Heat Treatment of Precision Machined Parts
In addition to the primary manufacturing process technologies, comprehensive heat treatment of precision machined parts can ensure products are capable of meeting the end user’s exact specifications. This controlled process of heating and cooling the parts to alter their physical properties is usually employed in order to increase hardness or strength, and enhance wear resistance. For certain applications, however, heat treatment may be indicated to improve machinability, enhance electrical or magnetic properties, increase ductility or softness, and alleviate internal stress.
The three steps followed in the heat treatment process are heating, soaking and cooling. During heating, the metal is brought to the temperature needed to affect the desired change in structural properties. The soaking process consists of maintaining the metal at this temperature until the part is heated evenly. Finally, the metal is cooled at a specified rate until it is once again at room temperature. In most cases, heat treatment is used on steel and steel alloys, but it can also be used on some aluminum grades.
Types of Heat Treatment for Precision Machined Parts
End results achievable through heat treatment include:
- Hardening: Hardening makes the metal stronger. The material is first heated and soaked, and then plunged into oil or water for rapid cooling. Hardening can sometimes make the metal more brittle, which may then require the additional process of tempering.
- Tempering: Tempering alleviates the internal stresses that may be caused by hardening. The three-step process remains, but is completed at lower temperatures than those seen in hardening. Cooling is usually completed in air, not in a liquid environment.
- Annealing: Annealing softens the metal, and makes it less likely to crack. During annealing, the material is heated slowly, soaked for a set period, and then slowly air-cooled in the furnace.
- Normalizing: Normalizing relieves internal stresses caused during machining. Parts are removed from the furnace after heating and soaking and quickly air-cooled outside the furnace.
- Solution treatment of stainless steel: Heat parts or materials to a high temperature single-phase zone to maintain a constant temperature, so that the excess phase is fully dissolved into the solid solution and then rapidly cooled to obtain a supersaturated solid solution. Carbon and other alloying elements are too late to precipitate so a pure Austenitic structure is created. This is intended to improve the toughness and corrosion resistance of parts.
Equipment Used in Heat Treatment of Precision Machined Parts
Manufacturers usually employ an automated, CNC-controlled heat treatment line to perform multiple operations, and move the product through the various stations on a 24/7 basis. Equipment in the line may consist of:
- Furnaces: Heat treatment furnaces are capable of achieving specified temperature and handling loads up to 1200 kilograms.
- Carburizing treatment: In order to increase the carbon content of the steel surface and form a certain carbon concentration gradient in it, the workpiece is heated in a carburizing medium, maintained for a long time so that carbon atoms are infiltrated into the workpiece.
- Vacuum Heat Treatment: Air is removed from the furnace to create a vacuum. The parts may be heated with or without an inert gas to achieve the desired properties and protect their surfaces. After treatment, the metal is quickly cooled.
- Cryogenic Processing: Workpieces go through a very low temperature process, achieving benefits for certain metal alloys. It can enhance the hardness and impact toughness of a workpiece, improve corrosion and wear resistance, and reduce workpiece deformation and cracks. Temperatures reach an extreme -80° Celsius.
- Aluminum Alloy Heat Treatment: This process is used to heat aluminum parts to a predetermined temperature at a controlled rate, hold the temperature for a specific duration, and then cool down at a controlled rate. This will transform the alloy’s internal structure, thereby enhancing mechanical properties and wear resistance, while improving machinability and dimensional stability.
- Annealing and Stress Relieving: Annealing improves ductility and reduces brittleness of the workpiece. Stress relieving heats workpieces to a temperature below their lowest transformation temperature, and then cools to room temperature. This releases internal stresses that have been absorbed by the metal from processes such as casting, forging and welding due to varying cooling speeds in different areas of the workpiece, or from straightening, machining or rolling.
- Gas Nitriding: This process heats normalized and machining-processed steel parts in nitrogen-rich carrier gasses, such as ammonia gas. They are held at a temperature in the range of 500-540° Celsius for a specified duration, resulting in a hard, wear-resistant and corrosion-resistant surface of a glowing white color, with a penetrating depth.
- Induction Heat Treating: This process heats designated areas of a part by an induction heating coil which receives controlled electrical input from the magnetic field generated by the equipment. The part surface can be heated to a specified depth, leaving the core of the piece untreated.
Learn More About Heat Treatment of Precision Machined Parts
Impro uses heat treatment to process a variety of parts, such as bearings, valve, drive shaft, plate -butterfly, piston, flange, and diffuser. We also offer NADCAP-certified heat treatment processes for aerospace products to ensure these components meet the high dimensional accuracy and stringent strength and fatigue property requirements for aerospace, energy, and medical applications. If you are interested in finding more information about our heat treatment of precision machined parts, please don’t hesitate to contact our team of experts today.