Machine maintenance

Let’s face it: Everything about machine tools and their operation is expensive. If you run your own shop, then you know how much a good machining center or turning center can cost. If you ever have worked for a large company and tried to get capital for a new machine, then you know how many hoops must be jumped through to get the money. Machine tools are not only expensive to acquire but expensive to maintain, and when they go down the results can be catastrophic to budgets and customer relations.

Every minute of downtime costs a shop money, and those lost minutes and dollars never can be recovered. For machinists, engineers and maintenance personnel, excessive downtime creates a stressful work environment and unwanted overtime and generally makes for a less-than-desirable workplace. Preventing unplanned downtime is critical to successful machining operations.

Preventing unplanned downtime can be difficult in the best of times, but the shortage of skilled craftspeople and the increasing complexity of modern machine tools have added an extra layer of difficulty. However, some simple things can be done to help stave off downtime and expensive repairs.

Machines are designed, built and marketed differently based on the work they are expected to perform. High-volume manufacturers like automotive companies often require very robust, heavily built machines whereas smaller shops frequently can suffice with less robust machines. Understanding the capabilities of machine tools is important when preparing the code and tooling for machines.

When I started machining, there was a heavy focus on horsepower, torque and rigidity of guide ways. CNC machines were being purchased in an attempt to automate machining processes, so engineers and machinists were transitioning traditional machining methods to CNC machines. This meant that CNC machines of the time were expected to take heavy cuts in the interest of productivity. Since early CNC machines were controlled versions of old manual
machine designs, this was not an issue.

As the market evolved, machine builders started marketing to smaller shops and lighter, more cost-effective designs appeared on the market, requiring a different approach to programming. Ensuring the longevity of machines requires programmers to adapt to the capabilities of a machine tool and prepare code that does not overburden the machine. Generating toolpaths and cutting parameters that are within the capabilities of a machine prevents premature wear and tear of critical components. Seeing that cutting parameters, such as depth of cut, rotational speed (rpm) and feed rate, are appropriate for a machine is paramount in maintaining a properly functioning machine.

Unintended misuse and abuse of machine tools at the hands of well-meaning craftspeople can significantly shorten the life expectancy of critical components. Ensuring that machine tool operators and machinists have been trained well goes a long way toward extending machine life.

Learning proper setup techniques helps prevent crashes that put undue wear and tear on spindles, servos and guide ways. Correct assembling of toolholders and cutting tools extends the life of spindles and turrets. Learning the right way to load tools into automatic toolchangers assists with eliminating toolchanger crashes. Even the most advanced machines that operate autonomously need trained personnel to keep them operating properly. Also, don’t assume that someone with experience listed on a resume knows what to do. Everyone needs to be trained to operate machines in accordance with the best practices of a company.

Large manufacturers with deep pockets and bountiful resources often implement total productive maintenance. TPM uses data and analytics, combined with the machine builder’s recommendations, to create a detailed maintenance routine focused on preventing unplanned downtime. The foundation of TPM is preventive maintenance practices that go beyond ordinary activities like fluid changes. TPM programs include replacement of major components, such as spindles when their known life spans have expired. Planning and scheduling maintenance of critical machine tools prevents disruptions to production schedules and product delivery. TPM works for big companies because unplanned downtime is far more costly than maintenance.

Although TPM is a highly effective practice, small and medium-size shops usually don’t have the resources to implement robust TPM programs. However, smaller shops can do several things to emulate TPM and promote longevity of critical components.

Just like cars, machine tools need to have fluids and filters replaced at proper intervals. Clean fluids and filters prevent premature wear and blockages of small lines and orifices. Modern machines monitor lubrication systems and will notify users when levels are low or pressures are insufficient. Unfortunately, blocked lubrication lines can go undetected in the most sophisticated machines, ultimately starving them of lubrication in critical areas.

All good machinists understand the importance of wiping down the table of a mill or cleaning the lathe chuck. Wiping chips and dirt from the toolchanger, cleaning the spindle and keeping toolholders clean are just as important. Cleaning the electrical cabinet and changing the fan filters prevent contamination of electrical components. Clearing up the outside of electric motors improves cooling airflow, which reduces operating temperatures, thereby increasing life. Keeping the toolchanger free of chips and grime prevents malfunctions and increases reliability.

Cleaning and fluid maintenance promote longevity and increase life, but they cannot stave off the inevitable. Mechanical components wear out even with the best maintenance, which is why companies implement TPM. They want to replace worn components before failure. Monitoring major components for signs of wear and degradation is not difficult and doesn’t consume large amounts of time. Small companies can do some things, such as checking runout and backlash, to better predict failure, which can help plan for repair expenses.

Checking spindle runout can be done with basic shop tools. Check the spindle at regular intervals, and log the runout. The runout data will show bearing wear over time and allow a shop to budget for repairs.

As ballscrews and couplings wear, a machine will begin to exhibit backlash. This is detected most often when the machine no longer can hold tolerances, which is usually at an inconvenient time. When a spindle is checked, it is a good idea to check the various axes for backlash. Most machine tool manuals have instructions for checking and correcting backlash. Logging and monitoring allow a shop to anticipate an oncoming failure so the work can be planned for a time that doesn’t interrupt production and deliveries.

Of course, there are other inspections and monitoring that a shop can perform to ensure longevity and prevent unplanned downtime. Machine builders, much like automakers, have routine maintenance plans for machines. Following the builder’s recommended maintenance schedule is the best place to start. Also, builders often provide a recommended parts list for inventory. Although a small shop may not be able to keep a complete list of spares, the list can be used as a predictor for components that are likely to go bad.

Maintenance and monitoring are no guarantee that a machine will not break down. However, a strong maintenance regime increases the life of components, and monitoring critical aspects will alert users of impending failures.