In a machining project, the choice of machined metal directly determines the success or failure, cost and service life of the project. The strength, corrosion resistance, processing difficulty and other characteristics of different metal materials vary greatly, and blind selection will not only increase processing costs, but may also lead to products not meeting the needs of working conditions. This article will dismantle the selection logic of machined metals from the three core dimensions of metal type cognition, project demand matching, and processing technology adaptation, and help you accurately select the metal materials suitable for the project based on real cases and data comparison.
1. Introduction
Machined metal is the basic material for various industrial projects, widely used in automobile manufacturing, aerospace, electronic equipment, construction machinery and other fields. According to industry statistics, about 40% of machining project failures are due to improper selection of metal materials, such as misuse of ordinary steel in corrosive environments leading to premature failure of parts, or the use of high-density metals to increase product weight in lightweight demand. Therefore, mastering the scientific machined metal selection method is the key prerequisite for improving project reliability and controlling costs.
2. Understand the different types of machined metals
2.1 Aluminum alloy
Aluminum alloy is based on aluminum, with magnesium, silicon and other alloying elements, and its core characteristics are low density (2.7g/cm³, only 35% of steel), excellent machinability, and good corrosion resistance. Its advantages are significant lightweight effect, low tool wear and high efficiency during processing; The disadvantage is that the strength is relatively low, and the performance is easy to decay in high temperature environments. Applicable scenarios: Aviation parts, automobile body structural parts, electronic equipment shells and other projects with high lightweight requirements. Case: A new energy vehicle manufacturer chose 6061 aluminum alloy to process the battery pack bracket, which reduced the weight by 42% compared with steel, while increasing the processing efficiency by 30% and reducing the unit cost by 25%.
2.2 Stainless steel
Stainless steel has a chromium content of ≥ 10.5%, has excellent corrosion resistance and oxidation resistance, and can be divided into three categories according to its structure (such as 304, 316), ferrite and martensitic. Among them, 304 stainless steel is the most widely used, with good corrosion resistance and medium machinability; 316 stainless steel adds molybdenum element, which has better resistance to salt spray and high temperature, but the cost is higher. The advantages are long service life and low maintenance costs; The disadvantage is that it is difficult to process, easy to stick to the knife, and the processing cost is higher than that of ordinary steel. Applicable scenarios: food machinery, chemical equipment, marine engineering and other corrosive environmental projects.
2.3 Steel
Steel is the most widely used metal in machining, which can be divided into low-carbon steel, medium-carbon steel, and high-carbon steel according to carbon content, and carbon steel and alloy steel (such as 40Cr, 20CrMnTi) according to alloy content. The core characteristics are high strength, good toughness, low cost, and processability decreases with the increase of carbon content. No. 45 medium carbon steel has moderate strength and good machinability, which is suitable for ordinary mechanical parts; 40Cr alloy steel has greatly improved its strength after quenching and tempering treatment, making it suitable for heavy-duty parts. The advantage is that it is cost-effective and has a wide range of applications; The disadvantages are high density (7.85g/cm³) and poor corrosion resistance, which requires subsequent anti-rust treatment. Applicable scenarios: construction machinery drive shafts, machine tool spindles, ordinary mechanical gears and other projects.
2.4 Copper and its alloys
Copper and its alloys (such as brass and bronze) have excellent electrical conductivity, thermal conductivity and corrosion resistance, and have good machinability. Brass (copper-zinc alloy) has a lower cost and is suitable for batch processing; Bronze (copper-tin alloy) has high strength and good wear resistance, making it suitable for wear-resistant parts. The advantage is outstanding electrical and thermal conductivity; The disadvantages are high density (8.9g/cm³) and higher cost than steel and aluminum alloys. Applicable scenarios: electrical components, heat dissipation components, pipeline valves and other items. Case: An electronic equipment manufacturer chooses copper processing heat sinks, which have a thermal conductivity 60% higher than aluminum alloy to ensure the heat dissipation needs of long-term operation of equipment.
2.5 Special alloys
Special alloys include titanium alloys, superalloys, cemented carbides, etc., designed for special working conditions. Titanium alloy has high strength, low density and excellent corrosion resistance, but it is extremely difficult to process and extremely costly; Superalloys can maintain stable performance in high-temperature environments above 600°C, making them suitable for aerospace engine projects. The advantage is that it can meet the needs of extreme working conditions; The disadvantage is high processing cost and long cycle time, which is only suitable for high-end precision projects. Applicable scenarios: special needs projects such as aerospace, medical devices, and high-end equipment.
3. Consider project needs
3.1 Strength and durability requirements
First of all, it is necessary to clarify the requirements of the project for metal strength, and screen materials through tensile strength, yield strength and other indicators. For example, the drive shaft of heavy-duty construction machinery needs to withstand large torque, and 40Cr alloy steel (tensile strength ≥980MPa) should be selected; while the bracket of ordinary electronic equipment only needs to bear light load, and 6061 aluminum alloy (tensile strength ≥205MPa) can be selected. At the same time, durability needs to be considered, and long-term high-frequency vibration parts should choose materials with good toughness to avoid fatigue and fracture.
3.2 Influence of weight and density
Weight-sensitive projects (such as aviation and new energy vehicles) need to give priority to low-density materials. Data comparison: Under the same volume, aluminum alloy parts weigh 65% lighter than steel, and titanium alloy is 43% lighter than steel. Case: A drone project initially used steel to process the propeller shaft, with a battery life of only 20 minutes, and the weight was reduced by 50% after replacing it with titanium alloy, and the battery life was increased to 35 minutes. Non-weight-sensitive projects (such as fixed mechanical bases) can be made of high-density steel to ensure stability.
