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Mechatronics and Control for Production Plants > 05 Numerical Control 1 - Structure, Programming, CAM > Flashcards

05 Numerical Control 1 - Structure, Programming, CAM Flashcards

1
Q

Components of Control Systems

A
  1. Supervisory Control and Data Acquisition Layer (SCADA)
  2. Human Machine Interface Layer
  3. I/O Layer
  4. Drive Layer
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2
Q

Components of Control Systems: SCADA Layer

A

a. Manufacturing Execution System (MES) distributes manufacturing orders and corresponding data, incl. NC programs and cutting tool lists/tables
b. Network communication by e.g. Industrial Ethernet or PROFINET

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3
Q

Components of Control Systems: Human Machine Interface Layer

A

a. PC-based console with standard operating system allowing for a simplified exchange of data via internal network
b. Local interface for the machine operator

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4
Q

Components of Control Systems: I/O Layer

A

a. For communication at the sensor and actor layer standards like PROFIBUS-DP are utilized
b. NC and Programmable Logic Control (PLC) are physically separated, but synchronized and share tasks

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5
Q

Components of Control Systems: Drive Layer

A

Use of internationally normed (open or proprietary) protocols for high dynamics and precision at servo level

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6
Q

Core Task of Numerical Control

A

Generation of relative motion between the cutting tool and the (raw) workpiece
- NC programs can be edited directly using the NC panel at the machine

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7
Q

Process of the execution of an NC program

A

NC interpreter decodes the information and splits it into geometry and technology data as well as switching commands

 Geometry Data: Comprised of all information describing the tool path to be moved in order to create the geometry of the finished workpiece.

 Technology Data: Used to set e.g. spindle speeds and feed rates

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8
Q

Structure of a Numerical Control
(NC Program, PLC, NC-Interpolator)

A
  • NC programs can be edited directly using the NC panel at the machine. However, many NC programs are created externally and then transferred to the machine
  • PLC is used to map machine-independent NC functions to trigger machine-specific hardware components
  • NC interpolator computes the sequence of synchronized movements of the feed drive axes -> needed to create the workpiece contour
    o It outputs the setpoint values for the position control loops for feed drives
    o The slowest axis (e.g. due to weight) sets the standard/maximum for the velocity parameters
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9
Q

Task distribution between NC and PLC in Machine Tools: Tasks of NC

A
  • Geometrical path information
  • Technical instructions
  • Identification of switching commands inside the NC program
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10
Q

Task distribution between NC and PLC in Machine Tools: Tasks of PLC

A
  • Link between switching controls and feedback from the machine
  • Conversion of control commands for switching units
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11
Q

NC-internal Information Flow: NC-Interpreter

A

o Functions as a syntax analyzer (parser)  translates different NC program formats and input data into a consistent internal form (kept in random access memory)

o NC interpreter sends commanded boundary coordinates, the interpolation mode and the feed rate for each NC sentence to the Geometry Data Preparation module

o Switching commands are transferred to the PLC -> Still have to be synchronized

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12
Q

NC-internal Information Flow: Geometry Data Preparation

A

o NC computes several geometric transformation (e.g. zero point offset, tool corrections) -> Tool Path offset is continuously calculated based on the current tool geometry
o Velocities and accelerations for speed profile preparation are adapted to the boundary conditions of the machine
o Look-Ahead functionality: Analyzes multiple NC sentences ahead of the movement

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13
Q

NC-internal Information Flow: Interpolator

A

o Computes intermediate points along the path, defined by the NC sentence -> Aggregated path movement is divided into its partial contributions of all single axes

o Linear, circular and spline segments are discretized by a set of interpolated points -> Distribution is equidistand in time (IPO cycle time), depends on the pre-processed speed profiles

 The more points are calculated, the closer the approximation is to the real shape (-> also depends on the clock time of the processor)

o Integration of compensation functionality and compensation tables

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14
Q

NC-internal Information Flow: Axis Control

A

Feed drives are provided with cyclically transferred setpoint values
-> All steps from interpolation until output of axis setpoint are performed within NC channels. -> Each channel may contain multiple axes and spindles (synchronously or asynchronously controlled)

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15
Q

Instructions for Numerical Controls -> What needs to be described in the program?

A

Description of tool path
 Indirectly: Workpiece geometry
 Directly: Tool center point (TCP) trajectory including (position) compensations

Technology Information:
 E.g. number of revolutions or feed rate

Switching commands
 Spindle on (clockwise/counter-clockwise)
 Tool changes

Synchronization (Different tools on the same workpiece)
 Wait commands for multi-slide machining
 Control commands for switching tables, loading systems etc.

