CNC machining
CNC machining is an advanced subtractive manufacturing process that operates and manipulates materials using computer-controlled machine tools. Computer programs guide the operation of cutting tools and other machine components.
This automatic and highly precise process starts with computer-aided design (CAD) of the part, followed by CNC program creation, machine setup, the machining process, and finally, the finishing steps.
Apart from being a precise process capable of achieving tight tolerances, CNC machining is repeatable, cost-efficient, less prone to error, and highly versatile for designs and materials.
Its versatility extends to the variety of operations available- CNC milling, CNC turning, CNC hole-making, and others. The processes could be used in combination depending on a part’s complexity.
With so many options and capabilities of CNC machining, it is worthwhile to engage CNC machining professionals from the very beginning of a machining project to optimize time, material selection, costs, and so on.
Continue reading for more details about CNC machining and how it can add value to your projects.
What is CNC Machining?
Computer Numerical Control (CNC) machining is an advanced subtractive manufacturing process that manufacturers value for its cost-effectiveness, precision, and accuracy. They use it to make market-ready items and prototypes.
This process involves a specific mechanism that enables G-code programs to control precise material removal operations.
G-code is a special CNC programming language used in CNC machines. It is a “Geometric Code” that instructs the machine on position, speed, and time.
The majority of CNC machining is performed through conventional cutting operations, but there are operations like laser cutting, waterjet cutting, and electrical discharge machining (EDM), whose connection is the precision of computer control.
The fundamental parts of CNC machines are input devices, the Machine Control Unit (MCU), the driving system, the machine tools, the feedback system, and the display unit. For conventional ones like the CNC lathe, further parts include the tailstock, headstock, chuck, and coolant system.
CNC machining is extremely popular for its capability to produce accurate parts repeatedly, handle a variety of operations in different materials, and operate cost-effectively at scale.
History Of CNC Machining
The pioneer Numerical Control (NC) machines can be traced back to the 1940s, before technological advances introduced the modern CNC machining capabilities. A lot of the initial CNC machining efforts are widely attributed to John Parsons and his punch card innovation.
Punched cards
CNC machining was first used for milling machine automation with the idea of reducing the time taken to design and feed instructions into a milling machine. The requirement for an expert machinist was a major challenge at first.
This prompted the Massachusetts Institute of Technology (MIT) to develop a programming language for automatic coordinate generation.
Over time, computers have significantly advanced and become more accessible, making CNC machining highly efficient, versatile, and cost-effective for CNC precision machining parts.
Basics of a CNC Machine And Working Process
Fundamentally, the CNC machine is built to use a CNC program to machine a part. The CNC machine manufacturing process can be broken into four main steps: CAD model design, CNC machine preparation, CAD file conversion to a CNC program, and machining operation.
Throughout these steps, several machine components work together to achieve the final result. The CNC controller reads the program, the machine axes move in predescribed directions, cutting tools rotate on the spindle (where applicable), the worktable holds the workpiece, and so on.
Step 1: CAD Model Design
A CAD model
The first step is the generation of a 3D CAD design, which bears information such as the type of geometry, the amount of material to be machined, and the Geometric Dimensioning and Tolerancing (GD&T).
Step 2: CAD File Conversion
Generating the G-code for the CAD model is the next stop. You want to feed the CNC machine with instructions it can understand. This process involves a CAM (Computer-Aided Manufacturing) program, which is in the machine’s computer. Whether the conversion is manual or robotic depends on the specific CNC machine.
Step 3: CNC Machine Preparation
CNC machine setup
When it comes to preparing the CNC machine for the task, this mostly entails ensuring the CNC program is uploaded to the machine.
Step 4: Machining Operation
The machining operation is preceded by setting the machine approach movement. The CNC machine can then be prompted to execute the program, using the G-code instructions to machine the workpiece.
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More About CNC Programming
CNC programming refers to the application of a set of commands to direct the CNC machining process. The most popular programming language for CNC machines is the G-code, also called RS-274D. The codes start with the letter ‘G’ in most cases, with each code instructing a particular machine movement.
Below are some common G codes with their meanings:
Some G-codes and meanings
Alongside G-codes, there are M-codes or miscellaneous codes. These commands are for non-geometric operations, such as shutting down the machine and coolant activation.
