Process Measures to Reduce Machining Deformation

Reducing Residual Stress in Blanks

Natural or artificial aging, as well as vibration treatment, can partially eliminate residual stresses in blanks. Pre-machining is also an effective method. For bulky blanks with excessive stock allowance, post-machining deformation tends to be significant. By pre-machining to remove excess material and balance stock allowance, subsequent machining deformation can be reduced. Additionally, allowing the pre-machined blank to rest helps release residual stresses.

Improving Tool Cutting Performance

Tool material and geometric parameters significantly influence cutting forces and heat generation. Proper tool selection is crucial for minimizing part deformation.

Optimizing Tool Geometry

Rake Angle:

A larger rake angle (while maintaining edge strength) enhances cutting sharpness, reduces chip deformation, improves chip evacuation, and lowers cutting forces and temperatures. Negative rake angles should be avoided.

Clearance Angle:

The clearance angle directly affects flank wear and surface finish. For rough milling with heavy loads and high heat, a smaller clearance angle improves heat dissipation. For finish milling, a larger clearance angle reduces friction and elastic deformation.

Helix Angle:

A higher helix angle ensures smoother milling and reduces cutting resistance.

Lead Angle:

A smaller lead angle improves heat dissipation and lowers average cutting zone temperatures.

Enhancing Tool Structure

Reducing Teeth Count & Increasing Chip Space:

Aluminum’s high plasticity demands larger chip pockets. Tools with fewer teeth and wider gullets are preferred.

Precision Edge Honing:

The cutting edge roughness should be below Ra = 0.4 μm. Lightly honing new tools with a fine stone removes burrs and micro-serrations, reducing heat and deformation.

Strict Wear Control:

Tool wear increases surface roughness, cutting temperature, and part deformation. Wear limits should not exceed 0.2 mm to prevent built-up edge. Workpiece temperature should stay below 100°C to avoid distortion.

Optimizing Workpiece Fixturing

For thin-walled aluminum parts with low rigidity:

Axial Clamping for Bushings

Radial clamping (e.g., 3-jaw chucks) causes post-machining deformation. Instead, use a threaded mandrel inserted into the part’s bore, secured axially with a endplate and nut to maintain precision during OD machining.

Vacuum Chucks for Thin Plates

Uniform clamping force distribution paired with light cuts minimizes distortion.

Filling Method

Fill hollow parts with a low-melting filler (e.g., urea-potassium nitrate melt) to enhance rigidity during machining. Dissolve the filler post-process in water/alcohol.

Strategic Process Sequencing

High-speed machining with large stock or interrupted cuts may induce vibration. A typical CNC process flow:

Roughing → Semi-finishing → Corner Cleaning → Finishing

For high-precision parts, repeat semi-finishing before final passes. Post-roughing natural cooling relieves stresses. Leave 1–2 mm stock after roughing; maintain 0.2–0.5 mm uniform allowance in finishing to ensure stability, reduce deformation, and achieve high surface quality.

Operational Techniques to Minimize Machining Deformation

In addition to the aforementioned causes, operational methods play a crucial role in controlling deformation during aluminum part machining.

Symmetrical Machining for Large Stock Parts

For better heat dissipation, use alternating symmetrical machining. Example: A 90mm plate machined to 60mm achieves 0.3mm flatness when processed in alternating passes versus 5mm with consecutive machining.

Layered Machining for Multi-cavity Parts

Machine all cavities layer-by-layer simultaneously to ensure uniform stress distribution, preventing deformation from uneven forces.

Optimized Cutting Parameters

Adjust depth of cut (ap) with corresponding feed rate and spindle speed increases in CNC high-speed milling to balance productivity and reduced cutting forces.

Strategic Tool Path Selection

Use conventional milling for roughing (maximum removal rate) and climb milling for finishing (better surface quality with progressive chip thickness reduction).

Thin-wall Fixturing Technique

Before final passes, briefly release and reapply minimal clamping force to allow natural recovery, applying force along the part’s most rigid direction.

Cavity Machining Method

Avoid direct plunging; pre-drill or use helical entry paths to prevent chip packing and tool breakage.

Wniosek

Aluminum part deformation stems from material properties, geometry, and processing conditions, primarily involving?blank residual stresses,cutting forces/heat,and clamping stresses.The integrated application of these process optimizations and operational techniques significantly reduces deformation, enhances precision and surface quality, providing reliable technical support for production.

Basic Definitions of Positive and Negative Rake Angle Tools

Positive Rake Angle Tool

A positive rake angle tool refers to a turning tool where the front face is inclined toward the interior of the workpiece relative to the cutting point, resulting in a positive rake angle (typically +5° to +15°). Its structural characteristic is a relatively sharp cutting edge, with a smaller contact area between the front face and the chip.

Negative Rake Angle Tool

A negative rake angle tool, on the other hand, has a front face inclined outward from the workpiece relative to the cutting point, resulting in a negative rake angle (typically -5° to -10°). Its structural feature is a blunter cutting edge, with a thicker and more robust tooltip.

Advantages and Disadvantages of Positive and Negative Rake Tools

Positive Rake Angle Tool

Advantages:

Lower Cutting Forces: A positive rake angle allows smoother chip flow and reduces deformation, decreasing main cutting forces by 15–25%.

Better Chip Evacuation: Shorter chip-tool contact length reduces built-up edge formation.

Suitable for Finishing: Minimizes vibration, enabling better surface finish (Ra < 1.6 μm).

Disadvantages:

Lower Tooltip Strength: The positive geometry reduces material support, making the tool prone to chipping in interrupted cuts or hard materials.

Poor Heat Dissipation: Smaller chip-tool contact area limits heat transfer, accelerating crater wear at high speeds.

Shorter Tool Life: Typically 60–70% of negative rake tools under the same conditions.

Negative Rake Angle Tool

Advantages:

High Tooltip Strength: The negative angle creates a “support wedge,” improving impact resistance by >50%.

Superior Heat Dissipation: Larger chip-tool contact area enhances heat conduction, reducing cutting temperatures by 15–30°C.

Multi-Sided Usability: Often designed with double-negative angles, allowing flipping for extended use.

Limitations:

Higher Cutting Forces: Negative rake increases chip deformation, raising main cutting forces by 20–30%.

Greater Power Demand: Requires 15–20% more motor power from the machine tool.

Vibration Risk: Prone to chatter in long overhang machining due to increased cutting forces.

Experimental Comparison

The following systematic experiment compares the performance of carbide positive and negative rake tools under different machining conditions, providing practical insights for tool selection.

Experimental Design

1.Materials & Equipment:

Positive rake tool (+8° rake angle)

Negative rake tool (-6° rake angle)

Both use YG8 w?glik substrate with TiAlN coating and 0.4 mm nose radius.

2.Workpiece:45# steel (Φ50×200 mm), quenched and tempered to HRC 28–32.

3.Machine:CA6140 lathe with 3-jaw chuck and tailstock center.

4.Measurement Instruments:

Surface roughness tester (Mitutoyo SJ-210)

Electron microscope (OLYMPUS DSX510)

Cutting force dynamometer (Kistler 9257B)

Infrared thermometer (Fluke Ti400)

5.Parameters

Fixed: Depth of cut (ap = 1 mm), feed rate (f = 0.15 mm/rev).

Variable: Cutting speed (v = 60–180 m/min).

Three repetitions per condition for reliability.

