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Five Decisions Before You Specify A Parts Washer
Overview
A cleaning machine is quoted against a specification, and most of the arguments that follow a purchase trace back to a specification that left one of five things undecided. Each of them is a choice the buyer has to make, and each one changes the machine.
They are: what the cleanliness criterion is and which regions it applies to, what unit the cycle time is expressed in, how dryness will be measured, how many variants the machine must cover, and how the machine will be validated. None of them is technical in the sense of requiring a specialist, and all of them are routinely omitted.
This article sets out the five decisions, the order they have to be made in, and what goes wrong when one is skipped. Big Bird Industrial (formerly Shimada Big Bird Industrial) has been building cleaning and deburring systems for automotive powertrain components since 2001, and the examples here come from specifications that reached a production line rather than from a template.
1. The Criterion And Where It Applies
The first decision is not the number. It is whether there is one number or several, and which surfaces each applies to.
One Figure Or A Set Of Regions
A single residual mass for a whole casting forces the process to the tightest feature, which in practice is an oil gallery, and leaves the machine oversized for every other surface. A per-region specification costs more to write and produces a machine that spends its energy where the measurement is taken. On a head, the spread between regions can be two orders of magnitude, which makes the single-figure approach untenable.
The Units Have To Be Stated
Milligrams per part, milligrams per unit area and milligrams per kilogram mean different things, and a specification that does not say which is intended cannot be quoted. A figure of ten milligrams on a threaded hole is not comparable with a figure of ten milligrams on the whole component, and both appear in real specifications. The particle size limit belongs with the mass limit for the same reason: a mass figure without a particle figure describes half of the requirement.
2. The Cycle Unit
The second decision is what one cycle produces, because a cycle time without a unit cannot be compared with anything.
Part, Set Or Basket
A machine that cleans two components on one pallet has a cycle expressed per set. A basket machine has a cycle per basket. A transfer line has a cycle per part. The same machine can be described by more than one of these, and the specification should name the one the buyer will use for capacity planning.
Handling Belongs Inside Or Outside
A wash cycle that excludes loading is shorter and not comparable with one that includes it. For a capacity calculation the figure that matters is floor to floor, including handling and changeover, and that figure should be the one in the contract.
3. How Dryness Will Be Measured
The third decision is the one most often left as a word rather than a number.
A Method, Not An Adjective
Dry is not measurable until a method is named. The two that appear in production specifications are a volumetric measurement, where the part is rinsed with a water-insoluble solvent and the separated water is measured in millilitres, and a gravimetric measurement, where the part is weighed before and after drying. Both produce a number with a limit; a visual check produces an opinion.
Dryness Interacts With The Criterion
Water left in a cavity carries dissolved solids and moves particles, so a part that passes a wet cleanliness measurement can fail after drying. That is why the dryness decision has to be made before the cleanliness decision is finalised rather than after the machine is built.
4. How Many Variants
The fourth decision sets the changeover concept, and it is usually answered with today's part list rather than with the one that will exist in three years.
The Envelope, Not The List
A machine can be programmed for fifty to eighty variants where they share an envelope. Stating the envelope in length, width, height and mass is more useful than listing the parts, because it tells a supplier what the fixture and the chamber have to accept. A part list without an envelope allows a machine that fits today's parts and none of tomorrow's.
What Changes Between Variants
The changeover concept follows from what actually differs: length only, mounting pattern, or the location of the critical features. Length differences can be absorbed by adjustable supports; pattern differences need variant pads; feature location differences may need a different nozzle arrangement. Each of those is a different machine.
5. How It Will Be Validated
The fifth decision is the acceptance sequence, and making it last is what allows it to become a negotiation.
Sample Size And Contamination
Cleaning a clean part proves nothing, so the test parts have to be deliberately contaminated with the actual process fluids. The sample size follows from the volume: a hundred consecutive parts and an eight-hour loaded run are feasible on a high-volume automotive line and impossible on a machine producing one large part per hour, where the validation is a few parts measured in detail.
Who Measures
The laboratory, the extraction method and the sampling location should be named before the order, because a machine that fails one method can appear to pass another. Agreeing them afterwards makes the measurement negotiable, which is not the same as making it accurate.
| Decision | What it fixes | If skipped |
|---|---|---|
| Criterion and regions | Stage list, pressure, filtration grade | Machine sized for one feature, weak on others |
| Cycle unit | Capacity, number of stations | Quotes that cannot be compared |
| Dryness method | Drying stage, orientation, vacuum | Clean when wet, stained when dry |
| Variant envelope | Chamber size, fixture, changeover | Next variant needs a new machine |
| Validation method | Sample size, contamination, laboratory | Acceptance becomes a dispute |
6. Why The Order Matters
Each decision constrains the next, and reversing them produces a specification that has to be reworked.
The criterion determines the stages. The stages determine the cycle. The cycle and the variant envelope together determine the chamber and the handling. The validation method then has to be achievable on the machine those decisions produced. A buyer who picks a cycle time first is choosing the answer before understanding the question, and the machine will be quoted to the cycle rather than to the requirement.
7. The One Decision That Cannot Be Delegated
A supplier can propose stages, pressures and filtration. The buyer is the only party who knows what the part must withstand downstream, and that knowledge is what makes the criterion decision impossible to delegate.
That decision, more than any other, determines whether the machine that arrives is the one the process needed.
8. What The Finished Specification Looks Like
The five decisions produce a document that is short and specific: a part list with an envelope, a table of regions with mass and particle limits, a cycle figure with its unit and its handling boundary, a dryness limit with a method, and an acceptance sequence with sample sizes.
The Page That Prevents Arguments
One page of tables covers all of it. The value is not the length but the fact that every number has a unit, a region and a method attached, so that a supplier cannot fill a gap with an assumption and a buyer cannot read a figure two ways.
Where a project runs without such a page, the missing decisions do not disappear. They are made by whoever quotes, and the buyer discovers them at commissioning, when the machine is already built and the only remaining variable is who pays for the change. That is the least useful moment to find out what the machine was designed against.
Frequently Asked Questions
Which Decision Is Most Often Missed?
The dryness method. It is usually written as a requirement that the part be dry, which cannot be measured and therefore cannot be accepted.
Can A Supplier Help Write The Criterion?
A supplier can explain what is achievable and at what cost, which is useful. The choice of what the part requires remains with the buyer.
Is A Tighter Criterion Always More Expensive?
Usually, but not linearly. Moving from thirty milligrams to ten may be a filtration and nozzle change; moving from ten to two usually requires plug-sealing and vacuum, which is a different machine.
How Many Variants Should I Plan For?
Plan the envelope rather than the count. A machine that accepts the envelope will handle the variants that appear inside it, which is a more durable statement than a list of part numbers.
Conclusion
Five decisions determine the machine: the criterion and its regions, the cycle unit, the dryness method, the variant envelope and the validation method. They are made in that order because each one constrains the next.
A specification that answers all five can be quoted, compared and accepted. One that answers three produces a machine that will be argued about at commissioning.
