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  • Writer's pictureCarlie Sitzman MA, CT

Words with Hidden Meanings in Manufacturing Terminology Part 2

Impression-Die Forging, Closed-Die Forging, Drawing, Metal Casting Defects

There are a number of seemingly normal, everyday words that take on completely different meanings when used in manufacturing or metalworking settings. This can make manufacturing terminology a bit confusing for laymen and might seem almost comical from an outside perspective. Today, I will take a closer look at some surprising terminology used for the manufacturing processes impression-die forging, closed-die forging, and drawing as well as terminology used to describe metal casting defects.

Impression-Die Forging

(German translation: das Gesenkschmieden mit Grat)

Impression-die forging involves the use of a mold that is cut in half and mounted separately. A piece of softer metal is placed between the two halves of the mold and the two halves are subsequently pushed together. This process squishes the metal into the shape of the mold. The procedure functions similarly to a household waffle maker, but with metal instead of delicious waffle batter.

1. Flash (German translation: der Grat)

When impression-die forging is performed, there will of course always be a bit of metal wanting to ooze out the side. The material that oozes out the side is called “flash”.

2. Die (German: die Matrize)

Die is the technical term for the mold used to shape the squished metal during an impression-die forging process. Dies are used in many different manufacturing processes and can take a variety of shapes. A die usually consists of a piece that comes in direct contact with the material to be worked (workpiece) in order to shape it in some way.

Closed-Die Forging or Flashless Forging

(German translation: das Gesenkschmieden ohne Grat)

Closed-die forging is very similar to impression-die forging. The difference is that the mold remains completely closed during closed-die forging and parts of squished metal are not allowed to leak out. It is more challenging to perform, since the metal to be shaped (workpiece) must have a volume precisely equal to the volume of the die cavity. This is not as important with impression-die forging, since there is space for excess material to leak out the side.

3. Coining (German translation: das Prägen)

Coining is a type of closed-die forging in which a design is stamped onto the surface of a metal object (workpiece). It is called “coining”, because it was first used to stamp designs onto coins.

Drawing (German translation: das Ziehen, das Tiefziehen)

Drawing involves pushing a piece of flat sheet metal into a mold, such that the metal is pushed into a simple hollow boxy or bowl shape. The mold is usually a depression across which the sheet metal is placed. A plunger positioned over the depression will then push the sheet metal into the depression to form a hollow object in the shape of the mold.

4. Earing (German translation: die Zipfelbildung)

Earing is what happens when the sheet metal itself isn’t quite the right size or shape and the top edges of the sheet metal become misshapen. The misshapen pieces at the top are called “earing” or “ears”.

Metal Casting Defects (German translation: der Gussfehler)

As in any human endeavor, metal casting does not always go as planned. The terminology used to describe some metal casting defects ranges from rather self-explanatory phrases to seemingly everyday terminology used in a different way. Here are a few examples of defect terminology with surprising meanings.

5. Inclusion (German translation: der Einschluss)

An inclusion defect occurs when a material in the environment of the metal being cast becomes embedded in the soft metal before it hardens.

6. Rat Tail (German translation: der Rattenschwanz)

A rat tail is a ridge on a cast surface. This occurs when pieces are cast using a mold made of sand and might be caused by sand that does not have appropriate expansion properties for the task at hand, metal that is too hot, or a mold that is designed badly. The ridges are formed when the sand is heated to the point where it begins to expand. When this happens, the sand will shear in certain places to allow for the expansion. It has to go somewhere after all! Ridges are then created on the surface of the metal casting along the sand shear lines. The ridges often snake along the surface, giving them the appearance of a rat tail.

7. Misrun (German translation: unvollständig ausgelaufener Guss)

A misrun occurs when molten metal poured into a mold is not able to fill the entire mold cavity. Reasons this might happen include: the metal not being sufficiently fluid to flow into parts of the mold, the metal being poured too slowly, or the mold cavity being too small for the metal to pass through.

8. Cold Shuts (German translation: die Kaltschweißstellen, der Kaltläufe)

A cold shut occurs when two different clumps of molten metal flow together, but do not fuse with each other.

9. Cold Shots (German translation: die Spritzkugeln, die Spritzperlen)

Cold shots occur when metal splatters as it is poured into a mold. The material in the splatter cools quickly and, if it becomes embedded in the final piece, may cause inconsistencies in the casting called “cold shots”.

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