Precision CNC Machining CNC Programming Processing Experience Sharing

Since CNC Machining Is Related To Different Machine Tools, Different Materials, Different Tools, Different Cutting Methods, Different Parameter Settings, Etc., Its Complexity Determines That Technicians Engaged In CNC Machining Must Reach A Certain Level In Both Operation Programming, Which Must Take A Relatively Long Time. This Article Is A Summary Of Some Experiences Summarized By Huiwen Zhizao's Masters In The Long-Term Actual Production Process On CNC Machining Technology, Procedures, Selection Of Commonly Used Tool Parameters, Monitoring During The Machining Process, For Your Reference. Huiwen Zhizao Has More Than Ten Years Of Machining Experience, With CNC Machining As The Core Technology. It Has Accumulated A Lot Of Experience In The Manufacture Of Metal Parts Mainly Made Of Raw Materials Such As Aluminum Alloy, Stainless Steel, Copper , Plastic Parts Such As ABS, PC, POM, PEEK, Nylon + Glass Fiber.

1. Division Of CNC Machining Processes

1. Tool Centralized Sorting Method

That Is, The Process Is Divided According To The Tool Used, All The Parts That Can Be Completed On The Part Are Processed With The Same Tool. Then The Second Third Tools Are Used To Complete The Other Parts That Can Be Completed By Them. This Can Reduce The Number Of Tool Changes, Compress Idle Time, Reduce Unnecessary Positioning Errors.

2. Sort By Processing Part

For Parts With Many Processing Contents, The Processing Parts Can Be Divided Into Several Parts According To Their Structural Characteristics, Such As Internal Shape, External Shape, Curved Surface Plane, Etc. Generally, Planes Positioning Surfaces Are Processed First, Holes Are Processed Later; Simple Geometric Shapes Are Processed First, Complex Geometric Shapes Are Processed Later; Parts With Lower Precision Are Processed First, Parts With Higher Precision Requirements Are Processed Later.

3. Rough Fine Processing Method

For Parts That Are Prone To Deformation During Machining, They Need To Be Calibrated Due To Possible Deformation After Rough Machining. Therefore, Generally Speaking, The Rough Fine Machining Processes Must Be Separated. In Summary, When Dividing The Processes, It Is Necessary To Flexibly Grasp The Structure Processability Of The Parts, The Function Of The Machine Tool, The Amount Of CNC Machining Content Of The Parts, The Number Of Installations The Production Organization Status Of The Unit. It Is Also Recommended To Adopt The Principle Of Process Concentration The Principle Of Process Dispersion, Which Should Be Determined According To The Actual Situation, But It Must Be Reasonable.

2. Principles Of Arranging Processing Sequence

The Arrangement Of Precision CNC Machining Sequence Should Be Based On The Structure Of The Parts, The Condition Of The Blank, The Need For Positioning Clamping. The Key Point Is That The Rigidity Of The Workpiece Is Destroyed. The Sequence Should Generally Be Carried Out According To The Following Principles:

1. The Processing Of The Previous Process Cannot Affect The Positioning Clamping Of The Next Process, The General Machine Tool Processing Processes Interspersed In The Middle Must Also Be Considered Comprehensively.

2. Carry Out The Inner Shape Cavity Processing Process First, Then Carry Out The Outer Shape Processing Process.

3. It Is Best To Carry Out The Processes With The Same Positioning, Clamping Method The Same Tool In Succession To Reduce The Number Of Repeated Positioning, Tool Changes Platen Movements.

4. When Multiple Processes Are Performed In The Same Installation, The Process That Causes The Least Damage To The Rigidity Of The Workpiece Should Be Arranged First.

3. Considerations For Determining The Workpiece Clamping Method

The Following Three Points Should Be Noted When Determining The Positioning Reference Clamping Scheme:

1. Strive To Unify The Standards Of Design, Technology, Programming Calculations.

2. Reduce The Number Of Clamping Times As Much As Possible, Try To Process All The Surfaces To Be Processed After One Positioning.

3. Avoid Using Manual Adjustment Solutions That Require The Machine To Be Occupied.

4. The Fixture Should Be Open, Its Positioning Clamping Mechanism Should Affect The Tool Movement During Processing (Such As Causing Collision). When Encountering Such A Situation, You Can Use A Vise Add A Bottom Plate To Clamp It.

