CNC Turning Explained: Process, Operations and Advantages
Computer numerical control (CNC) turning is a subtractive manufacturing process that applies a fixed cutting tool to remove material from a workpiece, which is typically cylindrical.
With the advent of technology, CNC turning continues to grow in popularity across the world. Manufacturers find the process suitable regarding speed, cost-effectiveness, and reliability.
This article focuses on the working principle of CNC turning, the types of CNC machines and operations, and the advantages of CNC turning.
What is CNC Turning?
CNC turning is a subtractive manufacturing process involving a rotating workpiece and a stationary machine tool that removes matter from the inner diameter or outer diameter of the workpiece. The CNC turning process typically produces cylindrical or conical surfaces and happens on the CNC lathe machine.
However, there are newer CNC turning machines that have multiple axes capabilities. Contemporary CNC machines have several turning centers that make it possible to turn non-cylindrical components.
CNC lathes generally rotate the workpiece and use a tool turret to bring the cutting tool to the rotating workpiece. The main spindle holds the rotating workpiece firmly. The cutting tool can move on multiple axes, therefore, CNC turning can achieve all geometry types.
How do CNC Turning Machines work?
The following are the main steps explaining how the CNC turning machine works:
1. Produce the CAD model
It is through the computer-aided design (CAD) software that the model that the machinist plans to produce is generated. Conversion of the CAD file to a suitable file format (DWG/DXF) and importation of the same to the CNC software follows.
Producing a CAD model can follow several techniques. Some people prefer to use vector cut paths to trace an image. They identify the silhouette of the image and trace it around, ensuring that all the main features are captured. Once saved in the DXF file, the details can then be sent to the CNC software.
Another approach is you convert the image automatically. You first scan the image. After saving it in PDF format, you convert it to a DXF file, ready for importation to the CNC program.
Optimizing the CAD Model
There are many ways of optimizing the CAD design. Here are some tips to keep in mind:
Model Wall Thickness
Take care not to make the wall thicknesses on the model too small. The smaller the wall thickness, the higher the susceptibility to vibrations. Vibrations will affect the surface quality of the final product even with the best single point cutting tool.
Corners and edges
Regarding corners and edges within the design for complex parts, the size of the cutting tool should be considered. If not, the surface finish will not be of the best quality. For an excellent surface finish, make sure that corner radii exceed the suggested figure by at least 1mm.
Size of Cavities
Most CNC milling and turning operations have limits as to how much cutting depth is possible. Make sure that the size of cavities on the model doesn’t exceed the diameter of the cutting tool by more than four times to safeguard the capabilities of the turning machine.
2. Convert the CAD Model for the CNC machine
The CNC machine does not recognize the CAD model file as it is. Most CNC machines use a not-so-advanced programming language based on RS-274 or G-code. That the CNC turning machine language cannot read the DXF file format from Autodesk necessitates this step.
But the conversion is not complicated. There are tools for converting the file to readable format, for instance, the Standard for the Exchange of Product Data (STEP). Another tool is the Initial Graphics Exchange Specification (IGES).
If you need the CNC technical drawing, this is the point at which you need to ensure it is available too. Some measurements are not clear from the model, so it is advisable to have a technical drawing on the side.
The technical drawing is particularly essential if the model has threads, extraordinary precise tolerance requirements, and special finishing specifications.
The machinist may also need the technical drawing for reference purposes.
3. CNC Milling Machine preparation
At this point, the model is ready for reproduction in the CNC turning or milling machine. Once you have the input from the rest of the team, it is time to turn your attention to the turning/milling machine. The machine needs prepping up before the manufacturing process can start.
That applies if you are not outsourcing the CNC turning and CNC milling service. If you were outsourcing the service, you would only need to contact several providers and choose the offer that impresses you the most.
Now, regarding preparing the lathe machine for turning, several things come into focus: The device(s) for holding the workpiece, the cutting tools, the tool turret, the allocation of tool numbers, and the adjustment of the program and machine.
Most importantly, all the activities taken on the CNC milling machine should be in line with the existing organizational policy and health & safety requirements. If there are any potential challenges in operating the machine to remove material, seek the necessary assistance to execute the CNC turning process successfully and safely.
Setting up the workpiece on the lathe
Selecting and mounting the machine tool in the turning center
Programming the lathe using CNC software
The workpiece rotates at the specified turning speed and feed rate
Replacing the turning tool with a finishing tool to achieve a smooth surface
Types of CNC Turning Machines
CNC machines are still instrumental in machining operations, despite the growing popularity of CNC turning centers. The most popular tasks on the CNC lathe machine are straight turning, contour turning, form turning, threading, and taper turning.
Let us now review the different types of CNC turning centers and CNC lathes based on axes.
