This Article takes an In-depth look at Machining Types, Tools and Uses
You will learn more about topics such as:
What is machining?
Tools used in machining
Forms of Burning Machining Technologies
Technologies of Erosion Machining
The CNC Machining Process
What is Machining?
Machining is a manufacturing process used to produce products, parts, and designs by removing layers from a workpiece. There are several types of machining that include the use of a power driven set of machining tools to chip, cut, and grind to alter a workpiece to meet specific requirements. Metal fasteners, costume jewelry, toys, and hand tools are all formed using the machining process. There are times when a finished part needs a touch up to meet quality standards or manufacturing requirements. In those instances, it may need to be machined to give it the proper appearance.
Though machining is used to shape metals, it can be used for other materials. Molding is a common way of producing plastic and rubber products. In some cases, after being molded, other features need to be added. This is normally completed by machining, which can add holes, remove burrs, or finish shaping. As soft and pliable as paper may be, it can be machined to match a special design or form.
A variety of machining tools are used to shape, deform, and mold metal to produce a specific geometric shape. Part of the machining process is to secure the workpiece using a gripping device to hold it in place while the tool runs across it. Prior to the industrial revolution, machining functions were performed by hand. Modern technology has taken those handcrafting skills, using computerized numerical control (CNC), and programmed them in machining equipment to be repeated multiple times accurately and precisely.
Several different tools are required to perform the multiple operations necessary to shape a workpiece. The types of tools chosen are carefully selected to ensure the quality of the final product.
Listed and described below are a few of the kinds of machining tools:
Drilling Tools
Machining drill bits are center, twist, or ejector types, each of which has a unique function. Center drill bits are designed for precision drilling of small holes on a workpiece, which is further drilled using a twist drill bit. Ejector drill bits are used to enlarge a hole and make it deeper. They come with single or multiple cutting heads where the single head version creates large holes while multiple head versions are capable of creating even larger holes.
The insert type drill bit is the least expensive and easiest to use. It has a ground point that assists in centering the bit. Unfortunately, the work of insert drill bits requires secondary processing due to the burrs it leaves when removed from a hole.
Twist drill bits have corkscrew flutes that are sharp and precise but require frequent sharpening. Unlike insert drill bits, twist drill bits do not leave burrs, a factor that removes the need to perform deburring. They are a multi-use drill bit capable of drilling into any material except for masonry and concrete. Twist drill bits are ideal for machining processes due to their ability to easily drill into metal.
Drilling removes material using a drill bit to cut a hole of circular cross section in the workpiece. It is the most common machining process, which is used about 75% of the time. A drill jig is placed into a chuck connected to a spindle, which is driven by a drill head powered by a pulley and electric motor. Either electronically or by hand, the drilling tool is lowered onto the surface of the workpiece.
Milling Tools
Milling produces three dimensional shapes using a rotating multi-edge cutting tool. In CNC manufacturing, the milling tool can be programmed to move in several directions on a fixed workpiece. The process can create parts in a wide range of shapes with features such as slots, pockets, and grooves. There are several kinds of milling tools depending on the type of cuts required.
End mills are like drill bits but are capable of applications beyond drilling holes. They have eight flutes arranged on their ends and sides that make it possible for them to quickly remove large amounts of material in a single pass. The popularity of end mills is their ability to drill straight into material without the need of a pilot hole. Much like drill bits, end mills come in different types with roughing end mills being the most common.
Face mills are used to flatten the surface of a workpiece to make it shine and are the most common form of milling tool. The face milling process involves cutting surfaces perpendicular to the axis of the cutter or the face of the workpiece. Shell mills and fly cutters are the most often used for face milling but are chosen in accordance with the desired surface finish.
Other types of milling tools include slab mills, thread mills, and hollow mills, each of which perform a specialized milling function. Slab mills have their teeth on the edge of the cutter while thread mills are used to cut threads into a workpiece. Hollow mills have the shape of a pipe with their teeth located at one end of the pipel.
Boring Tools
A boring tool is a cylindrical cutting tool that rotates in different directions on several axes with the ability to create shapes, slots, and holes as well as other types of cuts. The classification of boring tools is in accordance with the number of axes on which they can shape a workpiece. Most boring tools operate using 3 to 5 axes to produce shapes that are impossible for any other method.
There are several variations of boring, which depend on the shape and size of the final hole and how the workpiece is supported. The holes created by boring vary in their geometry and are precision controlled. Although boring is similar to drilling, it is a far more accurate and meticulous drilling method that uses a pilot hole that has been created during casting, by a drill press, or a mill.
Boring tools are used for high precision production and are used due to their exceptional accuracy. The capabilities of boring tools includes their ability to work extremely large workpieces, minimal tool deflection, and exceptional durability. Although other tools can perform the boring process, boring tools have extra power and stability in order to complete the process.
