Computer Integrated Manufacturing

Table of Contents
1. Introduction
2. Processes Involved
3. Why CIM?
4. Usages of CIM
5. Machine
6. NC (Numeric Control) - Open Loop Control
7. Stepper Motors
8. Basic Length Unit (BLU)
9. CNC (Computer Numeric Control) - Closed Loop Control
10. Direct Numerical Control (DNC)
11. Distributed Numerical Control
12. Flexible Manufacturing System (FMS)
13. Automated Guided Vehicles (AGV)
14. Preparatory Functions - G Codes
15. Miscellaneous Functions - M Codes
16. Interpolator
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Introduction

Computer Integrated Manufacturing (CIM) is a manufacturing approach in which computers control and coordinate the entire production process. In a CIM environment, individual processes exchange information and initiate actions automatically. Functions on the factory floor such as material handling, direct process control and monitoring, quality inspection and storage are linked with enterprise-level functional areas such as design, analysis, production planning and control, purchasing, cost accounting, inventory control and distribution. The goal of CIM is to achieve higher productivity, improved quality, reduced lead time and greater flexibility by integrating hardware, software and human resources into a cohesive automated manufacturing system.

Processes Involved

• Computer-Aided Design (CAD): creation and modification of product geometry and engineering drawings using CAD software.
• Prototype manufacturing: rapid prototyping and small-batch manufacture to validate design and processes.
• Process planning and cost determination: selection of manufacturing methods, estimation of costs, and consideration of production volume, storage and distribution requirements.
• Materials ordering: automated generation of purchase orders and material requirements planning (MRP).
• Computer-Aided Manufacturing (CAM): generation of NC/CNC programs and direct control of machine tools using computer numerical controllers.
• Quality control: in-process inspection, statistical process control and automated testing at various production stages.
• Automated product assembly: use of industrial robots and assembly stations for accurate and repeatable assembly operations.
• Automated storage and retrieval: automatic warehousing, inventory tracking and retrieval systems.
• Automated logistics: automatic transfer of finished goods to waiting trucks or dispatch areas using material handling systems.
• Automated data updating: automatic logging of production records, financial transactions and billings into enterprise systems.

Why CIM?

• Error reduction: automation of routine data entry, part-program generation and control tasks reduces human errors in manufacturing and reporting.
• Speed and lead-time reduction: faster information flow and automated operations reduce manufacturing lead times and increase throughput.
• Flexibility: the ability to reconfigure machines, programs and production schedules quickly enables rapid response to market changes and product variants.
• Integration: integration of factory-floor operations with enterprise-level software enables better resource utilisation, higher-value work for staff and improved decision-making across the organisation.

Usages of CIM

1. Industrial and Production Engineering - planning and optimisation of manufacturing systems.
2. Mechanical Engineering - design, simulation and manufacture of mechanical components.
3. Electronic Design Automation - design and verification of electronic hardware.
4. Printed Circuit Board design
5. Integrated Circuit design

Machine

A machine converts one form of energy into another to perform useful work. A machine that can perform multiple operations or accept a variety of tools is commonly called a machine centre. A tool magazine is a device attached to a machine centre to store and present the required cutting tools automatically during machining.

NC (Numeric Control) - Open Loop Control

Numeric Control (NC) is programmable automation in which tool motions are controlled by a sequence of coded instructions. Historically, NC programmes were stored on punched paper tapes or cards. A tape reader decodes the punched pattern and generates electrical pulse trains that drive the machine control electronics.

• Tape readers convert punched tapes into digital pulses which are used by the pulse generator.
• A pulse generator produces a sequence of pulses; a stepper motor receives these pulses and moves in discrete steps at a speed proportional to pulse frequency.
• The stepper motor is coupled to a lead screw (often through gearing) which converts rotary motion into linear table or carriage motion for machining axes.

Limitations of Open-Loop NC

• There is no feedback loop; the system does not verify that the commanded motion was actually achieved.
• Programs stored on tapes or cards are hard to modify; alteration is inconvenient and time-consuming.
• Long tapes and manual handling make program management labour-intensive and error-prone.

Stepper Motors

Stepper motors are electromechanical devices that move in discrete steps in response to electrical pulse trains. They are used for precise positioning of machine slides and workpieces in NC systems. Rotation of the motor shaft is proportional to the number of pulses received; the angular velocity is proportional to the pulse frequency. The angular distance corresponding to one input pulse is called the step angle.

