White Paper FANUC HMIs

Transcription

1 White Paper Document No. MWA-015-EN_06_1507 July 2015 Total Cost of CNC Ownership The total cost of a CNC over the life of a machine tool FANUC HMIs

2 1 Introduction 3 2 Costs of Ownership Competitive acquisition cost Lower running costs High-performance machining Better quality parts Lowest downtime costs Higher resale value Summary 11 Document # MWA-015-EN_06_ Page 2 of 12

3 1 Introduction Asset purchases typically start with a problem to solve and a list of requirements that includes must have and nice to have features. Some of the needs will be technical and pertain to a specific application. Others will be political and address a variety of strategic business issues such as Lean Manufacturing, better customer satisfaction, business system integration, growth and, of course, return on investment. In the next step, a list of potential solutions is generated and it must be determined which best satisfies the list of needs. It is often an iterative process, with new needs and new solutions being added along the way as the buying process uncovers new possibilities and needs. Each individual on a buying team may weigh the technical and political needs differently, but all would like to believe they are making the most informed decision. When it comes to purchasing machine tools, the global market will usually provide multiple choices of machine tool builders at a variety of different quality and price points. The well informed buyer understands that the CNC system is a significant part of a machine tool s capabilities, with the CNC, servo and spindle drives all contributing to a machine s ultimate performance. When narrowing down the options and making the final choice, acquisition price is certainly a factor, but it is equally important to consider the total cost of ownership over the productive life of the machine tool. For most companies, purchasing a CNC machine tool is a long term commitment. It is not like a PC or cell phone that is upgraded every few years, and it is appropriate to consider the total cost of ownership. The CNC system s total cost of ownership (TCO) includes: acquisition cost running costs performance part quality downtime costs resale value Considering the CNC system s total cost of ownership provides the most comprehensive and informed evaluation. 2 Costs of Ownership 2.1 Competitive acquisition cost Today s manufacturers use a variety of machines, from simple commodity lathes and mills to the most complex 5-axis machines working in multi-machine cells. Hybrid machines that can do both turning and milling are increasingly popular to reduce setup time and to improve quality and overall cycle time. Machining operations can be updated and expanded with the best-in-class machine tools that are optimal for a particular application and business strategy. A wide choice of machine tool manufacturers stimulates competition so that you can be assured to get the best value available for the machine tool selected. FANUC HMIs Document # MWA-015-EN_06_ Page 3 of 12

4 Since the CNC is an important part of a machine tools capabilities, it is beneficial if the best performance and best value CNC is available in combination with the best-in-class machine tool. A few machine tool builders only offer their own, proprietary CNC systems, which can be application and price optimized for their machines. However, most of the world s leading machine tool builders focus their resources on advancing machine tool and machining technologies and leverage the technology from the leading CNC manufacturers to provide the best total solution for performance and value. The result of combining the diverse resources of two larger development teams produces significant enhanced capabilities that are simply not possible from a single company. Manufacturing companies can create a standard CNC specification for their machining operations that includes essential features such as connectivity, part program storage, work and tool offset requirements. Applications such as 5-axis machining may require additional features to support the most efficient and effective CAD/CAM/Machine workflow. By providing a machine tool builder with a CNC specification, the purchasing evaluation can focus on machine technologies. By establishing a standard CNC specification, hidden costs for training or hiring operators, part programmers and maintenance personnel are avoided and logistics for issues like product support, spare parts and connectivity are simplified. One hidden acquisition cost might occur when integrating machines into manufacturing systems. Integration with robots can be as simple as a single Ethernet connection or it can be as complex as custom engineering and multiple discrete cables running between devices. Integrating into the factory system may require any of number of common field buses including Ethernet/IP, DeviceNet, Profibus, AS-I, I/O Link II, FL-net, Modbus/TCP and CC-Link. Only the leading CNC manufacturers can provide the most flexible connectivity required by today s complex manufacturing systems. Achieving the best acquisition cost is a combination of the widest choice of competitive solutions and minimizing the hidden cost and problems associated with an incompatible CNC system. 2.2 Lower running costs Acquisition costs have a one-time impact but running costs are an everyday expense. Studies have shown that approximately 20% of a machine s running costs can be attributed to electrical energy consumption, primarily for hydraulic and pneumatic pumps, and the servo and spindle drive systems. Preventative maintenance costs are minor for a world-class CNC system, limited to the annual replacement of consumable items such as batteries, fans and fuses. Modularizing these components for quick and easy replacement without specialized tools minimize the disruption to production for preventative maintenance. Tool management features in the CNC can have an impact on tooling replacement costs, at least by minimizing minor stoppages to inspect and replace worn tooling. Adaptive control can also be used to increase productivity and maximize tool life. Document # MWA-015-EN_06_ Page 4 of 12

