Screw Machined Parts and Products
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Screw machined parts are complex pieces that are typically cylindrical and threaded and a screw machined product is a family of automatic lathes for small to medium-sized components...
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This article contains everything you will need to know about precision turned products and their use.
You will learn:
Precision turned parts are machined with extreme care to reach exceptionally tight tolerances using Swiss and CNC machining or turning. The processes of precision turning involve a variety of methods that include facing, chamfering, threading, tapping, drilling, and knurling, with each process capable of deforming a workpiece to fit a specific application or process. During processing, the workpiece is turned in order to achieve the required form and dimensions using a cutting tool that removes material in the correct proportions to create the desired shape.
The results of precision turning are parts with high tolerances, accuracy, and functionality. The use of precision turned parts enhances the performance of equipment, machinery, and the completion of complex processes. Their wide use is due to their longevity and exceptional efficiency, which increases equipment life, lowers waste, and leads to energy savings.
Choosing the right manufacturer for precision turned parts is critical to the success of a part and an assembly for which it is produced. Quality precision turned parts manufacturers are International Organization for Standardization (ISO) certified, Europäische Norm (European Norm) (EN) certified, and American National Standards Institute (ANSI) certified, organizations that work together to guarantee the quality of manufactured products.
The machines for manufacturing precision turned parts are Computer Numerical Control (CNC) machining, Swiss screw machines, and CNC automatic lathes. Each of the methods has their advantages with CNC machining capable of performing multiple operations during a single cycle while a CNC lathe and Swiss screw machine can produce highly complex and intricate parts.
Several types of metals are used to produce precision turned parts. They include stainless steel, carbon steel, brass, titanium, silver, gold, and various alloyed metals. The methods chosen to produce precision turned parts is due to their accuracy, versatility, and efficiency since the process can be completed rapidly to reduce cycle times.
The original purpose of Swiss screw machining was to manufacture parts for watches, which could not be produced accurately by hand and has been used for decades to produce precision turned parts. The combination of CNC machining and Swiss screw machining has led to the production of exceptionally high-quality components that meet the needs of a large number of industries.
Although there are several varieties of Swiss screw machines, all types have basic components in common, which include the workpiece bar stock holder, chuck collet, guide bushing, and headstock. These four components work in unison to cut and shape a workpiece to conform to a part’s design.
In order to ensure the precision of the cuts to the workpiece bar stock, it must be held tightly in place to prevent vibrations or wobbling while it is being rotated during processing. Having the workpiece securely held protects the spindle and cutting tools and ensures the precision and accuracy of the cuts. The two forms of bar feeder holders are hydrodynamic and hydrostatic, which differ in how the workpiece is held.
Hydrodynamic part holders are breech loading bar feeders that hold the workpiece bar stock in place as it is inside a liner immersed in oil, a method that automatically centers the bar. Having the bar stock surrounded by oil reduces the amount of noise produced by the process and any vibrations. Bars are fed into a Swiss screw machine one bar at a time and require that feed tubes be changed when the diameter of the bar stock changes.
Hydrostatic bar feeders use guide channels or bushings that are clamped around the bar stock. An oil film surrounds the bar and supports it as it is moved to the chucking collet and guide bushing. Unlike hydrodynamic bar feeders, hydrostatic bar feeders can hold bar stock as long as 24 ft. (7.315 m). They are magazine type loaders that are capable of processing any diameter of bar stock without having to make adjustments or changes.
The workpiece bar stock feeder moves the bar stock into the chucking collet that uses force to hold the workpiece. The chucking collet has a three-jaw chuck, hydraulic cylinder, and drawtube. It is a small cylindrical component that uses the hydraulic cylinder to connect to the rear end of the spindle with the chuck placed on the front end. The drawtube creates the clamping force that connects the hydraulic cylinder and chuck to the spindle.
The size and type of chucking collet is determined by the spindle nose. International standards are used by all manufacturers to define the mounting interface dimensions with spindle nose configurations being A2-6, A2-8, and 140 mm. The size of the chucking collet is further categorized by the bore size of the drawtube. Once these initial factors are determined more specific parameters are used to choose the perfect chucking collet for a Swiss screw machine.
The guide bushing is a unique feature of Swiss screw machines and is the factor that differentiates them from traditional lathes. The purpose of the guide bushing is to support the workpiece during the machining process and prevent any deflection during cutting. Guide bushings make it possible for cutting tools to complete a cut in one cycle without having to make several passes to achieve the appropriate depth of cut. They are an aspect of Swiss screw machines that make it possible to achieve accurate and precision cuts.
