Is Alibre suitable for mould-making ?

[SpacedCowboy]

I'm planning on buying a home injection-moulding machine, and a CNC mill to generate the moulds. What I'm not entirely certain of is the software to make the moulds.

I was looking at this page and it doesn't look too hard to make a mould, but it needs a few things:

• The ability to create very fine structures - 0.005" by 0.05" for example - channels of this sort of dimension are used to allow air to escape from the mould as the plastic is injected
• The ability to model something then split it in half (for the upper and lower parts of the mould)
• The ability to create "negatives" of the model. Essentially a boolean subtract, but it would be nice to not have to worry about alignment etc.

I was hoping to get the Alibre design package for the CAD part, and then possibly use meshcam to import (from STL or DXF) the design that Alibre created, and mill it out.

Anyone got any comments, help, guidance etc.? I've used CNC before (I've got a 3D printer, and a PCB "engraving" machine) but I've not got into milling parts before, so I'm all ears

Cheers
Simon

[ben_jackson]

Alibre's strength is not "surfaces". It does have "lofting" but if you want to make complex "organic" 3D shapes then Alibre may not be for you. It does support "draft" (tapering for mold release) on extrusions and some other operations. It does have boolean operations. I have not tried them to know if they retain associativity to the parasolid geometry.

It has STL export (only) and 2D (only) DXF import/export.

Although I have never used it, I think people recommend Rhino (or, of course, Solidworks) for complex smooth shapes. Blender could also do that but it has a learning curve all its own.

[SpacedCowboy]

Alibre's strength is not "surfaces". It does have "lofting" but if you want to make complex "organic" 3D shapes then Alibre may not be for you. It does support "draft" (tapering for mold release) on extrusions and some other operations. It does have boolean operations. I have not tried them to know if they retain associativity to the parasolid geometry.

I guess I'm not after "organic" shapes, but I was looking here and those seemed to be about the sort of complexity I'm thinking of. The first things I want to make are brackets to fasten some LEDs onto some extruded aluminium. There's some complexity in the "star" shape of the LED heatsink, but I'm thinking more like the first of the three images in...

It has STL export (only) and 2D (only) DXF import/export.

Although I have never used it, I think people recommend Rhino (or, of course, Solidworks) for complex smooth shapes. Blender could also do that but it has a learning curve all its own.

[shudder] I've tried Blender; rather I should say that I have been tried by Blender. On the other hand, I have got 3d models working quite nicely in Sketchup, but it doesn't have the precision required for the mould. I guess it *was* designed for building-scale models, not 1/1000" scale models [grin]

Thanks for the insight

Simon

[HuFlungDung]

I'd advise that you need a NURBS modeller to get models that are smooth enough for precision machining. I've never worked with an stl modeller to know what the options are, but suffice to say, you need a lot of very small triangles to simulate a sphere, but only one NURBS surface to do the same thing.

A NURBS model is also something that you can do useful Boolean operations upon, and this is handy whenever you need to make male-female offsets for molds. You can also fabricate surfaces, extract edges from NURBS surfaces, and this is very much necessary to do precision machining or to add features to an existing model.

I won't say it is easy to make organic NURBS surfaces, because I don't run into that need in my work. But I make all sorts of engineered shapes such as your samples above.

I use OneCNC. This makes sense to me, since it is necessary to have a CAM system that can do something with your model. So if it comes with solid modelling capabilities (which it does have available in certain versions) then, why not use it to its maximum capability? I do and so far have not needed to look further.

There are other NURBS capable systems out there as well. I don't know if any of them are budget priced like Alibre, though. Darn it anyway!

[HuFlungDung]

You might need to check the various export options from Alibre. I'm sure that guys are exporting NURBS models using that software. The default file type that Alibre saves into might be an STL, but it may have other options.

[SpacedCowboy]

Not wishing to argue with those who know a lot more about this than I, but also wanting to clarify my requirements...

I don't really want or need curvy surfaces - I'm happy with flat, boring, plain ole squares If I could round-off my cube-like straight edges into quarter-round edges, it'd be a bonus, but it's not necessary.

