Plastic Products and Mold Design

The advantage is being able to have a legitimate injection molded part in a "real material" in a few days.

The biggest competitors are:

• casting urethane parts in soft silicone tooling
• directly 3D printing the parts

Each option has pros/cons, time constraints, and price points. We focused for the most part on 3D printed parts, and soft silicone tooling. But I made a number of hard 3D printed tools as well. Some were sent out for injection molding, but the work we did in the shop was limited to hand poured, or vacuum assist urethane casting.

The biggest pro for injection molding from a prototype tool is getting a real homogeneous part. This is really handy when working with parts that require specific material properties (i.e. a living hinge, or snap fit parts/features).

The biggest cons are the need for sanding/finishing which takes time and affect accuracy. The limitation of the SLA machine to produce some very fine details. And, accuracy/scaling issues which won't match what can come from machining traditional molds.

What if we finish the mold using cnc milling machines ? The process could be very slow compared to the traditional mold making process , but small companies can create there own prototypes indigenously.

Part of the point of 3d printing is to avoid the need for machining.

If you already have CNC equipment, you'd be better off machining the tooling out of metal or plastic and skipping the 3D printing process.

The largest drawback to finishing via machining is going to be any discrepency between the CAD data used to generate toolpaths, and the actual part which is printed.

Let's say the printed part is "off" by 1% in one or more axes. The CAD model won't reflect that difference, so the CNC equipment could end up taking off too little, or too much in some locations.

For a small company to injection mold their own parts, they will also need an injection molding machine, and someone with some skill/training to operate it.

That sounds like a small market.

If you are already setup to offer 3D printing, and CNC machining, you might consider adding a small capacity injection molding machine to the list of tools. You can then offer fast tooling, and quickly produce limited runs of say a dozen to 100 parts.

In my experience, companies will prefer to have you to the work.

Thank you for the insights. Unfortunately I am only set up for 3D printing at the moment and I'm trying to find a market to get into after finding out that my original plans are not viable. Using 3D printing for prototyping was my next idea.

As far as accuracy is concerned how much deviation from the nominal dimensions is usually accepted? If I can hold out to +/- .005 will that work?

With engineering resins designed to perform similar to materials like ABS what is the case for prototyping with injection molding vs. 3D printing? I can understand wanting an actual injection molded part for long term use or to prototype the actual process injection mold process before going into full production. Is there anything else?

In your experience is urethane casting using a 3D printed part as the master tool an option? It sounds like the market for that may be really small too.

Accuracy from a 3D printer is usually defined as +/- .0XX per unit. Meaning if I build a 1" cube it might be within .005" per side. If I build a 6" cube I might be looking at .030" for the tolerance. The tighter you can make those numbers, the better. But, that can also get expensive, and the results of finishing the part can also cause a lot of problems.

3D printing is great, but "ABS Like Materials" are just that. They are "like" ABS. They are not ABS. 90% of the time I'd suggest building a part with 3D printing since it is faster/cheaper. The times I found it best to use the real material was when dealing with parts that needed the actual material properties of the actual material. Living hinges are a perfect example. There are very few materials which will simulate a living hinge folding more than a few times before failure. If you want to evaluate a hinge before production, this type of rapid tooling is ideal. The cost is high though, so I'd make a mold of only the portion of the model which needed to be tested.

Urethane casting is a very large market for prototypes. In many cases we ran parts this way for short production runs until tooling was made, but the customer often stayed with urethane parts for the life of the product since it was rather low production numbers (hundreds of parts or less).

There is a lot of labor that goes into urethane parts, and a lot of rejects due to bubbles and other defects. The life of soft tooling can be limited to a few dozen parts, and then the cast parts often require some secondary work (i.e. painting, coating, machining, tapping, inserts...).

We did not use many of their materials, but check out Smooth On for some great examples of urethane castings.

Another market for urethane parts is for costumes. Check out some of the posts on this site. He (Harrison) does some amazing work.