The three ways boring is completed are spinning against a stationary bit, spinning into a workpiece, or stationary tool and spinning workpiece. The process can be completed horizontally, vertically, or at multiple angles at slower speeds and feed rates, which reduces noise and chatter.
Grinding Tools
Grinding or abrasive machining tools are a method for material removal that use a rotating wheel cutting across a metal surface to achieve high quality finish. The quality of the finish is created using light cuts and multiple passes to perform precision removal of material. The categories of grinding tools are surface, cylinder, centerless, internal, and specialty.
Surface grinding, known as hiraken or heiken, has a vertical or horizontal axis with a circular or square table. It is a finishing process that can be used on metallic and non-metallic materials. Surface grinding tools remove the oxide layer and imperfections on the surface of a workpiece using an abrasive wheel, chuck, and table.
Cylinder grinders are used on cylinders, rods, and similar shapes. The workpiece is placed between two centers and rotates in one direction. The grinding wheel rotates against the workpiece in the opposite direction of the workpiece’s rotation. The work of a cylinder grinding tool resembles that of a lathe and is used to create tapered, contoured, and straight surfaces.
With through feed centerless grinding tools, the workpiece is placed on a blade between a regulating wheel and grinding tool. The regulating wheel moves the workpiece as the grinding wheel removes material. Infeed centerless grinding moves the grinding wheel radially against the workpiece and is used to create complex surfaces.
Internal grinding tools are a form of internal diameter (ID) grinding or bore grinding and are used to remove material from the inside diameter of cylindrical or conical workpieces. As with cylinder grinders, internal grinders function like a lathe to accurately form holes in the center of a cylinder. The grinding tool is fed in and out of the workpiece to achieve a specific depth of cut.
Turning Tools
Turning tools are single point tools that are used with a lathe and placed against a rotating workpiece. Turning tools are divided into rough and fine categories with each type having a different cutting function. Rough turning tools remove large amounts of material and have a very small clearance. Fine turning tools are used for finishing and have a large clearance angle for removing small amounts of material to create a smooth finish.
The process of a turning tool is used to create axial symmetric shapes. The turning blade is held in a fixed position as the workpiece rotates. The cutting tool for a turning tool is a replaceable insert that can have a distinct shape, cutting material, coating, and geometry. The shapes of the cutting blade can be round for strength, diamond shaped with a sharp point, square, or octagonal to increase the number of edges.
The cutting blade has to be capable of withstanding the stress of the cutting process and is typically made of carbide with a protective coating to increase the cutting speed and the longevity of the blade. For many years, steel was used for turning tools, which had to be sharpened on a grinder but was replaced by carbide that has better wear resistance and hardness.
Turning includes a linear tool and rotational movement of a workpiece. The cutting speed is the rotational distance, surface feet per minute (SFM) or square meters per minute (SMM), traveled by a designated point on the surface of the workpiece with the feed rate being the linear distance the tool travels. Feed rates vary between rough cutting and fine or finish cutting.
Cutting Tools
There are five types of machining cutting tools that are used according to the type of machine, the project, and the required precision. The list cutting tools includes lathes, several forms of milling tools, routers, plasma cutters, and electrical discharge cutters (EDM). Of the five listed, milling tools are the most common.
The selection of a cutting tool influences the quality of the final part or product. Accuracy, cost of production, quality of finish, waste, and the effectiveness of a cutting machine are dependent on the tool holder and the selected cutting tool. Poor quality cutting tools and tool holders can lead to increased costs of manufacturing and damage to the cutting machine.
For an adequate representation of the cost of a cutting tool, it is necessary to examine the choices of tools, which include solid carbide spiral tools, insert tools, custom tools, and polycrystalline diamond (PCD) tooling. A company can go through several solid carbide bits when a PCD bit can do a complete production run, last longer, and reduce overall cost. Careful consideration and research in the beginning of a process can lead to cost savings in the long run.
The majority of cutting tools have flutes, helical grooves that run the length of the tool. The cutting portion of a cutting tool is its teeth, which are located above the flutes. As the cutting tool removes material from the workpiece, chips move down the flutes to be ejected from the machine. Cutting tools with more flutes are very aggressive and designed to remove more material from harder workpieces but are susceptible to having chips jam the flutes. Fewer flutes are ideal for cutting softer materials and have large chips to be removed.
The essence of the machining process is the removal of material from a workpiece and entails the use of some form of cutting tool. The hardness of a workpiece and the type of forming and shaping determine the type of cutting tool that will be used. Along with these factors, several other considerations have to be examined in order to match the correct cutting tool with the cutting process.
Sawing
Of the various machining processes, sawing is one of the oldest and most common. Over the centuries, the process has been updated, modernized, and adapted to meet the needs of new materials and concepts. The sawing process is used to remove sections of material from a workpiece without any concern for tolerances. CNC sawing is used for multiple functions including finishing and shaping.
