Precision CNC milling: Detailed explanation of high-precision machining technology for industrial manufacturing

In the field of modern industrial manufacturing, precision CNC milling is a key technology for achieving high-precision parts processing. From core components of aerospace to electronic devices used in daily life, this technology supports many high-end manufacturing industries with its micron-level or even nano-level processing accuracy. Next, we will deeply analyze the technical principles, practical applications, challenges and solutions of precision CNC milling.

1. Basics of precision CNC milling: definition and workflow

Precision CNC milling is a technology that uses a computer numerical control (CNC) system to control a milling machine to perform high-precision cutting processing on metal materials. Its processing accuracy can usually reach ±5 microns. In some ultra-precision processing scenarios, the accuracy can reach nanometers.

The specific workflow is as follows: First, engineers use CAD software to design a three-dimensional model of a part; then, they use CAM software to convert the model into CNC machining code (G code and M code), which contains detailed machining instructions such as tool path, cutting speed, feed rate, etc.; finally, the CNC system reads the code, controls the various motion axes of the milling machine, and drives the tool to mill the workpiece according to the instructions, completing the transformation from design to physical parts.

2. Analysis of core technologies of precision CNC milling: machine tools, tools and control systems

(1) Structure and performance of precision CNC milling machines

Precision CNC milling machines are composed of several key parts:

1) Motion axis system:

Commonly used are three-axis, four-axis and five-axis machine tools.

Three-axis milling machine: The tool moves along the three linear axes of X, Y and Z, which is suitable for plane and simple contour machining, and the operating cost is relatively low.

Four-axis milling machine: Adding A-axis (or B-axis) rotation on the basis of three axes can complete the machining of side features and long-axis symmetrical parts at one time, reducing secondary clamping errors.

Five-axis milling machine: Combines two rotating axes (A and C or B and C) to achieve multi-degree-of-freedom linkage between the tool and the workpiece, can efficiently process complex curved surfaces and deep holes, and is widely used in aerospace and mold manufacturing.

2) Guide rails and transmission mechanisms:

Air hydrostatic guide rails and liquid hydrostatic guide rails are widely used, and their friction coefficient is extremely small, which can ensure the smooth movement of the machine tool; high-precision ball screws or linear motors are responsible for converting the motor's rotational motion into linear motion to achieve precise displacement.

3) Spindle unit:

The high-performance electric spindle can reach a speed of 40,000 rpm, and the radial runout error is controlled within 1 micron, providing stable power for high-speed cutting.

4) Bed structure:

Made of low thermal expansion coefficient materials such as granite and polymer concrete, it can effectively reduce the impact of thermal deformation on machining accuracy when the temperature changes.

(2) Tool: The key factor that determines the processing quality

The material and geometry of the tool directly affect the processing effect:

1) Tool material:

Diamond tools have high hardness and are suitable for processing aluminum alloys, ceramics and other materials;

Ceramic tools are resistant to high temperatures and are often used for cutting difficult-to-process materials such as nickel-based high-temperature alloys;

Coated carbide tools are the most commonly used. By coating TiN, TiAlN and other coatings on the surface of the carbide, the wear resistance and cutting performance of the tool are improved.

2) Tool type:

Micro-diameter end mills, with a minimum diameter of 0.1mm, are used for micro-structure processing;

Ball-end milling cutters, suitable for curved surface contour processing;

Corn milling cutters, due to their large helix angle design, can achieve efficient material removal.

(3) CNC system: The "commander" of processing instructions

The CNC system is the core control unit of precision CNC milling. It fits discrete coordinate points into continuous tool motion trajectories through interpolation algorithms.

Taking the German Siemens 840D system as an example, it has nanometer-level interpolation accuracy and can achieve precise control of five-axis linkage. At the same time, the CNC system also integrates tool compensation, error correction and other functions to ensure processing accuracy.

3. Industry application examples of precision CNC milling

(1) Aerospace: high-precision processing of complex parts

The aerospace field has extremely high requirements for part accuracy and reliability. Taking aircraft engine turbine blades as an example, the difficulty in processing lies in the thin wall of the blade (thickness is about 0.8-1.5mm), complex surface and the material is mostly titanium alloy or nickel-based high-temperature alloy.

