CNC Machining
What is CNC Machining?
CNC Machining is a manufacturing process in which pre-programmed computer software dictates the movement of factory tools and machinery. The process can be used to control a range of complex machinery, from grinders and lathes to mills and CNC routers.
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Advantages of CNC Machining
Accuracy and Precision
CNC machining is accurate, allowing product manufacturers to make parts according to the intended design. Aside from that, it has high precision and tolerance; therefore, you can manufacture different batches of a product without losing accuracy. Furthermore, being an automated process reduces the errors during machining.
Fast and Efficient
You can get a CNC machined part in a few days. Therefore, it is production efficiency. However, the speed and efficiency depend on the type of CNC machine and the complexity of the product.
Cost-effectiveness
CNC machining has a high initial investment cost. However, it has a lower operational cost. Aside from that, the high output rate, little or no human error, and low production cost increase its cost-effectiveness. In addition, for most machining operations, less training is required, and training is most available online.
Better Capabilities
Most CNC machines can carry many tools for different purposes. Aside from that, they have sophisticated software that allows them to work on different products and complex workpieces. Therefore, they have enhanced capabilities and compatibility with workpieces of different sizes, shapes, or textures.
Wide Range of Compatible Materials
Machining operations are compatible with a large base of materials. Common examples are metal, plastic, and composite.
How Does CNC Machining Work?
CNC machining relies on computer programs to create the layout of the process in which the machine tool should function. Since users cannot directly communicate with the machine tools, Computer-Aided Design (CAD) software is used.
CAD software creates the 2-dimensional and 3-dimensional models for the required CNC machined parts. With this design, the machine knows what the final part looks like.
The computerized controls do the calculation required for removing material, so the workpiece looks like the final part created in the CAD software.
Let us go through the breakdown of various processes that occur during CNC machining. CNC machining occurs in four stages:
Stage 1: Creating the CAD Model
Before CNC machining begins, the 2D or 3D model of the final design is required. This model is created in CAD software. There are many CAD software programs available online, free and paid.
Creating CAD models is not difficult and can easily be learned. However, some complex parts might require more experience with CAD, for which expert designers can be hired.
Stage 2: Converting CAD Model to CNC File
No CNC machine understands CAD language directly. CNC machines only recognize movement based on coordinates. Therefore, the CAD model must be converted to a CNC understandable file called G code.
Many CAD software programs can write the output file directly in G code by using the particular setting before saving the file.
In other cases, converting the CAD design to G code will require dedicated software called Computer Aided Manufacturing (CAM). CAM software is a very functional tool when it comes to the automation of machine processes.
Besides using CAM software, many simple free tools can convert simple CAD designs to G code with the click of a button. However, they don't have the vast suite of features that CAM software offers.
Stage 3: Configuring the CNC Machine
Before starting manufacturing processes, the CNC machine must be set up the right way.
Think of this as configuring the printer before you print something. You need to feed the printer with pages and check specific settings. CNC machines operate similarly.
Before machining begins, there are many setup processes to complete. For instance, you must ensure the workpiece is properly positioned on the machine. The dies must also be set correctly, and other position settings.
Stage 4: machining operation execution
Once the configuration stage is complete, the machine operation can begin. For this, you can execute the program on the display panel of the CNC machine.
Depending on what you design, you might have to go through various program prompts to choose different types of settings and options.
Once the CNC program is executed, the machine keeps going till the end of the program. It only stops if switched off by the operator or in the case of an unexpected error or power disruption.
A CNC machine is not one specific machine, as it is a group of different types of CNC machines working on various machining processes. Some of the most popular CNC machining operations include:
CNC Milling
CNC milling is one of the most popular types of CNC machining processes. In fact, many professional machine shops often use a CNC machining and CNC milling process interchangeably. Face milling and peripheral milling are two of the most frequently used CNC mill applications.
In a CNC milling machine, rotating cutting tools move relative to the workpiece to remove material.
The cutting tool (also called a milling tool) is fixed on a spindle that can rotate. The rotation and movement of the spindle give CNC milling machines the ability to perform three or more axes milling operations.
CNC Drilling
The CNC drilling process is a lot simpler than using milling tools or the turning process. In CNC drilling, the workpiece is held stationary while a drill bit moves over the workpiece and creates holes.
The purpose of drilling holes might be to add screw bolts, aesthetic requirements, or any other use.
CNC Grinding
CNC grinding machines use a rotating flat abrasive wheel for removing material from rough workpiece surfaces. This machine process is usually applied to create a smooth-finished part. The grinding wheel rotates at a very high speed.
CNC Routing
CNC routers are very similar to CNC milling machines. The main difference is that in a CNC router, the workpiece is always stationary, and the cutting tool moves in X, Y, and Z dimensions. CNC routers create faster cuts than milling machines without compromising accuracy and design complexity.
The 7 Most Common Materials in CNC
Precision machining uses numerous processes to produce exact parts. These processes involve different operations, elements, chemicals, and tooling techniques. The wrong combination of textile and technique can be disastrous. That's why matching the method with the materials is so critical. It's also why understanding the connection is essential.