The two categories of sawing are continuous cutting and reciprocating cutting. The two processes perform the same functions but use different techniques to an application. Reciprocating involves moving the saw back and forth to remove material. Cutting takes place with each stroke of the saw or with one stroke and is part of CNC machining.
Continuous cutting refers to a saw that is in continuous motion in one direction to remove chips from a workpiece. There are several forms of continuous cutting that depend on how the tool is being used. Continuous cutting makes friction cutting and abrasive cutting possible. Friction cutting uses a high speed saw that heats up a specific point on a workpiece to melt away material. Such saws have no teeth.
Sawing tools are further divided in accordance with the desired results. Cutoff sawing removes large chunks of material when tolerances are not an issue and is used when the kerf is thin. Contour sawing is used to achieve a specific shape and is similar to milling. In CNC machining, milling or other tools can achieve the same results as sawing tools but require special forms of tooling to achieve the same results as a sawing tool.
Broaching
The broach in broaching is a cutting tool that resembles a saw but with varying tooth width and tooth configurations. The teeth on a broach are designed such that each tooth is slightly higher than the previous tooth. Unlike a saw, the individual teeth of a broach make a small cut on the surface of the workpiece as the teeth rise from the first tooth to the last tooth. The rise of a broach represents the amount of material a broach can remove.
Broaches are more complex than other forms of cutting tools and are designed for specific jobs with different shapes and sizes to fit the requirements of an application. There are multiple categories of broaches that relate to the type of job and the force supplied by the machine. The simplest forms of broaches cut a single surface and have a rectangular cross section with one set of teeth.
Simple broaching uses an arbor press. As broaching operations become more complex and demanding, specialized or dedicated broaches are used. The characteristic of a broach that is chosen for a process is dependent on the machine used to power the broach. Some broaching machines pull the broach while others push it with traditional broaching machines being vertical and move the broach up and down. Horizontal broaching machines are used for longer workpieces and hold the broaching tool in braces.
Broaching is a time saving method that can be easily performed by any worker since the technicalities of a broach are built into the tool, which avoids the necessity to make adjustments to the tool during production. Cutting is rapid, precise, and repeatable with the action on a workpiece being very forceful. A workpiece must be capable of withstanding the strength of the material removal of a broach.
Planing
Planing is a common and necessary machining process that is designed to shape and smooth a workpiece. It is used to change the size and shape of materials to fit the requirements of a design and involves pressing and rotating the workpiece against a fixed and stationary cutting tool. During planning, material is removed as the workpiece rotates. The cutting tool digs into the workpiece to sculpt its surface. The definition of planning is related to the characteristics of the created surface.
In some cases, planning and shaping get confused and are assumed to be the same process. In reality, they are two distinct and unique processes. The basic difference between them is their relationship to the workpiece. With shaping, the workpiece remains stationary as the shaping tool moves along it and changes its formation. With planing, the workpiece rotates as the cutting tool cuts into its surface. Shaping is used for small projects while planning is used with large workpieces that need more dynamic treatment.
The planing tool is used to make heavy cuts using a single point cutting tool and is used to flatten a surface or cut keyways. Planer machines are capable of performing different planning jobs in a cycle machine cycle. Factors that are essential to the success of the planning process are the cutting speed, feed rate, and the depth of the cut, each of which has to be precision set prior to beginning the process.
Chemical Machining
Chemical machining or etching uses an acidic or alkaline chemical to remove material from a workpiece without the use of force, pressure, or friction. The workpiece is immersed in a tank containing a chemical solution where it remains for a sufficient amount of time to have material removed by the chemicals in the tank.
The components of the process are a tank, heating coil, and stirrer. The tank is constructed of metal coated with a non-reactive material that is unaffected by the etchant. The heating coil maintains a consistent temperature in the tank and is mounted near the bottom of the tank. The stirrer mixes the etchant to help maintain its concentration and ensure that heat is spread evenly throughout the tank.
The etchant is a strong chemical that reacts with the metal of the workpiece to dissolve metal from the workpiece. To protect the part to be machined, the workpiece is coated with a non-reactive material, referred to as the maskant, that is not susceptible to the effects of the etchant. The maskant ensures that only portions of the workpiece that are to be machined are exposed to the etchant.
Prior to the workpiece being placed in the tank for machining, it is thoroughly cleaned to remove contaminants, rust, bacteria, and foreign substances. The cleaning process is an essential part of the success of chemical machining since poor cleaning can lead to the maskant not adhering to the workpiece. Once cleaned, the workpiece is coated with the maskant.
After the workpiece is machined and etched, it is demasked using a process that peels the maskant off the surface of the etched part. Once demasked, the part is sent back for cleaning for the removal of linkering etchant and masking material. Pressurized cold water is forcefully applied to the surface of the completed part to ensure a total and complete cleansing.
Chemical machining has several advantages compared to more forceful and aggressive methods. Material removal is uniform and free of chips or flakes and leaves a smooth even finish with exceptionally close tolerances. The workpiece is not mechanically stressed, and complex intricate contours can easily be machined.
