Steel is becoming the mainstay material in CNC machining because of its unmatched strength and durability. It is used across manufacturing industries to produce high-quality parts. However, many steel grades are used in product development. Choosing the right one can be challenging with the numerous options available. You must carefully go about the selection process, as using the wrong materials will not produce the desired results.
This article will guide you through the selection process. It will explain the common steel grades available for CNC machining and guide how to choose the perfect steel for specific applications.
Why is Steel a Common Choice for CNC Machining
Steel is one of the most widely used materials in CNC machining. It is usually the first choice alloy in modern manufacturing industries because of many reasons. Some of these reasons are
- Steel has a high strength and durability. It can withstand mechanical stress and extreme environmental conditions.
- There are many grades of steel alloy you can choose from to meet your specific requirements.
- Most steel grades are easily cut and machined into complex shapes and designs.
- You can easily heat-treat steel alloys using annealing, tempering, and carburizing techniques. This action helps enhance strength and wear resistance.
- Steel is relatively affordable and widely available. It comes in different forms, including sheets, bars, and tubes.
- Additionally, CNC machined steel components are highly resistant to wear, impact and abrasion.
- Steel is compatible with standard surface finishing techniques. For improved protection and corrosion, you can plate, powder coat, and anodize steel.
Common Steel Alloys Used in CNC Machining
While steel remains invaluable in CNC machining because of its durability and versatility, you should know that not all steel grades are the same. Below is an extensive discussion of six common CNC machining steel categories.
Stainless Steel
Stainless steel is popular for its aesthetic appeal and high strength. This alloy contains a minimum of 10.5% chromium content. This element forms a protective oxide layer when stainless steel is exposed to corrosive substances. The major downside of stainless steel is its toughness and work-hardening tendency, which makes machining challenging. Standard stainless steel grades for CNC machining include 303, 304, and 316.
Carbon Steel
Another type of steel alloy used in CNC machining is carbon steel. This material is made of iron and carbon, with trace amounts of other elements. Carbon steel, especially low carbon grades, is easy to machine. Additionally, they are affordable and have a good strength-to-weight ratio. Examples of applications where carbon steel thrives include cutting tools, gears, and fasteners.
Spring Steel
Spring steel is a high-carbon steel known for its high elasticity and fatigue resistance. This steel alloy, including 65Mn and 60Si2Mn, does not deform under stress and returns to its original shape after stretching. Furthermore, spring steel is strong and wear-resistant. However, you should consider heat-treating spring steel for easier machining and better mechanical properties.
Mold Steel
The use of mold steel in CNC machining is nothing new. As the name implies, they are reserved for fabricating injection molds and stamping dies. Mold steel such as P20, S136, and 718 have excellent toughness and high heat resistance. They can withstand repeated thermal cycles without breaking down. Because of the hardness of mold steel, carbide-coated tools are used to get the best results.
Tool Steel
Tool steel is a popular material for CNC machining for many reasons. It is of high strength and can withstand impact and shock. When used as tools like knife blades, punches, and dies, tool steel has the ability to remain sharp after prolonged use. However, it needs a lot of cutting forces to machine and proper cooling after processing. Standard tool steel grades for CNC machining include M2, H11, and H13.
Alloy Structural Steel
Another category of CNC machining steel is alloy structural steel. It contains other elements such as molybdenum, chromium and nickel to enhance its properties. Examples of alloy structural steel grades include 40Cr, 35CrMo, and 42CrMo. They are versatile and have an excellent strength-to-weight ratio.
Factors to Consider When Choosing Steel for CNC Machining
Now that you are familiar with the common CNC machining steel grades available, you have to choose the best for your project. There is no straightforward approach to this as you must consider some factors. Let’s discuss six crucial factors to consider.
Machinability
Ease of machinability is key when selecting a steel grade. It determines how easily you can cut, shape, and finish steel using CNC machines. Low-carbon steel is generally easier to machine than those with high-carbon content. The alloying elements also matter. The presence of sulfur and lead improves machinability. On the other hand, nickel and chromium reduce machinability. You can enhance machinability by optimizing feed rates and using proper lubrication.
Strength and Hardness Requirements
You should also consider the strength and hardness needs of your project. Different applications demand unique strength and hardness levels. Key metrics to look for include yield strength, tensile strength, and hardness. Steel with high strength resists mechanical stress. Hence, they are ideal for automotive and aerospace applications. However, there should be a balance when it comes to hardness. Tough steel grades may be challenging to machine.
Corrosion Resistance
Another factor to look out for is corrosion resistance. It determines how well the machined parts can withstand degradation as a result of chemicals and moisture. Corrosion resistance is essential in medical and food processing industries. The ability of steel to resist corrosion largely depends on the elemental content. Those with a high percentage of chromium resist oxidation and rusting.
Wear and Impact Resistance
Wear and impact resistance matter in CNC machining. Using wear-resistant materials prolongs the lifespan of components under friction. Impact-resistant steel absorbs shock and prevents damage. You increase wear and impact resistance when you heat treat by quenching and tempering. You can also apply coatings like titanium nitride for better toughness.
Surface Finishing and Coating Compatibility
Always look out for surface finishing and coating compatibility when choosing the ideal steel alloy for your part. This is because the ‘as machined’ finish may not be sufficient for aesthetics and performance. Surface finishes improve appearance and functionality. You have to be sure the steel grade can accept the coatings you want.
Cost and Availability
You should also make sure the grade you go for matches your budget. The cost of steel differs. High-performance ones like stainless and tool steel are more expensive than carbon steel. However, you don’t always have to choose the most cost-effective material. Always find the performance vs. cost balance.
Tips for Optimizing CNC Machining of Steel
Steel CNC machining may present some unique challenges because of the nature of this material. Keep in mind the following tips for optimizing the CNC machining of steel.
Choose the Right Cutting Tools
The tool type you use will determine the machining result. The wrong tool material or coating will lead to inefficient machining and chipping. The best tool materials for steel CNC machining are cemented carbide, cobalt, and ceramic. You can also go for those coated with titanium nitride or aluminum titanium nitride to reduce friction and increase tool life.
Optimize Machining Parameters
You should also adjust important machining parameters based on the particular steel grade you are working with. Optimize cutting speeds and feed rates to prevent excessive heat and poor surface finish. Additionally, you should adjust these parameters based on tool wear signs. Reduce speed and increase feed if burning occurs.
Prioritize Coolant and Lubrication
Steel CNC machining tends to generate heat which causes thermal expansion and work hardening. For this reason, you have to use proper cooling and lubrication systems to dissipate heat and clear chips. Invest in high-quality coolants to reduce built-up edge. Additionally, check coolant flow regularly to prevent contamination.
Optimize Tool Paths and Chip Evacuation
In all you do, optimize tool paths and chip evacuation. To do this, use adaptive clearing strategies and reduce tool engagement angles. This will prevent excessive cutting forces. For chip control, use chip breakers to aid evacuation. You should also slightly increase the feed rate to remove chips easily.
Conclusion
Choosing the correct steel grade is a critical decision as it impacts the success of your project. The most common steel alloys are stainless steel, carbon steel, and tool steel. You have to consider important factors such as machinability, corrosion resistance requirements, and costs. Using the best alloy reduces production costs and improves machining efficiency. Additionally, you can be sure of enhanced product quality and performance.
