Cleanliness standards are becoming commonplace with the onus being placed upon tier suppliers to deliver parts to specific criteria. So selecting the right cleaning method and media is no less important than choosing a suitable CNC machine to produce the parts in the first place. Most cleanliness standards are defined by the end-user who after looking at subassemblies or the fully assembled product, calculating the accumulated debris within a system derive a cleanliness standard. How cleanliness is achieved depends on several factors, but the primary considerations have to be: –
- How clean is clean?
- How many parts per hour must I clean?
- How best to handle components?
- What are the contaminants?
- How much contamination is there to remove?
- How should you manage the contamination building up in the machine?
How Clean is Clean?
The level of cleanliness required will vary significantly depending on the components end-use. The scale of cleanliness might start with a metal gardening tools and carry on through to kitchen appliances, automotive parts, automotive ICE parts, jet engine components, SpaceX and satellite components arriving at bio level cleanliness of medical implants. Each has its own challenges to overcome. Garden tools produced in millions, satellite components that must be “fit and forget” reliable, aircraft parts… well you get the picture. Cleanliness must match the use, and so probability versus risk becomes the backbone of any cleanliness standard assigned to a component or product.
Total particulate mass left on the product – mg/m2, geometry and magnetism all impact the total particulate mass left on the parts.
The organic matter left on the part – Painting, plating, furnace brazing, IVD coating, and bonding are just a few production processes impacted by organics like oil, greases and fingerprints. Again correct media selection is essential in removing these contaminants.
Maximum particulate size – the smaller the maximum particle size allowable, the more challenging it is to achieve. Anything with a maximum particle size below 200µ is considered more challenging, and the cost to achieve the desired outcome increases exponentially as you head towards 100µ and beyond.
The number of permissible particles per size category is usually defined by the end-user and its imperative that they are realistic about the standards required. They should be as relaxed as possible whilst safely achieving the service life of the assembled product.
How many parts per hour must I clean?
Production volumes have a significant impact on the design of your cleaning system and the cleaning media used. The more parts /hr cleaned and more hours worked per week, the more contamination enters the cleaning machine, and the less time is available for maintenance.
As such, this contamination must be managed proactively to maintain the cleanliness standards required.
How best to handle components?
Here we have a simple example with company 1 and 2 producing thousands of parts per hour where the components must be handled in two different ways. These are considerations that need to be thought through in the early stages of exploring new cleaning equipment. A poorly executed process will lead to increased labour, costs and potential for scrappage.
- Bulk cleaned in direct contact with each other and still achieving cleanliness.
- The components must not suffer any metal to metal contact.
Company A has the advantage of merely tipping parts into a basket and washing them. A contemporary solvent degreasing machine (typically German) can result in loads getting washed and dried every 5 mins.
Efficiency improvements include placing the washing basket at the CNC machine, rotating them out with empty ones as they fill up.
Whereas with Company B, each part must be placed into a protective carrier such as our FRIES TechTray system. This becomes labour intensive, or further investment is required in robotics.
The number of parts per load is significantly reduced, with up to 70% fewer components per load. Still, The number of components/hour hasn’t changed, so either two machines are required, or a larger capacity machine is needed to maintain throughput.
What are the contaminants?
Three primary contaminant groups exist, each having its own characteristics and compatibility with different cleaning media. Media selection becomes progressively more involved the more contaminant types are present on the component. It can be argued that in some cases a washing step between a change of contamination will produce more favourable results and fewer rejections
Polar contaminants are water-soluble, such as salts, emulsions, EP additives etc.
Non-polar contaminants a water-insoluble and include oils, waxes, fats and esters.
Solid contaminants include swarf, chips, grinding residues, and solids from lapping and polishing pastes.
How much contamination is there to remove?
Part geometry, surface area and viscosity all play a part in determining the total contamination removed. A simple but effective method of establishing the amount of contamination going through the machine can be found by: –
- Weigh the basket of parts before and after a cleaning trial. This difference is the total mass of contamination removed and provides an excellent indicator. You may need to make a judgement about the swarf and chip content in your calculations.
- Run several loads to get an average.
- Count the total number of parts per load to find the amount of contamination per part.
- It’s then a simple calculation of Number parts/hr x grams of contamination per part = total contamination per hour.
The total grams per hour can be converted in millilitres by multiplying the total by the contamination density. Most neat cutting oils, for example, have a density between 0.8 and 0.88.
Production volume 15,000/hr.
Contamination/part = 1.25g
Contamination density = 0.85
Total waste collected = 15000*1.25 = 18750g (18.75kg)
Total litres of contamination removed from the parts = 22l/hr.
How should you manage the contamination building up in the machine?
This total contamination figure is essential when defining machines specification and capabilities. Its a topic rarely understood by the purchaser and should be explored thoroughly with the seller. A clear understanding is required so the right optional extras are included in the machine specification. Questions such as: –
- How quickly is the cleaning media be recycled?
- How often will the machine need cleaning out?
- What is the downtime for cleaning down the machine?
- Can the machine clean itself automatically?
- What is the cost of automatic cleaning option versus the cost of labour, H&S requirements, and lost production to do this task manually?