Shell Moulding Process

Shell Moulding Process
http://thelibraryofmanufacturing.com/shell_mold_casting.html

From a Handbook
https://books.google.co.in/books?id=tMK6lummtq8C&pg=PA928#v=onepage&q&f=false

Comparison of Metal Casting Processes
http://www.engineershandbook.com/Tables/castchart.htm  Link not working


The Shell Moulding Process: A German Innovation U. Recknagel
To mark the 50th anniversary of the death of the inventor Johannes Croning
The inventor and entrepreneur
Johannes Carl Adolf Croning was born on May 22, 1886, in
Hamburg as the son of a tradesman.
http://www.ha-international.com/pdf/CroningShellMoulding.pdf

A patent for Jonannes Croning
https://patents.google.com/patent/US1966615A/en

Updated on 12 August 2019, 9 .9.2013

Engineering and Technology News July 2019

Process and Product Industrial Engineering Database

Methods Engineering and Value Engineering Database

The Engineer, UK  Manufacturing and Engineering Magazine, UK AZO Materials News

https://phys.org/chemistry-news/materials-science/   https://www.electronicsweekly.com/

Engineering & Management News


Engineering and Technology News August 2019

Safety Improvement - Tailor-Made Safety with FPGAs
July 31, 2019
FPGAs are proving to be extremely reliable and versatile embedded components when system uptime is of the highest priority.
https://www.eeweb.com/profile/mentcs/articles/tailor-made-safety-with-fpgas

Researchers Use Single-Electrode Material to Add Many Functions into a Microchip.
A noteworthy breakthrough in the mission to refine the miniature, self-powered sensors that will progress the Internet of Things. KAUST scientists have successfully combined energy-harvesting, sensing, current-rectifying, and energy-storage operations into one microchip.
https://www.azom.com/news.aspx?newsID=51792   https://discovery.kaust.edu.sa/en

Alibaba chip unit designs RISC-V core
26th July 2019
The core was developed by Alibaba’s IC unit called Pingtouge and called Xuantie 910.
Xuantie 910 is available for licensing and related code will be released on GitHub.
https://www.electronicsweekly.com/news/business/alibaba-chip-unit-designs-risc-v-core-2019-07/


Novel technique makes liquid droplets run uphill
25th July 2019
Hong Kong team moves liquid droplets at record high speed and long distance without extra power.  Mechanical engineers from the City University of Hong Kong (CityU) describe in "Nature Materials", can transport droplets of liquid against gravity and even for the first time along a vertical surface.
https://www.theengineer.co.uk/liquid-droplet-transporting-mechanism/

Versarien, UK-based advanced materials engineering group, has announced that it has secured its first graphene orders from the North American corporate research and development center of a Japanese headquartered company. The Company has placed development orders for 1kg each of Versarien's high purity graphene nano platelets ("GNP-HP") and Nanene.
https://www.graphene-info.com/versarien-receives-graphene-orders-japanese-automotive-company


July 24, 2019


Mazda Motor Corporation is streamlining automotive design on the system level through Siemen's Mentor’s “Capital,” an electrical design software suite designed to simplify the engineering of electrical systems for cars, aircraft, and other sophisticated machines.
https://saemobilus.sae.org/advanced-manufacturing/news/2019/07/mazda-drives-engineering-creativity-using-siemens%E2%80%99-model-based-generative-engineering-tools

LED for torches and worklamps
24th July 2019
Osram is aiming  Osconiq P 3030, it is build around a 1 x 1mm die that can be driven at 1.3A and comes in a specially-developed 3 x 3mm (1.63mm high) SMD epoxy package with lead-frame heat spreading and a silicone lens, at torches and work lamps with a long-life 160 lm LED.
It will have longer lifetime of 70,000h life.
https://www.electronicsweekly.com/news/products/led/660797-2019-07/

New in Metal 3D Printing: Copper
The latest material available in additive manufacturing is Copper (C18150), a chromium zirconium copper (CuCr1Zr) alloy defined by its excellent thermal and electrical conductivity. Additive C18150 was developed to fill the void in the AM market and the demand for additive copper.
https://www.stratasysdirect.com/materials/metals/new-in-metal-3d-printing-copper

LPBF ADDITIVE MANUFACTURING STEEL SUITABLE FOR HARDENING
Cetim, the French Technical Center for Mechanical Industries, has released a new steel grade for the Laser Powder Bed Fusion (LPBF) additive manufacturing.

Characterised as 33CrMoV12 steel, this material is designed for parts enduring nitriding, a hardening heat treatment that diffuses nitrogen into the surface of a metal. Such nitrided parts feature mechanical properties suitable for the power transmissions sector.
https://3dprintingindustry.com/news/cetim-releases-lpbf-additive-manufacturing-steel-suitable-for-hardening-158987/


A New Coating Promises to Make Fingerprints and Grease Stains Invisible on Stainless Steel Appliances.

