CNC machining parts are more than just programmed toolpaths. Before the machining begins, the CNC machining manufacturer reviews the available CAD model and drawing when provided, checks the applicable material, tolerance, GD&T, Threads, and other surface requirements. Then plans the machining operations, tooling, workholding, and sequence.
The process generally continues with CNC programming, toolpath verification, post processing, machine setup, first-part inspection, production machining, and final inspection. The exact work can change with the part and machining requirements, but each stage has a specific purpose. This guide follows the process from the initial drawing review to the completed part, showing what happens at each stage and how different factors can contribute to machining errors.
CNC Machining Process – Step by Step
The CNC machining parts manufacturer first reviews the part definition, then plans how to machine it and prepares the CNC program. The exact work changes with the part, machine, quantity, and requirements, but these stages form the basic planning path for many CNC jobs.
Step 1: Review the CAD Model, Drawing, and Requirements
First, the manufacturer reviews the available CAD model, drawing, and applicable product requirements before planning the job. The review covers applicable geometry, drawing revision, material grade and condition, dimensions and tolerances, GD&T, threads, critical features, surface texture, quantity, and inspection requirements. The manufacturer uses the current product definition as the basis for process planning.
Step 2: Plan the Machining Process and Select Tooling
The cnc machined part manufacturer then develops the machining plan. This includes selecting a suitable machine, defining the machining operations, choosing cutting tools and holders, planning workholding, and setting the machining sequence. Tool selection depends on factors such as the material, feature geometry, operation, machine capability, tool reach, and specified dimensional and surface requirements.
Step 3: Create and Verify the CNC Program
The programmer uses CAM software, where appropriate, to create toolpaths from the part geometry and assigns cutting data for the selected tools and operations. In workflows that use CAM post processing, the postprocessor creates NC code for the target machine and controller. The programmer verifies the program before machining, using machine-aware simulation when the programming system supports it to check tool motion, the workpiece, fixtures, and tooling.
Step 4: Set Up the Machine and Workholding
The operator loads the required stock, fixture, and tools, then positions the workpiece and establishes the work coordinate system. The operator sets the required tool and work offsets and verifies that the part, tools, and program match the planned setup.
Step 5: Prove Out the Program and Inspect the First Part
The manufacturer makes a controlled first run to confirm that the setup and program produce the required features. The first part then goes through the required dimensional checks, with attention to critical features. When measurements show a deviation, the manufacturer can apply the appropriate correction before continuing production.
Step 6: Machine the Parts and Perform In-Process Checks
The manufacturer continues production after the first part meets the required checks. When the process calls for in-process inspection, the operator checks selected features during production and takes the appropriate corrective action when the measured results require it.
Step 7: Finish, Perform Final Inspection, and Document Results
After machining, the manufacturer deburrs the part and completes any required post-machining processes. Final inspection then checks the completed part against the applicable specified requirements, including any requirements introduced by required post-machining processes. The manufacturer records the inspection results as required for the job.
Conclusion
A precise CNC machining process depends on controlling the job from the initial part requirements through programming, setup, machining, and final checks. When each stage follows the actual part requirements, the manufacturer can produce parts that meet the required specifications.
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