Reg: 19MCD0042 Assignment-1 Date:6-10-2020

Nishar Alam Khan

DFMA

1.Discuss any five DFMA guidelines to be followed to achieve the economic design
DFMA enables the identification, quantification and elimination of waste or inefficiency in product manufacture
and assembly.

The main principles of DFMA are:

1. Minimize the number of components:
Thereby reducing work-in-process. Assembly costs are reduced. The final product is more reliable
because there are fewer connections. Disassembly for maintenance and field service is easier. Reduced
part count usually means automation is easier to implement. Work-in-process is reduced, and there are
fewer inventory control problems. Fewer parts need to be purchased, which reduces ordering costs.

Fig: Self-Fastening Features

2. Use standard commercially available components:

Design time and effort are reduced. Design of custom-engineered components is avoided. There are
fewer part numbers. Inventory control is facilitated. Using quality standardized parts can shorten time to
production as such parts are typically available and you can be more certain of their consistency.
Reg: 19MCD0042 Assignment-1 Date:6-10-2020
Nishar Alam Khan
DFMA

3. Create Modular Assemblies:

Using non-customized modules/modular assemblies in your design allows you to modify the product
without losing its overall functionality. A simple example is a basic automobile that allows you to add in
extras by putting in a modular upgrade.

Modular design also opens up another window for product designers. With a modular design you can
add new parts to the product without having to buy new equipment. This lengthens the product life span
immensely

4. Integrate products for multifunctional use:

Multi-functional tooling system helps in saving time, cost by reducing machine downtime cost during
tool change. There are various types of multifunctional devices for example:
GE 100 helps in Facing, turning, internal and external chamfering of pipes and rods in only one operating
step. The flexibility of this modular tooling solution turns standard tool GE 100 into a “special tool” for
the most varying of machining tasks.

Task:

Workpiece Final product

Principle of operation up until now:
There were seven steps of processing carried out on given work piece to obtain the final product.
Reg: 19MCD0042 Assignment-1 Date:6-10-2020
Nishar Alam Khan
DFMA

Disadvantages
• A different tool for each processing step
• Uneconomical
• Time-and cost intensive
• Often inefficient

But with the help of Multi-functional tooling system GE 100 these steps can be rolled into one
Reg: 19MCD0042 Assignment-1 Date:6-10-2020
Nishar Alam Khan
DFMA

Advantages of Multi-functional tooling system GE 100

• Efficient and economical
• Saves time and personnel cost
• Saves warehouse costs and initial costs of tool
• Reduces machine downtimes
• Reduces production and unit costs

5. Design for ease of assembly:

This is a critical consideration for sheet-metal products. Engineers should strive to develop parts that
insert into one another easily and intuitively and always with the proper orientation. Self-locking features
contribute to short assembly times and lower parts counts.

Usually, it is a good practice to design the first part large and wide to ensure the stability and then
assemble smaller parts on top of it. It is also a good practice to design parts in such a way that they can
be assembled from one direction, rather than multiple directions, which extends assembly times further.
Reg: 19MCD0042 Assignment-1 Date:6-10-2020
Nishar Alam Khan
DFMA

2. The exploded view of a conventional motor drive assembly is shown fig. Modify the
assembly as per the DFMA guidelines and give justification for reducing the total
number of components.

1. Base: 1st part to be assembled, it is a theoretically necessary part.

2. Bushings (2): Base and bushings could be of same material.

3. Motor: standard subassembly of parts.

4. Motor screws (2): separate fasteners do not meet the criteria because an integral fastening arrangement
is always theoretically possible.

5. Sensor: Standard subassembly.

6. Set screw: Theoretically not necessary.

7. Standoffs (2): They could be incorporated into the base.

8. End plate: Must be separate for reasons of assembly of necessary items.

9. End plate screws (2): Theoretically not necessary.

10. Plastic bushing: Could be of the same material as the end plate.

11. Cover: Could be combined with the end plate.

12. Cover screws (4): Theoretically not necessary.

Reg: 19MCD0042 Assignment-1 Date:6-10-2020
Nishar Alam Khan
DFMA

Redesign:

Fig: Redesign of motor drive assembly following DFMA guidelines

 Motor and sensor subassemblies could be arranged to snap or screw into the base and a plastic cover
designed to snap on.

