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3D printing technology is attracting every science and technology enthusiast whether it is a mechanical, civil, architecture, electrical, manufacturing or medical application. Everybody is interested in creating models, prototype using 3D printing technology. It’s not a technology but a 3D printing evolution. The pace at which this industry is growing and the novelty that 3D printing has introduced, it is predicted that additive manufacturing will affect almost all the fields of daily life including trade and commerce in near future.
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Mechanical Engineering Interview Questions and answers for freshers on design, safety and maintenance.
1) What is an accident ?
An accident is a unexpected and unforeseen event which may or may not injury to a person or a machine tool.
2) What are the standard sizes of drawing board as per Indian Standards?
As per Indian Standards :1250×900,900×650,650×500,500×350,350×250 sizes are available.
3) What are the functions of a scale ?
(a) To measure distance accurately.
(b) For making drawing to scale either in full size, reduced size or enlarged size.
4) What is a sketching ?
This is freehand expression of the graphic language.
5) What do you mean by First Aid ?
First Aid is immediate and temporary care given to a person who affected accidental injury or a sudden illness before the arrival of doctor.
6) What is a Drawing ?
It is a graphical representation of a real thing to define and specify the shape and size of a particular object by means of lines.
7) What is Engineering Drawing ?
A drawing which is worked out an engineer for the engineering purpose is known as Engineering Drawing.
8) What are the methods of extinguishing fire ?
1) Starvation. Separating or removing the burning material from the neighbour hood of the fire.
2) Blanketing. Preventing the air flow to the fire.
3) Cooling. Lowering the heat created by burning materials.
9) What are the precautions to be taken to avoid fire ?
1) The buckets along with sand should be placed inside the workshop.
2) Switches and other electrical parts must be made of fireproof material.
3) Carbon dioxide gas should be place at required points in special containers.
4) Fire extinguishers of suitable type should be placed at accessible places.\
10) What safety precautions should be observed while working in the workshop ?
1) Keep shop floor clean, free from oil and other slippery materials.
2) Wear proper dress and avoid loose clothing and loose hair.
3) Wear shoes and avoid chapels.
4) Avoid playing, loose talk and funning inside the shop floor.
5) Keep good housekeeping and put all unnecessary items and rejected items in scrap box.
6) Learn everything about the machine before starting and clear all the doubts.
7) Keep a safe distance from rotating and sliding parts.
8) Never store inflammable materials inside or around the shop.
9) Never play with electricity, fire, parts with sharp edge etc.
10) Keep fire buckets and extinguishers ready for use.
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A Journal of Applied Mechanics and Mathematics by DrD
© Machinery Dynamics Research, 2016
Becoming An Expert -- Part 3
In the previous article on Becoming An Expert--Part 2, I mentioned that there were two big issues for the engineering analysis section at my Houston position, the first being the matter of seismic survivability and the second being torsional vibration. The first item was dealt with in Part 2, and in this article we will take up the second item of concern.
When I joined the engine distributor in Houston in the mid-1970s, the company was about 65 years old, and the torsional vibration problem was not new. This was a problem that they had been dealing with, in one way or another, for many years. There were lots of old torsional vibration analysis reports available to study. I was not at all familiar with torsional vibration of machine trains; I had not studied anything quite like that in school and it had not come up in my previous industrial experience. So I eagerly began reading the old reports, and that is when the problem became acute for me: They did not seem to make any sense. I could not, with any integrity, continue to write reports like that when I thought they were complete nonsense, but I did not know how to analyze the problem correctly. I was in a jam!
There were three major difficulties:
1. The entire crank assembly rotates endlessly, so the stiffness matrix for the system is singular. This results in a zero eigenvalue, something that did not take too long to figure out.
2. It is obvious that the system does more than just go round-and-around; it goes up and down as well. I was baffled for a long time about how to deal with the kinematics and their impact on the dynamics.
3. It is apparent that there is a torque acting on the crank, but it is not directly applied to the crank by the combustion process. There is the slider-crank mechanism between the two, and I was at a loss as to how to transfer the cylinder pressure into a crank torque. This is again directly related to the kinematic problem mentioned just above.
