Turning, a term that resonates throughout the industry, is a technique that paved the way for modern machining and has become the cornerstone of mechanical engineering.
With a single-point cutting tool and a rotating workpiece, it opens up a world of precision cuts and intricately shaped components.
This article will unravel the ins and outs of turning, revealing the parameters, operations, types and equipment involved. Get ready to explore the world of turning, where raw materials are shaped into engineered perfection.
What is turning?
Turning is a type of machining in which a cutting tool removes material from a workpiece as it rotates about an axis. This operation is performed on a turning machine or lathe, a specialized tool that can accommodate different geometries and materials.
Turning allows operators to achieve a good surface finish and produce parts with high tolerances. It’s a process that can create internal and external surfaces, even contoured ones, with unparalleled precision.
The dawn of turning: A Historical Perspective
Tracing the origins of turning takes us back centuries to when manual lathes were used to shape wood and metal. The transformation of the process came with the introduction of computer numerical control (CNC) technology in the mid-20th century, which revolutionized the industry.
Turning evolved from a manually controlled process to an automated one, enabling the production of intricate and precise diameter components limited only by the specifications of the machine and the skill of the operator.
How does turning work?
Turning works on a simple but effective principle:
The workpiece is rotated at high speed while a single-point cutting tool travels along the surface of the workpiece, removing a thin layer of material.
The cutting action occurs at the point where the tool’s cutting edge meets the workpiece.
This cutting speed, combined with the feed rate (the speed at which the cutting tool moves relative to the workpiece), determines the shape and surface finish of the final product.
What are the stages of turning?
The turning process unfolds in a series of carefully calibrated stages, which we will explore below.
Mounting the workpiece
First, the workpiece is mounted on the lathe. This is often accomplished by clamping the workpiece between two centers or by securing it in a chuck that allows it to rotate about a fixed axis.
Tool Setup
Tool Setup
Next, the single-point cutting tool is positioned perpendicular to the workpiece surface. The tool’s cutting angle, rake angle and relief angle, which determine the quality of the cut, are adjusted to achieve the desired result.
Cutting Process
After setup is complete, the lathe is started and the workpiece begins to rotate. The cutting tool moves longitudinally along the rotating workpiece, removing material in the form of chips.
Quality inspection and finishing
The final step is to inspect the part for any imperfections and make any necessary corrections. The finished part is then measured for dimensional accuracy and surface finish, which may require additional turning operations such as finish turning or sizing.
What are the different types of turning?
Turning is not a monolithic process, but rather a collection of processes, each with its own unique characteristics and applications. Here are some of the more common types:
Straight turning: Straight turning involves the removal of metal from the outer surface of a cylindrical workpiece. The cutting tool moves longitudinally along the workpiece, reducing its diameter. It is often used to ensure that cylindrical workpieces have a consistent diameter along their length.
Taper turning: In taper turning, the tool is not parallel to the axis of the lathe, but at an angle to create conical shapes. This technique is commonly used to produce machine tool spindles and drive shafts that require a tapered end for fitting components.
Facing: This operation reduces the length of a workpiece or creates a smooth end or face. The cutting tool moves radially across the end of the workpiece, removing material. It’s often used to clean up the ends of parts or to prepare surfaces for additional operations.
Groove Turning (or Grooving): This type involves cutting a narrow groove in the outer or inner surface of the workpiece. Groove turning is commonly used for oil grooves, retaining ring grooves, and parting off sections of a workpiece.
Parting: Parting is the process of cutting a piece from a larger workpiece. It involves the creation of a narrow slot down to the center of the workpiece, ultimately separating a section of material. It is typically the final operation after the part is fully formed.
Thread Turning: This type involves cutting a helical groove of a specified pitch along the external or internal surface of a cylindrical workpiece. Thread turning is used to produce threads for fasteners and other components that require threaded features.
Boring: Boring is the process of enlarging a hole that has already been drilled or cored. It can improve hole accuracy and provide a smooth internal surface. It’s used to finish internal surfaces or prepare them for additional operations such as threading.
Knurling: This operation creates a regularly shaped roughness on the workpiece surface, often to provide a better grip for handling. The knurling tool presses a pattern into the surface of the workpiece as it rotates.
Drilling: On a lathe, drilling is the process of creating a cylindrical hole by removing metal along the circumference of a pointed tool or drill bit. It’s usually the first step in creating an internal feature that will be further refined by operations such as boring or threading.