Researchers and chemists from the Fraunhofer Institute for Microstructure of Materials and Systems IMWS worked with experts from FEW Chemicals GmbH in Wolfen, Germany, to develop a new coating with added particles that help make it both water and oil repellent. The effectiveness of the new coating is being tested and optimized by the Fraunhofer Institute, but it expects a final recipe for the coating to be perfected by the end of 2020.
https://gizmodo.com/a-new-coating-promises-to-make-fingerprints-and-grease-1836730370

Porsche’s New Bioconcept-Car Features Natural-Fiber Composite Body Parts
Jul 23 2019
Automaker Porsche launches the new 718 Cayman GT4 Clubsport body parts made of natural-fiber composite materials developed in the Application Center for Wood Fiber Research HOFZET
https://www.azom.com/news.aspx?newsID=51758

The New Optical Defect Inspection System for Faster Defect Sourcing
Jul 18 2019
KLA Corporation (NASDAQ: KLAC) announced the 392x and 295x optical defect inspection systems and the eDR7380™ e-beam defect review system.
https://www.azom.com/news.aspx?newsID=51740

Isamill Reduces Specific Energy Requirements by up to 21.5% by Releasing New Conical Spacers
Jul 18 2019
Reducing the specific energy requirements from fine grinding by even a small amount is critical to cost savings and boosting the returns from mineral processing.
https://www.azom.com/news.aspx?newsID=51733


Beta-Gallium Oxide Shows Promise for Creating High-Power Semiconductors
Jul 23 2019
Electrical engineers at the University of Illinois (U. of I.) have added beta-gallium oxide—the field’s hottest material—to their arsenal, thus overcoming another barrier in the fabrication of high-power semiconductors.
https://www.azom.com/news.aspx?newsID=51765

New Epoxy Potting Compound with Excellent Flow Properties
UK adhesive specialists Techsil have launched a new potting compound for electronics with medium viscosity and small filler particle size: Structalit® 5894-1
https://www.azom.com/news.aspx?newsID=51778

Nano Dimension Ltd., an additive electronics provider,  has unveiled its new DragonFly Lights-Out Digital Manufacturing (LDM) printing technology, which the company presents as the industry’s only comprehensive additive manufacturing platform for round-the-clock 3D printing of electronic circuitry.
The initial deployment took place at the Munich premises of sensor and defense electronics provider Hensoldt.
https://www.memuk.org/technology/electronics/additive-electronics-provider-delivers-3d-printed-electronics-49874

BAE Systems demonstrates unmanned armed boat
By The Engineer 24th July 2019 11:55 am
An unmanned armed boat demonstrated by engineers at BAE Systems
https://www.theengineer.co.uk/bae-systems-demonstrates-unmanned-armed-boat/

Knee-powered energy-harvester keeps devices running
22nd July 2019 12:44 pm
Researchers at the Chinese University of Hong Kong have developed a knee-powered energy-harvester that generates  1.6 microwatts of power while the wearer walks without any increase in effort. The energy is enough to power devices like health monitoring equipment and GPS devices.
The article appeared in  Applied Physics Letters. The energy harvester is attached to the wearer’s knee.

Applied Physics Letters
Macro fiber composite-based energy harvester for human knee

Casting for lightweighting solutions
Quick Prototype “Make Like Production” concept (pioneered by the Warwick Manufacturing Group,  University of Warwick) in which the prototype part behaves like a production component.
2019-07-16

Grainger & Worrall has invested in computer-simulation methods for casting design, including Magma software packages for various materials. Aimed at producing right-first-time castings without extensive and time-consuming practical trials, more than 500 simulation projects have been completed—validated by x-ray, CT (computerized tomography), micro examination and tensile testing.
https://www.sae.org/news/2019/07/casting-specialist-grace--worrall

Additive Manufacturing
EOS Introduces Four New Materials for Laser Melting of Serial Products
Jul 2, 2019
EOS has developed four new metal materials for its direct metal laser sintering machines: EOS Stainless Steel CX, EOS Aluminum AlF357, EOS Titanium Ti64 Grade 5 and EOS Titanium Ti64 Grade 23. They are intended to make a wide variety of series applications possible, ranging from automotive engineering to medical technology.
https://www.spotlightmetal.com/eos-introduces-four-new-materials-for-laser-melting-of-serial-products-a-838920/


JULY 1, 2019

Porsche leveraging the benefits of organic materials in automotive manufacturing applications. The new 718 Cayman GT4 Clubsport features body parts made of natural-fiber composite materials developed in the Application Center for Wood Fiber Research HOFZET, which is part of the Fraunhofer Institute for Wood Research.
https://phys.org/news/2019-07-porsche-leveraging-benefits-materials-automotive.html


June 17, 2019
Rio Tinto unveiled  a new aluminum alloy that could reduce the weight of vehicle wheels by as much as 7%, while making them stronger 15% to 20% stronger than traditional wheels.

It has called its new product “Revolution-Al” and said it’s part of its high-strength 3xx Series Alloys.
https://www.mining.com/rio-tinto-unveils-new-aluminium-alloy-to-make-lighter-cars/

New strong, conductive, copper-alloy fasteners
June 05, 2019
Isabellenhütte is manufacturing fasteners made of their proprietary Isa-Con copper alloy materials. Isa-Con fasteners have comparable strength and conductivity to stainless steel and copper materials, respectively. Source: Isabellenhütte Gmbh

The fasteners are intended for fastener applications that need high electrical conductivity and heat resistance.
https://insights.globalspec.com/article/11993/new-strong-conductive-copper-alloy-fasteners

MAY 27, 2019

Scientists create new aluminum alloy with flexibility, strength, lightness
by National University of Science and Technology MISIS.

