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CNC Milling for Metal Parts: Precision in Practice

Author: Yaozu Deng
Published on: 2023-10-19

“CNC milling transforms raw metal in to functional part or products with perfect accuracy. With the correct tools, parameters, consideration, and equipment, it delivers reliable, precise, and innovative results in metal shaping.”

The nuances of CNC milling for metal parts have become critical in industries to push boundaries toward complex and refined products. Think of that sleek car you admire, the aircraft flying in the skies, or even the tiny components in your mobile phone. What’s common? Precision. CNC milling makes it possible to craft metal parts with exceptional accuracy, shaping our modern world in countless ways. Did you know that many industries heavily rely on this method for their intricate designs and durable products?

This article will discuss CNC milling for metal parts, its advantages, and the intricate details of working with metals in CNC machining.

 

Interpretation of CNC Milling for Metal Parts

CNC milling is the embodiment of tech-driven craftsmanship. Through a computerized interface, a design is fed into the milling machine. This design serves as a blueprint, guiding the milling tool with extreme precision along multiple axes.

  • Three-Axis System: Basic movement in the X, Y, and Z directions.
  • Five-Axis Machines: Besides X, Y, and Z, this advanced system possesses two additional rotational axes, offering a broader range of movement and design capabilities.

CNC milling can shape various materials from metal & plastic to ceramics. However, we will only deal with metal CNC milling in this article. So, let’s see some of the l used metals in CNC milling.

Table: Common Metals in CNC Milling

Metal Attributes
Aluminum Lightweight, malleable, good conductor.
Stainless Steel Durable, rust-resistant.
Titanium High strength-to-weight ratio, non-corrosive.
Brass Decorative, good machinability, anti-corrosive.

Each metal interacts differently with the CNC milling based on its distinct properties such as hardness, malleability, ductility, and more (Collectively known as machinability in milling). For instance, the malleability of aluminum allows for swift and smooth milling, while the toughness of titanium requires specialized tools and settings.

Why Use CNC Milling for Metal Parts?

CNC milling of steel alloy

CNC milling emerges as the method of choice as tight tolerances and intricate designs become industry standards. CNC machines can materialize intricate components that might challenge manual methods With the ability to interpret and execute complex CAD (Computer-Aided Design) drawings. Furthermore, automation reduces human error, ensuring consistent outputs regardless of the production volume.

The Following are the Key Advantages of CNC Milling for Metal Parts:

  • Precision & Accuracy: The ability to achieve tight tolerances is often as precise as ±0.005 inches.
  • Repeatability: Consistent production of identical parts, even in large quantities.
  • Versatility: Suitable for various metals, from aluminum to tougher alloys like titanium.
  • Safety: Minimized manual intervention leads to reduced workplace accidents.
  • Scalability: Ideal for both small prototype batches and large-scale production runs.
  • Complexity: Can produce intricate and detailed parts which would be challenging manually.
  • Flexibility: Easily adapt to design changes without significant downtime.
  • Automation: Reduced need for manual checks with computer-controlled operations.
  • Cost-Effective: Long-term savings from reduced wastage and efficient production.
  • Sustainability: Environmentally friendly due to less material waste and energy consumption.
  • Integration: Can be seamlessly integrated with other manufacturing processes and systems.

 

Common Tools Used in CNC Milling for Metal Parts

Metal CNC milling owes its precision and versatility in part to a diverse array of tools. Each tool serves a distinct purpose, ensuring that a wide range of machining tasks can be achieved with utmost accuracy. As industries innovate, these tools are further refined to cater to specialized requirements.

Let’s take a look at some of the common milling tools for metal parts;

1. End Mills

CNC end mills for metal milling

End mills are perhaps the most commonly used and regarded as the workhorse of CNC milling. They come in various profiles, each suitable for a particular operation. Whether it’s slotting, profiling, or contouring, there’s an end mill designed to do the job. Their versatility extends to material suitability, making them ideal for metals ranging from soft aluminum to hard stainless steel.

2. Face Mills

45 and 90-degree face mills

For those tasks where a smooth finish is paramount, face mills step into the spotlight. They are designed to achieve flat surfaces with multiple cutting edges. Particularly for parts requiring a refined finish or those that need a flat mating surface, face mills are invaluable.

3. Ball Nose Mills

Ball nose end mill with four flute

Ball nose mills emerge as the go-to tool when intricate detailing or contouring is the task at hand. Their spherical tip allows for a degree of detailing that other tools might find challenging. Whether it’s 3D carving or producing specific radii in pockets, ball nose mills are the prime contenders.

  1. Drill Bits

Various CNC drill bits for metal milling

Drilling operations require drill bits quite expected, but these aren’t your ordinary bits in CNC milling. CNC drill bits are designed to produce exact holes with tight tolerances. The differentiation in design also facilitates efficient chip removal, a factor that becomes crucial in prolonged drilling tasks.

