MYP Design Scales of Production Notes

How Many You Make Changes How You Make It

1. The same chair can be built four different ways, and the number of chairs wanted is what decides which way makes sense.
2. The four scales are one off, batch, mass and continuous production.
3. As the numbers climb, the money shifts away from skilled hours and towards machines, moulds and jigs bought up front.
4. A blacksmith making one gate bills you for forty hours of their time, while a factory making 100,000 hinges bills pennies of steel plus a slice of the press tool.
5. Settle the scale before you pick the process, because a process built for 100,000 parts is absurd for ten and the other way round.

One Off Production: Every Minute Is Setup

1. One off production, also called jobbing, makes a single item for one specific requirement: a wedding ring, a stage set, a bridge, or your MYP project.
2. Skilled people do most of the work using general purpose equipment, a lathe, a bandsaw, hand tools, that can be turned to almost any job.
3. Nothing repeats, so every stage is worked out once and there is no chance to get faster at it.
4. That makes the cost per item high, which is why a handmade oak dining table costs several thousand pounds and a flat pack one costs ninety.
5. The payoff is flexibility, since the customer can ask for a different handle halfway through and it costs an afternoon.
6. Quality rests on the individual maker, so the work is checked continuously as it is made rather than sampled at the end.

Batch Production: Make a Set, Then Change Over

1. Batch production runs a fixed number of identical items, then the same machines are reset to produce something else.
2. A bakery bakes 200 white loaves, cleans down the line, then bakes 200 wholemeal in the same ovens with different settings.
3. Changeover is dead time, because nothing is being made while jigs are swapped, tools are reset and the first few parts are checked.
4. Jigs, templates and go and no go gauges earn their keep at this scale, since one setup is used a few hundred times rather than once.
5. Batch suits anything sold in variety: five shoe sizes, six phone case colours, a seasonal range that changes every three months.
6. Half finished work piles up between stages waiting for the next machine, and that stock ties up both money and floor space.

Mass and Continuous Production: The Line Does Not Stop

1. Mass production turns out very large numbers of one identical product on a line, with each worker or robot repeating one small stage.
2. The line is laid out in assembly order, so the product travels and the tools stay where they are, which is how a car body reaches paint before it reaches seats.
3. Tooling is dedicated: a press tool that stamps one door panel does that job brilliantly and cannot do anything else at all.
4. Continuous production runs 24 hours a day for months at a time, making float glass, paper, petrol and aluminium.
5. It runs that way because stopping is ruinous, since a glass furnace takes days to come up to temperature and would crack if it were allowed to cool.
6. Both give very low cost per item and almost no flexibility, because changing the product means rebuilding a large part of the plant.

Setup Cost Against Unit Cost: Find the Crossover

1. Setup cost is everything paid once before the first item exists: moulds, jigs, machine programming, trial runs.
2. Unit cost is what one more item costs on top of that: material, energy and the minutes of labour it takes.
3. Cost per item works out as the setup divided by the number made, plus the unit cost, so the setup share shrinks as the run gets longer.
4. Take a plastic bracket: an injection mould at 20,000 pounds with 30p of polymer per part, against cutting and bending each one by hand for 6 pounds and no tooling.
   1. The two come out level at about 3,500 parts, so below that number the hand method wins and above it the mould wins by more and more.
5. That sum is why a small company sells its first 200 units made on a 3D printer and only buys a mould once the orders prove the demand is real.

Designing for 10,000 Is a Different Job From Designing for One

1. Part count falls, because a single moulded housing with clips built into it replaces four separate pieces and eight screws.
2. Parts get shaped so they can only go together one way, since a component fitted backwards on a line costs far more to find later than to prevent now.
3. Standard components take over: an M4 bolt or a common bearing size is cheap, available from several suppliers and never delays the line.
4. Tiny savings become large ones, so trimming 2 g of polymer from a part saves 20 tonnes of material across ten million parts.
5. The design has to be frozen before tooling is cut, so prototypes are tested to destruction while changes are still free.
6. A one off can be adjusted with a file on the day it is fitted, and a mass produced part has to be right before any steel is machined.