Fixture Design
My task was to design a fixture for milling the slots of angular
bearing housing.
What is Milling?
Milling is the machining process
of using rotary cutters to
remove material from a workpiece by advancing (or feeding) in a
direction at an angle with the axis of the tool. It covers a wide variety of
different operations and machines, on scales from small individual parts to
large, heavy-duty gang milling operations. It is one of the most commonly used
processes in industry and machine shops today for machining parts to precise
sizes and shapes.
The axis of
rotation of the cutting tool is perpendicular to the direction of feed. This
orientation between the tool axis and the feed direction is one feature that
distinguishes milling from drilling. Hence this life cycle heuristic is to
establish representative estimates of the energy and mass loss from the milling
unit process in the context of manufacturing operations for products. The
milling unit process life cycle inventory profile is for a high production
manufacturing operation, defined as the use of processes that generally have
high automation and are at the medium to high throughput production compared to
all other machines that perform a similar operation. This is consistent with
the life cycle goal of estimating energy use and mass losses representative of
efficient product manufacturing.
Milling is a
cutting process in which material is removed by a rotating multiple tooth
cutter typically aided by cutting fluids. In milling the tool
progressively generates a surface by removing chips from a work piece as it is
fed into a rotating tool and these chips are swept away by the rotation of the
cutter.
Because both workpiece and cutter can be moved in more than one direction at
the same time, surfaces having almost any orientation can be machined. The
milling process is used to machine external surfaces, slots, produce flat,
contoured, or shaped surfaces using multi-toothed milling cutters or end mills.
Many different types of cutting tools are used in the milling process.
Milling cutters such as endmills may have cutting surfaces across their
entire end surface so that they can be drilled into the workpiece (plunging).
Milling cutters may also have extended cutting surfaces on their sides to allow
for peripheral milling. Tools optimized for face milling tend to have only
small cutters at their end corners.
The cutting surfaces of a milling cutter are generally made of a hard and
temperature-resistant material so that they wear slowly. A low-cost cutter may have surfaces made of high-speed steel. More expensive but slower-wearing materials include cemented carbide. Thin-film coatings may be applied to decrease friction or further
increase hardness.
They are cutting tools typically used in milling machines or machining
centers to perform milling operations (and occasionally in other machines tools). They remove material by their movement within the machine (e.g., a ball
nose mill) or directly from the cutter's shape (e.g., a form tool such as a
hobbing cutter).
Tooling
Milling machines can
be outfitted with a number of tool heads to accomplish different machining
needs. Some of these tool heads include cutters, rounding mills, fluted mills, and ball end mills. Some milling machines have rotating tool ends that can
change depending on the needed task—computer programming communicates with the
machine when to change its tooling. The
different tooling used in milling machines is based on material and desired
shape. Because materials like wood and steel have different physical
properties, different tool bits are needed to properly machine the materials.
If a milling machine uses a tool bit that is not strong enough to machine
steel, the tooling and even the machine itself can be damaged. Tooling that is
too strong for softer materials can damage the workpiece. The basic tooling bit on a milling machine is
called the cutter. A cutter is a shaped bar that has seen teeth. The cutter
rotates rapidly to cut down and shape materials. The cutter is attached to an
arbor, which is sometimes called a mandrel or mandrill, a shaped bar that
varies in size, length and ending, and is used to hold the cutter firmly. A milling cutter’s saw ending can be spaced,
sized, and oriented in many ways. Generally, the teeth are either positioned in
a straight up-and-down orientation or angled in a helical orientation.
Straight teeth are preferable in operations on denser materials, while helical
teeth can create very smooth cuts on softer materials. There are a variety of
cutters within these categories, including dense end cutters, t-slot cutters,
and angle cutters. Cutters are subject to different standardized sizes.
Benefits of designing a fixture
v Reduce the non-productive time and raise production efficiency.
v Maintain the stability of machining accuracy.
v Enlarge the application scope of the machine tool.
v Release the working stress and ensure secure production.
Position Analysis
Firstly, we put our workpiece horizontally on the fixture with the
hole of 250 diameters and end surface as a base point, this helps us to cancel
the x (linear and rotation), z linear and helps to maintain the workpiece. Then
we put up a plate so that the workpiece doesn’t change its rotation and we use a hexagonal nut to lock it from the front so the workpiece remains in the same position
while we work on the top surface for milling. We use three locking pins that
cancel some Degree of freedoms and we use a guideway that is locked with a
hexagonal nut that is next to the surface of the workpiece yet to mill.
Clamp Mechanism Design
Since we are manufacturing in large scale quantity. The finished
object has to be highly precise full. Even though the fixture clamping force is
small and can be easily clamped manually, it is still suggested to avoid manual clamping. The main
reason for this is because by reducing labor workers, we reduce the labor cost
and improve the quality of the product itself. The machine is more productive,
accurate, and consistent than labor workers. We place a straight plate of
dimension 20x200 and lock it with a hexagonal nut, which prevents the workpiece from slipping away from the fixture.
Parts
in the Fixture
v Mandrel is a spindle used to support the workpiece during machining.
v Hexagonal nuts are used as fasteners to tighten the workpiece.
v Locating Pin is used to control the
tolerance positioning of the workpiece, it helps to position the workpiece and
help to stabilize the workpiece while milling.
v The cylindrical pin helps to position the cutting tool so that it
moves along its guideway.
v Clamps are used to fix the fixture so it doesn’t move.
v Setting block is used to set the relative position between the
fixture and the cutting tool.
v Guideway helps the fixture to be placed rightly in the machine tool.
v Hexagonal head screw is just used as a fastener to fix the fixture.
v Body of fixture is the basic part used to connect the different
parts of the fixture in order to make them integrated while it attaches to the
machine tool so that the jig has a definite position relative to the machine tool.
Conclusion
The workpiece was successfully milled with the help of a fixture,
where not all but some degree of freedoms were canceled in order to ensure
that fixture doesn’t move or rotate so the operation can be carried out with
safety and precision.
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