MIM Surface Treatment: The "Final Mile" for the Performance of Precision Components in Locks & Tools

The complete value cycle of Metal Injection Molding (MIM) hinges on surface treatment—a critical process. While most MIM components can achieve “near-net shaping,” they often face the challenge of “easy forming but difficult surface qualification” — especially in precision manufacturing fields such as locks and tools. The accuracy of surface treatment directly affects product service life, safety, and user experience. If forming and sintering lay the foundation for material and structure, surface treatment endows components with core properties like wear resistance, corrosion resistance, and precise adaptability through targeted optimization, directly determining the final value of precision parts. Truly the “final mile” of the MIM process.

I. Core Cognition: The Essential Nature of MIM Surface Treatment

MIM surface treatment is a systematic processing system for sintered components. Through physical, chemical, or combined physical-chemical methods, it focuses on two core values: first, correcting minor sintering defects (removing oxide scales, burrs, and micro-irregularities) to ensure dimensional accuracy; second, imparting special surface properties (enhancing wear resistance, corrosion resistance, and optimizing appearance texture) to meet the stringent requirements of various industries.

Unlike surface treatment in traditional machining, MIM components, due to their “near-net shaping” characteristic, impose unique demands of “minimally invasive optimization and precise adaptation” — it is necessary to avoid damaging the precision structure through excessive processing while ensuring uniform and stable treatment results.

II. Progressive Process: The Implementation Logic of Yibi Precision’s Four Core Procedures

MIM surface treatment is not a simple superposition of isolated processes, but a complete technical cycle progressing in the logic of “foundation guarantee → precision correction → corrosion protection primer → performance enhancement.” Each step’s control accuracy directly impacts the final outcome.

1. Step 1: Foundation Guarantee — Pretreatment

Thorough cleaning is the prerequisite for effective surface treatment, making pretreatment the “first line of defense” for subsequent processes. Targeting the complex structures of MIM components (e.g., microholes, deep grooves, thin walls), Yibi Precision adopts a customized solution of “ultrasonic degreasing + weak acid activation + vacuum drying”:

• 300-500W ultrasonic cleaning efficiently removes residual oil and additives from sintering;

• Short-term weak acid activation improves surface activity;

• Precision temperature-controlled vacuum drying at 60-120℃ prevents water accumulation in holes and secondary oxidation, ensuring thorough cleaning.

Validated in the processing of precision lock pins and key tooth grooves, this solution completely resolves residual cleaning issues in complex structures and avoids assembly jamming risks.

2. Step 2: Precision Correction — Mechanical Finishing

After pretreatment, precision correction begins to optimize surface finish and dimensional accuracy, rectifying minor sintering structural deviations. Yibi Precision selects equipment based on specific needs:

• Batch deburring and hardening: Crawler-type shot blasting machine (0.1-0.3mm steel shot, 0.4-0.6MPa spray pressure);

• Precision fitting components: Centrifugal grinding machine + ceramic abrasives, 30-60 minutes of precise grinding to achieve surface roughness ≤ Ra0.8;

• Appearance requirements: Additional automatic polishing machine + diamond polishing paste for uniform matte or mirror finish.

For core lock transmission parts (e.g., lock cylinder gears, opening/closing mechanisms), we stably control surface roughness between Ra0.4-Ra0.8 to meet the smooth fitting needs of high-frequency opening/closing scenarios. For precision engaging parts in tools (e.g., wrench jaws, screwdriver bits), precise grinding ensures dimensional tolerance ≤ ±0.01mm, guaranteeing engaging accuracy.

3. Step 3: Corrosion Protection Primer — Chemical Conversion Treatment

After mechanical finishing, chemical conversion treatment is required to form a dense protective base, which not only enhances corrosion resistance but also improves the adhesion of subsequent coatings — a key connecting link. Yibi Precision customizes solutions based on the “substrate adaptation” principle:

• Stainless steel components: Special passivation solution to form a dense protective film;

• Carbon steel components: Phosphating treatment (simultaneously optimizing subsequent assembly lubricity);

• Post-treatment: Sealing at approximately 40℃ and low-temperature drying to further strengthen protection.

Locks are often used outdoors, and tools frequently contact humid environments. Components treated with this process can achieve a salt spray test resistance of over 200 hours, significantly extending product service life and reducing after-sales maintenance costs.

4. Step 4: Performance Enhancement — Core Surface Treatment

As the core link, performance enhancement directly determines the final use value of components. Yibi Precision provides customized solutions based on the three-dimensional needs of “performance-cost-appearance”:

• High wear resistance solution: Hard chrome plating

Through precise control of current density at 20-30A/dm² with a DC electroplating power supply, an 8-15μm hard chrome coating is deposited in a titanium alloy chrome plating bath. The surface hardness reaches over HV800, withstanding high-frequency friction and high-intensity operations (suitable for high-frequency tool use scenarios).

• High-end performance + appearance solution: PVD titanium plating (TiN, TiCN, etc.)

Using a magnetron sputtering coating machine with a vacuum degree of 10⁻³-10⁻⁴Pa, a coating with hardness over HV1500 is deposited. It achieves salt spray test resistance exceeding 500 hours and presents textured appearances such as gold and black. This solution has been applied to high-end lock panels, anti-theft lock cylinders, and high-end hand tools in the tool industry — it not only meets wear and scratch resistance requirements but also enhances product appearance texture, helping customers achieve product premium.

• Cost-effective solution: Electroless nickel-phosphorus alloy plating

A 10-20μm coating is deposited in an 85-90℃ electroless plating bath without the need for electricity, balancing corrosion resistance and moderate wear resistance to meet basic use requirements of locks and tools.

After coating, all components undergo post-treatment including “rinsing and sealing + hydrogen relief baking (for high-strength components)”: A special sealant fills coating pores, and hydrogen relief baking is performed in an oven at 200-230℃ for 2-4 hours to completely eliminate hydrogen embrittlement risks and ensure components do not fracture under high-strength use.

III. Summary: The Core of MIM Surface Treatment Lies in “Precise Adaptation”

Alan Dunkan

Office