What's the Difference Between Mold and Die?

23 May 2022

SelfLube is the leading U.S. manufacturer of precision components for Molds and Dies.   

Molds and Dies are tools that cut and shape material and are in many ways similar. But what exactly is the difference? That’s a question with no simple answer, but we’ll do our best.

About Molds

There are many different types of molds that can form products in a variety of mediums. Some of the materials that molds can form include:

  • Soft clay for bricks 
  • Ceramic items
  • Concrete items 
  • Blow molds are one-sided molds used to form the outer surface of bottles
  • Fiberglass molds used to form boat hulls, vehicle bodies and many other products
  • Molds for carbon fiber products include a host of items, some as large as aircraft parts and wind turbine blades

SelfLube makes components for one type of mold: plastic injection molds. Such molds have an internal cavity that is the exact shape of the part (or multiple parts in the case of a multi-cavity mold). They are split in half so they can be opened and closed. When the mold is closed hot molten plastic is forced into the mold under high pressure. When it cools and hardens the mold opens and the part is ejected. The part could be a small toy or something big like the front end of a pickup truck.

About Dies

Like molds, there are is a large variety when it comes to dies, such as:

  • Cold heading - used to repeatedly hit the end of a steel rod to form a screw or bolt head
  • Extrusion die - used to form a long shape such as a strip of plastic or aluminum molding
  • Thread die - used to cut threads, is really a cutting tool not a die
  • Die Casting - this type of injection molding uses metal rather than plastic, but the mold that is used is called a “Die”

At SelfLube, we make components for one type of die: metal stamping dies. Similar to an injection mold, such dies are split in half and have an internal cavity in the shape of the part to be  formed. However, this is where the similarity ends. When the metal stamping die is open a thin sheet of metal somewhat larger than the finished part is placed in it. The die is then closed under great force. As it closes the thin sheet of metal is bent, cut and stretched to form the desired part. The die then opens and the part is removed. The parts that can be made from this process can range from a small kitchen item to the roof of an SUV.

Want to know more about specific offerings, product availability and more? SelfLube's full product line, along with downloadable CAD models, can be viewed online at www.selflube.com.