5 The servo and spindle motors of a machine tool are continuously accelerating and decelerating as they change speed and direction during machining. When motors are accelerating, they draw energy from the electrical system. When they are decelerating, their kinetic energy is converted back into electrical energy, which must be dissipated. Low cost drive systems simply burn the energy as heat in a resistive load in a process called dynamic braking, whereas more advanced drives systems use a variety of strategies to save energy. DC-bus servo drives may share some of the excess energy with other motors on the machine that may be currently accelerating. Energy may also be stored temporarily in banks of capacitors and then released during the next motor acceleration. State-of-the-art AC drive systems use high-speed, high-efficiency switching circuits to direct the energy back into the main electrical supply, reducing the net energy used. When combined with the more efficient machining processes provided by the CNC, machine electricity costs can be reduced by as much as 30% to 50%. The CNC may monitor and display the real-time energy usage and savings allowing part programs to be optimized for maximum efficiency. The data may also be collected via Ethernet and saved for trend analysis. Modern computers and mobile devices use multiple strategies to save battery power, dynamically turning off screens, disk drives, communication networks and other power hungry components when they are not actively being used. The CNC system includes a powerful programmable machine control (PMC) interface that the machine tool builder can use to implement similar strategies for their machine tools. When the machine is not in cycle, power hungry devices may be turned off based on an algorithm that considers how long the machine has sat idle, and the length of time it takes to restart each component when the machine is again required for machining. FANUC HMIs Document # MWA-015-EN_06_ Page 5 of 12

6 Though CNC preventative maintenance is mostly limited to a few batteries, fans and fuses it is essential that these tasks can be completed easily and quickly to ensure there are no disincentives in a busy work environment. World-class CNCs ensure that maintenance components are as reliable as possible and that they can be replaced quickly without special tools. Build-in diagnostics and component life tracking alerts the operator if a maintenance item is overdue so it can be addresses before unplanned downtime occurs. The CNC tool management feature implements a standardized tool maintenance strategy, monitoring tool usage by both cutting time and number of operations. This eliminates unplanned downtime due to tool breakages and excessive tooling costs due to premature replacements as a result of operator inexperience. If the capacity of the tool changer allows, multiple identical tools can be made available and the CNC will automatically select a fresh tool when the current tool reaches its maintenance life, prolonging the time between tool maintenance interventions. RFID tool ID systems can be interfaced with the CNC to automatically transfer tool life and tool geometry data between the machine and the tool room. Adaptive control monitors the spindle load during cutting and modifies the cutting feedrate within acceptable limits to maintain a constant tool load as the tool sharpness declines prolonging tool life. 2.3 High-performance machining The cycle time for machined parts is typically established by benchmarking. It is often assumed that the benchmark represents the fastest possible processing speed. However, machines are accelerating and decelerating (acc/dec) and feedrates are often limited below the capacity of the machine and the recommended material cutting parameters to accurately reproduce part geometries. Advanced CNC systems feature a suite of path and acceleration optimization functions to reduce cycle times and thereby lowering part costs. Accuracy and speed are competing factors in machining. There are several CNC features available to improve the dynamic accuracy of the machine tool and servo system, and the improved accuracy can be traded-off for higher machining speeds. Any instantaneous change in axis speed or direction may cause vibrations that be observed in the surface finish of the part. Machine resonance can be minimized by using a bell-shaped or S-shaped acc/dec profile. During the first microseconds of a move, the acceleration of an axis is ramped very gently until the linear section is reached. The same simple gentle ramping of the acc/dec rate occurs when the axes reach top speed, when going from top speed to decelerating, or when decelerating to a stop. This typically allows the linear section of the acc/dec profile to be set more aggressive than is possible with standard linear acc/dec, reducing the overall cycle time. Document # MWA-015-EN_06_ Page 6 of 12

7 AI Contour Control (AICC) looks ahead in the part program to eliminate the acc/dec and servo delays that limit feedrates when cutting short line segments or contours, and effectively eliminates machining trajectory error in corners and small radii. Nano smoothing converts CAM-generated line segments back into splines for faster execution and a superior surface finish with only minor modifications to existing part programs. Dynamic optimization techniques such as Smart Tolerance Control and Smart Overlap eliminate machine shock and wasted motion when changing axis directions or switching between rapid traverse and cutting feedrates. Smart Tolerance Control is especially effective in small segment programs where the data points are only approximations of a complex curve. Smart Tolerance Control will reduce machine shock, improve surface finish, reduce cycle time and maintain part accuracy within a programmable allowable error tolerance. Smart overlap analyzes the part program and identifies when switching from rapid traverse to machining for example, when approaching a cut and when switching from machining to rapid traverse for example, when exiting a cut. By replacing the linear moves with a radius, the axes can move faster and smoother, reducing aircut cycle time while maintaining part accuracy and geometric integrity, reducing the cycle time of programs with many positioning moves by as much as 10%. The only physical limit to the metal removal rate of a machine tool is the spindle horsepower available. However, variation in material hardness, depths of cut and width of cut means that the programmer ordinarily must select a conservative feedrate, and machine capabilities are underutilized. Adaptive control automatically adjusts the axes feedrate to maintain a constant horsepower that is suitable for a particular machine and tooling combination, reducing the cycle time by as much as 40%. At the same time, making constant horsepower cuts extends tool life, especially when machining very hard materials. High Response Vector (HRV) is an advanced form of field oriented control that uses high-speed DSPs and nano-interpolation to improve surface finish, cycle times and accuracy. Auto-following filters dynamically suppresses mechanical resonance even when the frequency changes. For example, HRV4 closes the current loop in µs, the velocity loop at 62.5 µs and the position FANUC HMIs Document # MWA-015-EN_06_ Page 7 of 12