These codes are preceded by ‘M’. Here are examples:
M00 – Program Stop
M02 – Program End
M05 – Spindle Stop
Tolerances In CNC Machining
Tolerance specifications are central to a comprehensive CAD design for CNC machining. The designer must understand the applications and cost implications of the main categories of tolerances.
Tighter machining tolerances are more expensive because they are challenging to attain. A standard tolerance of at least ±0.1mm is recommended where tolerance is not provided. Otherwise, the designer should provide a 2D drawing with the three tolerances.
The main types of tolerance for defining CNC machining parts are Dimensional Tolerances, Geometrical Tolerances (GD&T), Surface Texture Tolerances, Fits and Limits Tolerances (Hole/Shaft System), and Positional and Datum-Based Tolerances.
Dimensional Tolerances
It applies to diameter, thickness, length, and other feature sizes. Angular tolerance and linear tolerance are in this category. If not stated in the drawing, the machinist should use ISO 2768-1 for general tolerances.
Table 1: Linear Tolerances In CNC Machining
Geometrical Tolerances (GD&T)
The GD&T category is used for the orientation, position, and shape of a feature. Specific tolerances considered are form tolerance, location tolerance, orientation tolerance, and runout tolerance.
The UK standard BS 8888, which is related to ISO 1101, defines GD&T.
Surface Texture Tolerances
Surface texture tolerances define a CNC-machined part’s surface finish or roughness. The governing standard for these tolerances is BS EN ISO 1302, now ISO 21920-1:2021.
Fits And Limits Tolerances (Hole/Shaft System)
These tolerances are for two mating parts and are defined by BS EN ISO 286, formerly BS 4500. Clearance fit, transition fit, and interference fit apply here.
Table 2: A section of the ISO tolerance table for holes (source: https://www.tribology-abc.com/calculators/iso_holes.htm)
Positional And Datum-Based Tolerances
These tolerances are concerned with the location of features in relation to others.
What Are The Advantages Of CNC Machining?
CNC precision machining services can move a business to unexpected heights because they offer many advantages, from providing consistent results with the best precision to being versatile in the face of varying demands and also very helpful in saving cost and time. Here is a list of the advantages of CNC machining.
Superior Precision
The precision of CNC machines is mostly the first advantage a user and parts customer notices in comparison to alternative technologies, or even more manual machining methods.
With computer control at the core, CNC machining can achieve tolerances of up to ± 0.0025mm! Manual machining cannot even come close to this kind of performance. So, the machining results are consistent regardless of the number of production runs.
Cost And Time Savings
CNC machining is a big cost and time saver. When the program is ready, the machine does the rest with minimal human effort. Because there are no human errors to deal with, parts are produced within the stipulated time. Costs related to human errors are also avoided.
There are also various ways of enhancing CNC machining cost savings for products, including;
- Optimizing design elements
- Proper choice of materials
- Batch production
- Using automatic tool changers
- Preventive maintenance and care of the CNC machine
Versatile – Material Options
The manufacturer can use a wide range of materials for CNC machining with remarkable success. Be it metals like stainless steel, aluminum alloys, and titanium alloys, or plastics like polyamide, acrylic, and PEEK, CNC machining is usually a leading option for the production of parts.
What Are The Disadvantages/Limitations Of CNC Machining?
CNC machining is limited by its high initial cost, slowness, and the need for training. ;
High Initial Cost
The CNC machines are expensive to acquire, and the subsequent setup costs can also be daunting. However, it is noteworthy that the cost per unit part for large CNC machining is usually manageable for large production runs.
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Relatively Slow Process
CNC machining can be considered slow compared to alternatives like die casting and injection molding.
Training Requirements
CNC machist required
Despite its automation, the CNC machining process cannot be handled by everybody. Indeed, machinists are recognized professionals with knowledge of maths, machine software, machine maintenance, and problem-solving skills.
This is especially so for multi axis machining, for instance, 5-axis machining. Even 3-axis CNC machining requires a level of expertise beyond that of an average factory worker.
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Main Types of CNC Machines
Various types of CNC machines exist, each built for different tasks, including CNC lathes, CNC mills, CNC grinders, CNC drilling machines, and CNC Swiss Turning Machines. Others are Electric Discharge Machines (EDM), Plasma Cutters, Laser cutters, water jet cutters, and CNC routers.
