Prototype Plastic Mold Making And Molding

The demand for prototype plastic mold making is not as great as it once was, due primarily to the 3D graphic ability of high end CAD mold design software. Nevertheless, many advances have been made in the past few decades that make the prototype an attractive process for industrial designers, inventors and custom molders.

Then there is 3D printing, which has the potential to change everything about prototype mold making and molding. That is a whole ‘nuther thing to consider.

Prototype mold making is a special niche

There are many ways to build a prototype plastic mold, but the common theme is quick, as in very quick. Most markets reward the first one to the marketplace, and plastic molding is no exception.

You can build a prototype out of aluminum, pre-hard steel such as NAK 55, NAK 80, P-20 and PX5, or even heat treated tool steel such as H-13, 420SS, or S-7. The decision is based mostly on the detail involved in the plastic part, time constraints, and the expected life cycle of the mold.

Prototypes are great for injection moulding production runs

Obviously, if you want the prototype mold to make 100 parts you don’t need a hardened tool steel mold, but rather aluminum. On the other hand, many times the short-run tooling seems to just keep on performing and the next thing you know, it has produced 500,000 parts!

Rapid Injection Molding
Rapid Injection Molding

Using prototype molds for injection moulding production is one of the tricks of the trade. A well built soft tool can last much longer than most people think.

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Some companies claim the ability to provide an accurate prototype mold in less than a week, even within days. This means that the part design has to conform to certain standards, such as no slides or lifters to mold the undercuts.

Plastic molding design is central

If the designer is able to work around these types of constraints, it can be a great way to be the first one to the marketplace. Otherwise, you can go a more conventional route and have a short run production tool built.

Since speed and accuracy do not normally get along together very well, consideration must be made to decide which details are most important and just how critical are those features that are likely dimensioned with too close tolerances.

Many times designers simply use default tolerances because they are not familiar with the mold making side of tooling. This is tremendous waste of time and money in some cases. Who needs an ejector pin plate to be flat within .0002 in.? Or just how good a surface finish is necessary on the bottom of the part, which is never seen anyway?

Modular tooling to the rescue

The MUD style mold is another common way to get a precision part molded very quickly. Since it relies on the interchangeability of the core and cavity sets, there is no need to build a complete mold base.

MUD molds are quite versatile and have been used in the industry for decades. There are many variations on this theme, but the common denominator is interchangeability. You can also get a similar product that uses round inserts, which works well for specific applications.

Prototype mold making is here to stay

Despite the decline in prototype mold making in recent decades, the need is still very much alive. With the integration of CAD and CAM it is possible to produce an accurate, inexpensive prototype plastic mold very quickly and reliably.

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