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In machining, there are many processes used to complete specific jobs. Each process has its own set of guidelines and specifications. In this article, we will be learning about CNC Turning. This is a versatile and cost-effective manufacturing process capable of producing large amounts of parts in a variety of different materials.
CNC Turning is used across an array of industries, for an assortment of applications. In this article we will go in depth on what exactly CNC Turning is, how it works, it’s advantages & disadvantages, as well as comparing turning to other manufacturing processes such as milling or grinding.
To better understand this process, we can break the term down into two parts ‘CNC’ and ‘Turning’.
Computer Numerical Control (CNC) refers to too computerized systems that take control of the functions and motions of a machine. This is accomplished by means of a program that contains digital coded data. This code controls features such as tool movements, and speeds & feeds, depth of cut, as well as other functions such as spindle on/off and coolant applications.
‘Turning’ is a manufacturing process in which raw material is removed to create the desired part. The term turning refers to producing these parts by means of rotating the stock material at a high rate of speed while the cutting tool is feed to the surface face of the material. The turning process reduces the diameter of a workpiece to a specific dimension and produces a smooth part finish.
In the operation of a machine shop, CNC turning is used to make predominately cylindrical parts, and other shapes as well. Some examples of finished products can be shafts, hollow tubes, conical shapes, threaded rods, or bushings. Parts that are turned typically have a very smooth surface finish with a highly accurate tolerance of precision. CNC Turning is capable of producing parts within a tolerance of ± 0.0002”.
Overall, the CNC Turning process has numerous advantages. Some major advantages are consistency, precision, and redundancy. Another major advantage is the continuous use meaning unlike manual labor, CNC Turning machinery can work continuously over a length of time without a break. This increases productivity and efficiency. One person can also supervise and load multiple machines lowering the manpower needed.
Some other advantages to consider are:
Aside from the advantages, it is important to consider some of the negatives to CNC Turning. In general, the initial cost of setup is expensive and requires a greater initial investment than manually operated turning.
Some other disadvantages to consider are:
When weighing the benefits of CNC Turning, the advantages far outweigh the disadvantages. It is important to recognize both the pros and cons of the process.
While the cutting itself is pretty straightforward, we are going to break down the entire sequence from design to operation. This can be simplified into two parts each containing a set of steps.
The most critical set is first, which is using CAD software to creating a digital representation of the desired part and its G-Code required to machine the part. This is typically completed on computer software such as MasterCAM of AutoCAD Fusion. The programs allow us to draw and simulate the turning process and we can visualize from raw material to the final product.
Next comes the manufacturing aspect. Although most of this part is automated, the operator plays an important role. In this part, we first begin the setup & loading of the tool turret. The turret can hold many tools at once for a continuous operation from start to finish. At this time, we can place the stock material in the machine. The chuck holds the stock material in place. Before running the turning cycle, calibration shall be done on everything. The cut process begins which is called the cycle run time. This is lastly followed by the idle time which is the removal of the finished part and new stock material installed for another cycle.
The turning process is comprised of many different operation types. These operations produce various shapes such as straight edges, conical, curved, or grooved work piece. In general, turning uses simple single-point cutting tools. Each group of operation type has an optimum set of tools angles.
In the facing process, a single-point turning tool moves radially, along the end of the workpiece, removing a thin layer of material to provide a smooth flat surface. The depth of the face, typically very small, maybe machined in a single pass or may be reached by machining at a smaller axial depth of cut and making multiple passes.
This process is the gradual reduction in diameter from one portion of a workpiece to another portion.
Contouring involves the finishing of rounded, curved, or smoothed shaped part. Contouring produces a continuous curve of various degree.
The forming process uses a cutting tool ground with the form or geometry of the desired shape. This forming tool is advanced perpendicular to the axis of the work to reproduce its shape on the workpiece.
Typically, a chamfer is a 45-degree angle, which removes a 90-degree sharp edge. Chamfers are used to ease sharp edges, to prevent damage to the edge of the part, and in addition for the safety of handlers. A chamfered edge is much more resistant to damage than a square edge.
Cutoff refers to the operation of cutting the workpiece off by slicing a groove all the way through with a special parting tool.
Single point threading is cutting a helical groove in a drilled hole to match the uniform thread specifications of bolt.
This process involved enlarging or smoothing an existing hole in stock material or enlarging a hole created by drilling.
Drilling is used to create a hole and remove material from the inside of a workpiece. This process uses specialized drilling bits that are held stationary and the rotation of stock material creates the hole.
This is the cutting of a serrated pattern onto the surface face of a part. Knurling can be used to increase grip on the workpiece as well as for visual enhancement in certain applications.
Depending on the application of your design, there is a wide selection of materials that are compatible with CNC Turning. Utilizing and selecting the proper material for your needs is critical to the success of workpiece. Below we’ll introduce some of the most widely used materials in the industry, and also explain which applications each material is best suited for.
One of the most widely used material types for CNC Turning are metals. There are is an extensive range of metals to select from, each having its own characteristics and application types.
Aluminum is a great option and due to its softness, it is relatively quick to turn in comparison to harder metals. Aluminum is also extremely corrosion resistant when exposed to the environment, which leads to increased strength and durability. CNC turned aluminum is ideal for use in the automotive, aerospace, and healthcare industries. Some specific applications include fittings, electronic housings, and medical devices.