The three basic types of guide bushings are rotary, fixed, and precision. The difference between the three types is in regard to how they manipulate the workpiece during processing, which is determined by the required level of precision. A rotary guide bushing rotates with the workpiece and is used on wider, larger parts. Fixed guide bushings remain stationary as the bar stock turns and are chosen for precision parts that require tighter tolerances. While fixed and rotary guide bushings are capable of working with larger parts, precision guide bushings are similar to the original Swiss screw machines in that they are used for manufacturing small, intricate, and complex parts.
The headstock is another feature of Swiss screw machines that makes them unique since they make it possible for the workpiece bar stock to be positioned along the Z axis. With a traditional lathe, the work piece moves to the cutting tool to be shaped. The headstock of a Swiss screw machine moves to the workpiece as the collet holds it in place. It positions the workpiece to avoid lateral force and provides for exceptionally accurate and precise cuts.
As the guide bushing and chucking collet hold the workpiece, the headstock moves the cutting tools and workpiece to within a few mm or inches of the guide bushing to perform any number of cutting processes. Any portion of the workpiece can be shaped, cut, and formed during the process.
The spindle of a Swiss screw machine holds the tools that shape and form the workpiece bar stock. Although there are several forms of spindles, the three most common forms are direct drive, belt drive, and integrated, which have different configurations and drives. Belt driven spindles have an adjustable pulley and can achieve high torque with speeds that can reach 8000 rpm.
A direct drive spindle has its motor connected to the shaft of the spindle and can achieve 12000 rpm. This form of spindle has exceptional accuracy and is used for high-speed applications. The wide use of direct drive spindles is due to their low noise, which is unlike belt driven spindles that have problems with belt slippage.
The long list of spindles includes gear driven, air turbine, electric motor, woodworking, cartridge, and high frequency. The type and design of a spindle for a Swiss screw machine varies in accordance with the design and purpose of the machine.
In response to the frustration of having a single spindle operating a tool that works on a workpiece, a multi-spindle design was developed, which makes it possible to have a workpiece shaped by several tools at once. The introduction of multiple spindles has made it possible to integrate Swiss screw machines into high volume production.
CNC machining has become one of the most used forms of manufacturing due to its use of preprogrammed computer codes that instruct the CNC machine as to which operation to perform. Codes for CNC machining are input into the machine and determine the movement, cuts, angle, and other factors of the tools and machinery in the machine.
The use of the CNC process replaces the need for operator involvement. The programming of the machine gives commands to a CNC machine as to which cuts to perform, the depth of the cuts, and makes it possible to perform several different operations in one cycle.
The language used to program CNC machines is known as G-code and is created using computer software, which makes it possible to run a rendering of the program to check for errors. This aspect of the process eliminates design flaws that would produce poor quality products. Every aspect of the performance of a CNC machine is created using computer software, which determines the speed of the process, the position of the tool, and cycle times.
The Computer Aided Design (CAD) is changed into command codes for the CNC machine to follow. An initial trial run is completed to determine if there are any errors in the coding. N-codes are used to identify lines or blocks of G-codes and serve as the title for a block of G-codes, which helps the programmer organize code input.
Position control in a CNC machine is referred to as an open loop or closed loop system. With an open loop, there is no feedback during the machining process and tools stop according to a control system after completing a cut. It is a less expensive system and does not require the use of encoders or controllers. In cases where the amount of force needed is minimal, open loop control can be used to lower costs.
Unlike an open loop system, a closed loop system has sensors that supply data regarding the position of a moving object. The controller uses data from the sensors to discontinue movement when the desired position is reached. Closed loop systems can take several forms and guarantee proper positioning of the workpiece and tools along the X and Y axes. The movements in the system are determined by the G-codes.
In the modern era, Swiss screw machines have been combined with CNC machines in order to perfect and improve the precision of the machining process. Both processes use cutting tools that are mounted on a tool holder or spindle in order to position the tool for the most accurate cuts and tolerances. CNC Swiss screw machines use turning tools to reduce the diameter of the workpiece bar stock by rotating the workpiece or moving the cutting tool.
Although not all turning tools are the same, each type of turning tool has a basic structure that is common to all types. The four elements of a cutting tool are its holder, clamp, screw, insert, and seat. Inserts are engineered to achieve accuracy and efficient material removal. Each type of insert has received an ANSI classification regarding their shape, clearance, tolerance, type, size, thickness, and nose radius.
