The productive life cycle of any machine tool is limited. Be it a lathe, mill or grinder, a machine’s accuracy and reliability eventually will deteriorate. How long that takes depends on the machine’s basic structure; how often and hard it is used; and how it is maintained. Shops that carefully track machine utilisation find that downtime of 20% or more of available machine time – due to unanticipated stoppages, adjustment & maintenance – generally represents an unacceptable burden on scheduling, maintenance operations and profitability.
Two key options available to recover grinding production capacity include rebuilding the machine and retrofitting it with selected upgraded technology. Shops can also repurpose existing grinders for work different than their original intent, or replace them with brand new grinders.
Rebuilding or overhauling a grinding machine involves disassembling it entirely and examining every mechanical, electrical, pneumatic and hydraulic system. Components are replaced or repaired where necessary and re-qualified to OEM standards. Every bolt, nut, rivet, hose and pipe gets the same treatment. Newer technologies such as monitoring devices may be added. Other updates can include items such as LED lighting and controls.
Except for its basic structure, which is abrasive blasted and repainted, the reassembled machine is essentially brand new. A full rebuild costs about 75% as much as a new machine. The typical rebuild cycle might be 15 years; longer if the machine is lightly used and well maintained. But that span is much shorter if the machine runs three shifts a day, every day, with minimal maintenance. Large, specialised grinding machines such as those used in critical aerospace applications are prime candidates for renewal via a comprehensive overhaul.
Depending on a machine’s overall condition and how it has been used, a possible approach is a partial rebuild that retrofits a machine with newer technology. If a machine’s electrical systems and control are in top shape but the machine has been worked very hard and/or received minimal maintenance, only the mechanical systems may need to be overhauled. This involves a replacement of mechanical elements that are worn out or damaged beyond repair.
On the other hand, a machine’s mechanical systems may be in excellent condition, with inspections confirming that axes and accuracy match OEM standards. In that case, an electrical overhaul including replacement of the electrical cabinet, all wiring and the servomotors may be appropriate. The mechanics of the machine and the original enclosure would remain.
If a machine’s CNC unit is outdated, a new control will increase operational speed, productivity and convenience. An important consideration is the life cycle of the control itself. Control makers such as Fanuc and Siemens typically introduce new control technology about every ten years. So when needing a new control, it may be advantageous to look for a replacement control that is in the early phase of its cycle to benefit from the longer planned lifespan and control maker’s support.
A key element of control technology is the human-machine interface, or HMI. A control with a state-of-the-art HMI will incorporate an interactive, question-and-answer procedure that enables an operator who is far from an expert in programming to create productive grinding programs by simply answering questions and entering relevant part, wheel and machine data.
Some machines may work well overall but possess outdated subsystems. Many elements of machine technology have changed significantly over the last 15 to 20 years. The feedback systems that locate machine axes are good examples.
Machines with older motion encoders that do not feature glass scales must execute a multi-minute homing process to establish the positions of the machine axes each time the machine is turned on. The absolute encoders in glass scale systems, on the other hand, store the position of axes when the machine is shut off or if power fails. This eliminates the need for a homing routine when the machine powers back on. The new encoders also offer resolution 100 times higher than previous measurement methods. Servomotors have improved over recent decades as well, and are perhaps 50 times more accurate than earlier machine motion technology.
If a machine has not been updated in 15 to 20 years, adding new and upgraded technologies can extend the next rebuild cycle. For example, retrofitting a ball screw lubricating system that was unavailable on the machine twenty years ago will enable the ball screws to last significantly longer. If the machine’s ongoing workload remains unchanged, the time between rebuilds lengthens significantly.
In general, approximately 60% of overhauled machines return to their facilities to handle basically the s me operations and workload they did prior. The remaining machines undergo additional changes intended to repurpose them for upgraded or different tasks. The percentage of machines being repurposed will continue to grow as the industry continues to move away from long-term contracts for large volumes of identical parts to more flexible and dynamic manufacturing scenarios of rapidly changing part types and volumes.
Repurposing a grinding machine typically involves adding features that will enable it to carry out more complex and productive grinding or to work with ancillary systems such as automation. A machine originally built in an open configuration may require the design, fabrication and addition of an enclosure to permit use of high-pressure coolant and advanced technology grinding wheels. Another machine might be repurposed to employ robotic automation by fitting automatic doors with opening/closing drives and laser-based safety systems.
A machine without the capability for rotary dressing can be fitted with a rotary dresser and related drives and controls. True reverse engineering is rarely needed, but adding new systems can require re-engineering of hydraulic or pneumatic systems and design and fabrication of new sheet metal components.
An obvious alternative to a worn and unreliable grinder is replacing it with a new machine. In many cases, however, the choice between rebuilding and replacing is not so obvious.
Cost considerations play a key role in the decision to rebuild or buy new. The 25% savings of a rebuild compared with the price of a new machine is much less significant when applied to the price of a new, basic 3-axis production grinder than it is relative to the purchase of a multi-million dollar machine engineered for specialised work. A perfect example of such systems is those that grind aerospace blades and vanes.
Lead times are another important factor. The lead time for a new machine’s basic welded or cast iron structure alone can be four to six months, depending on the size of the machine. Adding those months to the time required to construct the rest of the machine results in an eight to fourteen month or longer total lead time — dependent again on the machine’s size, type and brand.
The lead time for a rebuild may be only half that of a new machine because the rebuild utilises the machine’s existing structure. But even that shorter delay can disrupt production excessively. For example, a busy shop with five 3-axis grinders that all perform similar operations will lose significant capacity during the months while a machine is off the floor for a rebuild. Buying a new grinder enables the shop to use the old machine to grind parts without interruption until the replacement is ready to install.
Corporate budgeting policies may be a final determining factor in the choice to rebuild or replace a grinding machine. Restrictions on capital spending can make an overhaul, which usually is considered a maintenance expense, the only way to reclaim the production capacity of a worn machine. On the other hand, some companies’ capital spending strategies and allocations promote purchase of new machines. Depreciation, incentives and other tax-related issues can vary in relation to the age of a machine.
Advanced grinding machines from United Grinding are engineered and manufactured to provide many years of trouble-free, accurate and profitable service. Ongoing maintenance, per manufacturer’s recommendations, will further extend service life. And when a machine moves toward the end of its initial life cycle, users have a range of options regarding the best path to continued productivity. ☐Courtesy: United Grinding