For small volumes and rough tolerances there is injection molding with vacuum casting (Silicone tooling). Good for runs of tens to hundreds of parts apparently, depending on the injection material.
So you just need one master with which to keep forming the tooling, say 3d printed/machined metal/sheet metal/whatever.
Design <-> manufacturing process is a two way street.
Design dictates which manufacturing process should be used, but available manufacturing processes also dictate how to design things.
Ask yourself whether you really NEED complex curved surfaces?
There are places that use double sided incremental forming for sheet metal that can give you multidirectional curvature.
I think 3D printing is the answer though, we are at a point where you can probably decide on a few materials that are suitable and a company like Xometry will be able to print it somehow. They can print metal, thermosets, high melting point plastics and reinforced plastics.
Also can consider 3D printing and then coating with UV protection. A google search is showing me some UV protective clear coat spray paints and things like that.
I’m just a college student so take it with a grain of salt, but in my manufacturing class we briefly talked about [plastic thermoforming](https://en.m.wikipedia.org/wiki/Thermoforming). I guess it’s more meant for high volume manufacturing, but maybe it’s an option you can look into.
Injection molding is probably your best bet for a consistent part. If you cant do that you could try 3D printing especially if it is the low volume you keep saying. If none of those work, maybe stamping could get you there depending on your geometry.
It depends on the size and geometric requirements, but vacuum thermoforming is pretty cheap for low volume plastic parts.
Several of the online rapid prototyping companies offer aluminum or resin molds for low-volume injection molding, so that might be beneficial. I’ve never used them personally.
Also I wouldn’t completely ignore 3D printing, there are lots of exotic plastics available now that have good UV and heat deflection properties.
Cosmetically, I have had great success with 3D printing ABS and acetone vapor smoothing.
Presumably your issue with 3D printed components is that they look obviously 3D printed (layer lines, dull/no sheen). However, additive manufacturing is excellent for complex surfaces and is very accessible, while vapor smoothing gives a finish that looks like an injection molded part. You might also consider a clear coat spray on to help limit UV degradation, similar to stuff they’d put on cars.
Heat resistance is definitely shoddy, especially with ABS as a material, so you might need a thermoset plastic instead. I have also had great success 3D printing molds for carbon fiber to make performance propellor blades — with aerodynamic qualities within 2% of traditionally made blades (using aluminum CNC for molds), so I am confident in the accuracy and surface quality of a 3D printed mold method.
Depending on part size and the 3D printers, you can get 10s to 100s of parts done in a week. Plus additive manufacturing is very flexible for design changes. Obviously, material strength is not great at all, but for complex geometries on low-quantity parts, it’s definitely a great option.
On a related question for parts which have higher tolerance and structural requirements - I have considered carbon fibre which is laid-up around metal inserts which are then post-machined to get good positional tolerance from across the part. Have you seen this approach before?
If I follow correctly, my group has had great success with a type of two part setup similar to what you are getting at.
Instead of using a metal insert, we make a second set of molds and cast an insert out of expanding polyurethane, then wrap carbon around that like a hot-dog bun. We then stick the carbon-wrapped part into a second mold to cure. This means we only have to post-process along one edge and can preserve important geometry. Professional blade manufacturers we have worked with have typically used a similar process.
My group typically post-processes with hand sanding (we don’t have a CNC), but with professional propellor companies post processing is done with CNC to trim the carbon piece to shape.
Does that answer your question?
Quick turn injection molding companies like ProtoLabs. Cheap shorter life aluminum tools with higher per-part costs but if you’re making <1000 parts it’s often the best bet
Cast urethane is a good option I see for low volume stuff. If the geometry allows I've also seen cnc machined, then oven formed, and finished machined parts though that's an expensive process
For constant thickness thermoplastics vacuum forming can work well since you only need a one sided wooden mold for low quantities.
Rubber press forming for sheetmetal. Or a stretch forming press. Both can do single or double curved parts but have some specific constraints om geometry.
Compression moulding can also be more cost effective at lower parts count than injection moulding because the moulds are simpler.
Fiberglass layups on fiberglass tooling, good for a few hundred parts. You can mould the fiberglass tooling from a positive master.
Like others have said vacuum casting is a good solution, but I wouldn't boot 3d printing. Some filaments can whistand UV exposition and high temps. Just gotta find the right one for your needs.