Results & Analysis

Tool Wear & Life Comparison

Using flank wear VB = 0.3 mm as the failure criterion:

Negative rake angle tools demonstrate significantly longer service life, exceeding positive rake tools by an average of 50-70%. Analysis of wear patterns reveals that positive rake tools primarily fail through crater wear on the rake face and tooltip chipping, whereas negative rake tools exhibit more uniform flank wear, demonstrating superior fracture resistance.

Cutting Force Comparison

The data shows that under all tested cutting speeds, negative rake tools generate significantly higher principal cutting forces than positive rake tools, with an average increase of approximately 17%. This is attributed to the negative rake design’s larger contact area between the tool’s rake face and chips, as well as intensified cutting deformation. Notably, while cutting forces for both tool types decrease with increasing cutting speed, the difference ratio remains essentially stable.

Cutting Temperature Comparison

Results indicate that negative rake tools maintain consistently lower cutting temperatures than positive rake tools, typically by 15-25°C. This thermal advantage primarily stems from the negative rake design’s enhanced tooltip strength and improved heat dissipation capacity. The temperature difference becomes particularly pronounced during high-speed cutting (v>120m/min), reaching approximately 30°C.

Surface Quality Evaluation

Surface roughness serves as a critical indicator of machining quality. At a feed rate of f=0.15mm/rev, measurements show:

Positive rake tool surface roughness (Ra): 1.6-2.0μm

Negative rake tool surface roughness (Ra): 1.2-1.5μm

Electron microscope observations reveal that surfaces machined with negative rake tools exhibit more uniform texture patterns with fewer burrs and vibration marks. This improvement results from the negative rake design’s enhanced system rigidity that reduces cutting vibrations. Furthermore, negative rake tools maintain more stable tooltip geometry during machining, avoiding the surface quality degradation caused by micro-chipping that often occurs with positive rake tools.

Conclusions

1.While carbide negative rake tools show slightly inferior performance in cutting force, they demonstrate clear advantages in cutting temperature control, surface quality, and tool life.

2.The performance advantages of negative rake tools become more pronounced at higher cutting speeds, making them particularly suitable for modern high-speed machining requirements.

3.Positive rake tools excel in reducing cutting forces and are better suited for machining systems with limited rigidity.

4.Optimal tool angle selection should comprehensively consider multiple factors including workpiece material, machine tool conditions, and specific machining stages.

Physical Nature of Coating Thickness and Functional Realization

The physical essence of coating technology lies in modifying interfacial properties of the substrate via surface engineering. For rotating tools like drills, coatings must simultaneously reduce friction, enhance surface hardness, and inhibit thermal conduction. When coating thickness ranges from nanometers to micrometers, significant size effects emerge in mechanical properties. Experimental data shows that TiN coatings reach peak microhardness (≈2300HV) at 2-3μm thickness; further increases reduce hardness due to accumulated residual stress. This stress heterogeneity creates preferential paths for microcrack propagation during drilling, especially under interrupted cutting conditions, where excessively thick coatings are prone to delamination.

Thermal barrier effects are vital, but thermal conductivity does not scale linearly with thickness. Finite element simulations reveal that beyond 5μm, AlCrN coatings show diminishing thermal resistance gains. Excessive thickness may impede heat dissipation, intensifying thermal stress concentration in high-speed machining.

Dynamic Evolution of Cutting Edge Geometry

Drill edge sharpness directly affects chip evacuation and force distribution. The “rounding effect” during deposition causes exponential growth in edge radius with thickness. For DLC coatings increasing from 1μm to 3μm, edge radius swells from 3.2μm to 8.7μm, raising cutting resistance by 23%. This geometric dulling is pronounced in ductile materials—aluminum alloy tests show a 15% rise in chip buildup probability per micrometer increase in edge radius. Paradoxically, moderate dulling suppresses edge chipping in brittle materials, highlighting the need for material-specific thickness optimization.

Coating thickness impacts flute hydrodynamics, often overlooked. 3D flow simulations show that when coating exceeds 12% of flute depth, secondary chip flow intensifies, causing blockages. In deep-hole drilling, this exacerbates radial vibration, increasing borehole deviation. A German toolmaker reduced straightness errors by 40% by decreasing TiAlSiN thickness from 4μm to 2.5μm.

Multiscale Correlation of Interface Failure Mechanisms

Coating-substrate bond strength does not monotonically change with thickness. Interface energy tests reveal a 30% strength drop when CrN exceeds ~4μm, due to lattice mismatch stress accumulation. This weakening is perilous under cyclic loading, with failures originating at nanoscale voids. Gradient transition layers enhance critical thickness—inserting a 50nm Ti interlayer between WC-Co and TiCN boosts critical thickness from 3.2μm to 5.1μm.

Cyclic loading reveals time-dependent failure. Accelerated life tests show 3μm AlTiN coatings reduce crack growth by 67% after 10? impacts, benefiting from crack closure effects. Beyond 2×10? cycles, thicker coatings exhibit larger spalling areas, indicating an optimal thickness for fatigue life. This non-monotonic relationship demands precise service life predictions.

Implicit Links to Machining Precision and Surface Integrity

Coating thickness has dual impacts on precision. In micro-hole drilling, a 2μm thickness deviation causes 0.8-1.2% diameter variation. A Japanese firm’s adaptive coating technology deposits 1.5μm at the tip and 2.2μm at margins, controlling diameter?floating?to 0.3%. Such differential designs surpass conventional uniform coatings.

Residual stress in workpieces couples with coating thickness. XRD analysis shows a drop from -450MPa to -280MPa when thickness increases from 1μm to 3μm, potentially reducing dimensional stability. However, thicker coatings reduce heat-affected zones by 35%, critical for aerospace aluminum.

Economic Considerations and Technological Trends

Coating cost scales with thickness squared, but lifespan gains have inflection points. An automotive plant found that increasing TiAlN from 2μm to 3μm raised costs by 18% while only improving life by 12%, resulting in negative ROI. However, nano-multilayered 2.5μm coatings outperformed 3μm by 25%, indicating that thickness alone is suboptimal.

Future coatings will feature intelligent thickness control. Digital twin-based optimization systems are operational, adjusting parameters via real-time force/temperature feedback. A German AI system predicts optimal thickness in 48 hours, enhancing performance by >30%. Dynamic adaptation may revolutionize traditional thickness determination.

Wniosek

Coating thickness orchestrates a precision symphony in drill performance, where each parameter adjustment triggers cascading effects. Modern engineers must transcend empirical selection, establishing multi-physics digital design paradigms. Future breakthroughs may lie in self-sensing smart coatings with dynamic thickness adjustment, potentially sparking a new revolution. In this era of precision and intelligence, mastering coating thickness will benchmark a nation’s advanced manufacturing prowess.

Wprowadzenie

Ordinary wood screws are widely used in the furniture manufacturing industry. Most wood screws are made of Q235A steel and are formed by cold extrusion, offering advantages such as low cost, high efficiency, and large-scale production. Although screws used in the human body are structurally similar to ordinary wood screws, they must possess certain strength and corrosion resistance. Medical screws made from 1Cr18Ni9Ti stainless steel are difficult to produce via cold extrusion on dedicated machines due to material properties, small-batch production, and the need for specialized tools.

