NC Machine Tools Overview

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Questions and Answers

What is the primary disadvantage of hydraulic systems mentioned?

Lower speed

Higher cost (correct)

Limited precision

Increased complexity

Which type of NC system is characterized by machining at specific positions?

Contour system

Straight line system

Point-to-point system (correct)

Continuous motion system

In which system does the tool move at a controlled feed rate in one axis direction at a time?

Open loop system

Straight line system (correct)

Contour system

Point-to-point system

Which power source is known for its precision and common usage in NC machines?

Electro-mechanical drives Signup and view all the answers

What equipment is commonly required for hydraulic power systems?

Reservoir Signup and view all the answers

Which type of NC machine system depends on constant feedback?

Closed loop system Signup and view all the answers

Which option best describes a contour system?

Simultaneous movement along multiple axes Signup and view all the answers

What is the primary function of adaptive control in machining processes?

To adjust feeds and speeds based on torque and forces Signup and view all the answers

Which component is NOT typically part of the control system of a numerically controlled machine?

Dimensional Transducer Signup and view all the answers

What is a key characteristic of closed loop systems compared to open loop systems?

Closed loop systems rely on sensors for process adjustments Signup and view all the answers

What is the main purpose of measuring dimensional accuracy in machining processes?

To allow for accurate compensation of tool wear Signup and view all the answers

Which type of NC machine path motion is appropriate for continuous machining processes?

Continuous path motion Signup and view all the answers

What capability does SPLIT possess in terms of positioning?

5-axis positioning Signup and view all the answers

In the absolute system, how are the coordinates expressed?

Relative to a reference point Signup and view all the answers

What is a primary application of NC machines?

Creating parts with complex designs Signup and view all the answers

Which of the following is NOT an advantage of using NC machines?

Higher production costs per piece Signup and view all the answers

What coordinates do points A and B represent in the incremental system for the mentioned example?

A(5,5) and B(5,10) Signup and view all the answers

Why are NC machines beneficial for parts frequently subjected to design changes?

They can accommodate quick adjustments Signup and view all the answers

Which feature regarding production does not apply to NC machines?

Inconsistent machining speeds Signup and view all the answers

What is a characteristic of the incremental system?

Coordinates are based on the last specified point Signup and view all the answers

What is a disadvantage of using NC machines?

Higher upfront costs for machines Signup and view all the answers

What advantage does computer-aided manufacturing (CAM) offer over conventional NC systems?

Increased flexibility in part manufacturing Signup and view all the answers

Which feature allows for easier troubleshooting in CNC systems compared to conventional systems?

Micro-processors with self-diagnostic features Signup and view all the answers

What is a significant disadvantage of DNC systems as mentioned in the content?

Increased cost and need for skilled software knowledge Signup and view all the answers

How does CNC compare in terms of program management to conventional NC systems?

Programs can be easily called and managed in CNC systems Signup and view all the answers

What does the term 'CAD/CAM software' refer to in the context of NC machine tools?

Programs generated directly from CAD files for machine tools Signup and view all the answers

What additional capability can be integrated with DNC systems for improved control?

Process management and control Signup and view all the answers

Which of the following is NOT an advantage of CNC systems?

Mandatory use of hard-wired connections Signup and view all the answers

Which type of computer is typically used in a DNC system?

Dedicated computers with large memory Signup and view all the answers

What advantage does CNC offer in terms of editing programs compared to conventional NC systems?

Simpler editing and debugging Signup and view all the answers

Which aspect of CNC technology contributes to its greater accuracy over conventional methods?

Advanced computer programming capabilities Signup and view all the answers

What is a significant benefit of using a machining centre?

It reduces work handling time by allowing multiple operations in one setup. Signup and view all the answers

How does the configuration of two work-tables benefit the machining process?

It allows one table to operate while the other is being set up, minimizing downtime. Signup and view all the answers

What role does the tool magazine serve in a machining centre?

It holds preset tools that can be automatically changed during operations. Signup and view all the answers

What is the primary use of machining centres?

They are primarily designed for batch production of small, expensive components. Signup and view all the answers

What aspect of machining centres contributes to their high versatility?

High metal removal rates and the ability to perform multiple operations. Signup and view all the answers

What is the purpose of adaptive control in machining?

