Comprehensive analysis of machined parts: types, materials and processing technology
In the modern industrial manufacturing system, machined parts are ubiquitous. They are widely used in aerospace, automotive industry, medical equipment, electronic appliances, mold manufacturing and other fields, and are one of the core components of mechanical equipment. With the continuous advancement of manufacturing technology, the market has put forward higher requirements for the accuracy, strength, structural complexity and surface quality of machined parts.
For product research and development, design, procurement and even end users, mastering the basic types of machined parts, common material properties and main processing technologies has become an important prerequisite for improving product competitiveness and controlling manufacturing costs. This article will conduct a comprehensive analysis around three dimensions: part type, material selection and performance, and processing technology methods to help readers build a complete knowledge system of machined parts.
1. Common types of machined parts
In actual manufacturing, machined parts of different forms and uses have their own structural characteristics and processing focuses. We can summarize them from several typical structures:
(1) Shaft parts
Shaft parts are one of the most representative rotating body structures and are widely used in transmission systems, rotating components and mechanical power mechanisms. Its typical characteristics are long length, support and connection structures at both ends or in the middle.
1) Processing characteristics:
Requires high-precision coaxiality and roundness;
High surface quality requirements, usually require precision turning or grinding;
Mostly equipped with complex details such as keyways, threads, fillets and chamfers;
High requirements for deformation control after heat treatment.
2) Application examples:
Motor spindles, reducer drive shafts, engine crankshafts, etc.
(2) Sleeve parts
Sleeve parts are hollow cylinders in structure and are often used to contain shafts or as sliding fitting elements. Compared with solid shafts, their inner cavity structure increases the difficulty of processing, especially when high precision requirements are required.
1) Processing characteristics:
There are requirements for both inner and outer circle processing, which is prone to eccentricity or uneven wall thickness;
The inner hole often requires precision boring or internal grinding to ensure the fitting tolerance;
The deformation of the inner wall after heat treatment needs special control.
2) Typical products:
Sleeves, bushings, hydraulic cylinders, connecting sleeves, etc.
(3) Disk and shell parts
The geometric features of these parts are flat or box-shaped structures, and they are often used in mechanical equipment for connection, fixing, support, sealing and other positions.
1) Processing difficulties:
Multi-station and multi-directional processing requires high fixture stability;
Often contains multiple through holes, threaded holes and positioning surfaces;
Thin walls are easy to deform, and thermal stress is difficult to control;
There are special-shaped surfaces or complex cavity structures.
2) Typical products:
Flanges, end covers, valve bodies, pump housings, reducer housings.
(4) Non-standard complex structural parts
1) Part characteristics
As the customization trend of industrial products increases, the demand for non-standard complex parts continues to increase. These parts often contain multi-degree-of-freedom surfaces, cavities, thin walls, and multiple material nesting, which puts higher requirements on processing technology and equipment.
2) Application areas:
Mold manufacturing, automated mechanical structural parts, high-end equipment assembly parts, etc.
2. Materials and performance characteristics selected for machined parts
The choice of materials not only affects the mechanical properties of the parts, but also directly determines their machinability and manufacturing costs. Parts with different structural functions have different requirements for material strength, toughness, hardness, corrosion resistance, thermal stability, etc.
The following are several common materials and their performance in machining:
(1) Aluminum alloy
Aluminum alloy plays an important role in machining due to its light weight, good thermal conductivity and strong machinability.
1) Performance advantages:
Low density, suitable for lightweight design;
Good cutting performance and high processing efficiency;
Surface treatment such as anodizing can be performed to improve appearance and corrosion resistance.
2) Common grades:
6061: General grade, medium mechanical strength;
7075: High strength application, commonly used in aviation structural parts;
2024: Good fatigue resistance, suitable for high-load components.
3) Applicable scenarios:
UAV structural parts, mobile phone housings, automotive parts, sports equipment, etc.
(2) Stainless steel
Stainless steel has become the preferred material in the fields of medical, food, chemical equipment, etc. due to its excellent corrosion resistance and strength.
1) Performance characteristics:
Good corrosion resistance, adaptable to a variety of complex environments;
High strength, but large cutting resistance;
Some models are easy to harden, and the tool wears quickly during processing.
2) Typical grades:
304: General stainless steel, good weldability and oxidation resistance;
316: Strong seawater corrosion resistance, commonly used in high-end medical and marine industries;
420: Can be heat treated to high hardness, suitable for tools and bearings.
(3) Carbon steel and alloy steel
Carbon steel is a common material for structural parts and shaft parts, with low cost and mature technology.