Challenges in Machining Medical Screws

For small-batch production of medical screws, CNC machining can be used to compensate for the limitations of dedicated machines. Medical screws have small diameters and relatively large pitches, resulting in poor rigidity. When using forming tools on conventional lathes, the cutting resistance increases as the tool’s cutting depth increases. Due to the small diameter and long length of medical screws, even with supporting methods to counteract most of the cutting resistance, deformation often occurs, making machining difficult. CNC machining offers high efficiency and strong adaptability. Using macro programs for thread turning ensures that the contact area between the tool and the workpiece remains constant, preventing an increase in cutting resistance with deeper cuts. However, medical screws with poor rigidity are still prone to deformation and bending. This paper conducts an in-depth study on the machining of stainless steel medical screws, addressing the challenges of machining stainless steel through reasonable process settings on CNC lathes. By designing supporting fixtures and programming macros for layered turning, the issue of insufficient rigidity in thread processing is resolved.

Principles of CNC Machining for Medical Screws

The key to producing qualified parts lies in the rational planning of the toolpath based on the geometric characteristics of medical screws. CNC machining of threads uses coated carbide inserts. The appropriate spindle speed for turning medical screws must be calculated based on the insert’s allowable cutting speed (v) to ensure reasonable tool life. The formula is:

v=nD/1000

Where:

v is the cutting speed (m/min),

D is the workpiece diameter (mm),

n is the spindle speed (r/min).

In medical screw thread machining, the main cutting force accounts for over 90% of the machine’s total power consumption, while the feed resistance accounts for over 5%. If forming tools are used on CNC machines, the contact area between the tool and the workpiece increases with cutting depth, leading to higher cutting resistance. This can cause vibration, deformation, and bending of the workpiece, making machining impossible.

Therefore, traditional forming tools cannot meet the requirements for machining medical screws. To address this, the machining method is improved by using a 35° profiling turning tool. By programming macros to control the toolpath according to the thread profile, the tool completes the profile before performing layered cuts. This ensures that the contact area between the tool and the workpiece remains constant, and the cutting force remains stable and small, overcoming the drawback of increasing cutting resistance with traditional forming tools.

Implementation of CNC Machining for Medical Screws

Selection of Tool Materials

Medical screws are primarily used to connect artificial joints and bones, requiring strength and corrosion resistance. Therefore, 1Cr18Ni9Ti stainless steel, which is acid-resistant, alkali-resistant, and corrosion-resistant, is chosen. This stainless steel has high strength, significant plasticity, and severe hardening during machining, resulting in high cutting resistance and a tendency for deformation. Additionally, the tool is subjected to high cutting temperatures, leading to built-up edge formation.

Due to the tendency of medical screws to undergo work hardening, making machining difficult, tool inserts with low adhesion, high heat resistance, wear resistance, and thermal conductivity should be selected. Adequate cooling during machining is essential, and water-based cutting fluids with good heat dissipation properties are recommended.

Structure and Dimensions of Medical Screws

As shown in Figure 1, the medical screw specifications are M6-2.5mm × 55mm, with an outer diameter of 6mm, a pitch of 2.5mm, a root width of 0.4mm, a crest width of 0.05mm, a thread angle of 60°, a length of 55mm, and a maximum diameter of 11mm at the right end. Due to the poor rigidity of the part and the relatively large pitch compared to the diameter, challenges exist in enhancing workpiece clamping rigidity and programming CNC macros.

Machining Process

Medical screws are produced in small batches. If a conventional one-clamp-one-center method is used for thread turning, the poor rigidity of the workpiece makes it unable to withstand the cutting forces, leading to bending deformation in the middle. Therefore, the workpiece must be fully supported during thread turning to ensure stability and prevent deformation. A dedicated supporting fixture is designed to assist in supporting the screw.

To reduce cutting resistance and prevent deformation during thread turning, a 35° profiling turning tool with titanium carbide coating is selected. A macro program is written using the trajectory synthesis method for layered thread cutting, significantly reducing cutting resistance and maintaining stability.

The machining process for medical screws is shown in Figure 2. The specific steps are:

Two parts are machined together, with an extra 15mm in the middle for self-centering chuck clamping and 7mm at each end for center drilling.

Turn the 6mm and 11mm outer diameters using a one-clamp-one-center method.

Clamp the 6mm outer diameter and remove the process heads, eliminating the center holes and allowing complete taper turning at both ends.

Clamp the 11mm outer diameter, support the 6mm outer diameter with the fixture, and turn the threads using the macro program.

Cut the two connected screws and trim them to ensure a 60mm length.

Use a horizontal milling machine with a vertical rotary table to clamp the part and mill a 1.5mm wide slot with a saw blade cutter.

Working Principle of the Thread Turning Support Fixture

As shown in Figure 3, the thread turning support fixture supports the medical screw during machining. Two screws are machined together to facilitate small-batch production. The support sleeve is made of HT200 gray cast iron, which has a low friction coefficient. The protrusion on the support sleeve provides axial positioning, while two screws connect and secure the support sleeve to the fixture body. The left end of the fixture body positions the support sleeve, and the right end has a standard Morse taper No. 5. The fixture is mounted on the CNC lathe’s tailstock, and the tailstock is moved during thread turning to support the screw’s outer diameter, effectively counteracting the cutting resistance. CNC thread turning is shown in Figure 4.

Machining Precautions and Quality Inspection

During the machining of medical screws, the error in the 6mm outer diameter should be controlled within approximately 0.04mm. A larger error would reduce the fit between the 6mm semi-circular hole in the support fixture and the screw’s outer diameter, weakening the fixture’s support and causing vibration or deformation during turning. Additionally, the tool must remain sharp during thread turning, and tool changes should be avoided to prevent thread misalignment.

The 6mm outer diameter of the medical screw is measured with a micrometer, the thread pitch is measured with a caliper, and the surface roughness is checked with a comparator to ensure it meets the Ra 3.2μm requirement. After inspection, the parts fully meet the dimensional requirements and are suitable for use.

Wniosek

Through the analysis of CNC machining principles for medical screws, the design of supporting fixtures, and the programming of macros, the CNC machining of medical screws has been successfully implemented, addressing the shortcomings of cold extrusion for ordinary screws. This method achieves small-batch production of medical screws at a lower cost, providing a reference for machining similar screws made from special materials.

Because machine tools have systematic mechanical-related deviations that can be recorded by the system. However, due to environmental factors such as temperature or mechanical load, these deviations may still occur or increase during subsequent use.

Backlash Compensation

When transmitting force between the moving components of a machine tool and its driving components—such as ball screws—interruptions or delays can occur. This is because a completely gap-free mechanical structure would significantly increase machine tool wear and is also difficult to achieve from a technical standpoint. Mechanical gaps cause deviations between the motion path of the axis/spindle and the measurements from the indirect measurement system. This means that once the direction changes, the axis will move either too far or not far enough, depending on the size of the gap. The worktable and its associated encoder are also affected: if the encoder position leads the worktable, it reaches the commanded position prematurely, meaning the actual distance moved by the machine tool is shortened. During machine operation, by using the backlash tool compensation function on the corresponding axis, the previously recorded deviation is automatically activated when the direction changes, and this deviation is added to the actual position value.

Screw Pitch Error Compensation

The measurement principle of indirect measurement in CNC control systems is based on the assumption that the pitch of the ball screw remains constant over its effective travel range. Therefore, in theory, the actual position of the linear axis can be derived from the motion information of the drive motor.。

However, manufacturing errors in the ball screw can lead to deviations in the measurement system (also known as screw pitch errors). Measurement deviations (depending on the measurement system used) and installation errors of the measurement system on the machine tool (also referred to as measurement system errors) may further exacerbate this issue. To compensate for these two types of errors, an independent measurement system (such as laser measurement) can be used to measure the natural error curve of the CNC machine tool. The required tool compensation values are then saved in the CNC system for tool compensation.

