3P2

Developing average cost per item from machining

see lecture notes for more (handout 3-4)

Developing avg cost per item as a function of cutting speed

see lecture notes for more (handout 3-4)

Actuation

Using energy (e.g. hydraulic or electrical energy) to move mechanical parts or machines. The hydraulic jack conveys motion to other parts, by definition it is an "actuator".

Methods of measuring surface finish

surface stylus, and an interferometric microscope

3 regions of tool life curve

- break in period - steady state wear region - failure region

Economics of machining

- production cost and rate are v important - increasing production rate means producing more from available resources - decreasing production cost means less expenditure for the same volume of production - not so easy though - trade-offs occur

Effect of high cutting temperatures

- speeds up wear of cutting tool - can induce thermal damage to machined surface - causes dimensional errors in machined surface REDUCING CUTTING TEMPERATURE REQUIRES HEAVY REDUCTION IN CUTTING SPEED OR FEED => SLOWER PRODUCTION. Hence, coolants are used! Cribb Materials become weaker and softer as they become hotter, hence their wear resistance is reduced. Chemical reactivity generally increases with increasing temperature, thus increasing the wear rate. The effectiveness of cutting fluids can be compromised at excessive temperatures. Because of thermal expansion, workpiece tolerances will be adversely affected

Four common machining processes

- straight turning - cutting off - slab mill - end mill

Modelling cell design issues using petri nets: 1 CAUSALITY

1. Causality sequential firing of transitions via synchronisation e.g. Position part (A) -> start drill (B) -> stop drill (C) -> remove part (D)

An approach to petri net model for PLC program development

1. Check the model for boundedness, deadlock etc 2. Consider additional model elements to ensure system can run continuously, over multiple cycles 3. Identify locations in model where external triggers are needed [inputs] and where actuation signals [outputs] are required. 4. Introduce the necessary handshaking required to ensure appropriate confirmation of PLC- equipment communications 5. Convert PN to ladder logic [or other appropriate IEC61131 standard form] See attached crib

Using petri net models for cell automation

1. Checking the logic of the cell control design 2. Additional Logic for Continuous Operations 3. Interfacing to the Physical Systems 4. Generating Ladder Logic from Petri Nets

An approach to petri net modelling

1. Determine key processing steps/states 2. Determine resources/equipment required 3. For each resource specify: - Triggers [control inputs] - Operations - Pre requisites - Constraints 4. Develop PN model to reflect key processing steps 5. Introduce materials handling steps into PN from 4. 6. Identify allowable states for each resource and develop a PN for that resource 7. Check each PN in 5., 6. to ensure causality, conflict and concurrency conditions and that any upper bounds on capacity are reflected. 8. Combine PNs from 5., 6. to form an overall system PN

Adaptive control definition

Advanced control for machining is defined as the on-line adjustment of process parameters for the purpose of: • optimising production rate [using feed rate, speed] • optimising quality [force, speed] • minimising cost of materials and components [force, speed] • Protecting machine [force, torque, power] NB 1. Requirements are often conflicting 2. Referred to as "adaptive" as control involves adapting process parameters

Robots in manufacturing

Applications - arc welding - cut, grind, debur, polish - palletizing, packaging - spot welding - handling - loading - handling, deburring - unloading - painting - assembly Robot Components - teach pendent - robot controller - robot arm - end effector Types and DOFs See attached Performance measures a) Working Volume b) Payload c) Speed ] operation selection d) Resolution e) Accuracy f) Repeatability g) safety ] operation performance

Greatest factor affecting surface finish

BUE

Machining parameters with greatest effect on surface finish?

Feed per rev (turning): lower feed per rev gives a better surface finish since it reduces the frequency of surface undulations (spiral marks). As feed increases and tool nose radius reduces, tool marks become greater. Cutting tool radius (machining): a larger radius can lead to a -ve rake angle for small depths of cut, leading to burnishing of the surface, surface damage such as tearing and cracking Built-up edge (BUE): BUE refers to metal particulates which adhere to the edge of a tool during machining of some metals. BUE formation causes increased friction and alters the geometry of the machine tool. This, in turn, affects workpiece quality, often resulting in a poor surface finish (scuffing) and inconsistencies in workpiece size.

Controlling automated cell operations

Need to: • Determine logic to ensure acceptable sequence of operations • Communicate logic with equipment But also: • Identify causal/concurrent relationships between operations • Identify possible conflicts between resource movements • Identify possible conflicts / priorities for multiple part productions And: Convert logic model into appropriate PLC logic program (e.g. Ladder Logic) e.g. see attached

PLC functions

See lecture 11/12

Types of chip formation: serrated or segmented

Serrated/Segmented/Discontinuous chips are formed by a series of ruptures occurring approximately perpendicularly to the tool face. Each chip element passing off along the tool face in the form of small segmented chips that may adhere loosely to each other. Formed under the following conditions: i) Brittle workpiece materials ii) Materials with hard inclusions and impurities iii) Very low or very high cutting speeds iv) Large depths of cut v) Low rake angles vi) Lack of an effective cutting fluid vii)Low stiffness of the machine tool

Communications for Manufacturing Decisions: Determinism vs Non Determinism

TRAFFIC LIGHT (deterministic) •guaranteed flow •predictable •inefficient •always a chance of stopping GOOD FOR ?? Heavy traffic (individual) => token passing parallel -- lower in manufacturing hierachy ROUNDABOUT (non deterministic) •not guaranteed - potential bottlenecks •maximum use made of the intersection •only stop in heavy, constant traffic GOOD FOR?? light traffic Heavy traffic (total flow) => ethernet parallel

