CNC machining has revolutionized metal fabrication. As manufacturing needs evolve, technological advancements have fostered a synergistic merger between CNC machining and metal fabrication. As a result, it has added an element of automation that boosts quality, accuracy, speed, and precision. CNC machining enhances metal fabrication, performing diverse roles such as cutting, assembling, and finishing.
This ultimate guide is a comprehensive discussion of CNC machining for metal fabrication, beginning with the fundamentals of CNC machining and metal fabrication, transitioning into the role of CNC machining, the materials employed, as well as associated challenges and solutions.
Table of Contents
Understanding CNC Machining
What is CNC Machining?
Computer Numerical Control (CNC) machining is a manufacturing process where programs, written in languages like G-code and M-code, direct and operate machine tools. Often, the programs direct the tools to cut or shape material, creating parts with distinct forms and features. CNC programs achieve this by:
- Directing the movement of the tools along the various axes
- Regulating spindle speed, cutting speed (the distance the tool moves inward relative to the machined part), or feed rate (the distance the tool travels in relation to one complete revolution of the part)
- Initiating automatic tool changes
- Executing on-and-off functions like controlling how and when the machine sprays the coolant
- Regulating the rotational speed of a part around the z-axis, typical in a turning center.
Importance of CNC Machining
CNC machining offers numerous advantages, which have influenced the ballooning use of CNC machines in manufacturing. In fact, the global CNC machine market size is projected to grow immensely from $86.83 billion in 2022 to $140.78 billion in 2029. Driving this expected growth are the following benefits:
1. Greater Efficiency
Typically, an operator or technician checks the path in computer-aided manufacturing (CAM) software before post-processing. During such checks, the software simulates the cutting action, allowing the technicians to identify and correct actions that the machine or its tools cannot perform practically.
2. Enhanced Flexibility
CNC machining supports a variety of operations within the same machining cycle, provided the program contains code that directs all these operations.
3. Better Safety
CNC machining promotes safety by automating processes and operations that were previously conducted manually. This means operators no longer need to handle certain tasks like changing cutting tools or adjusting feed rates manually. They instead sit or stand in a safe position, away from the orderly mayhem of the machine.
4. Improved Accuracy
By doing away with manual operations, CNC machining eliminates human errors, thus boosting part accuracy. It, therefore, makes it possible to achieve tighter tolerances.
5. Less Lead Times
CNC machining reduces lead times by expediting machining jobs. Moreover, the machines can optimize the feed rate and cutting speeds based on the material. What’s more, the CNC machines ensure less part handling. Combined, these factors significantly reduce machining time.
6. Better Mass Customization Capabilities
With workshops and manufacturing plants increasingly adopting technology to improve efficiencies, digital manufacturing has become a reality. With it, mass customization has equally gained traction. Currently, with the use of online tools, it is possible for customers to order personalized designs or to personalize existing designs. Their orders are then incorporated into the production process using product lifecycle management (PLM) software. But that’s not all. The design files are converted to instructions that are fed into CNC machines for production. CNC machining, thus, enables machine shops to produce bespoke products at scale with little to no variations in the cost per unit.
7. Increased Production
By reducing the machining time, CNC machining facilitates increased production. More parts can be produced within a short time.
8. Ability to Machine Complex Parts
The machines can produce complex parts by simply following a predefined path. Moreover, CAM software and the integrated post-processors can generate instructions for even the most complex parts. Thus, you need not have a background in creating G-code or M-code to machine intricate features that form complex parts.
9. Reduced Storage Space and Inventory Requirements
CNC machining reduces setup time and increases the speed of production. At the same time, these advantages minimize the wait times, which means materials spend less time in storage awaiting fabrication. Combined, these advantages diminish storage space and inventory requirements.
10. Less Scrap
CNC machines automate manual processes, eliminating errors that would have arisen from human input. Moreover, depending on the machining process, these systems can achieve tighter tolerances. Combined, these factors increase the accuracy of cuts or welds, leading to less scrap.
11. Improved Production Scheduling
CNC machines can optimize cutting speeds and feed rates. This, coupled with the fact they take away the need to have humans handling, loading, and unloading times, leads to known production times. And working from such a point of knowledge enables operators to accurately schedule when to fabricate parts as part of an ongoing production process.
12. Longer Tool Life and Lower Tool-Related Costs
Machining technology has advanced significantly; CAM software can now generate tool paths that align with the tool’s shape. This eliminates the need to create precision-ground form tools, as was the case before the advent and increased popularity of CNC machining in metal fabrication. Moreover, CNC machining optimizes the cutting speed and feed rate. This results in longer tool life because the fabrication process does not result in unnecessary tool wear associated with the imposition of an unnecessary amount of force.
