Milling 101: What are the considerations when it comes to milling operations, and how can operators reduce vibration in milling? Read on. Article by Sandvik Coromant.
Milling has been evolved into a method that machines a very broad range of operations. In addition to all the conventional applications, milling is a strong alternative for producing holes, threads, cavities and surfaces that used to be turned, drilled or tapped.
There are different types of milling operations. They are:
Groove milling and parting off
Holes and cavities/ pocketing
The following are the initial considerations for milling operations:
The milled configuration
The features to be milled have to be carefully considered. These can be located deep, requiring extended tooling, or contain interruptions and inclusions.
Workpiece surfaces can be demanding, with cast skin or forging scale. In cases of bad rigidity, caused by thin sections or weak clamping, dedicated tooling and strategies have to be used. The workpiece material and its machinability must also be analyzed to establish optimal cutting data.
The choice of milling method will determine the type of machine needed. Face/shoulder or slot milling can be performed in 3-axis machines, while milling 3D profiles require alternatively 4- or 5-axis machines.
Turning centres today often have milling capability due to driven tools, and machining centres often have turning capability. CAM developments mean that 5-axis machines are increasingly common. They offer increased flexibility, but stability can be a limitation.
How to Reduce Vibration in Milling
Milling vibration can arise due to limitations in the cutting tool, the holding tool, the machine, the workpiece or the fixture. To reduce vibration, there are some strategies to consider.
Tungaloy has announced that its TungMeister series of exchangeable-head end milling system now includes long-flute end milling heads and new high-rigidity shank holders.
With TungMeister, significant reduction in tool changeover time can be achieved through the ability to replace used heads instead of an entire tool. Since it takes no more than one minute for tool exchange, setup time can be significantly reduced to as short as one tenth of the time it would typically take to replace solid carbide end mills for maximum productivity and cost effectiveness.
Responding to market demands, TungMeister now offers a range of VEH-style square shoulder end milling heads whose maximum cutting depth (APMX) is twice the length of that of the existing range. This provides the new VEH head with a capability of 1.5xD. Its variable-pitch and variable-helix cutting edge design, combined with tapered core geometry, will enhance the tool’s chatter stability while machining at demanding depths of cut.
The new VSSD-style shank holder is offered with thicker shank diameters than those of the existing range, increasing the tool’s flexural rigidity by 200 percent to 320 percent for added more reliable and productive machining.
With over 13,000 possible head-shank combinations available, TungMeister is able to readily provide tooling flexibility that enables users to find a solution for almost every application.
Ten VEH-style end milling heads and five VSSD-style shank holders are added in this expansion.
The aircraft milled parts market is projected to grow at a healthy rate over the next five years to reach an estimated value of US$ 4.3 billion in 2025, according to a report by Stratview Research.
Milled parts or components are those machined components which are mainly produced through the milling process. Rapid advancements in the milling process i.e. from conventional milling machines to advanced CNC (Computer Numerical Control) milling machines and high-speed machining centers have paved the way for milled components/parts in the aerospace industry. These advancements have also helped the industry to achieve its main objective of optimising metal removal rates and minimising chatter.
The outbreak of COVID-19 is ending the longest 16 years of the industry boon, which had begun when the industry had emerged out from another infectious disease SARS (2002-2003). The aerospace industry is projected to be one of the most severely impacted industries due to the COVID-19 outbreak.
As per the recent estimates of IATA, the airline industry is expecting to record a possible loss of US$ 252 billion of passenger revenues, an equivalent of a 38 percent loss in RPKs in 2020 from 2019. Complete lockdown of many countries, due to the pandemic, has forced several airlines to cut their flying capacity due to grounded fleets and operate at a reduced capacity of five percent to 40 percent of their total strength.
The overall impact of the outbreak is still unpredictable; however, currently, it is anticipated to be graver than the SARS (2002-2003) and the MERS (2015). And yet the industry is optimist about its recovery as it did during SARS (2002-2003).
The demand for milled parts in the industry is largely dependent on the overall health of the aviation industry. Huge order backlogs of Boeing and Airbus (13,237 aircraft at the end of Feb 2020), accelerating demand for replacing iconic aircraft such as A380 and B747, which are forced to retire early by several airlines due to the outbreak, with A321, A350XWB and B787, and the market entry of new aircraft programs such A321XLR, B777X, C919, and MC-21; are anticipated to assure a speedy recovery of the aircraft industry including milled parts.
