Introduction

There are different types of castings which include resins and die-casts. In this article, we will explain the meaning of resin and die-cast, and note the differences between them.

Let’s dive in.

What is a Resin?

This is a highly viscous substance of plant or synthetic origin that can be converted into polymers. It refers to a natural organic compound in liquid form.

When it is combined with the hardener, a chemical reaction takes place which binds the molecules of the resin. This forms a solid, durable plastic substance.

Natural resins are obtained from nature, mostly plants and rarely animals. They are fusible and flammable organic substances that are yellowish or brown.

They are transparent or translucent. They are formed in plant secretions and are soluble in various organic liquids, but not in water.

Conversely, synthetic resins are any sort of resins that change over into solid and unbending polymers by way of curing. Put differently, these resins are normally in a fluid state but do change to a solid state after casting.

Types of Resin

• Polyester resin

Polyester resin is formed by mixing organic acids with polyhydric alcohols.

This resin uses a catalyst for the chemical reaction, and this speeds up its curing process. So, you can easily control its speed of reaction.

A ready-made polyester resin consists of a mixture of the resin and a harder. To harden the resin, you need to apply a catalyst such as ultraviolet (UV) light or a chemical.

Unlike the epoxy resin, polyester resin is not weakened by exposure to UV. So, you can apply UV curing to polyester resin.

Polyester resin is highly resistant to corrosion and acidic substances. It has excellent water-proofing properties. It can withstand high heat.

It has lower shrinkage and good wetting qualities. You can use it with structural enhancements (such as glass fibres) to manufacture solid plastic shell structures.

However, polyester resin is not as durable as epoxy resin. It is also less effective as a gap-filling resin than the epoxy. It doesn’t bond with another metal at an atomic level,

so its adhesive quality is lower than epoxy. Also, the polyester resins are made with inimical chemicals, and so require maximum care to handle.

• Epoxy resin

This refers to a reactive prepolymer and polymer containing epoxide groups. It is packaged as two separate compounds– a resin and a hardener.

When using it in casting, you need to mix both (the resin and the hardener) to initiate the casting process and manufacture the solid, plastic-like cast parts. It needs a special hardener to cure.

Also, it forms ionic bonds with other materials at an atomic level. This makes it stronger than the polyester resin.

Epoxy resin does not shrink when curing, and this makes it an ideal casting resin and gap-filling substance. It is resistant to moisture and chemicals. Also, it has electrical insulating properties, and it is impact-resistant.

What is Die-cast

Die-casting is an automated process of pressing molten alloy into a mold under high pressure and at high speed.

It’s a method of heating alloys to a high temperature till they are molten. Here, liquid alloy is injected under high pressure into a mold.

The mold comprises two halves, separated to reveal the cast parts after the molten aluminium has solidified. One of the two halves is static, while the other is mobile.

After injecting molten metal into the mold, it solidifies. This results in cast parts with a precisely formed and smooth surface.

A single mold can be used multiple times. This makes die casting preferable for bulk casting.

Also, there are two different types of die-casting machines. These are the hot chamber and cold chamber machines.

Different alloys are used in die-casting. These include aluminium, zinc, copper, magnesium, lead and tin alloys, among others.

The casting process is seamless as it requires minimal assembly. You can also integrate all the assembly features, such as bosses, holes, students, etc., into the mold design at a go.

Contrasting Resin and Die-cast

• Resin refers to a solid or highly viscous substance of plant or synthetic origin that can be converted into polymers.

Die-casts are the casts made when molten metal is poured into a mold, and it solidifies. In die-casting, the materials used are metals (mostly non-ferrous metals), and not resin.

The different types of metals you can use include aluminium, zinc, copper, magnesium, lead, tin, etc.

Note that you can also cast a synthetic resin.

Simply, resins are not similar to die-casts. Resins are highly viscous substances of plant or synthetic origin. However, you can cast synthetic resins and in such case, the produced resin-casts are similar to die-casts.

Essentially, what is similar to die-casts are resin-casts. This is because they both have similar casting processes, but with some differences in casting processes and qualities.

Now let’s consider the processes of resin casting and die-casting; while noting the differences and similarities between them.

• Processes of Resin-casting and Die-casting

(a.) Mold preparation: In resin-casting, you can create the mold from an already-existing plastic or a completely new 3D design. 

For accuracy, use CAD to draw the designs of the mold. The 3D-printed mold would have the same geometry, design, and shape as the original item.

Other than plastic mold, you can use silicone mold too. You can also use latex, plaster, fibreglass, etc. However, note that softer mold materials such as silicon and softer rubbers simplify the ejection of the finished resin cast.

For die-casting, the above mold preparation method also applies.

However, in die-casting, the mold can only be made of high-quality metal. This is unlike resin-casting where the mold can be made of plastic, latex, fibreglass, metals, etc.

To make a mold in die-casting, you need to use a material with higher strength and melting temperature than the material you want to cast. Otherwise, the mold can get damaged during the casting process.

(b.) Casting: In resin casting, the synthetic resin is readily manufactured as a liquid substance. You have to mix the liquid synthetic resin with a curing agent–typically at room temperature or near-room temperature.

After mixing, pour the (mixed) substance into the mold cavity. The curing agent then converts the resin into rigid polymers, thereby hardening it.

For die-casting, the only materials you can use are metals, not resins. Also, unlike in resin-casting, you need to firstly heat the metal in a melting furnace until it turns molten. After heating the metal to turn molten, mix the molten metal into a chamber where you can inject it into the mold.

There are two types of chambers in die-casting. These are the hot and cold chamber die-casting. In hot chamber casting, you would inject the molten metal at a high pressure into the mold. Usually, the pressure ranges between 1,000 – 20,000 ps.

(c.)  In resin-casting, after casting, the resin begins to cool off. You need to remove the resin-cast from the mold only after solidification. Similarly, in die-casting, until the molten metal has solidified, you can’t properly remove the die-casts from the mold.

(d.) Surface treatment and CNC machining can be applied on both resin-casts and die-casts. Resin-casts can be coloured, either by using airbrush paint, pigment powder or alcohol-based inks. You can explore different colours on resin casts.

Note that:

• Resin casting, when compared with die-casting, is a slower casting method. The synthetic resin used in resin casting is highly aggressive when exposed to a curing agent. So, each mold typically lasts for around 50-100 uses. This is unlike die-casting molds that you can use hundreds of times.

• Resin-casting is cheaper than die-casting. However, die-casts are more durable than resin-casts.

Conclusion

In this article, we have taken you through the concepts of resins and die-casts. We also contrasted resins and die-casts. This knowledge will help you appreciate both types of casting and choose the one suitable for you.