Manufacturing of Custom Flanges
Posted: Nov 5, 2023 | Posted in: Blogs
Introduction
Custom flanges are precision components manufactured through a carefully controlled process. Understanding the steps ensures you know what quality standards apply and what to expect from your flange supplier. This article walks through the seven-step manufacturing process from initial design to final quality assurance.
Step 1: Design and Specification
Requirement Definition
Manufacturing begins before any metal is cut. Design starts with clear requirements:
- Standard or Custom? Are you starting with ASME B16.5, EN 1092-1, JIS, or a completely custom design?
- Dimensions: Size, bore, bolt circle diameter, flange face thickness, and overall thickness.
- Material and Grade: Carbon steel, stainless, alloy, nickel alloy, or other specialty material.
- Pressure and Temperature Rating: What service conditions will the flange endure?
- Special Features: Custom drilling, lifting lugs, drain holes, test ports, or dished faces.
CAD and Drawing Creation
Once requirements are defined, a CAD (Computer-Aided Design) drawing is created showing:
- All dimensions with tolerances
- Material callout
- Surface finish requirements (e.g., ≤125 µin Ra)
- Heat treatment specifications
- Testing and inspection requirements
The CAD drawing guides every subsequent manufacturing step. Accuracy at this stage prevents costly errors later.
Step 2: Material Selection and Sourcing
Raw Material Procurement
Flanges start as raw billets or forgings. Material must be:
- Certified Grade: Material from mills with verified certifications (ASME, ASTM, DIN).
- Appropriate Size: Billet size should minimize waste while providing enough material for machining.
- Verified Chemistry: Spectrographic analysis confirms material matches the specified grade.
Material Testing
Incoming material is tested to verify properties:
- Tensile Properties: Yield strength, tensile strength, and elongation per ASTM standards.
- Hardness: Rockwell hardness testing verifies material hardness falls within specification.
- Chemical Composition: Spectrographic analysis confirms alloying elements are within range.
These tests provide the "Mill Test Report" (MTR) — documentation that material meets specification.
Step 3: Forming and Primary Shaping
Forging (if applicable)
For larger or heavier flanges, raw billet is forged to approximate shape:
- Hot Forging: Billet is heated to 2,000°F+ and shaped under high-speed hammer or press.
- Near-Net-Shape Forging: Forging produces a shape close to final dimensions, minimizing subsequent machining.
- Grain Structure Improvement: Forging refines material grain structure, improving strength and fatigue resistance.
Cutting (if applicable)
For smaller flanges or those with simple geometry, raw material may be cut to approximate blank size using:
- Bandsaw or abrasive cutoff wheel
- Plasma or waterjet cutting for precise blanks
Step 4: CNC Machining and Precision Finishing
Setup and Tool Loading
The CAD drawing is converted to CNC machine code (G-code). Cutting tools are selected and loaded:
- Roughing Tools: Remove large amounts of material quickly (less precise but faster).
- Finishing Tools: Final light cuts to achieve specified dimensions and surface finish.
Machining Operations
CNC machines perform multiple operations:
- Face Turning: Flatten and size the flange faces.
- Boring: Machine the bore to precise diameter and position.
- Drilling: Create bolt holes at specified positions and sizes.
- Grooving (if RTJ): Machine ring joint grooves to exact depth and width.
- Threading (if applicable): Create threaded holes or tapered bores.
- Raising or Facing: Machine raised face or flat face sealing surface.
Surface Finish Control
Sealing surfaces must be smooth and controlled:
- Surface Finish Specification: Typically 125 µin Ra (microinches absolute roughness) or better.
- Finishing Tools and Speeds: Final cuts use fine-pitch tools and optimized speeds to achieve smooth finish.
- Post-Machining Polishing: For critical applications, additional polishing may improve surface finish.
Step 5: Inspection and Testing (Intermediate)
Dimensional Verification
After machining, dimensions are verified:
- Coordinate Measuring Machine (CMM): 3D measurement system verifies all dimensions to specified tolerances.
- Caliper and Micrometer: Hand tools verify critical dimensions (bore, thickness, OD).
- Surface Plate Flatness Check: Sealing surface flatness is verified (typically ±0.002" or tighter).
Visual and Surface Inspection
Surfaces are inspected for defects:
- Cracks or inclusions
- Surface corrosion or mill scale
- Machining marks or improper finish
Any defects are either reworked or the part is scrapped if repair is not possible.