Communication Standards

The ISO/OSI Reference Model for Communications a general framework for describing different communications standards

Digital manufacturing

The application of digital information [from multiple sources, formats, owners] for the enhancement of manufacturing processes, supply chains, products and services

What affects cost of RM fabrication

The costs of RM parts depends on these parameters: - Volume of the part - Cost of materials - Cost of consumables - Height of the part - Height of supports - Number of slices Labour 0,1-0,5 FTE Space requirements Approx. 25-30m2 for the machine, container, generator stocking room Auxiliary equipment (temporary) - Electro erosion, milling machine and compressed air Peripherals & Consumables - Lifting and transportation device for material handling - Build platform ( first set is delivered with the order) - Cleaning and handling: hand sieves , brush, gloves filter mask - Recoater blades - Antistatic waste bags Maintenance - Software maintenance - Machine maintenance

When might a -ve rake angle be wanted?

This would give much more tool material, making the tool stronger. This would be more useful when shearing harder materials. (but also harder to shear)

Factors affecting workpiece accuracy

Tool design, machine design, installation, material

Internet of Things (IoT)

a world where interconnected, Internet-enabled devices or "things" can collect and share data without human intervention The Internet of things (IoT) is the network of physical devices, vehicles, home appliances, and other items embedded with electronics, software, sensors, actuators, and network connectivity which enable these objects to connect and exchange data..

Discontinuous chips in metal cutting?

consists of segments attached firmly or loosely to each other form because of: - brittle workpiece materials - materials with hard inclusions and impurities - v low or v high cutting speeds - large depths of cut - low rake angles - lack of an effective cutting fluid - low stiffness of the machine tool

Which values in cutting ratio (shear angle phi, rake angle alpha) are set?

rake angle is pre set into machine

Independent variables in cutting process

these include (A) the tool material and coatings, (B) tool shape, surface finish, and sharpness, (C) workpiece material and condition, (D) cutting speed, feed, and depth of cut, (E) cutting fluids, (F) characteristics of the machine tool, and (G) work holding and fixturing

Selective laser melting effect of track overlapping

trade off between small track overlapping, giving rise o a larger unmelted zone, or jhigh track overlapping, leading to a hih temperature zone which can cause vapour formation in the overlap. This leaves as gaseous bubbles and causes the liquid metal to splutter everywhere

Informal approaches to logic

• Immediate: Can execute a solution immediately • Inspection: Solution can be determined after examining the problem • [Structured] Inspection: Solution can be determined after following a set of checks/inspections • Planning Procedure: A formal set of steps is used to determine the approach to solving the problem • Algorithm: An algorithm is executed which generates a solution to the logic problem

See lecture 11/12 for PLC programming examples

Drilling operation Conveyor-Robot coordination

How many a's give same cutting ratio for given shear angle?

2

Modelling cell design issues using petri nets: 2 CONCURRENCY

2. Concurrency 2 states/operations can be enabled simultaneously e.g. Attaching two components to a circuit board

Significance of cutting ratio?

Measure of how thick chip has become

What are V_s and V_c?

Velocity along shear plane and cutting velocity

Heat sources in mechanical cutting operation

In decreasing order of their heat generating capacity 1) The shear front itself, where plastic deformation results in the major heat source. Most of this heat stays in the chip. 2) The tool/chip interface contact region, where additional plastic deformation takes place in the chip, and considerable heat is generated due to sliding friction. 3) The flank of the tool, where the freshly produced workpiece surface rubs against the tool.

Cell automation: automating the decision loop

Objective: Ensuring the required production operations are carried out for each part and that the part is moved between operations as required Decision: how to manage the flow of materials between operations, when to initiate different operations and in what sequence Sensing: machine status, part status Actuation: machine settings, material handler triggers Operations: machining tasks, transportation tasks

Power dissipated in friction

P = F*V_c

Hierarchical nature of manufacturing control system

Production operations -> parts -> products -> orders

P, PI, PID controllers

Proportional control: K = kp • Quick response • Disturbance rejection • There is always a steady-state error • Might cause stability problems (if K is too large) Proportional Integral control: K = kp + ki/s - As above + • Zero steady-state error • Might cause stability problems and oscillations Proportional Integral Derivative control: K = kp + ki/s + kd s - As above + • Improved stability • Increased damping • Sensitive to noise

Cell automation requirements

Receive and interpret part schedules • Ensure the production of one or more parts is completed • Communicate part completion reports to factory computer network • Coordinate the functions of different automated machines/devices • Distribute operational commands to machines/devices • Receive status/task complete reports from machines/devices

Robot control challenges

SERVO - Tracking to desired position (path control options) KINEMATIC - Actuator - end effector conversion DYNAMIC - Load, inertia compensation [as per machining]

Main challenges to AM

SPEED - high volume production is considerably slower compared to conventional manufacturing AFFORDABILITY - financial overheads for running machines and buying feedstock is expensive and potential barrier to commercialisation of AM RELIABILITY - AM not as realiable (cannot attain rejection rates of a few parts per million) IP - potential to infringe copyright on part designs STANDARDS - need a set of standards to provide much needed assurances to businesses and manufacturers that AM processes, materials and technology are safe and reliable EDUCATION - important! to! educate! every1!1!

