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a)   What is a digital microscope?
The digital microscope functions as a standard stand-alone microscope, but since it includes a digital camera, it can also be connected to the computer with the included USB cable and becomes a digital video microscope. Once connected, the included microscope software allows the user to view a live image on the computer. Visuals can be captured as still images or motion video, saved and edited. The software can also be used to make measurements.
Extracted from https://www.microscopeworld.com/c-442-digital-microscopes.aspx



b)   What should I know about digital microscope?
1)     A digital microscope can be achieved by integrating a camera into the microscope or by adding a digital microscope camera to a regular microscope.

2)     An external digital microscope camera lends greater flexibility - you can use different cameras on the same microscope and vice versa.

3)     Most digital microscopes and microscope cameras include basic image capture and documentation software.


4)     Check to ensure the retailer can support the software - sometimes, post sale support is useful.

5)     If you are not planning to do much high quality printing, you may not need higher resolution than 2.0 megapixel since most computer monitors are limited to 2 MP resolution.
Extracted from https://www.microscope.com/education-center/five-things-you-should-know/about-digital-microscopes

c)   Digital Microscope vs Optical Microscope
A microscope that's digital differs from an optical microscope in a few ways:

  • Image viewing - A digital model utilizes its optics and a camera to capture images. These images are then transferred to a computer monitor for viewing. The design of the digital microscope has eliminated the eyepiece, so viewing the specimen can only happen when the images are uploaded.
  • Magnification - This design of a digital model gives it more magnification power than the average optical microscope. An optical microscope's magnification power is determined by multiplying the eyepiece magnification by the lens magnification. Since the digital unit has eliminated the eyepiece, the influencing factor of magnification becomes the monitor size of the computer.
Image produced using digital microscopeImage taken using digital microscope

  • Image quality - The quality of the images is typically better on digital, as the optics on an optical microscope work with the limitations of the human eye. By going digital, the unit can project the image directly to the camera. Without the adjustment factor in the equation, image quality is much higher
Extracted from http://www.microscope-detective.com/digital-microscope.html#sthash.m9PStN1d.dpbs


d)   What is the advantage of using digital microscope?
Using digital microscope is not mean to replace the application of stereo microscope in the production. It is an upgrade that you can make in your company to make sure that the quality of your production can be maintained or increasing. Using the digital microscope, there are several advantages rather than stereo microscope.


Firstly, using digital microscope will increase the productivity of the operator by improving their ergonomic structure of the body. Previously, when using the stereo microscope, operator need to bend their body to view sample from the lens. After few hours, their eyes will started to feel dizzy. Stereo microscope also can be seen by one person at a time. When you are using the digital microscope, which is directly transmitted to monitor, this will reduce the need to bend their body and lessen the eye stress and physical fatigue. Digital microscope also can be viewed by everybody in the site so that if there's any defect occured, they can view it right from the monitor for training and discussion purposes.
Secondly, digital microscope are capable in configuring with other accessories for more advance function such as saving image, video recording, image processing and basic measurement.

e)   Which digital microscope should I choose? HDMI or USB? 
When choosing the type of digital microscope, make sure you understand your application. If you want to do real time inspection, go for HDMI digital microscope. If you want to save image, record video and do measurement, go for USB digital microscope for saving in high pixel images.

f)   How to calculate the effective magnification and the size of your sample on your monitor when using a digital microscope?
In order to determine the total magnification on the TV monitor, the following variables must be known:

  • Objective magnification
  • Microscope adapter magnification
  • CCD chip diagonal dimension
  • TV monitor diagonal dimension

The formula used to calculate total magnification on the TV monitor is:

Total magnification = Objective magnification x Microscope Adapter Magnification x Video Magnification

The video magnification is determined by dividing the TV monitor diagonal (mm) by the CCD chip diagonal (mm). A reference chart is given below which shows video magnification for various monitor and chip sizes. To determine "Video Magnification" on a computer monitor, divide the actual image diagonal (as measured on the screen) by the CCD chip diagonal.


What is the magnificationon the TV monitor whe using a 10x objective, 0.45x video coupler, a 1/2" format CCD and a 19" monitor?


Determining the Size of your Specimen
The approximate real size of a specimen can be determined by dividing the length of the specimen measured on the monitor screen by the total magnification on the monitor.