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16
Q

NC-Programming Approaches

A
  • Textual -> Drawing
  • Shopfloor-oriented -> Drawing/CAD File
  • CAx-based -> CAD file
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17
Q

NC-Programming Approaches: Textual

A

o Worker separates the final workpiece into manufacturing features based on a technical drawing (usually paper-based) -> Largest amount of work is consumed by the description of the tool path
 Sampling points not depicted in the drawing have to be calculated manually by the programmer

o Tables, Experiences, Computations
o Programming of geometry
o Programming of technology

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18
Q

NC-Programming Approaches: Shopfloor-oriented (SFP)

A

Programmer gets to set up a sequence of manufacturing operations which he can parameterize with the help of graphical templates -> Corresponding NC code is automatically generated

o Simulation features
o Graphically-interactive, problem-oriented programming of a machine tool:
 Predefined programming interfaces
 Query and suggestions for parameters
 Could allow programming without explicit knowledge of NC code

 Textual and SFP yield a machine-dependent NC program output -> Direct transfer of NC programs onto other machines is usually not feasible
 Changes done by machine operator are normally not fed back into planning department

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19
Q

NC-Cycles

A

 Bundle specific commands and manufacturing operations (e.g. tap machining)
 Sub-program-like structure
 Contain a set of multiple NC lines that can be parameterized via input parameters

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20
Q

NC-Programming Approaches: CAx-Based

A

o Main idea: Utilizing the CAD model received from product design and augmenting it with manufacturing information and commands
o Advantage: High level of automation that can be realized by using existing models and connecting the CAM software with different databases
o Translation of CAM program into NC program is done via a processor and a subsequent post-processor

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21
Q

NC program (G-Code)

A
  • NC code is organized in modal groups -> A code or variable stays in effect until replaced or cancelled by another permitted code
  • A NC program consists of a series of information blocks, which correspond to a particular step in the working process
  • The NC program contains all movements and switching operations which have to be executed in order to move the tool and the workpiece while machining the part -> Part’s geometry is simplified to single linear and circular movements
  • In addition to the standard commands there are special commands, defined and provided by control vendors or developed by machine tool users (for special requirements) -> Cannot be exchanged and executed on different machine tools
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22
Q

NC in the production process: Development&Design

A

Definition of product shape

–> Workpiece Geometry
–> Workpiece Surface
–> Tolerances
–> Material

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23
Q

NC in the production process: Process Planning

A
  • Definition of the manufacturing process
  • Creation of NC programs
  • Simulation of the manufacturing process
  • Machine Scheduling
24
Q

NC in the production process: Manufacturing

A

o (Automated) creation of the final product
o Execution of the created NC programs
o Problem: Programming errors can only be detected by deficient products

25
Q

Process Data Feedback

A

Feedback and subsequent analysis can potentially unlock unused economic potentials (e.g. process-parallel quality analytics) -> Elimination of rejection costs and decreasing lead time

26
Q

Process Data Feedback: Steps

A
  1. Process Data streaming (real-time)
  2. Process-parallel analytics of part & process quality (model-based)
  3. Evaluation assistance software
  4. Process monitoring and optimization
27
Q

One of the biggest challenges in manufacturing data analytics

A

Synchronization and mapping of different data and information sources

28
Q

Data Contextualization within PLM Cycle

A

Contextualization is needed to enable efficient automated optimization processes (deep learning, machine learning etc.) and to derive feasible use cases e.g.
o Monitoring of processes
o Monitoring of machine tool condition
o Workpiece quality estimation
o Cutting tool analytics

29
Q

Computer Aided Manufacturing (CAM)

A

Describes methods and softwares used for the computer-based creation of NC programs

30
Q

Advantage of CAM

A

Complex and time-intensive steps, that cannot be handled economically by humans, are automatically handled by the CAM system

31
Q

Factors to determine if the investment in CAM is reasonable

A

o Number of parts and variants to be machined
o Frequency of changing parts
o Complexity of parts to be machined
o License cost of the CAM system

32
Q

Application fields of CAM (5)

A

o Tool path generation and optimization
o Simulation
o Creation of manufacturing documents (machining plans, clamping plans, tool lists)
o Management of tool and equipment data
o Distributed Numerical Control (DNC)

33
Q

Post-Processor

A

The Post-Processor is a parser which converts one code (CAM-internal tool path description) into another code (NC code). It adapts the machine-independent data to the NC of a specific machine tool.

