Metrology and Inspection MCQ Quiz - Objective Question with Answer for Metrology and Inspection - Download Free PDF

Explanation:

Profilometer Instrument

• A profilometer is a high-precision measuring instrument used to measure the surface topology, roughness, waviness, and other surface characteristics of a material. It is widely used in manufacturing and quality control processes to ensure that surfaces meet the required specifications and standards.
• A profilometer typically works by tracing the surface of a material using a stylus or an optical sensor. The sensor moves over the surface and measures its deviations from a reference plane. These deviations are then analyzed to determine surface roughness, waviness, and the presence of any flaws or irregularities.
• A profilometer is designed to measure multiple surface characteristics, including surface roughness, waviness, and flaws. Surface roughness refers to the fine irregularities on the surface, waviness corresponds to the larger undulations or deviations over a broader area, and flaws refer to defects such as scratches, cracks, or pits. Modern profilometers are equipped with advanced sensors and software that can measure and analyze all these parameters accurately.

Applications:

• Inspection of machine parts to ensure high-quality finishes.
• Measurement of surface roughness in industries such as automotive, aerospace, and electronics.
• Analysis of wear and tear on components over time.
• Evaluation of surface coatings and their adherence to specifications.

Explanation:

Interferometry:

• Interferometry is a precise measurement technique that uses the phenomenon of interference of light waves to measure small distances, surface irregularities, and refractive index changes. Interferometry is widely used in metrology, which is the science of measurement, to ensure the accuracy and precision of measurements in various applications.

Working Principle: In interferometry, a beam of light is split into two or more paths. These beams travel different paths and are then recombined to create an interference pattern. The resulting interference pattern is a function of the differences in the path lengths that the light has traveled. By analyzing the interference pattern, precise measurements of distance, surface profiles, and other parameters can be obtained.

Advantages:

• High precision and accuracy in measurements.
• Non-contact measurement, making it suitable for delicate surfaces.
• Can measure very small distances and changes in distances.
• Capability to measure a wide range of physical properties.

Disadvantages:

• Requires a stable environment to avoid disturbances in the interference pattern.
• Complex setup and analysis, requiring specialized equipment and expertise.
• High sensitivity to vibrations and temperature changes, which can affect accuracy.

Applications: Interferometry is commonly used in various metrological applications, such as:

• Inspecting machine parts for straightness: Interferometry is extensively used to inspect the straightness of machine parts. By analyzing the interference patterns, deviations from the straightness can be detected with high precision.
• Surface topography measurements: Used to measure the surface roughness and flatness of materials.
• Thickness measurements: Used to measure the thickness of thin films and coatings.
• Refractive index measurements: Used to measure changes in the refractive index of materials.
• Displacement measurements: Used to measure small displacements and vibrations in mechanical systems.

Explanation:

Surface plates are essential tools in precision engineering and manufacturing, playing a crucial role in ensuring the accuracy of measurements and the quality of manufactured parts. The correct option for the given statement is option 4, which states that all the provided statements (i, ii, and iii) are true. Let's delve into the details of each statement and understand why option 4 is the correct choice.

Statement Analysis:

(i) It is used for linear and angular measurement.

Surface plates are flat, stable platforms used as a reference plane for precision measurement. They provide a reliable base for linear measurements, such as the length, width, and height of an object. Additionally, they are used for angular measurements, where tools like sine bars, angle gauges, and other angular measuring devices are placed on the surface plate to ensure accurate measurement. The flatness and stability of the surface plate ensure that measurements are not affected by surface irregularities, thus confirming the truth of statement (i).

(ii) It is used for testing the flatness of a surface.

One of the primary functions of a surface plate is to test the flatness of other surfaces. By placing the workpiece on the surface plate and using a dial gauge or other measuring instruments, engineers can detect deviations from flatness. This process is critical in quality control and ensuring that manufactured parts meet the required specifications. Surface plates, therefore, serve as a benchmark for flatness, making statement (ii) true.

(iii) It is made of cast iron or granite.

Surface plates are typically made from materials that offer excellent stability, durability, and resistance to wear. Cast iron and granite are the most commonly used materials due to their favorable properties. Cast iron surface plates are robust and can withstand heavy loads, whereas granite surface plates are highly resistant to corrosion and have minimal thermal expansion, ensuring long-term stability. Both materials provide the necessary rigidity and flatness required for precise measurements, validating statement (iii).

Explanation:

"A comparator with higher magnification has a small range."

Magnification vs. Range Trade-off:

• Comparators amplify small dimensional differences for precise measurement.
• Higher magnification means finer resolution (ability to detect tiny changes).
• However, increasing magnification reduces the measurable range because the instrument's mechanism (mechanical, optical, or pneumatic) can only handle limited displacement before losing accuracy.

Statement (ii):
"Brooke’s level comparator is a mechanical comparator."