Friction Compensation (Quadrant Error Compensation) and Dynamic Friction Compensation

Quadrant error compensation (also known as friction compensation) is suitable for all the aforementioned scenarios to significantly improve contour accuracy when machining circular profiles. The reason is as follows: During quadrant transitions, one axis moves at the maximum feed rate while the other axis remains stationary. As a result, the different friction behaviors of the two axes can lead to contour errors. Quadrant error tool compensation effectively reduces this error and ensures excellent machining results. The density of narz?dzie compensation pulses can be set based on an acceleration-related characteristic curve, which can be determined and parameterized through roundness testing. During roundness testing, deviations between the actual position of the circular contour and the programmed radius (especially during direction changes) are quantified and graphically displayed on the human-machine interface.

In newer versions of the system software, the integrated dynamic friction tool compensation function dynamically compensates for friction behavior at different machine speeds, reducing actual machining contour errors and achieving higher control accuracy.

Sag and Angular Error Compensation

If the weight of individual components of the machine tool causes displacement or tilting of moving parts, sag tool compensation is required because it can lead to sagging of relevant machine tool parts, including the guiding system. Angular error tool compensation is used when moving axes are not correctly aligned with each other (e.g., not perpendicular). As the offset from the zero position increases, the positional error also increases. Both types of errors are caused by the machine tool’s own weight or the weight of the tool and workpiece. During commissioning, the measured tool compensation values are quantified and stored in the SINUMERIK system in a form such as a compensation table, corresponding to specific positions. During machine operation, the positions of the relevant axes are interpolated based on the stored tool compensation values. For each continuous path movement, there is a base axis and a compensation axis.

Temperature Compensation

Heat can cause expansion in various parts of the machine tool. The extent of expansion depends on factors such as the temperature and thermal conductivity of each part. Different temperatures may cause changes in the actual positions of the axes, which can negatively impact the accuracy of the workpiece being machined. These changes in actual values can be offset through temperature tool compensation. Error curves for each axis at different temperatures can be defined. To ensure accurate compensation for thermal expansion, temperature compensation values, reference positions, and linear gradient parameters must be continuously transferred from the PLC to the CNC control system via functional blocks. Unexpected parameter changes are automatically corrected by the control system to prevent machine overload and activate monitoring functions.

Volumetric Compensation System (VCS)

The positions of rotary axes, their mutual narz?dzie compensation, and tool orientation errors can lead to systematic geometric errors in components such as turrets and rotary heads. Additionally, small errors may occur in the guiding systems of feed axes in every machine tool. For linear axes, these errors include linear position errors, horizontal and vertical straightness errors; for rotary axes, pitch, yaw, and roll errors may arise. Other errors, such as perpendicularity errors, can occur when aligning machine components. For example, in a three-axis machine tool, this can result in up to 21 geometric errors at the tool center point (TCP): six error types per linear axis multiplied by three axes, plus three angular errors. These deviations collectively form the total error, also known as the volumetric error.

The volumetric error describes the deviation between the actual TCP position of the machine tool and the TCP position of an ideal, error-free machine tool. SINUMERIK solution partners can determine volumetric errors using laser measurement equipment. Measuring errors at a single position is insufficient; errors across the entire machining volume must be measured. Typically, measurement values for all positions are recorded and plotted as curves, as the magnitude of errors depends on the position of the relevant feed axis and the measurement location. For example, deviations in the x-axis may vary when the y-axis and z-axis are in different positions—even at nearly the same x-axis position. With “CYCLE996 – Motion Measurement,” rotary axis errors can be determined in just a few minutes. This allows for continuous monitoring of machine tool accuracy and, if necessary, corrections can be made even during production.

Deviation Compensation (Dynamic Feedforward Control)

Deviation refers to the discrepancy between the position controller and the standard during the movement of a machine tool axis. Axis deviation is the difference between the target position and the actual position of the axis. Deviation causes speed-related unnecessary contour errors, especially when the contour curvature changes, such as in circles, squares, or other shapes. Using the NC advanced language command FFWON in the part program, speed-related deviations can be reduced to zero during path movement. Feedforward control improves path accuracy, resulting in better machining outcomes.

FFWON: Command to activate feedforward control

FFWOFF: Command to deactivate feedforward control

Electronic Counterbalance Compensation

In extreme cases, to prevent damage to the machine tool, tool, or workpiece caused by axis sagging, the electronic counterbalance function can be activated. In load axes without mechanical or hydraulic counterbalances, a vertical axis may unexpectedly sag once the brake is released. After activating the electronic counterbalance, unintended axis sagging can be compensated. Upon releasing the brake, a constant balancing torque maintains the position of the sagging axis.

Pre-Drilling Entry

Characteristics: One of the safest cutter entry methods

Applicable Scenarios: Machining materials prone to chip accumulation

Operation Method: Pre-drill a hole in the workpiece (5%-10% larger than the end mill diameter), then enter the milling cutter through the hole.

Advantages:

Prevents premature tool wear

Ensures smooth chip evacuation, reducing the risk of chip accumulation and tool breakage

Particularly suitable for machining materials like aluminum and copper that tend to stick to the tool

Disadvantages:

Additional Process: Requires an extra pre-drilling step, increasing machining time and cost.

Precision Limitations: The diameter and position of the pre-drilled hole must be precise; otherwise, it may affect subsequent milling accuracy.

Unsuitable for Thin-Walled Workpieces: Pre-drilling may cause deformation or damage to thin-walled workpieces.

Material Waste: Pre-drilling removes some material, which may not be suitable for scenarios requiring high material utilization.

Helical Entry

Characteristics: Safe and efficient

Applicable Scenarios: High-precision machining, such as aerospace and medical device manufacturing

Operation Method: Use a corner-radius end mill to enter the workpiece gradually along a helical path. During programming, the helical diameter should be 110%-120% of the cutting insert diameter.

Advantages:

Reduces tool wear and breakage risk

Provides excellent surface finish

Suitable for deep cavity machining and complex contours

Disadvantages:

Complex Programming: Requires precise CNC programming, demanding higher technical skills from operators.

Longer Machining Time: The helical path is longer, potentially increasing machining time.

High Tool Cost: Requires high-quality corner-radius end mills, increasing tool costs.

Unsuitable for Shallow Grooves: In shallow groove machining, the advantages of helical entry are less pronounced and may reduce efficiency.

Ramp Entry

Characteristics: Efficient with minimal impact on workpiece deformation

Applicable Scenarios: Contour machining, pocket machining

Operation Method: The milling cutter enters the workpiece at an angle (usually 1°-10°) and gradually increases the cutting depth.

Advantages:

Reduces axial force, minimizing workpiece deformation risk

Improves dimensional accuracy

Suitable for machining high-strength materials

Disadvantages:

Complex Tool Forces: Ramp cutter entry applies multiple torsional forces on the tool, potentially leading to fatigue damage.

Chip Evacuation Issues: Poor tool design may result in poor chip evacuation, affecting machining quality.

Angle Selection Difficulty: Requires precise angle selection based on material properties; otherwise, machining effectiveness may be compromised.