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Nearly Forty years ago, a fellow engineer told me a story that must now be 70 years old. This engineer was born and educated in Egypt. His first job was a large civil engineering project with massive amounts of earth moving. Having a formal education but no local real world experience, he started to estimate how many steam shovels and trucks were required for the job. A Sr. engineer asked, what he planned do with all the equipment once the project was done, and what about the 99 local laborers left idle for each machine that does the work of 100 men and requiring only one operator?
The Sr. engineer told the young engineer to base his calculations on the required number of donkeys, basket weavers, strong men, little boys, and laborers that would be required. I was puzzled as was my colleague that many years ago.
The Sr. engineer explained that picks and shovels would be the main tools and the local laborers the muscle. The laborers loosen the soil and then fill the woven baskets with the soil. The strong men would lift the baskets onto the donkeys. The young boys would ride the animal off site and dump the soil. This kept the local population employed and able to feed their families. Manual labor as it was may not have been a great way to make a living but it was far better than starvation.
The situation in ancient Rome was similar. The Romans build magnificent structures but the preferred method was brute force. There was no push for efficiency as we think of it today. Even then, there were labor issues. Better to keep everyone working and fed, if only at subsistence levels, than to have massive unemployment and the making of a revolt.
If the laborers were in a position to demand higher and higher wages mechanization may have advanced faster. It will be interesting to see how many jobs robots and computers will replace as the minimum wage increases to $15/hour regardless of the local economies.
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With so much scientific tools, why do designs fail?
Why the unsinkable Titanic sank? Why did the thoroughly tested Columbia space shuttle burned out on return? Why Toyota had to call back thousands of cars designed by expert engineers?
Design might fails because somebody made a stupid mistake in his calculations, like in the old joke about the bridge that fell down because the engineer forgot to multiply by two. It might happen, but it is extremely rare. Most design failures happen because one specific mode of failure was never checked against, because it was never identified as risky.
The sad truth is that we cannot design anything to work. We can only try to find out if a certain design might fail in a certain specific way. This is one reason why we cannot send computers to design things. They are excellent in optimizations, when we tell them what parameter to optimize and for what mode of failure.
The Tacoma narrows bridge collapsed in 1940 because nobody thought that wind might arouse resonant vibrations in the bridge. It was OK for what it was designed for: for static loads. No computer would have suggested another mode of failure.
The Titanic sank because nobody asked what happens if the ship scratch its side on an iceberg. Had it been thought, maybe the designers would have ordered that it would be better to throw the engines to full back and bump into the iceberg head on! It would have been damaged badly, but it would not sink.
If only the designers of the Columbia would have only thought of the possibility of losing their thermal shield bricks on launch, the Columbia would have still be in service today. For a fact, once they identified the problem, they had no big difficulty to fix it.
The philosopher of science, Karl Popper, said that in order to be scientific a claim must be "falsifiable". Moreover, he suggested that a claim cannot be proved by repeating experiments with positive results. No matter how many times it passes a test, there is always a chance that one more test will prove it wrong. To prove a theory requires infinite number of successful tests. One failure is enough to disprove it.
So it is in our world of design. The failures described, all have shown that these designs were not perfect. They had errors embedded in them. And these errors are all the result of not being able to foresee the single mode of failure that could go wrong. No scientific calculation can help against an unidentified mode of failure.
What is the lesson to be learned? Be paranoid! Always look around searching for the mode of failure you might have missed.
I like to call rules by names. The name I gave this rule is "the law of the wild west".
It goes as follows:
The guy who kills you will be the one hiding behind the bush, that you failed to notice
What will happen if we condense the exhaust gas of coal gasification after passing through the gas Generator and then feed it to water treatment plant and then drain that water to the ground or reuse it. Can this be possible? No exhaust gas or reduced exhaust gas issue to environment.
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Today we have introduced the android app version 1 - the very basic app which will show you the latest discussion on your mobile phone.
