What Precision Standards Can Be Achieved In Drilling Holes In A Machining Shop?

As The Most Common Tool For Hole Processing, Drill Bits Are Widely Used In Mechanical Manufacturing, Especially For The Processing Of Holes In Parts Such As Cooling Devices, Tube Sheets Of Power Generation Equipment Steam Generators. The Application Is Particularly Wide Important. Let Huiwen Briefly Analyze What Kind Of Precision Standards Can CNC Machine Processing Factories Achieve In Drilling Holes?

1. Drilling Accuracy

Drilling Is A Basic Method Of Hole Processing. Drilling Is Often Performed On Drilling Machines Lathes, Can Also Be Performed On Boring Machines Milling Machines. The Processing Accuracy Of Drilling Is Low, Generally Only IT10, The Surface Roughness Is Generally 12.5-6.3μm. After Drilling, Expansion Reaming Are Often Used For Semi-Finishing Finishing.

The Accuracy Of The Hole Is Mainly Composed Of Factors Such As Hole Diameter, Position Accuracy, Coaxiality, Roundness, Surface Roughness Hole Burr.

Factors Affecting The Accuracy Of The Processed Hole During Drilling:

① The Clamping Accuracy Cutting Conditions Of The Drill, Such As Tool Holder, Cutting Speed, Feed Rate, Cutting Fluid, Etc.;

② Drill Bit Size Shape, Such As Drill Bit Length, Blade Shape, Drill Core Shape, Etc.;

③ Workpiece Shape, Such As Hole Side Shape, Hole Shape, Thickness, Clamping Status, Etc.

1. Hole Expansion

Hole Expansion Is Caused By The Swing Of The Drill Bit During Processing. The Swing Of The Tool Holder Has A Great Influence On The Hole Diameter The Positioning Accuracy Of The Hole, So When The Tool Holder Is Severely Worn, A New Tool Holder Should Be Replaced In Time. When Drilling Small Holes, The Measurement Adjustment Of The Swing Are Difficult, So It Is Best To Use A Coarse-Shank Small-Diameter Drill With Good Coaxiality Between The Blade The Shank. When Using A Re-Ground Drill Bit For Processing, The Reason For The Decrease In Hole Accuracy Is Mostly Due To The Asymmetric Shape Of The Back. Controlling The Height Difference Of The Blade Can Effectively Suppress The Amount Of Hole Cutting Expansion. Huiwen Zhizao Is A Machining Factory With More Than Ten Years Of CNC Machining Experience . It Has A Full Range Of Equipment, CNC Turning/Milling/Grinding/Drilling/Machining. Partners With Parts Processing Needs Are Welcome To Call Us For Quotes.

2. Hole Roundness

Due To The Vibration Of The Drill Bit, The Drilled Hole Is Easy To Be Polygonal, Rifling-Like Lines Appear On The Hole Wall. Common Polygonal Holes Are Mostly Triangular Pentagonal. The Reason For The Triangular Hole Is That The Drill Bit Has Two Rotation Centers When Drilling, They Vibrate At A Frequency Of 600 Exchange Intervals. The Main Reason For The Vibration Is The Unbalanced Cutting Resistance. When The Drill Bit Rotates One Turn, The Roundness Of The Processed Hole Is Good, Causing The Resistance To Be Unbalanced During The Second Turn Of Cutting, Repeating The Last Vibration Again, But The Vibration Phase Has A Certain Offset, Causing Rifling Lines To Appear On The Hole Wall. When The Drilling Depth Reaches A Certain Level, The Friction Between The Edge Of The Drill Bit Blade The Hole Wall Increases, The Vibration Attenuates, The Rifling Disappears, The Roundness Improves. This Hole Type Has A Funnel-Shaped Orifice The Longitudinal Section. For The Same Reason, Pentagonal Heptagonal Holes May Also Appear During Cutting. In Order To Eliminate This Phenomenon, In Addition To Controlling Factors Such As Chuck Vibration, Cutting Edge Height Difference, Asymmetry Of The Back Face Blade Shape, Measures Should Also Be Taken To Increase Drill Bit Rigidity, Increase Feed Per Revolution, Reduce Back Angle, Grind The Chisel Edge.

