Surface wear is one of the primary causes of locating pin replacement in fixture and assembly applications. MISUMI’s R-DLC whitepaper tests Rainbow Diamond-like Carbon coating head-to-head against three common pin materials—measuring hardness, indentation modulus, coefficient of friction, and wear rate under controlled conditions.
Introduction
Material surfaces wear over time—particularly in fixture applications where there is repeated surface-to-surface contact between a steel locating pin and an aluminum or steel workpiece. This progressive wear degrades pin precision, increases replacement frequency, and adds to machine downtime.
Wear-resistant coatings are a practical solution. By applying a hard, low-friction surface layer to a locating pin, engineers can extend service life significantly without changing the underlying pin geometry or material. R-DLC is one such coating: a variant of Diamond-like Carbon engineered specifically for this class of application.
What is Diamond-like Carbon (DLC)?
Diamond-like Carbon (DLC) is a class of amorphous carbon material that exhibits properties characteristic of diamond—high hardness, chemical inertness, and a low coefficient of friction. Unlike crystalline diamond, DLC can be deposited as a thin coating onto metal components at relatively low temperatures, making it practical for precision machined parts like locating pins.
R-DLC (Rainbow Diamond-like Carbon) is a unique variant. The “rainbow” designation refers to its visible iridescent surface appearance, which results from the coating’s optical properties—a consequence of its specific amorphous carbon structure.
Key features of R-DLC coating:
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Extreme hardness. 6,000–7,000 HV provides superior surface durability against repeated workpiece contact
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High abrasion resistance. Minimizes wear in demanding, high-cycle fixture applications
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Prevention of cold welding in aluminum components. Prevents galling and material build-up, prolonging the service life of both the pin and the workpiece
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Low coefficient of friction. 0.15–0.2 against steel (dry) for smooth, repeatable pin insertion and removal
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Chemical resistance. Withstands exposure to aggressive substances in the manufacturing environment
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Extremely high thermal conductivity. Approximately 5× higher than copper, helping dissipate heat at the contact interface
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Biocompatibility. Coating causes no harm or adverse effects, making RDLC pins suitable for medical device fixture applications
Materials tested
The study compares four material types across all tests. Understanding the baseline properties of each material helps contextualize the R-DLC coating’s performance advantage.
Tests performed
The whitepaper covers three primary test categories, each with associated statistical analysis:
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Hardness (HIT) and Indentation Modulus (EIT)—measures surface resistance to permanent deformation and the elastic stiffness of the coating under an indentation load. Higher HIT indicates a harder surface; higher EIT reflects greater stiffness.
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Coefficient of Friction and Wear Rate—quantifies how much resistance the surface generates under sliding contact, and how quickly material is lost over repeated cycles. Both directly predict service life in fixture applications.
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Statistical Tests for Each—each measurement set is analyzed statistically to confirm that observed differences between materials are significant rather than artifacts of test variation.
| Test | Metric | Relevance to locating pins |
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| Hardness | HIT (Indentation Hardness) | Determines resistance to surface denting and deformation from workpiece contact |
| Elastic modulus | EIT (Indentation Modulus) | Indicates how much the coating deforms elastically—affects contact stress distribution |
| Friction | Coefficient of Friction (CoF) | Lower CoF reduces galling and heat generation during pin insertion and removal |
| Wear | Wear Rate | Directly predicts replacement interval and total cost of ownership for the pin |
Download the full whitepaper
The complete study includes all raw test data, methodology, equipment specifications, and statistical test results for each material pair. It is intended for engineers evaluating locating pin material selection for fixture, welding, or assembly applications.