3.3 Corrosion and heat resistance
Judge the corrosion resistance and heat resistance requirements according to the environment of the project: 316 stainless steel or aluminum alloy is selected for humid and acid-alkali environments; Priority should be given to salt spray-resistant materials such as Hastelloy for marine environments. High-temperature environments (such as engine perimeter) are used for superalloys. If environmental factors are ignored, the service life of ordinary steel in a humid environment is less than 1 year, while 304 stainless steel can be extended to more than 10 years.
3.4 Cost-benefit analysis
It is necessary to balance material costs with project value to avoid excessive material selection. Ordinary civil projects give priority to low-cost materials such as steel and aluminum alloys; Special alloys can be selected for high-end precision projects according to needs. Data reference: The cost of titanium alloy material is 15-20 times that of steel, and 316 stainless steel is 1.5 times that of 304 stainless steel. Case: A civil pipeline project chose 304 stainless steel instead of 316 stainless steel, which reduced material costs by 30% under the premise of meeting the demand for corrosion resistance.
4. Processing technology and technology
4.1 Common machining methods
Different machining methods have different adaptability to metals, and the core processing methods include: turning, milling, grinding, EDM, etc. Turning and milling are suitable for aluminum alloys, steel, and brass with good machinability; grinding stainless steel and alloy steel suitable for high-precision requirements; EDM is suitable for special alloys that are difficult to machine.
4.2 Adaptability of different metals to processing processes
The processing adaptability of various metals varies significantly, and the specific adaptation relationship is as follows:
| Metal type | Adapt to the processing process | Processing difficulties and precautions |
| Aluminum alloy | turning, milling, stamping | It is easy to produce edges, so it is necessary to use sharp tools and optimize cutting parameters |
| Stainless steel | Turning, grinding, laser processing | High cutting temperature and easy to stick knives, it is necessary to choose coated tools and strengthen cooling |
| steel | turning, milling, grinding | High carbon steel processing is easy to break, and the cutting speed needs to be controlled |
| Special alloys | EDM, laser processing | The processing efficiency is low, and professional equipment and process parameters are required |
4.3 Requirements for precision and surface treatment
For high-precision projects (such as precision instrument parts), it is necessary to choose materials that are easy to process and have good stability, such as No. 45 steel and 6061 aluminum alloy, which can achieve accuracy within 0.005mm with the grinding process. The surface treatment needs to match the material characteristics, steel can be electroplated and painted to prevent rust, aluminum alloys can be anodized to improve wear resistance, and stainless steel usually does not require additional surface treatment. Case: A precision bearing project uses GCr15 bearing steel, which has a surface roughness of Ra0.025μm after grinding to meet the accuracy requirements of high-speed rotation.
5. Conclusion
Choosing the right machined metal needs to follow the matching logic of "material properties-project requirements-processing technology": first clarify the core requirements such as strength, weight, and corrosion resistance of the project, then screen the metal type accordingly, and finally optimize the selection based on the adaptability of the processing process. Ordinary projects give priority to cost performance, and choose steel and aluminum alloys; Special working conditions require targeted selection of stainless steel and special alloys, while balancing processing costs and cycles. Reasonable material selection not only improves product quality and service life, but also maximizes project benefits.
As a company focusing on precision machining technology, we believe that the core of machined metal selection is "precise matching" rather than "the higher the better". The misunderstanding of material selection in most projects is excessive pursuit of high performance, ignoring cost and processing feasibility. It is recommended that the core working condition indicators be clarified in the early stage of the project, and the material adaptability is verified through small-batch trial processing; In the future, with the increase in demand for high-end equipment, the processing cost of special materials such as titanium alloys and superalloys will gradually decrease, and their application scenarios will be further expanded.
FAQ
1. In civil projects, considering cost and corrosion resistance, which machining metal is the most suitable? Prefer 304 stainless steel or 6061 aluminum alloy. 304 stainless steel has good corrosion resistance, low maintenance cost, and is suitable for humid environments; The cost of 6061 aluminum alloy is close to that of 304 stainless steel, lighter in weight, suitable for lightweight needs, both of which are less difficult to process and suitable for conventional processing technology.
2. Which special alloy should be chosen for mechanical parts in a high-temperature environment (800°C)? It is recommended to choose Inconel 718 superalloy, which can maintain excellent strength and oxidation resistance in an environment of 800°C, and is the mainstream material in the field of aerospace and high-end engines. It needs to be combined with EDM or laser processing technology to ensure the processing accuracy.
3. How to choose between aluminum alloy and steel under the same strength requirements? If the project has lightweight needs (such as transportation, drones), choose high-strength aluminum alloy (such as 7075 aluminum alloy), although the cost is higher than steel, it can significantly reduce weight; If there is no weight limit, 40Cr alloy steel is preferred, which has lower cost and more mature processing technology.
4. How to control the processing cost of special alloys that are difficult to process? First, optimize the processing process, adopt "rough machining + semi-finishing + finishing" segmented processing to reduce the margin of high-precision machining links; second, choose professional coating tools to improve the service life of tools; The third is to share the cost of equipment commissioning in batch processing to avoid the cost increase caused by small-batch customization.
