And because urea is an extremely hard material, the tumbling process takes a long time: typically 10-12 hours in tumbling bins with a substrate that wears down the urea material a bit. And that reveals the first limitation with urea: the inability to maintain precision with dimensions. For example, standard 5/8” (or 16mm) spot dice right out of the mold are 16mm in dimension but after tumbling they end up between approx. 15.5 and 15.7 mm in dimension from side to side.

Another limitation is color. Urea material is typically only available in white, black, and the basic primary colors.

There are custom colors that can be provided, but because these colors are achieved by the urea supplier in its powder or granular form, the custom color (usually matched to a PMS number) is an approximation at best. The manufacturing process with custom colors requires a very large quantity of the material to be produced- usually two metric tons. That’s enough to make 200,000 standard 5/8” dice!

So now let’s focus on injection molding. This involves the process of melting a solid material into a pliable form, injecting it into a mold, and then letting it cool down and harden back into a solid.

But don’t take my word for it. Let’s consider a more scientific explanation: “ a thermoplastic is a class of polymer that can be softened through heating and then processed using methods such as extrusion, injection molding, thermoforming and blow molding. Thermoplastics harden once cooled and do not show any changes in chemical property after being heated and cooled multiple times, making them easily recyclable. Thermoplastics are made by joining small molecules, called monomers, together to form long chains using a process called polymerization. The atoms in a polymer chain are joined by strong covalent bonds, whereas the forces between chains are weak. Examples of amorphous polymers are polystyrene (PS), polyvinyl Chloride (PVC) and acrylonitrile-butadiene-styrene (ABS).

Have I lost you yet? Thought so. The old saying “don’t give me the recipe, just bake me the cake” applies here. The type of material that is used, the chemical additives required, the size and design of the mold, and even the size of the molding machine, are all in the category of the “recipe” for the product.  As I lead the article with – what you (and we) need to think about is more in the category of what the “cake” should look like. In other words, focus on the end product- what it should look like and how it should perform.

Injection molding, using various types of plastic resins and molding techniques, allows for a great deal of flexibility with color, clarity, special effects, shape, hardness & softness, etc.

When producing a component through injection molding, the benefits are numerous. The options are rather endless. Colors can be matched to PMS numbers (used in printing), and styles can include opaque, transparent, translucent, pearlized, iridescent, and glitter. Multiple colors of pigment can be mixed to form a swirl pattern. One object can be molded and then inserted into another mold to be encased into a different material around it.

The product can be very rigid and hard or soft and “squishy”. Again, it’s all about what your desire is for the appearance and performance of the item.