DIY Mold-A-Rama Update 3

A lot of progress has been made in the last few months on my version of the 1960’s classic Mold-a-Rama machine.

The design has been further refined

  • The frame where the mold cylinders attach has been changed from 80/20 to 1″ square aluminum tubing.
    • This change was made because I was having a hard time mounting and aligning the various components to the slots in the aluminum extrusion.
    • The mold halves will press against each other with several hundred pounds of force; the friction fit nature of t-slot construction would likely have failed under this load. The new frame is a one piece welded structure.
    • The new frame, while not re-configurable, will be much stronger and allow for easier alignment of the plastic tank and mold halves.

overview_2_15_13

  • The plastic pump has been completely redesigned
    • I’ve switched from a right angle gear motor to an air cylinder driven piston pump (think giant aluminum syringe)
    • This change eliminated a complex machined part ($$$) and replaced it with a much simpler welded tube and plate design ($)

melt pot complete_2_15_13

  • The actual mold cylinders have been selected
    • So much of the design decisions and components selections have been driven by what I can get on the surplus market  Case in point: the mold cylinders. I’ve seen that the actual mold-a-ramas have an enormous amount of play in their mold cylinders and mounts. I thought using a twin piston cylinder would help with the side loading on the pistons (due to the weight of the molds want to slide down on the angled frame. I found a good price for two twin piston SMC cylinder on eBay (with sensors and flow control fittings!)
    • I designed a robust mounting system using aluminum tube, bronze bearings, and 5/8″ steel shafting.

mold cylinders_2_13_15

 

Parts have been bought

I’ve also been spending quality time on eBay, at surplus stores, and throwing money at various other online retailers. Here’s where some of the money has gone:

photo 2

Left to right: Air compressor, air tank, compressor switch

The air compressor is a Thomas & betts unit I got at C&H surplus (super cool store, check it out if you’re in SoCal). It has twin cylinders and puts out more CFM at a lower decibel than most compact air compressors.

photo 3

Left to right: water pump, auger for plastic hopper, cartridge heaters

photo 1

The top two cylinders move the mold halves together, the bottom one moves the piston in the plastic injector, and the solenoid manifold on the right controls it all.

photo 4

50lbs of hard to find plastic

The ability to buy the plastic pellets was a make or break moment for this project. There were not a whole lot of suitable replacements for this particular plastic (more specifically, polyethylene wax). Fortunately the west coast distributor for this happened to be close and had several bags it was willing to sell to me (normally this product only sold in 1000kg pallets, which is about 950kg more than I need). Getting a hold of this was a major load off my mind.

BA6JS4JCcAAwIJm

It’s like the warehouse in Indiana Jones, but instead of ancient relics there’s plastic resin.

I’ve begun cutting metal for the frame and plastic melt pot, hopefully welding will start this week!

Advertisements

Cardboard Mockup: The Original Rapid Prototyping

I often find it hard to get a sense of scale when designing things using CAD software. Staring at a model on a 24″ screen can sometimes make small objects look massive, and large objects tiny. Placing  references (such as a person) next to your model helps some, and there are many free human models for pretty much all CAD platforms. However nothing beats a physical prototype. If your part is small enough 3D printers are perfect. For larger parts you have to get creative. The final frame will be made of 80/20 aluminum framing, but I did not want to commit to cutting it up just yet, as I was still playing with the frame dimensions. I needed a cheap material that was easily formable, yet sturdy enough to hold its own weight, next to my door was the answer: double wall cardboard.

Just as architects use cardboard to construct scaled down buildings, I built a 1:1 model of my mold-a-rama replica. Using only packing tape and cardboard, I was able to quickly (and cheaply) build a model that’s accurate to about 0.25″.

I started by measuring the outside dimensions of my model in solidworks, and transferring those to cardboard. Here’s some tips I learned from doing it:

  • The boxes I had on hand were medium to small-sized, with fold lines all over. If you can’t cut around the lines, take another piece of cardboard and tape it over the fold line to reinforce it.
  • Reinforce the corners by making a long  L-bracket and tape it to the inside.
  • Cardboard tabs can be used to prop up unsupported spans of cardboard.
  • Get some good blades for your utility knife, I like Irwin bimetal blades. They make cutting through thick double wall cardboard a breeze.

And here’s the end result:

Cardboard mockup

Those 3rd grade arts and craft skills are finally paying off.

As I suspected it was bigger in full-scale than what I thought it would have been.

Another benefit is that the interior volume is very close to the usable space inside the actual machine. I was able to place most of the bulkier components inside, allowing me to play with layout:

Interior layout

From left to right: air compressor, injection cylinder, plastic melt tank, water pump (blue thing peeking out), water chiller.

Moving components around inside the cardboard model was so much faster than doing it in CAD. It also gave me a better idea of how much space I need between components.

The layout above is mostly complete. I have since gotten an air tank that sits in the back left corner. The stainless box you see is the starting point for the plastic melt tank (I’ll go into more detail in the next post where I’ll show off some of the components  that have already been bought)

This method really only works if what you are building is mostly flat panels that meet at right angles. If you’ve got a contoured model and you are set on using cardboard, make an STL file of your part with layers that match your cardboard thickness and print out patterns. This can be done using the free software AutoCad 123D (http://www.123dapp.com/make)

DIY Mold-A-Rama: How it Works

One of the first steps in reverse engineering a product is understanding how it works. Ideally I would have access to the actual mold-a-rama (MAR), however they are rare and expensive. I could find an operating installation, but the closest operating MAR is at a zoo several hours away.  I also have been unable to find pictures or video of the mechanics below the cabinet. The only parts visible from the images I’ve seen are the molds, mold rams, and ejector. All the complicated bits are hidden from view in the cabinet. The last avenue is products documentation in the form of manuals and patents. Fortunately I am an awesome google-er and have found both. The operation and repair manual can be found here:

http://www.scribd.com/doc/37301298?secret_password=1ehb8rphnat7ykzt6zu3

Continue reading