You can download the same from
This is a very basic app to give a start .. we look forward for senior members , developers to associate to make it one of the best app for mechanical engineering profession
We request you to install the app on your phone and ask all your mechanical engineeirng friends to install the same..
Crystalline semiconductors such as silicon can catch photons and convert their energy into electron flows. New research shows that a little stretching could give one of silicon's lesser-known cousins its own place in the sun.Nature loves crystals. Salt, snowflakes and quartz are three examples of crystals – materials characterized by the lattice-like arrangement of their atoms and molecules.
Industry loves crystals, too. Electronics are based on a special family of crystals known as semiconductors, most famously silicon.
To make semiconductors useful, engineers must tweak their crystalline lattice in subtle ways to start and stop the flow of electrons.
Semiconductor engineers must know precisely how much energy it takes to move electrons in a crystal lattice.
This energy measure is the band gap. Semiconductor materials such as silicon, gallium arsenide and germanium each have a band gap unique to their crystalline lattice. This energy measure helps determine which material is best for which electronic task.
Now an interdisciplinary team at Stanford has made a semiconductor crystal with a variable band gap. Among other potential uses, this variable semiconductor could lead to solar cells that absorb more energy from the sun by being sensitive to a broader spectrum of light.
A colorized image, enlarged 100,000 times, shows an ultrathin layer of molybdenum disulfide stretched over the peaks and valleys of part of an electronic device. Just 3 atoms thick, this semiconductor material is stretched in ways to enhance its electronic potential to catch solar energy.
The material itself is not new. Molybdenum disulfide, or MoS2, is a rocky crystal, like quartz, that is refined for use as a catalyst and a lubricant.
But in Nature Communications, Stanford mechanical engineer Xiaolin Zheng and physicist Hari Manoharan proved that MoS2 has some useful and unique electronic properties that derive from how this crystal forms its lattice.
Molybdenum disulfide is what scientists call a monolayer: A molybdenum atom links to two sulfurs in a triangular lattice that repeats sideways like a sheet of paper. The rock found in nature consists of many such monolayers stacked like a ream of paper. Each MoS2 monolayer has semiconductor potential.
"From a mechanical engineering standpoint, monolayer MoS2 is fascinating because its lattice can be greatly stretched without breaking," said Zheng, an associate professor.
By stretching the lattice, the Stanford researchers were able to shift the atoms in the monolayer. Those shifts changed the energy required to move electrons. Stretching the monolayer made MoS2 something new to science and potentially useful in electronics: an artificial crystal with a variable band gap.
"With a single, atomically thin semiconductor material we can get a wide range of band gaps," Manoharan said. "We think this will have broad ramifications in sensing, solar power and other electronics."
Scientists have been fascinated with monolayers since the Nobel Prize-winning discovery of graphene, a lattice made from a single layer of carbon atoms laid flat like a sheet of paper.
In 2012, nuclear and materials scientists at Massachusetts Institute of Technology devised a theory that involved the semiconductor potential of monolayer MoS2. With any semiconductor, engineers must tweak its lattice in some way to switch electron flows on and off. With silicon, the tweak involves introducing slight chemical impurities into the lattice.
In their simulation, the MIT researchers tweaked MoS2 by stretching its lattice. Using virtual pins, they poked a monolayer to create nanoscopic funnels, stretching the lattice and, theoretically, altering MoS2's band gap.
Band gap measures how much energy it takes to move an electron. The simulation suggested the funnel would strain the lattice the most at the point of the pin, creating a variety of band gaps from the bottom to the top of the monolayer.
The MIT researchers theorized that the funnel would be a great solar energy collector, capturing more sunlight across a wide swath of energy frequencies.
When Stanford postdoctoral scholar Hong Li joined the Department of Mechanical Engineering in 2013, he brought this idea to Zheng. She led the Stanford team that ended up proving all of this by literally standing the MIT theory on its head.
Instead of poking down with imaginary pins, the Stanford team stretched the MoS2 lattice by thrusting up from below. They did this – for real rather than in simulation – by creating an artificial landscape of hills and valleys underneath the monolayer.
