CNC and Additive Manufacturing Notes

CNC: Introduction

  • Machining:
    • Fundamentally involves removing material, often metal, from a workpiece using cutting tools to achieve desired dimensions.
    • Various machining processes exist, including turning, milling, and boring.
  • Turning:
    • The workpiece rotates in a chuck while the cutting tool moves translationally in two dimensions.
  • Milling:
    • The cutter rotates on a spindle, while the workpiece, fastened to a table, moves in X-Y dimensions.
  • Requirements for Machining:
    • Precise and high-speed rotational motion for good surface finish.
    • Precise position and velocity control of the table drive for dimensional accuracy.
  • Important Parameters:
    • Cutting speed, feed, and depth of cut are crucial in all metal-cutting processes.

Why Computer Numerical Control (CNC)?

  • Modern Manufacturing Demands:
    • Extreme dimensional accuracy and surface finish, which are difficult to achieve manually, even by expert operators.
    • Manual machining can be time-consuming due to frequent dimensional measurements needed to prevent overcutting.

Numerical Control (NC)

  • Definition: Automatically controlling a machine tool based on pre-programmed machining and movement instructions.
  • Part Program:
    • Motion and machining instructions with related numerical data.
    • Used to be written on punched tape.
    • Arranged in blocks of information, each related to a specific operation in a sequence.
  • Punched Tape Operation:
    • Read one block at a time.
    • Each block contained information for a particular machining instruction (segment length, cutting speed, feed, etc.).
  • Information Contained:
    • Final dimensions of the workpiece (length, width, radii of circles).
    • Contour forms (linear, circular, etc.).
    • Motion commands for each axis.
    • Machining parameters (cutting speed, feed rate).
    • Auxiliary functions (coolant flow, spindle speed, part clamping).
    • Manufacturing specifications (tolerance, surface finish).
  • Obsolete Media:
    • Punched tapes have been replaced by magnetic and optical disks.

Computer Numerical Control (CNC)

  • Definition: Modern versions of NC machines with an embedded system involving microprocessors and electronics as the Machine Control Unit (MCU).
  • Development:
    • Developed in the 1970s in the US and Japan.
    • More popular in Japan initially.
  • Functionality:
    • Multiple microprocessors and programmable logic controllers work in parallel.
    • Simultaneous servo position and velocity control of several axes for contour cutting.
    • Monitoring of the cutting process and machine tool.

Parts of CNC Machine

  • Input Device:
    • Used to input part programs.
    • Common types: punch tape readers, magnetic tape readers, and computers.
  • Machine Control Unit (MCU):
    • Core of the CNC machine.
    • Performs all control functions.
      • Reads coded instructions.
      • Decodes instructions.
  • Machine Tools:
    • Sliding table and spindle to control position and speed.
    • Tables controlled in the X and Y axes.
    • Spindle controlled in the Z axis.
  • Driving System:
    • Amplifier circuit, drive motors, and ball lead screws.
    • MCU feeds position and speed signals to the amplifier circuit.
  • Feedback System:
    • Transducers act as sensors (measurement system).
    • Monitors position and speed of the cutting tool.

Classification of NC Systems

  • Point-to-point or Contouring:
    • Based on whether the machine cuts metal during workpiece movement.
  • Incremental or Absolute:
    • Based on the coordinate system used for motion commands.
  • Open-loop or Closed-loop:
    • Based on the control system for axis motion control.

Point-to-Point (PTP) Systems

  • Operation:
    • The workpiece or cutting tool moves to the desired position, then the cutting tool performs the task while stationary.
  • Typical Applications:
    • Hole operations (drilling, boring, reaming, tapping, punching).
  • Path Significance:
    • The path and feed rate between points are not significant since cutting occurs only when stationary.
  • Control Requirement:
    • Only the final position of the tool needs to be controlled.

Contouring Systems

  • Operation:
    • The tool cuts while the axes of motion are moving (e.g., milling).
    • All axes may move simultaneously at different velocities.
  • Nonlinear Paths:
    • Axial velocity changes, even within a segment.
    • Cutting a circular contour requires sinusoidal rates of change in both axes.
  • Motion Controller Requirement:
    • Synchronize axes of motion to generate a predetermined path (line or circular arc).

