Mold Lock

In the effort to develop pattern making expertise, I was disappointed in the lack of information about various types of mold and pattern locks to align the cope and drag sand molds for a flaskless sand casting process. The most common discussion I’ve seen is the flask alignment approaches which are primarily used in green sand. There are some really good backyard casting websites that overview the process. Let me start by acknowledging them, hats off to Gingery Foundry, Workshopshed, Backyardmetalcasting, kylehausladen’s instructables, Steven Chastain’s book, AFS Patternmaker’s Manual and others I’m sure to forget to include links. Let me give the caveat that I’m looking specifically for good strategies for pattern/mold alignment that I can just build into the patten for a flaskless mold.

Let me tell you things that don’t seem to work well, to start out with. First, you could depend on the edges of the mold to align the pattern. If there are no features in the either the cope or the drag then I believe this method would work well. That’s an obvious one. Second, you could add “pins” to the pattern. In fact, there are options like the Freeman Concentric Mold-Lock Buttons that are commercially available. I think a solution like this would work well if you take care to install them both in the right location and with three of them that are not symmetric so that the orientation of the mold cannot be reversed. But frankly, I really want to discuss an alternative mold lock that I’ve been playing with. Using Onshape, I created a 1/2 inch platform that the cope and drag patterns could be built from. This is simply a “picture frame” approach to aligning the cope and drag. The drag lock is simply creating a raised surface which when matched with the cope lock which creates a recessed surface. The outer edge is 10.5″ square which is roughly the limit on the desktop milling machine. One corner has been prepared with a corner knocked off to make sure the mold is oriented properly.

Drag lock in Onshape.com

Cope lock from Onshape.com

Please note that I’m probably a little premature in claiming this is my solution for this alignment issue. But the example below is the cope side of a little cast knife project I’m working on to see if we can cast some steel knives as part of an AFS student activity.

CAD

I’m going to post a short discussion about CAD packages and some of the current trends I see. A little background on me, I was initially trained on a drafting table at community college and only briefly exposed to ProE as an undergrad at Penn State. At Caterpillar, we used Teamcenter and ProE for most 3D modeling work I was involved with.

Also, there are many, many good CAD tools out there now for anyone to get started using. The basic division of approaches to CAD falls into two methods: parametric and direct modeling. These two methods were part of sales pitches in the past and currently it’s hard to see the difference these days. All 3D modeling requires watertight shapes that are constrained in some way by dimensions or relationships. So really you should work with the one that best suits you. This being said and in an effort to give you more directions to try…

I’ve had good luck with the free tool, FreeCAD, to mess around in to make STL files for 3D printing or other process modeling. Recently, I’ve been using Onshape to look at collaborating with students on geometries and it looks really powerful. Seems like it’s going to be limited to educational accounts for the free use, but this serves almost like an educational PLM which is definitely a great idea. For other shapes and more open part sharing, I recommend Thingiverse and GrabCAD.

As for trends, it seems like the basics will stay the same so if you’re happy with your CAD tool then I wouldn’t panic. But as for upcoming innovations, I want to highlight some things. First, integrating process modeling (heat transfer, fluid flow, solid deformation) is likely to continue in the CAD package world. ProE, Solidworks, AutoCAD and others all have options for directly doing analysis from their CAD interface. Also all the process modeling software offer some modeling capabilities such as ANSYS and MAGMAsoft. But as an academic soothsayer, I would say that the future has to feature optimization and machine learning. In this way, OpenSCAD probably has an interesting role to play in the future. OpenSCAD creates geometry from a programming procedure essentially like parametric modeling but driven from written lines of code instead of point and click operations. This approach and other software that uses this method has huge value to optimization because the parameters can be modified easily to experiment with the design.

I’ve got more to say on this considering implicit and explicit geometry but I’ll leave that for a future post.

Rapid Melting Applied to High‑Pressure Die‑Casting

… is the title of Carlos Larrazabal PhD dissertation work that he successfully defended last Thursday. Of interest was the power outage that occurred immediately after his presentation. The committee continued to question him in the dark and everyone persevered until he answered all aspects of his work.

Stay tuned for his first publication that is focused on modeling the electromagnetic and thermal aspects of induction heating a cylindrical billet of aluminum. This work is the basis for designing a rapid melting system. We believe that this effort will serve as a building block for designing several heating stages toward delivery of high-quality aluminum on-demand.

Rapid Prototyping

So, I’m working on a few things to help my “rapid prototyping” situation. As I see it there are a couple reasons that it’s difficult for me to complete patterns. So, let me discuss them below…

1. Time: this is the biggest problem and why rapid is so frustrating. If you only have 15 mins then you pretty much lose that time if you can’t get to the next milestone. You pretty much need to start over.
2. Software: what ones and what do we need? It’s not particularly clear what cad package, preprocessing steps, gcode writers, analysis, etc. is necessary to actually get a chance to machine or make something.
3. Tools: my tools are sufficient but not easy. So with much horsing around and persistence, sometimes you can get the equipment going. But most of the time, you end up back looking at the software again.
4. Finished examples: even if I found time / software / tools, the lack of examples of how to make a successful pattern, machined sample, tensile bar, etc. is a real problem when we run into difficulties.

Comment below if you think I missed anything. I’m hoping that I can take a significant leap in getting going in “rapid prototyping” where it is easy. Let me explain point by point…

1. You aren’t going to get more time (sorry). So we’ve got to find a way to make the milestones shorter to reach in the time available. So try to break whatever you are making up into milestones that you can use for the next piece. That will mean that you need to make some decisions about mounting holes, etc. early but leave yourself some flexibility so that if you need to remake that piece then it will be easy to replace.
2. We are quickly leaving the age of ProE, Solidworks, etc. most of those tools will be around, but others are taking their place (Onshape, OpenSCAD, etc.). The newer tools offer the traditional basic modeling capability but also better interoperability and data management. However, the lessons learned about how to draw engineering 3d shapes will survive.
3. Over the last 2 years, I’ve built several 3d printers and a desktop milling machine, MakerFarm and Ox CNC. These have affected my expectations just like the digital camera back in 2003 when Sarah and I got married. We had “digital photos” of our wedding day that we were thrilled to get on CD at the time. The reality is that they were scanned images of the printed photos, which for the time was still pretty awesome. However, anyone looking at those photos today would be pretty disappointed to reprint them compared to the digital images from a phone camera today. 3d printing and desktop milling machines have the same effect. I’m much more dissatisfied with my ability to cut and make something once you put that in my hands compared to before I had them.
4. Youtube, Thingiverse and GrabCAD have now made finished examples easy to get and use. The problem is that even with all the examples, the ones I’m looking for don’t exist.

My conclusion is that I think the time is right to see progress to being able to propose and think of a thing and then make it. However, until I reach a critical mass of 3d models and worked examples for myself and my lab then I’m still going to be whining about this rather than just making stuff.