In the modern production processes, precision and speed are the key indicators that define the effectiveness of a firm. CNC (Computer Numerical Control) has highly improved the process of machining because it enables the production of complex parts with a high level of accuracy. Among all the CNC machining processes, screw turning and lathe machining are special in their benefits and applications. This article clearly explains the difference between CNC screw turning and lathe machining and the details, the advantages and disadvantages of the two.
Screw turning or also known as Swiss screw machining is a precise CNC machining technique that is used to create small cylindrical products. This process makes use of the CNC Swiss screw machine which has a sliding headstock. In screw turning the cutting tool is stationary while the work piece is moved back and forth through a guide bushing. This kind of arrangement is ideal for maintaining tolerances that can be in the order of ±0.002 mm (±0.00008 inches). Bushing component assists in holding the workpiece at the time of CNC machining so that it cannot deflect or vibrate. This results in better surface finish and it can have Ra values of 0.2 µm. CNC Screw turning is used in electronics, medical devices, aerospace industries and all other industries that need high precision of small parts.
Single-Point Turning: This method involves the use of a single cutting tool to make the cuts along the length of the work piece which can be used for threading or any other linear operation. It is intended for use with thread pitch values between 0 and 300 TPI inclusive.
Multi-Spindle Screw Turning: Many cutting tools operate on different regions of the workpiece simultaneously, which raises the speed of production. Multi-spindle machines are capable of manufacturing as many as 10000 pieces per hour depending on the type of part.
High Precision
Screw turning is known to provide very high accuracy and can be done to very fine limits of tolerance of as low as ±0. 0002 mm This level of accuracy is important in manufacturing micro parts that require high accuracy such as those used in medical or aerospace industry.
Efficient for Mass Production
Multi spindle screw turning machines are particularly effective when it comes to mass production. This means that they can manufacture thousands of parts in a single hour making the process suitable for mass production. This efficiency is useful in cutting down the time and the cost of production.
Cost-Effectiveness
The accuracy of screw turning helps to eliminate subsequent operations, for example, finishing or rework. This results to lots of cost being saved especially when producing small and complex parts where each operation contributes to the overall cost.
Limited to Small Parts
Screw turning is very effective in making small cylindrical parts, but it is not very effective in making large or complex shaped parts. CNC Screw turning can accommodate workpiece diameter of up to 25 mm and is not suitable for large parts.
Less Versatile
Screw turning machines are usually designed for a particular purpose, for example, threading or turning. This specialization reduces their flexibility as compared to other CNC machines, and therefore they cannot be used for various machining operations.
CNC Turning is one of the most versatile and commonly used categories of the machining process. It is a process where a workpiece is revolved round a central axis while a cutting tool forms the part. The same process is done by modern CNC lathes and it is faster, more precise and accurate than the conventional techniques. In the CNC lathe machining, the tool path is pre-programmed, and the parameters include spindle speed (up to 4000 RPM), feed rate (from 0. 01 to 1.0 mm/rev), and depth of cut. This level of accuracy enables the creation of intricate components with tolerances of as low as ±0.005 mm (±0. 0002 inches).
Horizontal Lathes: The type of lathe in which the workpiece is held in a horizontal position, is the most frequently used one. This kind of setup is suitable in machining long parts with diameter of between 10mm and 500mm.
Vertical Lathes: In this type, the workpiece is positioned in the vertical plane. Vertical lathes are designed for the machining of large and massive parts with a diameter of up to 3,000 mm.
Swiss-Type CNC Lathes: These machines are a cross between screw turning and lathe turning in that they have the accuracy of the former and the flexibility of the latter. They are suitable for creating small and intricate parts with complicated cross-sectional profiles with the diameter of the workpiece ranging from 1mm to 25mm.
Versatility
Lathe machining is one of those machining processes that is quite versatile in its application. It can create forms of various shapes, from the basic cylinder to the most intricate curves. CNC lathes are versatile as they can accommodate parts with diameter of 1 mm to 3,000 mm.
