Machining and CNC milling is one of the most popular methods of manufacturing custom parts and prototypes. The process of computer numerical control is characterized by a high degree of automation and surpasses other traditional manufacturing processes in terms of speed, efficiency, and production precision. Choosing the right material for a CNC machining project can seem like a challenge, involving many factors to consider, including mechanical properties, cost, durability, weight, machinability, corrosion resistance, and surface finish. This machining is compatible with hundreds of metal materials, with stainless steel and aluminum being the most popular materials for custom parts and prototypes. How does aluminum machining differ from steel machining? What mechanical properties do both products have? What is the degree of hardening of the material machined using CNC? We write about all this below.
Aluminum and Steel - Overview
Aluminum and stainless steel have a similar appearance and are versatile, and products made from these two materials can be found everywhere around us. Stainless steel is used in everything from kitchenware and consumer goods to construction, and even medical equipment, ships, and much more. Aluminum is lightweight and widely used in sports equipment, bicycles, automotive and aviation. So how do you distinguish these two most popular metals? What is better for your CNC machining project, stainless steel or aluminum milling? Today we will analyze the difference between these two metals in various respects to help you choose a more suitable material.
Function of materials
Aluminum is preferred in consumer electronics projects due to its delicate texture and versatility. Producing countries are currently replacing steel and plastics with this material. Both of these materials are used to manufacture products. If you are buying a product for long-term consumption, such as jewelry, at some point you will need to understand the difference between these materials. If you have never bought an item made of machined aluminum or steel, you probably won't notice the most significant difference at first.
Stainless steel and aluminum: composition of elements and properties of alloys
The elemental composition of materials is crucial for CNC machining projects, as it can significantly affect hardness, corrosion resistance, durability, and strength. Stainless steel is an iron alloy that contains at least 10.5% chromium, and other elements include aluminum, silicon, sulfur, nickel, selenium, molybdenum, nitrogen, titanium, copper, niobium, etc., which account for about 0.03% -1%. The presence of chromium determines the excellent parameters of stainless steel in terms of heat resistance and overall corrosion resistance. The elements contained in aluminum are: aluminum, silicon, zinc, magnesium, manganese, copper, iron, titanium, chromium, zirconium, etc.
Stainless Steel and Aluminum: Corrosion Resistance
Since stainless steel contains chromium, iron, nickel, and other components, it means that stainless steel has excellent corrosion resistance. Chromium forms a passive protective layer on the surface, which has a self-healing function. Aluminum has excellent corrosion resistance because it has a protective oxide layer on its surface, which prevents rust and other forms of corrosion.
Stainless steel vs aluminum: conductivity
Copper is used as a standard of conductivity. This is due to the fact that it has a conductivity of 100%. Using copper as a reference for this element, it can be indicated that aluminum conducts 61% and is about 30% lighter than it. The electrical conductivity of stainless steel is 3.5% of copper conductivity, making it a poor conductor of electricity. Aluminum is the ideal material if electrical conductivity is a priority in a CNC machining project. In fact, aluminum is also the first choice for transmitting electrical energy and high-voltage cables over long distances.
Thermal Conductivity
Thermal conductivity is a fundamental factor considered in the case of non-standard prototypes of parts or radiators. For this reason, aluminum is often the ideal material for air conditioners or heaters. It has a thermal conductivity of 1460 BTU-in/hr-ft²-°F (210 W/mK), making it better than stainless steel, but it has a lower melting point and softens above 400 degrees Celsius. Stainless steel is also thermally conductive, which makes it better suited for working at high temperatures.
Melting Temperatures
The thermal properties of a material are very important in CNC machining projects. Parts operate at high temperatures, and if they reach this critical point, they will change from a solid to a liquid state, losing their function. Materials with lower melting temperatures are better suited for pressure casting or extrusion. The maximum temperature of stainless steel varies depending on the alloying elements and is about 1230°C to 1530°C. Machining aluminum is a process in which the product has a relatively low melting temperature - about 660.37 ° C. This means that stainless steel is more preferred over aluminum if heat resistance is the main factor considered in the CNC machining project.
