كل من لة الرغبة في معرفة طرق التصنيع الغير تقليدية


NONTRADITIONAL MANUFACTURING


PROCESSES
Definition
A group of processes that remove excess material by various techniques involving, mechanical, thermal, electrical, or chemical energy (or combinations of these energies) .
They do not use a sharp cutting tool in the conventional sense .
Developed since World War II in response to new and unusual machining requirements that could not be satisfied by conventional methods.
Importance of Nontraditional Processes
»Need to machine newly developed metals and non-metals with special properties that make them difficult or impossible to machine by conventional methods.
»Need for unusual and/or complex part geometries that cannot readily be accomplished by conventional machining.
»Need to avoid surface damage that often accompanies conventional machining
Classification of Nontraditional Processes
»Mechanical - typical form of mechanical action is abrasives or fluid (or both).
»Electrical -electrochemical energy to remove material (reverse of electroplating).
»Thermal –thermal energy usually applied to small portion of work surface, causing that portion to be fused and/or vaporized
»Chemical- chemical etchants selectively remove material from portions of workpart, while other portions are protected by a mask

Mechanical Energy Processes
»Ultrasonic machining(USM)
»Water jet cutting(WJC)
»Abrasive water jet cutting(AWJC)
»Abrasive jet machining(AJM)
Ultrasonic machining(USM)
Abrasives contained in a slurry are driven at high velocity against work by a tool vibrating at low amplitude and high frequencyTool oscillation is perpendicular to work surfaceAbrasives accomplish material removalTool is fed slowly into workShape of tool is formed into part
USM Applications
Hard, brittle work materials such as ceramics, glass, and carbides.
Also successful on certain metals, such as stainless steel and titanium.
Shapes include non-round holes, holes along a curved axis.
Water Jet Cutting (WJC)
Uses high pressure, high velocity stream of water directed at work surface for cutting.
WJC Applications:
Used to cut narrow slits in flat stock such as plastic, textiles, composites, carpet, leather, and cardboard.
Not suitable for brittle materials (e.g., glass).
No environmental pollution.
Ease of automation
Abrasive Water Jet Cutting (AWJC)
When WJC is used on metals, abrasive particles must be added to jet stream usually.
Abrasive Jet Machining (AJM)
High velocity stream of gas containing small abrasive particles
AJM Applications:
Usually performed manually by operator who directs nozzle.
Normally used as a finishing process rather than cutting process.
Applications: deburring, cleaning, and polishing.
Work materials: thin flat stock of hard, brittle materials (e.g., glass, silicon, mica, ceramics)
Electrochemical Machining Processes
Electrical energy is used in combination with chemical reactions to remove material.
Work material must be a conductor
Reverse of electroplating
Processes:
»Electrochemical machining (ECM)
»Electrochemical deburring (ECD)
»Electrochemical grinding (ECG)
Electrochemical Machining (ECM)
Material removal by anodic dissolution, using electrode (tool) in close proximity to work but separated by a rapidly flowing electrolyte
ECM Operation:
Material is deplatedfrom anode workpiece (positive pole) and transported to a cathode tool (negative pole) in an electrolyte bath.
Electrolyte flows rapidly between material, so it does not plate onto tool.
Electrode materials: copper, brass, or stainless steel
ECM Applications
Die sinking -irregular shapes and contours for forging dies, plastic
molds, and other tools.
Multiple hole drilling -many holes can be drilled simultaneously with ECM.
Holes that are not round, since rotating drill is not used in ECM
Burr-free surface, no thermal damage, no tool wear
Irregular cavities may not be produced to the desired shape, since controlling electrolyte flow is difficult
Electrochemical Grinding (ECG)
Special form of ECM in which grinding wheel with conductive bond material augments anodic dissolution of metal part surface
Thermal Energy Processes
Very high local temperatures
Material is removed by fusion or vaporization.
Physical and metallurgical damage to the new work surface.
In some cases, resulting finish is so poor that subsequent processing is required.
Processes..
»Electric discharge machining(EDM).
»Wire electricdischarge machining (Wire EDM).
»Electron beam machining(EBM).
»Laser beam machining(LBM).
»Plasma arc machining (PAM).
Electric Discharge Processes
Metal removal by a series of discrete electrical discharges (sparks) causing localized temperatures high enough to melt or vaporize the metal.
Can be used only on electrically conducting work materials.
Two main processe:
»Electric discharge machining.
»Wire electric discharge machining.
EDM Operation
One of the most widely used nontraditional processes.
Shape of finished work surface produced by a shape of electrode tool
Sparks occur across a small gap between tool and work.
Requires dielectric fluid which creates a path for each discharge
as fluid becomes ionized in the gap.
Material removal rate depends on melting point of work material.
Tooling for many mechanical processes: molds for plastic injection molding, extrusion dies, wire drawing dies, forging dies.
Production parts: delicate parts not rigid enough to withstand conventional cutting forces, machining of hard metals
Wire EDM
Special form of EDM uses small diameter wire as electrode to cut a narrow slot in workpiece
Wire EDM Applications
Used to cut plates as thick as 300 mm for making punches, tools and dies from hard metals, for cutting intricate components for electronics. industry
Wire material ; brass, copper, tungsten.
Electron Beam Machining (EBM)
Uses high velocity stream of electrons focused on workpiece surface to remove material by melting and vaporization.
EBM Applications:
Source of energy is high-velocity electrons.
Applications are similar to those for LBM, generally used for very accurate cutting of metals.
Works on any material.
Ideal for micromachining..
» Drilling small diameter holes(down to 0.05 mm) as compared to depth.
» Cutting slots only about 0.025 mm wide.
Laser Beam Machining (LBM)
Uses the light energy from a laser to remove material by vaporization and ablation.
Laser (Light amplification by stimulated emission of radiation) converts electrical energy into a highly coherent light beam.
LBM Applications:
Used in drilling and cutting metals, nonmetals and composite materials in electronics and automative industries.
Drilling small diameter holes -down to 0.025 m.
Plasma Arc Cutting (PAC)
Uses plasma stream operating at very high temperatures to cut metal by melting.
Source of energy is high-velocity plasma beams (ionized gas) in PAC.
Applications of PAC:
Most applications of PAC involve cutting of flat metal sheets and plates.
Hole piercing and cutting along a defined path.
Can be operated by hand-held torch or automated by CNC.
Can cut any electrically conductive metal.
Most frequently cut metals: carbon steel, stainless steel, aluminum.
Chemical Machining
Material removal through contact with a strong chemical etchant.
Processes include:
» Chemical milling.
» Chemical blanking.
» Photochemical machining.
All utilize the same mechanism of material removal
Applications of Chemical Milling:
Remove material from aircraft wing and fuselage panels for weight reduction. Applicable to large parts where substantial amounts of metal are removed.
Shallow cavities on plates, sheets, forgings and extrusions.
Maximum depth of removal 12mm.
May result in some surface damage.
Mainly used in aerospace industry, also in the fabrication of microelectronic devices.
Chemical Blanking
Uses chemical erosion to cut very thin sheetmetal parts -down to 0.025 mm thick and/or for intricate cutting patterns.
Conventional punch and die does not work because stamping forces damage the thin sheetmetal, or tooling cost is prohibitive, or both.