ANSI Insert Designations | |||||||
---|---|---|---|---|---|---|---|
C | N | M | G | - | 4 | 3 | 2 |
1 | 2 | 3 | 4 | 5 | 6 | 7 | |
Shape | Clearance | Tolerance | Type | I.C. Size | Thickness | Nose Radius |
Inserts are made of carbide, ceramic, cermet, or diamonds with ceramic, cermet, and diamonds being used for more demanding applications. To improve efficiency, inserts are coated such that they can cut faster and last longer. An insert is supported by a seat that is placed between the insert and the bottom of where the insert sets. The insert and seat are attached to the tool holder, which holds the insert tightly to avoid deflection and vibrations. All turning tools have holders made of heavy duty forged steel. While the body of a turning tool is not precision engineered, inserts are meticulously engineered and fine-tuned to ensure accuracy, high tolerances, and the ability to channel coolant to the cutting edge.
Chamfering Tool – Chamfering tools bevel the end of a workpiece and have an angled cutting surface to remove sharp edges on parts. The process is used to make parts stronger and give them a better appearance.
Knurling Tool – The knurling tool is used to create a pattern of straight, angled, or crossed lines on a cylindrical workpiece and has a shoulder and toothed wheels or knurls.
Modern manufacturing demands and requires that the parts that are used for assemblies be machined to precise specifications, be of the highest quality, and be capable of performing at the highest standards. Precision turning relies heavily on the accuracy of Swiss screw machines and CNC machines, which produce components that have the precision, accuracy, and tolerances 21st Century machines and users require.
The number and types of precision turned products includes an endless number of components that are used by several industries. Since precision turning creates essential components for complex machinery, many precision products are created in high volume to meet the demand. Precision turned parts are produced from raw material that is rotated in a Swiss screw machine or by CNC machining. Parts are sculpted and formed in order to reach the highest possible accuracy with exceptional consistency.
Precision fittings are used as connectors to join or fasten components and are manufactured with specific dimensions to ensure the strength of the connection. Fittings make it possible for elements to fit together and come in a wide variety of shapes, sizes, and configurations. The use of precision turning is necessary in order to get the correct dimensional tolerances. The slightest error can lead to product or part failure.
A common form of part that is manufactured in high volume by precision turning is bushings that are used to reduce friction between surfaces and help to maintain alignment. Referred to as pain bearings, bushings support rotating and sliding shafts. They are made of soft metals with uniform dimensions with a smooth surface, which is essential for the highest possible performance. As with fittings, bushings have to be machined with exceptional accuracy due to the types of metal from which they are made and the applications for which they are used.
The manufacture of rings requires the use of precision turning due to the applications for which they are made. As with bushings, rings must have a smooth surface and precise dimensions to fit into an application. They are used for sealing purposes and bearings for food processing equipment, medical devices, mining, and power generators. Due to the nature of the applications for which they are manufactured and the metals used, rings have to meet the most demanding parameters and complex geometries.
Flanges are circular shapes that are used for connecting and positioning pipes. An essential part of their structure is their bolt holes that have to be evenly spaced along the edge of the flange. Precision turning is capable of properly shaping flanges to the required dimensions and spacing their holes with exceptional accuracy, all of which is completed in a single cycle of a Swiss screw machine or CNC machine. Flanges come in a wide assortment of sizes and configurations in order to fit the many applications for which they are designed. They are made of heavy-duty metals capable of withstanding the stress and pressure that they endure.
The multiple uses of pins and dowels include use in precision assemblies to locate and hold parts as well as guides to adjacent parts. They are small cylindrical rods that are machined in different sizes to fit in holes connecting different surfaces and parts. Pins and dowels can be inserted and removed multiple times since they do not have threads or heads, which makes them ideal as a method for aligning parts. As with many forms for precision turned parts, pins and dowels are available in a wide assortment of sizes and styles with each type requiring precise dimensional tolerances.
The strength, thickness, and durability of pins and dowels make them a perfect tool for aligning joints in any type of material. They can be used in place of screws that have lost their thread and are used to secure hanging items. There are several forms of pins and dowels, which include standard, oversized, grooved, pull, and spiral grooved ones and are machined from all forms of metal and plastics.
Spacers are one of the simplest forms of precision turned parts. They are used to fill gaps and are required to have precision diameters and lengths such that their placement will not interfere with the operation of an application. Aside from their use in adjusting spaces between surfaces, spacers are used to prevent vibrations and provide corrosion resistance. The main use of spacers is to prevent vibrations, which can damage the quality of products and equipment.
Pulleys are used to change the direction of applied force and reduce the force necessary to lift a weight. They are used in all facets of industrial applications and are produced in several forms such that they specifically fit the requirements of an application. In many cases, pulleys are used in combination to further reduce the amount of force and the amount of required energy and motion.
Precision turning is used to produce a wide range of pulleys due to its exceptional accuracy since pulleys have to meet a set ratio to be the most effective. The machining of pulleys requires different sets of operations depending on the shape and type of pulleys with some pulleys having deep grooves while others have gripping teeth. In all instances, pulleys are an essential part of an application and are manufactured with the greatest precision.