They created this artificial landscape on a silicon chip, a material they chose not for its electronic properties, but because engineers know how to sculpt it in exquisite detail. They etched hills and valleys onto the silicon. Then they bathed their nanoscape with an industrial fluid and laid a monolayer of MoS2 on top.
Evaporation did the rest, pulling the semiconductor lattice down into the valleys and stretching it over the hills.
Alex Contryman, a PhD student in applied physics in Manoharan's lab, used scanning tunneling microscopy to determine the positions of the atoms in this artificial crystal. He also measured the variable band gap that resulted from straining the lattice this way.
The MIT theorists and specialists from Rice University and Texas A&M University contributed to the Nature Communications paper.
Team members believe this experiment sets the stage for further innovation on artificial crystals.
"One of the most exciting things about our process is that is scalable," Zheng said. "From an industrial standpoint, MoS2 is cheap to make."
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Atomic Number : 13
Density (20oC) : 2.70 g/cm3
Atomic Weight : 26.98
Melting point : 660o C
Boiling point : 2467o C
Aluminum finds use as a deoxidizer, grain refiner, nitride former and alloying agent in steels. Its ability to scavenge nitrogen led to its widespread use in drawing quality steels, especially for automotive applications. Since aluminum is so often added to high quality steels.
Metallic aluminum is the most common addition agent. It is sold in the form of notch bars, or stick, and as shot, cones, small ingots, chopped wire, “hockey pucks”, briquettes and other convenient forms such as coiled machine fed wire. These standard products are supplied in bulk or packaged in bags or drums. Purity for deoxidation grades is usually over 95%, the major tramp elements being zinc, tin, copper, magnesium, lead and manganese. Coiled aluminum wire is normally made to 99% minimum specification.
Ferroaluminum, a dense and highly efficient aluminum addition, contains 30-40% Al. It is supplied in lump form, 8 in. x 4 in., 5 in. x 2 in., 5 in. x D, and 2 in. x D, and nominal 12 lb. and 25 lb. pigs, packed in drums and pallet boxes.
Aluminum has a weak effect on hardenability (it is never added for this purpose) and, because of its grain refining properties, actually detracts from deep hardening. Heat treatable steels made to fine grain practice require slightly extra alloying to counteract this phenomenon. Aluminum is, however, a ferrite former and promotes graphitization during long-term holding at elevated temperatures. It also enhances creep, probably because of its grain refining property. Aluminum, therefore, should not be used in Cr-Mo or Cr-Mo-V steels specified for boiler or high temperature pressure vessel applications. Perversely, aluminum is otherwise beneficial to such materials since it reduces scaling through the formation of a more tightly adhering oxide film, particularly if chromium is present as well.
Beyond its important functions in deoxidation and grain size control, aluminum has several applications as an alloying agent. Nitriding steels, such as the Nitralloy family, contain up to 1.5% Al to produce a case with hardness as high as 1100 VHN (70 RC). The outer layer of this case must, however, be removed by grinding to prevent spalling in service. The oxidation (scaling) resistance imparted by aluminum is exploited in some stainless steels and various high temperature alloys. Precipitation hardening stainless steels (17/7 PH, 15/7 PH, etc.) make use of aluminum’s ability to form strength-inducing particles of intermetallic compounds. Aluminum is found in many superalloys for the same reason.
Aluminum combines very readily with nitrogen, and this effect has important commercial uses. Aluminum killed deep drawing steels will be nonaging since AlN is extremely stable. Such steels will not exhibit stretcher strains (Lüder’s lines) or a yield point, even after prolonged holding after cold rolling. Aluminum is also added to nitriding steels for its ability to form an extremely hard case.
Aluminum is an important addition to some HSLA steels, and AlN was the first nitride used to control grain size in normalised and heat treated steels. Again, Al removes nitrogen from solution and provides grain refinement. Both of these effects promote high toughness, especially at low temperatures.