Cell Level Operations/Cellular Manufacturing

"A style of manufacturing by which parts and products are manufactured in cell units by a single operator who performs much of the work on that part or product." • involving one or more machines • producing families of parts with similar characteristics. • integration of both work-piece and tool handling is typical • Much applies to a section of production line too.

Modelling cell design issues using petri nets: 4 CAPACITY CONSTRAINTS

4. Capacity Constraints e.g. storage buffer can only hold 4 parts

Types of adaptive control

- Adaptive Control Constrained (ACC) • Places a constraint on a process variable • E.g., if the thrust force and the cutting force is excessive, the AC system will changing the cutting speed or feed to lower the cutting force • Most common form of AC e.g. In this system for example if the thrust force and the cutting force is excessive, the AC system will reduce the cutting speed or feedrate to lower the force applied. ACC is relatively simple to implement and often part of the machine tools basic functions - Adaptive Control Optimised (ACO) • Systems that optimise an operation as well as features of ACC • E.g, maximising removal rate • More complex to implement e.g. in this system speed could be adjusted / increased for maximising removal rate while still staying with constraints of force limits. ACO is more complex to implement and tune than ACC

Factors affecting tool wear

- Cutting temp (affected by conditions, fluids) - tool material - contact stresses (affected by cutting conditions, tool shape) - work material Cribb Cutting tools are subjected to: i) High localized stresses at the tip of the tool ii) High temperatures iii) Sliding of the chip along the rake face iv) Sliding of the tool along the newly cut workpiece surface These all cause tool wear which is a gradual process. The rate of tool wear depends on tool and workpiece materials, tool geometry, process parameters, cutting fluids and the characteristics of the machine tool. Tool wear and the changes in tool geometry are characterised as: i) Flank wear Occurs on the relief (flank) face of the tool It is due to (a) rubbing of the tool along the machined surface and (b) high temperatures ii) Crater wear Crater wear occurs on the rake face of the tool. Factors influencing crater wear are: • The temperature at the tool-chip interface • The chemical affinity between the tool and workpiece materials • Diffusion rate increases with increasing temperature, crater wear increases as temperature increases • Location of the max depth of crater wear, KT, coincides with the location of the max temperature at the tool-chip interface iii) Corner (nose) wear Corner wear is the rounding of a sharp tool due to mechanical and thermal effects. It dulls the tool, affects chip formation and causes rubbing of the tool over the workpiece. iv) Notching plastic deformation of the tool tip Tools also may undergo plastic deformation because of temperature rises in the cutting zone. v) Chipping Tools may undergo chipping, where small fragment from the cutting edge of the tool breaks away. Chipping may occur in a region of the tool where a small crack already exists. Two main causes of chipping: Mechanical shock & Thermal fatigue vi) Gross fracture Tools may exhibit gross fracture (catastrophic failure) when subject to extreme conditions and excessive wear.

Serrated chips in metal cutting?

- aka segmented/nonhomogenous - semicontinuous chips with large zones of low shear strain and small zones of high shear strain (shear localisation) - chips have sawtooth appearance

Built-up edge (BUE) chips formed in metal cutting?

- consists of layers of material from workpiece that are deposited on tool tip - as it grows larger, chip becomes unstable and breaks apart ~ 0.5m/s

Types of chips produced in metal cutting?

- continuous chips - built-up edge (BUE) chips - serrated chips - discontinuous chips

Function of chip breaker?

- decreases radius of curvature of chip

What does shear angle affect?

- force and power requirements - chip thickness - temperature

Continuous chips formed in metal cutting?

- formed with ductile materials machined at high speeds and/or high rake angles - deformation takes place along narrow shear zone (primary shear zone) - continuous chips may develop a secondary shear zone due to high friction at tool-chip interface

3 types of wear in cutting tools

- general wear - flank wear - crater wear (increases rake angle if positive)

Why is it important to know cutting forces and power?

- gives power requirements - knowledge of forces assists in correct design of machine tools - workpiece must be able to withstand cutting forces without excessive distortion - affected by sharpness of tool tip, as well as shear angle Crib 1. Power and torque requirements for cutting a wide range of materials have to be determined before a drive motor of suitable capacity can be chosen. 2. Cutting force data enables the selection of an appropriate design of the machine tool structure that avoids excessive distortion of the machine tool elements and maintains desired tolerances for the machined part. 3. Selection of appropriate jigs and fixtures for the workpiece so that they can withstand the cutting forces without excessive movement. 4. Cutting forces are usually the main sources for forced vibration between the work and the tool, and therefore their magnitudes are important for the analysis of machine tool dynamics.

How to reduce BUE?

- increase cutting speeds - decrease depth of cut - increase rake angle - use a sharper tool - use an effective cutting fluid - use a cutting tool that has lower chemical affinity for the workpiece material

How to increase shear plane angle?

- increase rake angle - reduce friction angle (beta) or coefficient of friction

Shear strain?