CNC (Computer Numerical Control) turning: CNC turning uses computer programs to control the motion of the cutting tool. It allows complex parts to be produced at high speeds and with high precision. CNC turning is particularly useful for producing parts with complex radial features or when tight tolerances are required.
Turning Techniques and Methods
Turning Techniques and MethodsDifferent turning techniques have been developed to meet the needs of different applications. These include
Parting Off
Parting off, also known as cut-off, is the process of cutting a piece from the part being turned.
Grooving
Grooving is a turning operation in which grooves are made in the surface of a workpiece.
Facing
Facing is the process of cutting along the face of a workpiece, usually to flatten it or cut it to a specific length.
Knurling
Knurling doesn’t involve cutting, but rather pressing a pattern onto the surface of a workpiece. It is often used to create a serrated pattern for better grip or aesthetic appeal.
Reaming
Reaming removes a small amount of material from an existing hole to improve its dimensional accuracy and surface finish.
Turning Tools and Equipment
Turning tools and equipment
Turning, an essential machining operation, uses a variety of equipment for different purposes. Here are some of the critical tools involved:
Lathe
A lathe, also known as a turning machine, is the central piece of equipment in the turning process. Different types of lathes are used for different turning operations, such as turret lathes, special purpose lathes, and CNC lathes.
Single point cutting tool
A single-point cutting tool, typically made of high-speed steel or carbide, is used in the turning process. The characteristics of the tool, such as cutting edge angle and tool life, play a significant role in the success of the turning process.
Chuck
A chuck is a device used to hold the workpiece in place while it rotates.
Tailstock
A tailstock supports the end of the workpiece as it is rotated between centers.
Feed mechanism
The feed mechanism, usually controlled by a lead screw, controls the speed at which the tool moves along the workpiece.
Turning Parameters
Several parameters affect the turning process. Understanding them can help optimize the process and achieve the desired results. Some of the most important parameters are
Cutting Speed
Cutting speed, often expressed in meters per minute or feet per minute, refers to the speed at which the cutting tool or workpiece moves during the cutting process. It’s a critical factor that affects the quality of the cut, tool life and overall productivity of the turning operation.
There are many factors to consider when setting the cutting speed, such as
The type of material being machined
The hardness of the material
The type of cutting tool being used
The desired surface finish
Depth of cut
Another critical parameter in turning is the depth of cut, which is the distance the cutting tool penetrates into the workpiece. This factor can have a significant impact on production rate, surface finish and tool life.
To highlight a few considerations related to depth of cut:
It should not be so shallow as to waste time or so deep as to overwork the tool and machine.
The type of material, its hardness and the type of tool being used all play a role in determining the appropriate depth of cut.
Feed Rate
In turning, the feedrate is the distance the tool moves along the workpiece in one revolution of the workpiece. Like other parameters, it can have a significant impact on the quality of the finish, tool life and production speed.
Here are some key factors to consider regarding feedrate:
Higher feed rates can result in higher production rates, but can negatively affect tool life and surface finish.
Different materials and tool types may require adjustments to the feed rate for optimum results.
Other important turning parameters include
Tool geometry: This includes various angles on the cutting tool, such as rake angle and relief angle. They affect the cutting action and surface finish.
Workpiece material: Different materials have different cutting properties that affect the choice of cutting speed, feed rate and tool material.
Supported materials for turning
Turning is a versatile process that can be used on a wide range of materials. Commonly turned materials include metals such as steel, brass, aluminum, titanium and nickel alloys, and plastics such as nylon, polycarbonate, ABS, POM, PP, PMMA, PTFE, PEI and PEEK.
Some turning operations extend to wood and other materials, although metals and plastics remain the most common.
Turning is selected based on the machinability of the material, the complexity of the features required, and the desired surface finish.
More robust materials, such as steel and titanium, may require more power, specialized tools or specific cutting forces, while softer materials, such as aluminum and plastics, are relatively easy to machine.
Certain materials, due to their unique properties, may produce better surface finishes or allow for more intricate shapes and forms to be machined.
Pros and Cons of Turning
Like any manufacturing process, turning has its advantages and disadvantages.