Material hardness
The hardness of metal refers to the action on the surface of the metal by analyzing stresses, deformations, indentations, and scratches. The Brinell scale is often used as an indicator of material hardness. The hardness of stainless steel varies depending on the alloying elements. Its average on the Brinell scale ranges from 80 to 600, indicating that stainless steel has high hardness and is difficult to form. On this scale, aluminum is set at about 15H, which means it is relatively soft. Stainless steel is the ideal choice if hardness is the main factor in a CNC machining project.
Stainless steel versus aluminum: weight
Aluminum has a density of about 2.7 g/cm3, while stainless steel has 8.0 g/cm3. The same volume of stainless steel is about three times heavier than aluminum, so aluminum comes out as a significantly lighter material than stainless steel. Lightweight aluminum is widely used in airplanes, ships, construction, and other fields of application.
Stainless Steel vs Aluminum: Durability
Both stainless steel and aluminum offer excellent durability, however, the former material significantly surpasses its competitor. For this reason, stainless steel is often used in the production of parts for passenger and commercial vehicles. It is ideal if durability is the main concern in a CNC machining project.
Machinability - Stainless Steel or Aluminum?
The machinability of a material refers to the ease with which custom parts or prototypes can be manufactured by milling, CNC turning or stamping. Both stainless steel and aluminum are easier to process with CNC. Aluminum is softer and less hard, so CNC machining of aluminum is also relatively inexpensive. Comparing these two types of materials, stainless steel is about three times harder than aluminum in CNC machining, so if ease of cutting is the main factor in a CNC machining project, aluminum is better.
Stainless Steel vs. Aluminum in terms of Plasticity
Aluminum is softer, has a lower melting point, and is easier to shape than stainless steel. Steel is strong, does not warp or deform under stress, but aluminum is still the best choice if deformability is the main issue in your project.
Stainless Steel vs. Aluminum – Weldability Aspect
Both stainless steel and aluminum are considered easy to weld, but aluminum requires more knowledge and skills, and greater caution must be maintained during welding to avoid cracks.
Stainless steel and aluminum - yield strength limits
The yield strength is the stress at which a material begins to deform permanently. For stainless steel, it ranges from 25 MPa to 2500 MPa depending on the alloying elements. The yield strength of aluminum alloys ranges from 7 MPa to 11 MPa. Therefore, it is significantly higher in stainless steel than in aluminum.
Tensile Strength
The tensile strength of stainless steel ranges from 34.5 to 3100 MPa, while aluminum is 90 MPa, and for some aluminum alloys subjected to heat treatment, such as aluminum 7075, the tensile strength can be increased to over 690 MPa. It can be noticed that the range in this category for stainless steel is higher than for aluminum. This means that milling aluminum is performed with less tension.
Shear Strength
Shear strength refers to the resistance of a material to shearing loads. For stainless steel, it ranges from 74.5 to 597 MPa, and for aluminum from 85 to 435 MPa, which is why stainless steel, due to its higher shear strength, is a more preferred material than aluminum.
Production Costs
Stainless steel and aluminum exhibit different properties due to various alloying elements, including many types such as martensitic stainless steel, ferritic stainless steel, duplex stainless steel, austenitic stainless steel, hammer hardening, etc. Generally speaking, the CNC machining costs of stainless steel are higher than those of aluminum.
Summary
Aluminum and steel are often confused with each other. This leads people to believe that one material is better than the other, when they are very different products. Machined aluminum is a natural form of aluminum that has been developed for use in airplanes and spacecraft. It is significantly stronger and lighter than regular aluminum. The most common uses of this material include the production of parts for consumer electronics, including computer cases and spacecraft parts. While some consider machined aluminum to be a breakthrough in the steel industry, both materials differ significantly in terms of properties. Stainless steel is heavier, more durable, but harder to process. Both products are great, but each should be used for its individual characteristics to perform a specific task. When working on stainless steel, copper processing, or stainless steel, proper chip removal and an acceptable large linear expansion coefficient are also important. Our company provides milling services helpful in machine construction or aluminum processing.