• Mechanical Comparators rely on physical mechanisms (levers, gears, or linkages) to amplify small displacements.

Brooke’s Level Comparator:

• Uses a spirit level and a mechanical linkage system.
• Tilt in the spirit level (due to dimensional variation) is amplified via levers to give a reading.
• No optical/pneumatic components are involved.

Sigma Comparator is a mechanical comparator:

How It Works:

• Uses a twisted metal strip (or "sigma" strip) that rotates when displaced.
• The rotation is magnified via a pointer mechanism.
• No lenses, mirrors, or light beams are used (unlike optical comparators like Zeiss Ultra Optimeter).

Johansson Mikrokator is a mechanical comparator:

How It Works:

• Uses a thin metal strip twisted into a loop.
• Dimensional changes cause the strip to unwind, moving a pointer.
• No air pressure or fluid is involved (pneumatic comparators use air jets, e.g., Solex gauges).

Explanation:

The Ra value is used to measure the roughness of a surface. Surface roughness is a critical parameter in engineering and manufacturing, as it affects the performance, durability, and appearance of a component. The Ra value, or the arithmetic average roughness, is a widely used metric for quantifying surface roughness. It is defined as the average deviation of the surface profile from the mean line, calculated over a specified length. This measurement provides a single value that represents the overall texture of the surface.

Importance of Surface Roughness Measurement:

Surface roughness measurement is essential in various industries, including automotive, aerospace, medical devices, and consumer electronics. The roughness of a surface can influence several factors:

• Friction and Wear: Rough surfaces tend to have higher friction and wear rates, which can affect the efficiency and lifespan of moving parts.
• Lubrication: Surface roughness impacts the ability of a surface to retain lubricants, which is crucial for reducing friction and wear in mechanical systems.
• Fatigue Strength: Surface irregularities can act as stress concentrators, reducing the fatigue strength of a material.
• Aesthetic Appearance: In consumer products, surface roughness can affect the visual and tactile qualities, influencing customer perception and satisfaction.
• Sealing and Adhesion: The roughness of a surface can impact the effectiveness of seals and the adhesion of coatings or adhesives.

Measurement Techniques:

Several techniques are used to measure surface roughness, including:

• Contact Profilometers: These devices use a stylus that physically traces the surface profile, recording the deviations to calculate the Ra value.
• Optical Methods: Techniques such as laser scanning and interferometry use light to measure surface roughness without physical contact.
• Atomic Force Microscopy (AFM): AFM provides high-resolution measurements by scanning the surface with a fine probe.

Calculation of Ra Value:

The Ra value is calculated using the formula:

Ra = (1/n) × Σ |Zi|

Where:

• n = Number of measured points
• Zi = Deviation of each point from the mean line

This formula gives the arithmetic average of the absolute deviations from the mean line, providing a single value that represents the surface roughness.

Applications:

Surface roughness measurements are used in various applications, including:

• Quality Control: Ensuring components meet specified roughness criteria for optimal performance.
• Process Optimization: Adjusting manufacturing processes to achieve desired surface finishes.
• Research and Development: Studying the effects of surface roughness on material properties and performance.

Understanding and controlling surface roughness is crucial for producing high-quality components that meet the requirements of various applications.

Analysis of Other Options:

Option 1: Flatness

Flatness is a measure of how much a surface deviates from a perfect plane. It is an important parameter in machining and assembly processes, where components must fit together precisely. Unlike roughness, flatness is concerned with the overall shape of the surface rather than the texture.

Option 3: Roundness

Roundness is a measure of how closely the shape of an object approaches a perfect circle. It is commonly used in the inspection of cylindrical parts such as shafts and bearings. Roundness is critical for ensuring the proper function of rotating components and minimizing vibration and wear.

Option 4: Straightness

Straightness refers to the extent to which a surface or edge deviates from a straight line. It is an important parameter in the production of linear components such as rails, beams, and shafts. Straightness ensures the proper alignment and function of mechanical systems.

In summary, while flatness, roundness, and straightness are important geometric parameters, they differ from roughness, which specifically measures the texture of a surface. The Ra value is a key metric for quantifying surface roughness, providing essential information for optimizing performance and quality in various applications.

Concept:

• The Vernier principle states that two different scales are constructed on a single known length of line and the difference between them is taken for fine measurements.

Determining the least count of Vernier callipers:

In the Vernier calliper shown in Fig 

Calculation:

Given:

One main scale division (MSD) = 0.5 mm

24 divisions of main scale = 24 × 0.5 = 12 

One Vernier scale division (VSD) = 12/25 mm 

Least count = 1 MSD - 1 VSD

The GO plug gauge is the size of the low limit of the hole while the NOT GO plug gauge corresponds to the high limit of the hole.