Asia-Pacific is expected to witness the highest growth during the forecast period, driven by upcoming indigenous aircraft program i.e. COMAC C919 and Mitsubishi SpaceJet, and opening of assembly plant of Boeing and Airbus in China for B737, A330, A320, and A350. Further, key economies, such as India and China, in the region are incessantly increasing their defense budget with the purpose to acquire the latest military aircraft to solidify their defense capabilities along with their offset policy and development of indigenous military aircraft such as Tejas and J20.
Reducing CO2 greenhouse gas emissions has a considerable impact on the development of machining tools, as new fields of application are emerging, and existing ones need to be adapted. This is because alternative drives, new, lighter materials, and concepts that save energy and resources are now more in demand than ever before. Article by Walter AG.
The Walter Xtra·tec XT shoulder milling cutter and face milling cutter are suitable for virtually all requirements in shoulder and face milling, in all common material groups.
Reducing CO2 greenhouse gas emissions has become an objective throughout the world. In many places, there are now discussions about imposing taxes on CO2 emissions. The German government has set itself the objective of reducing carbon dioxide emissions in Germany by 55 percent by 2030.
This also has a considerable impact on the development of machining tools, as new fields of application are emerging, and existing ones need to be adapted. This is because alternative drives, new, lighter materials, and concepts that save energy and resources are now more in demand than ever before. Developers see great potential in design modifications to tools, new coatings, new machining strategies, and digital solutions, which respond to the existing framework conditions in real time.
Increase Tool Life
The current trend is for new, lightweight aluminium-lithium alloys. These materials quickly overwhelm conventional tools, resulting in an increasing demand for high performance tools specifically designed for this range of applications.
For instance, aircraft components made of aluminium alloys often have machining volumes of up to 90 percent. Depending on the required component geometry, numerous bevels and cavities need to be milled out of the metal, with the goal of ensuring stability and reducing weight. To manufacture the components economically and to a high quality, they need to be machined using high speed cutting (HSC) processes involving cutting speeds of up to 3,000m/min. Cutting values that are too low lead to build-up on the cutting edge, and therefore result in rapid wear and frequent tool changes. This results in high costs due to long machine running times. Machine operators specialising in aluminium therefore have good reason to demand above-average cutting data and tool life from their tools, as well as particularly high process reliability.
With the design of the M2131 ramping milling cutter, the tool developers at Walter AG have shown how such complex requirements can be dealt with. The 90 deg milling cutter is equipped with a new class of indexable inserts, with the grade designation WNN15. This refers to a new PVD coating, which is manufactured using the HIPIMS method. The term HIPIMS stands for “High Power Impulse Magnetron Sputtering”, a technology based on magnetron cathode sputtering. The special feature of the physical coating process is that it produces an extremely dense and smooth PVD coating, which greatly reduces friction and the tendency to cause built-up edges. At the same, this method increases cutting edge stability and resistance to flank face wear, enabling a maximum metal removal rate as a result. Field tests have confirmed the advantages of HIPIMS indexable inserts compared to standard types. Increases in tool life of up to 200 percent were achieved.
“We are seeing an increasing demand for high-performance tools for machining aluminium, particularly in the aerospace industry but also increasingly in the automotive industry,” explains Wolfgang Vötsch, Senior Product Manager for Milling at Walter AG.
Suitable workpieces, milling tools, machines and CAD/CAM systems are required for the dynamic milling strategy. Image: Walter AG
Milling Strategy with a Focus on Efficiency
Many sectors, particularly the supply industry, are under pressure to provide increased process reliability and faster machining—at ever lower costs and with consistent quality. The demands for surface quality and dimensional stability are often increasing at the same rate as requirements for process reliability and cost efficiency. Moreover, there is a growing need for lightweight or heat-resistant materials. However, these materials from the ISO M and ISO S material groups are often difficult to machine precisely because of these properties.
Dynamic milling provides a solution in this area, offering both productivity and process reliability. This is why a growing number of metalworking companies are relying on this method.
