In critical product cleaning, achieving throughput means assuring that residue is removed from parts in a short enough time and that the parts are clean enough. Part of the decision involves sizing the cleaning equipment for adequate throughput. Throughput also means assuring that manufacturing “traffic” flows smoothly – with no infamous Los Angeles-style traffic jams.
Cleaning cycle, sizing
Someone from a company selling the new cleaning machine may provide a throughput estimate. Throughput is provided in addition to the working dimensions of the chamber or the tank, or the conveyor belt width. Sometimes the phrase “sizing the equipment” is used. For batch cleaning, this involves estimating how many parts can reasonably fit into the process bath or process chamber and then multiplying by the cycle time. For in-line (conveyer belt) processes, the equipment supplier may size equipment based on the number of parts to be processed per unit time and the speed of the conveyor belt. The throughput estimate is essential information – but it is just that – an estimate. Consider a few more factors and avoid traffic jams, pile-ups, and complete freeway closures.
Bottlenecks
Selecting a cleaning system based on an estimated typical cleaning cycle alone is not a rational approach. For the best return on your equipment investment, consider additional factors. Be sure to ask, to question, and to look at your own manufacturing microclimate. Why are you cleaning? What do you expect to accomplish with the new cleaning equipment?
There can be bottlenecks. For example, estimating the rate of cleaning per hour alone can be a problem if there are peaks in production where cleaning must happen immediately after processing or where the next step in manufacturing must happen immediately after cleaning.
If a semi-automated cleaning system replaces hand-wiping by individual operators, the third shift may leave product to be cleaned for the following day. We don’t mean to make fun of you third shift people! Soil that remains on the part, even for a few hours, can be more difficult to clean. To cope with this problem, the third shift can learn how to use the cleaning machine. If the third shift people (or anyone else) can’t do the cleaning step right away, a preliminary pre-cleaning step may be the best approach. This can be as simple as a wipe-down of the product or submersion of the parts in a hydrocarbon (subject to the permitting situation in your location). If the downstream process is the pinch point, perhaps a slower cycle time or a smaller cleaning system would be the right approach. Perhaps the downstream process could be made more efficient.
Where there are bottlenecks, the cleaned product must be stored so that it is not recontaminated.
Are you removing the soils?
That cleaning cycle has to remove soils effectively. Are you certain the new cleaning system will adequately remove all of the soils your facility is likely to encounter? The best estimates of throughput are limited by assumptions of cleaning effectiveness. An effective process change team (yes, we have to remind you that process change is not a solo effort) tests cleaning efficacy. This means looking at the cleaning agent in the cleaning process with the soils that are on the parts. Coupon testing, where soils are placed on flat piece of metal, then run through the cleaning process, are not adequate. Flat coupons do not have the blind holes and tight spacing of most products. Also, the soil that is applied to a product is not the same as the residue. Residue includes a known and often an unanticipated mix of dirt (particulate and thin film) that is on the part after upstream processing, storage, and shipping. The actual cycle time is better estimated using actual hardware with actual residue. As always, we remind you to test new cleaning processes on scrap, not on hardware for the customer! Testing actual hardware, with representative materials of construction, can be eye-opening in that the default cleaning process may present a materials compatibility problem. A less aggressive cleaning process may be needed; and therefore it may take longer to remove soils and residue.
Fixturing and parts placement can become a bottleneck. To the extent possible, coordinate and consolidate the fixturing process. Managing the parts before, during and after the cleaning process impacts throughput. You can’t (or shouldn’t) just toss the part over your shoulder and into the cleaning chamber or onto a conveyor belt. Parts must be placed appropriately for effective cleaning. We sometimes see situations where parts arrive at the cleaning system fixtured from an upstream process. Then those parts have to be removed from fixtures for the upstream process, Then the parts are placed in different racks or fixtures for the cleaning process. Repeated fixturing, de-fixturing, and refixturing is labor intensive; and it slows down the overall manufacturing and assembly process, as well as increasing the risk of depositing new contamination. Conveyor belt systems, where the parts are sprayed in air, may also require parts fixturing. We see situations where electronics assemblies are so light that the force of the spray creates something that looks like a multi-car accident, a bunch of assemblies pushed one on top of the other. Those in the middle of the stack don’t get cleaned properly Sometimes the parts are driven off of the conveyor belt and get stuck. This clogs up the works! Once the process is in place, the only solution may be to individually attach each assembly to the conveyor belt. In one memorable instance, the cleaning system for cleaning metal parts broke down because of insecure fixturing. The parts were hung from overhead hooks and moved through the immersion cleaning process. Sometimes, a part would escape and fall into the process bath. There, the parts sort of marinated, corroded, and generally degraded, contributing to a process that no longer cleaned effectively. More secure fixturing kept the problem from recurring.
