Guys, Ladies.
I was absent from the board from July 2008 until April 2009. Lots of things happening which prevented me from logging on.
Some of you may remember that I work in plastics. Back in June 2008, I posted something which I will paste below, which may help shed some light on the economics of manufacturing plastic parts in small runs.
Before I get to that, the look of the site has changed while I was away. I have been able to reply to a couple of posts, including this one, but I am UNABLE TO FIND HOW TO START A NEW POST. Please help.
Here is what I have written in June 2008. I have seen how some of you have used something which had been written previously and pasted it in a coloured box. I don't know how to do that either.
Here is what I wrote last year:
“Some of you wanted to know more about plastics. There are two kinds; thermosets and thermoplastics .
Thermosets are used where extreme heat requirements need to be met. An example would be the ashtray in my wife 2001 Taurus wagon. The tip of a cigarette is roughly 900 degrees F and will melt any thermoplastic. This kind cannot be remelted after it has been given a shape so that is ideal for an ashtray.
Another example for thermosets is a boat. A fiberglass boat (or a Chevy Corvette for that matter) is really a thermoset polyester structure reinforced with a woven glass mat. Boats are generally small production runs (a few hundred per model), and thermoset polyesters can be manually layered onto a pattern (typically a wooden mould) and allowed to harden to match the shape of that pattern.
Pretty much everything else is thermoplastics (that is what I work in). In thermoplastics, there are several processes. A process like rotational moulding has low tooling cost and is therefore used for low production volumes (say a few thousand parts per year). Processing costs are high (highly labour intensive).
A process like injection moulding has low processing costs per part, but when you build a mould, you may be looking at 50, 100, 150 thousand dollars, depending on the complexity. When you build one of these, you are looking at making hundreds of thousand parts per year, sometimes several millions of parts per year (imagine 64 bottle caps every 5 seconds, 24/7). A mould like that would cost a half million dollars, and would run on a million+ dollar machine.
Here is the question you all want to ask. You have this broken or missing part you want to replace, Maybe you can get together with other Pinto nuts and split the cost. Can you build a mould and do that?
Technically yes, but the tooling cost is staggering. Once you have your mould, you will be looking for a moulder to colour match and mould this part. Typically, unless you want at least 5000 parts, nobody will touch it (or you will be getting your one part, but still paying for 5000).
Plastics allow my big 2006 Chevy Impala (sorry - company car - I only get to pick the colour) to get 45 miles per gallon doing 60 on the highway. That big thing only weighs maybe 3200 lbs. It is however a disposable car, along with everything that was built since the late seventies. These modern cars will never be economically restorable (aside from taking good parts from a donour car).
When things were made out of metal, you could reproduce them if you had enough talent and patience. You did not have to spend huge amounts of money. That fabricated part was made to replace an original part which was expensive to produce; plastics changed that. However that only works when you need to mass produce something. Plastics will always beat metals for part cost when the numbers are large.
The enemy of metal is corrosion caused by oxygen and moisture. The enemies of plastics are degradation caused by oxygen, prolonged heat exposure, some chemicals (depends on the plastic), and in the case of car parts, ultraviolet rays (sunlight).
Keep your plastic questions coming. Plastics are fantastic.”
