Homework 5: Arc Welding

Homework 5
Due: Dec 4th
Arc Welding
1. What is the difference between a gas shield and flux?
2. Describe the mechanism of a short circuit metal transfer.
3. Explain the role of high and low current in the pulse transfer mechanism.
4. What does current effect in arc welding?
5. What does voltage effect in arc welding?
6. How is current regulated in MIG welding?
7. Rods for Shielded Metal Arc Welding are coded as such “E6011”. Indicate what each
character represents.
8. From highest to lowest rank the temperature for the following gas shields: Argon,
Helium, CO2.
9. Why is tungsten selected as an electrode in TIG welding?
10. What classification of gas is needed to generate plasma?

2.   Homework Description: More fun with heat transfer
Recall that as part of homework 3 (‘Fun with heat transfer’) that you had written a C++ program to
determine how long it would take a heat plate to cool to a uniform temperature (you also created an output
file so that you could visualize the cooling plate in Tecplot). In this homework assignment, you will implement
a variation of your homework 3 task in Matlab. However, unlike in homework 3 where you created a Tecplotfriendly output file, since Matlab has its own graphics display capabilities, in this homework assignment,
you will directly display the cooling plate within Matlab rather than creating an output file. (You will also
be allowed to hard-code the parameters that were used in the input file for homework 3 at the top of your
Matlab script.)
In particular, you will work with the same equation as used in homework 3 to model the temperature
T (x; y; t) (in Kelvin) over a 2D grid of spatial locations (x; y) of a rectangular heat plate of length L meters
and height H meters at each time t seconds:
T (x; y) = To + Tme–2π2αt=L

As described more in homework 3, there other parameters in this equation other than just x, y, and t: α (the
thermal diffusivity with units of ms2 ), temperature parameter To (the fixed temperature at the sides of the
plate) and temperature parameter Tm such that a decaying multiple of Tm is added to To at each location
over time (note that Tm + To is the maximum temperature of the plate at t = 0, which is located at x = L=2
and y = H=2). Also recall that this equation denotes the temperature of a plate with an initial \hot spot”
in the middle of the plate (with temperature Tm + To) that has radiated outward with the top, bottom, left,
and right temperatures being held fixed at a different temperature, To. As t increases, the plate temperature
will eventually equilibrate to the temperature of the sides, To.
Similarly to homework 3, you will additionally have parameters dt, numXSensors, and numY Sensors.
For each time point (starting at 0 and increasing in increments of parameter dt), you should compute the
temperature of the heat plate over a 2D grid of spatial values (x; y) where x has numXSensors values
ranging from 0 to L (including 0 and L) and y has numY Sensors values ranging from 0 to H (including 0
and H) and display the temperature graphically using Matlab. For each time point, you should also compute
the difference between the maximum temperature of the plate and the minimum temperature of the plate
over the 2D grid of (x; y) spatial values. If the difference between the maximum temperature and minimum
temperature is less than 0.1, the plate can be assumed to have reached a uniform temperature of To. Your
script should also display the time it takes for the plate to reach a uniform temperature to the command
window.
Further details regarding Matlab implementation expectations
Defining parameters
Towards the beginning of your Matlab script (after your comment block), you should hard-code the parameter
values that were specified in the input file for homework 3 (choice of exact variable names is up to you):

numXSensors = 50; % number of sensors in the x-direction
numYSensors = 50; % number of sensors in the y-direction
Displaying the temperature at each time point
For displaying the grid of temperature values at each time point, you should update what is displayed in a
single figure window (i.e., do not attempt to create a separate figure window for each iteration over time as
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ENGR:1300 IEC Homework 7 Due Friday, December 7, 2018 5:00 p.m.
this would create too many figure windows). You may choose to display the temperature values as a surface
plot (e.g., see the surf function) with labeled x, y, and z axes (with or without a colorbar); as a surface
plot as viewed from the top (you can use the command view([0, 90]); to obtain a top view) with labeled
x and y axes with a colorbar (because it is a top view, a colorbar is required in this case); or a similar
meaningful graphical visualization of your choice. You should also title the plot appropriately, making sure
to indicate the current time in the plot title. Examples of traditional surface plots and a top-view surface
plot are shown in Fig. 1. Since you will be using the same figure window, you should take care that Matlab
displays the same range of temperature values at each time step on the z-axis and/or using the colorbar (e.g.,
see the axis and caxis functions). You may assume that the temperature values are all in the range from
To to To + Tm. You should also add a ‘pause’ (e.g., by calling pause(0.1) in each iteration) so that you are
able to see the changes in the temperature map/plot over time rather than just seeing the final temperature
map/plot.
Grading Rubric
100 points for working code1
• 35 points for computing Eq. 1 over a grid of 2D spatial points at each time point
{ 10 points for correctly setting up the spatial grid of 2D points (hint: consider use of linspace to
define an x vector and y vector and then using meshgrid to create appropriate 2D matrices of x
and y values for use for in the equation { use of meshgrid can be done outside your time loop
{ 15 points for correctly computing the 2D grid of temperature values given a particular time
value and grid of x/y spatial locations (hint: make sure to consider when element-by-element
multiplication may be needed)
{ 10 points for avoiding use of for loops in this step
• 30 points for appropriate display of the temperature values at each time point
{ 10 points for appropriate labeling of axes and having a title
{ 5 points for including the current time value in the title
{ 5 points for setting up the axes and/or colorbar to have a consistent range from plot to plot
{ 5 points for only creating one figure window for use of all plots
{ 5 points for including an appropriate pause at each time point
• 15 points for correctly computing the maximum and minimum temperature over the grid of 2D points
at each time step (hint: consider use of the max and min functions).
• 15 points for correctly using a loop to determine the time at which the difference between the maximum
and minimum temperature on the plate is less than 0.1
• 5 points for displaying the time it takes to reach a uniform temperature to the command window
1While not separately listed as a grading category, you are still expected to use good style. Up to 20 points may be deducted
for poor style.
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ENGR:1300 IEC Homework 7 Due Friday, December 7, 2018 5:00 p.m.
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Figure 1: Example acceptable Matlab plots of the 2D grid of temperature values at a single time point. In
all cases, make sure to label the axes and title the plot appropriately (to include providing the current time
value). (a) Surface plot without a colorbar. (With this option, please ensure that the z-axis range stays
consistent from one time to the next using the axis function.) (b) Surface plot with a color bar. (With
this option, please ensure that the z-axis range stays consistent from one time to the next using the axis
function and that the range for the colorbar stays consistent from one time to the next using the caxis
function.) (c) Top-view of surface plot with colorbar. (With this option, please ensure that the range for
the colorbar stays consistent from one time to the next using the caxis function.)
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