Manufacturing Resource Planning/ Enterprise Resource Planning. 13. Robotic ...
Control the activities of the manufacturing floor (production equipment,.
Assignment A (individual submission) Write a brief summary (two A4 pages single line spacing, font size 12) on each of the following concepts used in Advanced Manufacturing Systems. You will be required to make a 10 minutes presentation on your submission. The submissions will eventually be circulated to all students. Please note that you need to provide the list of references consulted in Harvard Style. 1. Concurrent/Simultaneous Engineering 2. Business Process Reengineering 3. Just in time Manufacturing 4. Quality Assurance v/s Total Quality Management 5. Lean Manufacturing 6. Flexible Manufacturing Systems/Cellular/Modular Manufacturing 7. Condition Based Maintenance Planning / Total Productive Maintenance 8. Finite Element Analysis 9. Productivity Management 10. Rapid Prototyping 11. Simulation of Manufacturing Systems 12. Manufacturing Resource Planning/ Enterprise Resource Planning 13. Robotic Applications 14. Material Handling Systems 15. Supply Chain Management Assignment B Write the part program for the design given. Note: For assignment C and D you may work in groups of two. You are required to submit details of the models (Complete 2D AutoCAD drawings) by the week mentioned in the time schedule. Assignment C Select a part of your choice (for turning application) and produce the NC part program for the part. Also, machine the part on the lathe. Assignment D Select a part of your choice (for milling application) and model the part on Mechanical Desktop. Post process the design using HyperMILL and download the data on the Vertical Machining Centre. Machine the part.
Prepared by: Dr D.K.Hurreeram August 04
1.1 • • •
Historical Perspective Design/Manufacturing Concept Contribution of Engineers Difference between needs of the past and the future • Product of high performance and reliability at low cost in shortest time scale • Use of computers: information processing
CAD Historical Perspective 1957-59 1965 1969 1970 1972 1974 1976 1977 Late 70’s Early 80’s 1982 1983
1985 1987 1988 1989 1991 90’s Mid 90’s 00’s
MIT Project, High Precision Engineering, Producing Complex Shapes Dec introduce first graphics mini computer called PDP8 Applicon, Computer Vision and Intergraph founded, First CAD/CAM system introduced by Dr P Hanratty and G Devere called ADAM S3 buys ADAM Tektronix introduces the first storage tube display terminal 4010 ComputerVision buy S3 Albert and Devere join Calma and develop Design, Drafting and Manufacturig (DDM) application software for mechanical draughting DEC introduces a 32 bit computer called Vax 11/780 ComputerVision the leading CAD/CAM supplier, Raster/refresh tubes are taking over as the most popular graphics tubes from the vector/storage tubes Apollo Computers launch DN100 a networked graphic terminal 32-bit computer AutoDesk exhibit an IBM PC based CAD system called AutoCAD Sun Microsystems founded Apollo computers launch DN300. GE Calma’s main CAD/CAM Systems based on Apollo computers, Intergraph and Applicon continue using DEC Vax’s computer Silicon Graphics launch the 2400 real time 3D graphics terminal DEC introduces micro Vax, its first 32 bit graphics terminal Compac introduces the first 386 PC called Deskpro 386 Sun Microsystems launches Sun 4, the first RISC workstation Prime Computer buy Computervision and Calma HP buys Apollo HP launches 9000 series the then fastest RISC (Reduced Instruction Set Computing) workstation Intel chip 80486, Pentium, clock speed of 33-66 Mhz with data address of 32 bits and memory of 1-16MB, LANs, WANs coming into operation. Wider application of LANs and WANs – Internet, Intranet, Extranet, EBusiness, SCM Pentium PCs running CAD/CAM packages with complete interfacing
Prepared by: Dr D.K.Hurreeram August 04
1.2
Role of Computers in the Design/Manufacturing Process
The Manufacturing System (What it is? Evolution in Manufacturing Practice: Past, Present and Future: Fig 3) o From mass production to mass customisation (Fig 1) o Flexible Manufacturing: manufacturing for Productivity, Quality and Flexibility (Fig 2) o Basic functions of a manufacturing facility (Fig 4) o Use of computer systems for planning, Sales, Purchasing, PP&C, design, QC, Administration, Manufacturing, material flow, Supplier information (Fig 5 & Fig 6) • Planning and Control Activities (Fig 7) • The Design Function (Fig 8) • CAD and CAM Activities (Fig 10 & Fig 11) Nomenclature CAD CAE CAP CAM CAQ CAD/CAM PP&C CIM
Computer supported design, draughting and engineering calculations CAD + NC Testing Computer Aided generation of technological plan to make the product. Process plan describes the manufacturing processes and sequences to make the part. Control the activities of the manufacturing floor (production equipment, management of materials, cutting tools, fixtures and maintenance. Quality control work within manufacturing systems Designate the sum of activities of the above Manufacturing resources planning, materials requirement planning, gross requirement planning, time phasing, order release and manufacturing control Combines CAD/CAM with PP&C