13. Overall Cost Savings
In summary, the combined advantages, including longer tool life, reduced production times, enhanced safety, and more, lead to overall cost savings in manufacturing.
Metal Fabrication and Its Importance
What is Metal Fabrication?
Metal fabrication is the process of shaping, assembling, or building a part, product, or equipment from raw metal stock. IIt encompasses various manufacturing steps and processes: cutting, burring, material removal, bending, assembling, welding, and finishing. The primary goal of metal fabrication is to produce products with a specific form or shape.
In an industrial context, metal fabrication also encompasses essential non-machining procedures, including planning, bill of materials preparation, raw material identification, purchasing, and storage. However, as mentioned above, CNC machining reduces storage space and inventory requirements. For the purposes of this article, we will concentrate on the machining procedures rather than the non-machining procedures.
Metal Fabrication Steps Explained
Cutting essentially involves removing material along a particular path to obtain a workpiece with a desired length. On the other hand, material removal entails indiscriminately removing material from a particular section of a workpiece or the entire surface of a workpiece.
Processes for cutting and metal removal encompass milling, drilling, plasma and laser cutting, flame cutting, turning, EDM, waterjet cutting, and punching. In cases where thermal processes are used to cut workpieces, deburring procedures are normally undertaken immediately thereafter. Deburring removes burrs (small imperfections) caused whenever the material in the heat-affected zone melts.
Assembling entails positioning all the parts accurately. In this step, the parts also need proper orientation relative to each other. And to prevent movement, you can tack weld or use clamps to hold them in place. Next, depending on what you are manufacturing, you can weld the parts permanently together. Alternatively, you can bolt the parts in place or use rivets to permanently join them. The subsequent step is finishing.
Finishing processes can include grinding to achieve a certain surface finish or remove imperfections. Alternatively, to enhance the product’s strength or achieve specific properties, various heat treatment methods can be employed.
Benefits of Metal Fabrication
The benefits of metal fabrication include:
- The ability to create complex parts
- Versatility and flexibility
- The ability to create products with certain properties
Complex Parts Creation
Metal fabrication can mold metals into distinct shapes and forms. And the advantage of combining CNC machining with metal fabrication lies in the use of CAM software, which simplifies the generation of tool paths that the machines follow when machining features into parts. The instructions are optimized based on the available tools, machines, and processes. Impressively, the software can auto-generate instructions, producing ready-to-use programs. You only need to load the programs to the CNC machine to begin metal fabrication.
Versatility and Flexibility
Various processes can be employed in metal fabrication, including cutting, welding, milling, drilling, turning, and folding, among others. Moreover, you can perform these processes manually or automatically, with the latter approach being more accurate and faster. To automate such processes, you can use CNC machines, which accentuate the role of CNC machines in metal fabrication.
Achieving Desired Properties
Metal fabrication leverages the inherent properties of metals, allowing the creation of parts and products that retain these desirable characteristics. Still, by using finishing processes such as heat treatment, you can improve the strength attributes of the parts or products.
The Role of CNC Machining in Metal Fabrication
CNC machining and CNC machines play a number of roles in metal fabrication. More specifically, they are used to complete multiple crucial operations, including:
Prototyping
Before a workshop or manufacturing plant decides to build a particular product, a lot has already taken place. For instance, the engineering team will have already used computer-aided design (CAD) software to come up with the designs. They will also have analyzed the models/designs and performed simulations using computer-aided engineering (CAE) software. However, software has its limitations. So, beyond a certain point, it is necessary to perform actual tests using physical models. Enter prototyping and rapid prototyping.
Rapid prototyping is a collection of techniques used to fabricate within a short time a scale model. This process aids in design evaluation, verification of the functions of models, obtaining customer feedback, and more. 3D printers, a type of CNC machine, are often used to perform rapid prototyping. You can also use CNC mills. Prototyping creates a physical sample for testing and improvements. However, it’s slower than rapid prototyping.
Milling
In milling, the mill cutter moves along two different axes. For simplicity’s sake, the cutter uses vertical movement while also moving horizontally. This enables the milling machine to create features with distinct shapes. The features can also have varying sizes, with their diameters being much larger than the diameter of the cutter. This contrasts with the capabilities of drilling, as discussed below.
CNC mill machines are used to automatically perform milling. They can work on hard materials such as titanium, steel, and aluminum. And given that a program dictates how they operate, these machines can make delicate and accurate cuts.
Drilling
In basic drilling, the drill typically moves along a single axis. This, therefore, means that CNC drilling machines only make cuts or holes of a given diameter or size based on the diameter of the drill. And like the CNC mill machines, the CNC drilling machines complete their operations automatically with minimal operator input.
