Part 2: Engineering Phase – Process Planning from Drawing to Part

This section is for process engineers or programmers, translating design into executable manufacturing instructions.

1. Process Route Planning

Operation Sequencing: E.g., "Cut stock → Rough mill 6 sides → Finish mill reference faces → Drill/Tap holes → Finish mill pockets → Deburr → Inspection."

Workholding Strategy: Design or select fixtures (vises, fixture plates, custom fixtures). Analyze how to minimize setups and ensure consistent datum references.

Machining Order Principles: Follow "Rough before finish, faces before holes, primary before secondary."

2. Tooling & Parameter Selection

Tooling List: Specify tool type (end mill, ball nose, drill, tap), diameter, flute length, and material (carbide, HSS) for each operation.

Cutting Parameters: Provide recommended Cutting Speed (Vc), Feed per Tooth (fz), Axial Depth of Cut (ap), Radial Depth of Cut (ae). Use tables for different materials.

*Example (Carbide End Mill for Aluminum): Vc=200-300 m/min, fz=0.05-0.1 mm/tooth, ap=0.5D, ae=0.1D*

3. CNC Programming Key Points

Coordinate Systems: Define workpiece coordinate system (G54-G59) setup and use of edge finders/touch probes.

Toolpath Strategies:

Pocketing: Use helical or ramp entry to avoid plunging.

Contouring: Mention climb vs. conventional milling (climb recommended for finishing).

Drilling Cycles: Use proper cycles (G81/G82/G83). Use peck drilling (G83) for deep holes to ensure chip evacuation.

Safety & Efficiency: Include clearance heights, retract planes, and use of subprograms/loops for code efficiency.

Part 3: Quality Control & Inspection

1. On-Machine Inspection: Use machine touch probes for preliminary checks of critical dimensions.

2. Final Inspection Methods & Tools:

General Dimensions: Calipers, micrometers.

Geometric Tolerances: Dial indicators, CMM (Coordinate Measuring Machine).

Surface Finish: Surface roughness tester.

3. Documentation: Inspection reports, First Article Inspection (FAI) reports.

II. Documentation Writing Tips & Format

1. Use Visuals, Charts, and Diagrams:

Use 3D model screenshots, 2D drawing callouts for key features.

Use flowcharts for process routes.

Use tables to compare material properties, tooling parameters.

2. Standardization & Templates:

Create standard CNC Design Checklist, Process Planning Sheet, Tooling Parameter Sheet.

Unify terminology (e.g., "roughing," "finishing," "corner cleaning").

3.Version Control:

Implement strict version control for design drawings and NC programs to ensure the latest files are used on the shop floor.

4. Include "Notes" or "Lessons Learned":

E.g., "When machining stainless steel, use tools with a large positive rake angle and ensure ample coolant to control work hardening."

"This long narrow slot is prone to deformation. Recommend finishing it in the final operation."

1. High-Speed Machining (HSM) & 5-Axis Machining: Strategies like small step-downs, high feed rates, full climb milling; benefits of 5-axis positioning and simultaneous machining.

2. Strategies for Difficult-to-Machine Materials (e.g., Titanium, Inconel): Low RPM, high DOC, maintaining constant chip load.

3. Machining Simulation & Optimization: Using software like VERICUT for collision checking and toolpath optimization to reduce trial cuts.

4. Automation & Digitalization: Integration with MES systems for automatic program dispatch and production data collection."a

Full-Process Optimization from Concept to Finished Product

1. Cost Engineering & Value Analysis

This bridges design and business, crucial for decision-makers.

1.1 Cost Breakdown Model:

Material Cost: Optimizing nesting (CAM programming) to minimize waste. Can standard stock be used instead of a solid block?

Machining Time Cost: Establish a "machine hourly rate." Analyze how optimized toolpaths (e.g., HSM, trochoidal milling) reduce cycle time.

Tooling Cost: Analyze the relationship between tool life and parameters. Compare high-cost/long-life tools vs. low-cost/frequent-change strategies with a cost-per-part model.