Advantages of CIM • • • • •
Reduction of design cost by 15-30% Reduction of in-shop time of a part by 30-60% Increase in productivity by 40-70% Better product quality; reduction of scrap by 20-50% Improved product design (use of FEA for instance)
Discussions on Assignment A
Prepared by: Dr D.K.Hurreeram August 04
2.3
Types of Design Model
Representations in the Model Function of the design Structure Form of the component parts Surface conditions and dimensions Mathematical models Production plans, scheduling etc… • • 2.4
Customer Fellow designer, production staff, workshop staff, users of the design, GM, design analyst, Assessors materials,
Drawings (Universal Engineering Language-represent material, form, structure, surface, tolerances, dimension, manufacturing processes involved) Systems Engineering Approach (Kinematics, Dynamic, Thermal, Stress Models) Modelling Using CAD systems
Apply computers to both modelling and communication of design. • •
Use computers to automate or assist in production of drawings or diagrams and the generation of list of parts in the design Provide new techniques which give the designer enhanced facilities to assist in the design process
Advantages • Automation of more repetitive and tedious tasks • Improved precision of models • Overcome limitations of conventional drawing • Provide means for design assessment and evaluation • Generates information for manufacturing • Provide basis for simulation 2.5
Functions • Model definition • Model manipulation • Picture generation • Utilities (picture representation) • Database management • Applications (design evaluation, analysis, manufacturing info.)
Defining a CAD Model •
Forms (components) and structures (the system assembly)
•
Use of Drawings (Descriptive Geometry) Three-dimensional forms in two-dimensional space on paper or on a computer screen (First angle and third angle projections + perspectives, development etc…) From French Military Engineer Garpard Monge (1746-1818).
Prepared by: Dr D.K.Hurreeram August 04
Shapes represented by projecting views of an object into mutually perpendicular planes of projection such as plans and elevations Details in standards such as ANSI, Y14 series or the BSI, BS 308 (1990) Layout of drgs, Line works, lettering and numerals, systems of projections (first angle, third angle, pictorial, perspective), views on drgs, sections, conventions, scales, principle of dimensioning, tapered features, tolerance dimensions, machining and surface texture symbols, electrical symbols BS 3939, general engineering symbols BS 1553, fluid power system elements BS 2917. Use of block diagrams 2.6
Strength & Weakness of Conventional Representation of Drawings • • • • • • • •
2.7
Any system (product) can be represented - bridges, aircraft, car, buildings... • Can take 100 000 or more drawings and other documents to represent car assembly Language understood by one and all (skilled craftsmen needed for interpretation) May have conflicting and erroneous models (mismatch between views) May have complex products (turbine blades difficult to represent using geometrical construction) In electronic systems drawing of thousands of components can be laborious by hand Modifications difficult Design evaluation (analysis) difficult More prone to human error Computer Representation of Drawings
CAD definition CAD is a technique whereby the geometric description of objects are defined in the form of mathematical models, and processed by a computer or it is the process which users a computer in the creation and modification of design. Applications Mechanical Engineering drawings, architectural drgs, electronic and electrical circuits schematic drgs, PCB design, business graphics etc... Benefits • Rapid response to changing demands because of reduced lead time in design. • Better use of design data bases • Helps standardisation of standard parts • Less mistakes e.g inconsistent dimensioning • Better drawing quality and market image • Drawing data used subsequently by other departments e.g BOM, MRP, CAM, Stress Analysis, flow simulation • Repetitive parts (bolts and nuts, transistors, capacitors, Ics) kept in CAD library • Parts drawn only once (used for assembly etc..) • Drawing size manipulation Prepared by: Dr D.K.Hurreeram August 04
• • • • • • • 2.8
Display functions (zooming) Layer functions Tangency functions Automated dimensioning Higher Productivity CAD/CAM integration Provide opportunity for implementing CIM systems Types of CAD systems
2D modellers • Virtually an ‘electronic drawing board’. Similar to manual draughting • Use of geometric entities for producing the design in 2D (Fig 9, 10, 11) pg 25,26,27 Mc • Front elevation, plan, side view, dimensioning, and texts...collection of lines, arcs, etc in one plane. • Lowest grade of CAD systems but can be very useful e.g. for PCB, floor plans, maps, artwork, electrical and electronic circuits etc... • Cannot correlate drawing entities in different views to form a 3D entity.