Suitable for Larger Workpieces
Screw turning is not able to handle large workpieces while lathe machining is able to handle large workpieces. This makes it suitable for creating large parts such as shafts and housings with maximum length of 5 meters. This capability is very important in industries where large parts are manufactured such as aerospace and heavy machinery industries.
Flexible Customization
CNC lathes are very versatile CNC machines. They can be set to manufacture almost any type of part with little or no adjustment. This flexibility is especially important in small-batch production where various components require to be made without having to spend a lot of time setting up the machines.
Less Efficiency for Small Parts
Although lathe CNC machining is very general, it is not as effective as screw turning when it comes to making small intricate parts in large quantities. The time taken to set up lathe machining may be longer and the process may not be as fast as screw turning especially when dealing with small parts.
Increased Material Waste
It is common to find that lathe machining requires a large amount of material to be cut or removed. The material removal rate (MRR) is in the range of 100-500 cm³/min and due to this more wastage is produced as compared to screw turning. This material waste can lead to increase in costs of production particularly where the material used is costly.
Screw Turning Precision
Screw turning also has a great advantage in the fact that it can produce parts with very high accuracy, normally within ±0.002 mm This is made possible by the guide bushing which holds the work piece near the cutting area thus reducing on the amount of deflection and hence the accuracy. This level of precision is important especially in manufacturing industries where the smallest variation can cause a product to fail such as in manufacturing of medical devices. For instance, in the production of a bone screw, such tolerances are important to guarantee that the screw will fit the bone perfectly to offer the required support without straining the bone.
Lathe Machining Precision
Although lathe machining provides high accuracy, it normally provides tolerances of ±0. 005 mm, which is quite suitable for most uses, particularly in automotive and aerospace manufacturing, where the parts are usually bigger and not as detailed. Nevertheless, for the highly accurate operations, for instance, in the micro manufacturing, lathe machining may not be as efficient as turning screws. The larger the workpiece, the more difficult it is to hold the small tolerances which is the strength of the Swiss screw machines.
Surface finish is one of the most important parameters in many fields especially in those applications where components have to be assembled with close tolerances or where there is relative motion between two surfaces. Screw turning can also produce a surface roughness (Ra) of as low as 0.2 µm which is very smooth as compared to other surfaces. This level of finish is typical in the medical and electronics industries where a rough surface can cause wear, friction or failure.
For example, in the manufacturing of electronic connectors, a smooth surface is more conductive and has less wear and tear that is very important in the durability of the part.
Conventional lathe machining normally yields a surface finish of about 0. 8 µm. This is relatively rougher than what can be achieved with screw turning but it acceptable for most industrial applications. For instance in automotive manufacturing a surface finish of 0. 8 µm is quite adequate for such parts as crankshafts and axles, which are lubricated and made with a certain degree of wear.
However, in application where a very smooth surface is needed, other finishing methods may be needed such as grinding or polishing.
A detailed comparison of six key technical aspects between screw turning and lathe machining is provided below:
|
Aspect |
Screw Turning |
Lathe MachiningPrecision |
|
Precision |
±0.002 mm (±0.00008 in) |
±0.005 mm (±0.0002 in) |
|
Surface Finish (Ra) |
0.2 µm |
0.8 µm |
|
Production Speed |
Up to 10,000 parts per hour |
100-1,000 parts/day |
|
Material Diameter |
1 mm to 25 mm |
1 mm to 3,000 mm |
|
Material Removal Rate |
Moderate (10-100 cm³/min) |
High (100-500 cm³/min) |
|
Flexibility |
Limited to small, cylindrical parts |
High versatility for various shapes and sizes |
Applications of Screw Turning and Lathe Turning
Each method has its benefits, and for this reason, it is suitable for specific manufacturing operations. In the next subtopics, the various application areas of screw turning and lathe machining will be discussed.