Tthe proposed material can be used primarily in aeronautics and automobile industry, as well as for the design of modern robotics, including copters, where reducing the weight of the drone is critical. The material can be used for the manufacture of complex parts via 3-D printing.
https://phys.org/news/2019-05-scientists-aluminum-alloy-flexibility-strength.html

Generative Design for Additive Manufacturing: The iteration generation: a new age of design
By Stuart Nathan 9th April 2019
https://www.theengineer.co.uk/iteration-generative-design/

NASA DEVELOPS NEW COPPER ALLOY FOR 3D PRINTING ROCKET COMPONENTS
MARCH 20TH 2019
https://3dprintingindustry.com/news/nasa-develops-new-copper-alloy-for-3d-printing-rocket-components-151593/

New welding process  for formerly unweldable lightweight alloy AA7075
February 13th, 2019

Developed in the 1940s, AA7075 is an aluminum alloy that's almost as strong as steel, yet it weighs just one third as much. But its pieces  couldn't be securely welded together.

Led by Prof. Xiaochun Li, a team at the UCLA Samueli School of Engineering wanted to develop welding solution for that problem. They fabricated thin rods made of 7075 infused with minuscule particles of titanium carbide. These rods were then placed between the pieces of the aluminum alloy which were about to be joined, acting as a filler. When the rods and adjacent material were subsequently melted in an arc welding process, the nanoparticles eliminated an  uneven flow issue and good welds were obtained. Nanoparticles make the elements in the liquid metal solidify together more uniformly, thus preventing phase segregation, which was happening earlier.

The resulting welded joints have a tensile strength of up to 392 megapascals – by contrast, the commonly-used 6061 aluminum alloy has a weld strength of 186 megapascals. It is believed that post-welding heat treatments could boost the strength of the 7075 welds up to 551 megapascals, which is on par with the weld strength of steel.

The alloy is already used in items such as airplane wings and fuselages but sheets of it typically have to be riveted together.
https://newatlas.com/welding-aa7075-aluminum-alloy/58449/

Researchers Develop New Aluminium Alloy Using Microscopic Diamonds
FEB. 11, 2019

A team of Russian and British scientists announced the development of a process to add nanoscale diamonds to molten aluminium, making a new aluminium alloy tailored to maritime transportation applications.
 new aluminium alloy shows promise for use in aerospace, automotive, and other industries where high strength, low density metals are needed. They say the new aluminium alloy may well replace more expensive aluminium-scandium alloys currently in use.
https://aluminiuminsider.com/researchers-develop-new-aluminium-alloy-using-microscopic-diamonds/

New Milling Cutters

M5130 shoulder milling cutter – Xtra·tec® XT – performance und reliability extend your perspective.
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Tiger·tec® cutting tool materials guarantee extremely high cutting data
Excellent handling thanks to improved accessibility
High number of teeth and small indexable inserts for maximum efficiency
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Xtra·tec® XT M5009 face milling cutter
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High level of stability – ideal for small machining allowances and variable conditions
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Very good handling thanks to easily accessible clamping screw at an angle – prevents typical installation mistakes
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More information
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ASU, Army Research Lab create new alloy with superhero-like strength

October 8, 2018
Now researchers from Arizona State University and the Army Research Laboratory have teamed and designed an alloy of copper and tantalum that can withstand extreme impact and temperature — bringing society one step closer to having real-life materials with superhero strength. Kiran Solanki, an associate professor in the Ira A. Fulton Schools of Engineering, is working on the copper and tantalum alloy, which has the potential to be used in protective equipment for the armed forces and on spacecraft for deep-space exploration.
https://asunow.asu.edu/20181008-asu-army-research-lab-create-new-alloy-superhero-strength

August 7, 2018

A new Copper Graphene (G/Cu) nanocomposite alloy has been developed recently: the addition of 3% graphene to pure copper has proven to be an alloy that significantly improves the yield strength, tensile strength, and elastic modulus if compared to pure copper. Even though the electric conductivity decreases, the resulting material is still considered highly conductive.
https://www.ennomotive.com/new-applications-graphene-copper-alloy/

July 11, 2018
Fiat Chrysler Automobiles (FCA) has created an aluminum alloy that exceeds the limitations of alloys currently used in vehicle engine cylinder heads.

