Comparison Between CNC and Conventional-Manual Machines

Manufacturing equipment and processes are constantly in a state of change. The marketplace is driving the need for new technology, that increases precision, efficiency, and productivity. Of all the technological developments that have impacted manufacturing in the last 40 years, the introduction of CNC machines have revolutionized the face of machining and manufacturing. CNC machines have almost completely replaced conventional-manual machines, especially for production purposes. Conventual-manual machines still have their place in the manufacturing world, but its role has been greatly reduced, primarily to training, prototype and maintenance. Being able to draw a comparison between CNC and conventional-manual machines and identify why or how this transition happened can be helpful for having a more complete understanding of the dynamics that  drive manufacturing needs and trends.

Precision and Accuracy

Both CNC and conventional-manual machines rely on the design and stability of the machine beds and slide assembly (depending on lathe or mill) for achieving precision. CNC machines are equipped with servo motors with electronic encoders, that drive the axis movements. The movement of the axes is directed to the motors and encoders by a machine controller. It has the ability to move and monitor the axes to exacting positions. In addition to the axes movement, the feeds and speeds are also  sent to a machine controller, via CNC programs which generate machine code. The machine code commands and feedback system are measured in milliseconds. The machine movements are fast and accurate. The machine stability and control software ensure precision and repeatability. CNC machines can produce parts within an extremely tight tolerance range. There is application for CNC machines in all sorts of markets (aerospace, medical, automotive, etc.).

Conventional-manual machines, in comparison  are operated and controlled manually by the operator. All axes movement, feeds and speeds are dependent on the operator. This type of equipment was used until the advent of CNC. Tight tolerances and accuracies could be  achieved, but primarily this is determined by the skill level of the machine operator. Replicating the same level of accuracy is difficult to maintain. You are at the mercy of the operator, and human error was an issue.  Conventional-manual equipment is still used today, but usually not a production piece of equipment. They are used primarily for maintenance, training, and proto-type.

Automation and Productivity

Most CNC machines manufactured today are designed to be adapted for some level of automation.  Adding automation is usually a function production batch or lot sizes. The larger the production lot, the more attractive automation becomes. One of the attractions of automation and adapting it to CNC machines is it enables machines to run over a prolonged period of time, with a minimum amount of operator intervention. Depending on cutting tool life and the number of available redundant tools, you can run virtually unattended. The CNC controller can not only run and monitor machining programs, it can also monitor tool  wear, and manage part counts. With the right materials and lot sizes, it can be a very efficient way to machine parts.

Traditional-manual machines are not suited for most levels of automation. They require a high degree of operator intervention. Each tasks has to be set up and ran, then torn down to accommodate the next operation. Setups can be time consuming. Raw material have to be introduced to the machine manually.  It does not lend itself to efficient automation.

Flexibility and Versatility

Another advantage of CNC machines is their flexibility. In today’s manufacturing many of the machined parts have complex shapes that require a high degree of precision. Programming  toolpath for these shapes can be generated offline using CAD (computer aid design) and CAM (computer aid machining). In many instances design updates can be modified within the computer program; hence, making small-batch runs viable.

Conventional-manual machines, while capable of performing complex machining  are limited by the level of competence of the operator. Complex  work requires a high operator skill level. Machining complicated parts requires can be very time consuming and part repeatability is subject to operator error. In addition, design changes on conventional-manual machines may involve significant re-configuration of the tooling, which further diminishes flexibility.

Skill Requirements

CNC machines, in contrast to conventional machines, require different skill sets. CNC machine operators need to have some degree of  software programming  and machine language understanding (G & M codes). Basic machining knowledge is always helpful, but not indispensable.

Conventional-manual machines are very much dependent on operator skills. Successful operators have a deep understanding of machining skills, including tooling knowledge, and machining techniques. The level of quality and repeatability of the machined parts are totally dependent on the operator.

Cost and Investment

The initial investment in a CNC machine is large as compared to conventional-manual equipment. CNC machines also require some level of offline software system, to support program generation. The overall initial costs need to be evaluated against increases in productivity (accuracy, repeatability, part complexity, availability and access to qualified labor.

Conventional-manual machines have a lower initial capital investment. They can be very cost-effective for simple prototype work and are useful for training of basic machining skills. However productivity for production work is miniscule compared with CNC machines.

Conclusion

Comparison of CNC machines versus conventual-manual machines  present-day is more of an “apples vs. oranges” comparison. Both types have their place in the manufacturing world. At one time as  CNC machines were being developed and coming into the machining marketplace, the comparison was more direct , but as CNC technology and supporting software has expanded, the market sees the growing application and flexibility of CNC machines and the limitations of the conventual-manual machines. The market for CNC is growing. The conventional-manual market is shrinking. This trend will continue.

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