What factors in machining cause deformation of workpieces?

The Problem Of Workpiece Deformation In Mechanical Processing Is A Relatively Difficult Problem To Solve. First, The Cause Of The Deformation Must Be Analyzed Before The Corresponding Measures Can Be Taken.

01. The Material Structure Of The Workpiece Affect The Deformation Of The Workpiece

   The Amount Of Deformation Is Proportional To The Complexity Of The Shape, The Aspect Ratio The Wall Thickness, Is Proportional To The Rigidity Stability Of The Material. Therefore, When Designing Parts, It Is Necessary To Minimize The Influence Of These Factors On The Deformation Of The Workpiece.

   Especially In The Structure Of Large Parts, The Structure Should Be Reasonable. Before CNC Processing, The Hardness, Looseness Other Defects Of The Blank Should Be Strictly Controlled To Ensure The Quality Of The Blank Reduce The Deformation Of The Workpiece Caused By It.

02. Deformation Caused By Workpiece Clamping

   When Clamping A Workpiece, First The Correct Clamping Point, Then The Appropriate Clamping Force According To The Position Of The Clamping Point. Therefore, The Clamping Point The Support Point Should Be Consistent As Much As Possible, So That The Clamping Force Acts On The Support. The Clamping Point Should Be As Close To The Processing Surface As Possible, The Position The Force Is Easy To Cause Clamping Deformation Should Be Selected.

   When There Are Clamping Forces Acting On The Workpiece In Several Directions, The Order Of The Clamping Forces Must Be Considered. The Clamping Force That Makes The Workpiece Contact With The Support Should Act First Should Be Too Large. The Main Clamping Force That Balances The Cutting Force Should Act Last.

   Secondly, The Contact Area Between The Workpiece The Fixture Should Be Increased The Axial Clamping Force Should Be Used. Increasing The Rigidity Of The Parts Is An Effective Way To Solve The Problem Of Clamping Deformation, But Due To The Shape Structural Characteristics Of Thin-Walled Parts, They Have Low Rigidity. In This Way, Deformation Will Occur Under The Action Of The Clamping Force.

   Increasing The Contact Area Between The Workpiece The Fixture Can Effectively Reduce The Deformation Of The Workpiece During Clamping. For Example, When Milling Thin-Walled Parts, A Large Number Of Elastic Pressure Plates Are Used To Increase The Force Area Of The Contact Parts; When Turning The Inner Diameter Outer Circle Of Thin-Walled Sleeves, Whether Using A Simple Open Transition Ring An Elastic Mandrel, Full-Arc Clamping Claws, Etc., The Contact Area When The Workpiece Is Clamped Is Increased. This Method Is Conducive To Bearing The Clamping Force, Thereby Avoiding The Deformation Of Precision Parts . The Use Of Axial Clamping Force Is Also Widely Used In Production. The Design Manufacture Of Special Fixtures Can Make The Clamping Force Act On The End Face, Which Can Solve The Bending Deformation Of The Workpiece Caused By The Thin Wall Poor Rigidity Of The Workpiece.

03. Deformation Caused By Workpiece Processing

   During The Cutting Process, The Workpiece Undergoes Elastic Deformation In The Direction Of The Force Due To The Cutting Force, Which Is What We Often Call The Tool Letting Phenomenon. To Deal With This Type Of Deformation, Appropriate Measures Should Be Taken On The Tool. During Fine Machining, The Tool Should Be Sharp, Which Can Reduce The Resistance Caused By The Friction Between The Tool The Workpiece On The One Hand, Improve The Heat Dissipation Capacity Of The Tool When Cutting The Workpiece On The Other Hand, Thereby Reducing The Residual Internal Stress On The Workpiece.

   For Example, When Milling Large Planes Of Thin-Walled Parts, The Single-Edge Milling Method Is Used, The Tool Parameters A Larger Main Deflection Angle A Larger Rake Angle In Order To Reduce Cutting Resistance. Because This Tool Cuts Lightly Reduces The Deformation Of Thin-Walled Parts, It Is Widely Used In Production.

   In The Turning Of Thin-Walled Parts, A Reasonable Tool Angle Is Crucial To The Size Of The Cutting Force During Turning, The Thermal Deformation Generated During Turning, The Microscopic Quality Of The Workpiece Surface. The Size Of The Tool Rake Angle Determines The Cutting Deformation The Sharpness Of The Tool Rake Angle. A Large Rake Angle Reduces Cutting Deformation Friction, But A Too Large Rake Angle Will Reduce The Wedge Angle Of The Tool, Weaken The Tool Strength, Poor Tool Heat Dissipation, Accelerate Wear. Therefore, When Turning Thin-Walled Parts Made Of Steel Materials, A High-Speed Tool Is Used With A Rake Angle Of 6° To 30°, A Carbide Tool Is Used With A Rake Angle Of 5° To 20°.

