Electric heating oil prototypes, widely used in heating equipment (such as oil-filled radiators and industrial heating plates), rely on CNC machining to achieve precise oil circuit sealing, efficient heat transfer, and safe structural design. The quality of the prototype directly determines whether the final product meets heating efficiency, leak-proof, and safety standards. This article systematically breaks down the full CNC machining process for electric heating oil prototypes, addressing core challenges like oil circuit tightness, heat dissipation uniformity, and material thermal compatibility.
1. Pre-Machining: Design & Material Selection
Scientific design and appropriate material matching are the foundations of a functional prototype. This stage focuses on balancing heating performance, structural durability, and machining feasibility.
1.1 Demand Analysis & 3D Modeling
Clarifying functional and structural requirements first avoids costly rework during machining.
Demand Analysis Breakdown
| Requirement Type | Key Details | Impact on CNC Machining |
| Heating Function | Confirm target power (800W-1500W), temperature range (60-90°C), and heating method (U-shaped heating tube/spiral heating tube) | Determines the size and position of the heating element installation cavity (tolerance ±0.05mm) and oil circuit volume (calculated based on heat capacity) |
| Structural Design | Define shell shape (e.g., rectangular industrial heating plate: 300mm×200mm×50mm), heat sink structure (fin spacing, tilt angle), and oil injection/exhaust port layout | Influences toolpath planning (e.g., machining fin grooves with uniform spacing; ensuring oil port thread accuracy) |
| Safety Standards | Ensure shell surface temperature ≤50°C (anti-scalding), oil circuit leak-proof level (0 leakage under 0.5MPa pressure), and anti-tipping power-off function | Requires precise machining of thermal insulation layers (1-2mm gap between heating zone and shell) and sealed oil circuit cavities |
3D Modeling & Engineering Drawing Tips
- Software Choice: Use SolidWorks or UG NX to create modular models—split the prototype into 3 core parts: oil circuit cavity (heating zone), heat sink (heat dissipation zone), and control component cavity (temperature control zone) for step-by-step machining.
- Critical Design Notes:
- Reserve 5-10% expansion space in the oil circuit cavity to avoid oil overflow due to thermal expansion of the heating oil.
- Design honeycomb-shaped reinforcing ribs (thickness 3-5mm) in the oil cavity to prevent deformation under high temperature and pressure—ensure rib positioning accuracy (±0.1mm) for uniform stress.
1.2 Material Comparison for Core Components
Material selection directly affects oil circuit tightness, heat transfer efficiency, and machining difficulty.
| Component | Optional Materials | Advantages | Disadvantages | Machining Recommendations |
| Oil Circuit Cavity | Aluminum Alloy (6061) | Excellent thermal conductivity (167 W/m·K), lightweight, easy to machine | Low corrosion resistance (requires anti-rust treatment) | Use carbide tools; coolant required to reduce burrs on cavity inner wall |
| Cold-Rolled Steel Plate | High strength, good pressure resistance (withstands ≥0.8MPa) | Poor thermal conductivity (15 W/m·K), heavy | Slow feed speed (80-120 mm/min); post-machining galvanizing to prevent rust | |
| Heat Sink | Aluminum Alloy (6063) | Good heat dissipation, easy to machine fin structures | Low hardness (prone to deformation during clamping) | Use spiral end mills to machine fins; control cutting force to avoid fin bending |
| Shell Insulation Layer | Engineering Plastic (PC) | Good insulation, heat resistance (up to 120°C) | Low impact resistance | High-speed steel tools; compressed air cooling to prevent melting |
| Oil Circuit Sealing | High-Temperature RTV Silicone Rubber | Temperature resistance (up to 200°C), good sealing | Slow curing (requires 24-hour curing time) | Cut to size post-CNC; no machining required for the rubber itself |
2. CNC Machining Stage: Setup & Execution
This stage transforms raw materials into precision components, requiring strict control over machine selection, toolpaths, and precision.
2.1 Machine Tool & Tool Selection
Matching machines and tools to component materials ensures efficiency and accuracy.
| Component | Recommended Machine Type | Suitable Tools | Tool Size (mm) | Machining Purpose |
| Aluminum Alloy Oil Cavity | Vertical Machining Center (e.g., Haas TM-1) | Flat Bottom Cutter (Roughing), Ball Head Cutter (Finishing) | Φ10-12 (Roughing), Φ3-5 (Finishing) | Machine oil cavity inner wall (surface roughness Ra ≤0.8μm); chamfer edges (0.5mm) |
| Steel Plate Shell | High-Torque Machining Center | Tungsten Carbide End Mill | Φ6-8 | Cut heat sink fin grooves (spacing 20-30mm); machine oil injection port threads (M10×1.5) |
| PC Insulation Layer | 3-Axis CNC Engraving Machine (e.g., 3018 Pro) | Spiral End Mill | Φ4-6 | Machine control component cavities; drill wire holes (diameter 5mm) |
2.2 Programming & Machining Parameters
Optimized G-code and parameters prevent material damage and ensure precision.