Well-designed, quality fixtures are important to achieve optimal throughput. Make sure fixtures are designed so parts can be easily placed and removed. Consider purchasing extra fixtures; and factor in enough time and money to be sure there are enough trained and educated people to load and unload parts.
Managing extremes and outliers
Consider the difficult extremes in selecting the right size equipment. Difficult extremes include worst-case parts, worst-case residue, very large parts, and very small parts. Complex parts with very adherent residue are likely to require different process parameters than usual. We have seen too many instances where a small percentage of difficult parts require repeated cleaning. Very large parts may be better cleaned manually. Very small parts may take up a significant time in the parts cleaner. For small parts, it may make sense to purchase a separate a smaller benchtop cleaning system. Very small “widgets” can often be cleaned with ultrasonics. Where there are a number of different small parts that require different cleaning agents, the parts can be in beakers that are placed in the tank. The tank is filled with a dilute surfactant solution.
Are the parts adequately rinsed? Is the product too hot to handle? Be sure the number of rinse cycles and drying time are considered in estimating throughput. Drying complex metal parts and parts containing plastics and other non-metal parts is time-consuming. Drying time is often underestimated. Do you need two drying steps? Cool-down time slows the process flow.
Location
A large, centralized cleaning system is usually easier to control compared with having smaller or cell systems. It’s easier to control process parameters and to monitor process baths. The system can designed to minimize air emissions and to institute engineering controls that protect workers.
Where is the cleaning system located relative to other manufacturing steps? In considering throughput, with a centralized cleaning system consider how long it takes for assemblers to move the part to and from the cleaning machine. Having assemblers trudge way across the facility to the cleaning machine and then repack and carry the cleaning product over to the next step can be a schlep (that’s a technical term). The time it takes to move product represents a hidden increase in cycle time.
Downtime
During downtime, the process flow is zero.
Downtime can be relatively short and it may occur on a regular basis. Aqueous cleaning systems must reach the operating temperature. It takes a significant amount of time and costly energy to heat water. Ultrasonic tanks have to be degassed or there will be ineffective cavitation.
Regular equipment maintenance is a must for all cleaning machines; and unexpected breakdown can occur. There are strategies to minimize downtime. Suppliers of cleaning equipment may offer remote monitoring either by you or by the company that makes the cleaning equipment. Breakdowns happen. We encourage clients to have spare parts in-house. We also encourage them to scope out who can repair the system and how responsive they are. Sometimes, in-house staff at your company have the skills and talent to take care of repairs.
Always, always, always get the Safety/Environmental folks involved; and get them involved early in the game. Even if you think they will say “no,” get them involved. They can stop a process dead in its tracks. In one extreme example – before you ask, this was NOT in California – new cleaning equipment was sitting alone and unused in a corner of the facility. Why? The safety group vetoed use of the cleaning machine. To avoid zero throughput, the facility was forced to use a cleaning system that was slow and that did not clean effectively. Safety/Environmental could have and should have implemented worker safety and environmental controls.
Solvent and water management can de-rail the process for days. The Safety/Environmental person on your team may be able to help at the planning stages on issues of storage and removal of hazardous waste. Details in cleaning equipment design can make the difference. Solvent that you can keep using is solvent that doesn’t have to go to a hazardous waste facility. In aqueous processes, the liquid in the wash and even the rinse tanks must be replaced. The spent process baths may have to be treated as hazardous waste.
Consider alternative cleaning options, particularly for where high volume, continuous cleaning throughput is required. If possible, have another cleaning system available. Consider contract cleaning at an outside facility that has been pre-qualified.
It’s a process, not a purchase
In the final analysis, estimating cyclic time and equipment sizing requires more than simple arithmetic. We’ve provided a few examples of what to look for. In our experience, in most instances, it is wise to factor in downtime, changes in upstream processes, and less than expected efficacy of cleaning. Also, factor in success – allow a little room for increases in production.
Your specific manufacturing environment is probably not the same as that of another company or even that of another facility within the company. While there are no guarantees, understanding factors involved in throughput, will markedly improve your chances of avoiding traffic jams and for coping with shut-downs.
Please also look at other episodes in the Quest for New Cleaning Equipment Series.
Part 1, Update or Replace
https://bfksolutions.com/update-or-replace-cleaning-equipment/
Part 2, Begin the Quest
https://bfksolutions.com/new-cleaning-equipment-part-2-begin-the-quest/
Part 3, Extreme Investment and High Power Cleaning
https://bfksolutions.com/the-quest-for-new-cleaning-equipment-part-3-extreme-investment-and-high-power-cleaning/
Part 4, What Can Go Wrong?
https://bfksolutions.com/the-quest-for-cleaning-equipment-part-4/
Changing the cleaning process is itself a process. In upcoming episodes of this series, we will provide you more food for thought, more ammunition to ask the right questions, make the best decision, and grow!
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