Flash in Injection Molding

What is Flash?

Flash is the excess material which forms on a molded or casted product and is generally caused by leakage of the material between the two surfaces of a mold.

Why is Flash important?

Product Cost

The main problem with Flash is that, in general, it must be removed. This means additional work (labour, time, effort …). Any time your product or component needs to be touched by human hands, it really affects the overall cost of goods. Injection molding is generally an automated process. Depending on the size/complexity of the product, the mold operator mostly sets up the machine and monitors it as it runs.

Product Safety

It can be unsafe to have these sharp areas on your product


Having Flash on your product or component could also prevent it from working properly. It could interfere with moving parts or parts which are designed to fit together.

Product Quality  and Appearance

It is unsightly and makes the product look unprofessional. There may also be scratches or other irregularities introduced as a result of the “hand work” which would be required in order to remove Flash.

How to avoid Flash on injection molded parts

It is far better to have the manufacturer avoid Flash than it is to remove it. Removing Flash is often a manual job although it can also be done by vibratory tumblers, which are pretty cool!

The Mold

Proper design and production of the mold can reduce or eliminate flash. The alignment of the two halves of the mould must be excellent to avoid the formation of Flash.

Molding flash can be caused from old or worn mold cavities that no longer fit tightly together.

Sometimes a product being moulded is very complex and it can be very difficult to avoid Flash.

The Injected Material

The properties of the material being injected is also an important factor (viscosity, temperature, pressure etc). Using a manufacturer with the right skills and experience will greatly help reduce the formation of Flash on your product.

The Manufacturer

Flash is something you should be aware of when discussing manufacturing of a molded or casted product. Be sure you work with your designer or manufacturer to either eliminate it or effectively remove it. The product you receive should not have Flash.

The Contract

Include quality inspections and standards in your sales agreement or sales contract. You can also include quality requirements on your production drawings.