Electrochemical Machining (ECM)
Electrochemical machining involves the use of a cathode with a negative charge that reacts under DC current in an electrolyte fluid to remove material from a workpiece that has a positive charge referred to as the anode. The cathode has the inverse of the shape that is being machined onto the surface of the anode or workpiece. Since the cathode does not have direct contact with the workpiece, it can be used multiple times due to the absence of thermal erosion.
The anode or workpiece is any type of conductive metal and normally consists of tough to machine metals such as iron, nickel, nitinol, titanium aluminide, and chrome based alloys in plate or bar stock form. The electrolyte is a conductive agent that provides the electrochemical reaction and serves as a flushing solution to remove dissolved metal. It is continuously pumped between the cathode and anode to assist in maintaining the stability of the process.
A power supply is necessary to provide the current for the electrochemical reaction and determines the speed of the process. ECM is a low voltage, high current machining method that uses DC current to power the reaction. More advanced forms of ECM use pulsed current to provide pulses of power.
ECM is a non-contact machining process that does not produce tool wear due to the gap between the cathode and anode. Without direct contact, completed parts have smooth even finishes free of burrs and chips. The hardness of a metal is irrelevant in the ECM process since it is able to cut through the toughest conductive metals.
Abrasive Jet Machining (AJM)
Abrasive jet machining blasts a workpiece with small, hard abrasive material propelled at high speed to erode material from a workpiece. The tool for AJM is powered by an air compressor that uses inert air or gas to propel the fine particulate matter that measures 0.001 in (0.0254 mm) in diameter. As particles strike the surface of the workpiece, they pummel it to remove material to form the product or part.
The continuous impact of the small particles is concentrated in order to cut into material and remove it through erosion. The speed of the grit is approximately 150 m/s up to 300 m/s carried by a gas stream. A filter is used to clean the gas to block dirt or impurities from interfering in the cutting process. The pressure of the propelling gas is closely monitored and controlled to ensure cuts are at the proper depth and have the appropriate amount of force.
Aside from the flow of gas that shoots the particles, an adjustable nozzle is attached to the gas stream to further control the flow of the gas. It is adjusted to achieve the desired angular cut in the workpiece and is made of tungsten carbide to be able to withstand the wear caused by the process. The head of the nozzle can be circular or rectangular and straight or at a right angle.
There are several types of abrasives that are used for AJM machining and include silicon carbide, aluminum oxide glass beads, and sodium bicarbonate for soft materials with regular and irregular shapes. The selection of an abrasive is dependent on its material removal rate (MRR), the type of material to be machined, and the required accuracy.
Ultrasonic Machining (UM)
Ultrasonic machining uses high frequency vibrations in conjunction with abrasive particles to remove small portions of material from a workpiece. The process is used to remove surface material without damaging the crystalline structure. The accuracy of UM makes it possible to create holes, cavities, and shapes with exceptional durability, strength, and close tolerances .
The equipment for ultrasonic machining is precision calibrated and made of steel or nickel, which vibrate at the ideal frequency. At the start of the process, a slurry of boron carbide, silicon carbide, diamond, cubic boron nitride, or aluminum oxide mixed with water is spread over the surface of the workpiece.
During the UM process, ultrasonic vibrations are directed at the slurry that causes the particles of the abrasive material to grind away the substrate. The ultrasonic tool is guided by a software program that adjusts and directs the frequency of the ultrasonic vibrations. The slow speed of the process makes it possible to remove minuscule amounts of material without creating stress in the workpiece, which results in strong durable components with tight tolerances and precision machining.
As accurate and precise as the ultrasonic process is, finished pieces still require the removal of residual particulate matter during the cleaning procedure. This aspect of the ultrasonic machining is especially essential for the production of optics and microelectronic components.
In many respects, ultrasonic machining is a specialized form of machining that is capable of working all forms of materials including those that are hard and brittle. It is the ideal process for working glass, ceramics, and quartz and does not involve the use of heat that can damage workpieces that are sensitive to thermal fluctuations.
Electronic Beam Machining (EBM)
Electronic beam machining involves the use of a high velocity beam of electrons focused at a workpiece to remove metal material. The speed of the electrons is half the speed of light, which makes the process best suited for microcutting. When the high speed electrons strike the surface of the workpiece, the metal material melts and vaporizes. This is due to the heat that is generated by the kinetic energy of the electrons striking the surface of the workpiece.
A negatively charged cathode is used to produce the electrons for electronic beam machining. A positively charged anode is placed after the annulus bias grid that attracts the electron beam that increases the velocity of the electrons to half the speed of light. The focus of the electron beam is guided by an electromagnetic lens while a deflector coil guides the rapidly moving electron beam to the proper location on the workpiece.