We discussed a few of the prominent tools, although there are other many tools. Let’s discuss more tools shortly with a table.

Table: CNC Milling Tools and Their Application Scenarios

Tool Preferred Scenario Types of Metals Applications
End Mills Slotting, Profiling Aluminum, Steel, Brass, Copper Grooves, Pockets, Side Milling
Face Mills Surface Finishing Steel, Cast Iron Achieving Flat Surfaces
Ball Nose Mills Detailing, Contouring Aluminum, Bronze, Mild Steel 3D Carving, Radii in Pockets
Drill Bits Drilling Nearly All Metals Producing Holes, Deep Drilling Tasks
Roughing End Mills Material Removal Most Metals Rapid Material Reduction
Finishing End Mills Detailed Finishing Most Metals Achieving Precise Finishes
Hollow Mills Hollowing Metals with Malleable Centers Creating Hollowed Sections
Chamfer Mills Edge Finishing Broad Metal Spectrum Producing Angled Edges, Beveling
Helical Mills Grooving Steel, Aluminum, Brass Crafting Grooves or Slots
Dovetail Cutters Joining Preparations Most Metals Creating Dovetail Grooves for Component Joining
Fly Cutters Large Surface Finishing Soft Metals like Aluminum Achieving Smooth, Large Surfaces
T-slot Cutters Slot Creation Broad Metal Spectrum Crafting T-slots for Mounting Tools or Fixtures

 

Machining Parameters: CNC Milling for Metal Parts

Machining parameters are the lifeline of the CNC milling process. These parameters dictate how the machine interacts with the metal, ensuring that the carved or shaped part adheres closely to its digital design blueprint. Correct parameters ensure efficient machining, minimal wastage, and reduced wear and tear on the tools. Furthermore, they are instrumental in achieving the desired surface finish, structural integrity, and dimensional accuracy of the milled part. In essence, machining parameters are the bridge between digital design intent and its tangible realization.

The following are the different machining parameters in CNC Milling

  • Cutting Speed (Vc): This represents the speed at which the cutting edge of the tool engages with the workpiece. It’s usually measured in meters per minute (m/min) or feet per minute (fpm) and varies depending on the type of metal being milled.
  • Spindle Speed (n): Indicative of how fast the milling tool or cutter rotates, it’s measured in revolutions per minute (RPM). Its value is often related to the cutting speed and the diameter of the tool.
  • Feed Rate (f): Represents the speed at which the tool advances through the workpiece, typically measured in millimeters per tooth (mm/tooth) or inches per tooth (in/tooth).
  • Depth of Cut (ap): The depth to which the tool penetrates the workpiece in a single pass.
  • Width of Cut (ae): Indicates the width of the tool engagement with the workpiece.
  • Coolant Flow Rate: Regulates the amount of coolant used to dissipate heat during milling, ensuring tool longevity and optimal cutting conditions.
  • Tool Path Strategy: Refers to the predetermined path the tool will follow, impacting machining time and surface finish.
  • Lead Angle: The angle between the tool’s cutting edge and the workpiece, influences chip thickness and tool loading.
  • Axial Rake Angle: The inclination of the main cutting edge, affects cutting forces and chip flow.
  • Radial Rake Angle: The angle at which the tool’s peripheral cutting edge is inclined, impacting the tool’s sharpness and strength.
  • Overhang Length: The distance from the tooltip to its holding device, affects stability and vibration during cutting.
  • Chip Load: The amount of material removed by each cutting edge during a milling pass.

Table: Different Parameters in CNC Milling for Various Metals and Alloys

Metal/Alloy Cutting Speed (Vc) m/min Spindle Speed (n) RPM Feed Rate (f) mm/tooth Depth of Cut (ap) mm Width of Cut (ae) mm Coolant Flow Rate ml/min Lead Angle (degrees) Axial Rake Angle (degrees) Radial Rake Angle (degrees) Overhang Length mm Chip Load mm³
Aluminum 500-1000 8000-15000 0.03-0.06 5-15 1-5 100-200 0-90 5-15 5-10 20-60 0.1-0.3
Stainless Steel 60-80 2000-3000 0.01-0.03 2-6 0.5-2.5 200-400 0-80 5-10 5-10 20-50 0.05-0.2
Titanium 40-60 1000-2000 0.01-0.02 1-4 0.5-2 300-500 0-75 5-10 5-9 15-40 0.04-0.15
Brass 200-300 5000-7000 0.03-0.05 3-8 1-4 50-150 0-85 5-12 5-10 20-55 0.1-0.25
Bronze 80-120 2500-3500 0.02-0.04 2-5 0.5-2.5 100-250 0-85 5-12 5-10 20-50 0.07-0.2
Copper 100-200 4000-6000 0.02-0.04 3-7 1-4 50-150 0-90 5-12 5-10 20-55 0.08-0.2
Nickel Alloy 50-70 1500-2500 0.01-0.03 1-5 0.5-2 250-450 0-80 5-10 5-9 20-45 0.05-0.15
Zinc 150-250 4000-6500 0.03-0.05 3-8 1-4 50-150 0-90 5-12 5-10 20-55 0.1-0.25
Cast Iron 80-120 2500-3500 0.02-0.04 2-5 0.5-2.5 50-200 0-85 5-12 5-10 20-50 0.07-0.2
Tungsten Carbide 40-60 1000-2000 0.01-0.02 1-4 0.5-2 200-400 0-75 5-10 5-9 15-40 0.04-0.15