To continuously measure variables and adjust them within programmed limits for better accuracy. Signup and view all the answers

Which feature enhances productivity in a machining centre?

High degrees of accuracy coupled with a single operation setup. Signup and view all the answers

What is a key characteristic of components produced in machining centres?

They often require high levels of machining and are expensive. Signup and view all the answers

How do machining centres affect the overall production process?

They simplify setups and improve the speed of production. Signup and view all the answers

What happens to the tool after a machining operation in a machining centre?

It is returned to its storage slot and replaced with another tool. Signup and view all the answers

What is the primary difference between NC and CNC machines?

CNC machines can process more complex paths than NC machines. Signup and view all the answers

In the context of NC systems, what does retro-fitting refer to?

The integration of advanced CNC technology into existing conventional machinery. Signup and view all the answers

Which type of control system is characterized by the ability to produce a smooth and flat surface finish?

Electro-mechanical drive systems known for precise position control. Signup and view all the answers

What is a notable drawback of hydraulic control systems in NC machines?

They require extensive maintenance due to fluid leaks. Signup and view all the answers

What role do PLCs play in modern NC systems?

They provide automation and control for complex manufacturing processes. Signup and view all the answers

What is a significant advantage of a closed loop system over an open loop system?

Higher precision in operations Signup and view all the answers

Which component is essential for providing feedback in a closed loop system?

Position feedback transducer Signup and view all the answers

What type of device provides velocity feedback in a closed loop system to ensure proper cutter path?

Tacho-generator Signup and view all the answers

Which of the following is NOT true about closed loop systems?

They are generally less expensive than open loop systems. Signup and view all the answers

Why might a closed loop system be considered more complex than an open loop system?

It integrates a variety of additional components. Signup and view all the answers

What is a primary role of the control unit in a closed loop system?

Generating command signals Signup and view all the answers

In what aspect do servomotors in closed loop systems significantly differ from those in open loop systems?

They provide a steady, non-incremental motion. Signup and view all the answers

Which programming language was the first to be used for NC machine tools?

APT Signup and view all the answers

What is the primary role of the post-processor programme in the computer programming process?

To convert output into a useable form for machine tools Signup and view all the answers

Which language was designed for the simultaneous servicing of multiple users from a remote computer?

COMPACT Signup and view all the answers

What distinguishes UNIAPT from the original APT language?

It has a different internal design of the processor. Signup and view all the answers

Which version of EXAPT is specifically tailored for milling operations?

EXAPT 3 Signup and view all the answers

When magnetic tape output is generated, what is the next step before being used in machine tool control?

Converting the output into punched tape Signup and view all the answers

What does the APT Long Range Program (ALRP) signify in the evolution of NC programming?

The change to Computer-Aided Manufacturing-I Signup and view all the answers

Which programming language was developed specifically for three axes point-to-point motion control?

AUTOSPOT Signup and view all the answers

What is a key characteristic of the programming features found in EXAPT?

It is technologically and geometrically oriented. Signup and view all the answers

What is primarily hindered by the lack of online measurement of dimensional attributes in NC machines?

Compensation for tool wear Signup and view all the answers

Which variable is NOT typically controlled by adaptive control in a machining process?

Material properties Signup and view all the answers

What must be improved for the growth of adaptive control in machining processes?

Process reliability Signup and view all the answers

Which characteristic differentiates continuous path NC machines from point-to-point NC machines?

Fluid motion along a defined path Signup and view all the answers

Which of the following is a significant challenge in the implementation of adaptive control systems?

Assessing the interaction of process variables Signup and view all the answers

What is an essential aspect of programming NC machines that distinguishes it from manual programming?

Incorporation of graphic simulation Signup and view all the answers

Which component of an NC machine has the primary responsibility of interpreting commands?

Machine control unit (MCU) Signup and view all the answers

Which type of NC system is characterized by frequent adjustment of parameters based on multiple feedback signals?

Adaptive control system Signup and view all the answers

Which of the following best reflects a limitation of conventional NC compared to CNC systems?

Flexibility to change programming quickly Signup and view all the answers

What is a primary feature of distributed numerical control (DNC) systems?

Real-time data gathering for multi-machine operations Signup and view all the answers

What is the primary benefit of using two work-tables in machining centres?

It enables continuous operation with minimal downtime. Signup and view all the answers

What does the term 'adaptive control' primarily imply in machining processes?