CNC Lathes
CNC lathes are engineered for turning operations, which entail a stationary cutting tool machining a rotating workpiece to produce symmetrical features. There are different categories of CNC lathes depending on the advantages and features offered:
- Motor Lathe – A standard lathe type that uses a motor in place of a pulley drive system
- Tool Room Lathe – Designed for making tools and dies, and similarly low-volume, high-precision jobs in the CNC machine shop.
- Turret Lathe – This type has a distinctive tooling system for more flawless part production
A turret lathe
- Quick Lathe – This has a simple setup for fast, efficient turning jobs
- CNC Turning Center – This is more advanced than the rest, with a turret feature, milling capability, and can have a pair of spindles. Some are vertical and others horizontal.
CNC Mills
A CNC mill removes material from a workpiece using a rotary cutter to produce simple to intricate geometries. It is designed to machine different types of materials, from metals to non-metals.
The two broad categories of CNC mills are Vertical Machining Center (VMC) and Horizontal Machining Center (HMC).
Vertical Machining Center (VMC) – The spindle is oriented vertically
Horizontal Machining Center (HMC) – The spindle is oriented horizontally
Horizontal machining center (HMC)
CNC Grinders
A CNC grinder comprises a grinding wheel that removes material from a workpiece, precisely, with the help of computerized control. This machine can perform surface grinding, cylindrical grinding, centerless grinding, internal grinding, and special grinding.
A CNC grinder
CNC Drilling Machines
A CNC drilling machine is built to produce precise holes in a material. It can help create complex parts.
CNC drilling machine
CNC Swiss Turning Machines
A CNC Swiss turning machine or Swiss lathe is engineered to manufacture tiny, complex parts.
Electric Discharge Machines (EDM)
This technology produces electrical sparks that machine a workpiece to the designed shape. It is ideal for machining hard materials that conventional methods are unable to machine.
Plasma Cutters
In CNC plasma cutting, a precisely controlled high-velocity jet of ionized gas (plasma) cuts electrically conductive material.
CNC plasma cutter
Laser Cutters
A laser cutter uses a controlled, powerful laser to cut or engrave materials. A computer program controls the movement of the laser head, which directs a laser to melt or vaporize a material.
Water Jet Cutters
A powerful jet, usually combined with abrasives, is computer-controlled to cut through a material. It can cut through granite, metal, composites, and wood.
CNC Routers
CNC routers are typically used in the woodworking industry, where they make precise cuts, engravings, and profiles. They may be used on other soft materials.
Different CNC Machining Operations
The number of CNC machining operations is high because there are many possible components. These operations can be widely categorized as turning-based, milling-based, hole-making, and Others.
CNC Turning Operations
These operations are defined by a rotating workpiece and a stationary cutting tool. The cutting tool alters the workpiece surface – removes material. Turning operations produce cylindrical or circular parts, for example, shafts and rods.
A shaft
Here is a list of CNC turning types;
- Boring
- Drilling
- Grooving/parting
- Threading
- Turning
CNC Milling Operations
In CNC milling, the workpiece is stationary while a multi-point cutting tool moves/rotates. The rotating tool removes material from the workpiece in a peeling-off manner.
CNC milling operations are perfect for making pockets, undercuts, and flat surfaces on workpieces. Like CNC turning, milling can be used on a range of materials, including metals, plastics, and wood.
The specific options in CNC milling are:
- Slab (peripheral) milling
- Face milling
- Plain milling
- Angular milling
- Pocket milling
CNC Machining For Hole-Making
The versatility of CNC machining is evident in its capability to produce holes, usually using a drill bit. Other than the drill bit approach, CNC hole-making is also possible through reaming and boring.
Drilling makes the basic hole, while reaming and boring improve an existing hole. CNC boring reduces defects and reduces surface roughness. It is a very slow process, like reaming, whose function is to enhance the surface quality and dimensional accuracy of the hole.