Using five-axis precision CNC milling technology, combined with special fixtures and micro-diameter ball-end milling cutters, layered milling can control the blade surface error to ±3 microns, and the surface roughness reaches Ra0.2 microns, meeting the stringent requirements of aircraft engines. Many key structural parts in aircraft are manufactured using precision CNC milling technology.

(2) Automobile manufacturing: efficient production of molds and parts

In automobile manufacturing, precision CNC milling is mainly used in mold processing and parts manufacturing:

1) Mold processing:

The size of large automobile cover molds can reach 2m×3m. Using a gantry-type five-axis machining center combined with high-speed milling technology, the mold surface processing accuracy can be controlled within ±5 microns, which is more than 40% more efficient than traditional EDM.

2) Parts manufacturing:

The tolerance requirement for the sealing groove processing of the motor housing of new energy vehicles is ±0.01mm. Through four-axis linkage milling and online measurement compensation technology, high-precision mass production can be achieved.

(3) Medical equipment: manufacturing support for precision medicine

Medical equipment has strict requirements on processing accuracy and biocompatibility:

1) Artificial joints:

The hip joint ball head is made of zirconium oxide ceramic material. Through nano-level cutting with a diamond milling cutter, the spherical error can be less than 50 nanometers and the surface roughness Ra0.02 microns can be achieved to ensure good fit with human tissue.

2) Dental implants:

On a 3.5mm diameter titanium alloy implant, a 0.2mm deep spiral groove is machined using a five-axis micro-milling machine with an accuracy of ±2 microns, improving the stability and success rate of the implant.

(4) Electronic information: Precision machining of micro-nano structures

The manufacturing of 5G communication equipment and semiconductor chips requires extremely high precision in the machining of tiny structures:

1) 5G filter cavity:

A 0.3mm wide through groove is machined on an aluminum alloy material. With the help of a 0.2mm diameter micro end mill and vibration suppression technology, the groove width accuracy can be controlled to ±5 microns, and the side wall verticality error is less than 0.1°.

2) Semiconductor lead frame:

On a 0.1mm thick copper alloy sheet, a 0.05mm wide finger structure is machined. Through high-speed milling and vacuum adsorption fixtures, the dimensional consistency error is less than 1%, meeting the chip packaging requirements.

4. Technical challenges and solutions for precision CNC milling

(1) The problem of maintaining accuracy

The thermal deformation and cutting vibration caused by high-speed operation of machine tools are the main factors affecting machining accuracy:

1) Thermal deformation control:

The oil cooling circulation system is used to cool key components such as the spindle, and the temperature control accuracy can reach ±0.1℃; at the same time, the thermal deformation error can be reduced by more than 90% by using the thermal error compensation algorithm based on BP neural network.

2) Vibration suppression:

By optimizing the tool path, analyzing the dynamic characteristics of the machine tool structure, and using active vibration control technology (such as piezoelectric ceramic actuators), the vibration amplitude can be controlled below 5 microns.

(2) Processing efficiency of difficult-to-process materials

Titanium alloys, high-temperature alloys and other materials have poor thermal conductivity and high hardness, making them difficult to process:

CNC milling parts

1) Ultrasonic vibration-assisted milling:

Applying 20kHz ultrasonic vibration to the tool can reduce the cutting force by 30% and extend the tool life by 2 times.

2) Laser-assisted preheating milling:

Using laser beams to preheat the processing area, reduce the hardness of the material, and increase cutting efficiency by 50%.

(3) Demand for intelligent upgrading

Traditional processing relies on manual experience, and intelligence has become the development direction:

1) Digital twin technology:

By establishing a virtual model of the machine tool and the processing process, simulating the processing state, optimizing the processing parameters, and reducing the cost of trial and error.

2) AI quality control:

Using machine vision and deep learning algorithms, real-time monitoring of the processing surface quality, automatic adjustment of processing parameters, and improving product qualification rate.

5. Summary

Precision CNC milling integrates advanced technologies such as CAD/CAM design, five-axis linkage, tool and fixture optimization, fine control of cutting parameters, and online measurement compensation, forming a complete production chain from digital design to high-precision processing.

It can not only achieve ±0.005 in or even ±0.0005 in tolerances and excellent surface quality on a variety of metals, but also meet the diverse needs of high-end manufacturing fields such as aerospace, medical, automotive, molds and consumer electronics through scientific tool and fixture selection, cutting parameter optimization and post-processing technology.