8 loop at 250 µs. HRV spindle control is also effective when the spindle is used as a positioning axis when rigid tapping for example producing higher-speed with better accuracy. Machine tools are delivered with only basic servo tuning to ensure stable operation for a wide range of applications. Most machines can be improved for specific applications, because the optimum servo tuning for large, heavy parts is significantly different than the optimal servo tuning for smaller, lighter parts. Servo system optimization for a particular class of part or application will significantly decrease cycle times, fine tuning the settings for acc/dec, feed forward and the suite of performance tools available in the CNC. System tuning can be optimized individually for speed, accuracy and surface finish. The programmer can switch between these optimized settings or a balance between the settings depending on the current machining operation. For example, speed may be emphasized during roughing cuts, accuracy during contouring and surface finish during final machining passes. 2.4 Better quality parts Many manufacturers inspect parts to make sure that the bad ones do not get to their customers, and most take manual samples during a batch to check to see if tool wear offset adjustments are required. The operator stops the machine, measures the part, makes a calculation and updates a tool offset. This can be a prolonged and error-prone process. The best quality parts are produced efficiently by ensuring the process is capable of making good parts. The machine must be capable both in precision and repeatability, and the whole machining process is monitored to ensure it stays in control. To achieve the highest precision possible, nanometer resolution is required throughout the entire motion system from the CNCs internal calculations and stored values, through to the interpolator, on to the servo and spindle drive systems and back through the 32-million countper-revolution position feedback devices. Nano-meter precision provides a superior surface finish quality whether you are machining simple prismatic parts or the most complex curves using advanced spline interpolation. In many cases, it minimizes the need for secondary operations reducing both the total part cycle time and the part cost. Mechanically good machine tools can be made better with a suite of compensation functions available, from the basic backlash and stored pitch error compensation to more specialized functions such as straightness, thermal growth, 3D Error and 3D volumetric compensation. Using a spindle probe or an automated inline gage station eliminates the dependency on an operator. It eliminates measurement variation between operators, and the potential for data-entry errors. Statistical Process Control (SPC) techniques can be used to update offsets to prevent the effects of tampering. The probe system is not used to directly inspect parts. It keeps the process inside Document # MWA-015-EN_06_ Page 8 of 12

9 statistical control limits so that it cannot make a bad part. This minimized scrap and improves part yield significantly and is the preferred strategy in today s just-in-time, low-volume or high workpiece cost manufacturing operations. Some part quality issues are created by setup errors between multiple machine operations. Manufacturers are increasingly investing in hybrid machines to complete all machining operations in a single setup. This may take the form of lathes with a C-axis and live tools or a Y- axis to perform milling operations on turned parts. More advanced, multi-axis, multi-path hybrid machines may have completely independent turning and milling axis and multiple turrets and/or cutting heads allowing multiple operations to be performed simultaneously. Sub-spindles for lathes and 4 th and 5 th axes for machining centers allow a part to be machined on all surfaces in a single setup. By focusing on the process capability of a machine rather than inspecting the final part, fewer measurements need to be taken to ensure part quality, and the automation allows the process to run unmanned through breaks and entire shifts as required. Any excess precision can often be traded for increased processing speed at an acceptable accuracy, reducing per part costs. 2.5 Lowest downtime costs Downtime costs have two primary dimensions. Mean Time Between Failures (MTBF) measures how often an equipment failures occur. Machine crashes due to setup errors is also a source of downtime. Mean Time to Repair (MTTR) measures how quickly equipment can get back into production. Considering that the most costly aspect of machine downtime is the lost production and its impact on customer satisfaction, both factors are equaly important. Only the largest machining operations can afford dedicated CNC service engineers, so over the phone technical support and highly skilled local technical resources also ensures the cost of machine downtime in minimized. Parts and labor warranties and parts availability also impact the direct cost of downtime over the lifetime of assets. The reliability of the most popular CNC control has reached an astonishing 52-year MTBF. That means you can go decades without a failure or a need to repair the CNC hardware. This is achieved with a relentless dedication to continuous improvement and attention to even the smallest detail. Unfortunately, this is not typical and it may be difficult to get a published figure from most CNC manufacturers. Machine crashes can occur for a variety of reasons. For example, machining processes often rely on the fact that a prior process was completed like when a tapping tool relies on the fact that a hole has been previously drilled. If the operator forgets to put the correct drill in the correct pocket in the tool changer, or sets the wrong offset or offset value, or the drill simply breaks during machining a severe crash can occur. Laser probes integrated with the CNC can visually check for missing or broken tools at highspeed. The Unexpected Disturbance Control feature monitors the torque generated by the axis drives and trips if it goes above a programmable threshold. Shock sensors mounted on the machine can also stop and retract axes when a collision is detected. Safe zones can also be establish around machine and workholding components. FANUC HMIs Document # MWA-015-EN_06_ Page 9 of 12