   The Larger The Back Angle Of The Tool, The Smaller The Friction The Correspondingly Reduced Cutting Force. However, Too Large A Back Angle Will Also Weaken The Tool Strength. When Turning Thin-Walled Parts, Use A High-Speed Steel Turning Tool With A Back Angle Of 6° To 12°, Use A Carbide Tool With A Back Angle Of 4° To 12°. Use A Larger Back Angle For Fine Turning A Smaller Back Angle For Rough Turning. When Turning The Inner Outer Circles Of Thin-Walled Parts, Use A Large Main Deflection Angle. Correctly Selecting The Tool Is A Necessary Condition For Dealing With Workpiece Deformation.

   The Heat Generated By The Friction Between The Tool The Workpiece During Processing Will Also Cause The Workpiece To Deform, So High-Speed Cutting Is Often Chosen. In High-Speed Cutting, Since The Chips Are Removed In A Relatively Short Time, Most Of The Cutting Heat Is Taken Away By The Chips, Reducing The Thermal Deformation Of The Workpiece; Secondly, In High-Speed Processing, Due To The Reduction Of The Softened Part Of The Cutting Layer Material, The Deformation Of The Parts Processing Can Also Be Reduced , Which Is Conducive To Ensuring The Size Shape Accuracy Of The Parts. In Addition, Cutting Fluid Is Mainly Used To Reduce Friction Reduce Cutting Temperature During The Cutting Process. Reasonable Use Of Cutting Fluid Plays An Important Role In Improving The Durability Of The Tool The Surface Quality Processing Accuracy Of The Processing. Therefore, In Order To Prevent The Deformation Of Parts During Processing, Sufficient Cutting Fluid Must Be Used Reasonably.

   The Use Of Reasonable Cutting Parameters In Processing Is The Key Factor To Ensure The Accuracy Of Parts. When Processing Thin-Walled Parts With High Precision Requirements, Symmetrical Processing Is Generally Adopted To Balance The Stress Generated On The Two Opposite Sides Achieve A Stable State. The Workpiece Is Flat After Processing. However, When A Certain Process Uses A Large Cutting Amount, The Workpiece Will Be Deformed Due To The Loss Of Balance Between Tensile Stress Compressive Stress.

   There Are Many Factors That Cause Deformation Of Thin-Walled Parts During Turning, Including The Clamping Force When Clamping The Workpiece, The Cutting Force When Cutting The Workpiece, The Elastic Deformation Plastic Deformation Caused By The Workpiece Hindering The Tool Cutting, Which Increases The Temperature Of The Cutting Area Causes Thermal Deformation. Therefore, We Should Use A Larger Back-Cutting Amount Feed Rate During Rough Machining; During Fine Machining, The Cutting Amount Is Generally 0.2-0.5mm, The Feed Rate Is Generally 0.1-0.2mm/R, Even Smaller, The Cutting Speed Is 6-120m/Min. When Fine Machining, Use The Highest Possible Cutting Speed, But Too High. Reasonable Selection Of Cutting Parameters Can Achieve The Purpose Of Reducing Part Deformation.

04. Stress Deformation After Processing

   After Processing, The Parts Themselves Have Internal Stresses, The Distribution Of These Internal Stresses Is In A Relatively Balanced State. The Shape Of The Parts Is Relatively Stable, But After Removing Some Materials Heat Treatment, The Internal Stress Changes. At This Time, The Workpiece Needs To Re-Balance The Force, So The Shape Changes. This Type Of Deformation Can Be Solved By Heat Treatment. The Workpieces That Need To Be Straightened Are Stacked To A Certain Height, Pressed Into A Straight State With A Certain Tooling, Then The Tooling The Workpiece Are Put Into The Heating Furnace Together. Different Heating Temperatures Heating Times Are Selected According To The Different Materials Of The Parts. After Heat Straightening, The Internal Structure Of The Workpiece Is Stable. At This Time, The Workpiece Only Has A Higher Straightness, But Also The Work Hardening Phenomenon Is Eliminated, Which Is More Convenient For Further Finishing Of The Parts. Castings Should Be Aged To Eliminate The Internal Residual Stress As Much As Possible, The Method Of Reprocessing After Deformation Should Be Adopted, That Is, Rough Processing-Aging-Reprocessing.

   For Large Parts, Contour Processing Should Be Used, That Is, The Deformation Of The Workpiece After Assembly Is Predicted, The Deformation Is Reserved In The Opposite Direction During Processing, Which Can Effectively Prevent The Deformation Of The Parts After Assembly.

   In Summary, For Easily Deformed Workpieces, Corresponding Countermeasures Must Be Adopted In Both The Blank The Processing Technology. They Need To Be Analyzed According To Different Situations, A Suitable Process Route Will Be Found. Of Course, The Above Methods Only Further Reduce The Deformation Of The Workpiece. If You Want To Get A More Precise Workpiece, You Still Need To Continue To Learn, Explore Research. Huiwen Zhizao Is A Machining Factory With More Than Ten Years Of CNC Machining Experience . It Has A Full Range Of Equipment, CNC Lathe/Milling/Grinding/Drilling/Machining. Partners With Parts Processing Needs Are Welcome To Call Us For Quotes.