Mention should be made of the effect of aluminum on nonmetallic inclusions, since these will always be present in AK steel. Because aluminum is among the strongest deoxidizers known, it can combine with, and partially or totally reduce, any other oxides present in steel. The subject is quite complex and depends not only on aluminum, but also on oxygen, nitrogen, sulfur, manganese, silicon, and calcium contents. For ordinary steels, however, the pattern is generally as follows: unkilled steels will contain oxides of iron, manganese and silicon, to the extent they are present. Steels deoxidized with silicon and aluminum will contain complex inclusions containing silica, alumina and manganese and iron oxides. As aluminum is increased, it gradually replaces silicon in the inclusions, and the principal inclusions in aluminum killed steels will be alumina and iron-manganese aluminates. Calcium-aluminum deoxidized steels will contain calcium aluminates, the composition and properties of which will depend on oxygen content (see Calcium). The residual Al2O3 in a ladle aluminum deoxidized steel will usually be in the range of 0.015-0.020%. This alumina range will be present regardless of the amount of aluminum used for deoxidation. It is assumed that the remaining alumina of iron aluminate is slagged off.
Aluminum also has a profound effect on the structure of sulfide inclusions. The three basic types of sulfides present in steels have been designated as Type I (fine, randomly distributed spheroids, usually oxysulfides), Type II (intergranular chains which are most harmful to mechanical properties) and Type III (large, globular particles with complex, multiphase structures). Incomplete deoxidation with aluminum results in Type I inclusions; complete, but not excessive deoxidation produces Type II inclusions, while excessive aluminum addition leads to the formation of the Type III particles.
High aluminum contents also promote the generation of interdendritic alumina galaxies, which can impair machinability. Aluminum is added in some stainless grades to improve machinability.
Aluminum as alumina in calcium aluminate slags has found extensive use as slag conditioners at LMF stations. These are used to remove sulfur and inclusions, to lower costs of dolomitic lime, fluorspar, aluminum and calcium carbide additions, to protect the refractory lining, and to improve castability. Applications include both aluminum- and silicon-killed steels.
MRP and MRP2 are predecessors of ERP. An effective organization works with a unified database system. This post is intended to explain the need and benefits of such systems.
" MRP II is an integrated information system that synchronize all aspects of the business."
MRP II system co-ordinates:
by adopting a focal production plan and by using one unified database to plan and update activities in all the systems.
MRP can be divided into three parts which are composed of:
Product Planning functions which take place at the top management level
Operations planning handled by staff units
Operations control functions conducted by manufacturing line and staff supervisors
Checkpoints among the three divisions provide feedback regarding
adequacy of overall resources
completeness of resource commitments
quality of performance in carrying out the plans
Advantages of MRP II:
MRP information systems helped managers determine the quantity and timing of raw materials purchases. Information systems that would assist managers with other parts of the manufacturing process, MRP II, followed.
While MRP was primarily concerned with materials, MRP II was concerned with the integration of all aspects of the manufacturing process, including materials, finance and human relations.
MRP is concerned primarily with manufacturing materials while MRP II is concerned with the coordination of the entire manufacturing production, including materials, finance, and human relations.
While MRP allows for the coordination of raw materials purchasing, MRP II facilitates the development of a detailed production schedule that accounts for machine and labor capacity, scheduling the production runs according to the arrival of materials.
It involves developing a production plan from a business plan to specify monthly levels of production for each product line over the next five years. (Long term planning)
Production department is then expected to produce at the committed levels, sales dept to sell at these levels and finance department to assure adequate financial resources to built this product.
Production plan guides the master schedule and gives the weekly quantities of specific products to be built.
If capacity is not adequate, then the schedule or capacity is changed.
Once settled, this MPS is then used in MRP to create material requirement and priority schedules for production.
Then the CRP assures that capacity is available at scheduled time periods.
Execution and control activities ensures that master schedule is met.
Important terms and concepts:
The forecasting function seeks to predict demands in the future. Long-range forecasting is important to determining the capacity, tooling, and personnel requirements. Short-term forecasting converts a long-range forecast of part families to short-term forecasts of individual end items.
Resource planning is the process of determining capacity requirements over the long term. Decisions such as whether to build a new plant or to expand an existing one are part of the capacity planning function.