 Only four separate items would be needed instead of 19.

 These four items represent the theoretical min number needed to satisfy the requirements of the product
design without considering practical limitations.

 Two screws are needed to secure the motor.

 One set screw is needed to hold the sensor.

 The design of these screws could be improved by providing them with pilot points to facilitate assembly.

 The two powder metal bushings are unnecessary.

 It is difficult to justify the separate standoffs, end plate, cover, plastic bushing, and six screws.

Table: Results of DFA Analysis for the Motor Drive Assembly Redesign
Reg: 19MCD0042 Assignment-1 Date:6-10-2020
Nishar Alam Khan
DFMA

3. Do literature survey on surface roughness parameters induced by the following

processes. (i) Shot peening (ii) Burnishing (iii) Grinding (iv) Electro-polishing
1. Shot peening:
ChangFeng Yao and JiYin Zhang carried out research on the change of surface integrity using
the shot peening process. Surface integrity measurements, fatigue fracture analysis, and fatigue life tests
are conducted to reveal the effect of surface integrity on crack initiation and fatigue life. The results show
that shot peening can reduce the dispersion and instability of surface integrity. although it increases the
surface roughness; the maximum residual compressive stress and depth of residual stress layer increase
significantly after shot peening, and the residual stress and hardening distribution are very good.

Figure: Surface roughness before and after shot peening

Fig: Morphology of microstructure after peening: (a) 1# Ra = 2.568mm, (b) 2# Ra = 2.584mm,

and (c) 3# Ra = 2.678 mm.
The results show that the effect of shot peening process on samples is very strong and causes a significant increase
in surface roughness. In the process of shot peening, the continuous random pellets strike the surface of the
specimen, the specimen surface craters or pellets are embedded in the surface, resulting in surface roughness
increase.
Reg: 19MCD0042 Assignment-1 Date:6-10-2020
Nishar Alam Khan
DFMA

Figure shows the microstructure of peening. Grain refinement, deformation, and elongation are evident in peening
direction. Depths of plastic deformation layer of the three specimens in Figure are about 20mm. Obvious
microstructure deformation generated mainly because of the impact of the projectile produced.

Fatigue test: Figure (a) shows the morphology of fracture and Figure (b) shows the fatigue source zone for the
shot peened fatigue specimen. It’s very interesting that the fatigue source locates in the subsurface, and the fracture
surface is relatively flat. For these peened fatigue samples, the average fatigue life is about 1.2×10⁶ cycles. From
Figure (a), it can be seen that the fatigue source zone of specimen is flat. In this small region, a lot of fatigue strips
extend outward from the source of fatigue. In the case of amplification, more obvious fatigue stripes are parallel
to each other, as shown in Figure (b).

Findings:
The surface roughness is one of the factors to evaluate the fatigue performance of the specimen. Although surface
roughness increased, it is not enough to influence fatigue properties. Shot peening process can identify the fatigue
source location in subsurface and improve the fatigue life

2. Burnishing:

Effect of Ball Burnishing Process on the Surface Quality and Microstructure

Properties of AISI 1010 Steel Plates. F. Gharbi, S. Sghaier, K.J. Al-Fadhalah, and T.
Benameur
A newly developed ball burnishing tool was designed and tested for surface finishing of large flat
surfaces in a shortest possible time. It was found that the burnishing force has the most influential effect
on the surface roughness and hardness, followed by the burnishing speed, and least influence by the feed
rate. In addition, microstructural examinations of the burnished surface indicate that burnishing force
more than 400 N causes flaking of the burnished surfaces. The optimal burnishing parameters for the
steel plates were a combination of a burnishing speed of 235 rpm, a burnishing force of 400 N, and a
feed rate of 0.18 mm/rev. Using these parameters, the mean surface roughness has been improved from
Ra = 2.48 to 1.75 ⴗm, while the hardness increases from 59 to 65.5 HRB.
Reg: 19MCD0042 Assignment-1 Date:6-10-2020
Nishar Alam Khan
DFMA

