CLADDING TECHNOLOGY SHANXI CO., LTDDesign of the Mechanical System for an Automatic Surfacing Machine
Introduction and Engineering Background
The study by Shi Hongxin, Duan Shixin, Li Weiwu, and Ding Shiwei, jointly conducted by Henan University of Science and Technology and CITIC Heavy Industries (2007), presents the mechanical design of a dedicated automatic surfacing machine tailored for mining machinery component repair and enhancement. This work bridges the gap between academic research on surfacing processes and the practical demands of heavy equipment manufacturing, where large and complex components require high-quality, repeatable overlay deposits.
Mechanical System Architecture
The automatic surfacing machine designed in this study incorporates several key subsystems that work in coordination to achieve precise and consistent surfacing operations:
- Main drive and positioning system: A gantry-type or bridge-type structure providing multi-axis movement (X, Y, Z) for the welding torch or surfacing head, with positioning accuracy of +/- 0.5 mm over a working envelope of 2000 x 1500 x 800 mm.
- Wire feed mechanism: A dual-drive or four-roll wire feeder providing constant wire feed speed with fluctuation less than 1 percent, essential for maintaining consistent deposition rates and bead geometry.
- Torch positioning and angle control: A servo-controlled torch holder maintaining the travel angle (typically 10 to 15 degrees) and stick-out length (12 to 18 mm for GMAW) throughout the surfacing pass.
- Workpiece clamping and rotation: For cylindrical components such as feed rolls or conveyor shafts, a hydraulic chuck with face plate provides secure clamping and synchronized rotation.
- Coolant and shielding gas delivery: Integrated systems ensuring adequate arc protection and thermal management during multi-pass operations.
Process Integration and Control Parameters
The mechanical system must be designed to accommodate the specific surfacing process parameters required for mining machinery applications. The table below summarizes typical operating parameters for the GMAW-based automatic surfacing system:
| Parameter | Typical Range | Design Requirement |
|---|---|---|
| Arc voltage | 22-28 V | +/- 0.5 V stability |
| Wire feed speed | 3-8 m/min | +/- 1% fluctuation |
| Travel speed | 100-400 mm/min | Programmable |
| Wire diameter | 1.2-1.6 mm | Feed roller compatibility |
| Shielding gas flow | 15-25 L/min | Laminar flow pattern |
| Torch angle | 10-15 degrees | Servo-controlled |
| Stick-out length | 12-18 mm | Maintained automatically |
The control system employs a closed-loop architecture where the arc voltage and current are regulated independently, with the wire feed speed serving as the primary control variable for current regulation. This ensures consistent arc energy delivery despite variations in travel speed or wire diameter.
Defect Prevention Through Mechanical Design
A well-designed automatic surfacing machine directly impacts deposit quality by minimizing common defects:
- Porosity: Prevented through consistent gas flow delivery and avoidance of turbulence at the torch nozzle. The machine design incorporates a gas nozzle with 20 to 25 mm diameter positioned 5 to 8 mm from the contact tip.
- Lack of fusion: Avoided through precise travel speed control and proper torch angle maintenance. The servo system ensures that the travel speed does not deviate from the programmed value by more than 2 percent.
- Excessive dilution: Controlled by maintaining consistent stick-out length and travel speed, which directly affect heat input and weld pool geometry.
- Cracking: Mitigated through preheat control and post-weld cooling rate management, with the machine incorporating a preheat plate or induction preheat coil as an optional accessory.
Engineering Insights and Practical Implications
The mechanical design of automatic surfacing equipment is fundamentally about translating process knowledge into reliable hardware. The experience from this study highlights that the mechanical system must provide not only positional accuracy but also dynamic stability during operation. Vibration from the wire feed mechanism, for example, can cause arc instability and surface roughness in the deposit. The use of harmonic drive reducers or precision ball screws in the positioning system is critical for achieving smooth travel without stick-slip behavior.
Furthermore, the integration of process monitoring capabilities into the machine design adds significant value. Real-time monitoring of arc voltage, current, and travel speed allows for immediate detection of process deviations, enabling corrective action before defects become established. This approach aligns with the PDCA (Plan-Do-Check-Act) quality management philosophy and supports the systematic improvement of surfacing quality in production environments.