Technical cleanliness is an analytical standard to determine the level of particulate contamination on machined parts. The goal of technical cleanliness is to characterize particles on the components and ensure that they are within certain defined thresholds – in terms of quantity, size, and hardness. Technical cleanliness ensures that manufactured parts adhere to industry standards for accepting or rejecting them.
Industries Where Technical Cleanliness Is Important
Technical cleanliness is a discipline of quality assurance finding widespread use across various branches of industry. Though mainly described in the context of automobiles, TC analysis is regularly implemented in electronics, medical devices, and, naturally, aerospace manufacturing as well. It is within these sectors that small particles if left unchecked, pose a threat to the safety and quality of every component.
Contaminant particles could cause significant degradation of the performance of the final product, and in worst-case scenarios, a complete failure. Indirect costs include the additional resources required to address the issues and the damage to the reputation of the product and the company. Stringent technical cleanliness standard enforcements are therefore necessary for ensuring product integrity remains uncompromised because the costs of contamination can be very steep.
How is Technical Cleanliness Regulated?
Many international standards are in place to guide manufacturers in effectively navigating technical cleanliness. One of the most significant standards is the International Organization for Standardization’s ISO 16232. This extensive document describes how to apply methods for determining particulate contaminants on functionally relevant components and systems of the automotive industry. Another standard for the quantitative determination of particulate contaminants on parts in the automotive industry is VDA 19, from the German Association of Automotive Industry. These standards are intended to provide information on how to define cleanliness specifications, improve comparability of cleanliness inspection results, and define actions when cleanliness limit values are surpassed. The standard does not define cleanliness limit values for specific components. Cleanliness specifications also need to consider the whole system that the components are built into, making it impractical to define limit values for specific components. To make the analysis results comparable, ISO 16232 defines the type and test volume of the extraction fluid, the method of collecting contaminants, and the settings of the analysis instruments. Cleanliness analysis is performed during initial inspection and evaluation, or quality control steps in the manufacturing process such as cleaning, surface treatment, or assembly.
What Parts are Studied for Cleanliness?
During the manufacturing process, machined parts go through several different steps including cutting, polishing, grinding, filing, welding, and deburring. These processes are likely to generate residues and foreign particulates that may linger on the parts, requiring extensive cleaning of the parts. But cleaning does not always work the first time around and this is where technical cleanliness standards play a critical role. Here is a non-exhaustive list of components that are subject to technical cleanliness standards:
Automotive Parts
Crankshaft bearing clamps
Valve blockages
Nozzles & injectors
Filters
Piston rings
Transmission gears
Engine cylinder liners
Fuel pump components
Brake calipers and pads
Suspension system parts
Aerospace and Aeronautics
Aircraft turbine blades
Avionics circuit boards
Landing gear assemblies
Wing & fuselage panels
Hydraulic system components
Flight control surfaces (flaps and rudders)
Spacecraft thermal protection systems
Medical Devices
Catheters
Pacemakers, stents (implantable devices)
Scalpels, forceps (surgical tools)
Ventilator components
Prosthetics
Hip replacements, spinal screws (orthopedic implants)
Insulin pumps, inhalers (drug delivery devices)
Dental implants and instruments
Electronic Parts
Integrated circuits
Printed circuit boards
Microprocessors
Capacitors and resistors
Connectors and cables
Memory modules
Power supply units
A Technical Cleanliness Workflow:
The first step in the workflow is to collect a sample from the component. This is usually accomplished by a fluid rinse with a defined volume of a specific fluid. This is typically done in a clean room to eliminate the chance of any additional contamination. The particles in the fluid are then collected on a filter membrane, dried, and examined. Not all manufactured parts have a compatible fluid with which they can be rinsed. Alternative methods of extracting particles include pressing adhesive tape against the surface of interest and lifting it off.
ISO 16232 provides guidelines for analysis using techniques such as gravimetric analysis, optical microscopy, and scanning electron microscopy. The gravimetric analysis involves simply weighing the filter membrane before and after collecting the particles. This method however only gives an idea about the bulk particulates and does not produce any data regarding individual particles such as size, shape, or composition. Information regarding individual particles can prove to be invaluable in efforts to isolate the origin of the particle.
Optical microscopy methods are capable of generating data at the single particle level but are limited by optical resolution and can not detect small particles. These methods also fall short when it comes to generating elemental composition data on the particles. Scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS) represents the most effective way of characterizing particles at high resolution and collecting information on the elemental composition.
Standard floor size SEM are expensive and require dedicated infrastructure and experts to analyze the samples. With the introduction of the Phenom Desktop SEMs, several of the hurdles in using an SEM for technical cleanliness have been eliminated. Even then, analyzing large areas for particles is time-consuming and monotonous. Automated SEM solutions, such as ParticleX, make the monotony of scouring the filter for particles effortless. The technical cleanliness routine of the ParticleX package consists of inspection, image optimization, measurements, and additions to a catalog of every detected particle.
The automated software of ParticleX is tailorable through user-defined recipes. These recipes dictate the parameters implemented during a run (beam energy, vacuum, detector type, EDS rules, particle size rules, etc.), setting the framework of the reports, once the analysis is complete. The filter is segmented into smaller fields and subsequently scanned with the electron beam. As particles are detected, they are imaged, quantified, and characterized with EDS. Geometrical properties, along with an EDS spectrum, are logged on a particle-by-particle basis. Learn more about ParticleX Technical Cleanliness in this technical note.
Because the bulk of the work is offloaded from SEM operators, managing the cleanliness code rules within the program will be the only main concern for manufacturers.
Conclusion
Technical cleanliness is a vital analysis of manufactured parts. As its name implies, the level of precision needed for ensuring quality goes well beyond simplistic dirt cleaning, necessitating the use of advanced techniques to probe the microscopic particles that threaten part functionality. Complete characterization of particles is best suited for the synergistic combination of SEM and EDS – accurate size distributions, particle morphology, compositional analysis, and industry standard-compliant reports are key capabilities enabled by these techniques that excel in the realm of technical cleanliness.