Aggregate planning is used to determine levels of production, staffing, inventory, overtime, and so on over the long term. For instance, the aggregate planning function will determine whether we build up inventories in anticipation of increased demand (from the forecasting function), "chase" the demand by varying capacity using overtime, or do some combination of both. Optimization techniques such as linear programming are often used to assist the aggregate planning process.
Rough-cut capacity planning (RCCP) is used to provide a quick capacity check of a few critical resources to ensure the feasibility of the master production schedule. Although more detailed than aggregate planning, RCCP is less detailed than capacity requirements planning (CRP), which is another tool for performing capacity checks after the MRP processing.
Capacity requirements planning (CRP) provides a more detailed capacity check.
Long range planning involves three functions: resource planning, aggregate planning, and forecasting. Intermediate includes production planning functions. The plans generated in the long- and intermediate-term planning functions are implemented in the short-term control.
You would want MRP 2 if you want the following:
1) You want the right materials landing on the right dock with the right quantities at the right time.
2) You want your receiving, storing, assembling and shipping of product to accurately flow.
3) You want to efficiently handle the movement of materials between multiple warehouses and destinations.
4) You want to be able manage high-volume vs low-volume materials differently.
5) You want to accurately fulfill orders in increased volume
Eg: Company is in the industrial goods wholesale distribution business.
Company has larger warehouses in China and in the India.
Company has 10 commercial outlets in the India and in Canada.
Each Outlet stocks high-volume products
Each warehouse aggregates product from around the world.
Company takes customer orders over the web, via customer service and walk-in outlet traffic.
Each warehouse fulfills orders from all sources.
The MRP would help operations and accounting manage material coordination around the world to ensure (1) efficiency and (2) profitability. It accomplishes these goals by providing insight into predictive purchasing, insight into material availability, and accountability of order execution.
Another important concept is material costing. MRP helps provide insight into accurate material costing (product costs, freight, duties, taxes, handling, etc...). Accurate material costing provides insight into product and customer profitability.
Benefits of MRP II in engineering, finance and costing
Better control of inventories
Productive relationship with suppliers
Improved design control
Better quality and quality control
Reduced working capital for inventory
Improved cash flow through quicker deliveries
Accurate inventory records
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Cr : Improves corrosion resistance and abrasion resistance
Cu : Improves corrosion resistance
Ni : Improves fracture toughness and machinability
Co& Mo : Melting point and servicing temperature
W & V : High temperature strength and hardness
S : Machinability
Mn : Hardenability
Ti : Hardenability and wear resistance
Al : Toughness,acts as deoxidant
Si : Hardenability and formability
Mg : Machinability
Recent EntriesNote-2: If a Class/division is not awarded, minimum of 60% marks in aggregate shall be considered equivalent to first class/division. If a Grade Point system is adopted the CGPA will be converted into equivalent marks as below:- Grade Point Equivalent percentage 6.25 55% 6.75 60% 7.25 65% 7.75 70% 8.25 75% Note-3: Ph.D. shall be from a recognized University.Note-4: Equivalence for Ph.D. is based on publication of 5 International Journal papers, each journal having a cumulative Impact Index of not less than 2.0, with incumbent as the main author and all 5 publications being in the authors’ area of specialization. Note-5: Experience at Diploma Institution is also considered equivalent to experience at degree level institutions at appropriate level and as applicable. However qualifications as above shall be mandatory.(B) EXPEREIENCE: Minimum of 05 years experience in teaching/research/industry of which 02 years post Ph D experience is desirable. DUTIES: To teach PG & UG students in Mechanical & Automation Engineering, lead guide and promote research, examination work, planning, governance and development of labs & curricula, promoting R & D work, any other duty assigned by the Head of Institution/higher authorities. HQ: New Delhi.
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Differences between Welding, Soldering and Brazing
Welding, Soldering and Brazing are the metal joining process. Each type of joining process has its own significance. Type of joining process to be used for joining two parts depends on many factors. In this article I have covered the differences between the joining processes welding, soldering and brazing.
