Precision Graphite Fixture and Jig for Vacuum Brazing
Product Overview
Our precision graphite brazing fixtures and jigs are custom-manufactured tooling used to hold and align components during vacuum furnace brazing operations. Graphite is the preferred fixture material for vacuum brazing because it maintains high strength at brazing temperatures (up to 1200°C), does not react with silver, copper, or nickel braze alloys, and has a low coefficient of thermal expansion that minimizes distortion of precision assemblies. Each fixture is CNC-machined from high-strength isostatic graphite to hold parts with exacting tolerances throughout the thermal cycle.
Vacuum brazing is widely used in aerospace, automotive heat exchanger, medical device, and electronics manufacturing where clean, flux-free joints are required. A well-designed graphite brazing jig must accurately locate parts, provide even loading to prevent sagging, and resist braze alloy wetting. At Jincheng Graphite, we design and fabricate custom graphite brazing fixtures from customer CAD drawings, including grid-style fixtures, ladder jigs, and complex nesting fixtures for multi-part assemblies. We also supply standard graphite support pins, buttons, and setter plates for production brazing lines.
Key Features
- High hot strength - maintains fixture rigidity at brazing temperatures up to 1200°C
- Non-wetting to braze alloys - silver, copper, and nickel braze do not stick to graphite surfaces
- Low thermal expansion - holds tight part alignment through heating and cooling cycles
- CNC precision machining - tolerances as tight as ±0.02 mm on locating features
- Custom fixture designs - from simple support plates to complex multi-cavity jigs
- Lightweight - easy to handle and load into vacuum furnaces
- Long service life - reusable for hundreds of brazing cycles before wear
- Repairable - worn locating surfaces can be re-machined to extend fixture life
Technical Specifications
| Parameter | Value |
|---|---|
| Material | High-strength isostatic graphite |
| Bulk Density | 1.75 - 1.85 g/cm³ |
| Shore Hardness | 60 - 70 HS |
| Flexural Strength | 50 - 65 MPa |
| Compressive Strength | 80 - 110 MPa |
| Max Service Temperature | 1300°C (vacuum) |
| Coefficient of Thermal Expansion | 2.0 - 3.0 × 10-6/K |
| Dimensional Tolerance | ±0.02 mm (locating features) |
| Flatness | < 0.05 mm per 200 mm |
| Surface Finish | Ra 1.6 - 3.2 µm |
| Available Configurations | Grid, ladder, nest, pin, plate |
| Max Fixture Size | 800 × 600 mm (larger assembled on request) |
Applications
- Aerospace turbine brazing - brazing of turbine blades, vanes, and heat exchangers
- Automotive heat exchangers - vacuum brazing of aluminum and stainless steel heat exchanger cores
- Medical device brazing - precision brazing of surgical instruments and dental components
- Electronics packaging - brazing of ceramic-to-metal seals and hermetic packages
- Sensor and instrumentation - brazing of thermocouple sheaths and pressure sensor housings
- Tool and cutter brazing - brazing of carbide tips onto drill and cutter shanks
Why Choose Jincheng Graphite?
- Custom fixture design - we work from your CAD files to produce exact brazing jigs
- Deep vacuum furnace knowledge - understand thermal expansion and sagging in brazing cycles
- Precision CNC capability - 3-axis and 5-axis machining for complex fixture geometry
- Material selection - recommend the right graphite grade for your fixture load and temperature
- Fast prototype turnaround - first article fixtures within 10-15 business days
- Refurbishment service - re-machine worn locating surfaces to extend fixture life
- Competitive pricing - factory-direct custom fixture manufacturing
- Global export - shipping to aerospace and medical device manufacturers worldwide
FAQ
Q: Can you design a fixture from our part drawings?
A: Yes. Send us your assembly drawing or STEP files, describe the braze alloy and thermal cycle, and our engineering team will design a graphite fixture that locates and supports the parts. We provide drawings for your approval before machining begins.
Q: How many brazing cycles will a graphite fixture last?
A: Under typical vacuum brazing at 1000-1200°C, a graphite fixture lasts hundreds of cycles. Wear occurs mainly on locating surfaces that contact braze alloy; these can be re-machined once or twice before replacement.
Q: Should we coat the graphite fixture to prevent braze sticking?
A: In most vacuum brazing applications, uncoated graphite is sufficient because braze alloys do not wet graphite well. If you are brazing with high-temperature nickel braze or experiencing occasional braze adhesion, we can offer a BN-coated or SiC-coated surface as an option.
Q: What is the lead time for a custom fixture?
A: Standard custom fixtures typically require 15-25 business days after drawing approval. Simple support plates and setter plates can often be delivered within 7-10 business days.
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