Coordinate Systems

  • Definition: Translational and rotational motion coordinates.
  • Translational Axes:
    • Each axis defines a direction in which the cutting tool moves relative to the workpiece.
    • Main axes: X, Y, and Z.
    • Z axis is perpendicular to both X and Y to create a right-hand coordinate system.
    • Positive motion in Z moves the tool away from the workpiece.
  • Origin:
    • Location is generally adjustable.
  • Lathe Coordinate System:
    • Infeed/radial axis is the X-axis.
    • Carriage/length axis is the Z-axis.
    • No Y-axis is needed because the tool moves in a plane through the rotational center.
  • Drilling and Milling Coordinate System:
    • X and Y axes are horizontal.
    • Positive motion in the drill moves the X axis from left to right, the Y axis from front to back, and the Z axis toward the top.
  • Lathe Specifics:
    • Only two axes are required.
    • Since the spindle is horizontal, the Z axis is also horizontal.
    • The cross axis is denoted by X.
    • A positive position command moves the Z axis from left to right and the X axis from back to front.

Incremental Systems

  • Definition:
    • Movements are expressed as displacements along coordinate axes relative to the final position of the previous program block.
  • Example:
    • For rectilinear motions (A-B, B-C, C-D, D-E, E-F, F-A), motion parameters along the X-axis would be given as 50, 20, 60, -30, -70, and -30, respectively.

Absolute System

  • Definition:
    • All position coordinates are referred to one fixed origin called the zero point.
  • Zero Point:
    • Can be defined at any suitable point within the machine tool table limits and can be redefined.
    • Remains valid until redefined.
  • Example:
    • Considering the X-coordinate for point A as zero, the X-coordinate for points B and C would be 50 and 70, respectively.
  • Modern CNC Systems:
    • Permit both incremental and absolute programming methods.
    • The method can be changed within a part program.

Part Programming

  • Definition:
    • A set of instructions (blocks) for the machining operation.
    • Each block contains code words in sequence.
  • Contents of Each Block:
    • Coordinate values (X, Y, Z, etc.) to specify tool motion relative to the workpiece.
    • Motion code words and interpolation parameters (point-to-point, continuous straight, continuous circular).
    • The CNC system computes motion command signals from these code words.
    • Machining parameters (feed rate, spindle speed, tool number, tool offset compensation).
    • Codes for initiating machine tool functions (spindle start/stop, coolant on/off, optional stop).
    • Program execution control codes (block skip, end of block codes, block number).
    • Statements for configuring subsystems (programming the axes, configuring the data acquisition system).
  • Typical Sequence of Operations:
    • Introductory functions (units, coordinate definitions, absolute or relative).
    • Feeds, speeds, etc.
    • Coolants, doors, etc.
    • Cutting tool movements and tool changes
    • Shutdown

G-Codes (Preparatory Functions)

  • G00 - Rapid move (not cutting)
  • G01 - Linear move
  • G02 - Clockwise circular motion
  • G03 - Counter-clockwise circular motion
  • G04 - Dwell
  • G05 - Pause (for operator intervention)
  • G08 - Acceleration
  • G09 - Deceleration
  • G17 - X-Y plane for circular interpolation
  • G18 - Z-X plane for circular interpolation
  • G19 - Y-Z plane for circular interpolation
  • G20 - Turning cycle or inch data specification
  • G21 - Thread cutting cycle or metric data specification
  • G24 - Face turning cycle
  • G25 - Wait for input to go low
  • G26 - Wait for input to go high
  • G28 - Return to reference point
  • G29 - Return from reference point
  • G31 - Stop on input
  • G33-35 - Thread cutting functions
  • G35 - Wait for input to go low
  • G36 - Wait for input to go high
  • G40 - Cutter compensation cancel
  • G41 - Cutter compensation to the left
  • G42 - Cutter compensation to the right
  • G43 - Tool length compensation, positive
  • G44 - Tool length compensation, negative
  • G50 - Preset position
  • G70 - Set inch based units or finishing cycle
  • G71 - Set metric units or stock removal
  • G72 - Indicate finishing cycle
  • G72 - 3D circular interpolation clockwise
  • G73 - Turning cycle contour
  • G73 - 3D circular interpolation counter clockwise
  • G74 - Facing cycle contour
  • G74.1 - Disable 360 degree arcs
  • G75 - Pattern repeating
  • G75.1 - Enable 360 degree arcs
  • G76 - Deep hole drilling, cut cycle in z-axis
  • G77 - Cut-in cycle in x-axis
  • G78 - Multiple threading cycle
  • G80 - Fixed cycle cancel
  • G81-89 - Fixed cycles specified by machine tool manufacturers
  • G81 - Drilling cycle
  • G82 - Straight drilling cycle with dwell
  • G83 - Drilling cycle
  • G83 - Peck drilling cycle
  • G84 - Taping cycle
  • G85 - Reaming cycle
  • G85 - Boring cycle
  • G86 - Boring with spindle off and dwell cycle
  • G89 - Boring cycle with dwell
  • G90 - Absolute dimension program
  • G91 - Incremental dimensions
  • G92 - Spindle speed limit
  • G93 - Coordinate system setting
  • G94 - Feed rate in ipm
  • G95 - Feed rate in ipr
  • G96 - Surface cutting speed
  • G97 - Rotational speed in rpm
  • G98 - Withdraw the tool to the starting point or feed per minute
  • G99 - Withdraw the tool to a safe plane or feed per revolution
  • G101 - Spline interpolation