10 Unintentional mistakes can be reduced by requiring operators to confirm things such as deleting part programs and starting programs in the middle. Limits can be placed on the tool wear and workpiece offset values entered to prevent machine crashes due to simple data entry errors. These error proofing features can minimize the damage to machines when a mistake occurs. A snapshot of any screen can be saved to a memory card to assist in troubleshooting or to document lessons learned to prevent future problems. Diagnostic tools are essential to troubleshoot and recover quickly when a problem occurs. Diagnostics pages provide a single, convenient location to monitor the status of the CNC, servo and spindle systems. The ladder and I/O status pages show the real-time condition of the CNCto-machine interface. Operational and message history capture the events that proceeded a control or machine problem. Advances in CNC communication and mobile device technologies and their associated software applications now make it possible to alert operators and maintenance personnel to a wide range of process variances and downtime failures. Notification of symptoms can be sent before a real problem even occurs, allowing predictive and preventative actions to be taken. Features such as tool management, tool life monitoring and tool breakage detection can be combined to apply preventative and automatic recovery strategies. Most new CNCs will have an Ethernet port and the most capable provide tools to remotely diagnose problems, allowing maintenance and industrial engineers to solve more problems over the phone, or at least arrive on site with appropriate tools and replacement parts. Maintenance training empowers operators and maintenance engineers to use the available diagnostic tools to quickly troubleshoot CNC and machine tool problems. Understanding the basic components of the CNC and machine tool interface, and how they work together, makes locating problems more efficient. Document # MWA-015-EN_06_ Page 10 of 12

11 One of the most complicated and costly problem to repair on a CNC occurs when critical files are lost, and there is no current backup. Files may be lost or corrupted due to an electrical component failure, a lightning strike, a flood, or some other unexpected event. If these files are not backed-up, it could take a week or more to get the machine back into production. Some controls incorporate automatic backup of files to flash memory within the CNC. A quick backup into flash memory is also useful whenever the CNC parameters or servo tuning are changed, so you can quickly revert to a known good state if the changes made do not produce the expected results. Automated backup across an Ethernet network is also possible. Replacement part availability also impacts long term costs. If parts are not available to fix a CNC, a total retrofit may be required to get a machine back into production. The leading CNC manufacturer provides a commitment to support a CNC as long as a machine is in production. Replacement parts are made available as long as the original or equivalent substitute components are available to manufacture or repair the CNC. If the components are not available a replacement part may be engineered with the same functionality, form and fit. Clearly the lowest downtime costs are achieved by minimizing downtime as it also eliminates the Mean Time to Repair (MTTR). The costs of a failure are minimized by long warranties, expert over the phone technical support, comprehensive diagnostic tools and the availability of internal or external engineers. 2.6 Higher resale value The resale value of a used machine tool has many practical factors including its application, age, condition and the number of similar machines available. However, a premium resale price will always be possible for machine tools from leading machine tool builders and that are equipped with a world-class CNC. The value of a CNC is established through prior experience or reputation and often considers the total cost of ownership, including running cost, performance, part quality and reliability. 3 Summary When purchasing a machine tool it is easy to get too focused on just the acquisition cost of the equipment and forget that a poor choice may mean significant additional costs over the lifetime of the asset. Whether you are purchasing a machine for all of its useful life or just for a specific contract period, it is insightful to consider the total cost of ownership over that time period including the acquisition cost, running costs, performance, part quality, downtime costs and resale value. FANUC HMIs Document # MWA-015-EN_06_ Page 11 of 12

12 1800 Lakewood Boulevard Hoffman Estates, IL FANUC-US ( ) Find more information at Technical data is subject to change without prior notice. No part of this document may be reproduced in any form. All rights reserved Document # MWA-015-EN_06_1507