- large shear strains arise due to low shear angles, or low or negative rake angles - deformation takes place in narrow zone thereofore high shearing rate

Process issues with laser melting

- parts are built on build platforms and need to be removed, usually by wire EDM - supports are sometimes needed (don't just anchor, often offer a conductive path) - complex heat flow paths can lead to reduced precision, due to reduced particle melting. It also leads to increased distortion, especially on thin sections - gas pores arise from powder surface chemistry modification and/or trapped gas in particles that are released during melting and locked in during solidification - balling - solidication of melted material into spheres, due to lack of wettability with previous layer, driven by surface tension and related directly to melt pool characteristics - delamination -separation of successive layers due to inappripriate melting overlap with previous underlying solidified powder or incomplete particle melting. macroscopic effect that cannot be repaired post processing Likely causes of variation from crib Possible Causes for the variations observed • The production of the cylinders is produced at various points on the bed. It is likely that there is a problem with the optical train given that the centre of the bed, near to the optical axis, is performing in control and within specification. This could be due to optical misalignment or a damaged imaging system (less likely since the symmetric about the bed). • Operator mistakes or set-up conditions may change process mean. The manufacturer may have only built cylinders in the middle of the machine, which may explain their data compliance. • It is important that all STL file code elements are the same for each cylinder, i.e equal number of tessellations across the part. Curved surfaces such as cylinder walls are particularly susceptible to low resolution STL files. Was this the case? • Are there material variations across the bed? • There may be powder level variations across the bed which will change the melt response of the material. Is the levelling arm working consistently across the bed? Has it been calibrated? Is it damaged? Corrective actions • Make at better assessment of the optical characteristics of the laser system. Repeat the validation trials using only positions, 7, 8, 9, 12, 13, 14, 17, 18 & 19. Looking at the charts, it is likely this will result in better compliance. If so, only operate the machine in these locations. This will reduce the build rates and increase costs.

What does cutting fluid do?

- reduces friction, which affects shear angle phi - reduces effect of BUE Crib it is clear that cutting fluid can reduce the power loading on a machine which would reduce any potential dynamic instabilities. In addition, cutting fluid removes heat by carrying it away from the cutting tool/workpiece interface. This prevents tools from exceeding their thermal operating range beyond which the tool softens and wears rapidly. Fluids also lubricate the cutting tool/workpiece interface, minimizing the amount of heat generated by friction. A fluid's cooling and lubrication properties are critical in decreasing tool wear, extending tool life, and maintaining part quality by achieving the desired size. finish and shape of the workpiece. A secondary function of metalworking fluid is to remove chips and metal fines from the tool/workpiece interface. To prevent a finished surface from becoming marred, chips generated during machining operations must be continually flushed away from the cutting zone.

Factors affecting SI (fatigue life and corrosion resistance)

- temperature - residual stresses - metallurgical transformations - surface plastic deform, tearing, cracking

Dependent variables in cutting process

- type of chip produced - force and energy dissipated during cutting - temp rise in workpiece, tool, chip - tool wear and failure - surface finish and surface integrity of workpiece

Sources of vibration in machine tools

- unbalanced mass - misalignment - pressure variations - teeth engagement faults - bearing defects - tools engagement Thermal errors largest single source of error in precision manufacturing today • Due to a combination of effects... - Room environment - Coolants - People (100 W bulbs) - Machine itself - Machining process • Energy transferred to the structure, tooling, workpiece and metrology or scales via conduction, convection and radiation. • Estimated to account for some 40% of all errors

Different types of automation

-Automation of basic operations - set up (fixturing, coolant, swarf, motors ...) - machine - shut down (fixturing, coolant, swarf, motors ...) -Automation of operation sequence -Automation of part handling -Automation of operation variety management - tool handling & selection - changing instructions -Automation of monitoring, maintenance functions

Human-like, "anthropomorphic" robots

3 aiii) Human like (Anthropomorphic) robots are becoming more popular in industrial robot applications because: a) This type of robot is the most dextrous allowing it to carry out a wide variety of tasks. (Packaging, Assembly, Welding..) b) Production systems and incorporated robots have to be as flexible possible to handle product change and customisation requirements. c) They can have a longer operational life as they can be repurposed to a wide range of activities.

Modelling cell design issues using petri nets: 3 CONFLICT/RESOURCE CONSTRAINT

3. Conflict/Resource Constraint e.g. Loading of two parts with one resource

Digital twin

A digital twin is a digital replica of a living or non-living physical entity. By bridging the physical and the virtual world, data is transmitted seamlessly allowing the virtual entity to exist simultaneously with the physical entity

Industrie 4.0

A framework for enabling the integration of physical and digital resources, services and humans resources in manufacturing in real time. • Vertical integration and networked manufacturing systems • Horizontal integration through value networks • End-to-end digital integration of engineering across the entire value chain Related technologies Vertical Integration Industrial internet • Data analytics • Intelligent control & optimisation • Human Machine interfaces • Machine to machine comms • Autonomous production Horizontal Integration • IoT infrastructure • Cloud based data management • Security & privacy methods • Real time SC control & optimisation • Automated identification Value Chain Integration • CAD • Simulation • Real time emulation • Digital twins • Customer in Design • AR/VR

The ISA95 / ISA88 Factory Decision & Control Standard

A standard way of describing manufacturing control processes in terms of - Object types - Data - Data flows - Functions at different levels of the control hierarchy

Types of chip formation: semi/discontinuous

Also called segmented or nonhomogeneous chips. They are semicontinuous chips with large zones of low shear strain and small zones of high shear strain (shear localization). Caused by cyclical chip formation. Formed under the following conditions: i) Associated with difficult to machine metals at high cutting speeds such as titanium alloys, nickel-base super alloys, and austenitic stainless steels. ii) Phenomenon also found with more common work metals (e.g., steels), when they are cut at high speeds.