The adjustment of parameters based on real-time measurements. Signup and view all the answers

Why are components produced in machining centres described as expensive despite being small in size?

They contribute significantly to the overall product value. Signup and view all the answers

What is considered a high capability of machining centres?

High metal removal rate. Signup and view all the answers

How does a machining centre enhance productivity during operations?

By allowing high degrees of accuracy in various operations. Signup and view all the answers

What type of system manages the storage and retrieval of tools in a machining centre?

Magazine systems. Signup and view all the answers

What is a common feature of machining centres that enhances their versatility?

Multi-operation capabilities in one setup. Signup and view all the answers

Which aspect of a machining centre's operation is recognized as improving through the use of adaptive control?

Improved accuracy of the finished part. Signup and view all the answers

In batch production using machining centres, what is the primary characteristic of the components produced?

They are generally small but have high material value. Signup and view all the answers

Study Notes

NC Machine Tools

NC machines use command signals to control the travel length and feed rates of machine tools, as well as other functions like spindle motor control, tool changes, and coolant supply.
The data processing unit (DPU) processes data from input sources (like tapes) and sends instructions to the control loops unit (CLU).
The CLU controls the drive mechanisms, receives feedback, and signals operation completion.
The control unit also sends signals to the electrical control cabinet (magnetic box) managing functions like spindle motor starting and stopping.

Classification of NC Machines

NC machines are classified based on power drive types:
- Electro-mechanical
- Hydraulic
- Pneumatic
Machine performance and applications depend on the power source.
- Hydraulic systems offer the most power, but are more expensive, with noise and possible fluid contamination risks, requiring additional equipment for reservoirs, intensifiers and valves.
- Pneumatic systems are the least expensive, but may offer less uniform movement.
- Electro-mechanical systems are the most precise and common.

NC Control System Types

Point-to-Point: Machining at specific positions, with the workpiece remaining stationary between movements
Straight Line: Controlled movement along one axis at a time
Contour (Continuous Path): Simultaneous coordinated movement of the tool and workpiece along multiple axes to create complex shapes.

NC Machine Systems

Open-Loop System: No feedback, lacks error detection.
Closed-Loop System: Uses feedback to monitor tool position and correct for errors. Feedback loops use transducers to send information about the actual position achieved to the control unit.

Programming for NC Machines

Information for NC machining is punched on a paper tape, including coordinate values, movement type (e.g., point-to-point, straight line, contour), and machine functions (e.g., start/stop, coolant).
Programming can be manual for simple tasks or via computer for complex ones.
Programmers use part drawings to determine operational sequence, tools, cutter paths, speeds, and feeds before generating the punched tape or program code. This includes defining co-ordinate dimensions for each operation, spindle traverse, speed, feed, and tool changes.

Computer Numerical Control (CNC)

Computer Numerical Control (CNC) uses microcomputers to replace the traditional hard-wired control logic of conventional NC systems, offering more flexibility for program storage and modification, minimizing errors in the programming process.
CNC systems use more flexible computer programs and often eliminate tape reading, reducing labor costs.

Direct Numerical Control (DNC)

DNC systems connect multiple NC machines to a central computer for simultaneous program execution, managing and communicating with each machine in the network.
DNC is more flexible than conventional NC because multiple machines can be controlled from a single location.
A central computer manages and distributes programs to multiple NC machines.

Machining Centers

Machining centers combine several machine tools (e.g., drilling, tapping, milling, boring, etc.)
This facilitates multiple operations on a single workpiece with reduced work handling time, and makes it highly versatile.
The automatic tool changer is the defining feature of machining centers.
Machining centers improve efficiency, by doing a variety of machining operations on one machine instead of multiple operations on different machines. This reduces the time required to complete machining operations.

Adaptive Control

Adaptive control combines decision-making aspects into CNC systems, incorporating measurements while machining, potentially improving accuracy by responding to and altering machining variables (speeds, feeds) that affect the quality of the machined parts during the manufacturing process. It also accounts for tool wear and adjusts parameters to maintain accuracy.

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Description

Explore the fundamentals of NC machine tools, including their operation, command signals, and data processing. Learn about the classification of NC machines based on power drive types and their respective performance characteristics. This quiz will help reinforce your understanding of these essential manufacturing technologies.