In the above example, if the measured length of a specimen was 100mm, the real size of the specimen would be:

Real life of specimen = 100mm x 271.35

                                          = 0.37mm

a)   What is Hardness Testing?
Hardness Testing measures a material’s strength by determining resistance to penetration. The Hardness Test is extremely useful in material selection because it provides a hardness value which indicates how easily a material can be machined and how well the material will wear. Material hardness testing is also valuable in making decisions about treatments and coatings.

b)   How many types are there in Hardness Testing?
Basically, there are few types of hardness testing. But, there are three most common hardness testing used in worldwide which are Vickers, Brinell, and Rockwell.

c)   What is the difference between Vickers, Brinell and Rockwell?

d)   How
do we select the hardness testing machine that should be used?
To select the hardness testing that suitable with your requirement, table below is the guideline on how to determine the selection of hardness testing based on their material, form and application.

Key: ● Well-suited  ▲ Reasonably suited


e)   What is the principle for the hardness tester?


ROCKWELL HARDNESS TESTER
An indenter of specified size, shape and material (diamond cone, steel ball or hardmetal ball) shall be forced into the surface of the specimen in two steps under specified condition. The permanent indentation depth, h under preliminary test force shall be measured after the removal of additional test force.

From the value of permanent indentation depth, h and two constant number N and S, the rockwell hardness is calculated according to formula (1):

Rockwell hardness = N - h/s ...................................................................(1)Symbols and designation:Scales of Rockwell hardness and Rockwell superficial hardness and related matters
Permissible repeatability and error of the testing machine
How to determine the relationship between Rockwell Hardness Tester and the minimum thickness of a specimen?
The relationship between Rockwell Hardness Tester and the minimum thickness of a specimen can be explained by diagram below:

Convex Cylindrical and Spherical Surfaces
For test on convex cylindrical surfaces and spherical surfaces, correction given in table C.1 to table C.4 and table D.1 shall be applied. The hardness after correction should be the hardness of the test piece. The hardness of the test piece should be obtained according to the formula below:

Hardness of test piece = reading + correction

For test on concave surfaces, due to the absence of corrections, test on such surfaces shall be upon the agreement between the parties concern with delivery.


Correction to be added to Rockwell hardness values obtained on convex cylindrical surfaces
For tests on convex cylindrical surfaces, the corrections as given in table C.1 and table C.4 should be applied.
Hardness correction for scales A, C and D
Hardness correction for scales A, C and D

VICKERS HARDNESS TESTER
A diamond indenter, in the form of a right pyramid with a square base and with a specified angle between opposite faces at the vertex, is forced into the surface of a test piece followed by measurement of the diagonal length of the indentation left in the surface after removal of the test force, F.
The vickers hardness is proportional to the quotient obtained by dividing the test force by the sloping area of the indentation, which is assumed to be a right pyramid with a square base, and having at the vertex the same angle as the indenter.

Symbols and designation thereof:Test ForcesPosition of indentationMeasures the lengths of the two diagonals. The arithmeticals mean of the two readings shall be taken for the calculation of the Vickers hardness.For flat surfaces, the difference between the lengths of two indentation diagonals should not be greater than 5%. If the difference is greater, this shall be stated in the test report.
Magnifications should be provided so that the diagonal can be enlarged to greater than 25% but less than 75% of the field vi
ew.

Maximum
permissible percentage error of the testing machine
Cylindrical surface
Table B.3 to B.6 give the correction factors when tests are made on cylindrical surfaces.
The correction factors are tabulated in terms of the ratio of the mean diagonal of the indentation to the diameter of the cylinder.Cylindrical surfaces

BRINELL HARDNESS TESTER
An indenter of hardmetal ball (diameter D) is forced into the surface of a test piece and, after removal of the test force (F), the diameter of the indentation (d) left in the surface is measured. The Brinell hardness is proportional to the quotient obtained by dividing the test force by the curved surface area of the indentation. (The indentation is assumed to retain the shape of the ball, and its surface area is calculated from the mean indentation diameter and the ball diameter. Symbols and designation:Distance between indentation centreThe distance between the centres of two adjacent indentations shall be at least 3d. The distance of the edge of the specimen (test piece) to the centre of each indentation shall be a minimum of 2.5d.
Tolerable value of repeatability and tolerance of error.: mean of the diameters of five indentations
: hardness of reference block

Hardness symbol and testing conditions
What is the principle of metallography?
Metallography Principles are based on the following conditions :
  • Standard Procedures
  • Reproducibility
  • Actual Microstructure
  • Economics


What is the best position to observe a microstructure?