Prepared by: Dr D.K.Hurreeram August 04
3D wire frame modellers • • •
A framework made of wire of infinitely small diameter. Each piece of wire represents an edge of the 3D object. e.g. a cube represented by 12 pieces of wire Construction in 3 dimensional space. Use of right handed Cartesian coordinate system Global and Work Coordinate Systems Wire frame model of a cube
A wire frame model does not include surface information. Computer does not know there are six surfaces
Corner of cube cut by a plane a triangle is obtained
• • •
In wire frame modelling only 3 points are obtained
Cutting a cylinder in wire frame model
Cutting a cylinder would normally generate an ellipse - can not be created by 3D wire frame modellers. Computationally most straightforward (computer time and memory requirements) Deficiencies • Ambiguity in representation • Deficiencies in pictorial representation (complex models difficult to interpret, no hidden line removal) • Ability to calculate mechanical properties, geometric intersections is limited • Limited value as a basis for manufacture or analysis
3D surface modellers • • • • •
Overcome the drawback of 3D wire frame modelling Contains surface information, each surface forming a single entity Developed from wire frame representations Most elementary surface is the flat plane between two parallel straight lines Other surfaces are (Fig 12)
Tabulated cylinder
projection of a generating curve along a line or a vector
Ruled surface
linear interpolation between two different generating or edge curves
Prepared by: Dr D.K.Hurreeram August 04
Surface of revolution revolving a generating curve about a centre-line or vector (modelling turned parts or parts possessing axial symmetry Swept surface
defining curve is swept along an arbitrary curve instead of a circular arc
Curved mesh
(sculptured surface) two families of generating curves intersecting in crisscross fashion so creating a network of interconnected surface patches
Fillet
surface connecting two other surfaces in a smooth transition (generally a constant, or smoothly changing radius of curvature
Solid modellers • • •
Representation of a solid object (real object) in CAD Has the flexibility of surface modelling In addition, can calculate volume, mass, centre of gravity, moment of inertia etc...
Two most commonly used methods 1. Boundary Representation (1970s, University of Cambridge, UK) • • • •
2D 3D wire frame 3D surface solid modelling An extension of surface modelling (Fig 13) Computer is able to distinguish the inside of a surface from outside Creation of a solid object by defining a shape by its boundaries (faces, edges and corners)
2. Constructive Solid Geometry • • • • •
Not an extension of 3D surface modelling Object represented by primitive solids (box, cylinder, cone, wedge, sphere, toroid, etc..) and the result of Boolean operations ( union, difference, intersection) on the primitives Fig 14 No need to define boundaries More logical and adaptable approach to design Cannot define complex shapes (recourse to surface modelling)
Prepared by: Dr D.K.Hurreeram August 04
2.9
Common CAD features in 2D • Entity • Position (object snap) • Creation of geometric entities (point, line, arc, circles, circular arc, fillet, chamfer, spline etc..) • Difficulty in 3D • Editing entities (trim, extend, break, detailing, dimensioning, hatching etc..) • Compatible with company draughting standards • Avoid errors by using automatic dimensioning • Avoid crowding of dimensions • Display commands (zoom, pan, window...) • Attributes (line type, colour, layer, etc...) • Important for drawing organisation • Up to 256 layers available (layer allocation scheme) • Transformation (translate, rotate, move, copy, join, mirror...) • Drawing Aids (Grid, Cursor tracking, Coordinates display etc...) • File functions (save, load, directory, plot, import, parts library....)