Types of control charts

Attributes - product characteristic that can be evaluated with a discrete response e.g. good-bad, yes-no p-chart portion defective in sample c-chart number of defects in an item Variables - for variables that have continuous dimensions e.g. length, weight, speed, strength R-chart used to control dispersion of process x-bar chart used to control central tendency of chart for x-bar and R, the process average and process variability (Range) must be in control to deliver a successful process operation

Control requirements in a machining operation

Can improve: - Better machine design for improved control [see Bill's lectures] - Design of effective control systems

Cell level operations

Cellular Manufacturing: "A style of manufacturing by which parts and products are manufactured on cell units by a single operator who performs much of the work on that part or product." • involving one or more machines • producing families of parts with similar characteristics. • integration of both work-piece and tool handling is typical • Much applies to a section of production line too.

Types of chip formation: continuous

Continuous chips are formed by the continuous plastic deformation of metal without fracture in front of the cutting edge of the tool, with a smooth flow of the chip up the tool face. Formed under the following conditions: i) Formed with ductile materials ii) Machined at high cutting speeds iii)Machined at high rake angles iv) Machined at small feeds v) Low tool/chip friction

The Manufacturing Control Hierachy

Control loop for each task within the factory - see attached At bottom of manufacturing hierachy: - Transforming • Machine Tools • Moulding • Heating - Transporting • Robots • Conveyors - Services • Pumps • Motors Crib explanation i) The responses for this question might refer to a diagram like the one below which was used as the basis for these discussions in the lectures. A good response will discuss the varying requirements for data in terms of timeliness, volume and complexity as the control focus shifts from task to part to product and to order. The hierarchy is important because the higher layer will aggregate data from the lower layers which keeps the communication and computing system manageable. Good students will also mention the determinisitic constraints on lower level operations where real time control required guarantees of control system performance. Diagram order - non-real time, complex data, large data volumes product - non-determinism part - real time/time critical, simple data, small data task - determinism

What happens in idealised cutting model?

Cutting tool moves to left along workpiece at a constant velocity and depth of cut

Meter Box Assembly Cell

Example of cellular manufacturing • Integrated machining and material handling • Fixturing • Multiple Parts • Programmable Logic Controller (PLC) Based Cell Coordination Loading Robot • Control/Trigger: Previous part loaded to output • Operations: Move part A, Part B to jig, Move screwed part to output • Pre Requisites: Parts A, B in buffers, Part in jig [for B loading] or Jig Empty [for A loading], Output buffer empty for unloading • Other Constraints: Table stationary, screwdriver Robot idle Screwdriver Robot • Control/Trigger: Detected part below • Operations: Fixturing / Screw Part A to B / Remove Fixturing • Pre Requisites: Screw available, jig in place, parts in jig • Other Constraints: Table stationary, Loading Robot idle Machine oriented logic (not part oriented logic) ... If loading robot available if jig 1 in position if jig empty if Part A in buffer move Part A to jig 1 endif endif endif Endif ...

Adaptive machine control

For expensive machines and / or components additional control requirements are sometimes employed. Advanced control for machining is defined as the on-line adjustment of process parameters for the purpose of • optimising production rate [using feed rate, speed] • optimising quality [force, speed] • minimising cost of materials and components [force, speed] • Protecting machine [force, torque, power] NB 1. Requirements are often conflicting 2. Referred to as "adaptive" as control involves adapting process parameters Adaptive Control Constrained (ACC) • Places a constraint on a process variable • E.g., if the thrust force and the cutting force is excessive, the AC system will changing the cutting speed or feed to lower the cutting force • Most common form of AC Adaptive Control Optimised (ACO) • Systems that optimise an operation • E.g, maximising removal rate • More complex to implement see attached for an example

What is cutting force?

Force that acts in direction of cutting speed and supplies energy required for cutting

Sensing

Issues • cost • accuracy • timeliness • repeatability • reliability • maintainability --> all make up: • Number of sensors • Location of sensors • Type of Sensors • direct v indirect • Overall "Value of Sensing" - trade-off between cost of purchase/install/maintain vs improved performance

AM in automotive

Large demand for complex metal components • Quality sensitive as parts have to match machined components • Production volumes and speeds requirements much higher than AM can provide • Currently only used in extreme high end applications • By 2021, 40% of manufacturing enterprises will establish 3D printing centres of excellence. (Gartner) BUT AM is out of reach of mainstream manufacturing enterprises AM slow to increase its current share of the machine tool market (0.6%)

Confirmation/handsaking

Most machines are equipped with an operational signal which can be incorporated as a confirmation flag for the cell controller (typically a PLC). This introduces an additional state into the controller operation but greatly enhances reliability and diagnostic capability. The process is called handshaking

PLC input languages

Notes • For simple systems: PLC coding can be intuitive and written as boolean expressions or as ladder logic directly by the engineer • For complex systems: require some form of methodology - Approach 1: produce state model to identify required internal variables (Finite State Modelling - see attached) - Approach 2: a more formal approach based on Petri Nets Crib • ladder logic: programming as a ladder of logic steps: simple, visual and intuitive • SFC (sequential function charts): programming as a graphical flow chart: visually appealing, follows flow chart logic, allows nesting Graphical environment for plc code development • Flowchart approach to logic representation • Allows for nesting of logic code • Uses 3 logical elements: - Step - Transition - Flow line • Can generate equivalent ladder code • IEC 848 standard • Function block diagram: extending ladder like approach by adding libraries of functions: easy reuse, allows nesting • A further graphical approach for representing PLC logic • Allows for more complex functions to be developed [and reused] in PLC environment • IEC1131 standard • Structured text: programming language approach: similar to standard programming languages, easy for programmers to use More formalised text based programming language • Recognising that PLCs now have full computer capabilities • Instruction list: low level assembler like code: efficient coding Use of standards enables re use of code/code modules/code libraries simplifies the task of plc programmersenables tools for developing and analysing PLC programmes to be developedenables multiple manufacturers PLC devices to be used simplifies portability of code • Low level programming language • Similar to assembler • Efficient coding