Space for Installation:

  • User Convenience
  • Safety
  • Enough Space


Arrangement for Device:

  • Device Classification
  • Noise
  • Vibration
  • Dust
  • Non-vibration
  • Clean Environment




1.  ABRASIVE CUTTING

a)   Why abrasive cutting is the most popoular method of sectioning in metallography compared to other methods (flaming, fracturing, sawing)?
It is the most appropriate method for metallography cutting due to its several benefit such as:

  • Using a coolant, thus it can prevent thermal damage
  • Use abrasive cutter and diamond cutter
  • Cutting direction – to soft material from hardened materials
  • Can remove small amounts of material, producing tiny chips
  • Abrasive processes can produce fine surface finishes and accurate dimensional tolerances.

b)   What is the type of abrasive used in the metallography?
Type of abrasive:


c)   What is the process of abrasive wheels?

1)   Select the appropriate abrasive wheel

2)   Secure specimen. Improper clamping may result in wheel and/or specimen damage

3)   Check coolant level and replace when low or excessively dirty. Note abrasive wheel break down during cutting and thus produce a significant amount of debris

4)   Allow the abrasive wheel to reach its operating speed before beginning the cut

5)   A steady force will produce the best cuts and minimize wheel wear characteristics, as well as maintain sample integrity (no burning)

6)   When sectioning materials with coatings, orient the specimen so that the wheel is cutting into the coating and exiting out of the base material, thereby keeping the coating in compression



d)   What is the common consumables used in abrasive cutting process?
There are two types of consumables used in abrasive cutting which are;


The property of consumables:

  • High speed cut-off for big specimen relatively (3,500 RPM)
  • Main material – SiC(Non ferrous metal), Al2O3 (Ferrous metal)
  • Bonding - Resin, Rubber.
  • Main size: 10”(250mm), 12”(250mm)
  • Necessary use with water soluble coolant
  • Coolant must has a good anti –rust, cooling, no smell



2.  PRECISION CUTTING

a)   What is the common material used in precision cutting?
There are two types of material used in precision cutting which are:

  • Cubic Boron Nitride (CBN)
  • Diamond


     1)   Cubic Boron Nitride (CBN)

  • CBN is recommended for cutting hard metals, specially iron and steel
  • CBN blades provide significantly reduced cutting times for tough, gummy materials, such as lead and titanium
  • CBN are not recommended for ceramics and other non metallic materials
  • CBN will provide precise cutting capability on difficult to cut samples/materials


     2)  Diamond

  • Diamond is the hardest material on earth (diamond blades) will cut hardest material






b)   What is the process of precision cutting?

1)   Select the appropriate precision wheel

2)   Secure specimen. Improper clamping may result in wheel and/or specimen damage

3)   Check coolant level and replace when low or excessively dirty. Note precision wheels break down during cutting and thus produce a significant amount of debris

4)   Allow the precision wheel to reach its operating speed before beginning the cut

5)   A steady force will produce the best cuts (weight selection) and minimize wheel wear characteristics, as well as maintain sample integrity (no burning)

6)   When sectioning materials with coatings, orient the specimen so that the wheel is cutting into the coating and exiting out of the base material, thereby keeping the coating in compression.


c)   What is the common consumables used in precision cutting process?

  • Precision wheel : CBN, Diamond, and Abrasive
  • Use oil soluble : Metal
  • Use water soluble oil : ceramic
  • Dressing stick : Aluminum oxide, Remove chip between diamond particle




3.  HOT MOUNTING MACHINE


a)   What is the important of mounting operation?

  • It protects the specimen edge and maintains the integrity of a materials surface features
  • Fills voids in porous materials
  • Improves handling of irregular shaped samples, especially for automated specimen preparation

Compression mounting is a very useful mounting technique which can provide better specimen edge retention compared to cast able mounting resins.