Key Machining Parameters by Material
| Material | Rotational Speed (RPM) | Feed Speed (mm/min) | Depth of Cut (mm) | Special Requirements |
| Aluminum Alloy (6061) | 10,000 – 15,000 | 150 – 250 | 1.0 – 1.5 | Use emulsion coolant; avoid high speed to prevent chip buildup in oil cavity |
| Cold-Rolled Steel Plate | 5,000 – 8,000 | 80 – 120 | 0.5 – 1.0 | Apply cutting oil; reduce depth of cut to avoid tool wear and shell deformation |
| PC Plastic | 8,000 – 12,000 | 200 – 300 | 0.8 – 1.2 | Compressed air cooling; no coolant (prevents material warping and oil circuit contamination) |
Toolpath Optimization Tips
- Oil Cavity Machining: Use a spiral interpolation toolpath for roughing to remove 90% of excess material—reduce cavity wall scratches compared to linear paths. For finishing, use a ball head cutter to ensure the inner wall is smooth (Ra ≤0.8μm) and avoid oil residue.
- Fin Groove Machining: Adopt a linear array toolpath to ensure fin spacing uniformity (±0.1mm). Tilt the toolpath by 15-30° (matching fin tilt angle) to improve heat dissipation efficiency.
- Oil Port Thread Machining: Use a tapping cycle (G84 code) after drilling—ensure thread pitch accuracy (e.g., M10×1.5) to avoid oil leakage at the seal.
2.3 Machining Precautions
- Fixing & Positioning:
- Secure metal blanks (aluminum alloy/steel plate) with a vise + precision locating pins (tolerance ±0.01mm) to avoid vibration-induced cavity wall unevenness.
- Fix PC plastic sheets with high-temperature resistant double-sided adhesive tape (adhesion strength ≥5N/cm²) to prevent surface scratches and displacement.
- Precision Control:
- Maintain flatness tolerance ≤0.1mm for the oil cavity top/bottom plates—ensures tight fit and no oil leakage after assembly.
- Control oil port thread tolerance (6H) to match the sealing plug—use a thread gauge to test after machining.
2. Heating System & Oil Circuit Integration
Integrating heating elements and sealing the oil circuit turns components into a functional prototype.
2.1 Heating Element Installation
Proper installation ensures efficient heat transfer and safety.
Two Common Heating Element Solutions (Comparison)
| Solution | Installation Steps | Advantages | Disadvantages |
| U-Shaped Heating Tube | 1. Clean the heating element cavity with alcohol to remove machining chips.2. Apply high-temperature sealant (thickness 0.2mm) around the cavity opening.3. Insert the U-shaped heating tube (stainless steel 304, power density 1-2W/cm²) and fix with M4 screws (torque 0.3 N·m). | Large heating area, uniform heat transfer | Requires precise cavity size (avoid tube deformation during installation) |
| Spiral Heating Tube | 1. Machine a spiral groove (depth 10mm, width matching tube diameter) in the oil cavity.2. Embed the spiral tube and fill the gap with thermal conductive silicone grease.3. Seal the groove opening with an aluminum alloy cover plate (sealed with RTV silicone). | Close contact with oil, fast heating speed | Complex groove machining; high requirement for toolpath accuracy |
2.2 Oil Circuit Filling & Sealing
Strict oil filling and sealing processes prevent leakage.
Oil Filling & Sealing Steps (Linear Narrative)
- Oil Selection: Use mineral oil (ISO VG32) or synthetic heating oil (high temperature resistance, low volatility)—filter through a 5μm filter to remove impurities.
- Oil Injection: Inject oil through the oil injection port (equipped with a one-way valve) to 80% of the cavity volume—reserve space for thermal expansion.
- Exhaust Treatment: Heat the prototype to 50-60°C (using a low-power preheating method) to expel air in the oil circuit—repeat 2-3 times until no bubbles emerge from the exhaust port.
- Sealing: Close the oil injection port with a sealed plug (wrapped with PTFE tape) and the exhaust port with a pressure relief valve (set pressure 0.6MPa).
- Leakage Test: Immerse the sealed oil circuit in water, apply 0.3-0.5MPa air pressure, and observe for 30 minutes—no bubbles indicate qualified sealing.
2.3 Temperature Control System Installation
This system ensures safe and precise temperature regulation.
Component Selection & Wiring
| Component | Model/Specification | Installation Notes |
| Temperature Sensor | NTC 10KΩ (±1%) | Embed in the oil cavity (5mm from the heating tube); seal the lead hole with high-temperature silicone |
| Thermostat | Bimetallic sheet thermostat (mechanical, low cost) or PID electronic thermostat (precision ±1°C) | Install near the oil cavity top (sensitive to oil temperature changes); fix with M3 screws |
| Anti-Tipping Switch | Gravity induction switch (auto power-off when tilted ≥45°) | Mount on the prototype base (horizontal installation); ensure no obstruction to switch movement |
| Wiring | High-Temperature Silicone Wire (18AWG) | Route through pre-machined wire holes; wrap with fiberglass tape (insulation grade Class H) to avoid oil contamination |
3. Assembly & Testing
Rigorous assembly and testing verify prototype functionality and safety.