Fig. Microstructural examination of cross-section of 1010-steel specimens using SEM. (a) Unburnished; (b)
burnished (burnishing conditions: F = 500 N, n = 235 rpm, and f = 0.18 mm/rev); (c) burnished (burnishing
conditions: F = 600 N, n = 235 rpm, and f = 0.18 mm/rev)

The two optimum parameters that were selected so far are a burnishing speed of 235 rpm and a feed rate of 0.18
mm/rev. The results indicate that the third optimum parameter, that is the burnishing force, can be either 500 or
600 N. Both of these cases gave comparable results with little advantage to the 600 N case. Observations made
by SEM on a cross-section of the burnished samples indicate that 500 and 600 N forces have both caused shattering
of the workpiece subsurface. The increase in the burnishing force from 500 to 600 N increases the depth of the
hardened layer from 35 to 50 ⴗm, respectively. In this layer, there is a large distortion of the grains due to the
plastic deformation accompanying the burnishing process. At these high forces, the surface hardness increases
with force until it reaches a limit beyond which flaking of the metal would occur. This situation causes lower
efficiency and failure of the workpiece and therefore a smaller burnishing force of 400 N was selected. The case
with 400 N did not cause flaking in the subsurface layer. Therefore, the optimum burnishing parameters for AISI
1010 steel plates are 235 rpm for the burnishing speed, 0.18 mm/rev for the feed rate and 400 N for the burnishing
force.

Findings:
• With the increase in burnishing force depth of hardness increases
• There is large distortion of the grains due to plastic deformation
• Surface hardness increases till flaking of metal would occur
• Flaking of surface should be avoided
Reg: 19MCD0042 Assignment-1 Date:6-10-2020
Nishar Alam Khan
DFMA

3. Grinding:
“Influence of grinding operations on surface integrity of stainless steels” by NIAN
ZHOU

Figure 10 Surface topography and surface defects after grinding by 60# grit size abrasive, 60% machine power
and without lubricant: (a) austenitic stainless steel 304L, (b) duplex stainless steel 2304.

Surface roughness resulting from different grinding parameters was measured through both Ra and Rz factors
The highest surface roughness was induced by using coarse grit size (60#) abrasives, giving an Ra value of 1.81μm
with an Rz value of 18.4μm for 304L and an Ra value of 1.45μm with an Rz value of 15.84μm for 2304. Much
smoother surfaces were obtained by using finer grit size abrasives as the final surface finish or grinding lubricant
during the operations. By using the finest grit size (400#) abrasives, Ra and Rz values decreased dramatically;
Ra=0.34μm, Rz=5.66μm were measured for 304L and Ra=0. 4μm, Rz=6.4μm for 2304. As illustrated in Figure
10, deep grooving, smearing, adhesive chips and indentations are the four types of defects found on the ground
surfaces. The ground surface finish was influenced by the complex interactions between the abrasive grits and the
workpiece surface. Deep grooving came from the uneven metal removal process, including chip forming and
ploughing. Material around abrasive grit particles was pushed out and moved across the surface, which led to the
formation of smearing areas. Abrasive particles broke down into small pieces during grinding; because of the
rubbing contact between these broke down particles or formed chips and the workpiece surface, indentations were
formed on the ground surfaces.