 

(Note: The values in the table are taken from various sources(1, 2, 3) and might vary based on specific alloy grades, tooling specifications, and machine capabilities. Therefore, always consult with the experts and conduct necessary tests).

Click here to download: The Basic of Metal CNC Milling

 

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Best Metal CNC Milling Tips

Whether you’re a seasoned CNC machinist, looking for related service, or just starting out a similar project, there are tips & tricks that can elevate the quality of your work and reduce waste.

1. Selection of the Right Tool The choice of the correct milling tool is paramount. Given the vast variety of metals and alloys, each has its own set of properties that require specific types of tools for optimal milling. High-speed steel (HSS) tools are versatile and can handle temperatures up to 600°C, making them suitable for milling softer metals like aluminum. Carbide tools are harder than HSS and are ideal for milling tougher metals such as stainless steel but tend to be more brittle.

2. Prioritize Rigidity Rigidity in both the machine and workpiece is crucial. A rigid setup minimizes vibrations, leading to better surface finishes and prolonging tool life. Using fixtures and clamps that firmly hold the workpiece can significantly reduce the chances of unwanted movement during milling.

3. Optimal Feed Rates and Speeds: Every metal has an optimal feed rate and speed for milling, which is determined by its hardness, ductility, and other properties. For instance, softer metals like aluminum can withstand faster feed rates than harder metals like titanium, which requires slower, more controlled feeds to prevent tool wear.

4. Use of Coolants Effective use of coolants can drastically increase tool life and improve the surface finish. Coolants serve to dissipate heat and clear away metal chips. According to John J. Uicker, Jr. in Theory of Machines and Mechanisms;

“Proper use of coolants not only prevents tool damage but can increase the speed of machining operations by up to 30%.”

5. Employ Climb Milling When Possible Climb milling, where the cutter moves with the feed, can result in better surface finishes and less tool wear, especially with modern CNC machines that have tight backlash controls.

6. Regular Machine Maintenance Regularly servicing your CNC machine ensures its longevity and maintains precision. This includes lubricating moving parts, calibrating the machine, and checking for wear and tear.

Table: Tool Life Expectancy Based on Material

Material High-Speed Steel Tool Life (hours) Carbide Tool Life (hours)
Aluminum 4-6 10-12
Stainless Steel 1-2 4-6
Titanium 0.5-1 2-4
Brass 3-5 8-10

7. Depth and Width of Cuts Adjusting the depth and width of cuts can influence both the finish quality and the tool’s life. For hard metals, it’s often more efficient to take multiple shallow passes rather than a single deep cut.

8. Avoid Prolonged Engagement Ensure that the tool isn’t engaged with the material for extended periods without breaks. This can cause the tool to overheat and become dull.

9. Post-Milling Inspection Always inspect the milled parts post-operation. Use calipers, micrometers, and other measurement tools to ensure the dimensions match the intended design.

10. Stay Updated with Software Modern CNC milling operations rely heavily on software. Regular updates can introduce new optimization techniques, improve tool paths, and offer better control over the machining process.

 

Applications of CNC Milling Metal Parts Across Different Industries

The exceptional precision, repeatability, and efficiency have made CNC milling the go-to method for producing complex and high-quality metal components. As industries strive to innovate and meet new market demands, CNC milling has become an indispensable tool.

 

Various aerospace parts made with CNC metal milling

In the aerospace industry, the precision of CNC milling is crucial for safety. The automotive and medical sectors value CNC milling for its consistency and fine detail, respectively. The electronics industry depends on it for miniaturized components, while defense values its ruggedness, and the energy sector requires its robust accuracy.

Let’s delve into the applications of CNC milling in different industries and its significance.

