CNC machining has rapidly dominated the manufacturing industry in recent years due to its high precision and repeatability. With several CNC technologies available today, understanding the CNC machining basics will help you distinguish their features. One of these innovative technologies is CNC turning.
It involves removing materials from a rotating rigid workpiece by using a non-rotating cutting tool of a turning center or lathe. The CNC turning process can produce components with different shapes and sizes based on the type of turning operation.
While this concept looks pretty straightforward, high-quality CNC turning can be complex. Suppose you’re wondering what this manufacturing process entails and what it takes to get the best results. In that case, this article will answer all your questions on CNC turning.
CNC turning is a highly precise and efficient subtractive machining process that works on the principle of the lathe machine. It involves placing the cutting tool against a turning workpiece to remove materials and give the desired shape.
The turning center or lathe stays secured while the raw material rotates at high speed. As the workpiece rotates along a dual CNC turning machine axis movement, a single-point cutting tool helps to shape the material. Computer programs help to control the turning center or lathe, ensuring the production of meticulously precise components.
People confuse CNC turning and milling, but they are different processes. CNC milling and most other subtractive CNC processes often secure the workpiece to a bed while a spinning tool cuts the material. In contrast, CNC turning uses a reverse process that rotates the workpiece while the cutting bit remains static.
Because of its mode of operation, CNC turning is typically used for producing cylindrical or oblong-shaped components. However, it can also create several shapes with axial symmetries. These shapes include cones, disks, or a combination of shapes. Some turning centers can even carry out polygonal turning operations with special rotating tools. That way, you can create hexagonal or square-shaped components.
Advantages of CNC Turning
CNC turning has several benefits, including the following:
The CNC turning machine can execute exact measurements and eliminate human mistakes using CAD or CAM files. Experts can deliver incredibly high accuracy using cutting-edge machinery, whether for the production of prototypes or the completion of the entire production cycle. Every cut is precise since the machine being used is programmed. In other words, the final piece in the production run is identical to the first piece.
Turning centers come in various sizes to accommodate your applications’ flexibility. The adjustment is rather easy because this machine’s tasks are preprogrammed. The operator can finish your component by making the necessary programming adjustments to your CAM program or even build something entirely different. Therefore, you can rely on the same precision CNC machining services company if you need many unique parts.
Manufacturing firms adhere to strict safety rules and regulations to guarantee complete safety. Since the turning machine is automatic, less labor is required because the operator is only there to monitor the machine. Likewise, the lathe body employs fully enclosed or semi-enclosed protective devices to avoid flying particles from the processed item and lessen harm to the crew.
There is a lower chance of error when tasks specified by programming are carried out on CNC lathes or turning centers. As a result, this machine can finish production more quickly without sacrificing the final output quality. Finally, you can receive the necessary components faster than with other options.
The CNC turning process can be quite complex. However, we will give you a simplified, stepwise breakdown of the process, from design to manufacturing.
The general steps of CNC turning are:
Step#1: Convert the CAD Design File to CNC Program
The first step involves preparing a CAD file for translation into CNC turning machine language. This does not involve advanced programming. You must already have some 2D drawings of your design. In that case, you need to capture these designs electronically using software such as AutoCAD or SolidWorks.
Once there is an electronic design in the CAD file format, you can then convert it to a CAM program. You can also use the same software tools mentioned above to export the drawing in CAM format. The manufacturing engineer can then use the software to test the manufacturability of the component.
Step#2: Prepare the CNC Turning Machine
The next step is the machine setup. Although most of the processes are automated, there is still a need for an operator. To effectively prepare the CNC turning lathe, you should follow these steps:
- Make sure you put the power off. The CNC machining process can get pretty dangerous. So, you should take extra care and check the power switches.
- Secure the part onto the chunk. The chuck is responsible for holding the part in place during the turning process. Not properly loading it can be dangerous and could result in components with the wrong dimensions.
- Load the tool turret. Several tools are involved in the turning operation, so you must ensure you’re picking the right tool for your specific finish. The turret will help hold as many tools as possible at once to give you a seamless operation.
- Ensure proper calibration. You must set the tool and the workpiece in the right way to ensure that the result meets the demands.
- Upload the CNC program. The last step before starting the operation is to upload the CNC code into the machine.
You need to keep two variables in mind at this stage. The first one is the turning speed (the speed at which the workpiece rotates). The second variable is the feed rate (the speed of the cutting tool as it moves along a rotating workpiece).
A Professional machinist must determine these values because wrong estimations will affect end results. In addition, improper estimations in some materials could lead to uneven finishes or irreparable damage to the workpiece.