Findings:

• Surface roughness and surface defects can be largely decreased by using smaller grit size abrasives or by
using grinding lubricant for both austenitic stainless steel 304L

• Surface defects can be reduced by using a higher machine power

Reg: 19MCD0042 Assignment-1 Date:6-10-2020
Nishar Alam Khan
DFMA

4. Electro-polishing:
Electropolishing of 304 stainless steel: Surface roughness control using experimental design
strategies and a summarized electropolishing model by Chi-Cheng Lin

Fig. 6. (a, c, e and g) SEM photographs results of 304 stainless steel electropolished in a solution containing (a)
H3PO4:H2SO4 = 2:1 (75 vol.%) and 25 vol.% glycerol at 80 ◦C and 0.5Acm−2 for 10 min; (c ) H3PO4:H2SO4
= 2:1 (75 vol.%) and 25 vol.% glycerol at 30 ◦C and 0.5Acm−2 for 5 min; (e) H3PO4:H2SO4 = 2:1 at 35 ◦C and
0.5Acm−2 for 6.25 min; (g ) raw 304SS without polishing

The morphologies of 304SS with electropolishing under various conditions are shown in Fig. Fig. 6a shows the
morphology of a 304SS sheet with a high Ra value of 44.7 nm, which was polished at a high temperature (80 ◦C)
for a relatively long time (10 min). As found in Oppositely, the 304SS with a low Ra value of 7.3 nm (see Fig c)
was obtained under a low temperature (30 ◦C) for a relatively short time (5 min). The surface is very flat due to a
uniform dissolution everywhere. This result is attributed to the whole coverage of layer B and a short polishing
time depresses the increase in Ra. Fig. e represents the result obtained from the solution of phosphoric acid and
sulfuric acid without glycerol at 35 ◦C. Its morphology is similar to that of a raw sheet (see Fig. 6g with very close
Ra values.

Findings:

The EP time is one of the key factors promoting Ra of 304SS, which does not involve in any interactions with
other polishing variables. The results showed that Ra of 304SS is decreased with decreasing the bath temperature
and polishing time but increased when the temperature was lower than 20 ◦C

4.The following figure shows the shaft-hole assembly. Basic size = 20mm; hole
tolerance = 0.005mm; shaft tolerance = 0.005mm; and allowance = 0.005mm. Sketch
various possibilities of clearance fit for the given dimensions.

Fig. Shaft-hole assembly

Reg: 19MCD0042 Assignment-1 Date:6-10-2020
Nishar Alam Khan
DFMA

Preferred clearance fit:

Reg: 19MCD0042 Assignment-1 Date:6-10-2020
Nishar Alam Khan
DFMA

5. Explain the symbols of form tolerance and position tolerance using suitable
sketches.

Form Tolerance:
Form tolerances can be state by four tolerance zone. These form tolerances are Straightness, Flatness,
Circularity, and Cylindricity. These form tolerances apply to individual features therefore the Form
Tolerances are not related to datums.

a) Straightness:
Straightness actually has two very different functions in GD&T depending on how it is called out. In its
normal form or Surface Straightness, is a tolerance that controls the form of a line somewhere on the
surface or the feature. Axis Straightness is a tolerance that controls how much curve is allowed in the
part’s axis. This is usually called out with an included call to maximum material condition. Both callouts
are very different from each other.
Symbol

Fig: Measurement using gauge

b) Flatness:
Flatness is a condition of a specified surface having all elements in one plane. Flatness tolerance provides a
tolerance zone of specified and defined by two parallel planes in where the specified surface must lie. Flatness is
applied to an individual surface; flatness tolerance does not need to be related to a datum. A feature control frame
is attached to the surface with a leader or extension line. When a feature control frame with a flatness tolerance is
applied with a size dimension, the flatness tolerance applies to the median plane for a noncylindrical surfaces. The
derived median plane is composed of the midpoint of the actual local size. The median plane is not necessarily
flat. The flatness tolerance may be used to control the form of derived median plane. Also, the straightness
tolerance may be used to control the form of the derived line.
Reg: 19MCD0042 Assignment-1 Date:6-10-2020
Nishar Alam Khan
DFMA

Symbol:

Fig: Tolerance Zone

c) Circularity:
Circularity is a condition of a surface of a part. Circularity tolerance is used to control the roundness of circular
parts or features. Circular features can be defined by cylinders, spheres, and cones. Circularity tolerance controls
each circular element of a cylinder independent of each other. Circularity tolerance is applied to an individual
surface, Circularity tolerance does not need to be related to a DATUM. The Circularity tolerance of the
manufacturing part specifies where all points of a surface of a circular part must lie in the zone bounded by two
concentric circles which radiis differ by the tolerance value of the concentricity.