GO gauges which constantly rub against the surface of the parts in the inspection are subjected to wear and lose their initial size. The size of go plug gauge is reduced. To increase the service life of gauges wears allowance is added to the go gauge in the direction opposite to wear. Wear allowance is usually taken as 5% of the work tolerance.

Explanation:

Fit is a relationship that exists between two mating parts, a hole, and a shaft, with respect to their dimensional difference before assembly.

There are three types of fits.

Transition fit: It may sometimes provide clearance and sometimes interference. Here the tolerance zones of the hole and shaft will overlap each other.

Examples: Tight fit and push-fit, wringing fit, 

Clearance fit: Clearance is the difference between the size of the hole and the size of the shaft which is always positive. Here the tolerance zone of the hole will be above the tolerance zone of the shaft.

Examples: Slide fit, easy sliding fit, running fit, slack running fit, and loose running fit.

Interference fit: Interference is the difference between the size of the hole and the size of the shaft which is always negative i.e. shaft is always larger than the hole size. Here, the tolerance zone of the hole will be below the tolerance zone of the shaft.

Examples: Press fit, Shrink fit, heavy drive fit, and light drive fit, selective fit, Snap-fit, Force fit

Explanation:

Zero error

• When the fixed jaw and sliding jaw are closed, but the zero on the Vernier scale coincides with zero on the main scale. Then the Vernier calliper does not have zero error.

• When the fixed jaw and sliding jaw are closed, but the zero on the vernier scale does not coincide with zero on the main scale. Then the vernier calliper said to have zero error.

There are two types of error

1. Positive error
2. Negative error

Positive zero error

• Positive zero error occurs if zero on the vernier scale lies on right side of zero on the main scale.
• If the error is positive, the correction is negative.

Negative zero error

• A negative zero error occurs if zero on the vernier scale lies on the left side of zero on the main scale.
• If the error is negative, the correction is positive.

Important Points

Zero error is always subtracted from the observed readings.  

Explanation:

A hermaphrodite caliper is a tool used to layout lines that are parallel with the edges of the workpiece. It can also be used to locate the center of cylindrical shaped workplaces.

Explanation:-

The surface roughness on a drawing is represented by triangles.

Surface texture or roughness representation

The basic symbol consists of two legs of unequal length inclined at approximately 60° to the line representing the considered surface.

The symbol must be represented by a thin line.

The value of roughness is added to the symbols.

1. Roughness ‘a’ obtained by any production process.

2. Roughness ‘a’ obtained by machining.

3. Roughness ‘a’ obtained without removal of material.

If it is necessary to impose maximum and minimum limits of surface roughness, both values are indicated. a1 = Maximum limit; a2 = Minimum limit

Explanation:

The Vernier principle states that two different scales are constructed on a single known length of line and the difference between them is taken for fine measurements.

Determining the least count of Vernier callipers:

In the Vernier calliper shown in Fig the main scale divisions (9 mm) are divided into 10 equal parts in the Vernier scale. i.e.

Least count = 1 MSD - 1 VSD

Calculation:

Given:

10 Main Scale Division (MSD) = 10 mm, 1MSD = 1 mm

10 Vernier Scale Division (VSD) = 9 mm, 1VSD = 0.9 mm

Least count = 1 MSD - 1 VSD

= 1 mm - 0.9 mm = 0.1 mm

The difference between one MSD and one VSD = 0.1 mm

Alternate Method
One main scale division (MSD) = 1 mm

One vernier scale division (VSD) = 9/10 mm

Least count = 1 MSD - 1 VSD = 1 mm - 9/10 mm

= 0.1 mm

The difference between one MSD and one VSD = 0.1

Explanation:

In this capital letter H denotes hole and small letter g denotes shaft. This combination H7-g6 denotes the clearance fit. It can be seen in the table below the various types of fit according to the hole shaft system.

Explanation:

• This is generally used to measure the small displacement of spindles.
• It is having a sensitive gauging head with a high-quality dial indicator mounted on the sturdy column as shown in the above figure.
• This consists of fixed block A & movable block B which are coupled together with the help of slip gauges at the middle portion.

• Sigma comparator → used to measure the roughness of the surface
• The optical comparator → used for a wide range of dimensional inspection applications
• The electric comparator → used to compare the dimensions of a given working component with the actual working standard.

Explanation:

The major purpose of V-blocks is to hold cylindrical pieces or, more to the point, to establish precisely the centerline or axis of a cylindrical piece.

• For special purposes such as checking triangle effects or taps and other three-fluted tools, 120°  included angle vee-blocks are also available.

Important Points

• Standard V-blocks come as 45° blocks, i.e., the V-slides slope 45 degrees from horizontal or vertical, the included angle of the V being, of 90°.
• Because they are made with sides and ends parallel and/or square to each other, they may be used lying flat or turned over on their sides, or up-ended vertically.