Step 6: Heat Treatment and Finishing
Heat Treatment (if required)
Depending on material and application, heat treatment is performed:
- Stress Relief: Heating to 1,000-1,200°F to relieve residual stresses from forging and machining.
- Quench and Temper: Heating, rapid cooling, and reheating to improve hardness and toughness.
- Annealing: Heating and slow cooling to improve ductility and machinability.
Surface Protection
Surfaces are protected against corrosion:
- Oil Coating: Light machine oil coating prevents rust during storage and shipping.
- Passivation (Stainless): Chemical treatment (citric or nitric acid) removes free iron and enhances corrosion resistance.
- Painting or Powder Coat (optional): For long-term storage or outdoor exposure, paint protection may be applied.
Step 7: Final Quality Control and Documentation
Hydrostatic Pressure Testing (if applicable)
For critical applications, flanges are pressure tested:
- Test Pressure: Typically 1.5x the rated working pressure.
- Procedure: Flange is capped and filled with water, then pressurized and held for a set time.
- Pass/Fail: If no leaks or permanent deformation occur, the flange passes.
Non-Destructive Testing (NDT)
Advanced flange testing may include:
- Ultrasonic Testing: Detects internal cracks or voids.
- Radiography: X-rays reveal internal defects or porosity.
- Magnetic Particle Inspection: For ferromagnetic materials, detects surface and near-surface cracks.
- Eddy Current Testing: Detects surface and subsurface defects in conductive materials.
Documentation and Certification
Final documentation includes:
- Mill Test Report (MTR): Verified material chemistry and mechanical properties.
- Inspection Report: Dimensional verification and surface inspection results.
- Pressure Test Certificate: Results of hydrostatic or pneumatic testing (if performed).
- CAD Drawing (approved): Copy of approved CAD drawing for traceability.
- Certification of Compliance: Statement that flange meets specification and applicable standards (ASME, API, etc.).
Final Packing and Labeling
Completed flanges are prepared for shipment:
- Wrapped in protective material (plastic, kraft paper) to prevent corrosion during transport.
- Packed in boxes or crates to prevent damage.
- Labels include part number, size, grade, heat number, and destination.
FAQ
Q: How long does the manufacturing process take?
A: For standard flanges, 2-4 weeks from order to delivery. Complex custom flanges with special materials or testing may take 6-8 weeks or longer. Rush schedules are possible but at a premium cost.
Q: What tolerances can be achieved?
A: CNC machining typically achieves ±0.005" tolerances. Tighter tolerances (±0.002" or better) are possible but increase cost and lead time. Specify only the tightest tolerances needed for your application.
Q: What surface finish can be achieved?
A: Standard CNC machining produces approximately 125 µin Ra (microinch) finish. Finer finishes (63 µin or better) require additional polishing. Specify surface finish requirements based on gasket and sealing needs.
Q: Is hydrostatic testing required?
A: Not always. Hydrostatic testing is required for ASME Code flanges and recommended for critical, high-pressure applications. It adds cost and lead time, so specify only if required by code or contract.
Q: Can I get rush delivery?
A: Yes. Expedited manufacturing is possible but costs more due to overtime labor and prioritized machine scheduling. Rush flanges must meet the same quality standards as standard lead-time parts.
Q: What happens if a flange fails inspection?
A: Flanges failing dimensional or surface inspection are either reworked (if possible) or scrapped. The cost of scrap is typically absorbed by the manufacturer if it's a manufacturing error. Material defects may be rejected to the material supplier.
Q: Are small quantities available?
A: Yes. Most custom flange manufacturers can produce single units or small batches. Pricing for small quantities is higher due to setup costs, but custom flanges are economical even for one-off jobs.
Q: Can I provide my own material?
A: Usually not recommended. Manufacturer-sourced material comes with verified documentation and mill test reports. Providing your own material introduces traceability issues and may void compliance certifications. Discuss with your supplier.
Conclusion
The custom flange manufacturing process is a controlled sequence of steps designed to transform raw material into precision components that perform reliably in service. Understanding these steps helps you specify requirements clearly, set realistic expectations for lead time and cost, and appreciate the quality standards your supplier must maintain.
Contact Custom Flanges to discuss your custom flange requirements and learn how our manufacturing process will deliver the quality and reliability you need.