That said, you can stick to a low turning speed and a high feed rate to “rough out” the shape. On the other hand, a high turning speed plus a lower feed rate is ideal for smooth finishes and parts with precise tolerance requirements.
Step#3: Manufacture the CNC Turned Parts
The final step is to manufacture your desired part. There are different turning operations you can choose, depending on the result you wish to get. Also, the part’s complexity will determine how many cycles you will have. The cycle time calculation will help you know the final time spent on the component, which is crucial for cost calculation.
Typically, the turning cycle time will comprise:
- Loading time. Although this is part of the setup, a cycle may require another means of loading the workpiece onto the machinery.
- Cutting time. This is the time it takes to cut the workpiece. Feed rate and cutting depth are factors that affect cutting time.
- Idle time. Any operation that does not involve cutting is an idle operation. For example, changing the settings of the turning center, the movement of the tool, etc.
The result of the manufacturing process will depend on the raw material used. A component obtained from plastic will differ in functionality and surface roughness from a metal component.
There are various types of lathe tools for CNC turning. As a result, you can perform several operations on a workpiece. These operations are categorized as external and internal operations. External operations help change the outer diameter of the component. On the other hand, internal operations change the inner diameter.
The individual operation is defined by the cutting tool used and the path it takes to remove the materials. Let’s check them out.
In this process, a single-point turning tool moves along the workpiece side to remove materials and form different features. The features it can create include tapers, chamfers, steps, and contours. The machining of these features typically occurs at small radial depths of cut, with multiple passes being made to reach the end diameter.
Tapered turning involves the production of conical surfaces by gradually reducing or increasing the diameter of a cylindrical workpiece.
This type of turning is performed on materials with Rockwell C hardness that is greater than 45. Heat treatment on the material is crucial before carrying out this process. Hard turning aims to limit or replace traditional grinding operations. It favorably competes with rough grinding when used for stock removal purposes. However, it may not be suitable for operations where dimension and form are critical.
During this process, the single-point turning tool radiates along the material’s end. This way, it removes thin layers of material, providing smooth flat surfaces. The depths of a face are typically very small, and the machining can occur in a single pass.
This operation also involves a radial movement of a single-point turning tool into the workpiece’s side. Thus, it cuts a groove that has equal width to the cutting tool. It is also possible to make multiple cuts to form larger grooves than the width of the tool. Likewise, some manufacturers use special tools to create grooves with varying geometries.
Like grooving, the cutting tool moves radially into the workpiece’s side. The single-point tool continues until it reaches the inner diameter or center of the workpiece. Therefore, it parts or cuts off a section of the raw material.
Boring tools enter the workpiece actually to cut along the internal surface and form features like tapers, chamfers, steps, and contours. You can set the boring tool to cut the desired diameter with an adjustable boring head.
It may be beneficial to perform boring operations after drilling a hole in the workpiece. This will help get more precise dimensions.
Drilling removes materials from the internal parts of a workpiece using standard drill bits. These drill bits are stationary in the tool turret or tailstock of the turning center.
This operation uses a single-point threading tool having a 60-degree pointed nose. This tool moves axially along the workpiece side to cut threads into the component’s outer surface. Machinists can cut threads to specified lengths, while some threads may require multiple passes.
This process involves cutting serrated patterns onto the workpiece’s surface using a special-purpose knurling tool. This pattern serves as a visual enhancement or a hand grip.
This sizing operation removes small amounts of metal from an already drilled hole. It helps to make internal holes with exact diameters. For instance, when you make a 6mm hole with a 5.98mm drill bit, you can easily read it to the accurate dimension.
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Types of CNC Turning Machine
You can use four major types of CNC turning machines for your project. They include:
Horizontal Turning Centers
These are enclosed machines that integrate both drilling and milling capabilities. This turning center uses a horizontally-oriented spindle and tools that are mounted above the rotating workpiece. The cutting tools cut across the material and use gravity to pull chips away as it is with milling. The chips go down into the bed for easier removal.
Vertical Turning Centers
A vertical turning center combines the horizontal turning center with the CNC mill. The design is such that the rotating chuck is set flat on the ground, ensuring the machining of large pieces at lower revolutions per minute (RPMs). In this case, the tool turret approaches from the side. There are also inverted vertical turning centers with the spindle and chuck in reversed positions.
Horizontal lathes have all the features of a conventional lathe. The only difference is that computer programs control them. Also, their primary operations are turning and boring.
Unlike a horizontal lathe, a vertical lathe holds the workpiece from the bottom before spinning it. This is a good option for machine shops with space constraints. Furthermore, it is the ideal option when working on heavy workpieces.