M-Codes (Miscellaneous Functions)

  • M00 - Program stop
  • M01 - Optional stop using stop button
  • M02 - End of program
  • M03 - Spindle on CW (clockwise)
  • M04 - Spindle on CCW (counter-clockwise)
  • M05 - Spindle off
  • M06 - Tool change
  • M07 - Flood with coolant
  • M08 - Mist with coolant
  • M08 - Turn on accessory (e.g., AC power outlet)
  • M09 - Coolant off
  • M09 - Turn off accessory
  • M10 - Turn on accessory
  • M11 - Turn off accessory or tool change
  • M17 - Subroutine end
  • M20 - Tailstock back
  • M20 - Chain to next program
  • M21 - Tailstock forward
  • M22 - Write current position to data file
  • M25 - Open chuck
  • M25 - Set output #1 off
  • M26 - Close chuck
  • M26 - Set output #1 on
  • M30 - End of tape (rewind)
  • M35 - Set output #2 off
  • M36 - Set output #2 on
  • M38 - Put stepper motors on low power standby
  • M47 - Restart a program continuously, or a fixed number of times
  • M71 - Puff blowing on
  • M72 - Puff blowing off
  • M96 - Compensate for rounded external curves
  • M97 - Compensate for sharp external curves
  • M98 - Subprogram call
  • M99 - Return from subprogram, jump instruction
  • M101 - Move x-axis home
  • M102 - Move y-axis home
  • M103 - Move z-axis home

Advantages of CNC Machining

  • Accuracy and Precision: High accuracy and precision in machining.
  • Time Efficient: Reduced job completion time.
  • Reduced Labor: Fewer operators needed.
  • Reliability: Reliable operation.
  • Design Complexity: Ability to create complex designs.
  • Low Maintenance: Low maintenance requirements.
  • Waste Reduction: Produces little to no waste.
  • Defect Reduction: Zero defects and greater accuracy.
  • Production Efficiency: Faster and more efficient production.
  • Assembly Efficiency: Quicker Assembly.
  • Safety: Enhanced personnel safety.
  • Energy Efficiency: Reduction in energy consumption.

Smart Manufacturing (SM)

  • Definition: A technology-driven approach using Internet-connected machinery to monitor production processes.
  • Goal: Automate operations and use data analytics to improve manufacturing performance.
  • Relationship to IIoT: A specific application of the Industrial Internet of Things (IIoT).
  • Deployment: Embedding sensors in manufacturing machines to collect data on operational status and performance.
  • Data Analytics:
    • Traditionally, data was kept in local databases and used for post-failure assessment.
    • Now, analyzing data across facilities allows engineers to predict failures and perform preventive maintenance.

Technologies Enabling Smart Manufacturing

  • Artificial Intelligence (AI) / Machine Learning:
    • Enables automatic decision-making based on collected data.
    • Analyzes data to make intelligent decisions.
  • Drones and Driverless Vehicles:
    • Increases productivity by automating rote tasks.
  • Blockchain:
    • Provides a fast and efficient way to record and store data with immutability and traceability.
  • Edge Computing:
    • Turns machine-generated data into actionable insights by enabling data analytics at the source.
  • Predictive Analytics:
    • Analyzes data from various sources to anticipate problems and improve forecasting.
  • Digital Twins:
    • Models processes, networks, and machines in a virtual environment to predict problems and boost efficiency.