2.10
Common CAD features in 3D • Coordinate system (RH rule, WCS, UCS...) • Views (Top, front, back, bottom, R/L side, Isometric, View ports...) • Construction Plane and depth
2.11
Integration of Design Analysis and CAD
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•
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Structure and form represented by using AutoCAD Design Evaluation - need for more information for judging the fitness for purpose • Detail of material, surface condition, etc.... Analysis in terms of weight, weight distribution, stress, thermal and dynamic performance, resistance to wear, corrosion, impact loading etc.... Geometric Analysis - direct from design • Slope and curvature of curves • Normal vectors and curvature of surfaces • Perimeter, area, centre of area and moments of area of closed planar profiles • Volume, surface are, mass and inertial properties of closed volumes and volumes defined by swept surfaces • Kinematics and dynamic analysis from modified systems Finite Element Analysis • Applied to all sorts of analytical tasks like stress, vibration, thermal, electromagnetic and fluid flow analysis • Problem domain - finite elements - nodes - mesh • To the mesh - apply boundary conditions e.g. loads, temperatures, displacement • Distribution of property of interest defined by some set of equations sorted out by the computer (Fig 16) Note some FEA software do provide flexibility for design or design importation • Pre-processors and post-processors System Customisation
Prepared by: Dr D.K.Hurreeram August 04
• • • • •
Customisable User interface Key log files Macro languages Graphics programming languages Interfaces
4.0 Numerical Control Numerical Control - Computer Aided Manufacturing
Production Planning and Control Computer Aided Process Planning Computer Aided Production Control Computer Aided Machining
Manufacturing Computer Numerical Control Machines Robotics Automatic Material Handling Automatic Storage/Retrieval Systems Computer Aided Quality Control
Computer Aided Machining Numerical Control History • Need for automation (use of perforated cards for transmission of mechanical actions • 40’s Project by John Parsons for generating profile of helicopter blades (coordinates generation, 2D contours generated using tabulating equipment). • MIT project with Parsons as leader - production of the 1st 3 axis milling machine using perforated tape as input of information • 60’s more and more NC systems - mostly with point to point control, other systems being very expensive • Late 70’s incorporate microprocessors in NC controller for upgrading the performance. CNC systems with programme storage, on screen editing, cutter compensation, programme repetition, graphic simulation of tool path and interactive programming. • 80’s use of DNC systems - replacement of tapes as input media. • 90’s CAD/CAM systems (CAD and CAM successfully interfaced). CNC machines now controlled by CAD systems Definition of Numerical Control From Electronic Industry Association A system in which action is controlled by the direct insertion of numerical data at some point. The system must automatically interpret at least some portion of this data.
Prepared by: Dr D.K.Hurreeram August 04
Numerical Data Input
NC Data interpretation
Mechanical Action
Elements of an NC System Input Device
Display Unit Machine Control Unit Data processing Control Loop Unit Unit position velocity Motion data
Miscellaneous functions
Drive System Feedback Devices
Program of instruction - detailed step by step commands that direct the processing equipment • Position of tool wrt spindle • Co-ordinate system, motion control, x, y, z, a, b, c, u, v, w • Absolute v/s incremental co-ordinate system • Assigning programme zero • Offsetting of work piece • Cutting tools (hardness and toughness considerations) see handouts • HSS tougher than cemented carbides but not as hard • Cemented Carbides (Tungsten, Titanium, Tantalum carbides…) Prepared by: Dr D.K.Hurreeram August 04
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• Ceramics • CBN and Diamond Cutting speed, spindle speed and feeds • Surface cutting speeds (m/min)
Tool Material Cemented Carbide HSS Feed rate for turning (mm/min)
Part Material Mild Steel Cast iron 170 100 28 18
Alum Alloy 250 120
Brass 180 75
.25
.3
.3
.25
♦ Spindle speed (rev/min) 1000 Cutting Speed (V, m/min)/# Work or cut diameter (mm) ♦ Feed (mm/min) for turning Feed (f, mm/min) = Feed (mm/rev) * Spindle speed (rev/min) ♦ Feed (mm/rev) for milling
Feed (mm/rev) = Feed (mm/tooth) * Number of teeth on cutting ♦ Metal Removal Rate (mm3/min)
MMR = 1000 Vfd (d = depth of cut in mm) ♦ Time for cutting operation T
T = L/f • •
The Part definition (see part programming) Miscellaneous Functions (spindle start, spindle stop, coolant ON/Off, select planes, Offsetting, etc…)
Input devices • Tape control • CNC with tape control • Floppy discs • Distributed Numerical Control • CAD/CAM Systems
Prepared by: Dr D.K.Hurreeram August 04
Machine control Unit • Electronics and control hardware to interpret the program of instruction and convert into mechanical actions of the machine tool or processing equipment •
Heart of the NC system
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Data Processing Unit Interprets and encodes the part programme into internal machine codes. Interpolator of the DPU calculates the intermediate positions of motion in terms of BLU. Data sent to CLU for action.
