Milling moulds

[Janger]

https://www.canadianmetalworking-di.../MobilePagedReplica.action?pm=2&folio=48#pg48

You might have to register view the article. It's about making moulds for food containers.

I note a couple things - look at how beefy this mold is. I'm guessing each side is 8" thick? Wow.

Second the tolerance is apparently 5 microns or 2 tenths for this kind of work. It is for food containers. Anybody work on this sort of thing? What would the cycle time be for a set of containers when the mould is in use? Maybe they are for cream cheese or dips? How much would a mould like this cost?

Here is a picture from the article - go read it! it's interesting. I hope the publisher is ok with reproducing this along with the plug to go read the article.

 

[Janger]

I found a video on the mill ( if you can call it that). Must be serious money. 12 pallets, 200+ tools, 5 axis, crash reduction.

 

[trlvn]

Second the tolerance is apparently 5 microns or 2 tenths for this kind of work. It is for food containers. Anybody work on this sort of thing? What would the cycle time be for a set of containers when the mould is in use? Maybe they are for cream cheese or dips? How much would a mould like this cost?

I'm an accountant but I did an assignment at a place that did injection moulding. The cycle time would only be a few seconds. The mould closes, the ram forces the plastic into a molten state and into the cavities. Chilled water cools the parts enough to hold their shape and the mould opens. Ejectors make the parts drop out. Quite hypnotic to watch.

Re cost, it depends if it is domestic or offshore. A North American-built mould in that size range is at least a quarter million. An offshore mould might be one-half or so. There is a lot of "art" in building a mould, however. The network of sprues and chilled water channels need to just the right sizes or some cavities won't work right. The major risk with an offshore mould is that you have to send it back for rework.

Craig

 

[DavidR8]

Years back I knew a fellow who bought into an injection moulding business in Calgary. One of their mainstay products was those three-legged plastic things that go into middle of a large takeout pizza.
Perfect product because they get thrown away with every order. If I recall correctly, they made a dozen at a time and the mould was on the north side of 50K.

 

[PeterT]

My buddy worked at an injection / mold making shop a while back & I got a tour. He happen to know some prices for molds he worked on. As mentioned above, BIG bucks for molds that made what we would call relatively simple, everyday plastic objects. I was guessing high but nowhere high enough. They had a large 'shelf of despair' which held a bunch of molds belonging to (or being held ransom for) entrepreneurs that raised the money, made a run or two, sales numbers weren't as planned or Walmart knocked the price down... poof there goes the investment/loan/house mortgage/etc.

 

[Dabbler]

My friend Bert did injection molds 'old style', before even DROs on mills. A simple box mold would take about 2 - 3 months to do, involved 3-5 mold makers/tool makers, and cost 100K$... in 1965!

With the advent of great CNC, they are cheaper - note 'er'... there is still a lot of hand work to do on the mold after it is 'finished' by the CNC.

On great feature on that mikron machine is the 'surface' feature. You can actually program your surface finish? WOW

 

[trlvn]

Years back I knew a fellow who bought into an injection moulding business in Calgary. One of their mainstay products was those three-legged plastic things that go into middle of a large takeout pizza.
Perfect product because they get thrown away with every order. If I recall correctly, they made a dozen at a time and the mould was on the north side of 50K.

I believe mould cavities are usually powers of 2: 2, 4, 8, 16, 32, 64. The reason is that the flow of plastic material needs to be divided to get to each cavity. Dividing the stream in half each time is the most likely to guarantee success. AIUI it keeps even pressure behind the flow so all cavities fill equally.

Craig

 

[Tom O]

Here’s what NYC CNC has on injection moulds.