How SM Differs from Traditional Manufacturing

  • Traditional Manufacturing:
    • Focuses on economy of scale and machine utilization.
    • Machines are kept running continuously.
    • Large inventories are kept to fulfill potential orders.
    • Batch-and-queue processing is used.
  • Smart Manufacturing:
    • Collaborative, fully-integrated system that responds in real-time to changing conditions and demands.
    • Optimizes the manufacturing process using Internet-connected machinery.
    • Identifies opportunities for automating operations and uses data analytics to improve performance.

Reverse Engineering Purposes

  • Dissection and Analysis: Analyzing existing product for improvements.
  • Experience and Knowledge: Expanding an individual's personal database.
  • Competitive Benchmarking: Comparing against competitors.

Introduction to Additive Manufacturing

Additive Manufacturing (AM) Definition

  • Definition: A process using digital 3D design data to build a component in layers by depositing material.
  • WYSIWYB: "What You See Is What You Build" Process.

Additive vs. Subtractive Manufacturing

  • Additive Manufacturing: builds parts layer by layer.
  • Subtractive Manufacturing (CNC) removes material to create parts.
  • Advantages of AM over CNC AM can produce parts with:
    • Deep cavities
    • Undercuts
    • Internal Features

Distinction Between AM and CNC Machining

  • Similarities:
    • Both are computer-based technologies used to manufacture products.
  • Differences:
    • CNC is primarily a subtractive process.
    • AM is an Additive process.
    • CNC requires a block of material at least as big as the part to be made.

The Generic AM Process

  • Eight Stages: CAD, Conversion to STL, Transfer to AM Machine, Machine Setup, Build, Removal, Post-processing, Application.
  • Step 1: CAD
    • All AM parts must start from a software model that fully describes the external geometry.
    • Any professional CAD solid modeling software can be used but the output must be a 3D solid or surface representation.
    • Reverse engineering equipment (e.g. laser and optical scanning) can also be used to create this representation.
  • Step 2: Conversion to STL
    • The CAD model is converted to an STL (stereolithography) file.
    • This file describes the external closed surfaces of the original CAD model and forms the basis for calculation of the slices.
  • Step 3: Transfer to AM Machine and STL File.
    • The STL file describing the part must be transferred to the AM machine.
    • Here, there may be some general manipulation of the file so that it is the correct size, position, and orientation for building.
  • Step 4: Machine Setup
    • The AM machine must be properly set up prior to the build process.
    • Such settings would relate to the build parameters like the material constraints, energy source, layer thickness, timings, etc.
  • Step 5: Build
    • Building the part is mainly an automated process and the machine can largely carry on without supervision.
    • Only superficial monitoring of the machine needs to take place at this time to ensure no errors have taken place like running out of material, power or software glitches, etc.
  • Step 6: Removal
    • Once the AM machine has completed the build, the parts must be removed.
    • This may require interaction with the machine, which may have safety interlocks to ensure for example that the operating temperatures are sufficiently low or that there are no actively moving parts.
  • Step 7: Post-processing
    • Once removed from the machine, parts may require an amount of additional cleaning up before they are ready for use.
    • Parts may be weak at this stage or they may have supporting features that must be removed.
  • Step 8: Application
    • Parts may now be ready to be used.
    • However, they may also require additional treatment before they are acceptable for use.
    • For example, they may require priming and painting to give an acceptable surface texture and finish.