Here's an image (hot off the 3D printer, and still with the printing-raft semi-attached [grin]) of the first prototype of the part I'm thinking of:



It's about 1/3 the size now (lengthwise), and slightly more "shaped" underneath, but it's still angular, flat, and geometric, not curved. Does that make a difference with needing NURBS ? Or would you recommend I use a NURBS modeller anyway ?

I'm trying to do this on a budget (aren't we all [grin]), so the cheap price of Alibre Design appeals. I went to the oneCNC website, but there's no details of any pricing anywhere I can find [sigh].

Thanks for the help

Simon

[HuFlungDung]

As the infamous owner of Practical Machinist forums once quipped something to the effect: I'm having trouble seeing the individual atoms in that picture. Could you make it bigger?

[DIYaholic]

HuFlungDung,
Careful there, watch what you say! I here that if Practical Machinist is mentioned here on the "Zone", the post gets deleted!

My bad! It's the other way around.

Randy,

[SpacedCowboy]

As the infamous owner of Practical Machinist forums once quipped something to the effect: I'm having trouble seeing the individual atoms in that picture. Could you make it bigger?

I sort of expected the forum s/w to thumbnail it down [grin]. It does rather look like what a scanning tunneling electron microscope produces, doesn't it

Perhaps I ought to have used links:

Here's the model of what it was supposed to look like on top, and here's the underside. That turned into this for the top of the bracket, and this for the underside.

What I was trying to show though was that all I'm after is relatively straightforward 90 degree angles...

Simon

[Edit: I ssh'd into the server from here at work, did 'sudo port install netpbm' and resized the images. Isn't unix great ? :-]

[tobyaxis]

I make molds with Alibre regularly. Of coarse the surfaces made aren't free form or organic it is fully capable of making mold models.

A correct plan of attack will allow you to make just about any shape.

Look through the Tutorials, the answers are in there.

[SpacedCowboy]

I make molds with Alibre regularly. Of coarse the surfaces made aren't free form or organic it is fully capable of making mold models.

A correct plan of attack will allow you to make just about any shape.

Look through the Tutorials, the answers are in there.

Cool - that's encouraging. Thanks

To be honest, I'd not thought it would be an issue for a CAD program to do what I wanted, but then I tried Sketchup, and it fails to render or cope with the tiny-resolution (0.003" x 0.05") channels I'll need to allow the air out of the moulds when the plastic is injected. Hence the questions

I'll have a look through the tutorials when I get my PC (for the first time in my life, I'm buying a PC to run windows...). I'm guessing I could probably run the s/w under VMWare, but I'll need an actual honest-to-god parallel port for the CAM part, so I figured I might as well get a dedicated PC...

Thanks for the help,

Simon

[ben_jackson]

To be honest, I'd not thought it would be an issue for a CAD program to do what I wanted, but then I tried Sketchup, and it fails to render or cope with the tiny-resolution (0.003" x 0.05") channels I'll need to allow the air out of the moulds when the plastic is injected. Hence the questions

That's surprising to me. Sketchup can definitely work in precise units. Where Alibre is better than Sketchup is when you change your mind about a dimension of some part way after you've drawn it. Alibre's method of operation remembers how you created your 3d part from a 2d sketch and when you go back and change your very first operation then everything else "replays" on top of that. In Sketchup if you change your mind later about the shape of a hole you cut through something you basically have to nuke the hole, redraw it to your new specifications and then cut it again.

(obviously it does other things better than Sketchup too, but that's probably the main thing when it comes to moldmaking)

You can download Alibre and try it for 30 days. Do the tutorials and see if you like it!

For what it's worth, I think the idea of going to STL files (or NURBs or whatever) for rectilinear shapes is a bad idea. If you really want a rectangular pocket you're better off drawing a rectangle and milling it with a conventional 2.5D cutting path. The results will be much better (and much faster) than milling a 3D mesh surface that happens to define a rectangular pocket.