Components of CNC Turning Machine
Getting the best results from a turning procedure will require a good understanding of the machine tool. Let’s check out the main components of a CNC turning center.
A turning center’s headstock makes up the machine’s front part. It is usually located on the machine’s left side as it houses the main spindle where the chuck attaches to hold the workpiece. Therefore, the headstock holds the driving motor and the mechanisms for powering the spindle.
The spindle bar’s capacity will determine the workpiece’s maximum diameter to mount through the headstock.
This is the other end of the turning center. The tailstock attaches to the lathe bed, intending to support longer raw materials. The quill of the tailstock offers this support using hydraulic force. While the driving force comes from the spindle, the tailstock runs along with the workpiece.
However, you shouldn’t use a tailstock when face turning is important. The tailstock will be in the way of the operation.
Many people refer to the spindle as the heart of the machine tool. The main spindle of the CNC turning lathe consists of a spindle drive system and a spindle assembly. They are moving parts of the machine tool, including motors, gears, and chuck.
Some CNC turning centers use a sub-spindle or dual spindles. These centers often use the second spindle instead of a tailstock. The sub-spindle moves longitudinally towards the primary spindle under the control of computer instruction. This way, it is possible to machine the backside of workpieces without needing additional loading/unloading during the process.
Chuck and Collet
The chuck holds the part by its jaws, attaching directly to the spindle. However, it is replaceable, allowing the machining of different-sized parts. On the other hand, a collet is a smaller version of the chuck, which allows the machining of smaller parts. The parts suitable for a collet are often about 60 mm since they provide better grips for smaller pieces.
The bed, usually made with cast iron material, is the base plate resting on the table under the workspace. This component provides support for several fixed and operational parts. The bed connects to the headstock and runs through to the tailstock. The tool turret and other attachments run across the length of the bed.
This component supports the tool turret, feeding and guiding it against the workpiece. The carriage consists of the turret, saddle, and cross-slide. CNC turning centers with live tool turrets usually have powered rotary tools for milling operations. This ability increases the machine’s functionality while reducing or eliminating secondary operations.
In place of the carriage, newer improved machines come with the tool turret. These ones can hold more tools at once, allowing you to change the cutting tools needed for a specific operation. This means you can switch from one operation to another without taking time.
Here is where the computer numerical control comes in. It is the brain behind CNC turning operations, allowing the operator to adjust programs before starting the process.
CNC lathes and turning centers look alike and perform the same tasks. However, there are some differences to note. Although lathes are some of the earliest tools for CNC machining, turning centers are upgrades. They take the capability to a higher level, adding automated tool changing, efficient chip removal, live rotating tools, and easy completion of several components.
One of the major differences is that turning centers are often housed with full machine enclosures, protecting the operator from chips and coolants used in the cutting process. Turning centers use “slant bed” configurations as opposed to the “flatbed” design. Therefore, this unique design can better control chip flow to ensure they drop directly under the part.
CNC turning centers also have higher RPM capabilities. Their robust and innovative designs allow them to remove material at extremely high rates. Furthermore, CNC turning centers can easily fit with “Live tools,” incorporating milling, tapping, and drilling across a tuning profile.
The automatic feeding of material and changing of tools within the programmed cycle ensures that CNC turning centers can produce more efficiently CNC turned parts than a CNC lathe turning center. Due to the higher efficiency and larger production capabilities, CNC turning centers are more expensive than lathes.
Therefore, if you desire a flexible machine that can complete a wide variety of tasks, the turning center is the better choice. However, a CNC turning lathe is ideal for short-run productions and simple parts like bushings and pins.
There are several materials for CNC machining processes. Many of these materials are also suitable for CNC turning operations. They include:
These materials require different lathes or turning centers because they have specific requirements such as turning speed and feed rate.
Now you know what CNC turning entails and its several benefits. However, you can only get these benefits when you get CNC turning services from a reliable manufacturing partner. In this case, RapidDirect is your best option for all CNC machining services.
We boast innovative technologies and advanced turning machines to help you upgrade your custom machining experience. We also combine the knowledge and expertise of our technicians with strict quality control and quality assurance to give you high-quality parts that meet your requirements.
When you upload your design file on our instant quotation platform, you will get an instant quote for your parts. We also offer free DFM analysis to ensure the manufacturability of your component. All these come at competitive pricing. Upload your CAD file today, and let’s get started!
CNC turning is one of the most crucial parts of the manufacturing industry, giving precise results for a wide range of components. Its flexibility and production capability ensure large-scale production with identical results.
This article discussed various aspects of CNC turning, including its unique benefits. This way, you can make the best decision for your project. However, if you need more professional advice on this manufacturing process, contact RapidDirect today.