The new alloy,  ACMZ, developed by FCA, the Oak Ridge National Laboratory and supplier Nemak, stays strong up to 300°C (572°F). This surpasses, by a wide margin, the limits of existing alloys, which begin to weaken and crack above 200°C (392°F).
https://www.engineering.com/AdvancedManufacturing/ArticleID/17231/Fiat-Chrysler-Creates-New-Aluminum-Alloy-for-Engines.aspx

JANUARY 26, 2018

New research yields super-strong aluminum alloy
Purdue University's School of Materials Engineering.
https://phys.org/news/2018-01-yields-super-strong-aluminum-alloy.html

https://www.dnaindia.com/science/report-new-research-yields-super-strong-aluminum-alloy-here-s-what-you-need-to-know-2579476

NASA-427: A New Aluminum Alloy
With Improved Impact Toughness and Mechanical Properties
https://technology.nasa.gov/patent/MFS-TOPS-8

New steel that beats the strength-ductilitiy trade-off
August 25, 2017
A Hong Kong-Beijing-Taiwan mechanical engineering team led by Dr Huang Mingxin from the University of Hong Kong (HKU) has recently developed a Super Steel (also called D&P Steel as it adopted a new deformed and partitioned (D&P) strategy) which addressed the strength-ductility trade-off. Its material cost is just one-fifth of that of the steel used in the current aerospace and defence applications.
https://www.sciencedaily.com/releases/2017/08/170825124908.htm

FACT SHEET Advanced steel applications - worldsteel
https://www.worldsteel.org/en/dam/jcr:4864507f-7f52-446b-98d6-f0ac19da8c6d/fact_Advanced+steel+applications_2016.pdf


Novelis introducing high-strength 7000-series aluminum alloys for automotive industry
18 August 2015

Novelis' Next Generation High Strength Automotive 6xxx Alloy: Advanz™ - 6HS-s650

Novelis; Next Generation 7xxx Aluminum Alloy for Automotive Applications
https://www.greencarcongress.com/2015/08/20150818-novelis.html

Scientists Invent a New Steel as Strong as Titanium
South Korean researchers have solved a longstanding problem that stopped them from creating ultra-strong, lightweight aluminum-steel alloys.
Feb 4, 2015
https://www.popularmechanics.com/technology/news/a13919/new-steel-alloy-titanium/

New Welding Process, "J-SolutionTM Zn", Suitable for Galvanized Steel in Automotive Industry ...
2013
https://www.kobelco.co.jp/english/ktr/pdf/ktr_32/016-023.pdf


March 1998
New Copper Alloys
Copper Applications in Innovative Technology
https://www.copper.org/publications/newsletters/innovations/1998/03/new_alloys.html


Engineering and Technology News August 2019


Updated on 29 July 2019

ISI Standards for Sheets, Plates and Bars - India

 The generally accepted meanings for  the terms, foil, sheet, strip and plate are as follows: 

Foil is sheet metal of varying widths having thickness not exceeding 1.6 mm. 

Strip is a metal rolled in any thickness between 1.6 mm and 10 mm and its widths vary from 100 mm to 1,550 mm. It is designated with letters ISST followed by the dimensions in mm in order of length, width and thickness. 

Sheet is a term used for metals having thickness lying between 0.4 mm to 4 mm and having a 

width varying from 1,800 mm to 4,000 mm. It is designated by letter ISSH followed by the dimensions in mm in order of length, width and thickness. 

Plates denote all widths of metals where the minimum thickness exceeds 5 mm and maximum upto 63 mm and all widths of metal and length varying from 2,200 mm to 13,500 mm. It is designated by letters ISPL followed by dimension in mm in order of length, width and thickness. 

18:1138-1958 gives sizes of metal strips, sheets, flats, plates, and bars round and square. Here the nominal sizes are given as well as the tolerances in the sizes kept in their manufacture are also specified. 

18:1731-1961 gives dimensions for steel flats, and their tolerances for structural and general engineering purposes while 18:1732-1961 gives dimensions for round and square steel bars for 

structural and general engineering purposes. 

Dimensions for steel plates, sheets and strips for structural and general engineering purposes are given in 18:1730-1961. The following 18 specifications also give the sizes of different structural 

sections made of steels for general purposes of engineering: 

18:808-1957 specification for rolled steel beams, channels and angle sections 

18 : 1173-1957 specification for rolled steel beams, channels and angle sections and for bars 

18:1250-1958 Specification for rolled steel beams, channels and angle sections, and bulb angles 

18:1863-1963 Dimensions for rolled steel bulb plates. 

All these structural steel sections are given combined in ISI standard handbook for structural engineers. 

18:6911-1972 gives dimensions of stainless steel plates, sheets and strips 

18:1079-1973 gives dimensions of hot rolled, carbon steel sheets and strip 

18:6527-1972 gives dimensions of stainless steel wire rods 

18:6528-1972 gives dimensions of stainless steel wire 

18:6529-1972 gives dimensions of stainless blooms, billets and slabs for forgings. 

18:6603-1973 gives dimensions of stainless steel bars and flats 

All sizes given in IS standards are not manufactured by companies. Only those sizes which are in large and continuous demand are made normally by them. So design engineers should refer to manufacturers' catalogues for the available sizes.

Milling Processes and Operations

7.6.5 Mullick and Bhattacharyya

Milling a slot - with a milling cutter

Milling  flat surface - with a helical tooth plain milling cutter

Millng a flat surface - with the side of a side millign cutter

Side milling with half-side milling cutter

Milling a semicircular groove
Milling a vee-groove

Straddle milling the sides of a projection with a set of half-side m milling cutters

Gang milling a complex form with a set of  milling cutters of various types

Vertical Milling Machine Operations

Milling a flat surface with an inserted  blade milling cutter

Milling a slot with an end mill

Milling two surfaces of a recess by an end mill.