The source of energy for the electron voltage is DC current that heats up a tungsten wire filament to 2500°C (4532°F). The high temperature causes electrons to be released by the tungsten filament to be guided by the anode grid cup toward the workpiece. The rapidly moving electrons are guided and focused by the electromagnetic lens. The generated high power density melts and evaporates the material on the surface of the workpiece in a few microseconds.
The wide use of EBM is due to its accuracy, close tolerances, and ability to cut the smallest size holes without making mechanical contact with the workpiece. The process is fast and can be used on the hardest materials without damaging the physical or metallurgical properties of the workpiece. Any type of material can be machined including brittle and delicate ones.
The types of machining listed here are a few of the methods used in modern production. Specialty and custom tools are continually being perfected to meet the needs of innovative designs.
Forms of Burning Machining Technologies
Mechanical methods of machining have been used for many years. Through innovation and technological advances, other processes have developed to remove layers without the need for grinding, boring, or mechanical tools. Some of these techniques are referred to as burning where the workpiece is heated and melted to achieve a shape or design. The most common types are laser, oxy-fuel, and plasma.
Laser cutting
A laser beam, of high energy, contacts the workpiece creating thermal energy. The heat created melts, burns, and vaporizes the surface of the workpiece to shape it into a design. There are two types of lasers – gas and solid state. With a gas laser, gases are used to generate heat, which are He-Ne, argon, and Co2. Solid state lasers have different forms, which include YAG (yttrium aluminum garnet), Nd:YAG ( neodymium-doped yttrium aluminum garnet), and ruby. The laser cutting process can shape steel or etch patterns. Its benefits include high-quality surface finishes and cutting precision. Laser machining produces accurately placed cuts of high precision and has the ability to cut or shape any type of material.
Oxy-fuel cutting
Oxy-fuel cutting, also known as gas cutting, is mostly used to cut thick steel plates. The heat source for oxy-fuel cutting is produced by combining oxygen with some type of fuel such as acetylene, gasoline, hydrogen, or propane. The oxy-fuel torch heats the workpiece to kindling temperature, around 960° C. Once the proper temperature is achieved, pure oxygen is directed through a nozzle onto the heated cut. The oxygen changes the heated and unprotected steel into an oxidized liquid by an exothermic reaction. The created slag is blown out of the heated cavity. The process can cut deeper angles up to 70o and is more economical than the other burning methods.
Plasma cutting
Plasma cutting is a popular economical method for cutting steel. The process of plasma cutting involves using a plasma torch to generate a plasma arc.
The torch fires an electrical arc that transforms an inert, ionized gas, or plasma, which reaches an extremely elevated temperature. The heat from the torch is applied to the workpiece at high speed to melt away unwanted material. Metals machined in this way are electrically charged since an electrical current flows between the electrode of the torch and the workpiece. Plasma cutting can cut thin or thick materials. Handheld torches can cut materials of up to 38 mm thick while CNC devices can cut steel sheets of up to 150 mm thick.
Technologies of Erosion Machining
While burning tools apply heat to melt excess stock, non-traditional methods use a form of erosion. Waterjet cutting and electric discharge machining are non-traditional methods that do not require tools to remove excess material from a workpiece. They use the force of abrasive filled water and electrical discharge.
Waterjet cutting:
Waterjet cutting is a versatile fabrication process that uses water under high pressure, mixed with an abrasive, to cut materials into custom shapes and designs. Water is pressurized using an intensifier or direct drive pump, which is capable of producing significant fluid pressure. As the water enters the cutting head, the water goes into an opening containing a hard jewel such as a diamond, sapphire, or ruby. The velocity of the water increases at the opening, which can reach 2500 mph. Abrasive powder is added to the water stream to cause erosion. Waterjet cutting is typically used on materials that can suffer damage or deformation from heat processes.
Electric discharge machining (EDM):
The EDM process is known as spark machining, spark eroding, die sinking, wire burning or wire erosion. Material is removed from a workpiece through the use of thermal energy without the use of grinding, drilling, cutting, pressure or force. Conductive materials are shaped and cut using an electrode that creates an electrical discharge between the workpiece and an electrode that melts and vaporizes material.
The EDM process is capable of machining complex intricate shapes in hard materials. The workpiece and electrode are submerged in a dielectric fluid where electrical current flows into the electrode creating plasma zones that are melted away. The process produces a cavity that has the opposite shape of the electrode.
EDM electrodes are made from any type of conductive material and determine the shape and accuracy of the cutting process. The most common metals used to manufacture electrodes are copper, brass, graphite, molybdenum, silver tungsten, and tellurium copper, which are selected by their conductivity and erosion resistance.
The three types of EDMs are die sinking, wire, and hole drilling. Die sinking is known as ram EDM or cavity EDM and is used for manufacturing parts with complex cavities and sharp corners. Wire EDM or wire erosion is used to produce extrusion dies and uses the same process as that used for die sinking. Hole drilling EDMs are used to machine holes and can cut deep minute holes without any burrs.