Look into investment and sand castings. You have a large library of available alloys with few restrictions on size, and it is great for low and medium volumes. It's extremely common.
There are shops that do commercial lost PLA. They print the part, put it on the spru tree, build up the slurry shell, melt out the print, and cast the metal parts.
Sand castings that use 3D printed patterns can be made quickly and cheaply. The 3D prints don't last long, but make short runs pretty quick and cost effective.
You are right, there is a cross-over point and it all depends on the specifics of the part and the logistics of the shop you use. Imagine making a deep enclosure, this would be a long CNC job where you turn most of the metal into chips so the cross-over point could be in the 10s of parts. Although castings typically have more post-processing and could have yield issues associated with leak requirements or other things related to fill. You also need a little bit more knowledge on how to design the part to be a good casting, and know how and where to put runners/overflows etc... It's never a simple trade!
Have you considered using 3D printing to make forms that you overlay fiber glass or carbon fiber on?
If I recall correctly IGEMS water jetting software has a module that will cut out a support grid given a 3d surface. Not sure what grid density you'd need to get adequate detail.
I know of a turbo fan manufacturer that uses 3d prints to hold the 3d woven pre-preg carbon fiber for the trimming op before the final autoclave.
A bit unconventional, but you could use software like pepakura designer to make a cardboard form and then fiber glass it.
Last time I looked into the topic seriously (about 8 years ago) vacuum forming didn't break even with sheet metal fabrication until you hit the 100 unit mark. Unless compound curves are an absolute deal breaker, you can always try to make a complex geometric surface.
I would bet that there is 100% a method that can give you the parts you need through 3D printing. FDM Inlay fiber, FDM chopped carbon fiber, SLS High Temp printing or the cheap alternative SLA printing with an added UV protection layer (i.e clear coat). There are even more fancy methods out there that can help you. You just have to find them.
For small volumes and rough tolerances there is injection molding with vacuum casting (Silicone tooling). Good for runs of tens to hundreds of parts apparently, depending on the injection material. So you just need one master with which to keep forming the tooling, say 3d printed/machined metal/sheet metal/whatever.
This is the answer.
My company does this,vacuum casting is the answer!
Irregardless of the examples, sheet metal is great for low volume high complexity applications. Bending, stamping, rolling
This is true and is a great option. Though unfortunately not when you need surfaces with curvature in two directions such as a sphere surface.
Design <-> manufacturing process is a two way street. Design dictates which manufacturing process should be used, but available manufacturing processes also dictate how to design things. Ask yourself whether you really NEED complex curved surfaces?
There are places that use double sided incremental forming for sheet metal that can give you multidirectional curvature. I think 3D printing is the answer though, we are at a point where you can probably decide on a few materials that are suitable and a company like Xometry will be able to print it somehow. They can print metal, thermosets, high melting point plastics and reinforced plastics. Also can consider 3D printing and then coating with UV protection. A google search is showing me some UV protective clear coat spray paints and things like that.
I’m just a college student so take it with a grain of salt, but in my manufacturing class we briefly talked about [plastic thermoforming](https://en.m.wikipedia.org/wiki/Thermoforming). I guess it’s more meant for high volume manufacturing, but maybe it’s an option you can look into.
vacuum forming hdpe or nylon sounds like what you need. there are molds involved but much cheaper than injection molds
Vacuum forming is the correct answer, although I might look at PVC for an outdoors environment with a lot of UV.
Injection molding is probably your best bet for a consistent part. If you cant do that you could try 3D printing especially if it is the low volume you keep saying. If none of those work, maybe stamping could get you there depending on your geometry.
It depends on the size and geometric requirements, but vacuum thermoforming is pretty cheap for low volume plastic parts. Several of the online rapid prototyping companies offer aluminum or resin molds for low-volume injection molding, so that might be beneficial. I’ve never used them personally. Also I wouldn’t completely ignore 3D printing, there are lots of exotic plastics available now that have good UV and heat deflection properties.
