CNC Maintenance Training

Most of today's major machine tool builders in conjunction with the CNC supplier offer a wide variety of end-user training on CNC machines. Some of the training is informal, some formal covering a wide variety of technologies such as: programming, machine maintenance, operation, servo drive maintenance, and CNC maintenance. Each of these categories of training plays an important role in the successful installation of a new machine and each imposes a different set of discipline on instructors and students. The following focuses on just one of these categories of training CNC maintenance.

The training methods used in CNC maintenance classes have changed significantly from the class conducted in the early years of NC largely due to the developments of new diagnostic tools in the controls. During the early years of hardwired NC, built-in diagnostic tools were almost non-existent and consequently maintenance training was based on teaching the theory of operation. In fact, control builders provided either a "Theory of operation" manual or a very thick chapter in their maintenance manual on "theory." This philosophy was greatly influenced by the fact that the first instructors as well as the first manual writers were often the engineers who participated in the design of the control since formal training departments as we know them today, had not yet evolved.

Today's CNCs have a high level of built-in diagnostic features and as such the maintenance training classes over the years have gradually been restructured to reflect their use. The amount of theory now taught in the classroom has been scaled down to just enough to provide the student with an overall understanding of the control's operation. Consequently a significant amount of the training time is devoted to understanding and using the diagnostic tools provided in the control. The emphasis has changed from "how it works" to "how to fix it."

Basic CNC maintenance courses offered by almost all control builders today last approximately one week, four and one half days on the average, with many offering in-depth or extended courses lasting two weeks or more. Classes are normally held at the control builders plant where adequate facilities and equipment for hands on experience are available, but a certain percentage of users request that the control builder bring the class to their facility. One control builder for example indicates that forty percent of their training (based on number of students trained) is done at the user's plant. The advantage of on-site training is obvious in that the user can send more employees since there are no travel expenses. The disadvantage is often inadequate training facilities and equipment for lab training. In addition the students are subject to being called out of the class to perform a routine maintenance job, breaking the continuity of the class.

Instructors all agree that adequate lab time with hands on experience is important for a successful CNC maintenance class. Even though instructors would like to see a ratio of one student per control for lab exercises, this is seldom possible. Generally instructors target the CNC maintenance classes for eight students with enough equipment to allow two students per control. Instructors all seem to agree that a class size of 12 with three students per control are numbers that should not be exceeded.

The practice of control builders differs when it comes to testing students. Some control builders require students take written exams, others do not. Cincinnati Milacron is one company that requires student testing and issues certification only when a student meets the requirements. The instructors evaluation of the student is based on both classroom work and lab exercises. The results are sent to the students supervisor since it is felt that companies are entitled to this information so they can properly assess their maintenance resources. But, "what is good for the student is good for the instructor." The student gets a chance to evaluate the instructor by filling out an evaluation form which is reviewed by the instructor's manager. This permits the training manager to assess the effectiveness of the training programs.

In the early years of CNC the most important prerequisite for a good control technician was a sound electronic background. Today a good understanding of electronics is still important but the ability to understand the control from a system standpoint (interrelationship of hardware and software) may have replaced electronic background as the most important factor. With today's diagnostic tools, faults are diagnosed to the module level. The service technicians today replace an entire plug in module rather than replacing individual components within a module. This has led to less emphasis being placed on the function of each electronic component and more on the control as a system.

One problem faced by all training departments is how to get a beginner student up the learning curve so that he does not slow down the class with elementary questions or even worse, not ask questions and stay confused. General Numeric addresses this problem by providing a book on request to students titled "Introduction to NC." Other companies have recommended levels of expertise and experience that a student should be at before they attend a specific class and recommend courses or books for achieving those levels.