Basic Length Unit (BLU)

The Basic Length Unit (BLU) is the linear distance travelled by the machine table (or axis) for one step or pulse of the stepper motor.

The linear velocity V of an axis driven by step pulses is given by the relation:

V = pulse frequency × BLU × 60 mm/min

CNC (Computer Numeric Control) - Closed Loop Control

Computer Numerical Control (CNC) is programmable automation in which programmes are stored in and executed by a computer or microprocessor-based controller. Unlike open-loop NC, CNC systems commonly use feedback from position encoders and closed-loop control to ensure the commanded position is actually achieved. A comparator compares the position feedback from encoders with the command signal (from the pulse generator or controller) and issues corrective action when there is a difference.

Direct Numerical Control (DNC)

In the 1970s, central computer systems were used to store and manage large and complex NC programmes that would otherwise be too big to hold locally at each machine. Direct Numerical Control (DNC) describes systems where an external central computer feeds programmes directly to machine tools, often over a serial link or network. This arrangement allowed centralised programme storage, editing and management.

Distributed Numerical Control

Distributed Numerical Control refers to architectures where a single host computer or a network of computers coordinates and controls multiple machine tools at different locations. Such systems provide central management with distributed execution and may include programme distribution, tool data management and shop-floor monitoring for several machines.

Flexible Manufacturing System (FMS)

A Flexible Manufacturing System (FMS) is an arrangement of machines, automated material handling and storage, and a central computerised control system designed to produce a family of parts with little manual intervention. Typical FMS components include machine tools, automated tool changers, pallets, industrial robots, automated guided vehicles (AGVs), automatic storage and retrieval systems (AS/RS), and a Manufacturing Execution System (MES) for scheduling and control. FMS provides flexibility in both product mix and production volume, reduces changeover time and improves machine utilisation.

Automated Guided Vehicles (AGV)

Automated Guided Vehicles are mobile robots used to transport materials and components between machines, workstations and storage locations. AGVs follow predefined paths or navigate using guidance systems such as magnetic tape, wires, optical markers, laser navigation or simultaneous localisation and mapping (SLAM). They reduce manual material handling, improve flow reliability and integrate with factory control systems for automated logistics.

Preparatory Functions - G Codes

Preparatory functions in NC/CNC programming are commonly specified by the G codes. G codes direct the movement mode and geometry of the machine axes, for example straight-line motion, circular interpolation, or absolute/ incremental programming modes. Standard ISO G codes typically have two digits (for example G01, G42, G90), though many controllers accept three- or four-digit codes. Common preparatory functions include linear motion, circular motion and programme frame formats.

Miscellaneous Functions - M Codes

Miscellaneous functions are specified by M codes and control auxiliary machine functions that affect program execution. Examples include spindle on/off, coolant on/off, program stop, tool changes and other machine-specific controls. ISO standard M codes provide a common set of such functions, though exact meanings may vary slightly between controller manufacturers and machine tools.

Interpolator

In many machining operations, the tool must follow continuous curves or contours. NC controllers are digital and therefore approximate continuous curves by calculating a sequence of closely spaced points on the desired trajectory. The controller moves the tool from point to point along short straight-line segments so that, when these segments are sufficiently close, the traced path approximates the continuous curve. The control resolution is the minimum distance that the machine can distinguish between adjacent points; higher resolution gives better accuracy. The computation of intermediate points on a trajectory is called interpolation. Common types of interpolators are:

1. Linear interpolator: calculates closely spaced points between given end points of a straight line to generate straight-line motion (G01 in many controllers).
2. Circular interpolator: generates points on an arc or circular profile so that connecting these points approximates a circle or arc (G02/G03 in many controllers).
3. Helical interpolator: combines circular interpolation in a plane with linear motion along an axis perpendicular to the plane to produce a helical path, useful for drilling threads and helical milling.
4. Parabolic and higher-order interpolators: generate points on parabolic or spline curves; these are less common but provide smoother trajectories for complex contours.

Well-designed interpolation algorithms and sufficiently fine resolution minimise contouring errors and produce smooth tool paths necessary for accurate part geometry and surface finish.

Summary

Computer Integrated Manufacturing integrates CAD, CAM, CNC, robots, material handling, quality control and enterprise software to achieve automated, flexible and efficient production. Understanding NC, CNC, DNC, FMS, AGVs, G/M codes and interpolation techniques is essential for designing and operating modern automated manufacturing systems.