What are the surface treatments used in machining mechanical parts?

What are the surface treatment processes used in machining mechanical parts? What key considerations should be taken into account during machining inspection?

In the machining of precision mechanical components, high demands are placed on strength and durability, and the component’s functional performance and service life are closely linked to its surface properties. However, enhancing these surface characteristics cannot be achieved through materials alone, nor is it economically viable. In practical manufacturing, to ensure that the required performance is met, surface‑treatment techniques are employed as needed.

Mold polishing is a critically important step in the field of mold surface treatment and an essential process in the machining and finishing of workpieces. Surface‑finishing techniques for precision mechanical components play a pivotal role throughout the manufacturing process. It is worth noting that the polishing of precision‑part molds is influenced not only by the polishing process and equipment but also by the mirror‑finish quality of the part material—yet this factor has not yet received adequate attention in current practices, underscoring that polishing itself is materially dependent.

Although machining techniques for surface functionalization of precision components are continually advancing, hard‑film deposition, nitriding, and carburizing remain the primary methods employed in their fabrication. This is because nitriding can deliver superior surface properties, and its process parameters exhibit excellent compatibility with the quenching processes used for steels in precision parts.

The nitriding temperature is very low; therefore, after nitriding treatment, a severe cooling process is not required, resulting in minimal distortion of precision parts. Consequently, nitriding has long been one of the techniques employed in the machining of precision mechanical components to enhance surface properties, and it remains widely used today.

When machining mechanical parts, engineers typically refer to the drawings prepared prior to machining. These drawings specify surface‑finishing requirements; however, they do not guarantee that every machined part will meet the specified tolerances. Therefore, during inspection, the following considerations should be taken into account.

I. Inspection Requirements

1. Visual Inspection

(1) Verify that the surface finish of the machined parts meets the requirements specified in the drawings.

(2) Inspect the machined parts for surface damage, rust, or scratches, and verify that the thread form and angle are correct.

(3) If any of the aforementioned issues are identified, detailed records shall be kept for future reference.

2. Quantity Inspection

(1) In accordance with the supply contract and processing vouchers, rigorously verify the raw materials, specifications, and quantities of the machined parts against the drawings, conducting a line-by-line check.

(2) Conduct a quantity inspection, specifying the inspection location, date and time, personnel involved, variety, product name, batch number, and the actual quantity of goods received.

3. Quality Inspection

(1) Perform assembly strictly in accordance with the rules and procedures specified in the general assembly drawing.

(2) Maintain thorough records of quality inspections. When quality issues arise with machined parts, promptly notify the external processing supplier in writing of the specific circumstances. Determine, based on the situation, whether to return the goods or arrange for a replacement. (3) If special requirements apply, coordinate with the processing supplier to jointly inspect and assemble the components; only after passing inspection may the inspection documents be signed.

II. Inspection Procedures

1. Upon receipt of the machined parts, two dedicated inspectors will conduct inspections of the raw materials, specifications, models, and quantities in accordance with the requirements specified in the contract’s drawings.

2. The inspection cycle is typically 1–2 days. In special cases, the application performance will be evaluated. If quality issues arise, returns and claims are permitted, and the responsible party shall bear any resulting financial losses.

3. Processing contracts signed by non-production departments shall be inspected directly by the requesting department, which will also complete the inspection report.

4. For parts that fail inspection, the inspector must process rework and return procedures within the inspection period.

5. For the inspection of specially finished parts, the dedicated inspector shall convene relevant personnel to conduct a joint inspection and complete the inspection report. For parts that fail inspection, a detailed inspection record must be prepared to identify areas for improving machining accuracy and to guide future decisions regarding the selection of external manufacturers.