1) Advantage analysis:
High strength, suitable for load-bearing and impact scenarios;
Can be heat treated to obtain higher hardness;
Processability varies depending on the carbon content, low carbon steel is easy to process, and high carbon steel requires stronger tools.
2) Representative materials:
45 steel (medium carbon steel): commonly used in mechanical transmission shafts;
GCr15: bearing steel, high hardness, good wear resistance;
40Cr: has both strength and toughness after quenching and tempering.
(4) Copper alloys
Copper materials play an important role in electrical, hydraulic and heat dissipation systems.
1) Advantages and characteristics:
Excellent electrical and thermal conductivity;
Excellent corrosion resistance, suitable for use in humid environments;
Good cutting performance, but the material is soft and easy to stick to the knife.
2) Common materials:
T2 pure copper: suitable for electrical connectors;
H62 brass: moderate mechanical strength, widely used in valve joints and other structural parts;
Tin bronze: strong wear resistance, suitable for sliding parts.
(5) Titanium alloys
Titanium alloys play an important role in aerospace, medical equipment, high-end manufacturing and other fields due to their excellent comprehensive properties, especially for parts with extremely high requirements for strength, weight and corrosion resistance.
1) Performance characteristics:
High specific strength: Titanium alloy has a very high strength-to-weight ratio, and its tensile strength can reach more than 800 MPa, but its density is only about 60% of that of steel, which can significantly reduce the weight of structural parts;
Good corrosion resistance: It is easy to form a stable oxide film on the surface, and it has excellent corrosion resistance in seawater, acid-base environment and various chemical media;
Good high temperature performance: It can maintain good mechanical properties within 400°C, and some high-temperature titanium alloys still have application value at 600°C;
Non-magnetic and good biocompatibility: Titanium alloy is non-magnetic, will not interfere with equipment such as magnetic resonance imaging, and is non-toxic to the human body. It is widely used in the field of medical implants;
Low thermal conductivity and high tendency to work hardening: Although this brings certain difficulties to its processing, it also makes it advantageous in certain thermal isolation applications.
2) Commonly used titanium alloy grades:
TC4 (Ti-6Al-4V): The most commonly used α+β type titanium alloy, which has strength, toughness and corrosion resistance, and is suitable for high-load parts such as aviation structural parts and fasteners;
TA2 (industrial pure titanium): Good plasticity and extremely high corrosion resistance, but low strength, suitable for low-load corrosion-resistant parts, such as chemical equipment and heat exchangers;
Ti-6Al-7Nb: While maintaining high strength, it has excellent biocompatibility and is a representative of implant-grade medical materials;
Ti-6242 (Ti-6Al-2Sn-4Zr-2Mo): A high-temperature titanium alloy suitable for aviation engine parts that work for a long time at 500~600°C.
3. Introduction to common machining processes
Machining technology is the whole process of transforming raw materials into parts with structure and functionality, usually relying on CNC equipment to complete high-precision cutting. The main processes are as follows:
(1) Turning process: the core forming technology of rotating parts
1) Definition:
The process of machining rotating surfaces such as outer circles, inner holes, end faces, and threads by rotating the workpiece and feeding the tool along the axis/radius.
2) Classification:
Horizontal turning: general-purpose equipment, suitable for long-axis parts (such as motor shafts), with a processing length of more than 5 meters.
Vertical turning: vertical spindle design, used for disc parts (such as flanges), with a maximum processing diameter of 3 meters.
CNC turning: integrated CNC system, supports complex curve processing (such as crankshaft neck), and positioning accuracy of ±0.001mm.
3) Typical applications and accuracy
Application scenarios: rough and fine machining of shafts (accounting for 70%) and sleeve parts, such as automobile engine crankshafts and bearing rings.
Accuracy range: dimensional accuracy IT6-IT11, surface roughness Ra1.6-Ra12.5, precision turning can reach less than Ra0.8.
(2) Milling process: the main processing force for complex planes and cavities
1) Definition:
The process of using rotary milling cutters (end mills, end mills, forming milling cutters) to process planes, grooves, and cavities on workpieces.
2) Classification:
End milling: Cutting with the end face blade, used for plane processing (flatness ≤ 0.02mm/100mm).
Peripheral milling: Cutting with the cylindrical blade, used for groove and contour processing (such as gear box housing grooves).
High-speed milling: spindle speed > 10000rpm, directly processing mold cavities (Ra1.6 or less, reducing polishing processes).
3) Typical applications and precision
Application scenarios: end faces of disk parts (such as gear disks), planes and cavities of shell parts (such as pump body flow channels), accounting for more than 60% of complex parts processing processes.
