Rapid Prototyping and Model Making: Subtractive Manufacturing (Constraints…
Rapid Prototyping and Model Making: Subtractive Manufacturing
Computer Numerical Control (CNC)
A manufacturing process in which the movement of the cutter, is controlled by a NC program.
A manufacturing process in which pre-programmed computer software dictates the movement of factory tools and machinery.
Parts of CNC Machine
code, or sometime known as
How it works
The process is programmable. Tool movement is controlled by NC program.
Remove material from a solid workpiece until the desired shape
Pros of using CNC
Can produce a fine surface finish
Cut on hard-metallic material
Constraints of using CNC
5-axis Machining Center
This is a higher end CNC machine, it is more expensive and more complex to program than a 3-axis machining center.
Sometimes, each half of a 3D part is machined separately, and later glue together to give a complete 3D prototype.
Work Holding Device
Can only shape the top-half of a design. To machine out a complete 3D shape of the prototype, the workpiece needs to be flipped over manually, and be able to clamp tightly when the second half of the design is being designed.
Limitation of cutter size
There is a minimum diameter size of a machining cutter. Hence, it is not possible to machine a sharp inner corner. Moreover, the cutter length is shorter when the cutter diameter size is smaller. Hence, programmer need to take note to avoid cutter holder colliding with the part.
CAM programming Skill
To generate the NV program for CNC machining center, we need to use a CAM (Computer Aided Manufacturing) software. Special training in using the CAM software is required.
One must have the knowledge and skill of machining process to use a CNC machine.
Work Flow of CNC
: CAD --> CAM --> CNC
How does CAM system works
Parameter setting for toolpath (CAM)
Better surface finish, but longer machining time
Feed rate (mm/min), Spindle Speed (rpm)
Depends on the workpiece material
A soft material allows deeper cut, and can remove material faster
Define how deep can the cutter plunge into the workplace
Cutter will need to plunge down more times for hard material, due to smaller depth of cut
Roughing and finishing toolpath (CAM)
: Aim to cut the part to accurate dimension, and
: Aim to remove bulk material at shorter time, ignoring the surface finishing.