3. Drilling On Inclined Curved Surfaces

When The Cutting Surface Penetration Surface Of The Drill Bit Is An Inclined Surface, A Curved Surface A Step, The Positioning Accuracy Is Poor. Since The Drill Bit Cuts Radially On One Side At This Time, The Tool Life Is Reduced.

To Improve Positioning Accuracy, The Following Measures Can Be Taken:

① Drill The Center Hole First;

② Use End Mill To Mill The Hole Seat;

③ Choose A Drill Bit With Good Penetration Rigidity;

④Reduce The Feed Speed.

4. Burr Treatment

    During Drilling, Burrs Will Appear At The Entrance Exit Of The Hole, Especially When Processing Tough Materials Thin Plates. The Reason Is That When The Drill Is About To Penetrate, The Material Being Processed Undergoes Plastic Deformation. At This Time, The Triangular Part That Should Be Cut By The Edge Of The Drill Near The Outer Edge Is Deformed Bent Outwards Under The Action Of The Axial Cutting Force, Further Curled Under The Action Of The Chamfer Of The Outer Edge Of The Drill The Edge Of The Land, Forming A Curled Edge Burr.

2. Characteristics Of Drilling

    A Drill Bit Usually Has Two Main Cutting Edges. During Machining, The Drill Bit Cuts While Rotating. The Rake Angle Of The Drill Bit Increases The Center Axis To The Outer Edge. The Closer To The Outer Circle, The Higher The Cutting Speed Of The Drill Bit. The Cutting Speed Decreases Toward The Center. The Cutting Speed Of The Drill Bit's Rotating Center Is Zero. The Chisel Edge Of The Drill Bit Is Located Near The Center Axis Of Rotation. The Secondary Rake Angle Of The Chisel Edge Is Large, There Is No Chip Space, The Cutting Speed Is Low, Which Will Generate A Large Axial Resistance. If The Chisel Edge Is Ground To Type A Type C In DIN1414, The Cutting Edge Near The Center Axis Has A Positive Rake Angle, The Cutting Resistance Can Be Reduced The Cutting Performance Can Be Significantly Improved.

    Depending On The Shape, Material, Structure, Function, Etc. Of The Workpiece, Drill Bits Can Be Divided Into Many Categories, Such As High-Speed Steel Drill Bits (Twist Drill Bits, Group Drill Bits, Flat Drill Bits), Solid Carbide Drill Bits, Indexable Shallow Hole Drill Bits, Deep Hole Drill Bits, Sleeve Drill Bits Interchangeable Head Drill Bits.

3. Chip Breaking Chip Removal

     The Cutting Of The Drill Is Carried Out In A Narrow Hole, The Chips Must Be Discharged Through The Drill Groove, So The Chip Shape Has A Great Influence On The Cutting Performance Of The Drill. Common Chip Shapes Include Flake Chips, Tubular Chips, Needle Chips, Conical Spiral Chips, Ribbon Chips, Fan-Shaped Chips, Powder Chips, Etc.

The Key To Drilling: Chip Control

When The Chip Shape Is Appropriate, The Following Problems Will Occur:

① Fine Chips Block The Cutting Edge, Affecting Drilling Accuracy, Reducing Drill Bit Life, Even Breaking The Drill Bit (Such As Powdery Chips, Fan-Shaped Chips, Etc.);

② Long Chips Entangle The Drill Bit, Hindering The Operation, Causing Damage To The Drill Bit Blocking The Cutting Fluid Entering The Hole (Such As Spiral Chips, Ribbon Chips, Etc.).

How To Solve The Problem Of Improper Chip Shape:

① The Chip Breaking Chip Removal Effects Can Be Improved By Increasing The Feed Rate, Intermittent Feed, Grinding The Chisel Edge, Installing A Chip Breaker, Etc., Respectively In Combination, To Eliminate The Problems Caused By Chips.

