Choosing materials: cost and availability

Why could you hardly buy a PlayStation Five for more than a year after it went on sale in November twenty twenty? It was not the price. Shops sold out within minutes, and millions of people had the money ready. What could not be found in enough numbers were tiny parts inside it: computer chips. A product the whole world wanted could not be made fast enough. Behind an empty shelf like that sits a factor designers weigh whenever they pick parts.

A material you cannot get is no use, however good it is. That is the availability factor: how readily a material or component can be sourced, which means found and bought from a supplier, in the quantity and form you need, when you need it. Some materials sit on every supplier's shelf. Stock forms are the standard shapes materials are sold in, such as sheets, bars and tubes. Standard sheets of plywood, standard lengths of steel tube and standard screws are stocked by many suppliers, so they can be reordered quickly. A specialist material is different. It may be made to order, or imported from one supplier, so it can mean weeks of waiting. Supply can also be hit from outside: by the seasons, by slow-growing trees, by ores that are hard to extract, by politics, or by a sudden rush of demand. So every availability point ends on what it means for the maker: waiting, a stopped production line, a missed deadline, or a redesign. The console shows how far that goes. Its main chip was custom-made for it, so when chips ran short there was no standard part to swap in, and production could not keep up. Here is an availability point a student might write about pine for a shelf: pine is available in shops. What does that point about the pine still need before it scores? A consequence for the maker. Pine is sold in standard planks by many timber merchants, so the maker can reorder within days and production never has to stop. Standard components help twice. They are quick to source, and they are quick to replace, so a broken product can be repaired with a part from almost any supplier. One examiner's report describes answers that handled this well. Availability was considered in terms of sourcing available stock forms and standard components for ease of replacement and repair. The habit behind those answers is the consequence. Each one names what the stock form or the standard part means for the maker, or for the person repairing the product. A student needs a hinge for a jewellery box prototype by Friday. One choice is a standard brass butt hinge, in stock at the school's supplier. The other is a hand-made decorative hinge with a three-week wait. Which hinge should the student choose, and what would the other one mean? The standard butt hinge. The decorative one means three weeks of waiting, so the prototype misses Friday. That is the rule for every prototype: choose what is in stock or quick to deliver, so testing is not held up.

Cost starts with how you buy. Bulk buying means ordering a large quantity at once, and it lowers the price of each unit, each single item you buy. The reason has a name: economies of scale. A supplier has fixed costs for every order, like setting up the machines, the paperwork and the delivery. Those costs stay much the same whether the order is big or small. In a big order they are shared across more units, so each unit carries less of them, and suppliers add a discount for big orders too. Take a school-uniform company ordering polyester fleece and zips for next year's hoodies. Say the supplier's set-up and delivery charge is three hundred pounds. Shared across one hundred hoodies, that is three hundred pounds divided by one hundred. Three hundred divided by one hundred is three, so the charge adds three pounds to each hoodie. Share the same three hundred pounds across a thousand hoodies: what does it add to each? Thirty pence. Three hundred pounds over one thousand hoodies is nought point three of a pound, which is thirty pence each. That is economies of scale at work: each metre of fleece and each zip costs less. The company can sell the hoodies for less than its rivals, or keep the saving as profit. A year's order in one go also means one dye batch, so every hoodie matches. But the money is spent up front, the rolls of fleece need storage space, and if the school changes its colour, the company is left with fabric it cannot use. For school uniform, is bulk buying worth that risk, and why? Yes, because demand is steady and predictable. The school needs hoodies every year, so the stock gets used and the saving is real. Bulk buying only pays when every unit bought is used and sold. Writing cheap and stopping there explains nothing about cost. One examiner's report puts it plainly: candidates struggled to offer explanations regarding the cost factor. The fix is never to write cheap on its own. Every cost point carries a because and a so: plywood is cheaper per sheet because it is bought by the pallet, so each product costs less to make. Other costs follow from the material itself. A specialist material costs more than a common stock one. A material that needs special tools or extra processes costs more to work. And a mock-up can use cheap card, while the final prototype uses the real material.

Put both factors on one real business. A small business makes two hundred plywood phone stands a month, and fixes each one together with two small brass screws. What is one availability point and one cost point for the plywood, each with a so? Availability: six millimetre birch plywood is sold in standard sheets by many timber merchants, so the business can reorder quickly and never stops for lack of stock. An imported, exotic veneered board could mean weeks of waiting, and could run out halfway through an order. Cost: buying plywood by the pallet rather than by the sheet lowers the price of each sheet, so each stand costs less to make. And it cuts cleanly on the laser cutter the business already owns, so no new tools are needed. The screws work the same way. They are standard components stocked everywhere, so a lost box is replaced the same day. Bought in boxes of a thousand, each one costs far less than buying a few at a time. Some questions ask for considerations other than a material's properties. Here are two answers to one like that, about plywood. One answer says plywood is tough and stiff. The other says plywood is sold in standard sheets by local suppliers, so it can be reordered quickly. Which of those answers fits a question about considerations other than properties? The standard sheets answer. Tough and stiff are working properties, which that question ruled out, so the first answer earns nothing there. One examiner's report, on a question asking for considerations other than a material's properties, records what went wrong. Many candidates gave working properties. The fix is to answer the factor the question names, such as cost or availability, and to leave the properties for a question that asks for them. Where a material comes from is a cost and availability question too. A designer is planning fifty thousand phone cases. Carbon-fibre composite is carbon fibres set in resin, very strong and light. Polypropylene or carbon-fibre composite for fifty thousand phone cases: which, and why? Polypropylene. Its granules are made from oil by many producers around the world, so enough for fifty thousand cases is quick to buy and cheap per kilogram. Carbon fibre needs a specialist supplier. It costs far more per case, supply is limited, and a hold-up at that one supplier would stop production. Cost and availability never decide alone, though. If buyers would pay for carbon fibre's look and strength, it could still be the right choice, so the cheapest material is not always the right one. If you already link a material's source to what it costs, you are in good company. One examiner's report says common responses considered how a material or component might be selected based on extraction costs. The habit to add is the consequence for the maker.

Three questions to finish, each one on a product this video has not used. A bike maker buys ten thousand standard bolts at once. Why is each bolt cheaper? Economies of scale. The supplier's fixed costs for the order are shared across every bolt in it, and a big order earns a discount. Try this: what is the availability point for rare timber from one supplier abroad? One supplier abroad means any hold-up leaves the workshop waiting, so orders go out late, or the product has to be redesigned. Here's another: why is bulk buying risky for T-shirts printed with one year's date? Any shirts left over cannot be sold next year, so the money spent up front is lost, and the saving goes with it. And the console from the start: shoppers had the money, but its chips could not be sourced in enough numbers, so the shelves stayed empty.

Cost and availability points that always end on a consequence mean you could teach this one. Press the thumb under this video, and there is no need to sit through it again. Still unsure, then keep it in a playlist for now and try a few exam questions on these two factors. Three questions in, it starts to feel normal.

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