Some of the most common applications include:Some of the most common application are as follows:
1. Medical and Dental Devices
● Surgical Instruments: CNC Screw turning is most appropriate for creating fine instruments such as surgical instruments like scalpel, forceps, and clamp where precision and surface finish are of great importance.
● Orthopedic Implants: Screw turning is used in manufacturing of medical devices such as bone screws, plates and pins used in orthopedic surgery where small tolerances and smooth surface finishes are required to enable the body not to reject the devices.
● Dental Components: Screw turning is very useful in dental operations because dental implants, abutments and other precise parts that are used in dental operations require high precision.
2. Electronics and Microelectronics
● Connectors and Terminals: For instance in electronics screw turning is used in the production of small connectors, terminals and other components that require high precision and conductivity.
● Micro-Components: In microelectronics that is used when sizes of components can be very small, screw turning is very effective because it is possible to maintain very small tolerances so that all components fit tightly.
3. Automotive Industry
● Fuel Injector Nozzles: There is need to be very precise when manufacturing fuel injector nozzles because they are expected to release fuel in measured quantities and at certain angles. Screw turning ensures that these nozzles are of good quality as is needed in their application.
● Sensor Housings: Most automotive sensors are currently considered as regular parts of modern cars and their construction may require tiny and complex shells that can be produced using screw turning at a reasonable cost.
4. Watchmaking and Jewelry
● Watch Components: Screw turning is used on small items such as gears, screws and other parts of a watch due to the delicateness of the work and the finish that is required.
● Jewelry Findings: Screw turning is used in jewelry making in the manufacturing of small parts that are usually delicate and ornamental like clasps, earring backs and other findings.
5. Aerospace
● Small Engine Components: The aerospace industry demands very precise parts for small engines such as fuel system parts and actuators and screw turning is a typical approach to manufacturing.
Some of the key applications include:Some of the key applications include the following:
1. Aerospace Industry
● Turbine Shafts: Lathe machining is very important in the production of large and complex parts such as the turbine shafts that require high tolerance, high stress and high temperature strength.
● Aircraft Landing Gear: Landing gears are big and the loads on them are high during manufacturing; therefore, CNC lathe machining is versatile in the manufacturing of the parts of the landing gears.
2. Automotive Industry
● Crankshafts and Camshafts: Crankshaft and camshaft are some of the most important components of internal combustion engines and lathe machining is often employed in their manufacture..
● Brake Drums and Rotors: Brake drums and rotors are also lathe machined products since these parts have to be round and balanced for use in automobiles.
3. Oil and Gas Industry
● Pipeline Components: Lathe machining is used to produce large and very durable parts such as flanges, couplings, and valves for the oil and gas industry where precision and strength are paramount.
● Drill Bits: Another area of application of lathe machining is in the machining of drill bits because the cutting edges of the drill bits need to be sharpened to cut through hard materials.
4. Industrial Machinery
● Gears and Pulleys: Lathe machining is used in the production of gears and pulleys of industrial machinery that need precise dimensions and smooth surface finish in order to perform their duties.
● Bearings: The big bearings that are used in the manufacture of heavy machineries also demand the lathe machining.
5. Heavy Equipment Manufacturing
● Hydraulic Cylinders: Cylinders that are used in construction and agricultural machineries are hydraulic cylinders and these cylinders need lathe machining to produce the internal bores and external surfaces that are needed in sealing and functioning of the cylinders.
● Tracks and Rollers: Some of the parts that are produced through lathe machining are tracks and rollers for heavy duty equipment because of the size and the material used.
CNC Screw turning vs lathe machining are two identical CNC processes in the precision manufacturing. Each process has its own merits and demerits and suitable applications. Screw turning is most appropriate for the production of small parts with intricate shapes that require exact dimensions, and precision. Therefore, it is used in the creation of such products as medical equipment, electronics, and automobiles. On the other hand lathe machining can be used on various sizes and shapes of work piece hence making it appropriate in aerospace industries, automobile industries, oil and gas industries and the heavy equipment manufacturing industries.
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