What can go wrong when using a CNC machine to cut stainless steel? While the metal is very useful, thanks to how strong and rust-resistant it is, it can be tricky to cut with a metal CNC machine. It’s easy for defects to happen that mess up the parts.
There are a number of issues that manufacturers face when CNC machining stainless steel. Chips getting stuck, breaking of tools, and poor surface finishes are some of the most common defects to deal with. So, if you know what to watch out for, they can be avoided.
We’ll share some tips for troubleshooting and making adjustments to eliminate common defects. With the right settings and strategies, your stainless steel parts can come out just as you intended every time. Keep reading to learn about machining stainless steel with CNC.
What is CNC Machining Stainless Steel?
CNC machining has become a very common way to work with metals, like stainless steel, in precision machining services. CNC involves using a computer to guide a tool as it cuts and forms raw materials into custom parts and prototypes. The automated process is much faster and more precise than doing things by hand.
Stainless steel has certain physical qualities that make it well-suited for this type of machining. It is strong and durable, with excellent corrosion resistance. For these reasons, products made from this metal last a long time, even in harsh conditions.
The machinability of stainless steel is also good, since you can cut and shape it easily. It holds its form well during the machining process. Also, its high formability allows for forming or bending into many different shapes as needed for a design.
Some additional advantages of using stainless steel for CNC machining include:
- Homogeneous material structure: The metal can be machined consistently for its uniform composition.
- Weldability: Stainless steel can be easily joined to itself through welding for assemblies.
- High ductility: It can stretch or deform without breaking during machining or forming.
- Variety of finishes: CNC allows different surface appearances of the metal, including shiny, brushed, and textured.
The strength, durability, and versatility that stainless steel provides have made it a top choice for precision CNC machining parts in many industries like medical, aerospace, and automotive.
Causes and Solutions of CNC Machining Stainless Steel Defects
Stainless steel can harden or deform at the time of CNC milling, drilling or cutting. As a result, the production does not turn out what you intended it to be. What works instead?
We’ve discussed the causes and solutions of some CNC machining stainless steel defects:
a. Machine Vibration (or Tool Chatter)
Machine vibration (or chatter) during operation can seriously harm your workpiece and tools. It happens when the cutting tool moves back and forth quickly against the workpiece, causing waves on the machined surface. Such erratic movements can damage the parts involved.
Stainless steel tends to cause more vibration than other metals because of its toughness. As the tool cuts into it, the stiffness and strength of the steel may make the tool chatter more.
Causes
Worn out or loose parts, like tool holders, cutters, and mounting components, cause the vibration to start. Stainless steel is difficult on tools, so it can degrade their condition faster.
Solutions
To prevent vibration, make sure all the connections between the tool and tool holder are tight. Check them regularly for looseness. Also, firmly clamp the workpiece, so it doesn’t move during cutting.
A secure setup prevents any play or shaking that leads to chatter. Proper speed and feed settings for the material being cut also help eliminate vibration issues.
b. Work Hardening
Work hardening occurs when the cutting tool applies heat and pressure to the material during the machining process. It causes the stainless steel to harden more in the areas that have been cut.
As it hardens, it becomes more challenging for the cutting tool to remove additional material. This leads to increased tool wear, lower cutting speeds, and a rougher surface finish on the workpiece.
Causes
Heat generated from cutting is one reason for work hardening. During the operation, friction and pressure cause stainless steel to heat up. The extra heat distorts the metal’s crystal structure, making it harder.
The alloying elements in stainless steel also play a role. What gives the metal its corrosion resistance makes it more prone to work hardening. Austenitic and duplex grades contain more alloying, like chromium and nickel, which stabilize the steel’s austenite phase at room temperature. This phase is more vulnerable to distortion from heat during machining.
Tool wear is another culprit. When cutting tools become dull or damaged, they put more pressure on the metal and generate more friction heat. The extra stress hardens the surface.
Taking deep cuts too fast can also harden stainless steel. The tool may labor excessively or ride the edge of the material.
Solutions
One way to reduce work hardening is to use cutting tools made of carbide or ceramic. These materials have a higher heat resistance and hardness than other tool materials. They stay sharp longer when machining stainless steel.