2018

M5130 shoulder milling cutter – Xtra·tec® XT – performance und reliability extend your perspective.
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Lower tool costs and minimal administrative effort thanks to universal usability
No additional finishing operations thanks to exact 90° angle
Tiger·tec® cutting tool materials guarantee extremely high cutting data
Excellent handling thanks to improved accessibility
High number of teeth and small indexable inserts for maximum efficiency
More information

Available:
With AC.T0602.. indexable insert | From 1st January 2019
With BC.T1605.. indexable insert | From 1st May 2019
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Xtra·tec® XT M5009 face milling cutter
Fullscreen
Xtra·tec® XT M5009 face milling cutter – small indexable inserts, high productivity.
High level of stability – ideal for small machining allowances and variable conditions
Maximum feeds, tool life and productivity thanks to small indexable inserts and high number of teeth
High level of process reliability due to tough double-sided indexable inserts
Very good handling thanks to easily accessible clamping screw at an angle – prevents typical installation mistakes
Highly cost-effective thanks to low cutting tool material costs
https://www.walter-tools.com/en-gb/tools/innovations/milling/pages/innovations-milling-2/new-products-milling-2.aspx


2017
Writing in the February 2017 issue of the Journal of Manufacturing Science and Engineering, the Missouri S&T researchers describe an approach that can greatly improve the accuracy of five-axis machine tools used to fabricate large parts
"Five-axis machine tools are known to have 41 basic geometric errors.
The research is related to compensating for the errors to hold errors to five thousandths of an inch over 120 feet in case of aircraft body etc.
https://www.sciencedaily.com/releases/2017/01/170118103451.htm


Updated on 30 July 2019, 7 September 2018

Machine Element Materials - Fabrication Characteristics - Design for Manufacturability

Fabrication Characteristics and Processes of Fabrication - Materials Suited for Specific Fabrication Processes

The fabrication characteristics of metals are explained under the heads:  formability, castability,  machinability and weldability.

(a) Formability:

The ability of a metal to be formed is based on ductility of the metal. Ductility is based on its crystal structures. The metal that has the face centred cubic crystal structure is most ductile because the crystal has the greatest opportunity for slip in four distinct nonparallel planes and three directions of slip in each plane.

The other factors which control ductility of the material are grain size, alloying elements and softening heat treatments such as annealing and normalizing. The small grain sizes are recommended for shallow drawing of copper and relatively large grains for heavy drawing on the thicker gauges.

Hot and cold working, also have an effect on ductility. The high pressure applied in hot drawing distorts the grains which determine the ductility; cold working also results in distortion of crystals. Generally, cold worked crystals are more distorted and are usually less ductile than the hot worked crystals.

Alloying elements in a pure metal normally reduce its ductility, because if they replace the atoms of pure metal it reduces the number of slip planes as it occurs in steel, which is an alloy of carbon and iron and so steel is less ductile than iron. If the alloy finds its room in the spaces between the atoms of pure metal it offers increased resistance to slip, which happens in steel when iron carbide precipitates in slip planes when steel solidifies. By softening heat treatment such as annealing which consists of heating the metal to the re-crystallisation temperature at which at first the grains may be very small but they grow in size as long as the metal is exposed to the high temperature, when the desired size is obtained the metal is allowed to cool. During recrystallization ductility of metal is

restored because distorted crystals are reformed in re-crystallisation.

The processes using the property of formability of metal are under two major categories: (i) Hot working and (ii) Cold working.

Hot working processes:

Rolling, forging, extrusion and hot pressing are hot working processes. In hot working the metal is heated sufficiently to make it plastic and easily worked. The temperature of the heated metal or alloy should be above the re-crystallisation temperature. This temperature is different for different metals.

Hot rolling is used to create a bar of material of particular shape and dimensions. The principal rolled steel sections arc plates, angles, tees, channels and joists; round, hexagonal and square bars for forging and machining operations; sheets, rails, etc. All of them are available in many different sizes and in different materials. The materials most available in the hot rolled bar sizes are steel, aluminium and copper alloys. Tubes may be manufactured by hot rolling of strips or plates; the product may be butt welded or lap welded.

Forging is the hot working of metals by hammers, presses or forging machines. For small work forging is carried out with hand hammers but for large work hammers and forging machines are used. Forging alters the internal structure of metals which results in increased strength and ductility. Compared with castings, forgings have greater strength for the same weight. Forging should be

carried out within proper temperature range. If the temperature is too high the metal will be weak and brittle. If the temperature is too low, there will be internal stresses which may lead to distortion or cracking.

Many small parts are drop forged. In drop forging, solid lump with little or no previous treatment by hand is squeezed between dies to the shape required with one or more blows from a drop hammer. The component can be made to dimensions and with a good surface so that machining may be unnecessary. The limitations of this process are that the number of parts should be great (production volume has to be high) and complicated shapes cannot be produced as they can not be removed from dies.