3.1 Assembly Process (Linear Narrative)
- Heat Sink Installation: Attach the CNC-machined aluminum alloy heat sink to the oil cavity outer wall—apply thermal conductive silicone grease (thickness 0.1mm) between them to improve heat transfer. Fix with M5 screws (torque 0.5 N·m).
- Shell Assembly: Cover the oil cavity and control components with the PC insulation shell—align the shell with the base positioning pins (tolerance ±0.1mm) and fix with snaps (ensure no gaps).
- Wiring & Debugging: Connect the heating tube, thermostat, anti-tipping switch, and power cord to the PCB board—test the circuit continuity (no open circuit) and insulation resistance (≥100MΩ at 500V DC).
- Final Check: Verify all components are securely fixed; ensure the oil injection/exhaust ports are sealed tightly.
3.2 Key Test Items & Standards
| Test Category | Test Method | Pass Standard |
| Heating Performance | Set temperature to 80°C; use an infrared thermometer to measure 5 points on the heat sink | Temperature difference ≤±5°C; reach target temperature in ≤15 minutes |
| Oil Circuit Tightness | 1. Apply 0.5MPa air pressure to the oil circuit for 1 hour.2. Tilt the prototype to 45° and hold for 24 hours | No pressure drop; no oil leakage at joints or ports |
| Temperature Control | Set the thermostat to 80°C; monitor temperature for 2 hours with a data logger | Temperature fluctuation ≤±2°C; auto-power-off when exceeding 90°C |
| Safety | 1. Measure shell surface temperature after 1 hour of continuous operation.2. Test anti-tipping function (tilt ≥45°) | Shell temperature ≤50°C; power off within 10 seconds of tilting |
4. Post-Processing & Optimization
Refine the prototype based on test results to improve performance and reduce production costs.
4.1 Appearance & Structural Optimization
- Surface Treatment:
- Aluminum alloy oil cavity/heat sink: Sandblasting (matte finish, anti-slip) or anodization (black/silver, anti-corrosion)—ensure coating thickness 8-12μm.
- PC shell: Polishing (remove machining marks) or silk-screen printing (add temperature labels and safety warnings).
- Structural Improvement:
- Lightweight Design: Machine 6-8 lightening holes (diameter 10mm) in non-load-bearing areas of the shell—reduce weight by 10-15% without affecting strength.
- Heat Dissipation Optimization: Adjust fin tilt angle to 20° (improve natural convection) or add PC plastic spoilers (guide airflow) to reduce heat sink temperature by 3-5°C.
4.2 Small-Batch Validation
- Replica Production: Use aluminum alloy die casting (for oil cavity) or resin pouring (for shell prototypes) to produce 10-20 small-batch samples—verify machining process repeatability.
- Iterative Improvement: If heating uniformity fails to meet standards, increase heating tube quantity or adjust tube position; if oil leakage occurs, re-machine the oil cavity seal surface (improve flatness to ≤0.08mm).
Yigu Technology’s Viewpoint
For CNC machining of electric heating oil prototypes, oil circuit tightness and thermal balance are core. Yigu Technology suggests prioritizing material matching: aluminum alloy 6061 for the oil cavity ensures efficient heat transfer, while cold-rolled steel is suitable for high-pressure industrial prototypes. In machining, focus on the oil cavity inner wall smoothness (Ra ≤0.8μm) and thread accuracy—even tiny defects can cause leakage. Post-assembly, strict pressure and high-temperature leakage tests are non-negotiable. Looking ahead, integrating smart functions (e.g., APP temperature control) will require CNC machining to reserve smaller cavities for wireless modules—demanding tighter tolerances (±0.03mm) and micro-tool applications.
FAQ
- What CNC machine is best for machining the aluminum alloy oil cavity’s inner wall?
A vertical machining center (e.g., Haas TM-1) is ideal. It offers high rigidity and precision (±0.005mm), ensuring the oil cavity inner wall is smooth (Ra ≤0.8μm) and flatness meets requirements—critical for tight sealing and uniform heat transfer.
- How to prevent the PC shell from warping during CNC machining?
Use high rotational speeds (8,000-12,000 RPM) and moderate feed speeds (200-300 mm/min). Additionally, use compressed air to cool the material continuously—avoids localized heat buildup that causes warping. Avoid machining deep grooves in one pass; split into 2-3 passes with 0.4-0.6mm depth each.
- Why is it necessary to reserve expansion space in the oil circuit cavity?
Heating oil expands when heated (volume expansion coefficient ~0.0007/°C). Without reserved space, the oil will exert pressure on the cavity, leading to seal failure and oil leakage. Reserving 5-10% space ensures safe operation even at the maximum working temperature (90°C).