4. How To Determine The Reasonable Tool Setting Point?

1. The Tool Setting Point Can Be Set On The Part Being Processed , But Please Note That The Tool Setting Point Must Be The Reference Position The Part That Has Been Finely Processed. Sometimes The Tool Setting Point Is Damaged After The First Process, Which Will Make It Impossible To Find The Tool Setting Point In The Second Process Later. Therefore, When Setting The Tool In The First Process, Pay Attention To Setting A Relative Tool Setting Position At A Place With A Relatively Fixed Size Relationship With The Positioning Reference, So That The Original Tool Setting Point Can Be Found According To The Relative Position Relationship Between Them. This Relative Tool Setting Position Is Usually Set On The Machine Tool Workbench Fixture. The Selection Principles Are As Follows:

(1) It Is Easy To Align.

(2) Easy To Program.

(3) Small Tool Setting Error.

(4) Easy To Inspect During Processing.

2. The Origin Of The Workpiece Coordinate System Is Set By The Operator. It Is Determined By Tool Setting After The Workpiece Is Clamped. It Reflects The Distance Position Relationship Between The Workpiece The Zero Point Of The Machine Tool. Once The Workpiece Coordinate System Is Fixed, It Is Generally Changed. The Workpiece Coordinate System The Programming Coordinate System Must Be Unified, That Is, In Precision CNC Machining, The Workpiece Coordinate System The Programming Coordinate System Are Consistent.

5. How To Choose The Cutting Route?

The Tool Path Refers To The Movement Trajectory Direction Of The Tool Relative To The Workpiece During CNC Machining. The Reasonable Selection Of The Machining Path Is Very Important Because It Is Closely Related To The Machining Accuracy Surface Quality Of The Parts. The Following Points Are Mainly Considered When Determining The Tool Path:

1. Ensure The Machining Accuracy Requirements Of Parts.

2. Facilitate Numerical Calculations Reduce Programming Workload.

3. Seek The Shortest Processing Route Reduce The Idle Time To Improve Processing Efficiency.

4. Minimize The Number Of Program Segments.

5. To Ensure The Roughness Requirement Of The Workpiece Contour After Surface Processing, The Final Contour Should Be Arranged To Be Processed Continuously In The Last Pass.

6. The Tool's Entry Exit (Cutting In Out) Routes Must Also Be Carefully Considered To Minimize Tool Marks Caused By Stopping At The Contour (Elastic Deformation Caused By A Sudden Change In Cutting Force), To Avoid Scratching The Workpiece By Cutting Vertically On The Contour Surface.

6. How To Monitor Adjust During The Processing?

After The Workpiece Is Aligned The Program Is Debugged, It Can Enter The Automatic Processing Stage. During The Automatic Processing, The Operator Must Monitor The Cutting Process To Prevent Abnormal Cutting Causing Workpiece Quality Problems Other Accidents. The Following Aspects Should Be Considered When Monitoring The Cutting Process:

1. Process Monitoring Rough Machining Mainly Considers The Rapid Removal Of Excess Allowance On The Workpiece Surface. During The Automatic Machining Process Of The Machine Tool, According To The Set Cutting Amount, The Tool Automatically Cuts According To The Predetermined Cutting Trajectory. At This Time, The Operator Should Pay Attention To Observe The Changes In The Cutting Load During The Automatic Machining Process Through The Cutting Load Table, Adjust The Cutting Amount According To The Tool's Bearing Capacity To Maximize The Efficiency Of The Machine Tool.

2. Monitoring Of Cutting Sound During Cutting During The Automatic Cutting Process, When Cutting Begins, The Sound Of The Tool Cutting The Workpiece Is Stable, Continuous, Brisk, The Machine Tool Moves Smoothly. As The Cutting Process Progresses, When There Are Hard Spots On The Workpiece, The Tool Is Worn, The Tool Is Clamped, The Cutting Process Becomes Unstable. The Instability Is Manifested By Changes In The Cutting Sound, Collision Sounds Between The Tool The Workpiece, Vibration Of The Machine Tool. At This Time, The Cutting Amount Cutting Conditions Should Be Adjusted In Time. When The Adjustment Effect Is Obvious, The Machine Tool Should Be Stopped To Check The Condition Of The Tool The Workpiece.

3. Process Monitoring Of Finishing Finishing Is Mainly To Ensure The Machining Size Surface Quality Of The Workpiece, With High Cutting Speed Large Feed Rate. At This Time, Attention Should Be Paid To The Influence Of Built-Up Edge On The Machined Surface. For Cavity Machining, Attention Should Also Be Paid To Overcutting Tool Letting At Corners. To Solve The Above Problems, First, Attention Should Be Paid To Adjusting The Spray Position Of The Cutting Fluid So That The Machined Surface Is Always In The Best Cooling Condition; Second, Attention Should Be Paid To Observing The Quality Of The Machined Surface Of The Workpiece, By Adjusting The Cutting Amount, The Quality Change Should Be Avoided As Much As Possible. If The Adjustment Still Has No Obvious Effect, The Machine Should Be Stopped To Check Whether The Original Program Is Reasonably Programmed. In Particular, Attention Should Be Paid To The Position Of The Tool When Pausing For Inspection Stopping For Inspection. If The Tool Stops During The Cutting Process The Spindle Stops Suddenly, Tool Marks Will Be Produced On The Surface Of The Workpiece. Generally, The Machine Should Be Stopped When The Tool Leaves The Cutting State.

