Surface Finishes for CNC Machining

Hardening: Hardening is performed to address metal’s deficiencies, especially those that affect overall durability. It is performed by heating the metal and quenching it quickly right when it reaches the desired properties. This freezes the particles so it gains new qualities.

Annealing: Most common with aluminum, copper, steel, silver or brass, annealing involves heating metal to a high temperature, holding it there and allowing it to slowly cool. This makes these metals easier to work into shape. Copper, silver and brass can be cooled quickly or slowly, depending on the application, but steel must always cool slowly or it will not anneal properly. This is normally accomplished before machining so materials do not fail during manufacturing.

Normalizing: Often used on steel, normalizing improves machinability, ductility and strength. Steel heats to 150 to 200 degrees hotter than metals used in annealing processes and is held there until the desired transformation occurs. The process requires steel to air cool in order to create refined ferritic grains. This is also useful for removing columnar grains and dendritic segregation, which can compromise quality while casting a part.

Tempering: This process is used for iron-based alloys, especially steel. These alloys are extremely hard, but often too brittle for their intended purposes. Tempering heats metal to a temperature just below the critical point, as this will reduce the brittleness without compromising the hardness. If a customer wishes for better plasticity with less hardness and strength, we heat metal to a higher temperature. Sometimes, though, materials are resistant to tempering, and it may be easier to purchase material that is already hardened or to harden it before machining.
Case hardening: If you need a hard surface but a softer core, case hardening is your best bet. This is a common process for metals with less carbon, like iron and steel. In this method, heat treatment adds carbon to the surface. You will normally order this service after pieces are machined so you can make them extra durable. It is performed by using high heat with other chemicals, as that reduces the risk of making the part brittle.

Aging: Also known as precipitation hardening, this process increases the yield strength of softer metals. If metal requires additional hardening beyond its current structure, precipitation hardening adds impurities to increase strength. This process usually happens after other methods were used, and it only raises temperatures to middle levels and cools material quickly. If a technician decides natural aging is best, materials are stored in cooler temperatures until they reach the desired properties.