Most machine shops and metal fabrication facilities already stock high-quality materials for primary assemblies. However, it pays to know what to expect so you can help teams select the best resources. Start by learning these seven most common CNC materials and their typical use cases:
Aluminum
Aluminum is perfect for CNC machining because it's highly pliable, non-magnetic, and resistant to corrosion. It's also inexpensive compared to other materials. Machinists enjoy working with aluminum sheet metal because it can handle tight tolerances and be plated with various hardeners or conductive coatings.
Hardened Steel
Hardened steel is valued for its inherent durability and long-lasting strength. Like other metals, the machinable properties depend on the grade. However, hardened steel is generally easy to weld and can be fashioned into countless products. It's also prone to corrosion without metal plating, metal finishing, or heat treating.
Copper
Copper is a common CNC machining material, and it has been for decades. Machinists prize it for precision projects because of its versatility, conductivity, and durability. Copper is also corrosion-resistant, making it perfect for parts exposed to moisture. However, it doesn't hold tolerances as well as other materials and often requires coating or plating for enhanced performance.
Stainless Steel
Stainless steel is one of the most commonly used materials in precision metal fabrication. Product designers love its strength and resistance to corrosion. It's also lightweight, easy to machine, and an affordable alloy alternative to other textiles. Stainless steel offers practical solutions to numerous problems while acting as a wildcard for innovative projects.
Brass
Brass is an economical alternative to several CNC materials. It's easy to machine, offers a smooth finish, and doesn't spark during the tooling process. This textile also tolerates relatively well, perfect for intricate designs and complex parts with unique geometries.
Titanium
CNC machining uses titanium because of its heat and pressure resistance. The material doesn't lose durability from corrosion, and it offers an ideal weight-to-strength ratio. Titanium is also biocompatible for easy disposal and inert for delicate applications. Meanwhile, this textile can be challenging to machine without excellent tools, skills, and rigs.
Engineered Plastics
Engineered plastics require injection molding, die casting, and other specific processes. However, they're non-conductive and inert, providing a smooth finish and pliable form at a relatively low cost. Fabricated plastic is also easy to clean and self-lubricate with the correct processing.
CNC Machining: Understanding Feeds & Speeds
Feeds and speeds refer to two separate velocities for machine tools: feed rate and cutting speed. They are often considered as a pair because of their combined effect on the cutting process.
Cut speed (or surface speed) is the speed at the outside edge of the part as it is rotating. It is expressed as a unit of distance along the work piece surface per a unit of time.
Feed rate is the velocity at which the cutter is advanced along the spinning work piece. The units are typically distance per spindle revolution.
Cutting Speed
Cutting speed is the speed that the material moves past the cutting edge of the tool. Cut speed can be defined as revolutions per minute (RPM) or as surface feet per minute (SFM).
Revolutions Per Minute (RPM) relates directly to the speed, or velocity, of the spindle. It represents the number of turns completed in one minute around a fixed axis. RPM maintains the same revolutions per minute throughout the entire operation.
What are Revolutions Per Minute (RPM) modes useful for?
Center cutting operations (drilling)
When the diameter at the beginning and end of a cut only differs slightly from the beginning.
During threading to allow the perfect synchronization between spindle revolution and Z-axis motion to allow precise threads
Surface Feet Per Minute (SFM) is a combination of the cut diameter and RPM. The faster the spindle turns, and/or the larger the part diameter, the higher the SFM.
For example, if two round pieces of different sizes are turning at the same revolutions per minute, the larger piece will have a greater surface speed because it has a larger circumference and has more surface area. As the tool gets further into a workpiece, the same spindle speed will produce a decreasing surface speed. This is because each revolution represents a smaller circumferential distance, but takes the same amount of time.
Most CNC lathes have Constant Surface Speed (CSS) to counteract the natural decrease in surface speed. This speeds up the spindle as the tool moves closer to the turning axis. By utilizing CSS the lathe is adjusting the revolutions per minute to maintain a constant surface speed at every distance from the center.
What are Constant Surface Speeds (CSS) useful for?
A uniform surface finish.
When the diameter at the beginning a cut will differ significantly from the diameter at the end of the cut.
Better tool life and machining time because tools will always cut at the appropriate speed.
Feed rate is the velocity at which the cutter is advanced along the work-piece. Feed rate is expressed as units of distance (inch) per minute or per single revolution.
Feed rate can be defined as an inch per minute (IPM) or inch per revolution (IPR). IPR is more commonly used.
Selection of Tools, Feeds, and Speeds
Cutting tool selection has a direct impact on the proper programming of feeds and speeds at the machine.
That said, there are many other variables that affect feeds and speeds, such as:
Work-piece material class and condition
Work-piece diameter
Cutter material
Cutter geometry
Type of cut
Depth of cut
The condition of the machine
Our Factory
King Siu Metal Products (Shen Zhen) Limited is located in Sun San Ping Xi South Road, Lunggang District, Shenzhen City, China. The main product range is Audio cabinet, Speaker grille, Heat sink and Metals accessories. In February, 1998, the factory acquired the ISO9002 quality system certification. It covers an area of more than 6,000 square meters, with around 102 employees, management and technical personnel exceed 20 people.
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