Symbol:
Reg: 19MCD0042 Assignment-1 Date:6-10-2020
Nishar Alam Khan
DFMA

Tolerance Zone:

Gauging: Circularity is measured by constraining a part, rotating it around the central axis while a height gauge
records the variation of the surface. The height gauge must have total variation less than the tolerance amount.

d) Cylindricity:
Cylindricity is a condition of a manufacturing part surface of revolution in where all points of the circular surface
are equi-distant from actual axis. Cylindricity tolerance is applies where cylindrical part features must have good
circularity, straightness and taper. Thus, Cylindricity tolerance applies both longitudinal and circular element of
the surface. Cylindricity tolerance is applied to an individual surface, cylindricity tolerance does not need to be
related to a datum. Cylindricity tolerance controls the entire surface of a cylinder.

Symbol:

Drawing Callout
Reg: 19MCD0042 Assignment-1 Date:6-10-2020
Nishar Alam Khan
DFMA

Measurement with gauge:

Cylindricity is measured by constraining a part on its axis, and rotating it around while a height gauge
records the variation of the surface in several locations along the length. The height gauge must have total variation
less than the tolerance amount.

Position Tolerance:
Positional tolerance is a three-dimensional geometric tolerance that controls how much the location of a
feature can deviate from its true position. Positional tolerances are probably used more than any other geometric
control. Positional tolerances is used to locate features of size from datum planes such as a hole or keyway and
used to locate features coaxial to a datum axis. A position tolerance is the total permissible variation in the location
of a feature about its exact true position. Positional tolerances for cylindrical features, the position tolerance zone
is typically a cylinder within which the axis of the feature must lie. Positional tolerances for other features, the
center plane of the feature must fit in the space between two parallel planes. The tolerance defines a zone that the
axis or center plane of a feature of size may vary from. The concept is there is an exact or true position that the
feature would be if it was made perfect however since nothing is made perfect a tolerance zone allows deviation
from perfection. The exact position of the feature is located with basic dimensions. Datums are required. The
true/exact location of a feature of size is defined by basic dimensions which is shown in a box and are established
from datum planes or axes. When a material condition modifier is specified a boundary named virtual condition
is established. It is located at the true position and it may not be violated by the surface or surfaces of the
considered feature. Its size is determined by adding or subtracting depending on whether the feature is an external
or an internal feature and whether the material condition specified. LMC or MMC can apply to feature of size
apply to feature of size.

Symbol:

Tolerance Zone:
Reg: 19MCD0042 Assignment-1 Date:6-10-2020
Nishar Alam Khan
DFMA

Measurement

Concentricity:
Concentricity tolerance zone controls the median points of a feature of size. Concentricity tolerance is a condition
in which the axes of all cross-section elements of a feature’s surface of revolution are common to the axis of a
datum feature. A concentricity tolerance specifies a cylindrical tolerance zone whose axis coincides with a datum
axis and within which all cross-sectional axes of the feature being controlled must lie. The tolerance zone is
equally disposed about the datum axis for concentricity. The Concentricity requires that the median points of the
controlled feature, regardless of its size, to be within the tolerance zone.

Symbol:

Drawing Callout: Tolerance Zone:

Gauging / Measurement
Reg: 19MCD0042 Assignment-1 Date:6-10-2020
Nishar Alam Khan
DFMA

Symmetry:
GD&T Symmetry is a 3-Dimensional tolerance that is used to ensure that two features on a part are uniform across
a datum plane. An established “true” central plane is established from the datum and for the symmetry to be in
tolerance, the median distance between every point on the two surface features needs to fall near that central plane.
Each set of points on the reference features would have a midpoint that is right between the two. If you take all
the midpoints of the entire surface, this must lie within the tolerance zone to be in specification. Symmetry is not
a very common GD&T callout since it has very limited functional uses (centering location is done with Position)
and the verification and measurement of symmetry can be difficult

Symbol:

Tolerance Zone:

Gauging / Measurement