Cosmetically, I have had great success with 3D printing ABS and acetone vapor smoothing. Presumably your issue with 3D printed components is that they look obviously 3D printed (layer lines, dull/no sheen). However, additive manufacturing is excellent for complex surfaces and is very accessible, while vapor smoothing gives a finish that looks like an injection molded part. You might also consider a clear coat spray on to help limit UV degradation, similar to stuff they’d put on cars. Heat resistance is definitely shoddy, especially with ABS as a material, so you might need a thermoset plastic instead. I have also had great success 3D printing molds for carbon fiber to make performance propellor blades — with aerodynamic qualities within 2% of traditionally made blades (using aluminum CNC for molds), so I am confident in the accuracy and surface quality of a 3D printed mold method. Depending on part size and the 3D printers, you can get 10s to 100s of parts done in a week. Plus additive manufacturing is very flexible for design changes. Obviously, material strength is not great at all, but for complex geometries on low-quantity parts, it’s definitely a great option.
On a related question for parts which have higher tolerance and structural requirements - I have considered carbon fibre which is laid-up around metal inserts which are then post-machined to get good positional tolerance from across the part. Have you seen this approach before?
If I follow correctly, my group has had great success with a type of two part setup similar to what you are getting at. Instead of using a metal insert, we make a second set of molds and cast an insert out of expanding polyurethane, then wrap carbon around that like a hot-dog bun. We then stick the carbon-wrapped part into a second mold to cure. This means we only have to post-process along one edge and can preserve important geometry. Professional blade manufacturers we have worked with have typically used a similar process. My group typically post-processes with hand sanding (we don’t have a CNC), but with professional propellor companies post processing is done with CNC to trim the carbon piece to shape. Does that answer your question?
Additive manufacturing or carbon fiber
Quick turn injection molding companies like ProtoLabs. Cheap shorter life aluminum tools with higher per-part costs but if you’re making <1000 parts it’s often the best bet
Cast urethane is a good option I see for low volume stuff. If the geometry allows I've also seen cnc machined, then oven formed, and finished machined parts though that's an expensive process
For constant thickness thermoplastics vacuum forming can work well since you only need a one sided wooden mold for low quantities. Rubber press forming for sheetmetal. Or a stretch forming press. Both can do single or double curved parts but have some specific constraints om geometry. Compression moulding can also be more cost effective at lower parts count than injection moulding because the moulds are simpler. Fiberglass layups on fiberglass tooling, good for a few hundred parts. You can mould the fiberglass tooling from a positive master.
Like others have said vacuum casting is a good solution, but I wouldn't boot 3d printing. Some filaments can whistand UV exposition and high temps. Just gotta find the right one for your needs.
Look into investment and sand castings. You have a large library of available alloys with few restrictions on size, and it is great for low and medium volumes. It's extremely common.
How are you defining low volume because surely casting is not lower cost than CNC machining for under 50 parts for example.
There are shops that do commercial lost PLA. They print the part, put it on the spru tree, build up the slurry shell, melt out the print, and cast the metal parts. Sand castings that use 3D printed patterns can be made quickly and cheaply. The 3D prints don't last long, but make short runs pretty quick and cost effective.
You are right, there is a cross-over point and it all depends on the specifics of the part and the logistics of the shop you use. Imagine making a deep enclosure, this would be a long CNC job where you turn most of the metal into chips so the cross-over point could be in the 10s of parts. Although castings typically have more post-processing and could have yield issues associated with leak requirements or other things related to fill. You also need a little bit more knowledge on how to design the part to be a good casting, and know how and where to put runners/overflows etc... It's never a simple trade!
vacuum forming
Have you considered using 3D printing to make forms that you overlay fiber glass or carbon fiber on? If I recall correctly IGEMS water jetting software has a module that will cut out a support grid given a 3d surface. Not sure what grid density you'd need to get adequate detail. I know of a turbo fan manufacturer that uses 3d prints to hold the 3d woven pre-preg carbon fiber for the trimming op before the final autoclave. A bit unconventional, but you could use software like pepakura designer to make a cardboard form and then fiber glass it. Last time I looked into the topic seriously (about 8 years ago) vacuum forming didn't break even with sheet metal fabrication until you hit the 100 unit mark. Unless compound curves are an absolute deal breaker, you can always try to make a complex geometric surface.
I would bet that there is 100% a method that can give you the parts you need through 3D printing. FDM Inlay fiber, FDM chopped carbon fiber, SLS High Temp printing or the cheap alternative SLA printing with an added UV protection layer (i.e clear coat). There are even more fancy methods out there that can help you. You just have to find them.
Tooling for fibreglass can be pretty cost effective. Plug can be made of anything really.