Machine tool automation and control

Operation • Transforming a part with one or more (cutting) operations from state A to B within specification Control problem • Ensuring the selected cutting process provides a result that is within specification - Sensing: tool position - Actuation: start, movement, finish - Decision: trajectory to be followed referred to as position control Automation needs • Providing instructions for start, operation, finish • Auxiliary Support

Robot automation and control

Operation • Transport or transform part with one or more operations from location A to B, and from State A to B within specification Control Problem • Ensuring the selected transportation process provides a result that is within specification - Sensing: dimension (robot position, part location) - Actuation: start, movement, finish - Control: following selected process (trajectory) within tolerance Automation Needs Providing instructions for start, operation, finish • Auxiliary Support • Standalone Operation Control Challenges SERVO - Tracking to desired position (path control options) KINEMATIC - Actuator - end effector conversion DYNAMIC - Load, inertia compensation [as per machining] (can be disturbances as well)

Power input in cutting

P = F_c*V

Power dissipated in shear plane

P = F_s*V_s

PC vs PLC for cell automation

PC - graphical user interfaces - easy and open networking - excellent computational / memory facilities - relatively low initial cost (for multiple applications) BUT easier to hack PLC - operating systems designed for multi tasking capabilities - robustness of input/output handling - reliability - easy problem diagnosis/recovery - real time performance Clibb • reliability: PLCs rarely crash and are able to run 24/7 • programmability: programmability is standardised on PLCs. It is often more cumbersome • safety: PLCs are equipped to programme for safety measures as a matter of standard operation • ruggedness: PLCs come with built in I/O isolation • security: there are fewer instances of security breaches with PLCs although this has occured • cost: for the amount of computing power PLCs are far more expensive • Computing capability: PCs are a more flexible and extendable platform

Role of PLC in factory automation

PLC programming provides a software environment for building sequences of logical operations Most common input is ladder logic Roles: Receive and interpret part schedules • Ensure the production of one or more parts is completed • Communicate part completion reports to factory computer network • Coordinate the functions of different automated machines/devices • Distribute operational commands to machines/devices • Receive status/task complete reports from machines/devices

Communications for Manufacturing Decisions: Real time vs non-real time communication

Real-time communication is a category of software protocols and communication hardware media that gives real-time guarantees, which is necessary to support realtime computing guarantees • Latency free • Uninteruptible operations • Time dependent decisions, actions, operations (at a lower level in manfacturing hierachy) Non real-time communication is a category of software protocols and communication hardware media that don't require realtime guarantees, and for which communication efficiency is more critical than performance • Batched communications • Trial and error communications • No time dependency

Roughness, lay, waviness in context of surface finish

Roughness: Roughness consists of surface irregularities which result from the various machining process. These irregularities combine to form surface texture. Roughness Height: It is the height of the irregularities with respect to a reference line. It is measured in mm or microns. Roughness Width: The roughness width is the distance parallel to the nominal surface between successive peaks or ridges which constitute the predominate pattern of the roughness. It is measured in mm. Lay: Lay represents the direction of predominant surface pattern produced and it reflects the machining operation used to produce it. Waviness: This refers to the irregularities which are outside the roughness width cut off values. Waviness is the widely spaced component of the surface texture. This may be the result of workpiece or tool deflection during machining, vibrations or tool run out. Waviness Width: Waviness height is the peak to valley distance of the surface profile, measured in mm

Merchant's Circle

See Lecture 1&2 in notes for more This is the Merchant's circle diagram which is a convenient way to determine the relationship between the various forces and angles. Two force triangles have been combined with R' and R being replaced by R. The force R can be resolved into two components Fc and Ft (F_c in direction of cutting velocity) 1) Fc and Ft can be determined experimentally, The rake angle a can be measured from the tool, and forces F and N can then be determined. The shear angle f can be determined by the cutting ratio. Now Fs and Fn can also be determined Crib (referring to F_c and F_t) - also see excel The accurate measurement of these two forces is carried out with the use of dynamometers that measure the piezoelectric charges of quartz or the deflections (or strain) in elements supporting the cutting tools. These two components may be used to calculate many important variables in the process of chip formation. The resultant force can also be resolved into two components on the tool face: a friction force, F, along the tool-chip interface, and a normal force, N, perpendicular to the interface. The resultant force is balanced by an equal and opposite force along the shear plane and is resolved into a shear force, Fs , and a normal force Fn. Causes in variation of shear angle Geometry and form violations (non zero angles of inclination, non-sharp tools, radius ends) • Shear takes place over a volume not a plane • Cutting is never continuous • Cracks in the material which is not homogenous • Size effect (larger stresses are required to produce deformation when the chip is small)

Rules of thumb for for determining process for metal AM

Selecting the right technology for your application is crucial and can be boiled down to the following rules of thumb: • CNC machining is best suited for medium to high quantities (less than 250-500 parts) and relatively simple geometries. • 3D printing is generally best for low quantities (or one-off prototypes) and complex geometries (aero, bio, jewellery etc). • When considering metals, CNC can be price competitive even for low quantities, but geometry limitations still apply. • When quantities are high (more than 250 - 500 parts) other forming technologies are more suitable (forging, die casting, metal injection moulding etc) Metal AM vs machining - see attached

