The techniques for the smooth transition between rough processing and fine processing

In the processing of precision castings for valves, pumps and mining machinery, rough machining is "shaping and laying the foundation", and finishing is "exquisite carving". The rationality of their connection is the key to determining casting precision, quality and efficiency. Only by ensuring good connection can we avoid deformation, dimensional deviation and other problems, form a closed loop of the two processes, maximize their advantages, and ensure controllable casting precision and stable quality.

The core of rough machining is to quickly remove allowance and initially form the workpiece, reserving reasonable space for finishing; finishing focuses on micron-level precision to meet the stringent requirements of core components of valves, pumps and mining machinery.

 

1. Precisely Reserve Machining Allowance to Lay a Solid Foundation for Connection

Reserve uniform and reasonable machining allowance according to casting material and structure, avoiding insufficient or excessive allowance. After rough machining of valves, pumps and mining machinery castings, a uniform allowance of 0.1-0.5mm should be reserved (0.5-1.0mm for large castings); slightly larger allowance and symmetric rough machining are adopted for deformable parts; the hole wall allowance of hole parts should be uniform after rough boring, and deviations should be calculated and distributed in advance to ensure sufficient finishing space.

 

2. Eliminate Internal Stress from Rough Machining to Avoid Deformation Hidden Dangers

If internal stress generated by rough machining directly enters finishing, it will cause workpiece deformation and precision damage. Stress relief treatment must be added between rough and finishing: natural aging (24-72 hours) or low-temperature annealing for cast iron and cast steel parts; low-temperature aging for stainless steel and wear-resistant alloy parts; semi-finishing transition can be added for high-precision components. Re-inspect after stress relief to confirm stable size before entering finishing.

 

3. Unify Datum Positioning to Ensure Precision Continuity

The same positioning datum must be used for rough and finishing to avoid datum offset affecting precision. Select the core datum surface of the casting as the common datum, and initially finish the datum surface during rough machining; use unified tooling for clamping, adjust the force to avoid deformation, and ensure consistent positioning precision for each clamping; special positioning tooling can be customized for special-shaped castings to ensure unified and firm datum.

 

4. Optimize Connection Details to Improve Efficiency and Precision

Core details: 1. Timely clean chips and burrs after rough machining to avoid affecting finishing precision; 2. Rough machining focuses on cooling, and finishing focuses on lubrication, avoiding shared cooling schemes; 3. Establish a connection inspection mechanism, conduct sampling inspection after rough machining, and rework unqualified parts in time; 4. Reasonably plan processes, giving priority to rough machining of difficult-to-process and deformable parts.

 

Good connection between rough and finishing, achieving "precise allowance, stress elimination, unified datum and controllable details", can not only avoid processing defects, improve casting precision and stability, but also reduce costs and improve efficiency, laying a solid technological foundation for the competitiveness of precision castings for valves, pumps and mining machinery.