Some of the advantages of turning include
Efficiency in mass production through automation
High level of precision and accuracy
Ability to handle complex shapes and geometries
Provides good surface finish
On the other hand, the disadvantages are
Initial setup can be time consuming
Less efficient for non-cylindrical or complex shaped parts
Operator skill and experience is critical
The process may require frequent tool changes due to tool wear.
Design Tips for Turning
When designing for turning, there are a number of critical issues to consider. The following guidelines can help you achieve optimal results:
Keep the design as simple as possible.
Avoid sharp internal corners; they can cause stress concentration and are difficult to machine.
Maintain a uniform wall thickness to prevent distortion during machining.
Choose standard thread sizes to reduce cost and machining time.
Design parts that can be machined in a single setup to save time and maintain accuracy.
Turning Software
With the advent of computer numerical control (CNC) technology, turning operations have become highly automated and precise. CNC lathes are controlled by specialized software that allows complex geometries to be machined accurately and repeatably. Some of the most popular software used in turning are AutoCAD, SolidWorks, Mastercam and Fusion 360. These software tools allow the operator to design the part, plan the machining operations, and generate the necessary G-code that controls the movement and operation of the CNC lathe.
Potential Hazards of Turning
Turning, like any other machining operation, has potential hazards. Accidents can occur due to tool breakage, flying chips, or entanglement with rotating parts. It’s important to ensure that all safety measures are in place and followed, including the use of protective clothing and equipment, regular maintenance and inspection of the machine, and proper training of operators. It’s also important to maintain a clean and organized work area to reduce the risk of accidents.
Possible side effects of turning
Turning involves the removal of material from a rotating workpiece using a single-point cutting tool. This machining operation can produce several side effects, largely depending on the operating parameters, the nature of the workpiece material, and the characteristics of the cutting tool.
A key concern is tool wear, which is an inevitable occurrence in turning operations and is influenced by factors such as cutting speed, feed rate and the angle of the tool’s cutting edge. Wear leads to a reduction in tool performance, which affects the accuracy and surface finish of the machined component. In addition, the chips produced, a byproduct of material removal, can present handling and disposal challenges.
Often, turning operations require continuous monitoring to control these side effects. Despite these advances in CNC turning automation, the operator’s role in maintaining tight tolerances, reducing tool wear and ensuring a good surface finish remains essential.
Environmental Impact of Turning
7 Environmental Impact of Turning
Like other machining processes, turning can have an impact on the environment. The energy consumption of turning machines, the generation of waste from the material removed, and the disposal or recycling of used cutting tools are significant environmental factors.
In addition, the coolants and lubricants used to reduce friction, cool the cutting tool and extend tool life often pose an environmental hazard due to their chemical composition. As the machining industry evolves, the search for environmentally friendly alternatives is increasing, with the goal of a more sustainable turning process.
The economics of turning
The cost effectiveness of turning is largely dependent on several factors, including machine cost, operator cost, tool life and maintenance cost.
What is the average cost of turning per hour?
The cost of turning services can vary widely based on factors such as part complexity, material type, required tolerances and regional labor costs. On average, however, you can expect to pay between $50 and $100 per hour for CNC turning services.
Where to Get Turning Services?
Several companies offer professional turning services, one notable provider is 3ERP. They specialize in various CNC turning services for a wide range of parts. Turning at 3ERP is performed on a variety of metals such as aluminum, magnesium, steel, stainless steel, brass, copper, bronze, titanium, and nickel alloys, as well as plastics such as nylon, polycarbonate, ABS, POM, PP, PMMA, PTFE, PEI, and PEEK.
Alternative Technologies to Turning
Although turning is an essential operation for producing cylindrical or tubular components, there are other technologies that can produce similar results. Milling, for example, although fundamentally different in operation, can be used to produce components with cylindrical characteristics and even contoured surfaces.
Conclusion
In addition, advances in additive manufacturing or 3D printing offer an alternative approach to creating complex geometries without the need for subtractive processes such as turning.
The bottom line
Turning is an integral part of the machining industry, enabling the creation of intricate components through high-precision cutting. Its versatility is demonstrated by its ability to machine a variety of materials and produce a wide range of shapes and geometries.
While turning offers many benefits, it also presents challenges such as tool wear and environmental concerns. As the technology advances, there is an ongoing effort to optimize the process to make it safer, more efficient and more sustainable. The fascinating world of turning will continue to evolve and shape the future of mechanical engineering.
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