Problems Associated with the Conventional NC Machines, Advantages of the CNC Machines

Though the NC machines worked automatically as per the program fed in the punched tape and though they increased the productivity, a number of problems were associated with them. These problems posed a major obstacle in the further development of the NC machines. With the introduction of the computers in the NC machines their further developments were enabled and these automatic machines came to be popularly known as the CNC (computer numerical control) machines.

Here are some of the problems associated with the conventional NC machines:

1) Mistakes related with part programming (programming for the parts to be manufactured): When the programs of instructions related to the particular part to be manufactured are written on the punched tape, the syntax or numerical mistakes are quite common. The NC tape is not completed correctly in a single pass and at least three passes are required to get the correct program written. Another major problem with the part programming is achieving the best sequence of steps required for the machining the part.

2) Nonoptimal speed and feeds: For most economic manufacturing of the object from the raw material it should be given optimum speed and feeds during manufacturing. The conventional numerical control does not provide opportunity to change the speeds and feeds during the cutting operations, so the programmer is compelled to set the speeds and feeds for the worst-case conditions that can result in highly expensive manufacturing due to wastages, and low quality jobs. This also results in manufacturing of the jobs at lower than optimum productivity.

3) Punched tape: The punched, which is made up of paper and on which the program is written is the problem in itself. This tape is fragile and susceptible to wear and tear so it has short life and cannot be reliable enough for the repeated use. Instead of paper, other media like Mylar can be used for writing the program of instructions, but these materials are quite expensive.

4) Unreliable tape reader: The tape reader reads the program of instructions from the punched tape, but it is considered to be highly unreliable hardware component of the NC machine. When the NC machine breaks down the first thing the maintenance personnel checks is the tape reader.

5) The inflexible controller: The conventional NC machine has the controller unit which is hard wired and the making the changes in the controls of the machines is a tough task. The controller used in the CNC machines is the computer, which is highly flexible.

6) Important information: The conventional NC machine cannot provide crucial information to the operator and the supervisor like the number of pieces manufactured, tools changes and others.

The problems associated with the NC machines have been solved over the time with the improvement in the NC technology mostly due to advancement in the electronics. The major change obviously came when mini or microcomputers were introduced in the NC system. The computers have had major impact on the NC system and with their introduction the whole technology has come to be known as the CNC (computer numerical control) technology. For the common man and also to the engineers the automatic machine tools are now known by the name CNC machines and not the NC machines.