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Control Loop Unit Data from DPU converted into electrical signals for controlling driving system to perform the required motions. Also other functions (Miscellaneous) •
Open Loop control • No access to real time data about the performance of the system • No immediate corrective action taken in case of disturbance • Applied where output is predictable and almost constant e.g. wire cut machine (no force involved in cutting) • No feedback - use of stepping motors (driven and controlled by electrical pulses generated by MCU)
each pulse drive motor by step angle equivalent to fraction of 1 rev. step angle α=360/ns ns=no. of step angle on stepping motor angle of rotation = Pα (P= no. of pulses generated) = ftα f = pulse rate t = duration of pulse train rotation of stepping motor = 60f/ns Disadvantage of stepping motor in Open Loop Control Systems ♦ Loss of pulses possible – limitation on accuracy and repeatability ♦ Most appropriate for small loading conditions (point to point and non machining applications) ♦ Closed loop control • Use of feedback devices (optical encoders, photoelectric cells etc) • Output monitored by feedback devices and disturbances corrected in real time • High system accuracy is achieved • Most NC systems
Prepared by: Dr D.K.Hurreeram August 04
table
Stepping Motor
Gear
Pulse train Leadscrew
Input Comparator
DC Servomotor
DAC
Gear
Feedback signal
Open and Closed Loop Control Systems Angle between openings α=360/nd nd = no. of openings on disc angle of rotation = Pα (P= no.of light pulses generated) Angle of rotation used to determine linear position of NC machine table axis Pulses compared with input signal command – compared till error is zero
Accuracy and Repeatability Two important features of NC systems Accuracy is a measure of the control system’s capacity to position the machine table at a desired location. It is related to the systems Control Resolution CR. CR refers to MCU capability to divide the range of a given axis into closely spaced points that can be identified by the Controller. Function of ♦ Bit storage capacity ♦ NC Drive System (step angles on stepping motor) Prepared by: Dr D.K.Hurreeram August 04
Sensor
♦ Capability of feedback sensor (no of sensors generated by optical encoder) n = no. of bits for an axis then Number of control points = 2n Control Resolution defined as distance between adjacent points is given by CR = range of axis movement / 2n The worst case would be that the position is in between the adjacent points. This can be due to a number of factors which can be summed as mechanical errors (gear backlash, lead screw play, deflection of machine components etc..) Assuming the mech. Errors follow a statistical distribution (normal distribution) then accuracy defined by Accuracy = CR/2 + 3 (std. deviation of mech. Errors) Repeatability is defined as the ability of the control system to return to a given location that was previously programmed. Their principal source of errors is mechanical hence Repeatability = + 3 (std. deviation of mech. Errors) The Machine Tool • Any type of machine tool or equipment. • For high accuracy and repeatability machine slide and driving lead screw of vital importance. (Resistance against friction, avoid backlash at bearing, rigid and heavy machine structure, short machine table overhang, quick change tooling system etc…) Types of NC Machines • Positional or Point to Point Control • Straight Line Control • Contouring Path Control • Motion types on NC Systems • Rapid traverse G00 • Straight line motion G01 • Circular motion G02/03 NC Machine Classification •
2 axis, 21/2 axis, 3 axis, 4 axis, 5 axis
Types of Machines • Drilling Machine • Lathe • Turning Centre • Milling Machine Prepared by: Dr D.K.Hurreeram August 04
• • • • • • • • •
Machining Centre Turret Press and Punching Machine Wire Cut Electro Discharge Machine Grinding Machine Laser Cutting Machine Water Jet Cutting Machine Coordinate Measuring Machine Robotic Applications Medical Sciences
Advantages of CNC Machines Productivity • Highly skilled operator not required. Programmers off site • High machining time, down time largely reduced • Decision time reduced. Easier drawing interpretation • Tool change automatic • Multiple machining operation Flexibility • •