High Performance Cutting vs. High Dynamic Cutting
The main differences between conventional high performance cutting (HPC) and high dynamic cutting (HDC) are in the movement of the milling cutter and the forces generated. During HPC, the milling tool moves with relatively low depths of cut. During HDC, the CAD/CAM control system adapts the machining paths so that the tool moves according to the shape of the workpiece. This prevents non-cutting time, or at least reduces it. Moreover, the depth of cut is significantly greater during HDC than during conventional HPC, meaning that travel distances are also reduced because the complete tool length can be used.
The engagement angle is usually very large during HPC. The forces that occur in the process are accordingly high. This in turn quickly causes signs of wear to appear on the tool and the machine spindle. Dynamic milling, on the other hand, is characterised by a high level of process stability and a long tool life. The engagement angle chosen for HDC is normally small, meaning that the forces which impact the tool and machine are much lower than for HPC. Higher cutting parameters, less non-cutting time and increased process stability result in a much higher metal removal rate for HDC milling compared to HPC.
Cutting Data Optimisation Using Live Data
Automation, digitalisation and networked processes have been everyday aspects in many areas of metalworking for a long time. In particular, the hardware and software used to collect and analyse live data have produced huge leaps in performance.
The Comara iCut software tool demonstrates how this provides opportunities to optimise processes. The adaptive feed control analyses incoming machine data in real time and adjusts the machining accordingly. This answers one of many users’ key questions. Namely, how can you get the most out of a machine without making major changes to the process or carrying out complex reprogramming work?
The iCut software enables the machining time per workpiece to be significantly reduced. This software is integrated into the existing control programme and applies the data from this for the machining process. During the first cut, iCut “learns” the idling output of the spindle and the maximum cutting efficiency per cut. Subsequently, it measures the spindle output up to 500 times per second and automatically adjusts the feed in each case. This means that the machine always operates at the maximum possible feed for each tool. Should the cutting conditions change (depths of cut, machining allowances, wear, etc.), iCut adjusts the speed and output in real time. This not only has a positive effect on the machining time for the workpiece, the optimised milling characteristics also increase the process reliability. The forces acting on the spindle are more constant and this also results in a longer service life.
If the tool is in danger of breaking, iCut reduces the feed straight away or stops the action altogether.
Florian Böpple, Digital Solutions Manager at Walter, says, “We have already achieved astonishing increases in efficiency for customers using iCut. If the machining operation is compatible, a 10% reduction in machining time is always achievable. We have already managed to reduce machining times by double this amount. When the quantity is high, this frees up considerable machine capacity.”
In addition, this works irrespective of whether Walter tools are used; all that is necessary is for the machine’s system requirements to be met.
Milling with ‘Xtended Technology’
Walter recently showed the potential of the tools themselves with the entirely new generation of Xtra·tec XT milling cutters. They combine design improvements with high-performance cutting tool materials. This means that the focus is always on increased productivity and process reliability. The most striking design feature is the installation position of the indexable inserts, at a greater incline and with a larger contact surface. This reduces the surface pressure in the seat while increasing the stability. The larger screw hole cross-section stabilises the indexable insert and the longer screws hold it in place more securely. The cutter body has also been made stronger, now with much more material behind the insert seat.
Besides increased process reliability, the special installation position of the inserts also allows for the addition of an extra tooth, thereby increasing productivity. The precise 90 deg shape of the shoulder milling cutter helps to reduce what would otherwise be additional required finishing operations. Clamping screws which are easier to access optimise handling and help prevent assembly errors.
Another new feature, which applies to the face milling cutter M5009, is the smaller indexable inserts which can be fitted to the milling cutters. These continue the current trend towards reduced machining allowances. The M5009 milling cutters combine small depths of cut with the economic advantages of double-sided indexable inserts—with eight usable cutting edges rather than the usual four. Thanks to these cutting edges, as well as a reduced number of finishing operations, the milling cutter achieves increased efficiency.
Our innovation also extends to sustainability. As part of Walter Green, the production and supply chain of the Xtra·tec XT milling cutters is CO2-compensated.
The four examples illustrate where we are heading in the metalworking industry—with respect to tools, machining strategies and the field of digital innovation. At the same time, they highlight four approaches showing where the opportunities lie and how the trends and challenges of the future can be dealt with successfully.
Kennametal announced the latest addition to its best-selling HARVI line of high-performance solid end milling tools, the HARVI I TE four-flute solid carbide end mill. With a radical new design, the HARVI I TE delivers outstanding performance in a broad range of materials, including steel, stainless steel, high-temperature alloys and cast iron –with tool life to match. And thanks to significantly reduced cutting forces, this game-changing tool can be used on any machining center or mill-turn center in the shop.