Unsuitable for Brittle Materials: Brittle materials may develop cracks or chipping during ramp entry.

Circular Entry

Characteristics: Smooth cutter entry, reducing impact

Applicable Scenarios: Mold manufacturing, 3D contour machining

Operation Method: The milling cutter enters the workpiece from the side along a curved path, gradually increasing the load and decreasing it upon exit.

Advantages:

Avoids impact loading, extending tool life

Improves surface finish and machining efficiency

Suitable for complex surface machining

Disadvantages:

Complex Programming: Requires precise curved path programming, demanding higher CNC system capabilities.

Long Tool Path: The circular entry path is longer, potentially increasing machining time.

Unsuitable for Narrow Grooves: Circular entry may not be feasible for narrow groove machining, limiting its application.

Concentrated Tool Wear: Circular cutter entry may cause concentrated wear on a specific part of the tool, affecting its lifespan.

Plunge Entry

Characteristics: Simple but high-risk

Applicable Scenarios: Machining with center-cutting tools

Operation Method: The milling cutter enters the workpiece vertically from the top.

Advantages:

Simple operation, suitable for quick machining

Applicable to center-cutting tools like drills

Disadvantages:

High Tool Breakage Risk: Plunge entry is prone to tool breakage, especially when machining hard materials.

Poor Chip Evacuation: Chip evacuation is difficult, leading to chip accumulation and affecting machining quality.

High Workpiece Damage Risk: Plunge cutter entry may cause surface damage or deformation of the workpiece.

Unsuitable for Deep Grooves: In deep groove machining, plunge entry poses higher risks and is more likely to damage the tool.

Straight-Line Side Entry

Characteristics: Simple and direct, but causes significant tool wear

Applicable Scenarios: Simple cutting operations

Operation Method: The milling cutter enters the workpiece from the side and gradually increases the cutting depth.

Advantages:

Simple operation, suitable for low-precision machining

Effectively resolves tool entry difficulties

Disadvantages:

Severe Tool Wear: Straight-line side entry causes significant tool wear, especially when machining high-strength materials.

Feed Rate Limitation: The feed rate must be reduced by 50% during cutter entry, affecting machining efficiency.

Chip Evacuation Issues: Poor chip evacuation may lead to tool breakage or workpiece damage.

Unsuitable for Complex Contours: Straight-line side entry is less effective for complex contour machining, limiting its application.

Roll-In Entry

Characteristics: Ensures consistent chip thickness

Applicable Scenarios: Grooving, contour machining

Operation Method: The milling cutter enters the workpiece in a rolling manner, gradually increasing the cutting depth.

Advantages:

Maintains consistent chip thickness, improving surface finish

Reduces tool wear and heat generation

Suitable for high-speed machining

Disadvantages:

Feed Rate Limitation: The feed rate must be reduced by 50% during entry, affecting machining efficiency.

Complex Programming: Requires precise CNC programming, demanding higher technical skills from operators.

High Tool Cost: Requires high-quality rolling tools, increasing tool costs.

Unsuitable for Shallow Grooves: In shallow groove machining, the advantages of roll-in entry are less pronounced and may reduce efficiency.

Podsumowanie

Each milling cutter entry method has its unique advantages and disadvantages. In practical machining, the appropriate entry method should be selected based on workpiece material, machining requirements, and tool characteristics. By effectively utilizing these methods, machining efficiency can be maximized, tool life extended, and workpiece quality ensured. Additionally, addressing the disadvantages of each method through measures such as optimized programming and adjusted cutting parameters can further enhance machining results

Precision Boring Technology

Precision boring is a hole machining process that pursues ultimate precision. Its main feature is the use of specialized precision boring tools to achieve high-precision machining through precisely controlled cutting parameters. In practical operations, the selection of precision boring tools is crucial and typically needs to be determined based on the properties of the material being machined and the precision requirements, including the material and geometric parameters of the tool. The precision boring process requires strict control of cutting parameters. The cutting speed is generally chosen between 60-120 m/min, the feed rate is usually controlled at 0.1-0.2 mm/r, and the single-cutting depth generally does not exceed 0.5 mm. The selection of these parameters directly affects the machining accuracy and surface quality. At the same time, to ensure machining accuracy, special attention must be paid to the use of coolant, typically using a cutting fluid that provides sufficient cooling and lubrication to ensure temperature stability during the machining process. In specific applications, precision boring is most commonly used in the manufacturing of high-precision parts such as precision bearing housings, cylinder liners, and hydraulic valve bodies. These parts usually require the roundness error of the holes to be controlled within 0.005 mm, and the surface roughness to reach Ra 0.8 μm or better. To achieve such machining precision, it is necessary not only to select high-precision tools and appropriate cutting parameters but also to consider factors such as the accuracy of the machine tool and the rigidity of the fixtures.

Rough Boring Technology

Rough boring is a machining method that primarily aims to remove material efficiently. During the rough boring process, the operator mainly focuses on the efficiency of material removal, with relatively lower precision requirements. This machining method is usually used as a preliminary process before finish machining, reserving appropriate machining allowances for subsequent finish machining. When selecting cutting parameters, the rough boring process seeks to achieve a larger cutting volume. The cutting speed can generally reach 100-150 m/min, the feed rate can be selected between 0.3-0.8 mm/r, and the single-cutting depth can reach 2-5 mm. Such parameter settings can greatly improve machining efficiency, but they also require the machine tool to have sufficient power and rigidity. In actual operation, special attention must also be paid to chip evacuation, usually requiring the use of high-pressure cooling fluids and special chip evacuation groove designs. Rough CNC boring is mainly applied to the machining of large parts, such as marine engine blocks, large machine tool beds, etc. These parts typically involve a large amount of material removal and have high requirements for machining efficiency. During the machining process, it is necessary to focus on changes in cutting forces and workpiece deformation. If necessary, process measures such as intermediate tempering should be taken to release stresses and ensure machining quality.

Step Boring Process

Step boring is a highly efficient complex hole machining method characterized by its ability to complete the machining of multiple different diameters in one pass. With the use of specially designed step boring tools, the number of tool changes can be significantly reduced, thereby improving machining efficiency. In terms of tool design, special attention must be paid to the relative positions between the cutting edges and the matching of cutting parameters. The selection of machining parameters is particularly important in step boring. Since all the steps are cut simultaneously, the distribution of cutting forces is complex, necessitating a reasonable choice of cutting speed and feed rate. Generally, the cutting speed is chosen between 80-120 m/min, and the feed rate is controlled at 0.2-0.4 mm/r. Additionally, it is necessary to consider the distribution of cutting allowances between the steps to ensure a stable cutting process. Step boring is widely used in the machining of parts with multi-step stepped holes, such as valve bodies and bearing caps. This machining method not only ensures high machining efficiency but also maintains the coaxiality between the steps. In practical applications, special attention must also be paid to the manufacturing and maintenance of the tools, as step boring tools are costly to produce and their service life directly affects the machining cost.

Back Boring Technology

Back CNC boring is an important method for solving hole machining problems under special working conditions. It is mainly used for machining internal holes or back holes that are difficult to access with conventional tools. Back boring tools typically employ special mechanical structures or hydraulic mechanisms to achieve cutting movements in confined spaces. During the back boring process, the operation is challenging and requires precise control of the tool’s feed and expansion. The selection of cutting parameters is relatively conservative, with cutting speeds generally ranging from 40-80 m/min and feed rates between 0.1-0.3 mm/r. At the same time, due to the specialties of the machining position, higher demands are placed on chip evacuation and cooling lubrication. Back boring technology plays a crucial role in the machining of complex parts such as engine crankcases and valve bodies. Although this machining method is relatively less efficient, it is irreplaceable under certain special conditions. In practical applications, special attention must be paid to the selection and maintenance of tools, and it is necessary to develop specialized process procedures and operating protocols.