Approach to ladder logic programming (STATE MACHINES)

State Machines are used to clarify the different allowable states of the operation in a graphical manner and these states in turn can be used as "internal states" of the ladder logic code. 1. Determine key processing steps 2. Determine resources/equipment required 3. For each resource specify: - Triggers [control inputs] - Operations - Pre requisites - Constraints 4. Identify allowable states for each resource 5. Using key processing steps (1) and allowable state (5) - Identify single or joint states required for the process - develop state model for required operations 6. For each process state identify: - Required inputs from equipment - Required output signals to equipment - Any latching, counting, timer requirements 7. Generate equivalent ladder code to represent each state Limitations of state machines are the lack of analysis tools available and also it is not always 100% straightforward to map state machines into ladder logic or similar control systems codes

Rules for STL format

The STL file format provides two different ways of storing information about the triangular facets that tile the surface of a 3D object. These are called the ASCII encoding and the binary encoding. In both formats, the following information of each triangle is stored: • The coordinates of the vertices. • The components of the unit normal vector to the triangle. The normal vector should point outwards with respect to the 3D model, as shown below. VERTEX RULE - each triangle must share two vertices with neighbouring triangles ALL POSITIVE OCTANT RULE - coordinates of triangle vertices must all be positive TRIANGLE SORTING RULE - triangles appear in ascending z-value order (not always followed) 2019 CRIB gives a different answer instead of triangle sorting rule The STL file format approximates the surface of a CAD model with triangles. The approximation is never perfect, and the facets introduce coarseness to the model as shown. The perfect spherical surface on the left is approximated by tessellations. The figure on the right uses big triangles, resulting in a coarse model. The figure on the centre uses smaller triangles and achieves a smoother approximation. Hence STL file representations of a CAD model can greatly influence the resolution of the additively manufactured part. - see attached image

Computing and communications systems

The figure below outlines the different communication and computing system required for a factory control environment. The systems reflect the properties mentioned in the previous question Computing - PC/Server/Cloud - low cost, high volume data storage - PLC - lower data capacity, time guarantees, electrical isolation Communications - serial, device NET - deterministic, high speed, low volumes - etherCAT, fieldbus - deterministic, higher data volumes - Ethernet, internet - non deterministic, efficient for high volumes

List the principal error generating processes that occur during the operations of a machine tool.

The principal error generating processes are shown in the following figure showing their connection with machining accuracy in terms of contour accuracy, surface roughness, and dimensional accuracy. The machine, cutting tool, and the workpiece form a structural system that has complicated dynamic characteristics. Under certain conditions, vibrations of the structural system can occur which can be divided into three classes 1. Free or transient vibration: resulting from impulses transferred to the structure through its foundation, from rapid motion of heavy masses such as machine tables, or the engagement of the cutting tool. The structure is deflected and oscillates at its natural frequency until the inherent damping causes this vibration to slowly fall away. 2. Forced vibrations: resulting from periodic forces of the system such as imbalanced masses or periodic cutting actions as in multi-tip tools or vibration transmission from nearby machinery. An important consideration when choosing machine tool location in workshops. The machine tool will oscillate at the driving frequency and if this is close to the resonant frequency, the tool will vibrate in natural mode. 3. Self excited vibration: resulting from a dynamic instability: usually resulting from a dynamic instability of the cutting process. This phenomenon is referred to as 'chatter' and operates at a natural mode of vibration.

Statistical Process Control (SPC)

The process of testing statistical samples of product components at each stage of the production process and plotting those results on a graph. Any variances from quality standards are recognized and can be corrected if beyond the set standards. SPC is used to detect and eliminate the sources of variation in the process that could not be attributed to the routine operation of the process. A process that is operating with only chance causes of variation present is said to be in statistical control. • A process that is operating in the presence of assignable causes is said to be out of control. See attached clibb

Types of chip formation: built up edge (BUE)

This type of chip is very similar to the continuous chip. With the difference that it has a built up edge adjacent to tool face. Consists of layers of material from the workpiece that are deposited on the tool tip. As it grows larger, the BUE becomes unstable and eventually breaks apart. Formed under the following conditions: i) Ductile materials ii) Low to medium cutting speeds iii) High tool/chip friction (wrong tool material) iv) Low levels of cutting fluid

How to get thrust force = 0 or negative thrust force?

effects of negative rake angle large shear strains

Numerically Controlled (N/C) Machines

machines that perform operations by following mathematical processing instructions Numerical Control (NC) is a method for automating the movements and support operations of machining components via the insertion of coded instructions Computer Numerical Control (CNC) integrates computer based instructions into NC machines. Programming of NC Machines Based on the dimension specifications of the workpiece and the manufacturing operations to be performed a set of constructions and commands are produced in programme code. These relate to: - geometric movements between workpiece and tool - spindle speeds - feeds - tools - types of travel - adjustments - coolant supply - clamping on/off - etc

Why is economics of metal cutting interesting?

