core skill:

Pattern Development Methods:

Parallel Line Development:
Used for prisms and cylinders:
- All bend lines are parallel
- Measure true lengths directly
- Examples: rectangular ducts, round pipe

Radial Line Development:
Used for cones and pyramids:
- Bend lines radiate from apex
- Calculate true lengths for each element
- Examples: conical transitions, pyramidal shapes

Triangulation:
Complex shapes with no parallel elements:
- Divide surface into triangles
- Calculate true length of each side
- Most versatile but time-consuming
- Examples: offset transitions, complex fittings

Key Calculations:

Bend Allowance:
Material stretches at neutral axis during bending:
- BA = π × (R + K × T) × A / 180
- R = inside radius
- T = material thickness
- K = K-factor (neutral axis location, typically 0.4-0.5)
- A = bend angle in degrees

Bend Deduction:
Amount to subtract from flat pattern:
- BD = 2 × (R + T) × tan(A/2) - BA
- Critical for accurate final dimensions

Software Tools:
Modern sheet metal relies on CAD:
- SolidWorks Sheet Metal
- AutoCAD with sheet metal packages
- Specialized HVAC layout software
- Automatic bend allowance calculation
- Flat pattern generation from 3D models

Traditional Layout:
Still valuable for custom work:
- Dividers for marking
- Protractors and squares
- Scratch awls
- Pattern templates

Sheet metal forming uses specialized techniques and equipment:

Press Brake Operations:

Air Bending:
- Punch does not bottom into die
- Bend angle depends on punch depth
- Same tooling for multiple angles
- Most common method

Bottom Bending:
- Punch bottoms against material in die
- More accurate, higher force required
- Specific tooling for each angle

Coining:
- Maximum pressure, material flows
- Sharp corners, high precision
- Highest tonnage requirement

Tooling:
- Punch profiles: acute, gooseneck, hemming
- Die openings: V-width affects bend radius
- Specialized tools for complex forms

Other Forming Equipment:

Slip Roll (Plate Roll):
- Creates cylindrical shapes
- Three-roll configuration
- Slip roll for sheet, plate roll for heavier
- Adjustable for various diameters

Box and Pan Brake:
- Segmented fingers
- Form boxes with flanges
- Manual operation typically
- Limited depth capacity

Rotary Bending:
- Continuous bending of long pieces
- Used for architectural panels
- Standing seam roofing
- High production capability

Hand Forming:
- Seaming stakes and mandrels
- Mallets and hammers
- Planishing for smoothing
- Shrinking and stretching

HVAC Specific:
- Pittsburgh lock forming
- Drive cleat machines
- Duct beading
- Snap lock machines

Sheet metal assembly uses techniques suited to thin materials:

Mechanical Fastening:

Rivets:
- Solid rivets (aerospace quality)
- Blind rivets (pop rivets) for access limitations
- Self-piercing rivets for dissimilar materials
- Proper edge distance and spacing critical

Screws:
- Sheet metal screws (self-tapping)
- Self-drilling (Tek screws)
- Machine screws in tapped holes
- Avoid over-tightening thin material

Clinching:
- Mechanical interlock without fastener
- Fast, no consumables
- Requires access to both sides
- Tool cost offset by speed

Seams and Joints:

Pittsburgh Lock:
- HVAC duct standard
- One piece hooked, other inserted
- Hammer or machine closed
- Air-tight when properly made

Standing Seam:
- Roofing and cladding
- Allows thermal expansion
- Weather-tight design
- Machine-formed on site or shop

Grooved Seam:
- Hand-formed connection
- Decorative and functional
- Traditional metalworking skill

Welding:

Spot Welding:
- Fast, clean appearance
- No distortion if proper
- Limited to lap joints
- Common in automotive

TIG Welding:
- Precision, minimal distortion
- Requires skill for thin gauge
- Aerospace and precision work

MIG Welding:
- Production speed
- Requires good fit-up
- Heat management important

Adhesive Bonding:
- Structural adhesives growing in use
- Distributes load over area
- Seals and bonds simultaneously
- Surface preparation critical

Sheet metal work offers diverse career opportunities:

HVAC Sheet Metal:

Apprentice:
- 4-5 year programs common
- Combination of shop and field
- Union and non-union paths
- While training: $35,000-$45,000

Journeyman:
- Full fabrication capability
- Field installation
- Layout and development
- $50,000-$80,000

Foreman:
- Lead crews
- Coordination with other trades
- Quality responsibility
- $70,000-$100,000

Architectural/Industrial:

Fabricator:
- Precision enclosures
- Custom architectural work
- Higher precision requirements
- $45,000-$70,000

CNC Programmer/Operator:
- Laser/punch programming
- Press brake operation
- CAD/CAM proficiency
- $50,000-$75,000

Aerospace:

Sheet Metal Mechanic:
- Aircraft structures
- Strict quality requirements
- Specialized training
- $50,000-$85,000

Certifications:
- SMACNA (Sheet Metal and Air Conditioning Contractors)
- AWS certifications for welded sheet metal
- FAA certifications for aerospace
- OSHA safety training

Skills for Advancement:
- CAD proficiency (SolidWorks, AutoCAD)
- CNC programming capability
- Estimating and project management
- Supervision and leadership

Union vs. Non-Union:
- SMART union represents many HVAC sheet metal workers
- Apprenticeship through union training centers
- Non-union paths through employers or trade schools
- Both offer good career potential

Physical Requirements:
- Standing for extended periods
- Lifting materials (up to 50 lbs regularly)
- Working from ladders/scaffolds (field work)
- Precise hand-eye coordination