Extrusion is a process where a heated blank is caused to flow through a restricted orifice under great pressure. Very complicated shapes may be produced by the extrusion process. The process is restricted to materials of low melting points such as brass, aluminium and certain alloys of tin, lead and other soft metals.

Hot pressing consists of forming metal to shape in a very rigid type of power press. A hot piece of metal is pressed and extruded in suitable dies into a smoothly finished piece to accurate dimensions. Automobile valves are formed by this process. 

Cold working processes:

In cold working is the forming of a metal is done usually at room temperature. In some cases, higher  temperatures are used but always, the temperature is lower than re-crystallisation temperature of the material. Cold working may vary from a simple bend to great deformation produced by deep pressing and tube drawing. The result of cold work is to increase hardness and tensile strength but to decrease ductility and shock resistance. Cold worked parts have a bright new finish, are more accurate and require less machining. Where cold work is considerable, the part may be annealed at some intermediate stage or stages of work. In cold working the surface of a material is very important as scale may be worked into the finished article with serious results. Some of cold working processes are drawing, heading, spinning, stamping, etc.

Drawing is a process by which the cross section of a metal is diminished by pulling it through an accurately formed hole in a drawing die. The operation is performed cold and only simpler forms can be produced without excessive resistance and tearing.

Heading is a cold working process in which the metal is gathered or upset . This  operation is commonly used to make screw and rivet heads. The blank is usually a piece of wire of suitable length and cross section; one end is cold forged in dies to form the desired shape of the head. Annealing may be required after cold heading.

Spinning is the operation of working sheet material around a rotating form into a circular shape. Pressure is applied to the sheet by means of a blunt nosed tool which presses it against the former. This is an economical method of forming parts if the quantities are small.

Stamping is the term used to describe punch press operations such as blanking, coining, forming and shallow drawing.

Powder metallurgy :

It is the art of making small components by heat treatment of compressed metallic powders, sometimes with inclusion of non-metallic material.

The powdered metals in desired proportions are compressed in moulds under a very high pressure varying from 700 to 14,000 kg/sq cm depending on the metal. The compacted part is heated at a temperature which is less than melting point of the major ingredient. T'he disadvantages of this method are (i) low strength of the component (ii) higher cost of material and (iii) the limited range of materials which can be used.

Filaments of refractory metals such as tungsten, self lubricating bearings, tungsten carbide tips for cutting tools and iron alloys for permanent magnets are examples of articles made from powdered metal. By this process small components can be made out of some metals whose melting point is too high to allow use of die casting.

(b) Castability:

Castability of a metal is judged to a large extent on the following factors: solidification rate, shrinkage, segregation, gas porosity, and hot strength.

Solidification Rate:

The ease at which a metal will continue (o flow after it has been poured in the mold depends on its analysis and pouring temperature. Some metals such as grey iron are very fluid and can be poured into thin sections of complex castings.

Shrinkage :

Shrinkage refers to the reduction in volume of a metal when it goes from a molten to a solid state. For steel, the amount of contraction amounts to about 6.9 to 7.4% by volume, or 2 cm per metre; grey  iron contracts half as much. This shrinkage factor has to be taken into account by the pattern maker and designer, not only to allow for the proper finished .size, but also to sec that undue strains will not be encountered during shrinkage due to the mould design. Various elements can be added to the alloy to control fluidity and shrinkage as discussed later in this chapter.

Segregation :

As the metal starts to solidify tiny crystal structures resembling pine trees and referred to as dendrites start to form at the mold edges. As they form, they tend to exclude alloying elements. Subsequent crystals that form are progressively richer in alloy content as the metal solidifies. Thus the surface of the casting is not of the same quality as that in the centre. This is overcome in part at least by subsequent heat treatment, or very slow cooling.

Gas Porosity:

Some metals in the molten state have a high affinity for oxygen and nitrogen. These gases become trapped as the metal solidifies creating voids or pinholes.

Hot Strength:

Metals are very low in strength right after solidification. This is especially true of the non-ferrous metals. Precautions must b(‘ taken at the lime of casting to avoid stress concentration that causes flaws and hot tears to develop as the metal solidifies .

Casting is the oldest form of metal shaping and is still the basic engineering process since most metals are melted and cast from ores. Castings are made of iron, steel, various brasses and bronzes, aluminium and its alloys and the various white metal alloys.

Patterns may be made of wood or metal and with its help the sand mould is formed in which molten metal is poured. The mould is dried before the metal is poured. Metal in cooling solidifies to the form outlined in the mould.

In die casting process the mould is usually made of steel and molten metal is poured or forced under pressure into the mould. This method is used for mass production only.

Non-ferrous alloys arc sometimes cast centrifugally. Molten metal is poured into a rapidly rotating cylindrical mould and is held against the mould by centrifugal force so that core is not required. On cooling the casting is complete. Such castings are generally denser and more homogeneous than ordinary sand castings. This process is limited to simple shapes and to fairly large quantities.

The following precautions should be observed in design of castings :

(i) All sections should be designed as far as possible with a uniform thickness.

(ii) All walls should be sufficiently thick to allow the molten metal to flow freely into all corners.