② You Can Use A Professional Chip-Breaking Drill To Drill Holes. For Example, Adding A Designed Chip-Breaking Edge To The Groove Of The Drill Will Break The Chips Into Debris That Is Easier To Remove. The Debris Is Discharged Smoothly Along The Groove Will Be Blocked In The Groove. Therefore, The New Chip-Breaking Drill Has A Much Smoother Cutting Effect Than The Traditional Drill.

     At The Same Time, The Short Broken Iron Chips Make It Easier For The Coolant To Flow To The Drill Tip, Further Improving The Heat Dissipation Cutting Performance During Processing. Because The Newly Added Chip Breaker Penetrates The Entire Groove Of The Drill Bit, It Can Still Maintain Its Shape Function After Multiple Grinding. In Addition To The Above Functional Improvements, It Is Worth Mentioning That The Design Strengthens The Rigidity Of The Drill Body Significantly Increases The Number Of Holes Drilled Before A Single Grinding. Huiwen Zhizao Is A Machining Factory With More Than Ten Years Of CNC Machining Experience. It Has A Full Range Of Equipment, CNC Turning/Milling/Grinding/Drilling/Machining. Partners With Parts Processing Needs Are Welcome To Call Us For Quotes.

4. Drilling Processing Conditions

    The General Drill Product Catalog Has A "Basic Cutting Quantity Reference Table" Arranged By Processing Material. Users Can Refer To The Cutting Quantities Provided To The Cutting Conditions For Drilling. Whether The Cutting Conditions Are Appropriate Should Be Judged Comprehensively Based On Test Cutting Processing Accuracy, Processing Efficiency, Drill Life Other Factors.

1. Drill Bit Life Processing Efficiency

    On The Premise Of Meeting The Technical Requirements Of The Workpiece Being Processed, Whether The Drill Is Used Properly Should Be Comprehensively Measured Based On The Drill Service Life Processing Efficiency. The Evaluation Index Of The Drill Service Life Can Be The Cutting Distance; The Evaluation Index Of Processing Efficiency Can Be The Feed Speed.

    For High-Speed Steel Drills, The Service Life Of The Drill Is Greatly Affected By The Rotation Speed Less By The Feed Rate Per Revolution, So The Processing Efficiency Can Be Improved By Increasing The Feed Rate Per Revolution, While Ensuring A Longer Drill Life. However, It Should Be Noted That If The Feed Rate Per Revolution Is Too Large, The Chips Will Become Thicker, Making It Difficult To Break The Chips, So It Is Necessary To Determine The Feed Rate Per Revolution Range That Can Successfully Break The Chips Through Trial Cutting.

    For Carbide Drills, The Negative Rake Angle Of The Cutting Edge Is Ground With A Larger Chamfer, The Optional Range Of Feed Per Revolution Is Smaller Than That Of High-Speed Steel Drills. If The Feed Per Revolution Exceeds This Range During Processing, The Service Life Of The Drill Will Be Reduced. Since Carbide Drills Have Higher Heat Resistance Than High-Speed Steel Drills, The Rotation Speed Has Little Effect On The Life Of The Drill. Therefore, The Method Of Increasing The Rotation Speed Can Be Used To Improve The Processing Efficiency Of Carbide Drills Ensure The Life Of The Drill.

2. Reasonable Use Of Cutting Fluid

    The Drill Bit Cuts In A Hole With A Narrow Space, So The Type Of Cutting Fluid The Injection Method Have A Great Influence On The Drill Bit Life Hole Processing Accuracy.

    Cutting Fluids Can Be Divided Into Two Categories: Water-Soluble Non-Water-Soluble. Non-Water-Soluble Cutting Fluids Have Good Lubricity, Wettability Anti-Adhesion Properties, Also Have Anti-Rust Properties. Water-Soluble Cutting Fluids Have Good Cooling Properties, Are Non-Smoky Non-Flammable. In Recent Years, Water-Soluble Cutting Fluids Have Been Used In Large Quantities For Environmental Protection.

    However, If The Dilution Ratio Of The Water-Soluble Cutting Fluid Is Inappropriate The Cutting Fluid Deteriorates, The Service Life Of The Tool Will Be Greatly Shortened, So Care Must Be Taken During Use.

