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Engineers should know that two-shot injection molding can be sped up or slowed down based on how the substrate is transferred to the other chamber of the mold. Hand and robot arm transfers take longer than a rotary plane, but rotary platen molding is more expensive and generally only an efficient option for high volume production runs.

Alternately does anyone have any experience in having moulds and sprues made from a local or offshore place? Short run stuff?

To start the overmolding process, an engineer injection molds a substrate out of the more rigid overmold material. Then, the substrate is placed in an overmold tool or overmold cavity within the same tool. The molten overmolding material is then ejected into, onto, or around the substrate. After the molten material cools, the substrate and overmold are chemically or mechanically bonded. The entire overmolding process can take as little as 30 seconds.

Injection molding is a popular manufacturing process that’s ideal for quickly creating precise parts with intricate shapes, all without leaving behind a lot of material waste. Common applications include packaging, automotive dashboards, mechanical parts like gears, and even popular kids’ toys.

Two-shot molding, also known as dual-shot, multi-shot, or double-shot molding is a subcategory of injection molding that allows engineers to create multi-material or multi-colored parts without adding extra assembly steps.

Two-shot plastic injection molding is an excellent technique for efficient and cost-effective manufacturing. This process also produces highly durable end parts and components.

The two-shot injection molding process is best understood in terms of the different layers of materials or colors that are created by the injection molding machine. The first material is injected into a mold to create the substrate, around which the other material or materials will be molded. The substrate solidifies and cools before being transferred — by hand, robot arm, or rotary plane — to the other chamber of the mold.

My impression is that injection molding takes a pretty expensive setup.  In addition to the molding machine, the dies are usually metal, and a reverse of the part.

Also looking around and saw this stuff Mold Max 60, the site shows them pouring pewter into it, so I figured, heck if it can do pewter it should be good for plastic right?https://www.smooth-on.com/tutorials/casting-pewter-mold-max-60/

Two-shot molding and overmolding are both simple and effective processes for creating durable parts made of two or more materials or two or more colors. To choose between the two, engineers should consider the size of their production run.

Compared to two-shot molding, overmold designs are also easier to make because engineers can use any standard injection molding machine to conduct this process.

The high capital costs of injection molding is why so many small firms go for resin casting.  For the individual, or for a low capital startup, this seems to be the way to go.  You use RTV to encase your pattern and create a mold.  In addition to the standard urethane resins for casting the parts, the RTV molds will stand up to a limited number of casts of low temperature metals like those Micro Mark sells.  Micro Mark also sells a kit to get started in urethane plastic- the kit includes RTV for molds, the urethane casting resin, and some mixing supplies.  Such a kit is a good way to get started, and you can then buy the resins and rtv individually once you have caught on to the process.

Many different processes fall under the umbrella of injection molding, including two-shot molding and overmolding. These two processes are similar but have a few key distinctions — here’s what engineers and designers need to know:

Overmolding, like two-shot molding, is a multi-shot injection molding process that produces a single end product from two or more different thermoplastics. This process is ideal for engineers who want to build strong, functional, aesthetically pleasing parts that won’t separate over time.

In terms of disadvantages, the tolerances of parts made via overmolding are often inferior to those that can be achieved with two-shot injection molding. It’s also important to remember that plastic compatibility requirements can constrain designers.

Overmolding and two-shot injection molding share many of the same advantages. They’re both ideal for quickly creating durable, reliable, and vibration-resistant parts with complex geometries, but overmolding is best suited for low-volume production runs.

Then yesterday in Canadian Tire I saw RTV gasket silicone, just happend to randomly walk down that isle and past silicone stating "High Temp" on it, it caught my eye. It's good to 600 deg, so well within the range of molten plastic in an injector and that tube just went right in the basket.

However, if two plastics with less-than-ideal compatibility must be used, teams can design mechanical bonding features into the part after the fact, though this is likely to result in higher costs.

If you can produce masters, then you can produce sillicon/RTV/Vulcanising rubber moulds and produce your parts in resin, plaster, etc.

Additionally, it’s critical that molds are made out of materials that will easily bond together and that the molds align correctly to prevent deformities in the part.

Further, since one machine makes the whole part and no post-processing is required, engineers can dramatically reduce manufacturing time, which in turn keeps costs low. However, it’s worth noting that the initial two-shot mold costs can be high and the two-shot molding machine is more expensive than a standard injection molding machine. Luckily, these costs are often offset by labor savings and assembly costs on large production runs.

From a design standpoint, two-shot molding offers designers a lot of flexibility because this process can create complex geometries and accommodate multiple colors, making for more aesthetically pleasing parts.

Above is alink to a piece I did on using sprue and silicone. I've been doing this sort of stuff for twenty plus years and if you don't mind a little clean up time it works great and is very cheap.

Nowadays all the rapid prototyping is CNC cut/lathed, or LASER cut, or 3D printed, but knowledge of 3D design is needed, as is access to printers, but there are companies like Shapeways if you don't have the printers etc.

Product teams must keep in mind that all thermoplastics used in the overmolding process must be chemically or thermally compatible with one another. Compatibility generally is not an issue with metal substrates because they can be used with any plastic overmold, but product teams can encounter compatibility issues when overmolding plastic with plastic. If the substrate and overmold aren’t compatible, the end product might be deformed or poorly bound.

Tomorrow I've got the day to myself, so I'm going to make a box and put a random plastic and foam object in there and see if I can make a mould of it. If it works, it might just be a really cheap good way to make my own injection parts. Even if the mould is good for say 10-20 uses it's still a really cheap way to make some high temp moulds.It might be a terrible idea, if so then I've got some gasket sealant for my 61' Alpine mk2 I'm restoring, if it does work then welcome to cheap high temp silicone moulds :)

From there, the mold opens and the side with the substrate rotates 180° to meet the other mold chamber and injection molding nozzle. Once the substrate is in place, the second material is injected and bonds with the substrate to form a firm hold.  Once the second layer cools, the final part is ejected.

Two-shot molding usually only makes sense for larger production runs, whereas overmolding is better for low volume production runs. Still, teams must do their due diligence and evaluate all critical considerations of each potential manufacturing process against their specific project requirements to ensure they’re making the right choice.

Hi all, I figured this might be a good place for this conversation.DIY Injection Moulding.Has anyone here done it? How did you do your moulds and what was the result like?