LESSONS LEARNED: CNC Machined parts Cleaning Procedure for Magnesium Manifolds
For decades, manufacturing process R&D has been an integral part of shaping MacFab’s service capabilities and technological advancements. Our lessons learned include “what not to do” as well as “what to do”. Although many of our research projects were, at the time, product specific, the knowledge and experience gained were transferable to a variety of other product challenges.
A client came to us this year with a complex problem producing susceptible portable detectors. We love the hard cases, and we recognized that this project requires advancement in physical chemistry, material science, and engineering. The following are some of those lessons learned from recent and not-so-recent research projects. You can see how they informed our research into solving his problem.
These detectors have been manufactured from aluminum but machining the air manifolds from magnesium would make them considerably lighter. Aluminium is a rather inert metal, not so magnesium. Sniffer detectors like this work with parts per billion. That means the air absolutely cannot handle being exposed to contaminants once it enters the machine.
“Normal” Parts Cleaning Won’t Work
The normal procedure is to wash the parts first with water-based cleaners, followed by a solvent, then bake them to drive off any residue. That works for aluminum, but magnesium begins to anneal at typical baking temperatures. Not only will it deform slightly from the heat, but tiny features like the screw threads in tapped holes will weaken. We knew that typical wasn’t an option, so we needed to find an alternative.
We knew CNC machining magnesium means no water-based coolants. CNC machining magnesium is always exciting because the metal catches fire easily, and once it ignites it’s very difficult to extinguish. It burns hot enough to melt steel. Machining it without coolant can overheat it to the point of ignition. Machining magnesium also means taking every step to avoid fine cuttings, as those are the most flammable. We had to develop cost-effective, customized micro-fixturing to facilitate component manufacture and assembly. We even had to avoid high humidity and only handle them with clean nitrile gloves to avoid moisture.
Acids could clean the contaminants but would eat away the surface of the magnesium parts. Ultrasonic cleaners will cause microscopic surface pitting. Because of their intended use for sniffing out explosives and drugs, we had to avoid halogens in the cleaning regimen. Even traces of chlorine or fluorine would render them useless. Commonly used cleaning solvents like alcohols and ketones were also out of the question. The entire drying/ baking process had to be carried out in a vacuum. Newly cleaned parts then have to be packaged immediately to protect them from contamination and humidity.
Testing, Research, and More Testing
Macfab’s clean room facilities were invaluable for this project, like many before it. The procedure we developed for this project included prohibiting anyone from touching the parts unless they have been specifically trained. Each part had to go through the ultra-cleaning process after each handling. Cleanliness inspections required microscopes as high as 40X and unique borescope inspections for internal surfaces with all inspection and packaging processes have to be carried out under a laminar flow hood with particle-free compressed air.
The Value of Quality CNC Machining
All of our experience has gone into the development of a rigorous manufacturing regimen covering every aspect of producing components from start to finish. It did in fact involve many different talents, from designing the micro-fixtures to environmental control to cleaning and cleanroom protocols. Every step has had to be tailored for this project, and the end result is a development not many CNC machine shops could produce.
This is the work we love. The projects that others have said couldn’t be done or have hit walls in their attempts provide us with the opportunities to push ourselves. That’s why we invest heavily in facilities like our clean room and the incredibly sensitive testing equipment. We love advancing the state of the industry. Our research and discoveries on this project will inform future demands, which are always evolving to push past our current state of knowledge.
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