1.2 Secondary Operation Cost: Fixturing time, inspection, and post-processing (e.g., anodizing).

Design-for-Cost Optimization:

Part Consolidation: How can multiple components be cleverly designed as one CNC part, eliminating assembly and inventory costs?

The "Good Enough" Philosophy: Case studies showing how relaxing non-critical surface finish (e.g., Ra1.6 vs. Ra0.8) or tolerance (±0.05mm vs. ±0.02mm) dramatically reduces cost.

Alternative Manufacturing Comparison: Comparative cost analysis charts: CNC Machining vs. 3D Printing (Metal/Plastic) vs. Sheet Metal Fabrication vs. Die Casting for low-volume vs. medium-volume production.a

2. Application-Specific Design & Engineering

Design is meaningless without context.

2.1 Aerospace & Defense:

Lightweighting: Combining topology optimization with CNC machining. Designing conformal cooling channels.

Material Challenges: Strategies for machining titanium, high-strength aluminum to prevent burn and stress distortion.

Traceability & Certification: Requirements for full traceability of material batch, machining parameters, and tooling records.

2.2 Medical Devices:

Biocompatible Materials: Machining considerations for titanium, cobalt-chrome, PEEK.

Surface Finish & Cleanability: Designing crevice-free, sterilizable geometries. Polishing process selection.

Micro-Machining: Programming and process challenges with micro-tools (<1mm).

2.3 Automotive & Molds:

Prototyping & Low-Volume: Rapid workflow from CAD to functional CNC prototypes.

Mold & Die Making: Electrode design for EDM collaboration. Application of 5-axis machining for complex cavities.

3. Collaborative Design & Digital Workflow

The nervous system of modern manufacturing.

3.1 The Digital Thread from CAD to G-Code:

Seamless Data Transfer: Using neutral formats (e.g., STEP) to prevent data loss between CAD and CAM systems.

Model-Based Definition (MBD): Promoting MBD - embedding all dimensions, tolerances (GD&T), and notes within the 3D model as the single source of truth.

CAM Automation: Feature-Based Machining (FBM) and template-based programming for automatic, optimized toolpath generation on standard features (holes, pockets, threads).

3.2 Integration with Simulation & Digital Twin:

Process Simulation: Using software for toolpath verification, material removal simulation, and machine collision checking.

Virtual Commissioning: Testing CNC programs within a digital twin environment to verify logic and cycle time.

4. Emerging Technologies & Trends

Demonstrates industry foresight.

4.1 Hybrid Additive-Subtractive Manufacturing:

Designing for "print then machine" workflows (e.g., DED + CNC). Planning the transition interface.

4.2 AI & Machine Learning in CNC:

Adaptive Machining: Real-time sensor monitoring of cutting forces/vibration, with AI adjusting feed/speed for optimized, unattended machining.

Predictive Maintenance: Analyzing spindle load, tool vibration to predict wear and machine failure.

4.3 Automation & Lights-Out Manufacturing:

Designing parts for automated fixturing (standardized datums, minimal custom jigs).

Integrating pallet systems with CNC for 24/7 production.

5. Sustainable Manufacturing & Green Engineering

Aligns with ESG principles and enhances brand value.

Material & Energy Efficiency:

Lightweight design as a driver for energy savings.

Analyzing the environmental impact of cooling methods (flood, MQL, cryogenic).

Best practices for cutting fluid management and recycling.

Tool Lifecycle Management:

Feasibility analysis of tool re-grinding and re-coating.

Processes for recycling scrap carbide tools.

6. Knowledge Management & Training Systems

Ensures long-term organizational competency.

6.1 Defect Library & Solution Database:

Create a visual "failure mode" library. Example:

Problem: Chatter marks on surface.

Root Causes: Excessive tool overhang, poor workpiece clamping, aggressive parameters, worn tool.

Solutions: Reduce overhang, check fixture, adjust feed/speed, replace tool.

6.2 Internal Technical Case Studies:

Regularly document post-mortems of significant parts (especially challenging, successful, or cost-optimized), capturing the complete journey from design to delivery as institutional knowledge.