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The forging industry has a broad range of manufacturing processes, making many different types of products. From aerospace fasteners and the automotive industry to hardware and tools, forged products can be found just about everywhere you look. The Forging Industry Association provides a great brief overview video of all the different types of forging processes. Aluminum, copper, steel and titanium are the most popular metals that are used in the forging process. While there are a number of different ways to forge metal, the process essentially remains the same. It requires heating a piece of metal and then deforming that metal into a particular shape. For some forged parts, temperature control is critical in achieving the desired metallurgical and structural properties of the newly forged part. Here are three essential temperatures that need to be measured in the forging process.

1. Billet Temperature

There are really two types of billet temperature, one that is done inside a billet furnace (done for batch heating), the other is done prior to die entry to make sure that the part is hot enough before it enters the die.

1a. In-Furnace Measurement

In a forging plant, aluminum, brass, or steel billets are heated in furnaces before they are loaded into the forging die to be formed. Billets may be large or small and the billet furnace may be gas-fired or induction-heated. In some cases only the end of a product, such as the end of a rod or tube, is heated and formed. In other cases, the entire billet is heated. The efficiency of the heating process and the consistency of the formed product rely on a well-controlled billet preheat temperature.

When measuring inside a gas-fired furnace wavelength selection is critical to sensor performance. Infrared temperature sensors need to be filtered at wavelengths that view through flames and combustion byproducts without interference in order to make an accurate reading. Ratio pyrometers are typically recommended as they automatically compensate for emissivity variation and can tolerate moderate surface scale. If you have a wide tolerance for temperature error, single-wavelength pyrometers filtered at a short-wavelength can be used to minimize sensitivity to emissivity variation and scale.

1b. Die Entry Measurement

An infrared thermometer is an essential tool when heating a billet with an induction heater or as a final temperature verification before the billet is inserted into the die. Temperature feedback is necessary to assure consistent billet temperature, to avoid die damage, and to assure quality production of the formed parts.

The infrared thermometer is most effective when used to measure the temperature during the heating cycle rather than simply as a verification after the billet has already left the heater. Sometimes the sensor may be mounted to view into the induction furnace between the windings of the coil, or through the furnace exit port. In other cases it may be desirable to insert a fiber optic probe (nonconductive light pipe) through the induction coil side wall.

2. Die Temperature

The forging die temperature has a significant impact on the consistency of the forged part. A die that is too hot or too cold will wear prematurely, will require excess lubricant to assure proper forming or to prevent sticking, and will affect the quality of the formed part. If the die is too hot, then surface blemishes melting may result. If the die is too cold, then surface cracks may occur.

Measurement of the die temperature is complicated by an intermittent target, intermittent flames, lubricant sprays, and the insertion and removal of the billet and forged part. Certain Williamson infrared thermometers are supplied with a patented signal conditioning technique that allows the sensor to recognize valid measurement conditions. Using this unique feature, the pyrometer measures only the die temperature. Interference from flames, lubricants, billets, and forged parts is completely eliminated, and only the die temperature is measured. This innovative capability provides for a simple and easy die temperature measurement.

3. In Process Temperature

An infrared thermometer may be used to monitor process temperatures during the forming process for those forging procedures where the metal part is exposed to view during as it is formed. While the formed part can not be viewed during the closed die forming process, it may be viewed in an open die process, including hammer-formed and ring-formed parts.

The temperature of the part being formed is critical for the forging process. Once the part is removed from the preheat furnace it gradually loses heat. If the part were to become too cool, then it will crack as it is formed, and the deformation tooling will wear prematurely. In addition, the part temperature may be used directly for process feedback, as a well-heated part may undergo a greater deformation with each strike than one that is approaching the lower temperature limit of deformation. Therefore, the impact may be adjusted to optimize each strike according to the temperature of the part to be deformed.

By accurately controlling for temperature at these three different parts of the forging process, you can improve product quality, reduce scrap, and improve process efficiency. To learn more about which pyrometer technology is most appropriate for your application, download our free wavelength selection guide.

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