4. Tool Monitoring The Quality Of The Tool Determines The Machining Quality Of The Workpiece To A Large Extent. During The Automatic Machining Cutting Process, The Normal Wear Abnormal Damage Of The Tool Should Be Judged Through Methods Such As Sound Monitoring, Cutting Time Control, Pause Inspection During Cutting, Workpiece Surface Analysis. The Tool Should Be Handled In Time According To The Processing Requirements To Prevent Machining Quality Problems Caused By The Tool Being Handled In Time.

7. Types Selection Methods Of Machining Tools

According To Material Classification, Cutting Tools Are Generally Divided Into Ordinary Hard White Steel Knives (Made Of High-Speed Steel), Coated Cutting Tools (Such As Titanium-Plated Tools, Etc.), Alloy Cutting Tools (Such As Tungsten Steel, Boron Nitride Cutting Tools, Etc.).

There Are Three Selection Methods:

1. When Plane Milling, You Should Use Carbide End Mills End Mills That Do Need To Be Reground. When Milling In General, Try To Use Two Passes. The First Pass Is Best To Use An End Mill For Rough Milling, Pass Continuously Along The Surface Of The Workpiece. The Width Of Each Pass Is Recommended To Be 60%-75% Of The Tool Diameter.

2. End Mills End Mills With Carbide Inserts Are Mainly Used For Processing Bosses, Grooves Box Surfaces.

3. Ball Cutters Round Cutters (Also Called Round Nose Cutters) Are Often Used To Process Curved Surfaces Variable Angle Contours. Ball Cutters Are Mostly Used For Semi-Finishing Finishing. Round Cutters With Carbide Inserts Are Mostly Used For Roughing.

8. Purpose Content Of Processing Procedure Sheet

1. The Machining Procedure Sheet Is One Of The Contents Of CNC Machining Process Design. It Is Also A Procedure That The Operator Needs To Follow Execute. It Is A Specific Description Of The Machining Procedure. The Purpose Is To Let The Operator Know The Content Of The Procedure, The Clamping Positioning Methods, The Tools Selected For Each Machining Procedure, The Issues That Should Be Paid Attention To.

2. The Contents Of The Machining Program Sheet Include: Drawing Programming File Names, Workpiece Name, Clamping Sketch, Program Name, Tool Used For Each Program, Maximum Cutting Depth, Machining Properties (Such As Rough Machining Fine Machining), Theoretical Machining Time, Etc.

9. Preparation Before CNC Programming

After Determining The Processing Technology, Before Programming, You Need To Understand:

1. Workpiece Clamping Method;

2. The Size Of The Workpiece Blank - To Determine The Scope Of Processing Whether Multiple Clamping Is Required;

3. The Material Of The Workpiece - In Order To Choose The Tool To Be Used For Processing;

4. What Tools Are In Stock? This Can Help You Avoid To Modify The Program When You Don’t Have The Tool. If You Must Use The Tool, You Can Prepare It In Advance.

10. Principles Of Safety Height Setting In Programming

The Principle Of Setting The Safety Height Is Generally Higher Than The Highest Surface Of The Island. Set The Programming Zero Point At The Highest Surface, Which Can Also Minimize The Risk Of Collision With The Tool.

11. Post-Processing After Tool Path Editing

Different Machine Tools Can Recognize Different Address Codes NC Program Formats. It Is Necessary To The Correct Post-Processing Format For The Machine Tool Used To Ensure That The Compiled Program Can Run.

12. DNC Communication

There Are Two Ways Of Program Transmission: CNC DNC. CNC Means That The Program Is Transmitted To The Memory Of The Machine Tool Through Media (Such As Floppy Disks, Tape Readers, Communication Lines, Etc.) Stored There. During Processing, The Program Is Called Out The Memory For Processing. Since The Capacity Of The Memory Is Limited By Size, When The Program Is Large, DNC Can Be Used For Processing. During DNC Processing, The Machine Tool Directly Reads The Program The Control Computer (That Is, It Is Processed While Being Sent), So It Is Limited By The Size Of The Memory Capacity.

13. Elements Of Cutting Parameters

It Is Divided Into Three Major Factors: Cutting Depth, Spindle Speed Feed Speed.

14. Principles For Selecting Cutting Parameters

The General Principle Is: Less Cutting, Faster Feed (I.E. Smaller Cutting Depth, Faster Feed Speed).