    Whether It Is Water-Soluble Non-Water-Soluble Cutting Fluid, The Cutting Fluid Must Fully Reach The Cutting Point During Use. At The Same Time, The Flow Rate, Pressure, Number Of Nozzles, Cooling Method (Internal Cooling External Cooling) Of The Cutting Fluid Must Be Strictly Controlled.

5. Refurbishing The Drill Bit

1. Drill Bit Regrinding Judgment

The Criteria For Determining Whether A Drill Needs To Be Resharpened Are:

① Wear Of Cutting Edge, Chisel Edge Land Edge;

②Dimensional Accuracy Surface Roughness Of The Processed Hole;

③The Color Shape Of The Chips;

④ Cutting Resistance (Indirect Values Such As Spindle Current, Noise, Vibration, Etc.);

⑤Processing Quantity, Etc.

    In Actual Use, Accurate Convenient Judgment Criteria Should Be Determined The Above Indicators According To Specific Conditions. When The Wear Amount Is Used As The Judgment Criterion, The Best Re-Grinding Period With The Best Economic Efficiency Should Be Found.

    Since The Main Grinding Areas Are The Back Of The Head The Transverse Edge, If The Drill Wears Too Much, The Grinding Time Is Long, The Grinding Amount Is Large, The Number Of Times The Drill Can Be Re-Grinded Will Be Reduced (The Total Service Life Of The Tool = The Tool Life After Re-Grinding × The Number Of Times The Drill Can Be Re-Grinded), Which Will Shorten The Total Service Life Of The Drill. When The Dimensional Accuracy Of The Processed Hole Is Used As The Judgment Standard, A Column Gauge A Limit Gauge Should Be Used To Check The Cutting Expansion, Non-Straightness, Etc. Of The Hole. Once The Control Value Is Exceeded, The Drill Should Be Re-Sharpened Immediately. When The Cutting Resistance Is Used As The Judgment Standard, The Machine Can Be Automatically Shut Down Immediately When The Set Limit Value (Such As The Spindle Current) Is Exceeded. When The Processing Quantity Limit Management Is Adopted, The Above Judgment Contents Should Be Combined To Set The Judgment Standard.

2. Drill Bit Sharpening Method

    When Resharpening A Drill, It Is Best To Use A Special Drill Sharpening Machine A Universal Tool Grinder, Which Is Very Important To Ensure The Service Life Processing Accuracy Of The Drill. If The Original Drill Shape Is In Good Condition, It Can Be Re-Sharpened According To The Original Drill Shape; If The Original Drill Shape Has Defects, The Rear Shape Can Be Appropriately Improved According To The Purpose Of Use The Cross-Edge Can Be Re-Grinded.

The Following Points Should Be Noted When Sharpening:

①Prevent Overheating Avoid Reducing The Hardness Of The Drill Bit;

② All Damage On The Drill Bit (Especially Damage On The Edge Of The Cutting Edge) Should Be Removed;

③ The Drill Type Should Be Symmetrical;

④ Be Careful To Damage The Cutting Edge During Sharpening, Remove The Burrs After Sharpening;

⑤ For Carbide Drills, The Grinding Shape Has A Great Influence On The Performance Of The Drill. The Drill Shape When Leaving The Factory Is The Best Drill Shape Obtained Through Scientific Design Repeated Tests. Therefore, The Original Blade Shape Should Generally Be Maintained When Re-Sharpening.

Shenzhen Huiwen Intelligent Manufacturing Technology Co., Ltd. Was Established In 2010. The Address Is Located At 1F, Building F3, Tianyou Maker Industrial Park, Lixinhu, Fuyong, Bao'an District, Shenzhen. It Has Long Been Committed To The Processing Of High-Precision, High-Difficulty, Easy-To-Deform Metal Plastic Parts , Small Medium-Volume Production Manufacturing Of Light Alloy Composite Materials (Such As Aluminum Alloy, Carbon Fiber, Etc.),  Robot Parts Procurement Customization Services. Huiwen Intelligent Manufacturing Can Currently Provide High-Quality, Low-Cost, On-Time Delivery Products In The Following Aspects.