Compression mounting resins are available in different colors and with various fillers to improve hardness or conductivity.

Several compression mounting characteristics include:

  • Convenient means to hold the specimen
  • Provides a standard format to mount multiple specimens
  • Protects edges
  • Provides the ability to label and store the specimens



b)   What is the example of mounting defect?
Thermosetting mounting defects are:

  • Radial split
  • Edge shrinkage
  • Circumferential split
  • Burst
  • Unfused
  • Bulging
  • Porosity
  • Void
  • Bond between specimen with ram
  • Inner crack




c)   What is the characteristics of type of consumbales for mounting process?



d)   What is the recommendation consumables to be used in the mounting process?
Phenolic are popular because they are low cost, whereas the diallyl phthalates and epoxy resins find applications where edge retention and harder mounts are required.

The acrylic compression mounting compounds are used because they have excellent clarity.

However, the recommendation consumables to be used in the mounting process are:

Acrylic Resin

  • High Clarity by Small additional charge than phenolic resin
  • Easy to check its drawback such as Void, Circumferential split, Inner crack, etc.
  • Heavier Hardness than phenolic resin

Recommended Configuration for Acrylic Resin:
  • Set Temp. : 180 degree
  • Holding Time : 200 sec
  • Pressure : 210 bar
  • Cooling Temp. : 40 degree
  • Cooling Time : 360 sec
  • Total Molding Time : approximately within 12 min including pre-heating


4.  POLISHING

a)   Why do we need the polishing process in metallography process?
Grinding&Polishing is a most important operation in specimen preparation.
  • During grinding & polishing, the operator has the opportunity of minimizing mechanical surface damage that must be removed by subsequent polishing operations.
  • Even if sectioning is done in a careless manner, resulting is severe surface damage, the damage can be eliminated by prolonged grinding & polishing.

b)   What is the basic procedure for polishing?



c)   What is the common consumables used in polishing process?
     1) For grinding,


     2) For polishing,





What is a Coordinate Measuring Machine (CMM)?
At its most basic a coordinate is a point, a fixed singular location in three-dimensional space. A series of points can be used to define the parameters of a complex shape. Therefore a coordinate measuring machine (CMM) is any device that is able to collect this set of points for a given object and to do so with an acceptable degree of accuracy and repeatability.



What are the components of the CMM?
The foundation of the system is just that: a heavy base plate or table which serves as the foundation for an object placed on it to be measured. This is often a massive slab of granite or some other dense material that is stable, rigid, immune to fluctuations caused by the environment, and ground with a very flat top face.

To this table is mounted a moveable bridge or gantry. Vertical posts support a horizontal beam, and on this beam will be suspended another vertical column that holds the measuring probe. The bridge or gantry is able to move along the X-axis. The vertical spindle can move along the bridge thus defining the Y axis. And the probe on the vertical column can move up and down which defines the Z-axis over the table.


At the end of the spindle is the probe. There are different technologies available that can be used as a probe, partly depending on the objects to be measured and the degree of accuracy required. In our case, a precise sphere of ruby is mounted on the tip of the stylus.

Finally, the tip of the probe communicates its information to a computer which interprets the data with specialized software to create a 3D map of the part in question from the cumulative set of points.
Extracted from https://www.starrapid.com/blog/what-is-a-coordinate-measuring-machine/

How many types of CMM are available on the industry?

There are four basic types of stationary CMM:

  • Bridge
  • Cantilever
  • Horizontal Arm
  • Gantry


Do I want to bring my parts to the machine or do I want to bring a measuring device to my parts?
The answer to this question will depend on what you’re measuring and where you’re measuring it. If you plan on bringing the part to the machine, then you’ll want a stationary CMM. If it’s the other way around, then you’ll want a portable unit (or a stationary one and a lot of muscle).
Extracted from https://www.engineering.com/AdvancedManufacturing/ArticleID/11460/3-Tips-for-Choosing-the-Best-Coordinate-Measuring-Machine-for-Your-Quality-Process.aspx


About MSP METROLOGY

MSP METROLOGY which are a one stop solutions provider company who specialized in Optical, Hardness and Metallography Systems, to serve and optimize our customers' revenues and costs effectively in conjunction with our strong technical backup, calibration services in traceable ISO/IEC 17025 standard and Training.

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