Clean Parts Immediately for Improved Efficiency

For a more efficient cleaning process, lower overall manufacturing costs and satisfied customers, it’s best to clean parts immediately after machining is complete. Resist the temptation to pass the cleaning step on to the next department or the customer.

The critical cleaning step usually happens long before final assembly or coating, and machinists can be the cleaning superstars of manufacturing. Oils, lubricants and coolants that are left on the part can combine with metal fines and particles. The longer the length of time between machining and cleaning, the higher the potential for product malfunction. Soils change chemically with time. Soils oxidize in air, making them difficult to remove. Dried particles become increasingly adherent. Exposure to heat speeds up reactivity of thin films and makes particles even more difficult to remove. 

Immediately after machining, immerse large parts in mineral spirits or clean them in a small, aqueous parts washer. For parts with blind holes or helicoils, add benchtop ultrasonic cleaning. Make cleaning requirements part of machining requirements, and make sure cleaning equipment is conveniently located.

One manufacturer achieved customer satisfaction because machinists stepped up to the plate and cleaned the parts immediately. The final assembly step called for ultrasonic cleaning at 40 KHz to remove residual oils. However, the product released particles, and more cycles of ultrasonic cleaning resulted in more particles. The customer decreed excess particles in the “bath water” to be unacceptable. The manufacturer could have invested time and money to purchase new equipment and qualify a new process. Instead, the cleaning group took the one-minute leisurely stroll from the cleaning area to the machining area and discussed the problem. The machinists agreed to clean each part immediately. Results were astounding. Cleaning time decreased from three to four cycles to a single cycle of less than five minutes.

A manufacturer of coated consumer products solved yield problems with immediate cleaning and direct communication. Surface defects in the coated product were linked to inadequate cleaning. During a site visit, we found that the surface prep for the successfully coated products included buffing and that the buffing process included initial, immediate cleaning. When the manufacturer put all products through the buffing process, yield increased dramatically. 

In addition, after two hours of brainstorming involving production and quality assurance (QA), the customer revealed that in-house QA was a bit too enthusiastic for rejecting minute surface defects. The solution was to clarify acceptance criteria. Because all parties involved met face to face, getting everyone on the same page was simple. If there were numerous people at multiple locations, process documents with both written and photographic examples of acceptable surfaces would avoid misinterpretation.    

But how clean is clean enough? Does the cleaning process mesh with current customer requirements? Can the cleaning process grow and change as the customer base changes? Cleanliness requirements for aerospace, military, automotive and even medical are all closely related—except where they aren’t. Specific standards, accepted practices and “hot buttons” differ depending on industry segment. For example, potential toxicity residue is a major issue with implanted medical devices. And for automotive applications, assuring low particle levels is important (for example, VDA 19).

Understand how cleaning works. Find resources in the cleaning section of Production Machining. Talk with cleaning experts and suppliers of cleaning agents and cleaning equipment, and ask them questions. Make critical, immediate cleaning integral to production. For in-house or captive shops, keep tabs on what is being cleaned. Problem-solving discussions during coffee breaks and brainstorming sessions are better than audits and are more likely to yield more productive cleaning processes.