For the most part, steel is used typically in parts that will be subject to high stress applications and parts that will later be welded together. Some applications of high stress circumstances are gears & shafts. The continuous rubbing requires extreme durability.
A major advantage to using stainless steel is it can be heat treated to supply additional strength and corrosion resistant properties. The potential applications with this material are vast, from automotive to consumer electronics. Stainless steel alloys are also commonly used in the aerospace industry and surgical equipment where the margin of error is minimal.
Titanium provides strength that makes it well-suited for applications like medical implants, aircrafts, as well as even jewelry. Titanium is a distinctive material because of its high temperature melting point making it a practical choice for many applications. It is also considered to be corrosion resistant.
Brass is a great option for turned parts that are often found in plumbing and steam fitting industries. Brass has a low friction coefficient and high corrosion resistant property, which makes it ideal and utilized for pipe fitting.
In addition to all the metals mentioned above, plastics play an important role in the CNC Turning process. The selection of plastics is not as advanced, however there are still many options, each having its own characteristics and application types. Plastics can be turned into finished parts as well as used in the development and prototype phase of production.
PVC is used widely in almost all turning applications from consumer toy products to water and gas fittings. It is more cost effective to purchase and turn PVC as it is a lesser expense material and the tooling required to turn PVC does not wear as quickly. PVC provides highly desirable properties, including resistance to chemicals and environmental corrosion.
This is a versatile low-cost plastic that is typically used on parts requiring a high compressive strength with the ability to be turned to very tight tolerances. In some applications it can be used in place of metal, which allows for longer wearing parts that require less replacement. The resistant properties that nylon has are thermal, chemical and abrasion resistant.
This is a lightweight and extremely strong plastic material. Its durability and strength come from fine glass fibers woven into the material. Different glass types and patterns can provide a range of strength and flexibility in the material. Its high strength-to-weight ratio makes it ideal to be used in airplane parts.
Aside from the most common materials like metal & plastics, wood can also be used in the CNC Turning process. Solid woods like oak can be turned into hand railing for houses as well as posts in other applications. Woods are mostly turned for furniture and housing industries, where an aesthetically pleasing materials is required.
In today’s day and age, CNC Turning is found in almost every industry type, from small scale shops to large complex companies. CNC Turning is used in the professional world, and found in aerospace to medicine, and from prototyping to production. It is not limited to any sector. Machining is used practically everywhere, helping to create parts for aircrafts to surgical tools. Applications of CNC machining can be categorized into different industries. The table below provides this information.
Metal aircraft components can be turned to a high level of precision, which is critical for safety applications. The range of metals compatible with CNC Turning provides aerospace engineers with adequate options. Some typical aerospace components manufacture are engine mounts, fuel flow mechanisms, and landing gear components.
The automotive industry frequently uses machining for either prototyping or production. Metal can be machined into cylinder blocks, gear boxes, valves and many other components required for vehicles. Plastics on the other hand can be turned into components like bushing and rods.
Production of rugged and reliable parts is critical to withstand large amounts of wear and tear with minimal maintenance. Many of these turned parts are similar in nature to other industries such as aerospace and electronics, though the ability for the Military to machine its own replacement parts with classified specifications is specifically valuable in an industry that demands continuous innovation and security.
In the electronics industry, turning is used to create plastic cylindrical housings, jigs and fixtures.
Most medical grade equipment is made from Titanium. In the medical industry, almost all equipment is highly specialized and turned to extremely tight tolerances. Instruments and tools needed by doctors are essential to performance surgical operations and implants.
The oil & gas sector is another industry in which small tolerances are necessary for safety-critical applications. CNC turned parts for precise, reliable pistons, cylinders, rods, pins, and valves are essential for daily function. These parts are used heavily in pipelines and refineries. The oil and gas industry often require metals that are corrosion resistant.
CNC machining is comprised of a few different process types. The two we will be comparing here are Turning and Milling. Both of these are CNC machining methods; however, they are not the same. Material is removed in CNC milling by uses a rotating tool, while CNC turning uses a rotating part for cutting. In Milling a tool is spun at a high rate of speed, while in Turning the stock material is spun at a high rate of speed. When Milling, the stock material remains stationary fixed to machine, while in Turning the tools remains stationary fixed to machine. The two use different techniques to create a part. Milling machines make complex parts from blocks of material while turning is predominately used for cylindrical parts such as shafts. While these two are often bundled under the same term they are not the same. These complement each other in the manufacturing process to produce parts of all shapes and sizes with high precision. For example, turning a shaft may later require Milling features like pockets drilled or facing of flat material.
The major difference between CNC Turning and Grinding, is the machine uses a rotating grinding wheel to removal material on the workpiece. In Turning the tool is a sharp-edged cutting tool, however in Griding, the grinding wheel is the actual tool. Grinding wheels are spun against the part and its abrasive grit removes material. Grinding machines are typically used for fine machining of parts. The surface finish for CNC Grinding produces a high quality smooth polished surface. In many CNC applications you can find CNC Grinding after CNC Turning as a finishing process.
This wraps up the topic of CNC Turing. We have explored the main aspects of the process and touched on some of the advantages as well as disadvantages. We also covered the major operation types like straight turning and tapering. Furthermore, we spoke about the common material types used in this process and the many industries which rely heavily on CNC Turning.
If you are seeking a professional CNC turning supplier, please feel free to contact us at any time, DEK is a professional company you can trust!
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