Other CNC Machining Operations
Other CNC machining operations fall outside the basic categories highlighted above, but they are equally essential in CNC manufacturing. The most popular ones are;
- Electrical Discharge Machining (EDM)
- Grinding
- CNC laser cutting
- CNC waterjet cutting
CNC water jet cutting
- CNC plasma cutting
- CNC honing
- CNC broaching
Read more:
CNC Machining Vs Injection Molding,
CNC Machining Materials
CNC machining materials are mostly metals and plastics. Metal parts are mostly preferred for strength, durability, thermal resistance, and hardness. Machined plastic parts are chosen for their low weight, chemical resistance, and electrical insulation.
Metal Alloys For CNC Machining
The most common CNC metal alloys for parts are;
Aluminum Alloys
Aluminum alloys are common in CNC machining because they offer good machinability, a high strength-to-weight ratio, corrosion resistance, and conductivity. CNC machining services for this alloy often focus on aluminum 5083, aluminum 6061, aluminum 7075, and aluminum 6082.
CNC-machined aluminum parts
Alloy Steel
To add to carbon, alloy steel has other alloying elements for added hardness and durability. Despite having poor corrosion and chemical resistance, alloy steels have good mechanical properties. The varieties of alloy steel used in CNC machining are 4140 and 4340.
Mild Steel
Mild steel is another name for low-carbon steels, a category of weldable and machinable metals. Mild steel is also very common, especially 1018 in CNC machining.
Stainless Steel
Stainless steel alloy machined parts are renowned for their strength and corrosion resistance. The metals are also weldable and highly machinable. Some popular options for steel CNC machining are stainless steel 304, stainless steel 316, stainless steel 303, and duplex 2205 stainless steel.
Tool Steel
Tool steel is extraordinarily hard with excellent abrasion and thermal resistance. The material makes highly dependable dies, molds, and other manufacturing tools. Tool steel D2 and tool steel A2 are the most popular options.
Plastics For CNC Machining
Common plastics for CNC machining are;
- ABS(Acrylonitrile Butadiene Styrene)
- Acetal/POM(Polyoxymethylene)
- PC(Polycarbonate)
- PMMA (Polymethyl Methacrylate) or acrylic
- HDPE(High-density polyethylene)
- PEEK (Polyether Ether Ketone)
Each of these and other plastics has its advantages and limitations, so there are several considerations to make before choosing. Important points to keep in mind when identifying a plastic for CNC machining are;
- Appearance
- Machinability
- Temperature resistance
- Shrinkage
- Cost
Different Applications Of CNC Machining
The versatility, precision, cost-effectiveness, CNC machining cutting speed and Feed rate of CNC machining appeal to a wide range of applications within various industries, including aerospace, automotive, healthcare & medical, electronics, defense, energy, automation & robotics, marine, and sports..
CNC machining for electronics
Below is a table summarizing these applications:
| Industry | CNC Machining Applications |
| Aerospace | Landing gear parts, seat frames, cockpit parts, engine components |
| Automotive | Cylinder head, piston, suspension parts, gearbox cover, steering wheel |
| Healthcare & medical | Orthopedic implants, surgical devices, and imaging equipment parts |
| Electronics | Heat sinks, enclosures |
| Defense | Vehicle parts, weapon parts |
| Energy | Drilling equipment, valves |
| Automation & robotics | Gears, robot frames |
| Marine | Engine parts, propellers |
| Sports | Skateboards, gears, golf club heads |
| Consumer products | Electronics, kitchen appliances |
How Much Does CNC Machining Cost?
CNC machining cost can be gauged using the per-part or per-hour criterion. Each of these approaches gives varied answers because many factors are involved.
The hourly costs will mostly depend on the CNC machine types used and the attached expertise. The per part rate is dependent on elements like raw material, complexity of the part, and the production volume.
Of course, there are price ranges, but these are merely baselines. Above these starting points, the CNC machining cost varies widely based on batch size, life cycle of CNC parts, and raw materials availability/cost.
For an accurate estimate of CNC machining cost, it is better to get insights from a seasoned CNC machining services provider.
Conclusion
CNC machining is the hallmark of many industries, providing accurate, durable, and attractive parts for many applications. The aerospace, automotive, defense, and robotics industries are only a few of the beneficiaries of this technology.
Whether you are looking for custom CNC-machined parts or batch-manufactured ones, there is always a solution for you.
Ask the experts. Contact ProleanTech today!
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