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[Subtractive Manufacturing] Computer Numerical Control (CNC) (Features…
[Subtractive Manufacturing]
Computer Numerical Control
(CNC)
How it works
Remove material from a solid workpiece until the desired shape
The process if programmable. Tool movement is controlled by NC program
Pro's and Con's
Disadvantages
Work Holding Deviec
It can only cut top-half design
Work piece needs to be held tightly
Work piece needs to be flipped over to design the second half
5-axis Machining Center
More expensive
More complex programming
Post-processing neede
Sometimes half f the 3D part is machined separately
Need to be glued together to complete the 3D prototype
Limitation of cutter size
Minimum diameter size of the machine cutter
Cannot machine a sharp inner corner
Cutter length is shorter when the cutter diameter size is smallet
Need to avoid cutter holder colliding with the part
CAM Programming Skill
CAM software is needed to generate NC program
Special training is required to use CAM software
Trained Machinist
Must have knowledge of machining process to use a CNC machine
Advantages
Able to cut hard metallic material
Produce fine surface finsih
Accurate
Priogrammable
Features of CNC Machine
Computer Numerical Control
Manufacturing process in which movement of cutter is controlled by NC program
Parts
Control Panel
Starts machining program
Spindle Unit
Hole the cutter
Travels in X and Z direction
Spindle rotates the cutter when cutting
Work Table
Hold the work piece
Travels in Y direction
NC Program
Known as Alpha-Numeric code or G-code
X. Y, Z values in the program dictates the cutter location with respective to the work piece zero reference
Work Flow
CAD
CAM
CNC
The NC Part Program is downloaded into CNC Machine Control Unit
(e.g 3-axis CNC Router)
The program drives the cutter movement to shape the raw materials
Tool Path programming is done from the CAM System
NC Program exports from the CAM System
How does CAM System works
CAD
CAM
Post-processor
& Machine Simulation
Part Machining
NC program drives the CNC Machine
Optimizes CAM tool path & NC program
Tool path & tool definition
Part & Assembly design
STL file export from CAD system
(CAD Model)
CAM
Step Depth
Depends on work piece material
Soft material allow deeper cut and remove material faster
Cutter will need to plunge down more times for harder material, due to smaller depth of cut
Define how deep the cutter plunge into workpiece
Step Over
Define how far apart can the cutter progress when moving in X-Z direction
Usually very narrow when the ball mill cutter is shalping a curved surface
Spindle Speed/Feedrate
Defined by the Spindle Revolution per Minute (RPM) and the cutter forward movement known as Feed rate
Roughing and Finishing Toolpath
Roughing process aim to remove bulk material at shorter time ignoring the surface finish
Finishing process aim to cut the part to accurate dimension and good surface finish