Low cost molds. Can such molds be produced?

Question

I recently found the following link https://anglingai.com/224b-4-4-blood-line-swim-bait-mold/. There you will see that they sale hundreds of different aluminum molds related to fishing. These molds are really inexpensive (from 50 up to 200 USD). How they are producing them? I though that molds cost thousands of dollars.

I am currently in progress on designing a product and I will need a mold for the enclosure of the product for low production runs (no more than 200-300 items per month). The enclosure will need to be either from ABS or some other kind of strong material that is not brittle. Probably also, the material will need to somehow be manually injected in order to reduce the total cost.

Where can I find someone to produce me low cost molds (like the above) for a product design that I will create with Fusion 360? Can this be done or I am really naive? I am mostly interested for the outside finish of the enclosure. Inside it there will be electronics that will be potted with special type of resin in order to protect them from the elements. As such, the inside will be as simple as possible.

Answer 1

Judging from the pictures, they are CNC machined out of solid aluminium.

That isn't an expensive process, so long as you have the CNC machine. A basic one that isn't junk for sale on E-bay would cost a few thousand dollars, which isn't a big deal for a commercial company if their selling price amounts to hundreds of dollars per hour of machining time.

Answer 2

These types of molds are for casting and curing. There is basically zero injection pressure so they can be small and require minimal machining. You can keep them closed with paper binding clamps. You can see from the photo they took a piece of stock aluminum, faced it with a fly cutter and machined the cavity. Easy and Inexpensive.

When you inject thermoplastics, like ABS, the injection pressures can be 1000 atmospheres. This is required because of the high viscosity and fast filling times required before the plastic solidifies. The molds are very thick to withstand the internal pressure and clamping loads required. Aluminum tools generally are for short runs and hard chromed tool steel is required for high volumes or abrasive plastics. The mating surfaces of the mold have to be near perfect to prevent flashing so they are machined in many steps and hand finished and polished. A simple aluminum injection or compression mold can cost tens of thousands.

For your application you could get away with using aluminum for the mould but at small scale thermoplastic injection moulding is difficult and expensive. You could consider casting the enclosure with a mineral filled epoxy or similar. The best option if you can make it work in your design is vacuum forming. I have done lots of short run enclosures using vacuum formed hair-cell textured abs. It hides all the defects on the surface and won't show scratches. ABS is very soft, you can scratch it with your finger nail.

The best source for standard sizes of enclosure I have ever found is poly-case. If you have different connectors that need to come out from the case they have options with blank face plates that can be cut to accommodate your connectors. https://www.polycase.com/abs-enclosures

Answer 3

You could look into Protolabs. They provide a range of services from 3D printing, CNC machining, short run injection molding using aluminum tooling, production molding and more. They are really fast. They have an online quoting and ordering system which includes an analysis of the moldability of your part.

Low cost aluminum tooling is cheaper and faster to make then traditional steel molds, but surface finish isn't as good and the number of parts that can be made before the mold wears out is much lower. Just having a mold isn't enough as you still need a molding machine to create parts.

Just to be clear, I have no association with Protolabs other than once being a customer. Undoubtedly there are other good shops.

Answer 4

The auto industry does/did used molds of zinc ( Zamack , kirksite) to make steel forming molds for limited numbers. I expect if you make a clay ( or equal) model of the part . Then pour molten zinc around it ( melts a little under 800 F). You will need parting lines , gates , etc, in the mold to get the clay out and your plastic in.

Answer 5

cheap molded parts are made by sharing space in a larger mold used to make parts for many customers at once. such a setup is called a MUD mold; each individual customer owns an insert in the master mold and when the molding shop runs the mold they open up the gates to those mold cavity inserts whose customers desire parts at that time.

The parts exit the mold "treed" to one another on a common sprue. this is then inserted into a press with razor knives that detach each part from the sprue and catch it in its own box. the individual boxes are then sent to the customers.