Classification of AM Processes

  • Liquid Based
    • Stereolithography
    • Jetting Systems
    • Direct Light Processing
  • Powder Based
    • Selective Laser Sintering
    • Three-Dimensional Printing
    • Fused Metal Deposite Systems
    • Electron Beam Melting
    • Selective Laser Melting
    • Selective Masking Sintering
    • Selective Inhibition Sintering
    • Electro photographic Layered Manufacturing
    • High Speed Sintering
  • Solid Based
    • Fused Deposition Modelling
    • Sheet Stacking Technologies

Additive Manufacturing Processes: Stereolithography (SL)

  • Description:
    • First 3D printing process.
    • Laser-based process using photopolymer resins.
    • Resins react with the laser to form a solid.
    • Produces very accurate parts.
  • Process:
    • Photopolymer resin held in a vat with a movable platform.
    • A laser beam is directed in the X-Y axes across the surface of the resin.
    • The resin hardens where the laser hits the surface.
    • Once the layer is completed, the platform drops down in the Z axis.
    • Subsequent layers are traced out by the laser until the entire object is completed.
  • Support Structures:
    • Required for parts with overhangs or undercuts.
    • Need to be manually removed.
  • Post-Processing:
    • Objects need to be cleaned and cured.
    • Curing involves subjecting the part to intense light to fully harden the resin.
  • Advantages:
    • One of the most accurate 3D printing processes.
    • Excellent surface finish.
  • Limitations:
    • Post-processing steps required.
    • Material stability over time (can become more brittle).

Additive Manufacturing Processes: Laser Sintering and Laser Melting (SL, SLM)

  • Description:
    • Interchangeable terms for a laser-based 3D printing process using powdered materials.
  • Process:
    • A laser is traced across a powder bed of tightly compacted powdered material.
    • The laser sinters or fuses the particles to each other, forming a solid.
    • As each layer is completed, the powder bed drops incrementally.
    • A roller smoothes the powder over the surface before the next pass of the laser.
  • Build Chamber:
    • Completely sealed to maintain a precise temperature, specific to the melting point of the powder.
  • Post-Processing:
    • The powder bed is removed from the machine.
    • Excess powder is removed, leaving the 'printed' parts.
  • Advantages:
    • The powder bed serves as an in-process support structure for overhangs and undercuts.
    • Complex shapes that could not be manufactured in any other way are possible.

Additive Manufacturing Processes: Fused Deposition Modelling (FDM) & Freeform Fabrication (FFF)

  • Description:
    • 3D printing utilizing the extrusion of thermoplastic material.
    • Most common 3DP process.
  • FDM:
    • Trade name, registered by Stratasys.
    • Industrial-grade 3D printing process since the early 1990s.
  • FFF:
    • Similar process to FDM, but in a more basic form due to patents held by Stratasys.
    • Utilized by entry-level 3D printers.
  • Process:
    • Plastic filament is melted and deposited, via a heated extruder, layer by layer, onto a build platform.
    • Each layer hardens as it is deposited and bonds to the previous layer.

Additive Manufacturing Processes: Laminated Object Manufacturing (LOM)

  • Description:
    • A rapid prototyping system.
  • Process:
    • Layers of adhesive-coated paper, plastic, or metal laminates are successively glued together and cut to shape with a knife or laser cutter.
    • Objects printed with this technique may be additionally modified by machining or drilling after printing.
  • Layer Resolution:
    • Defined by the material feedstock.
    • Usually ranges in thickness from one to a few sheets of copy paper.

Additive Manufacturing Materials

  • Liquid Based
    • Resins.
  • Powder Based
    • Nylon
    • Alumide
  • Solid Based
    • ABS.
    • PLA.

AM Materials: Polymers

  • Nylon (Polyamide):
    • Commonly used in powder form (sintering) or filament form (FDM).
    • Strong, flexible, and durable.
    • Reliable for 3D printing.
    • Naturally white but can be colored.
    • Can be combined with powdered aluminum to produce Alumide.
  • ABS:
    • Common plastic for 3D printing.
    • Widely used on entry-level FDM 3D printers.
    • Particularly strong.
    • Available in a wide range of colors.
  • PLA:
    • Bio-degradable plastic material.
    • Used in resin format (DLP/SL) and filament form (FDM).
    • Available in a variety of colors, including transparent.
    • Not as durable or flexible as ABS.

AM Materials: Ceramics, Paper, Bio Materials and Food

  • Ceramics:
    • Relatively new for 3D printing.
    • Require firing and glazing post-printing.
  • Paper:
    • Used by the proprietary SDL process supplied by Mcor Technologies.
    • Cost-effective material supply.
    • Models are safe, environmentally friendly, easily recyclable, and require no post-processing.
  • Bio Materials:
    • Research into 3D printing bio materials for medical applications.
    • Printing human organs for transplant and external tissues for replacement body parts.
    • Developing food stuffs (e.g., meat).
  • Food:
    • Experiments with extruders for 3D printing chocolate, sugar, pasta, and meat.
    • Research to produce finely balanced whole meals.
  • Digital Materials (Stratasys):
    • Standard Objet 3D printing materials can be combined during the printing process.
    • Form new materials with required properties.
    • Up to 140 different Digital Materials can be realized.