Turning
Turning is a machining process in which a non-rotary cutting tool moving linearly along two axes (normally the x- and z-axes) removes material from a workpiece rotating along the z-axis. The tool’s movement along the x-axis represents inward and outward movement intended to alter the thickness of the material. On the other hand, the tool’s movement along the z-axis helps the tool reach the entire outer cross-section of the workpiece. This promotes uniformity of material removal. Typically, CNC machines known as lathe machines perform turning operations.
Electrical Discharge Machining (EDM)
Electrical Discharge Machining, or EDM, is a popular, non-conventional machining process that uses thermal energy to remove material from a workpiece’s surface. It uses electrical current discharges between the cathode (the tool) and the anode (the workpiece) to promote the erosion of material. For the process to work as desired, there must always be a small spark gap between the cathode and anode. The tool feed rate controls the width of the gap.
EDM can machine any material regardless of its hardness. However, its efficiency is limited by a lower material removal rate and significant tool wear. It is also known to result in poor surface quality and residual stresses. That said, hybrid manufacturing methods have been developed to overcome these challenges. These methods include abrasive-assisted EDM, Electrochemical Discharge Machining, and vibration-assisted EDM.
EDM typically requires electrodes of various shapes. The electrodes can be tube-shaped with one or more bores to drill holes into the workpiece. On the other hand, sinker electrodes remove material by erosion, creating cavities or imprints. They have a 3D configuration and are immersed in the dielectric. However, wire EDM was developed to replace the variety of tools initially required when performing conventional EDM.
Metal Cutting
There are multiple distinct ways to cut metals using CNC. These include waterjet cutting, laser cutting, plasma cutting, metal punching, and flame cutting.
Waterjet Cutting
CNC waterjet cutting machines fire highly pressurized water through a diamond or ruby nozzle at a workpiece. The high-pressure stream of water erodes material from the workpiece along a path dictated by the program. However, in some cases, the water stream alone is ineffective at eroding material. In such cases, granular abrasives are added to the waterjet to enhance its cutting power. Modern CNC waterjet cutting machines are advanced enough to allow users to switch between cutting purely using water or adding abrasives to the water based on the properties of the workpiece.
Plasma Cutting
Plasma cutting is a thermal cutting process because it uses heat to melt a material. CNC plasma cutters pass electric current, in the form of an electric arc, through a compressed stream of gas. As a result, the arc raises the temperature of the gas to a very high value and ionizes it. The gas is in a highly electrified state known as plasma. (Plasma is considered the fourth state of matter.)
The machine then forces the plasma gas through a very tiny opening. The plasma strikes the surface of the material at a very high temperature and speed, increasing the temperature above the boiling point. The material is melted and vaporized.
Laser Cutting
Also known as laser beam machining, laser cutting is a thermal process that removes material by melting and vaporization. In this process, a laser beam of high energy density focuses the heat energy on a particular point of the workpiece at a time, removing material at the micron level. Lasers work best for steel (carbon steel and stainless steel). Metals such as aluminum and copper are difficult – or perhaps more accurately slower – to cut using lasers because they reflect the light and conduct/absorb the heat.
Flame Cutting
Flame cutting, like plasma cutting and laser cutting, is a thermal cutting process. CNC machines that use this process to cut materials combine oxygen and a fuel source to create a cutting torch that melts material from a workpiece along a predefined path. But the cutting process is often much more complicated than this.
More technically, the oxygen oxidizes the material, generating heat from the exothermal reaction of oxidation. This heat supports ignition, meaning it must be sufficient to maintain the ignition temperature. On the other hand, the oxidation forms an oxide. And for successful material removal, the oxide must have a lower melting point than the surrounding material. If all these requirements are satisfied, a fast-flowing stream of oxygen mechanically blows away the melted oxide, effectively removing material from a section of the material in which the chemical reactions have taken place.
Usually, the fuel source is a gas such as propane or acetylene. The flame-cutting process is mainly used to cut steel. It can cut workpieces with a thickness of up to 100 inches (about 2.5 meters). Flame cutting differs from laser cutting because the touch flame is not focused on a very tiny spot. The flame affects a broader area compared to the focused spot in laser beam machining.
Metal Punching
Metal punching exerts a tremendous amount of cutting force using a steel punch tool, removing material from a sheet. The shape of the punch tool dictates the shape of the hole or material removed. The consistent shape of the punch tool is why metal punching is ideal for creating precision metal parts.
The metal punching process can be used on iron, aluminum, copper, and steel. However, the pressure and force exerted by the punch tool varies from material to material, given they each have their own strength and hardness. Another property to consider whenever you intend to punch metals is the thickness of the material. Typically, the process can be used to cut sheet metals and materials with a thickness of up to 30 mm.