Five Chamfer Boring Processes

Chamfer boring is an indispensable process in modern machinery manufacturing. It not only improves the appearance quality of parts but more importantly, enhances the assembly performance and service life of the parts. The design of chamfer boring tools needs to consider both radial and axial cutting capabilities, usually achieved with a special blade structure for a stable cutting process. During the chamfer boring process, the selection of cutting parameters should comprehensively consider the size of the chamfer and the surface quality requirements. Generally, the cutting speed is chosen between 60-100 m/min, and the feed rate is between 0.2-0.4 mm/r. It is particularly important to note that the accuracy of the chamfer angle directly affects the assembly quality of the parts, so tool positioning accuracy must be strictly controlled during machining. Chamfer boring technology is widely used in the machining of parts that require a large number of chamfers, such as automobile engine blocks and valve bodies. Through reasonable process design, the chamfering process can be organically combined with other CNC boring operations to improve machining efficiency. In practical applications, attention should also be paid to the detection methods of chamfer dimensions and the establishment of a comprehensive quality control system.

Podsumowanie

With the development of modern manufacturing, CNC boring technology continues to innovate. The five main types of boring methods each have their own characteristics and play important roles in different application scenarios. Mastering the technical features and application essentials of these machining methods is of great significance for improving machining quality and efficiency. In actual production, it is necessary to select the appropriate machining method and develop a scientific process plan based on specific machining needs to achieve the desired machining results.

Wprowadzenie

Water jet machining, also known as water jet cutting, is a versatile and innovative manufacturing process that uses a high-pressure stream of water to cut through various materials. This technology has gained significant popularity in industries ranging from aerospace to automotive, and from food processing to art and design. Water jet machining is renowned for its precision, flexibility, and environmental friendliness. Unlike traditional cutting methods that rely on heat or mechanical force, water jet cutting uses the kinetic energy of water to achieve clean, precise cuts without altering the material’s intrinsic properties. This article explores the principles, applications, advantages, and limitations of water jet machining, as well as its future potential in modern manufacturing.

The Principles of Water Jet Machining

Water jet machining operates on a simple yet powerful principle: a high-pressure stream of water is directed at a material to erode and cut through it. The process can be divided into two main types:

1. Pure Water Jet Cutting: This method uses only water, pressurized to levels as high as 60,000–90,000 psi (pounds per square inch). The water is forced through a small nozzle, typically made of sapphire or diamond, to create a fine, high-velocity stream. Pure water jet cutting is ideal for softer materials like rubber, foam, paper, and food products.
2. Abrasive Water Jet Cutting: For harder materials such as metals, ceramics, and composites, an abrasive substance (usually garnet) is added to the water stream. The abrasive particles accelerate the cutting process by enhancing the erosive power of the water jet. This method can cut through materials several inches thick with remarkable precision.

The key components of a water jet machining system include:

• High-Pressure Pump: Generates the ultra-high-pressure water stream.
• Nozzle: Focuses the water into a fine, high-velocity jet.
• Abrasive Delivery System: Introduces abrasive particles into the water stream (for abrasive cutting).
• CNC Controller: Guides the nozzle along the desired cutting path with high accuracy.
• Catcher Tank: Collects the spent water and abrasive particles after cutting.

Applications of Water Jet Machining

Water jet machining is used across a wide range of industries due to its versatility and precision. Some of the most notable applications include:

1. Metal Fabrication

Water jet cutting is widely used in the metalworking industry to cut materials such as steel, aluminum, titanium, and copper. Its ability to cut without generating heat makes it ideal for materials that are sensitive to thermal distortion. This is particularly important in aerospace and automotive industries, where precision and material integrity are critical.

2. Stone and Tile Cutting

In the construction and interior design industries, water jet cutting is used to shape natural stone, ceramic tiles, and glass. The process allows for intricate designs and precise cuts, making it a favorite for creating decorative elements and custom fixtures.

3. Food Processing

Water jet cutting is a hygienic and efficient method for cutting food products. It is used to slice bread, cut meat, and portion fish without compromising food safety or quality. The absence of heat ensures that the food’s texture and flavor remain intact.

4. Composites and Plastics

Water jet machining is ideal for cutting composite materials, which are often challenging to process using traditional methods. It is used in the production of carbon fiber components, fiberglass, and other advanced materials.

5. Art and Design

Artists and designers use water jet cutting to create intricate patterns and shapes in materials like wood, acrylic, and metal. The technology enables the production of highly detailed and customized pieces.

6. Medical Device Manufacturing

In the medical industry, water jet cutting is used to fabricate precision components for devices such as implants, surgical instruments, and diagnostic equipment. The process ensures clean edges and minimal material waste.

Advantages of Water Jet Machining

Water jet machining offers numerous advantages over traditional cutting methods, making it a preferred choice for many applications:

1. No Heat-Affected Zone (HAZ): Unlike laser or plasma cutting, water jet cutting does not generate heat, eliminating the risk of thermal distortion, warping, or changes in material properties.
2. Versatility: Water jet cutting can handle a wide range of materials, from soft and delicate substances to hard and durable ones. This makes it a one-stop solution for many industries.
3. Precyzja: The process allows for extremely tight tolerances, with cutting accuracy as high as ±0.001 inches. This level of precision is essential for industries like aerospace and medical device manufacturing.
4. Environmental Friendliness: Water jet cutting is a clean process that produces no harmful fumes, dust, or waste. The water used can often be recycled, and the abrasive materials are non-toxic.
5. Minimal Material Waste: The narrow kerf (cut width) of the water jet reduces material waste, making it a cost-effective option for expensive materials.
6. No Tool Wear: Since water jet cutting does not involve physical contact between a tool and the workpiece, there is no tool wear, reducing maintenance costs.
7. Ability to Cut Complex Shapes: The CNC-controlled nozzle can follow intricate paths, enabling the cutting of complex geometries and fine details.

Limitations of Water Jet Machining

Despite its many advantages, water jet machining does have some limitations:

1. Cutting Speed: While water jet cutting is precise, it can be slower than other methods like laser or plasma cutting, especially for thick materials.
2. Material Thickness: Although water jet cutting can handle thick materials, the process becomes less efficient as thickness increases. For extremely thick materials, alternative methods may be more suitable.
3. Operating Costs: The high-pressure pumps and abrasive materials can be expensive to maintain and replace, leading to higher operating costs compared to some traditional methods.
4. Surface Finish: While water jet cutting produces clean edges, the surface finish may require additional post-processing for certain applications.
5. Noise and Vibration: The process can generate significant noise and vibration, which may require mitigation measures in some environments.

Innovations and Future Trends

Water jet machining continues to evolve, driven by advancements in technology and the growing demand for precision manufacturing. Some of the key trends and innovations in the field include:

1. Hybrid Cutting Systems: Combining water jet cutting with other technologies, such as laser or plasma cutting, to leverage the strengths of each method.
2. Automation and Robotics: Integrating water jet cutting systems with robotic arms and advanced CNC controls to enhance precision and efficiency.
3. 3D Water Jet Cutting: Developing systems capable of cutting complex three-dimensional shapes, opening up new possibilities for manufacturing and design.
4. Eco-Friendly Abrasives: Research into alternative abrasive materials that are more sustainable and environmentally friendly.
5. Improved Pump Technology: Advances in high-pressure pump design to increase efficiency and reduce energy consumption.
6. AI and Machine Learning: Using artificial intelligence to optimize cutting parameters and improve process control.