Precision range: dimensional accuracy IT8-IT12, surface roughness Ra3.2-Ra25, precision milling can reach IT6 level (such as aerospace structural parts).
(3) Drilling process: basic process of hole processing
1) Definition:
The process of processing through holes, blind holes and stepped holes on the workpiece by rotating the drill bit + axial feed.
2) Classification:
Ordinary drilling: Processing shallow holes (hole depth ≤ 3 times the diameter), using high-speed steel drill bits (speed 500-2000rpm).
Deep hole drilling: Processing deep holes (hole depth ≥ 5 times the diameter), using BTA drill/gun drill, combined with high-pressure cutting fluid chip removal (pressure 3-5MPa).
CNC drilling: Realize high-precision positioning of the hole system on the machining center (coordinate accuracy ±0.02mm).
3) Typical applications and accuracy
Application scenarios: Flange bolt holes (accounting for 80%), box connection holes, which are the key basic processes for parts assembly.
Accuracy range: dimensional accuracy IT10-IT14, surface roughness Ra12.5-Ra25, subsequent expansion/reaming is required to improve accuracy (up to IT7 level).
(4) Grinding process: the ultimate means of processing precision surfaces
1) Definition:
The process of using high-speed rotating grinding tools (grinding wheels, grinding belts, grinding stones) to remove trace amounts of workpiece surfaces to achieve high-precision processing.
2) Classification:
External cylindrical grinding: machining the outer circle of shafts (roundness ≤ 0.001mm, such as bearing raceways).
Surface grinding: machining precision planes (flatness ≤ 0.002mm/100mm, such as gauge reference surfaces).
Internal cylindrical grinding: machining the inner surface of deep holes (cylindricity ≤ 0.003mm, such as hydraulic sleeves).
3) Typical applications and precision
Application scenarios: Finishing of parts after quenching (accounting for 90%), such as gear tooth surfaces (precision IT5 level) and guide rail surfaces (straightness ≤ 0.005mm/m).
Precision range: Dimensional accuracy IT5-IT7, surface roughness Ra0.1-Ra1.6, ultra-precision grinding can reach Ra0.025 or less (mirror level).
(5) Multi-axis linkage processing: Breaking through the limitations of three-dimensional surface processing
1) Definition:
Through the linkage of the coordinate axes of CNC machine tools with more than 3 axes (commonly 4/5 axes), the spatial posture adjustment of the tool relative to the workpiece is achieved, and the technology of processing complex surfaces is realized.
2) Core advantages:
One-time clamping and molding: Avoid multiple clamping errors and improve the processing accuracy by 30% (such as the surface error of aviation blades ≤ 0.02mm).
No processing blind spot: 5-axis machine tools (X/Y/Z linear axes + A/C rotary axes) can process structures such as undercuts and deep cavities that traditional 3-axis machines cannot reach.
Efficiency improvement: The processing time is shortened by more than 50% compared with 3 axes (such as mold core processing is reduced from 48 hours to 20 hours).
3) Typical machined parts
Aerospace: engine blades, integral blade disks
Automotive molds: cover mold profiles
Precision medical: artificial joint ball heads
(6) Turning and milling: full process integration of rotating parts
1) Definition:
A technology that integrates turning, milling, drilling, tapping and other functions on a single device to complete the processing of complex rotating parts in one clamping.
2) Core functions:
Turning module: Processing of outer circles, inner holes, threads (such as shaft body molding).
Milling module: Processing of radial holes, planes, curved surfaces (such as keyways and eccentric structures on shafts).
Linkage function: Through the linkage of the C axis (spindle indexing) and the X/Y axis, spiral grooves, eccentric holes and other processing (such as screw pump rotors) can be realized.
3) Typical machined parts and advantages
Aerospace: Integral impeller (blade + hub integrated processing), the process is reduced from 32 to 12, and the geometric tolerance is controlled within 0.01mm.
Medical devices: joint prosthesis (ball head + handle formed in one step), surface roughness Ra0.1, avoiding positioning errors caused by multiple clamping.
4. Summary
The quality of machined parts depends not only on the equipment and process level, but also on the preliminary design. Whether the structure is easy to process, whether the material is easy to cut, and whether the size and tolerance are set reasonably will directly affect the manufacturing cost and delivery cycle.
Therefore, it is an important strategy of modern efficient manufacturing system to introduce the concept of process collaboration from the part design stage, optimize the structure with processing engineers, and select suitable materials and processing technology.
Under the industrial trend of "high precision, low cost, and fast delivery", a deep understanding of the core knowledge of machined parts will help enterprises stand out in fierce competition.
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