“The HARVI I TE consistently outperformed competing four-flute end mills in both wet and dry machining tests on a variety of materials and applications, with unprecedented tool life in many cases,” said Bernd Fiedler, Manager, Solid End Milling.
“It performs exceptionally well on heavy roughing and finishing cuts alike – from deep cavities and full width slots to shoulder and dynamic milling.”
Kennametal engineers designed the HARVI I TE to address four key problems that plague more than 90 percent of all milling applications: chip evacuation, tool deflection, corner stability, and breakage due to radial cutting forces. The result is a tool that’s durable and versatile enough to tackle the lion’s share of milling applications.
Consider chip evacuation. The HARVI I TE has an innovative flute design that helps curl and break chips into manageable pieces, while a series of chip gashes within the flute lift those chips up and away from the workpiece. Both serve to promote coolant flow, eliminate chip re-cutting, and improve tool life. A twisted end face and unique gashing further promote chip evacuation but are also responsible for the HARVI I TE’s awesome ramping and plunging capabilities.
Tool deflection is reduced thanks to the tool’s parabolic core, as well as an eccentric, faceted relief along the entire flute length that significantly lowers cutting friction. This relief also increases edge strength, making the tool a versatile solution.
Together with a variable helix angle and asymmetric flutes it dampens vibration before it can negatively affect machining operations.
“The HARVI I TE improves process stability, surface quality and chip evacuation,” said Fiedler. “Most importantly, it maintains these benefits even at increased feeds, speeds, and depths of cut – delivering maximum metal removal, tool life and productivity.”
The continuous dirt accumulation poses the biggest challenge for the deep-hole drilling and milling machine. This article looks at how the energy supply for such machines can be maintained reliably under extreme environmental conditions. Article by igus.
The AX-TLF series from Auerbach Maschinenfabrik GmbH combines conventional milling techniques with modern deep-hole drilling systems in one machine.
In machines combining milling and drilling functions, extremely high demands are made on the energy supply system for the main spindle. Dust, dirt and drilling fluid account for maximum loads from the outside. From the inside, heavy hydraulic hoses, in particular, affect the stability. Most of the time, the manufacturer relies on the very thick plastic energy tube for supply so that the performance data of the universal machine remains correct in the long run. This also protects and routes all cables and hoses.
“The continuous dirt accumulation poses the biggest challenge for the deep-hole drilling and milling machine,” says Thomas Gemeinhardt, managing director of the Auerbach Maschinenfabrik GmbH in Ellefeld. “In addition, the performance data of the machine tools increase, but the availability of interior space remains the same. To supply energy to the main spindle reliably, Auerbach uses the new energy tube ‘RX’ in its multi-function ‘AX-TLF’ type, which combines the milling and deep-hole drilling systems in one machine.” According to Gemeinhardt, it is 100 percent tight and ensures safe cable protection even in continuous use.
Milling and Deep-hole Drilling Systems in One
Manufacturing machine tools for over 60 years, Auerbach Maschinenfabrik manufactures not just the traditional milling machines, but also multi-functional machines.
Gemeinhardt comments, “Our customers want multi-functional machines. As a result, our specialty today is the combination of conventional milling techniques with modern deep-hole drilling systems in one machine.”
The ‘AX-TLF’ type series not only saves on purchase costs. The necessary set-up times can be reduced because the complete machining is possible with only one clamping. Depending on the design, the machines work on workpieces with drill diameters from 6mm to 65mm—in special cases up to 100 mm—whereby in one move, drill depths of up to 2.1mm, and in special cases up to 3mm, are possible. “We feel well-equipped for the future,” says Gemeinhardt.
Quality is top priority at the company. “With our high-quality machines, we want to constantly maintain our position as a special supplier in the market,” says Gemeinhardt. “For this, we have our own development department to implement specific customer requirements. We place value on the traditional German engineering quality. This also applies to the selection of suppliers.”
The AX-TLF type series consists of five basic machines, which serve as a platform for numerous variation options. This modularity pays off. In addition to the traditional mold-making and tooling, the combination machines are used in, among other things, the aviation and aerospace industry, general mechanical engineering, solar industry, apparatus engineering, and the oil and gas industry. This wide-ranging spectrum of applications brings more than the most varied machining demands. Even the choice of materials is wide, ranging from soft graphite through aluminum, and standard steels up to high-strength stainless steels and titanium alloys.