The introduction of precision turned parts to industrial manufacturing has greatly enhanced the quality, performance, and resilience of products and assemblies. The tight tolerances and accuracy of precision turning has made it possible for producers to ensure the longevity of their products. In turn, the improved quality of products has attracted more buyers and increased profits.
The key to the success of precision turned parts is their accuracy and the ability to form materials to tolerances within a few microns. This aspect of precision turned parts is the reason for their wide use. From the computer rendering to the packaging of the final product, precision turned parts have near perfect forms and shapes.
Precision turned parts guarantee that every part that is produced will have the same size, shape, and quality due to the close control of the process and the CAD renderings that are used to produce them. Consistency ensures that parts will be reliable and have fewer production errors, which, in the case of CNC and Swiss screw machining, is seldom a problem. In addition, every finished part is of the highest quality.
With the removal of defects, rejects, and production errors, the resources used to produce parts are maximized producing little waste. Parts are produced quickly and efficiently in reduced production time. These advantages lower the cost of individual parts, leading to greater profitability and a competitive advantage.
The fact that precision turned parts are produced quickly and with accuracy turnaround times are faster and inline with customer requirements. In the 21st century, rapid turnaround times are a necessity due to the pressure of competition and the requirements of assemblies and production. This is especially helpful to businesses that have demanding production schedules and deadlines.
Any form of material can be shaped and formed using precision turning. Parts that are produced have exceptional strength and durability, a factor that makes them useful for a wide range of industries, including aerospace, automotive, medical, and electronics, which are industries that require the greatest precision and accuracy.
Since precision turned parts are manufactured to the highest standards, they tend to be stronger, more resilient, durable, and able to withstand higher levels of pressure and stress. For these reasons, they are required for use in assemblies that have to be reliable over time without failure or malfunction.
Since precision turned parts originate as CAD renderings, they can be easily adjusted and configured to fit the unique needs of a special or unusual application. This aspect of their characteristics makes it possible to make changes in a configured part during production as the requirements for a part changes due to design or assembly factors.
The precision planning of precision turned parts takes into account the amount of waste being produced by the production process. Computerization is the main reason that there is limited waste with precision turned parts since the computer rendering is designed to economically and efficiently produce parts without the need for additional processing.
Finishing is one of the amazing benefits of precision turned parts, which have exceptional surface finishes that can be polished, treated, or coated to give parts a professional and consistent appearance, a factor that increases the value of parts and enhances their reliability.
Precision turning is capable of shaping any type of metal due to the strength of the cutting and shaping tools, which are adjusted in accordance with the density and toughness of a metal. As may be expected, all forms of steel, bronze, brass, aluminum, copper, and titanium can be shaped, formed, and configured using precision turning. In addition, certain forms of engineering plastics are included, which are compatible with precision turning.
The many positive properties of aluminum make it an ideal material for the manufacture of precision turned parts. Machining of aluminum allows for very tight tolerances and the manufacturer of complex and intricate shapes. The properties of aluminum can be further enhanced with the addition of plating materials that increase aluminum’s hardness and conductivity, a process that makes aluminum an alternative to copper, steel, or stainless steel.
Brass is used for precision turned parts that are not required to have a high level of strength. The clean bright finish of brass as well as its easy machining make it an ideal metal for precision turned parts. Brass is normally chosen for the manufacture of complex and intricate designs that have sophisticated details, which is due to its easy formability. The tin and zinc content of brass restrict its use to precision turned parts that do not involve vacuum applications.
Careful consideration is given to the use of copper in the production of precision turned parts due to its high cost. The attraction of copper for the process is its corrosion resistance, conductivity, and being non-magnetic. As with brass, copper has high formability and is ideal for electronic components and various types of hardware. Copper can be easily turned and comes in forms that effortlessly integrates into precision turning.
Titanium is found in nature as a chemical oxide that is reduced to a silver colored, low density, high strength metal that is resistant to corrosion. It is alloyed with several other metals to create exceptionally strong, lightweight, and resilient alloys for a wide range of applications from aircraft production to jewelry and sporting goods. A characteristic of titanium that has increased its use in medical procedures is its biocompatibility. The attraction of titanium for precision turned parts is its high strength to weight ratio, a factor that makes it ideal for applications that require strength and low weight.
All forms of steel, including stainless steel and carbon steel, have been used for decades in the manufacture of precision turned parts due to steel’s strength, durability, and machinability. The properties of steel vary in accordance with how it is alloyed, which determines the grade of steel. The addition of various alloys are the deciding factor in regard to the applications for which steel can be used and the types of precision turned parts.
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