(iii) Adjoining sections should be designed with generous fillets or radii.

(iv) Parts should be designed so that patterns may be drawn readily from the moulds.

(v) A complicated part should be designed in two or more castings. These castings are assembled by fasteners.

(vi) Where the section uniformity is not possible, light sections should be blended into heavy sections.

Thickness of casting determined by calculations is often too small to permit production of good castings. Minimum values of the thicknesses for various castings are prescribed.


Material                                 Minimum thickness in mm


Grey cast iron                                    6

Malleable cast iron                           6

Steel casting                                     6

Brass                                                3

Bronze                                             3

Aluminium                                      3

(c) Machinability :

Machinability is the ease with which metal can be removed in operations such as turning, drilling, reaming, etc. Ease of metal removal requires that the forces acting against the cutting tools should be relatively low and the chips will be broken up, a good finish should result and the tools should last a reasonable period of time before it has to be replaced or resharpened. Machinability is also expressed as a machinability rating for each material. 

This rating is given for most ferrous metals using steels 13S25  in the cold drawn conditions as the basis of 100% machinability. This value involves turning at a cutting speed of 54.9 surface metre per minute for feeds upto 0.1778 mm per revolution and depths cut upto 6.35 mm using appropriate cutting fluid with high speed steel T70W18Cr4V1 tools. Machinability of other metals will be judged with respect to this basis.

This property plays a predominant role in deciding the selection of material for components manufactured using  machining on automatic machine for mass production. By adding alloying materials like sulphur and lead in steel its machinability can be increased, however, some reduction in tensile strength in takes place.

(d) Weldability:

It may be said that all metals are weldable by one process or another. However, the real criterion in deciding on the weldability of a metal is weld quality and the ease with which it can be obtained.

In deciding on weldability of a metal, the characteristics commonly considered are the heating and cooling effects on the metal, oxidation, and gas vaporization and solubility.

Heat and Cooling:

The effect of heat in determining the weldability of a material is related to the change in microstructure that results. For example, steels are sometimes considered weldable or not weldable on the basis of the hardness of the weld. The deposited weld metal may pick up carbon or other alloys and impurities from the parent metal that make it hard and brittle so that cracks result upon cooling.

The opposite effect may also be considered. A metal may have a certain hardness temper that will be changed by the heat of the weld. Although both of these conditions can be corrected by added precautions and heat treatment, they add to the cost and hinder the simplicity of the weld.

Hot shortness, a characteristic which is indicated by lack of strength at high temperature, may result in weld failures during cooling of certain metals.

Oxidation :

Oxidation of the base metal, particularly at elevated temperatures, is an important factor in rating weldability of a metal. Metals that oxidize rapidly, such as aluminium, interfere with the welding process. The oxide has a higher melting point than the base metal, thus preventing the metal from flowing. It also may become entrapped in the weld metal, resulting in porosity, reduced strength, and brittleness

Gas:

Large volumes of troublesome gases may be formed in the welding of some metals. These gases may become trapped in the weld because certain elements vaporize at temperatures below those needed for welding. Not only will this cause porosity, but some of the beneficial effects of these elements are lost.

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Mechanical Properties of Materials Used in Machine Elements

Mechanical properties of materials 

The proper and efficient use (value engineering) of materials in machine elements requires considerable knowledge of their mechanical properties. The mechanical properties describe the behaviour of the material under use as a machine element in machine.  

The most important mechanical properties are creep,  ductility,  elasticity, hardness, machinability. malleability, resilience, stiffness, strength, and  toughness.

Strength

Strength is the ability of the material to resist stress without failure.  The measure of the strength is the ultimate stress. Ultimate strength refers to the force needed to fracture the material.

When materials are subjected to a pulling force (tensile force) they stretch as the stress increases. The stress-strain relationship can be graphed,  when test specimen is subjected to tensile load. The diagram is a graph between stress and % elongation. With the help of this diagram different-strengths of material can be defined.

When material is subjected to a pulling force the point where the stretch suddenly increases is known as the yield strength. In many design problems when the yield strength of materials is passed it is considered unsafe for further service. When mild steel is subjected to a pulling force it indicates a distinct point where the stretch suddenly increases. This is known as yield point. Some materials like high nickel alloys, monel metal and other similar non-ferrous materials do not show a definite break in the stress strain curve. In this case it is difficult to assign yield point for them. For such materials yield strength of material is defined at the point where 0.5% elongation takes place.

Proportional limit is the maximum stress under which a material will maintain a perfectly uniform rate of strain to stress. However, it is difficult to measure the exact proportional limit.

The maximum stress from which a material can recover is called the elastic limit. It is difficult to specify the elastic limit and so the idea of proof stress has been developed.

Proof stress is the maximum stress a material can withstand without taking more than small amount of set. The amount is usually specified as the smallest that can be measured by an extensometer.

The proportional limit is yield strength at 0.00% offset in the stress-strain relationship graph. Proof stress is yield strength at 0.01% offset and yield strength is yield strength at 0.2% offset on stress elongation curve under tensile load.

