Fixture Design
Mass Production

Fixture สำหรับ induction brazing ไม่ใช่แค่ "ที่จับ" tube — เป็น precision tooling ที่กำหนด joint gap 0.05-0.15 mm, tube alignment ±0.05 mm, coil-to-workpiece distance 2-5 mm consistent ตลอด thermal cycle · 1 fixture บกพร่อง = 1,000 joints leak/day · บทความนี้อธิบาย design rules, material selection, automation integration

The 5 Critical Functions ของ Brazing Fixture

1. Joint Gap Consistency — 0.05-0.15 mm at braze temperature
2. Tube Alignment 360° — ป้องกัน lopsided heat
3. Coil-to-Workpiece Gap — 2-5 mm consistent for coupling
4. Thermal Expansion Accommodation — Cu expand 1.2% ที่ 700°C
5. Loading/Unloading Speed — cycle time impact

Fixture Material Selection

Material	Pros	Cons	Use Case
Alumina Ceramic	Non-conductive · high temp · low wear	Brittle · expensive	Contact surface, guide
Machinable Ceramic	Easy to fabricate · non-conductive	Lower strength	Custom complex shapes
Stainless 316	Strong · low EM coupling	Some heat loss	Structural support
Inconel 600	High temp tolerance	Expensive · heavy	Severe duty
Graphite	High temp · self-lubricate	Wear → contamination	Surface plate only
Aluminum (NO!)	Light · cheap	Heats up + melt risk	ห้ามใช้
Carbon Steel (NO!)	Cheap	Couples + rust	ห้ามใช้

Joint Gap Control — Precision Approach

Calculate Room-Temp Gap

Cu thermal expansion α = 16.5×10⁻⁶/°C · ΔT = 700°C - 25°C = 675°C · ΔL/L = α × ΔT = 1.11% · สำหรับ tube OD 12 mm fit ใน socket ID 12.10 mm: gap room-temp 0.10 mm · ที่ 700°C: tube OD 12.13 mm + socket ID 12.23 mm = gap 0.10 mm (uniform expansion) · Adjust ตาม geometry

Mechanical Stop Strategy

• Precision-ground ceramic block ที่ depth control
• Spring-loaded clamp maintain contact
• Visual inspection clearance gauge first article
• Gauge pin verification ระหว่าง batch

Tube Alignment 360° Strategy

1. V-block หรือ 3-jaw chuck สำหรับ concentric clamp
2. Indexing pin สำหรับ rotational orientation
3. Spring-loaded support accommodate thermal expansion
4. Quick-release สำหรับ fast unload

Quick-Change Fixture Architecture

สำหรับ multi-product line ที่ต้อง changeover < 2 minutes:

• Modular base + product-specific top — base ติดตั้ง permanent
• Kinematic mount — 3-point support, ไม่ over-constrain
• Pneumatic latch หรือ ¼-turn quick-release
• Indexing pin ±0.02 mm repeatability
• Color-code/RFID per recipe — operator ไม่ผิด
• Tool-less change — no wrench required

Robot Loading Integration

6-axis robot pick-place ใส่ tube + filler + fitting · Fixture design considerations:

1. Open access ให้ gripper เข้าจาก top หรือ side
2. Auto-clamp pneumatic หลัง robot release
3. Anti-collision sensor safety
4. Position confirmation switch verify part placed
5. Ergonomic backup สำหรับ manual operator

Cell layout: 1 robot ต่อ 2 brazing station (cycle 5-10 sec robot vs 15-30 sec brazing)

Thermal Expansion Accommodation

Cu α = 16.5×10⁻⁶/°C · ที่ ΔT 700°C: 100 mm tube ขยาย ~1.2 mm

• ฟิกซ์ปลายข้างหนึ่ง + อีกข้างฟรี slip (ห้ามฟิกซ์ทั้ง 2 = thermal stress crack)
• Spring-loaded support maintain contact during expansion
• Ceramic guide + Cu-Be wear strip (low friction sliding)
• Allow rotational expansion — joint area ขยายแบบ radial

Maintenance + Wear Life

1. Daily: visual inspect alignment surfaces, clear flux residue
2. Weekly: brush ceramic, check spring tension
3. Monthly: verify kinematic mount + pin fit
4. Quarterly: replace wear strips
5. Annual: full tear-down + rebuild

Wear life: ceramic 100,000-500,000 cycles · Stainless 50,000-200,000 cycles · Cost amortized ~USD 0.01-0.05 per joint

Common Design Mistakes

• ❌ ใช้ aluminum สำหรับ structural — heats up, melt risk
• ❌ ฟิกซ์ tube ทั้ง 2 ปลาย — thermal stress crack
• ❌ Coil mount on fixture — sets up vibration
• ❌ ลืม flux drainage path — flux pool corrode fixture
• ❌ Single-point alignment — depends on operator
• ❌ ไม่มี indexing — no traceability of orientation

SHINRAI Fixture Design Service

1. Joint geometry analysis from your drawing
2. Fixture concept design (CAD 3D)
3. Material selection (ceramic/stainless/Inconel)
4. Prototyping + first article qualification
5. Production fixture fabrication (Thailand local)
6. Installation + alignment
7. Cpk validation
8. Operator training fixture handling
9. Spare parts kit + maintenance training
10. [email protected], 098-978-9952