The CNC Machining Process
Computer numerical control machining is a technological process developed in the 1950‘s for the manufacturing of helicopter rotors. In the late 50‘s, a project devoted to producing computer aided design software was financed from which came AutoCAD. AutoCAD combined with CNC has become an advanced technological method for producing parts by machining at a lower cost.
CNC has been applied to a broad range of manufacturing, production, and processing equipment. Software and programming, using the G-code computer language, develop commands and instructions to guide a machine through the shaping of a workpiece. The implementation of CNC has led to a decrease in losses due to human error and a significant drop in the amount of waste. Once a CNC machine is coded, it needs minimal maintenance or downtime and completes production at a faster rate.
Speed and lowered labor costs have made CNC a highly cost efficient method for producing high volume production runs. Down times for mishandled materials, insufficient supplies, or other production errors are eliminated. Every product and part is precision produced in accordance with exacting design specifications. Producers using CNC have the added benefit of more control of the total production process.
Precision Machining
Precision machining produces parts with very few errors or imperfections and close tolerance finishes. There are several forms of precision machines that include milling, turning, and electrical discharge. The process demands focused attention to the specific requirements of the design.
The process of precision machining is chosen because of its adherence to the exact dimensions of the design. Every part includes a set of tolerances that allows for deviations caused by machining. Parts that require precision machining have very low tolerances for machining errors and become useless. Tolerances can vary between 0.0005 and 0.2 for precision machined parts depending on the parts initial dimensions and the type of metal.
The introduction of CNC machining significantly improved precision machining providing for higher tolerances and the production of high quality finishes. Designs can be downloaded directly from the design computer into the CNC machine, which is programmed to every detail of the design. The variance in quality depends on the type of CNC machine being used.
A key factor in precision machining is the finish of the final part. Surface finishing is measured by its texture characterized by the lay, roughness, and waviness. Each of these factors has a mathematical formula to determine the quality of the finish. Manufacturers of machining equipment provide the specifications regarding the quality of the finishes their equipment produce.
Precision machining is critical for the manufacture of parts for spacecraft since they require parts that exactly meet their specifications and requirements. Also, the aerospace industry and certain medical manufacturers have the same requisites.
5 Axis CNC Machining
The 5 axis machining process uses the traditional X, Y, and Z axes with the addition of A and B axes, which makes it possible to shape a workpiece on five sides without extra turning or additional setup. Machining using a 5 axis machine allows for faster cycle times, less waste, increases spindle up time, and is easy to operate without a highly trained staff.
With a 3 axis CNC machine, a part moves sideways along the X axis, vertical on the Y axis, and back and forth on the Z axis. The addition of the A and B axis makes it possible to tilt the work table on the A axis and rotate the table along the B axis. The swivel rotate style of 5 axis machine uses rotary axes to rotate the spindle, which is ideal for working heavier parts. The trunnion style of 5 axis machine has a moving table that is ideal for high volume production.
The benefits of 5 axis CNC machining:
Setup - 5 axis machines make it possible to machine complex, intricate, and complicated shapes with a single setup.
Cutting Tools - The shorter cutting tools of 5 axis CNC machining makes it possible to achieve higher cutting speeds without additional pressure placed on the cutter, which leads to fewer vibrations and better surface finishes.
Complex Parts - Complex parts and prototypes can easily be produced.
Tool Life - 5 axis CNC machining provides constant chip load and optimum cutting position to improve cycle times and tool longevity.
Hole Drilling - With 5-axis machining, holes with compound angles can easily be drilled
Tool Interference - The ability to tilt the table or cutting tool makes it possible to avoid them from running into the tool holder.
In many ways, 5 axis CNC machining makes it possible to achieve the impossible by programming the machine to complete all of the cuts for a part in one cycle. Milling, boring, tapping, threading, and grinding become a one step operation to create complex and intricate parts. Single parts or high volume orders are all possible using a 5 axis CNC machining system.
Materials Used to Produce Machined Parts
Machined parts are produced by machining, which was formally a labor intensive activity. With the advent of CNC machining, modern machined parts are produced on CNC machines that are programmed to perform various functions to produce exceptionally accurate and precision cuts to create high quality parts. Machined parts are different from parts that have been cast or forged and are produced with greater precision and accuracy.
Unlike forging and casting, the machining process makes it possible to easily produce a prototype that can be examined and altered to better fit the needs of an application. The beginning of the CNC process is the creation of a CAD rendering whose programming is downloaded into a CNC machine that quickly produces a prototype. This particular feature avoids losses in mass production.
Machined parts are manufactured from a wide range of materials that include steel, aluminum, brass, copper, titanium, stainless steel, and various types of plastics. The selection of which material to process is dependent on the type of part to be produced and the materials mechanical properties, durability, strength, and versatility. While the various metals are used to produce machined parts for the automotive industry, aerospace, and construction, plastics are used for electronic devices, medical equipment, household products, and the automotive industry.
