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What Is Cold Heading?

What Is Cold Heading?

Published by Rusty Spanner on Jun 14th 2024

Bad news, everyone: there is no magical fastener tree, growing nuts and bolts waiting to be plucked from its branches. Fasteners must be manufactured, and one of the most popular and efficient methods of production is called cold heading. So let BelMetric–the masters of metric fasteners–give you a lesson in how these products are made.

WHAT IS COLD HEADING?

Cold heading, also known as cold forming, is a process used to create high-quality fasteners by taking cut lengths of wire or cylindrical rods, often made of steel, and using a series of dies and punches to press them into different shapes via mechanical force at high speeds.

Although the name suggests that there might be some kind of deep freeze involved, cold heading is actually performed at an ambient temperature; in contrast, another popular method of creating fasteners, hot rolling, often occurs at temperatures exceeding 1000° Fahrenheit.

Cold heading can be used with a variety of different metals. It is most often used with aluminum, brass, carbon steel (including boron) and stainless steel, but can also be applied to other types, including bronze, copper and nickel.

HOW DOES COLD HEADING WORK?

Cold heading begins with slugs. Not the lethargic garden pest, of course: these slugs are pieces of wire steel rods, cut from a progressive source to prescribed lengths. Slugs are also alternately referred to as ‘blanks.’ The slug is then fed into machinery consisting of two basic components: dies and punches. 

WHAT ARE DIES & PUNCHES?

Dies and punches are used in conjunction with one another to create fasteners. Perhaps the simplest way to explain the two is that the die is the negative impression of the intended fastener and remains stationary throughout the process. the punch acting as the positive. The chosen metal is run through one or more die and punch configurations, depending on how intricate the final product will be.

Additionally, the die and punch combination is sometimes augmented by two different processes: upsetting and extrusion.

UPSETTING

Upsetting is the process that is most often used to create heads on fasteners. The initial piece of material prior to upsetting has a longer length than its diameter. When force is exerted on the material, this dynamic reverses, and the resulting product is wider than it is long. Depending on the end product desired, this process must sometimes be done in multiple stages.

EXTRUSION

Extrusion, according to Merriam-Webster’s dictionary, is a verb meaning “to force, press or push out.” When it comes to fastener production, there are two types of extrusion commonly used: forward and reverse.

Forward extrusion utilizes a die with a smaller diameter than the initial slug; using great amounts of pressure, the metal slug is forced through the die, resulting in a reduction of the metal’s diameter but an increase in its length.

There are two different types of forward extrusion: open and trapped. The main difference between them is that open extrusion punches through the die with nothing on the other side, whereas trapped extrusion has the metal slug in a completely contained space, allowing for more intricate shapes. Forward extrusion is typically used to create screws and bolts.

Backward extrusion involves a die that is smaller than the slug’s beginning diameter. When the punch is driven into the material, there is nowhere else for it to go, and it reforms backwards around the die, creating a concave depression. Backward extrusion is used for nuts and rivets, as well as various cylindrical designs.

ADVANTAGES OF COLD HEADING

HIGHER PRODUCTION SPEED

The technology involved in cold heading has significantly improved since its initial development; nowadays, advanced machinery can create hundreds of fasteners per minute. As the name suggests, cold heading requires no heating, which means less energy is required during manufacturing.

This quick turnaround is possible because, with cold heading, the parts are formed to their net shape, and there are fewer, if any, secondary processes involved. This includes not needing a secondary finishing, as the surface resulting from cold heading is typically smooth.

Interchangeable dies and punches within certain production facilities also allow for the creation of highly intricate fasteners in unique shapes. It is also possible to replace installations that require multi-part assemblies with a single-piece component via cold heading.

GRAIN FLOW

One major advantage to cold heading is the retention of the original grain flow of the material, where other processes such as screw machining would interrupt the flow. By not disturbing the grain flow, the resulting fastener has better yield and tensile strength, as well as giving greater fatigue strength, particularly in crucial corners.

REDUCE SCRAP RATES

Cold heading is advantageous because it uses less raw material than screw machining, which can only remove raw material and not reform it. Cold heading is volume specific, so the material is reshaped; this means that the diameter of the initial slug can be smaller than the output diameter. With less raw material being used, the end result is cost-efficient.

SAVES MONEY

All of the advantages to cold heading cumulatively contribute to reduced costs in manufacturing–an attractive proposition for the companies that produce fasteners. This savings is (hopefully!) passed onto the consumer, who receives durable and attractive fasteners at a reasonable cost.

DRAWBACKS OF COLD HEADING

Although cold heading offers many advantages when producing fasteners, there are a few downsides. One is that a great amount of energy and pressure is required for cold heading; therefore, it can be cost-prohibitive to make larger fasteners via this method.

Certain hard metals are not suitable for cold heading. Also, there are some processes that cold heading machinery cannot perform, including bending, rolling and stamping.

CONCLUSION

Cold heading takes a metal slug and runs it through a series of dies and punches to reform the material into a designated shape. Additional processes called upsetting and extrusion can be applied to create more intricate designs. Cold heading is a cost-effective process where less scrap metal is being wasted, and because material is being reshaped instead of cut away, the original grain flow of the source material is retained, resulting in a stronger, more attractive fastener.