Table: Applications of CNC Milling Metal Parts Across Industries

Industry Description Why Preferred Examples
Aerospace The aerospace industry requires components with intricate designs and extreme precision. It ensures high precision and meets tight tolerances, essential for flight safety. Aircraft frames, engine parts, landing gear components, turbines, propellers.
Automotive Automotive parts need to be durable and fit perfectly to ensure the safety and performance of vehicles. CNC milling offers the ability to produce large volumes with consistent quality. Engine blocks, gearboxes, brake systems, fuel systems, exhaust parts, drive shafts.
Medical Medical devices and instruments demand the highest standards of precision and hygiene. It can create complex shapes with finishes that are easy to sterilize. Surgical instruments, orthopedic implants, dental equipment, prosthetics, MRI parts.
Electronics The electronics industry needs miniaturized components with high precision. Provides the precision needed for compact and intricate parts. Circuit boards, casings, connectors, heat sinks, switch panels, enclosures.
Defense & Military Defense equipment demands ruggedness, precision, and reliability. CNC milling ensures durable and accurate components that can withstand harsh conditions. Weapon systems, communication devices, armored vehicles parts, missile components.
Energy & Power This industry requires robust parts capable of withstanding extreme conditions. It can handle materials and precision suitable for high-demand scenarios. Turbine blades, drilling equipment, connectors, power transmission components.

 

Make Your Precise Metal Parts with Prolean CNC Milling Services

In today’s manufacturing scenario, precision is more than just a buzzword – it’s a necessity. Prolean CNC Milling Services stands at the forefront, ensuring every metal component we produce meets the highest standards of accuracy and quality. Using cutting-edge technology and a team of skilled professionals, we transform your designs into tangible, top-notch metal parts.

Choosing Prolean CNC Milling Services is choosing a legacy of excellence. Our expertise spans across diverse industries, and we pride ourselves on our ability to tackle even the most complex of projects. From intricate components to large-scale productions, our commitment to precision remains unwavering. We leverage the power of CNC milling to breathe life into your vision.

CNC Milling

Conclusion

CNC milling for metal parts stands as a testament to the confluence of technology and craftsmanship in modern manufacturing. From understanding its intricate workings to realizing the paramount importance of precise machining parameters, every facet of the process underscores its relevance in today’s industries. Key tools, each tailored for specific tasks, drive the quality and precision inherent to CNC milling.

The array of applications, ranging from aerospace to electronics, highlights the versatility and indispensability of CNC milling in contemporary production lines. The CNC milling for metal parts offers a blend of reliability, precision, and innovation, pushing the boundaries of what’s achievable in metal fabrication.

Read more: CNC Milling Prototyping: Process, Benefits & Applications

 

FAQs

What does CNC milling entail?

It’s a process where machinery, guided by computer programming, shapes and cuts materials, primarily metals.

Why is metal CNC milling pivotal?

It offers unparalleled precision, efficiency, and versatility in producing metal parts.

Are all metals suitable for CNC milling?

Most metals can be CNC milled, but it’s crucial to choose the right metal for the desired application and finish.

How does CNC milling cater to different industries? From aerospace to medical fields, CNC milling creates parts that adhere to industry-specific requirements and standards.

What’s the importance of regular calibration in CNC milling?

It ensures the machine’s accuracy and precision, leading to consistent high-quality outcomes.

How does the future look for CNC milling of metal parts?

With technological advancements, the future looks promising with more automation, precision, and versatility.

References

  1. https://www.sciencedirect.com/science/article/abs/pii/S2214785322023677
  2. https://www.sandvik.coromant.com/en-gb/knowledge/milling/milling-different-materials
  3. https://technologicalprocess.com/milling-machining-parameters/

7 Comments

  1. Sophie tera

    Perfect ! Loved how you present detailed parameters in CNC Milling for Various Metals and Alloys.

    Reply
  2. Bharat45

    Loved the discussion on CNC milling of metal parts. It could be more helpful for me if you included the relation of Hardness(Rockwell number) with corresponding milling tools.

    Reply
    • Dikendra

      In CNC milling, the hardness of the material being milled, often measured by the Rockwell scale, influences the choice of milling tools. Harder materials require more robust milling tools, typically made of materials like carbide or cobalt, to withstand the stresses of cutting without wearing down quickly. Below is a simplified table showing the relation of material hardness to the corresponding milling tools:

      Rockwell Hardness (HRC) Milling Tool Material
      < 30 High-Speed Steel (HSS) 30-45 Cobalt (HSS-Co) 45-65 Carbide > 65 Diamond or CBN
      This table is indicative and can vary based on specific milling conditions and tool quality.

      Reply
  3. Saraya

    Aw, this was an incredibly nice post. Taking the time and actual effort to create
    a very good article…

    Reply
    • Dikendra

      Thanks for your words Saraya!

      Reply
  4. SASHI Heat Sink

    Hello, i found this article very informational. We are small business work on aluminum heat sink for electronics. We usually work work with EDM, but we are going to test new designs with CNC milling. I am looking for manufacturing consultation and prototyping service? Please reply

    Reply
    • Dikendra

      I think CNC milling can give better results in some cases, Also how about combination of CNC and EDM? Send us design we will get back to you!

      Reply

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