Although metals and plastics are the most common materials for producing machined parts, the process is capable of forming and shaping composite materials and ceramics, which have special characteristics capable of meeting the demands of specific applications. Composite materials are used for their high strength to weight ratio, stiffness, and corrosion resistance and include epoxy resin, fiberglass, and Kevlar. Ceramics are hard and brittle with thermal and chemical resistance. Much like composite materials, ceramic is known for its high strength, wear resistance, and non-conductivity.
The Advantages of Machined Parts
The wide use of machined parts is due to the many advantages that they offer, which cannot be found in any other type of manufacturing process. Since machining does not require the creation of molds, dies, or other processing tools, the cost of the process is less than that of casting and molding methods. Part runs can be single parts with complex and intricate features or thousands of parts rapidly produced. Additionally, production runs can be momentarily stopped to produce a special order without losing the requirements of the original order.
MOQ
Machining does not have the requirements of a minimum order quantity, which is a necessary part of molding and die processes that require the creation of a mold or die. Machined parts require the use of a blank that is placed into a CNC machine that forms, shapes, bends, cuts, and crips the blank until it takes the form of the desired part. This aspect of machining makes it possible for small companies to complete massive production runs without the need to change tooling or produce specialized tools.
Prototyping
Prototyping is a unique feature of machining, which can be completed multiple times at minimal cost. Clients can submit a computer rendering to a machining engineer who recreates it in CAD. From the CAD rendering, a prototype can be quickly created for a client's examination. If there are errors, flaws, or inaccuracies, the CAD design can be adjusted to accommodate the necessary changes and produce an additional prototype. Although there may be cost associated with the prototyping process, it is far less than having to change molds, cast new dies, or create alternate solutions.
Design
The machining of parts makes it possible to create any shape, form, size, and dimensions of a part regardless of wall thicknesses or tapering. Parts produced by machining can be very robust, strong, and resilient or intricate, detailed, and refined. With all of these advantages, it may seem that machined parts can be produced without any limitations, which is true to some extent. There are design limitations on internal sections and the depth of channels. Even with these constraints, design engineers have more latitude and freedom with the machining process.
Quality
This particular aspect of machining is one of the reasons that it is so widely used. Machining makes it possible to adhere to the tightest possible tolerances since the parameters of a part are input into a CNC machine that performs each operation to perfection for each and every cycle. The typical tolerance for CNC machining is ± 0.005 inch (0.127 mm) with the possibility of achieving tolerances as precise as ±0.001 inch
(0.0254 mm), the width of a human hair. It is this adherence to design parameters that makes it possible to produce the most precise and accurate parts that easily fit into a design.
Lead Times
CNC machining is a fast and efficient process that can be completed without extra preparation or the development of tools. Since it is technological and computer oriented, it can be completed using the simplest of diagrams or computer created designs. Large production runs can be interrupted to do a small project without losing any quality. Theoretically, a client can bring in a request for a part early in a day and have it available by the end of the day. It is this flexibility of machining that makes it such a viable and efficient process.
Adjustments
In die and molding processes, the tool for the process has to be shaped and formed prior to beginning the process. All of the dynamics of a part are scrutinized and examined to ensure the die meets part requirements. Once a die or mold has been cast, it is impossible to make corrections or adjustments. This is not the case with machining. Initially, and in best practices, a prototype of a part is completed prior to it being placed in production to guarantee that it meets the parameters of the design.
After the approval of the prototype, CAD data is downloaded into the CNC machine and production begins. Even in the middle of production, the process can be stopped to make further adjustments or completely change the design at minimum cost. Machining makes it possible to change, adjust, and alter factors of a part at any stage of the process, which is a cost and waste savings.
Strength
Machined parts are produced from a solid piece of metal referred to as a blank. Since the bending and shaping of the blank does not change the grain structure, the blank retains its initial strength when it is formed into the final product. This aspect of machined parts is essential since many machined parts are critical elements of various applications and processes.
Surfaces
Some of the common factors related to molding and casting processes are flash, sprues, flow lines, and jetting that have to be removed before the part can be used. The removal of these flaws is labor intensive and time consuming, which further increases the cost of production. None of these factors are related to machining since gates, sprues, or flow lines are not part of the process. A blank is placed in a CNC machine where it is bent, crimped, cut, and drilled to the specified commands of CNC programming. Once each operation is completed, the part is ready for its addition to an application or shipping.
Custom Machining
Custom machined parts are produced for a variety of reasons such as the lack of part availability, special requirements, one offs, or immediate need. In the past, such parts were produced using a lathe, mill, stamping machine, or other manual machining method. With the advent of CNC machining, the production of custom machine parts has become easier and more efficient.
CNC machining is capable of producing parts that do not exist and are unique in their design, structure, and capabilities. Custom machine parts can be as simple as an unusually formed gear or be as complex as a multifaceted machine component. In all cases, a CAD rendering of the part is translated into the code of a CNC machine such that the machine can create the part.