34
Q

Goal of the post-processor

A

Post-processors are used for translating general CAM tool path data into machine specific NC programs

35
Q

Different Milling Setups

A
  • 3-Axis Milling
  • 3+2-Axis Milling
  • Simultaneous 5-Axis Milling
36
Q

3-Axis Milling

A
  • Constant orientation along the entire path
  • Cutting conditions cannot be adjusted locally
  • Simple process planning
  • Low risk of collision
37
Q

3+2-Axis Milling

A
  • Adaptable relative orientation between tool and workpiece
  • Optimization of cutting conditions possible
  • Medium effort for process planning
  • Low risk of collision after initial orientation setting
38
Q

Simultaneuous 5-Axis Milling

A
  • Simultaneous adjustment of relative orientation may ensure optimal cutting conditions
  • Increased accessibility features
  • Significantly increased planning complexity
  • High risk of collision
39
Q

Advantages of 3- and 3+2-axis milling operations

A

o Smaller amount of axes simultaneously engaged -> Calculations for the path are less complex and less time consuming
o Collisions can easier be predicted
o Singularities (unique mapping of Cartesian positions to complementary axis positions) don’t exist
o Higher feed rates/velocities can be reached, since the positioning is only based on the linear axes

40
Q

Advantages of five-axis milling

A

o Allow an optimal orientation of the cutting tool in relation to the workpiece contour -> May yield a better surface quality and consistent material removal conditions
o Complex workpieces can be manufactured in one or two clamping setups -> saving the time for re-clamping and adjusting the workpiece

41
Q

Simulation

A

Simulation either takes place as a CAM-internal simulation before the post-processor run or as an external simulation after post processor run

42
Q

Necessity for simulation

A
  • Increasing complexity of product portfolio
  • Complex machining technology
  • Simulation of the manufacturing process
43
Q

Simulation types - CAM internal Simulation

A
  • Toolpath-based verification
  • Toolpath-centred machine simulation
44
Q

Simulation: Toolpath-based verification

A

No consideration of machine kinematics and fixtures)

 Consideration of blank, tool and holder geometry in simulation
 Simulation based on the paths generated by the CAM system in the CAM internal format

45
Q

Simulation: Toolpath-Centred machine simulation

A

 Extension of the tool-path-based verification
 Consideration of machine workspace and kinematic behavior (machine model)
 Additional collision checks with further components in the workspace

46
Q

Boundaries of CAM-internal simulation

A

 Errors caused by Post Processor cannot be detected
 Cycle times obtained are not exact, because dynamic limits of the machine are neglected
 Simulated path may deviate from real path

47
Q

Simulation Types: Machine Simulation

A
  • Machine simulation based on NC code
  • Machine simulation with virtual numerical control (VNC)
48
Q

machine Simulation based on NC code

A

 Simulation in CAM system based on machine-specific NC programs after the post-processor run
 Use of an NC emulation to interpret the G-Code
 Transfer of setpoint values to machine model

49
Q

Machine Simulation with virtual numerical control

A

Extension to toolpath-centered simulation

 Provided by controller vendors
 VNCs use the same software kernel for motion generation as the real machine’s NC -> Increased precision of the simulation
 Transfer of realistic lead values from the virtual control machine models

50
Q

Simulation Types - Virtual Machine

A

o May consist of machine model, drive model, control model and optional process model
o Virtual representation of machine control and HMI
o Consideration of the entire machining situation by using a machine and drive model with parameter settings corresponding to the real machine
o Avoiding extensive test using the real machine
o Modifications of individual components are possible
o Effects on other parts of the machine can be analyzed
o Small deviations of predicted and real manufacturing time

51
Q

Benefits of Virtual Machines

A

o Virtual set-up planning
o Virtual process run-in and collision avoidance
o Optimization of NC programs

52
Q

Challenges of Virtual Machines

A

Unknown process physics
 Ideal material removal
 Ideally rigid mechanical systems
 Lead tool paths only

Fixture consideration
 Machining forces
 Vibrations
 Overloads

53
Q

Application of Virtual Machines

A
  • CAM/NC Programming
  • Machine Design
  • Electronics Design
54
Q

Opportunities of today’s NC simulations

A

o Damage-free testing of NC programs
o Virtual ramp-up of NC processes without occupation of machines
o Optimization or preventive compensation possible
o Increased understanding of the process through expert systems at different levels
o Detection of interactions by coupling of multiple simulation systems
o Teaching new employees on virtual machines

55
Q

Limitations of today’s NC simulations

A

o Reliability of the results varies depending on the application
o Often results are not suitable for automated evaluation and must be interpreted by experts
o Modeling effort may be uneconomically high (depends on detail and scope)
o Models are not complete and neglect effects that can have significant impact

o Not fully mature coupling mechanisms between simulation systems
-> Understanding of the process
-> Technical and organizational implementation

56
Q

NC-Internal Information Flow (Steps)

A
  • NC Interpreter
  • Geometry Data Preparation
  • Interpolation
  • Position Control
  • Drive Control

Mechatronics and Control for Production Plants (12 decks)

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