Remote control Design changes
• • • •
Accuracy Repeatability Scrap rate Inspection and rate of inspection
Quality
Production Management and Control • Machine scheduling • Routine time (control of various CNC machines - DNC) • Lead time (use of special jigs and fixtures) • Product inventory Others • • •
Product design Prestige Factories of the future
Limitations of CNC Systems • High capital investment • Machine maintenance • Training • Investment in other systems (tooling, CAD etc)
Prepared by: Dr D.K.Hurreeram August 04
Factors to be considered in CNC Machine Selection • Evaluation with respect to (Comparison chart for requirements and various suppliers) The overall system • Size • Dimension of working area • Number of controllable axes • Rapid traverse speed • Power of the main spindle • Accuracy and Repeatability • Reliability of the Machine The Basic machine • The types of the machine • The types of attachment necessary • The structure of the machine such as type of slideway, anti friction design, coupling design, backlash compensator and stiffness of the machine The control system • Input media • Data format and data storage size • Ability to interface with external computer • Graphic simulation capability • CNC functions, standard and options • Special canned cycles, standard and options • Ability for future upgrading and modification Other • • • • • • • •
Swarf handling facility Tool handling device work piece handling device Installation and commissioning After sales service Documentation and manuals Training courses COST
Introduction of a CNC into a factory • Feasibility study • Management decision • Project leader • Detailed evaluation of various CNC machines & machine selection • Staff training plan • Production Planning and Control • Programming Section • Maintenance Department Prepared by: Dr D.K.Hurreeram August 04
CNC Part Programming • Axes of motion (RHR) Lathe and Milling Machine (Boxford and VMC) • Programming • Machining sequence • Cutting conditions • Selection of cutting tools • Programme Structure • Block (a sentence) • Word (identification letter and series of numerals) • Address (identification letter) • Refer to manuals for exact definitions of Words Address O N G X,Y,Z I,J,K F S T H D M
Function Program Number used for program identification Sequence Number used for line identification Preparatory Function Co-ordinate Word Parameters for Circular Interpolation Feed Function Speed Function Tool Function Tool length offset designation Tool radius offset designation Miscellaneous Function
The Preparatory Functions G00 G01 G02/03 G17 G18 G19 G33/34/35 G40-G52 G70-G79 G80-G89 G90 G91
Rapid movement Linear movement, specify feedrate Circular interpolation, specify feedrate XY plane selection ZX plane selection ZY plane selection Thread cutting Cutter Compensation Milling and Turning Cycles Drilling and Tapping Cycles Absolute Programming Incremental Programming
The Miscellaneous Functions M00 M02 M03 M04 M05 M06
Program stop Program end Spindle rotation – clockwise Spindle rotation – counter clockwise Spindle stop Change tool
Prepared by: Dr D.K.Hurreeram August 04
M08/09 M10/11 M30
Coolant ON/Off Clamp ON/Off Program end and ready for another start
Part Programming Examples
Safety Features while NC machining ♦ CNC programme safety ♦ Safety features on the CNC machines (Boxford and VMC) Steps for NC programming and machining • Study part drawing • Select suitable zero • Determine machining operations • Determine method of work clamping • Select cutting tools and determine spindle speed and feeds • Write programme • Check program for safety • Prepare tool chart diagram (tool offsetting) • Clamp work and set machine • Enter compensation value if necessary • Check and test programme • Dry run programme • Start machining The Boxford Machine ♦ The Various components on the machine ♦ Programming on the Boxford Lathe ♦ Workpiece offsetting ♦ Demonstration ♦ Assignment The Vertical Machining Centre ♦ The various components of the VMC ♦ Programming on the VMC ♦ Demonstration ♦ Assignment Computer Aided Machining (Mechnical Desktop/HyperMill CAD/CAM System) ♦ Geometric Modelling on Mechanical Desktop ♦ Tool Motion Definition (HyperMill) ♦ Post Processing ♦ Data Transmission to the VMC ♦ Machining Demonstration Prepared by: Dr D.K.Hurreeram August 04