Advantages of Additive Manufacturing

  • Design Complexity and Freedom:
    • Enables production of complex products that cannot be produced in any other way.
    • Lighter and stronger components.
  • Speed:
    • Complex parts can be created within hours.
    • Limited human resources needed.
  • Customization:
    • Allows for mass customization.
    • Products can be personalized according to individual needs at no additional cost.
  • Extreme Lightweight Design:
    • Enables weight reduction via topological optimization.
  • Tool-less:
    • Eliminates the need for tool production.
    • Reduces costs, lead times, and labor.
    • Products can be designed to avoid assembly requirements.
  • Sustainable / Environmentally Friendly:
    • Energy-efficient technology that provides environmental efficiencies.
    • Utilizes up to 90% of standard materials, creating less waste.
    • Lighter and stronger designs reduce the carbon footprint.
  • No Storage Cost:
    • Products can be printed as and when needed.
  • Increased Employment Opportunities:
    • Increases the demand for designers and technicians to operate 3D printers and create blueprints.

Disadvantages of Additive Manufacturing

  • Questionable Accuracy
    • Accuracy disclaimer for many plastic materials.
    • For instance, many materials print to either +/−0.1mm+/- 0.1 mm in accuracy, meaning there is room for error.
  • Support material removal
    • When the volumes are much higher, it becomes an important consideration. Support material that is physically attached is of most concern.
  • Limitations of raw material
  • Considerable effort required for application design and for setting process parameters
  • Material cost Today, the cost of most materials for additive systems ( Powder ) is slightly greater than that of those used for traditional manufacturing .
  • Material properties A limited choice of materials is available. Actually, materials and there properties (e.g., tensile property, tensile strength, yield strength, and fatigue) have not been fully characterized. Also, in terms of surface quality, even the best RM processes need perhaps secondary machining and polishing to reach acceptable tolerance and surface finish.
  • Intellectual property issues The ease with which replicas can be created using 3D technology raises issues over intellectual property rights. The availability of blueprints online free of cost may change with for-profit organizations wanting to generate profits from this new technology.
  • Limitations of size 3D printing technology is currently limited by size constraints. Very large objects are still not feasible when built using 3D printers.
  • Cost of printers The cost of buying a 3D printer still does not make its purchase by the average householder feasible. Also, different 3D printers are required in order to print different types of objects. Also, printers that can manufacture in colour are costlier than those that print monochrome objects.
  • Unchecked production of dangerous items Liberator, the world’s first 3D printed functional gun, showed how easy it was to produce one’s own weapons, provided one had access to the design and a 3D printer. Governments will need to devise ways and means to check this dangerous tendency.

History of 3D Printing

  • Early Technologies (Late 1980s):
    • Called Rapid Prototyping (RP) technologies.
    • Conceived as a fast and cost-effective method for creating prototypes.
  • 1983 Charles Hull invents Stereolithography (SLA)
    • Charles ‘Chuck’ Hull was the first to develop a technology for creating solid objects from a CAD/CAM file, inventing the process he termed ‘stereolithography’ in 1983.
    • SLA works by curing and solidifying successive layers of liquid photopolymer resin using an ultraviolet laser. The field that came to be known variously as 'additive manufacturing', 'rapid prototyping' and '3D printing' was born.

3D Printing, Additive Manufacturing and Rapid Prototyping

  • 3D Printing & Additive Manufacturing: Synonyms for the same process.
    • Building parts by joining material layer by layer from a CAD file.
  • Rapid Prototyping: Technique of fabricating a prototype model from a CAD file.
    • Rapid prototyping is one of many applications under the 3D printing/additive manufacturing umbrella.

Current and Future Applications of 3D Printing

  • Biomedical Engineering:
    • Creating body parts and parts of organs.
  • Aerospace and Automobile Manufacturing:
    • Prototyping tool.
  • Construction and Architecture:
    • Creating models of layouts or shapes of buildings.
    • Creating entire buildings.