A1 Current Manufacturing Equipment & Techniques Flashcards
(35 cards)
What is manufacturing & why is it important?
Conversion of raw materials into end products & key part of many countries economies e.g. in UK it is 13% GDP & employs 2.5 million people
Difference between manufacturing technology vs system?
Technology is equipment
System is group of resources (plant, people etc.)
Modern manufacturing is about optimising system to get the best out of your technology
5 Ps of Production Operation Management
Product - interface between marketing & production
Plant - tools to manufacture product
Process - combo of people, skills & equipment to manufacture product
Programme - system which organises & controls production operations
People - everyone involved
How does UK Government define HVM (high value manufacturing)?
Application of leading-edge technical knowledge & expertise to creation of products, production services & associated services which have strong potential to bring sustainable growth & high economic value to the UK
What does HVM mean in practice for the UK?
UK will never be able to compete with lower cost base countries, but can compete by adding value to manufactured goods through technological improvement e.g. component/process
3 main process parameters in machining
Speed - of cutting tool relative to workpiece
Feed - distance tool travels per revolution of tool/workpiece
Depth of cut
Main driver in developing machining processes & tooling
Increase productivity & reduce costs
General evolution of cutting tools
Carbon steels, high speed steels, tungsten carbides, ceramics/superhards
For machining of advanced tools (e.g. aerospace alloys), in what way are carbide tools limited?
Surface speed - heat generation at cutting face
Feed per tooth - material toughness
So smaller cuts need to be made at slower speeds to avoid premature tool wear/failure > drop in productivity
How do ceramics/superhard tool inserts help?
Much better heat resistance than carbides so maintain mechanical properties e.g. strength at much higher temperatures (soften at -22000C rather than -870) so productive levels of speed, feed & depth of cut can be used
How did process modelling develop use of ceramics/superhard inserts?
Initial attempts to prevent tool breakage with advanced materials were to reduce speed, feed & depth. Modelling discovered if machining run at very high surface speed (100m/min), inserts get hot enough to soften slightly to overcome brittleness but maintaining cutting performance. Productivity goes up 10x faster than carbide tools
3 different types of vibration during machining operations
Free vibrations - rapid reversals of reciprocating masses, initial engagement of cutting tool
Forced vibrations - unbalanced rotating shafts in machine, intermittent engagement of teeth on milling cutter, transmitted through foundations from other nearby machines operating
Self-excited vibrations/chatter - unwanted relative movement between workpiece & tool during machining
Why is chatter bad & how to avoid
Causes poor surface finish by generating waves, unstable cutting (varying forces) breaks tools
Operator needs to change process parameters to avoid self-excitation > lowers productivity as can’t operate at optimum process parameters
What causes chatter/self-excitation?
Mode coupling (relative motion between tool/workpiece exists in at least 2 directions causing periodic elliptical motion of tool tip) & regeneration of surface waviness (when tool tip moves over the surface already cut)
How does process modelling avoid chatter?
Changes process parameters (increase cutting speed/depth of cut) in real time for stable cutting by knowing what to change to move to nearest stable region (faster/slower) & maximising depth of cut > productivity increases
How to avoid/minimise chatter?
Design machines/tools to be self-damping
Avoid regenerative effects
Use self-tuning machines
Why inspect machined parts?
Process control (helps select process parameters & develop new ones)
Acceptability & conformance (maintain quality & commercial relationships)
Post-assembly performance e.g. balancing of turbine blades
Inspecting equipment
Metrology equipment e.g. vernier callipers, dial gauges, micrometers, profilometers, ultrasonic sensors, endoscopes, coordinate measuring machines
What are CMMs (coordinate measuring machines)?
Structures supporting a sensitive probing system connected to data acquisition system. Enables points in 3D space to be recorded as CAD data > compare against original data for inspection reasons/create new data as part of reverse engineering
Main problem that limits productivity of a CMM
Very slow to allow time between touches for vibrations due to machine motion to dissipate & wait for probe to reposition at pre-calibrated positions
How to improve CMM productivity?
Machine design to promote damping, environment it’s operated in (thermal stability)
Calibration of machine to compensate for systematic errors
Spherical Revo heads for probe systems for optimised movement
Minimise vibrations by moving continuously in 1 direction
Small distances between measuring points
Use machine controller to calculate optimised routes
What’s AM (additive manufacturing)?
Family of automated technologies to create physical parts layer by layer from 3D CAD files
Also known as rapid prototyping/tooling/manufacturing
3D printing, Solid Freeform Fabrication, Direct Digital Manufacturing etc.
Types of materials used in AM
Polymers, metals, ceramics, composites, biocompatible/active materials, food
Stereolithography
UV light solidifies/cures layers of light-sensitive liquid polymer