Wniosek

Water jet machining is a transformative technology that has revolutionized the way materials are cut and shaped. Its ability to deliver precision, versatility, and environmental benefits makes it an indispensable tool in modern manufacturing. While it has some limitations, ongoing advancements in technology are addressing these challenges and expanding the potential applications of water jet cutting. As industries continue to demand higher levels of precision and efficiency, water jet machining is poised to play an increasingly important role in shaping the future of manufacturing. Whether it’s cutting intricate designs in metal, slicing food products, or fabricating medical devices, water jet machining proves that sometimes, the simplest element—water—can be the most powerful tool.

Functions of Cutting Fluid

Imagine the harsh working conditions when a twist drill rotates at astonishing speeds, penetrating deep into the workpiece for deep hole drilling. High temperatures, high pressures, and rapid rotation are extreme conditions that put immense stress on both the cutting tool and the workpiece. This is where cutting fluid steps in as a silent hero, playing a crucial role in cooling, lubricating, and cleaning during the drilling process.

Cooling Function

One of the primary functions of cutting fluid is cooling. During twist drill deep hole drilling, the friction between the tool and the workpiece generates a significant amount of heat. Without timely cooling, the tool is prone to damage due to overheating. Cutting fluid acts like a refreshing spring, carrying away the heat, protecting the tool, and ensuring the smooth progress of the drilling process.

Lubrication Function

In addition to cooling, cutting fluid also serves as a lubricant. During drilling, the contact area between the tool and the workpiece is very small, yet the pressure exerted is very high. Without sufficient lubrication, the tool can easily scratch the surface of the workpiece, affecting the quality of the hole. Cutting fluid acts like a lubricating film, reducing friction between the tool and the workpiece, decreasing wear, and improving the finish of the drilled hole.

Cleaning Function

Certainly, the cleaning function of cutting fluid should not be overlooked. During the drilling process, a significant amount of chips and metal powder is produced. If these chips are not removed in a timely manner, they can easily accumulate inside the drilled hole, leading to blockages and even damaging the tool. Cutting fluid acts like a diligent cleaner, continuously flushing the inside of the hole, carrying away the chips and metal powder, ensuring the hole remains unobstructed.

Distribution of Cutting Fluid

However, the distribution of cutting fluid in twist drill deep hole drilling is not uniform. Due to the limitations of the depth and diameter of the hole, it is difficult for the cutting fluid to reach the bottom of the hole directly. In some areas of the hole, the cutting fluid may form dead zones where the flow rate is very slow or almost non-existent. This results in the tool not receiving adequate cooling and lubrication in these areas, increasing the risk of tool wear and hole blockages.

How Cutting Fluid Affects Chip Removal

Chip removal is equally crucial in twist drill deep hole drilling. Chips are metal fragments produced during the drilling process, and if not removed promptly, they can easily accumulate inside the hole, forming blockages. Once a blockage occurs, it not only affects the quality of the hole but also puts tremendous pressure on the tool, which can lead to tool breakage. Therefore, timely chip removal is key to ensuring the smooth progress of the drilling process.

In twist drill deep hole drilling, the chip conveyance mechanism is relatively complex. Due to the limitations of the hole’s depth and diameter, chips cannot be easily expelled through the hole. They need to navigate through the tiny gap between the tool and the workpiece and then be carried out of the hole with the flow of cutting fluid. However, this process is fraught with challenges. The shape, size, and density of the chips all affect their conveyance efficiency. If the chips are too large or dense, they can easily form blockages inside the hole, leading to drilling failures.

Using 3D Simulation to Optimize Cutting Fluid Distribution for Improved Chip Removal

To optimize the distribution of cutting fluid and the removal of chips, scientists have conducted extensive research. They have utilized advanced 3D multiphysics simulation methods to conduct detailed simulations and analyses of the twist drill deep hole drilling process. These simulations not only reveal the flow characteristics of the cutting fluid inside the hole but also demonstrate the chip conveyance mechanism within the hole. Through these simulations, scientists have gained a deeper understanding of the reasons behind uneven cutting fluid distribution and inefficient chip removal, providing strong support for optimizing the drilling process.

In simulation studies, the coupled particle simulation (SPH-DEM) method has played a significant role. This method accurately simulates the movement and interaction of cutting fluid and chips inside the drilled hole. Through the SPH-DEM method, scientists can observe the flow trajectory of the cutting fluid within the hole, as well as the conveyance process of chips in the cutting fluid. These observations not only validate the accuracy of the simulation method but also provide an important basis for optimizing the distribution of cutting fluid and chip removal strategies.

In addition to coupled particle simulation, CFD (Computational Fluid Dynamics) simulation has also played a crucial role in the analysis of cutting fluid flow. CFD simulation can model the flow state of cutting fluid inside the drilled hole, including parameters such as flow velocity, pressure, and temperature. Through the analysis of these parameters, scientists can understand the distribution of cutting fluid within the hole, as well as the impact of different cutting fluid parameters on hole quality. These analytical results are of significant guiding significance for optimizing cutting fluid formulations and process parameters.

In the experimental validation phase, scientists designed a series of experiments to verify the accuracy of the simulation results. They selected different cutting parameters, types of cutting fluids, and concentrations for the experiments, and recorded data such as the quality of the drilled holes, the flow rate of the cutting fluid, and the chip removal situation. By comparing the experimental data with the simulation results, the scientists found a good consistency between the two. This not only verified the reliability of the simulation method but also provided strong support for optimizing cutting fluid distribution and chip removal strategies.

During the experimental process, the scientists also discovered some interesting phenomena. For example, under certain cutting parameters, although the flow rate of the cutting fluid was high, the quality of the drilled holes was not ideal. After analysis, they found that this was due to the formation of dead zones of the cutting fluid inside the hole, which resulted in insufficient cooling and lubrication for the tool in certain areas. To address this issue, they adjusted the injection angle and flow rate of the cutting fluid, successfully improving the distribution of the cutting fluid and enhancing the quality of the drilled holes.

In addition, scientists have also found that the chip removal is closely related to parameters such as the flow rate and viscosity of the cutting fluid. When the flow rate of the cutting fluid is too high, chips are easily carried away by the fluid; however, when the viscosity of the cutting fluid is too high, chips tend to form blockages inside the hole. Therefore, when optimizing the cutting fluid formulation, it is necessary to consider the flow rate, viscosity, and other parameters of the cutting fluid to ensure the smooth removal of chips.

Podsumowanie

Through extensive experimentation and simulation studies, scientists have successfully optimized the cutting fluid distribution and chip removal strategies in twist drill deep hole drilling. They have found that by adjusting parameters such as the injection angle, flow rate, and viscosity of the cutting fluid, the distribution of the cutting fluid inside the hole can be significantly improved; at the same time, by optimizing the structure of the cutting tool and cutting parameters, the efficiency of chip removal can also be enhanced. These research findings not only improve the quality and efficiency of twist drill deep hole drilling but also provide valuable references for precision manufacturing in other fields.