Using coolant is also effective at preventing work hardening. The coolant washes away metal chips and cools the cutting zone, which reduces the generated heat.
Maintaining a consistent depth of cut can help as well. Shallow cuts mean less overall friction and heat at the tool-workpiece interface.
Replacing worn tools promptly is also important to minimize work hardening and run the machining stainless steel with CNC smoothly.
c. Fume and Dust Generation
CNC machining stainless steel releases fumes and loads of tiny particles. As the tool cuts into the metal, very small pieces break off in a process called chip formation. If these chips and broken-off particles aren’t contained properly, they can float around the work area as dust or rise into the air as fumes.
Causes
Lack of lubrication at the tool-workpiece interface is the main cause of fume and dust generation.
Stainless steel has low thermal conductivity, which means heat from cutting the metal doesn’t dissipate easily. Without proper lubrication, the heat can cause chips and dust to cling to the material and tool. The friction and heat also accelerate tool wear.
Solutions
To reduce fume and dust issues, you must use lubricants. The fluids help carry chips away from the cutting edge and prevent material from building up. They also transfer heat away so it doesn’t promote dust or damage tools as quickly.
Specifically for stainless steel, soluble oil-based coolants work well because their soapy nature attracts and suspends small chips and particles.
d. Tool Breakage
Tool breakage happens when the tool you use to cut stainless steel snaps or chips off during machining. It’s never good when your tool breaks since it slows down work and can damage expensive parts.
Causes
There are a few main things that cause tools to break when cutting stainless steel:
- Stainless steel is very hard, so it puts a lot of pressure on tools during machining. This stress can make tools snap if they’re not tough enough.
- Old tools aren’t as sharp, so they must use extra force to cut, which may make them break.
- Moving too fast during cuts also puts more strain on tools and causes them to break.
Solutions
You can use tougher carbide cutting tools designed for stainless steel. These are more durable. Also, keep your tools sharp, which will help them cut efficiently instead of forcing cuts.
To reduce putting pressure on the tools, take shallow cuts in multiple passes instead of going deep at once. Always machine at lower cutting speeds for stainless steel. And watch for uneven ramp angles. Keep ramps low and smooth to lower stresses.
e. Overheating
Stainless steel is a poor conductor of heat, so it doesn’t transfer heat very well. This means heat from cutting and grinding can get trapped in the steel instead of being conducted away, which causes overheating during the machining process.
Causes
Cutting with speeds that are too fast generates a lot of heat in a short amount of time. Plus, inadequate lubrication means that any heat generated has no way to be removed from the steel’s surface.
Also, tool wear can cause excess rubbing and friction that produces extra heat.
Solutions
To prevent overheating, you must cut with slower speeds and feed rates according to the manufacturer’s recommendations. And always use a cooling solution like flood coolant to flush heat away from the cutting area.
Don’t forget to monitor tool condition and replace worn or damaged ones. Sharp tools cut efficiently with minimal heat.
f. Chip Sticking
Chip sticking occurs when small metal chips adhere to or melt onto the cutting edges of tools during CNC machining of stainless steel. These chips can form tumors on the tool, negatively impacting the quality of machined parts.
Causes
Stainless steel has a higher melting point which allows chips to adhere better to hot tool surfaces. Also, its high work hardening nature makes chips want to squeeze together tightly rather than break off in long strings. This is especially problematic in internal holes where space is limited.
Solutions
To combat chip sticking, you can use a machine with chip breakers. They are special designs added to cutting tools (or milling cutters, to be specific) that help fracture long chips into shorter pieces before they can weld to the tool.
High-pressure coolant or direct air blasts also help to flush away chips immediately. Frequent tool changes are also needed with stainless since chips cause tools to wear down more quickly.
Conclusion
Stainless steel is a great choice for its strength and corrosion resistance, but machining it with CNC requires extra attention to avoid defects. You can follow our tips to avoid problems and get quality parts made exactly as planned. Taking the time to set up CNC machining of stainless steel correctly ensures a smooth process from start to finish.
Zintilon’s specialized CNC machining services for stainless steel can eliminate common defects through expertise and proven strategies. Contact us to discuss your project needs and get defect-free parts delivered on time.
