What is CNC machining?
CNC machining refers to the manufacturing and processing of parts and products controlled by computers. It involves the use of computer numerical control (CNC) machine tools to automatically remove excess material from a workpiece by processing and adjusting it.
Metal is the most commonly used material in CNC machining, and the end result is a finished product or part.
This process is known as subtractive manufacturing, and computer applications are used to control machine tool movements for better CNC machining. The most common types and processing processes for CNC machine tools include milling, turning, grinding, and EDM.
Milling uses a rotary cutter to remove material from the workpiece surface by moving along 3, 4, or 5 axes. This process is used to quickly process complex geometric shapes and precision parts with metal by cutting or trimming the workpiece.
Turning, on the other hand, involves using a lathe to manufacture parts with cylindrical features. The workpiece rotates on the shaft and contacts the precision turning tool to form circular edges, radial and axial holes, grooves, and grooves.
Compared to traditional hand machine machining, CNC machining is much faster, with high dimensional accuracy and minimal errors. The finished product meets the design’s computer code.
CNC manufacturing can be used to manufacture final products and components, but it is usually cost-effective only for short-term production of low batches, making it an ideal rapid prototyping manufacturing method.
Multi axis CNC machining
NC milling is a process that utilizes rotary cutters to remove materials. The workpiece can either remain stationary while the tool moves onto it or enter the machine tool at a predetermined angle.
The complexity and speed of the forming process depend on the number of moving axes the machine has. The more axes a machine has, the faster and more intricate the process can be.
3-axis NC machining
3-axis NC milling is still one of the most widely used and popular machining processes.
In 3-axis machining, the workpiece remains stationary, and the rotary cutter cuts along the X, Y, and Z axes.
This machining method is relatively simple and can produce products with a simple structure. However, it is not suitable for machining complex geometries or products with intricate components.
Since cutting can only be performed on three axes, the processing speed may be slower than that of 4-axis or 5-axis NC machining. This is because the workpiece may need to be manually repositioned to achieve the desired shape.
4-axis NC machining
4-axis NC milling adds a fourth axis to the motion of the cutting tool, enabling rotation around the X axis.
This method involves the use of four axes: the X-axis, Y-axis, Z-axis, and A-axis (rotating around the X-axis).
Most 4-axis CNC machines also have the capability to rotate the workpiece, known as the B-axis. This allows the machine to function both as a milling machine and a lathe.
If you require drilling on the side of a part or on the surface of a cylinder, 4-axis CNC machining is the ideal choice.
It significantly enhances the machining process and achieves high accuracy in machining.
5-axis NC machining
5-axis NC milling has an additional rotation axis compared to 4-axis NC milling.
The fifth axis is typically the B-axis, which rotates about the Y-axis.
Some 5-axis CNC machines also allow for rotation of the workpiece, known as the B-axis or C-axis.
Due to the high versatility of 5-axis NC machining, it is often used for manufacturing complex and precise parts, such as medical components like artificial limbs or bones, aerospace parts, titanium parts, oil and gas mechanical parts, military products, and more.
Advantages and disadvantages of CNC machining
CNC machining has the following advantages:
① Reduce the number of tooling required and eliminate the need for complex tooling to process parts with intricate shapes.
If you need to alter the shape or size of a part, simply modify the processing program for that part, making it ideal for the development and modification of new products.
② Machining quality is consistent with high accuracy and repeatability, making it suitable for the stringent machining requirements of aircraft.
④ It can efficiently handle complex profiles that are difficult to process using conventional methods, and can even work on parts that cannot be seen during processing.
Disadvantages of CNC machining
The downside of NC machining is that the cost of the machinery and equipment is quite high, and maintenance personnel must have a high level of expertise.
Steps of CNC machining
CNC machining is currently the most widely used machining method.
When conducting CNC machining, it’s important to not only understand its characteristics but also the steps involved in the process in order to improve machining efficiency.
What are the steps involved in CNC machining?
1. Analyze the processing drawings and determine the processing process
Based on the machining drawings provided by the customer, the machining personnel can analyze the shape, dimensional accuracy, surface roughness, material of the part, type of blank, and heat treatment status. This information is used to choose the machine tools and tools, determine the positioning and clamping device, machining method, sequence, and cutting parameters.
When determining the machining process, consideration must be given to the control capabilities of the CNC machine tool being used. This will maximize the efficiency of the machine tool and result in a more efficient machining path, reducing tool travel time and shortening machining hours.
2. Reasonably calculate the coordinate value of the tool path
To calculate the motion trajectory of the center of the tool path, the geometric dimensions of the machined parts and the set programming coordinate system are taken into account. This results in the determination of all tool position data.
Most CNC systems have the capabilities for linear interpolation and circular arc interpolation. For the processing of relatively simple planar parts, such as those made up of lines and circular arcs, the starting and ending points of geometric elements, the center of circular arcs (or the radius), and the coordinate values of the intersection or tangent points are calculated.
If the NC system does not have tool compensation capabilities, the coordinate values of the motion path for the tool center must be calculated.
For parts with more complex shapes, such as those made up of non-circular curves and surfaces, the actual curves or surfaces must be approximated using straight segments (or arc segments) and the coordinate values of their nodes must be calculated based on the required machining accuracy.
3. Compile part CNC processing program
Based on the tool path for the part, the data for tool movement and the determined process parameters and auxiliary actions are calculated.
The programmer then writes the part processing program in sections, following the functional instructions and program section format specified by the NC system being used.
Considerations should be given to:
- Standardizing program writing to improve clarity and communication;
- Having a thorough understanding of the performance and instructions of the CNC machine tool being used and effectively utilizing each instruction when writing program segments.
By following these three steps during CNC machining, the machining process can be carried out more efficiently.