n Production cost and production rate are critically important for a manufacturing operation. n Increasing production rate means producing more from the available resources. n Decreasing production cost means less expenditure for the same volume of production. n If the conditions are so selected to maximize the production rate and minimize the production cost, profit can be maximized. n This cannot always be satisfied....lets try to determine the conditions leading to min. production cost and max. production rate. Crib 4. Machining at low cutting speeds and feed rates increases production cost because of higher machine and operator usage times 5. At high cutting speeds and feed rates, the production cost is also high because of the increased costs of frequent tool replacement, tool re-working, and high power consumption. 6. If the conditions are so selected to maximize the production rate and minimize the production cost, profit can be maximized. 7. The manufacturing engineers role is to minimise the production time and the production cost. These are two contradictory criteria cannot be met simultaneously and a compromise must be made 8. In general feed rates must be set at the maximum possible. Cutting speed has the dominant influence on tool life, which influences the cost of tooling 9. Selecting cutting speeds can be considered in a number of ways: optimum cutting speed for minimum production cost (Vc), or maximum production rate (Vp). 10. Better answers will discuss the existence of the high efficiency operating range as shown in the figure below,

What is Merchant's hypothesis?

shear plane is located where shear stress s maximum, or in order to minimise cutting force

Which of merchant's assumptions accounts for most error in his shear angle predictions?

shear surface is a plane extending upwards from cutting edge Other assumptions A model of this sort is two-dimensional, and to be closely approximated by this ideal model, a machining process should satisfy the following assumptions: • perfectly sharp tool, • plane strain, • constant depth of cut, • constant and uniform cutting velocity, • continuous chip formation, • no built-up edge on tool, • uniform shear and normal stress along shear plane and tool.

Limitations of State Modelling

• Capture of STATE information can be cumbersome • No explicit method for representing transition conditions between states • No formal way to express complex logic - Conflict between operations requiring - Representation of causality - Ensuring events occur concurrently • Lack of analysis tools for assessing - Feasibility of sequence of operations (e.g. avoiding deadlocks) - Boundedness of buffers - Reachability of required conditions - Potential for process simplification

Quality control

• Control - the activity of ensuring conformance to requirements and taking corrective action when necessary to correct problems • Importance - Daily management of processes - Prerequisite to longer-term improvements Examples 1. Hazard analysis 2. Critical control points 3. Preventive measures with critical limits for each control point 4. Procedures to monitor the critical control points 5. Corrective actions when critical limits are not met 6. Verification procedures 7. Effective record keeping and documentation

AM in aerospace market

• Demand from aerospace high due to part consolidation and light-weighting of components • Composite aircrafts lend themselves to the use of Ti instead of Al parts - if costs reduced • However quality is major issue as cost of failure is very high • Attractive market due to existing knowledge and enthusiasm for cost reduction • By 2021, 75% of new commercial and military aircraft will fly with 3D-printed components. (Gartner) BUT Restricted build volumes and speed limits keeps costs high and take-up low. Part precision remains low leading to significant postprocessing requirements and high part costs

AM in bio medical market

• Largest market for AM parts • Demand based on tailoring and complexity • Currently adopting AM, both laser and e-beam • As in aerospace, quality and certification is paramount • Increasing demand for AM • Seeking speed increases and cost reduction BUT AM remains a niche production process for advanced users AM only used for complex features and fails to move beyond specific implants

Automated part handling systems

• Materials integration between cells, between machining centres and other processing operations • Vary in degrees of flexibility => predetermined routing and sequences => predetermined routing variable sequence => free movement in all directions. CONVEYOR Rail, some AGVs, AGV, ROBOT • Selection Criteria material task (s) - variety of them workpiece loads workplace size and environment Cost load

Part storage systems

• Part storage between cells, between machining centres and other processing operations to enable batch / semi batch operations • Vary in degrees of flexibility & control => FIFO Buffers / Accumulation Buffers => Sorting Buffers => Random Access Buffers • Selection Criteria location: in situ vs storage size: part size, volumes manual vs automated access

Introduction to petri net approach for system modelling

• Petri Nets (PN) are a graphical tool which can be used for the modelling, planning, control design and evaluation of manufacturing systems (invented by Carl Adam Petri in 1962). • A Petri Net is a discrete event model which models the change of conditions before and after an event, and the factors required for that event to occur. Need to mark with a 1xN vector

Types of controller: P, PI, PID

• Proportional control: K = kp • Quick response • Disturbance rejection • There is always a steady-state error • Might cause stability problems (if K is too large) • Proportional Integral control: K = kp + ki/s - As above + • Zero steady-state error • Might cause stability problems and oscillations • Proportional Integral Derivative control: K = kp + ki/s + kd s - As above + • Improved stability • Increased damping • Sensitive to noise

Benefits of AM

• Replaces inefficient conventional manufacturing processes • Reduces the amount of waste material • Reduces energy and transport requirements • Compresses the supply chain • Produces optimised products that are more efficient

Merchant's assumptions

• Shear surface is a plane extending upwards from the cutting edge. • The tool is perfectly sharp and there is no contact along the clearance face. • The cutting edge is a straight line extending perpendicular to the direction of motion and generates a plane surface as the work moves past it. • The chip doesn't flow to either side, that is chip width is constant. • The depth of cut remains constant. • Width of the tool, is greater than that of the work. • Work moves with constant, uniform velocity relative tool tip. • No built up edge is formed.

Process capability

• The natural variation of a process should be small enough to produce products that meet the standards required • A process in statistical control does not necessarily meet the design specifications • Process capability is a measure of the relationship between the natural variation of the process and the design specifications Ratio of spec width to 6x standard deviation See lecture 7&8 for full

Servo: Robot Path Control Options

• Trajectory planning and control is a computationally involved task • each trajectory represents a sequence of joint configurations and operations which must be compatible with allowable and desirable movements • Obstacles in work space must be avoided • trade off between true trajectory and point to point control is employed