September 18, 2019 Reviewing Heat Treatments in CNC Machining

A look at the heat treatments that are commonly used for metal alloys in CNC machining.

September 18, 2019

Part of the designing and engineering process is to determine what physical properties the part needs and the best metal chose to provide those requirements. Having metal alloys heat treated, either before or after machining, can immensely improve key physical properties. Heating treatments can add to the hardness of the metal, its strength, or its machinability.

In the heat treatment process, metals are heated to extreme temperatures and allowed to cool in a controlled manner.

The temperature to which the material is heated, the time it is allowed to stay at that temperature, and how fast or slow it is allowed to cool, all have an effect on the final physical properties the metal alloy will obtain.

This article will review the heat treatments that are most commonly used for metal alloys in CNC machining. By explaining how these processes affect the properties of metal alloys, this article will help you decide which material is best for your application.

When are heat treatments applied?

Here are a couple of basic rules that are followed as to when heat treatment is applied to metal alloys:

Before CNC machining:

• Before CNC machining: When the grade of metal requested is a standardized grade, then the part is made out of stock that has already been heat treated to the proper degree.

Post CNC machining:

• Post CNC machining: If the metal alloy needs to be significantly harder than a standardized grade, then the heat treatment happens after the machining process. Harder metals are more difficult to machine. This post machining heat treatment is common when tool steel is being used.

What are some common heat treatment processes for CNC materials?

1. Annealing: In the annealing process, metals are heated to an extremely high temperature and slowly cooled. Annealing is usually applied after the metal alloys are formed to soften them and enhance their machinability.
2. Stress-relieving: Machining causes stress in the metal. To relieve this stress and create consistent mechanical properties within the metal part, the finished part is heated to a high temperature and slowly cooled.
3. Quenching: Quenching is a post CNC machining heat treatment process where the metal is heated to a very high temperature and cooled rapidly. The result is a metal that is extremely hard. The quenching of tool steels after being machined is done to attain their very high hardness properties.
4. Tempering: After quenching, some metal alloy parts will be put through a tempering process. The metal is heated to a high temperature and allowed to cool slowly. Tempering reduces some of the brittleness added to the metal during quenching.
5. Case hardening: Case hardening is a heat treatment process that only hardens the surface of the metal while leaving the interior soft. This hardening process is sometimes preferred to keep the whole metal part from being brittle.

How to specify a heat treatment with 3D Hubs CNC services

3D Hubs provides online CNC quotes. As part of those services, we can assist you in choosing the right material for your application and provide you with the heat treatment that your application requires.

When you place an order with 3D Hubs online CNC services, you have three ways to request a heat treatment:

1. Give a reference to a manufacturing standard: Provide the standardized heat treatment indicator, like T6 for aluminum alloys.
2. Specify the required hardness: This method is normal for requesting hardness that is applied to the metal after machining is done.
3. Specify the heat treatment cycle: If you understand how different heat treatments affect metal, then you can specify which heat treatment processes you want.

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