The distribution of cutting fluid and chip removal in twist drill deep hole drilling is a complex and important process. Through scientific experimentation and simulation studies, we can gain a deeper understanding of the physical mechanisms and influencing factors in this process; by optimizing cutting fluid formulations and process parameters, we can significantly improve the quality and efficiency of drilling. In the future, with the continuous advancement of technology and the development of the manufacturing industry, it is believed that twist drill deep hole drilling technology will have an even broader development prospects and a wider range of applications.

Experimental Method

TiN, TiAlN, TiN-MoS?, and CrTiAlN composite coatings were deposited on YT14 cemented carbide cutters using a closed-field unbalanced magnetron sputtering ion plating equipment from Teer Company. The nano hardness and elastic modulus of the coatings were measured using a Nano Test 600 nano hardness tester. To reduce experimental errors, the hardness and elastic modulus values were the average of five measurements. The hardness of the coatings was also verified using a Vickers microhardness tester, and the morphology and phase structure of the cutter coatings were observed and analyzed using a Quanta 200 scanning electron microscope (SEM) and an Advance 8 X-ray diffractometer (XRD). The cutting tests of the coated cutters were conducted on a CNC machining center, with PCNiMoVA steel as the cutting material. The flank wear was observed and measured using a 30x tool microscope. The cutting time when the wear strip width on the flank face exceeded 0.6mm was used as the basis for evaluating the tool’s life, and the cutting life of the tools was compared.

Experimental Results and Analysis

Coating Hardness and Elastic Modulus Testing

Figure 1 shows the loading and unloading curves obtained during the nano hardness measurement process of the CrTiAlN composite coating. The loading and unloading curves not only provide the hardness of the CrTiAlN film but also its elasticity. Define R = (ha – h) / h as the elastic recovery coefficient, where ha is the indentation depth at maximum load, and h is the residual depth of the indentation after unloading. According to the definition of R, the greater the value of R, the greater the elasticity of the film. Therefore, based on the nano indentation curve in Figure 1, the hardness of the CrTiAlN film is 33 GPa, and the elastic modulus is 675 GPa. Figure 2 is a comparative analysis chart of the nano hardness of TiN, TiAlN, TiN-MoS?, and CrTiAlN coatings. It can be seen from the figure that the nano hardness measurement values of the four coatings are 18 GPa, 30 GPa, 15 GPa, and 33 GPa, respectively. The nano hardness ranking is as follows: CrTiAlN > TiAlN > TiN > TiN-MoS?.

Figure 3 shows the measured elastic modulus values of each coating. It can be seen from the figure that the elastic modulus of the four coatings are 214 GPa, 346 GPa, 164 GPa, and 675 GPa, respectively. The ranking of the elastic modulus is as follows: CrTiAlN > TiAlN > TiN > TiN-MoS?. This indicates that the elastic modulus of the coatings is directly proportional to their hardness. However, the CrTiAlN coating shows the greatest relative increase in elastic modulus, with a value significantly higher than other coatings, reaching 675 GPa, which suggests that the deposited CrTiAlN coating has both high hardness and high elasticity.

Meanwhile, the Vickers microhardness tester was used to perform microhardness verification tests on each cutter coating, with a indentation load of 15g and a duration of 10 seconds. The measurement results are shown in Figure 4. By comparing the coating nano hardness in Figure 2 with the coating microhardness values in Figure 4, it can be found that the microhardness variation trend of each coating is the same as the nano hardness variation trend, with the CrTiAlN coating having the relatively highest Vickers microhardness at HV1560.

Analysis of Coating Surface Morphology

The surface morphologies of the TiN, TiAlN, TiN-MoS?, and CrTiAlN coated cutters are shown in Figure 5. It can be observed from the figure that there is a significant difference in the surface morphology of the four coatings, indicating that the addition of composite elements has caused a great change in the crystalline state of the TiN compounds. Among them, the TiN coating surface phase tissue is uniform, with relatively fine particles, while the TiAlN coating surface morphology is relatively rough, with coarser particle tissue. The TiN-MoS? coating surface is distributed with a large amount of flaky mixed structure, mainly due to the uniform distribution of MoS? phase in the TiN coating, tending towards a composite structure in the mixed state, which serves a self-lubricating function. The CrTiAlN coating surface grains are relatively fine, the coating is dense and uniform, and the surface is distributed with a large number of hard points.

Drilling Test

The four types of coated cemented carbide cutters were used to machine PCNiMoVA steel, and the wear condition of the cutters was inspected to compare the durability of different coated cutters.

The cutting test conditions for the coated cutters were as follows: the cutting method was external cylindrical cutting, the cutting speed was 160 m/min, the feed rate was 0.15 mm/r, the cutting depth was 0.5 mm, and dry cutting was performed. The cutting time when the wear strip width on the flank face exceeded 0.6 mm was used as the basis for evaluating the tool’s life, and the cutting life of the tools was compared.

A comparison of the cutting life of the coated cutters is shown in Figure 6.

From the figure, it can be seen that under dry cutting conditions, the cutting life of the uncoated cutters was the shortest, and the service life of the coated cutters was significantly better than that of the uncoated cutters. Among them, the CrTiAlN coated cutter had the longest cutting life. The ranking of the cutting life of the four coated cutters was as follows: CrTiAlN > TiN-MoS? > TiAlN > TiN. This indicates that Cr and Al elements form hard phases in the TiN coating, and the addition of Al elements is beneficial for the formation of Al oxides, which avoids further oxidation during the cutting process, improves the oxidation resistance of the cutters, and is conducive to increasing the cutting life of the tools. Meanwhile, the MoS? lubricating phase helps to reduce the friction coefficient of the cutters, improve the anti-wear capability of the tools, and also extends the service life of the cutters.

In summary, due to the comprehensive utilization of the advantages of various coating components in the multi-component composite coatings, they achieve better comprehensive performance, ensuring excellent wear resistance and toughness, reducing the formation of built-up edge, and possessing mechanical shock and thermal shock resistance, which can greatly improve the tool life.

XRD Test Analysis

XRD analysis method was used to characterize the phase structure of the CrTiAlN tool coating with the best cutting performance, and the results are shown in Figure 7. The XRD spectrum analysis indicates that the crystal phases of the coating are mainly composed of Cr, CN, CEN, and TiN at room temperature, and the amorphous phase in the coating was not detected. At the same time, high magnification scanning analysis of the tool coating revealed a large number of hard phase particles distributed on the coating surface. Combined with X-ray diffraction analysis, it is known that these hard phases are mainly CN, CrN, TiN, and AlN phases. These hard phases are beneficial for improving the cutting life of the coated cutters.

Wniosek

The author has prepared TiN, TiAlN, TiN-MoS?, and CrTiAlN composite coatings using a closed-field unbalanced magnetron sputter ion plating PVD coating process. Comparative tests on the mechanical properties and cutting performance of the coatings show that:

The nanoindentation analysis obtained the nano hardness ranking of the four types of cutter coatings as follows: CrTiAlN > TiAlN > TiN > TiN-MoS?. The elastic modulus of the coatings is directly proportional to their hardness.

Under dry cutting conditions, when drilling PCNiMoVA steel, the cutting life of the coated cutters is ranked as: CrTiAlN > TiN-MoS? > TiAlN > TiN. This indicates that the cutting performance of the multi-component composite coatings is significantly better than that of the simple TiN coating, suggesting a direction for the future development of coated cutters.