Thick, taut hydraulic hoses that are as hard as an iron bar increase the pressure within the energy tube.
Addressing Continuous Dirt Accumulation
“Our machines are versatile,” says Gemeinhardt. In general, they can handle all types of materials. The requirements for a machine vary, such as the components used. And in this instance, dirt accumulation plays a major role. Graphite, for example, is machined dry and is extremely abrasive and lubricating. If it is not exhausted, the entire environment would be black in the shortest time. When it comes to deep-hole drilling, where a lot of drilling oil is used, this creeps in everywhere and is extremely aggressive.
One option is the minimum quantity lubrication. It only works with customers who machine a defined material. Here, lubricated air cooled at high pressure is used for deep-hole drilling. Due to the atomized oil, the particles fly through the work area before they settle everywhere.
While supplying energy to the main spindle, the plastic energy tube lies always in the immediate chip area. This means that hot chips remain partially on the tube, and it is exposed to continuous dirt accumulation and drilling oil. In the process, the machines, depending on orders, work in three shifts for seven days a week. In addition to the extreme environmental conditions, there is a particularly small bending radius of 100mm. And taut hydraulic hoses that are as hard as an iron bar increase the pressure within the energy supply system.
The rounded design of the energy supply system simply makes the chips bounce off. In addition, the pin/hole connection elements and the stop dogs are covered, so that no chips can stick there.
Enter the RX Energy Tube
“Due to increased milling capacity, we sought an even more robust solution for the energy supply for a customer as part of a retrofit with new built-in pressure hoses,” recalls Gemeinhardt. Since that time, only the RX energy tubes in the size 40 are used in the combination machine for milling and drilling.
The RX e-tube enclosed cable carriers from igus offer extreme protection against chips and dirt.
“Our universal machine tool needs to assert itself in a tough competition. Improvements are in the details,” says Gemeinhardt. “Accordingly, we are constantly improving the performance data of our machines. We are currently developing, for example, a water-cooled spindle. Here, the machine is equipped simultaneously with sealing air, which means we must lay two more cables.” Therefore, here, the new large RX size with an inner height of 73mm should be used to ensure energy supply.
Producing threads in hardened steel is costly. This applies to blind hole machining in particular because reversing the tap during this process can cause torque peaks when the root of the chip is sheared off, resulting in fractures.
Walter is solving this problem with two new taps – offering its customers a full product range for producing threads in hardened steels with an additional thread milling cutter: The TC388 Supreme (50–58 HRC) or TC389 Supreme (55–65 HRC) and the TC685 Supreme (> 44 HRC). The TC388 and TC389 Supreme solid carbide taps boast special cutting geometries. These fully shear off the root of the chip when reversing; torque peaks are minimised. This prevents fractures, prolongs the tool life and increases process reliability. Lubrication with oil, which was often necessary until now, is no longer required. Instead, emulsion can be used, which optimises handling and saves additional machining time. Both taps are characterised by a short machining time.
The TC685 Supreme orbital drill thread milling cutter enables maximum process reliability and the highest possible tool life quantity. The core hole and thread (chamfer if required) are produced in a single operation, thereby saving tool spaces. The milling geometry on the face produces stabilising forces in the axial direction. This improves the stability when milling and reduces the deflection. Advantages for the user: Fewer radius corrections and reduced wear, with a high tool life quantity and minimal costs per thread. The 15° helix angle and internal coolant from M6 guarantee reliable chip evacuation. This allows even tougher steels and deep threads to be machined reliably. Common applications for all the tools mentioned include mould and die making, for example.
Sodick’s CNC High Speed Vertical Machining Centres (VMCs) feature linear motor drives on the X, Y and Z axes. They’re designed and engineered for prime speed exactitude edge and have unmatched accuracy.
The advantage of high-speed edge machining is that the top quality machining of sophisticated minute and little shapes. This machining method is wide used for low professional lupus multi-core connectors that are engineered into communication devices with slim pitches for compact transportable phones together with sensible phones, and mold elements for moulding little optical components that need high accuracy and top quality surface finishes wherever it’s troublesome to use polish machining.
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