Direct Numerical Control (DNC): Definition, Functionality, and Key Types

What is Direct Numerical Control?

Direct numerical control (DNC), also known as distributed numerical control (also DNC), is a common manufacturing term for networking CNC machine tools. On some CNC machine controllers, the available memory is too small to contain the machining program (for example machining complex surfaces), so in this case, the program is stored in a separate computer and sent directly to the machine, one block at a time.

If the computer is connected to a number of machines, it can distribute programs to different machines as required. Usually, the manufacturer of the control provides suitable DNC software. However, if this provision is not possible, some software companies provide DNC applications that fulfill the purpose.

DNC networking or DNC communication is always required when CAM programs are to run on some CNC machine control.

Wireless DNC is also used in place of hard-wired versions. Controls of this type are very widely used in industries with significant sheet metal fabrication, such as the automotive, appliance, and aerospace industries.

Understanding the DNC machining

Direct Numerical Control (DNC) is a process set in a manufacturing unit where a set of machines is controlled by a programmed computer with the help of a direct connection to the same.

Set of machines mentioned above use computer numerical control (CNC). It is based on real-time data and involves data collection from the machines and passing the same to the mainframe, at regular intervals. The operator will be in control of the mainframe computer through remote access.

A DNC will not contain a tape reader. Instead, it has several part programs that are transferred to the machines from the computer memory.

In a few scenarios, the machine controllers will not be able to store the entire program because of the lack of memory space. In such situations, the program is stored in a different computer and the directions are sent directly to the machines from that location.

The DNC is designed in such a way that it provides separate instructions to every machine on the system. In case, where the machine immediately controls the command, they are sent across immediately.

Functions of Direct Numerical Control (DNC) system

• The central computer is used to store and edit the programs for all machine tools connected to it
• On requirement, basis gives the stored program to the connected machines
• Having a common database, it combines CAD with CAM
• Provides a link between the central computer and plant computers connected through network even though plant computers are very far

Types of DNC system

Following are the main two types of DNC system:

• Behind the Tape Reader (BTR) system
• Specialized MCU

1. Behind the Tape Reader (BTR) System

In this type of system, the computer is connected directly to the regular NC controller unit. The operation of the system is similar to conventional NC, except for the source of command instructions.

The controller unit employs two temporary storage buffers to get the blocks of instructions from the DNC computer and turn them into machine operations. The one buffer is getting a block of data, the other is providing control instructions to the specific machine tool. This system cost is very low.

2. Specialized MCU

In a specialized MCU system, replace the normal controller unit with the special machine control unit. The special control unit is created to help communication between machine tools and computers. The specialized MCU configuration achieves a better balance between the accuracy of interpolation and the faster removal rate of the metal than is usually possible with the BTR system.

Advantages of DNC

• Direct numerical control avoids the usage of punched taps and the reader from the system.
• It helps the business to understand production performance by getting several reports and useful data from the machines.
• It helps in building a centralized control for the machines.
• Useful for time management and increased productivity.
• Convenient storage of part programs in several computer files.
• Helps the company to make higher-level decision
• It helps the business to increase computational ability
• It supports management information system effectively

Disadvantages of DNC

• DNC is very expensive and it requires high automated areas
• Because of its central control system, if the computer fails then all the activities of machines would be stopped

Differences between Direct Numerical Control and Computer Numerical Control

• DNC means direct numerical control; CNC means computer numerical control.
• In CNC working operations cannot be controlled remotely. But in DNC we can control working operations with remote.
• CNC transfers machine instructions. DNC controls the information and manages the information distribution to more verities of computers.
• CNC machine controls only one NC machine, whereas by using a DNC programmer you can control more than one NC machine as per the requirements.
• DNC systems can be placed at a distance from machines. Because it not an integral part of machines. But CNC is an integral part of machines.
• CNC system has low processing power, DNC system has high processing power.
• DNC did not remove the tape, while CNC is a feedback system.
• The maintenance cost of the DNC machine is low but the maintenance cost of the CNC system is high.
• CNC system amplifies the capacity of the particular computing machine tool. DNC system controls the equipment and also acts as a management information system.