Cleanliness requirements and specifications are an essential part of the manufacturing process. To better understand their role and the difficulties that may arise in meeting such specifications, it's essential to consider the following aspects:
Previous PROCECO blogs such as Aqueous Cleaning Fundamentals and Standards of Cleanliness provide a solid background for the first two points. This blog focuses on factors that make meeting cleanliness requirements difficult and how we can address them.
The contaminant particles that impact cleanliness requirements are extremely small. While pollen grains and white blood cells are both 30 microns in diameter, many particles affecting cleanliness test results measure only 15 microns or less.
Choosing the appropriate filtration can help reduce the quantity of such particles, but once they're deposited on a surface, these particles can be very difficult to remove. Forces of adhesion such as humidity in the air, capillary forces, and metal working fluids (MWF) cause such particles to adhere to workpiece surfaces.
Dedicated research and materials expertise at OEM technical centers have concluded that remaining abrasive particles are a primary cause of premature war of internal components in assemblies. To mitigate this, cleanliness requirements are implemented to limit the remaining number of particles on the part.
Particles that are 25 microns and below in size can impact assembles that involve constant metal-to-metal contact (ex. transmissions). The acceptable number of particles, based on new standards, are grouped in a range of sizes and have been reduced in quantity by as much as a factor of 10.
This more stringent particle count requirement is increasingly problematic for Tier 1 suppliers to consistently meet on machined parts. It's not practical to replace ceramic abrasives with anything else in the machining process, so the problem of particle contamination can only be addressed by identifying the source of the contamination and taking action to reduce it as much as possible.
Particles are often produced by upstream processes necessary for the production of a component: grinding, polishing, and blasting. These require abrasive media that is harder than metal to lightly remove material from the surface, typically to reduce the surface roughness or prepare the surface for non-abrasive processes such as heat treatment or welding. The presence of such particles on workpieces is a by-product of machining and finishing, which are among the primary work activities for component manufacturing. Since these are necessary manufacturing activities and value-added processes, their contribution of contaminants must be managed and reduced as much as possible.
Other particle sources are related to conditions in the parts washing environment, such as the following:
There may also be deficiencies in the testing process, procedures, or environment. For example, one customer facility we analyzed included a laboratory with an insufficient ventilation system and that was located close to a machining facility. Additionally, while test personnel wore gloves during the testing process, they wore no special clothing such as laboratory coats, so these conditions all combined to increase the risk of contamination during the testing and handling process.
PROCECO proposes two ways to address this problem:
Meeting increasingly demanding cleanliness specifications is not a problem that will go away. It's going to continue to assert a stronger presence, especially as electric vehicles become more prominent. Therefore, it's vital that parts manufacturers address the issue directly and thoroughly.
It's not a matter of cleaning more aggressively, we have to clean smarter, and more strategically. These strategies require the collaboration and efforts of Tier 1 manufacturers, parts washer manufacturers, and chemistry suppliers to improve the overall cleaning conditions.
To achieve this, we need to understand the problems, process, and sources; this includes the materials science and chemical properties in addition to the mechanical aspects.
PROCECO recognizes this and encourages you to contact us to help you solve these complex problems!