What Is CNC Machining? Types, Pros, Cons and Machining Steps

What is CNC machining?

CNC machining is the manufacturing and processing of parts and products under the control of computers.

CNC machining involves the use of computer numerical control (CNC) machine tools to process and adjust a piece of material (i.e., workpiece) by automatically removing the excess part of the material.

Usually, the material we will use is metal.

After removal, the finished product or part has been produced.

This process is also called subtractive manufacturing.

In order to better carry out CNC machining, computer applications are used to control the movement of machine tools.

The types and processing processes of common CNC machine tools include the most common milling and turning, followed by grinding and EDM.

During milling, the rotary cutter is used for the workpiece surface and moves along 3, 4 or 5 axes.

Basically, it is to cut or trim the workpiece, which can quickly process complex geometric shapes and precision parts with metal.

When turning, the lathe is used to manufacture parts with cylindrical features.

The workpiece rotates on the shaft and contacts with the precision turning tool to form circular edges, radial and axial holes, grooves and grooves.

Compared with traditional hand machine machining, CNC machining speed is much faster.

The computer code is correct and meets the design.

The finished product has high dimensional accuracy and small error.

CNC manufacturing can be used to manufacture the final products and components, but it is usually cost-effective only in the short-term production of low batches, so it is an ideal rapid prototyping manufacturing method.

Multi axis CNC machining

NC milling involves the removal of materials and the use of rotary cutters.

Either the workpiece remains stationary and the tool moves onto the workpiece, or the workpiece enters the machine tool at a predetermined angle.

The more moving axes a machine has, the more complex and faster its forming process will be.

3-axis NC machining

Three axis NC milling is still one of the most popular and widely used machining processes.

In 3-axis machining, the workpiece remains fixed and the rotary cutter cuts along the X, Y and Z axes.

This is a relatively simple NC machining form, which can manufacture products with simple structure.

It is not suitable for machining complex geometries or products with complex components.

This is a relatively simple NC machining form, which can manufacture products with simple structure.

It is not suitable for machining complex geometries or products with complex components.

Since cutting can only be performed on three axes, the processing speed may also be slower than that of 4-axis or 5-axis NC, because the workpiece may need to be manually repositioned to obtain the desired shape.

4-axis NC machining

In 4-axis NC milling, the fourth axis is added to the motion of the cutting tool, allowing rotation around the X axis.

There are now four axes – the x-axis, the y-axis, the z-axis, and the a-axis (rotating around the x-axis).

Most 4-axis CNC machines also allow the workpiece to rotate, which is the so-called b axis, so that the machine can act as both a milling machine and a lathe.

If you need to drill on the side of a part or on the surface of a cylinder, 4-axis CNC machining is the only choice.

It greatly speeds up the machining process and has high machining accuracy.

5-axis NC machining

5-axis NC milling has an additional rotation axis compared with 4-axis NC.

The fifth axis is about the y axis, also known as the b axis.

The workpiece can also rotate on some machines, sometimes called b-axis or c-axis.

Because of the high versatility of 5-axis NC machining, it is used to manufacture complex and precise parts.

Such as medical parts of artificial limbs or bones, aerospace parts, titanium parts, oil and gas mechanical parts, military products, etc.

Advantages and disadvantages of CNC machining

CNC machining has the following advantages:

① Greatly reduce the number of tooling, and do not need complex tooling to process parts with complex shapes.

If you want to change the shape and size of a part, you only need to modify the part processing program, which is applicable to the development and modification of new products.

② The machining quality is stable, the machining accuracy is high, and the repetition accuracy is high, which is suitable for the machining requirements of aircraft.

④ It can process complex profile difficult to be processed by conventional methods, and even process some processing parts that cannot be observed.

Disadvantages of CNC machining

The disadvantage of NC machining is that the cost of machine tools and equipment is expensive, and maintenance personnel are required to have a high level.

Steps of CNC machining

CNC machining is the mainstream machining method at present.

When we carry out CNC machining, we should not only know the characteristics of CNC machining, but also know the steps of CNC machining, so as to better improve the machining efficiency.

What are the steps of CNC machining?

1. Analyze the processing drawings and determine the processing process

According to the machining drawings provided by the customer, the process personnel can analyze the shape, dimensional accuracy, surface roughness, workpiece material, blank type and heat treatment status of the parts, and then select the machine tools and tools to determine the positioning clamping device, machining method, machining sequence and cutting parameters.

In determining the machining process, fully consider the command function of the CNC machine tool used, give full play to the efficiency of the machine tool, and achieve reasonable machining route, less tool walking times and shorter machining hours.

2. Reasonably calculate the coordinate value of the tool path

According to the geometric dimensions of the machined parts and the set programming coordinate system, the motion trajectory of the center of the tool path is calculated, and all the tool position data are obtained.

The general CNC system has the functions of linear interpolation and circular arc interpolation.

For the contour processing of planar parts with relatively simple shape (such as those composed of lines and circular arcs), it is only necessary to calculate the starting point and ending point of geometric elements, the center of circular arcs (or the radius of circular arcs), and the coordinate values of the intersection or tangent point of the two geometric elements.

If the NC system has no tool compensation function, the coordinate value of the motion path of the tool center should be calculated.

For parts with complex shapes (such as those composed of non-circular curves and surfaces), it is necessary to approximate the actual curves or surfaces with straight segments (or arc segments), and calculate the coordinate values of their nodes according to the required machining accuracy.

3. Compile part CNC processing program

According to the tool path of the part, the tool movement path data and the determined process parameters and auxiliary actions are calculated.

The programmer can write the part processing program section by section according to the functional instructions and program section format specified by the NC system used.

Attention shall be paid to:

First, the standardization of program writing should facilitate expression and communication;

Second, on the basis of being fully familiar with the performance and instructions of the CNC machine tool used, the skills of using each instruction and writing program segments.

The above three steps are CNC machining steps, which should be followed when CNC machining is carried out, so that machining can be carried out more efficiently.

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