Several materials such as structural steel, copper, aluminium, etc. have equal strength in tension or compression, but their strength in shear is about two-thirds of the strength in tension while in grey cast iron the strength in tension and shear is a fraction of the strength in compression.

Shear strength is the force per unit area produced to fracture a specimen when it is impressed along the cross section of material. The material may be subjected to single shear or double shear. The shear strength of steels compared to their ultimate tensile strength ranges from about 50 to 80 per cent, the lower values for the harder materials.

Elasticity

Elasticity is the property of regaining original shape after deformation. All materials used in machine elements and structures (construction) are elastic but the degree of elasticity varies with different materials. This property is exceedingly important in precision tools and machines. Steel is highly elastic material.

Plasticity is the property that enables the formation of permanent deformation in a material. Stiffness is the property by virtue of which a material can resist deformation. Measure of stiffness is the modulus of elasticity. This property is desirable in materials used in machines, columns, beams and machine tools.

Ductility

Ductility is the property of material that enables it to be drawn out or elongated to an appreciable extent (subject to tensile force) before rupture occurs. The percentage elongation and the percentage of reduction of area before rupture of a test specimen are measures of ductility of the material.

Percentage elongation depends on gauge length and so gauge length is required to be stated when percentage elongation is given. Indian Standard Institution recommends gauge length of  5.65 SQRT( A) where A is the cross sectional area of the test specimen.

Brittleness is opposite to ductility. It shows lack of ductility. Brittle materials show little deformation before rupturing.

Materials with more than 15% elongation are usually considered ductile. Those with less than 5% elongation are considered brittle. Those between 5 and 15% elongation are of intermediate ductility. Property of ductility is desirable in machine parts which may be subjected to sudden and severe loads.

Mild steel, wrought iron, copper and aluminium are ductile materials. Cast iron is a brittle material. 

For a variety of engineering uses a material requires good combination of strength and ductility. Usually if two materials having the same strength and hardness the one that has the higher ductility is more desirable in engineering practice.

Malleability

Malleability is the property of a material that enables it to undergo great change in shape under compressive stress without rupture.Malleable materials may be hammered or rolled into any desired shape without rupture. 

Soft steel, wrought iron, copper and aluminium are malleable metals.

Hardness 

Hardness is that property of a material that enables it to resist penetration, indentation, abrasion or plastic deformation. 

In selecting a metal to withstand wear or erosion, mainly three properties are considered: ductility, toughness and hardness. However, the most important from wear resistance point is hardness Wear, which  may be either due to friction or erosion by steam, oil, and water  is resisted by materials having higher hardness. This property is decreased by heating.

Several methods have been developed for hardness testing. Those most often used are Brinell, Rockwell, Vickers, and Scleroscope. The first three are based on indentation tests and the fourth

on the rebound height of a diamond-tipped metallic hammer.

In order to relate one method of testing hardness with another, hardness conversion charts are available. 

Tensile strengths are often listed on hardness conversion charts. Although relationships exist between hardness, and tensile strength and yield strength, but there are chances for error. Therefore, use of tensile testing machine is preferred to determine strength.

Resilience

Resilience is that property of a material which enables it to store energy and resist shock and impact. The measure of resilience is the amount of energy that can be stored per unit volume after being stressed to elastic limit. This property is desirable in materials for springs.

Toughness

Toughness is the property which enables a material to be twisted, bent or stretched under a sudden impact or under a high stress before rupture. It is measured by the Izod test or Charpey test. The measure of toughness is the amount of energy that a unit volume of material has absorbed after being stressed up to the point of fracture. This property is decreased by heating.

Creep

Creep is expressed as the plastic behaviour of the metals or plastics under constant load and at constant temperature.Creep is observed as the material deforms slowly but progressively over a period of time under the same load and temperature. There are three stages of creep. In the first stage the material elongates rapidly but at a decreasing rate. In the second stage which is ordinarily of long duration the rate of elongation is constant. In the third stage the rate of elongation increases rapidly until the material fails.

Design engineers are  most concerned with second stage of creep, where elongation takes place at a constant specific rate. The percentage of elongation and time required are decided by the requirements of the particular application, viz, 0.1 per cent elongation in 10,000 hours. In rapidly rotating structural members such as rotors and blades of of steam and gas turbines, the clearances are extremely small and critical. The designer will be satisfied with nothing short of experimentally determined stress of 1 creep rate unit (CRU) or 1 per cent in 100,000 hours.

Determination of mechanical properties:

In order to determine the mechanical properties of the material,  tests are carried out in mechanical testing laboratories. These tests are carried out according to standard procedures laid down.  The simplest test that can be made on most materials is the static tensile test. The procedure to carry out this test is suggested by Indian Standards Institution. The values for the following properties are obtained from the test:

(i) Ultimate tensile strength

(ii) Proportional limit

(iii) Elastic limit or Proof Stress

(iv) Yield point or Yield strength

(v) Percentage elongation

(vi) Percentage reduction in area.


IS 1608 — 1960 is to be adhered to while carrying out the static tensile test.

Other tests commonly employed are compression, torsion, flexure, cold bending, hardness, impact and fatigue. Data of these various tests are usually shown graphically by the stress strain diagrams. 

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