Horizontal Turning Centers
In horizontal turning centers, the spindle carrying the turning tool is mounted parallel to the floor. In other words, the spindle and sub spindle are in a horizontal position in this CNC turning center.
Vertical Turning Centers
This CNC turning center has the spindle placed in the vertical position. The turning operation on the workpiece is performed from above. Typically, the table in advanced CNC turning centers will move on the Y and X axes (horizontally), so you can achieve tri-axial machining.
In place of a spindle, the horizontal lathe comes with a horizontal arbor. The arbor holds a range of heads. This way, the horizontal lathe can produce a wide range of part sizes and shapes. Also important is the force of gravity helps maintain the cleanliness of the workpiece during the CNC machining process.
The vertical lathe is less complicated than the horizontal lathe. It sets its spindle along the vertical plane and in a fixed position. The workpiece moves along the vertical plane – up and down movement.
Based on this setup, the vertical lathe is most suited for sizeable metal plates and other workpieces that need to be machined on only one side using special rotating tools. If there is a risk of workpiece sagging, the vertical lathe is preferable to the horizontal lathe.
Types of CNC Turning Operations
The CNC lathe can perform several turning operations including facing, turning, drilling, and boring. Others are threading, grooving/parting, and knurling. Let’s look at these operations in more detail:
In this CNC lathe operation, the single point cutting tool moves along the diameter of the rotating workpiece in a linear motion. The result of this operation is a cylindrical part. When placed at different angles, the turning operation can produce a wide range of shapes.
The drilling operation helps make a round hole in a workpiece. There are two ways of achieving this: Using a live tool that rotates the drill bit or by rotating the workpiece. Remember to apply the center drill first to prevent the drill from wandering off.
Boring operations typically happen after the drilling operations. The machinist uses a single point turning tool to remove material on the inner diameter and enlarge the drilled hole.
The CNC machine produces helical screw threads on the workpiece. Machine shops can optimize the capability of the CNC machine to apply canned cycles with specifications for threading parameters such as offset, size, and length of the thread.
Grooving or Parting
Grooving or parting applies a sharp cutting tool on the rotating workpiece to create a cavity. Parting is applicable when the machinist wants to disengage a finished component from the stock material. In grooving, the machinist does not remove the whole part from the original.
Knurling is the formation of troughs and crests on the workpiece to increase the surface friction of the part (for better grip) and enhance the aesthetic appeal of the part.
A knurl holder, which is firmly fixed on the worktable, holds the knurling wheels. The knurled wheel sits perpendicularly to the central axis of the workpiece. As the knurl holds onto the piece, the patterns on the wheels are transferred to the workpiece.
Advantages of CNC Turning
CNC turning is instrumental in the manufacturing environment. Let’s review some of the advantages the process offers as compared to alternatives.
The capability of CNC turning to adhere to requirements for accuracy and tight tolerances makes the operation popular in industries such as military, medical, and aerospace. These industries often use precision machined parts in their manufacturing processes.
The conventional manufacturing industry also finds high precision useful, even when you consider an aspect such as the amount of raw material likely to be lost due to inaccuracies.
Even where the CNC lathe doesn’t meet the extremely tight tolerance requirements in some of the industries, there is a chance to enhance the accuracy of these machines. Outsourcing your CNC turning jobs to specialists is also an excellent solution to accuracy requirements.
The flexibility that CNC turning offers is an advantage that a modern business can use. The lathe machine can work on a wide range of materials including metal, plastic, wood, and glass. It not only allows for the use of more tools but also different settings.
Because of this versatility, many businesses choose CNC turning for their part production needs. There is also the option of integrating the CNC lathe with other cutting tools to achieve even more diverse results.
Safety of CNC Turning Centers
The safety of the CNC machinist and any other personnel within the machine shop is much higher compared to where traditional machining options are used. Since the machine is largely computer-controlled, the level of manual labor requirement is minimal.
The role of the machinist is usually only to oversee everything as the CNC turning rotates. Since the rotating parts of the CNC lathe machine are typically well covered, the chances of pieces flying out and causing injury are minimal.
Today’s marketing environment is highly competitive, so even the speed of delivering products to customers matters. CNC turning is not only capable of applying high turning speed but it is also less prone to errors. With a CNC lathe, one can deliver accurate products faster.
Those in mass production activities particularly find the turning and milling capabilities CNC turning center option essential in satisfying high demand without compromising on quality.
Are you wondering how to produce parts for your business in the most cost-effective, accurate, and safe way? The answer lies in CNC technologies that include the CNC milling and CNC turning processes. CNC-turned parts mean more profit for your business because you have a competitive edge.
Aria offers various types of CNC turning services for your automotive parts and other industry components. We can partner with you and handle your custom part production requirements, that is the desired shape, size, and so on. We will carefully review your part types, quantities, and budgetary considerations. We will then recommend the best CNC turning procedure on an advanced CNC turning center.