March 19, 2014
Must be typed except calculations. They can be written
(3 points) Why is machining so
difficult to analyze
For the following show all work. If there is something not included, make an
assumption and WRITE it down. 5 points each unless otherwise specified
(10 points) I have an unknown material in
which I have been asked to turn for an experiment. The people contracting me want to know the
shear strength of the material. I
measure the cutting force at 400 lbs and the thrust force at 285 lbs. The tool I am using has a rake angle of 8º. The width of cut is 0.210 inches and the chip
thickness before the cut is 0.010 inches.
If the chip thickness ratio is 0.4 inches what is the shear strength of
(10 points) A turning operation is
to be performed on a lathe with an efficiency of 85%. The material being machined is an alloy steel
with a unit horsepower of 1.6 hp / (in3/min). Cutting speed is 350 ft/min and feed is .012
in/rev. Depth of cut is .010
inches. Can this job be performed on a 10
hp lathe. Show all work.
Some tools use coatings that
reduce the coefficient of friction. How does this affect the cutting process?
What are the three parameters that
you as an engineer can affect in a machining operation
How does the heat generated during
cutting affect the operation?
What are the main failure types
found in tools (5 of them)? Where do these typically occur on the tool?
What properties are desired in a material for
a cutting tool?
(10 points) In a turning operation
the operator obtained a tool life of 10 minutes at a speed of 400 ft/min and a
tool life of 50 minutes at a speed of 200 ft/min.
What is the tool life at a speed
of 100 ft/min?
What speed would he have to run if
he wanted a tool life of 30 minutes?
10)(10 points) If a bar of SAE 1040 is to be turned with a high
speed steel tool with a feed of 0.015" per revolution, and a depth of
0.050". Previous experiments have revealed that the following cutting
velocities yielded the following tool lives,
90 fpm for 30 min.
80 fpm for 90 min.
75 fpm for 150 min.
a) estimate the
cutting speeds to get tool lives of 60 and 120 minutes.
b) calculate the mrr at the two
speeds found in part a).
11)(10 points) The parameters in a tool life equation come out to
be n = 0.4 and C = 450. What % increase
or decrease occurs in the tool life if the speed
Is increased by 20%
Is decreased by 30%
12)(10 points) You are going
to machine a .25 inch hole in a block of 1020 CRS for a depth of .16
inches. Please specify a drill for this
and all its parameters. Also specify its
feed and speed. Finally give me a cycle
13)(10 points) You are to
machine a piece of bar stock. The
material is 6061 aluminum. You are to
turn the material from a diameter of .5 inches to .3 inches. Please specify an insert to do this job. Be specific (use the internet) Also specify a feed, speed and depth of
cut. The length of cut will be the
letters in your last name * (.2). Tell
me how long this will take