1 Welding joints are strongest joints used to bear the load. Strength of the welded portion of joint is usually more than the strength of base metal. Soldering joints are weakest joints out of three. Not meant to bear the load. Use to make electrical contacts generally. Brazing are weaker than welding joints but stronger than soldering joints. This can be used to bear the load up to some extent. 2 Temperature required is 3800 degree Centigrade in Welding joints. Temperature requirement is up to 450 degree Centigrade in Soldering joints. Temperature may go to 600 degree Centigrade in Brazing joints. 3 Work piece to be joined need to be heated till their melting point. Heating of the work pieces is not required Work pieces are heated but below their melting point. 4 Mechanical properties of base metal may change at the joint due to heating and cooling. No change in mechanical properties after joining. May change in mechanical properties of joint but it is almost negligible. 5 Heat cost is involved and high skill level is required. Cost involved and skill requirements are very low. Cost involved and sill required are in between others two. 6 Heat treatment is generally required to eliminate undesirable effects of welding. No heat treatment is required. No heat treatment is required after brazing. 7 No preheating of workpiece is required before welding as it is carried out at high temperature. Preheating of workpieces before soldering is good for making good quality joint. Preheating is desirable to make strong joint as brazing is carried out at relatively low temperature.
Did you know that approximately 75% of the total manufacturing costs are already committed at the Conceptual Design phase?
Committed Manufacturing Costs by product design stage
This means that product design optimisation during the conceptual design phase can optimise on 75% of the committed product manufacturing costs. If you start optimising after the end of the conceptual design phase then you can only optimise on the remaining 25% of the committed product manufacturing costs. Therefore the most effective and beneficial optimisation approach starts as early as possible within the product design process.
Being able to predict product maximum variation using minimum and maximum worse case values within the conceptual design phase, and to identify and fine tune the main contributors, will dramatically decrease the expected product costs as well as increase the overall product quality. Knowing the main contributors to the maximum product variation will also help you to use larger tolerances for low impact contributors which will decrease the product costs even further.
Applying optimisation at the Product Conceptual Design Phase most likely will result in the following benefits for you:
- Acceleration of product’s time-to-market
- Reduction of associated costs for design changes
- Increase of product quality and robustness
- Analysis and correction of potential failures and associated risks as early as possible
- Identify and assess risks during conceptual product design
All the best,
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Fatigue failures occur when a structural member is subjected to fluctuating stresses or strain due to the action of repeated loading of varying or constant magnitude for a period (time). Failure of the member will occur at a stress below it tensile strength. The mechanics of the failure will depend on whether the material is considered brittle (sudden fracture) or ductile (gradual fracture).
Engineers undertake fatigue life calculations to design against fatigue failure, although absolute fatigue life is near impossible the fatique life calculated by available methods allows for very good prediction of fatique life that enables successful engineering design.
There are three main method used to calculate fatique life. These methods are stress life method, strain life method and crack propagation method. An engineer must determine which method is best for the particular physical problem pose to the design at hand because each method has assumptions which must truly represent the physics of the project problem. In addition, design philosophies need to be taken into account, when choosing fatigue life calculation methods
Stress life method or S-N method is used when the cycle of the stress acting on the structure is high (HCL) > 10^3 cycles and the fatique life is required in the elastic range of the material.
Fatigue life can vary greatly for small changes in stress or strain levels therefore fatigue life calculation requires close attention to be paid to the stress and strain calculation process and the stress and strain magnitude obtained.
Depending on the problem and material for which fatigue life is required, physical test or finite element analysis may be performed to determine the stress and strain level of the material. FEA is a mature technology and offers many benefit to engineering process hence it is commonly used alone or combined with testing (note that testing can be an expensive venture). Testing is sometimes used to validate FEA analysis result while FEA is used to reduce testing cost. When there is reason to believe that either the FEA is correct by analytical method or from historical test result, testing should be ignored.
After testing or FEA has been undertaken, the fatigue life is predicted base on S-N curve of the material in the stress – life approach.
Note that fatigue failure is affected by stress concentration, corrosion, temperature, overload, metallurgical structure, residual stress and combined stress.
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