The types of custom machining covers a wide spectrum of processes with 5 axis CNC machining being the most common due to its versatility and flexibility. The initial phase of custom machining is the production of a prototype to determine the viability of the presented concept. CNC machining makes this aspect of the custom machined parts process easier since any form of computerized format can be downloaded into a CNC machine.
Custom machined parts come from designs created by clients as an integral part of an innovative concept. In most cases, the presentation of a custom part is the final stage in the production of a design, which is a concept that has been tested and reviewed. Companies selected for such special manufacturing are tried and true CNC machinists with the highest qualifications and expertise.
Finishes for Machined Parts
In certain conditions, machined parts may require additional treatments and finishing to meet the requirements of their design. These functions are completed to alter their surface texture, enhance a parts appearance, or to carve a design. The various finishing processes can be functional, cosmetic, or aesthetic and have the goal of meeting design parameters.
Blasting
Blasting is a very aggressive finishing process that is used to create a particular surface texture. It involves firing small miniscule abrasive materials such as beads, sand, or gravel at the machined surface. Since the process is very aggressive and can cut into a part, it has to be carefully monitored and controlled to achieve the desired effect. Blasting is used to alter the surface of larger parts that are capable of withstanding the process.
Anodizing
Unlike blasting, anodizing is an electrochemical process used to give the surface of a machined part an aesthetically appealing appearance. Additionally, the process enhances the durability of a part and provides resistance to corrosion, wear, and prolonged use. Anodizing places a coating on a metal part with an oxide surface layer that gives the part additional sturdiness and attractive finish. The three types of anodizing are Type I chromic acid, Type II sulfuric acid, and Type III known as hardcoat. Anodizing is customized to fit the requirements and use of a part.
Powder Coating
Powder coating is similar to painting a piece of metal. It involves spraying the surface of a part with powdered paint after which the part is baked in an oven to force the paint to adhere to the surface of the part. The baking process creates a strong bond, which makes a part wear and corrosion resistant and exceptionally durable.
The Top CNC Machines
Programmable CNC machines are produced by several companies all across the United States. Each company provides a unique and innovative approach to CNC machine processes using technological techniques that enhance the qualities of their products with exceptional customer service.
Creator Pro from Laguna Supermax
The creator pro has 4-axis capabilities with an electro spindle and rotary machining abilities. Its 6.5 in gantry clearance and liquid cooled 3 HP electro-spindle guarantee smooth and accurate quiet machining. The strength of the Creator Pro is found in its strong durable steel frame and interlocking aluminum that are designed to withstand the rigors of constant use. Additionally, it has precision ball screws and primatic guides for fast and efficient operation. The DSP controller on the Creator Pro makes processing input easy and trouble free.
Datron M8Cube
The Datron M8Cube is designed to simplify the manufacture of complex and intricate parts. It is a high performance milling machine that provides versatility and efficiency at a low price with a large work area that is encompassed in a small footprint. The M8Cube is ideal for machining aluminum and other nonferrous metals. It provides fast cycle times and is capable of working multiple jobs simultaneously, which makes it easy to be reprogrammed when a rush job comes in. The spindle of the M8Cube operates at up to 60,000 rpm with a feed rate of up to 22 m per min (72 ft per min). Datron has a complete line of CNC machines in different sizes to fit the requirements of any manufacturing operation.
MAG-CX3 500
The MAG-CX3 500 is a vertical CNC machine designed for high precision repeatable machining. It is a vertical and adaptable CNC machine that can be used for industrial and non-industrial applications. The MAG-CX3 500 is programmed with software for easy management of machine functions with a graphical interface that is compatible with the most recent internet browsers. Included in the software package is real time readouts regarding the condition of the machine through remote access. Various features of the MAG-CX3 500 can be custom designed to match customer requirements including custom graphics and software interface.
T Series Super-Precision from Hardinge
T Series Super-Precision CNC machines provide extraordinary precision CNC machining for hard turning applications. The series is designed to produce and manufacture the most challenging and demanding parts and is ideal for two axis machining as well as complex multitask processes. The essence of the T Series is the high level of its precision and exceptionally gentle handling of delicate parts. The horsepower of the T Series varies between 15 HP up to 35 HP with a spindle speed of 4000 RPM up to 6000 RPM. Available chucks are 6 inches (150 mm), 8 inches (200 mm), and 10 inches (250 mm) and use a FANUC 31i control unit for programming machining processes.
EC-400 from HAAS
The EC-400 is designed for unmanned high production using a 4-axis rotary system for synchronous motion and chip management. It has a large work envelope and an exceptional tool management system designed to enhance tool life. A main feature of the EC-400 is its in-process probing that can be completed between operations to ensure part consistency. The EC-400 comes with a 30+1 tool side mount tool changer, built-in pallet change for 400 mm pallets, and a 6 station pallet pool. Unattended machining is made possible by the EC-400’s automation system that allows for unattended production of pallets from start to finish.
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