3D Printing vs. CNC Machining -CNC Part ，CNC Time

The factors that influencethe time to manufacture a part are distinctly different for 3D printing and   CNC.

Manufacturing times for 3D printing are dictated primarily by the volume of material in a part and the part’s height.

Feature count and featuretype have little impact on time. The opposite is true for CNC. Size and volumehave marginal impact, but the number of features and their design characteristics dictate time.

Because the time factors areso dissimilar, it is not prudent to state that one process is faster than the othernor to offer general rules of thumb.

Finish/Assemble

Upon completion of the manufacturing process, 3D printed parts will require post-processing.

Most, but not all, will need removal of a sacrificial support structure that attaches the part to the build plate of the printer and holds unrestrained features in place. Unlike the manufacturing process,the time for support removal is geometry dependent. This step may be a manual operation   that takes between five minutes and one hour to complete or an automated,

batch operation that takes between one and four hours. CNC parts on the other hand, have no mandatory secondary operations.

TIME DRIVERS

Excluding set up and finishing for both 3D printing and CNC ,the question of which process has higherthroughput can only be answered after selecting a part design.

The time factors for 3D printing are simple and straight forward. A part’s volume and height dictate most of the manufacturing time. The only design-related consideration that adds time results from support structures.When features need to be supported, a small amount of build time is added,usually in the 5% to 15% range.

Unlike CNC, adding features that remove material, such as pockets and holes, will decrease the time needed to make a part.

CNC time is determined by the volume of material subtracted and the rate at which it is removed.

The amount is dictated by the design and the size of the raw material stock. The rate is dictated by many factors, such as:

• Specified tolerances:Tighter tolerances require more machining time.

• Size and depth of holesand pockets: Deep and narrow require smaller cutters and slower cutting speeds,which adds time.

• Wall thickness: Smaller cutting depths and slower speeds are needed to prevent walls from deflecting.