While you can manually carry out metal punching by controlling the punch tool, CNC punching machines are a great alternative that not only boosts accuracy and productivity but also reduces the amount of scrap (unusable material) left after punching. CNC punching machines automatically move the punch tools. They also optimize the cutting process to ensure they cut back on wasted material.
Folding
CNC machines perform folding procedures by applying compressive forces to a particular section of material/sheet to create a bend. Often, the machines use a punching tool or hydraulic press to apply the forces against the worksheet. The tool presses the worksheet against a die, aligned to predefined axes, that matches the shape of the punching tool, like shown below.
An Illustration of the Folding Metal Fabrication Process (source)
The number of axes along which the forces are applied dictates the number of bends. The more the bends, the more complex the part’s shape. Folding creates parts or products with distinct, permanent shapes. These products can then be assembled and subsequently finished. For instance, they can be welded, riveted, or bolted together.
You can program CNC machines to fold sheets of metal. These machines can perform folding procedures of up to eight axes, meaning they fold material along eight different axes in a single operation. However, the thickness of materials affects the folding capabilities of the machine. Thicker materials lead to larger tolerances because of the large curvature formed along the edges of the folds. Inversely, folding thinner materials leads to tighter tolerances.
Welding
Welding is an assemblage technique that permanently joins parts together. While you can manually weld the parts together, the speed at which you assemble the parts improves with the use of CNC. CNC welding machines follow a welding path. As a result, they can assemble both simple and complex parts with a high degree of accuracy and precision.
Grinding
Grinding is a metal polishing process carried out towards the end of the metal fabrication cycle. Fabricators use it to achieve the desired finish, enhancing the surface quality of the machined part. For instance, grinding helps remove defects and spatters due to defective welds. It, therefore, smooths the surface.
CNC grinding machines control the movement of the rotating wheel using programmed instructions written in G-code and M-code. The program dictates the rotation speed, the path along which the wheel will move, and the number of passes. The program also automatically decides when to spray coolant based on programmed logic statements. In this regard, a CNC grinder only requires minimal intervention from the operator; it executes every function automatically.
Casting
CNC machining also indirectly facilitates casting. Casting is a form of metal fabrication in which molten metal is poured into a pre-made mold to create a desired shape or pattern. CNC machines can be used to create molds of various forms and shapes. The fabricator will then pour molten metal into the mold. This creates a part whose shape conforms to that of the mold.
Materials Used in CNC Machining for Metal Fabrication
There are various materials you can use in CNC machining for metal fabrication. However, the choice depends on the exact machining process you are employing. For instance, laser beam machining works best with steel. On the other hand, EDM machines work with electrically conductive materials, which include most metals.
Challenges and Solutions in CNC Machining for Metal Fabrication
The main challenges affecting CNC machining for metal fabrication are:
- High capital requirements
- Need for secondary operations and processes
- Quality control
- Programming knowledge
Fortunately, as discussed below, there are solutions to these challenges.
High Capital Requirements
Indeed, CNC machines are quite expensive. The cost might seem more justified if a single machine could handle multiple fabrication processes. However, most machines specialize in only one or two operations. Thus, if you wish to carry out all the metal fabrication procedures, you have to purchase multiple CNC machines. This translates to high capital requirements.
That said, you do not have to purchase all these machines in one go. You could start with the necessary equipment and expand your offerings as your workshop or machine shop grows.
Need for Secondary Operations and Processes
Even with a full suite of metal fabrication machines, post-fabrication care is often necessary. For instance, your customers may need you to paint the parts.
Quality Control
While CNC machines drive automation, they need to be constantly monitored to ensure they continuously meet the desired level of quality, accuracy, and tolerance. Fortunately, you can also infuse automation into quality control and quality assurance.
You can, for example, integrate predictive maintenance with preventive and reactive approaches. Predictive maintenance predicts failure before it occurs, allowing your technicians to service the equipment long before it breaks down or its components get out of sync.
Moreover, you can rely on probing in CNC machines. Probing inspects the lengths of tools, automatically loading offsets. The tool offset compensates for the identified tool wear, which maintains the consistency of the cuts. Probing also checks for tool breakage and damage, alerting the machine. This stops further machining that would have otherwise impacted quality.
Programming Knowledge
CNC machines in metal fabrication are controlled using programs. This means you may need to know how to write the programs. However, the existence of CAM software means that you do not have to possess programming knowledge to write the programs.
Conclusion
CNC machining and metal fabrication are interconnected in a number of ways. And as manufacturing practices increasingly demand more accuracy, speed, and efficiency to accommodate growing market needs, the popularity and adoption of CNC machining in metal fabrication are rapidly growing. CNC machines not only automate various metal fabrication processes but also execute them with high precision and accuracy. As manufacturing needs continue to grow and evolve, CNC machining will continue to play a crucial role in how metals are fabricated.
