Beginners Guide to
Fabriation Techniques This article covers some basic techniques of fabrication used in the making of Hexapod and the machines for Robocon team IITK
Atulya Shivam Shree 3rd April,2012
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Beginners Guide to Fabriation Techniques
Designing:
The first and foremost job in creating any machine is the designing. For this you can use any CAD
software and make the basic design of the structure beforehand. The softwares we used were:
1. AutoDesk Inventor Professional 2012-main 3D designing software
2. AutoCAD 2012
3. Corel Draw X5- used in Laser Cutting
You can also use 3Ds MAX for designing, however the industrial convention is for Inventor for
mechanical purposed. Both these softwares can be downloaded for free on the internet. Also the help
materials and tutorials are easily available on the internet.
Central Workshop Facilities:
The central workshop of IIT Kanpur has got a large collection of tools and machines. The
machines that we have used commonly include Lathe machine, Metal Bending machine, and
Metal cutting. There are other tools that can be of use in the project. For this you can go and
contact the staff at the workshop. They can help with the designing and manufacturing phase of
the parts.
If you want your parts to be made by the skilled staff at the workshop it is also possible but a
permission of the project supervisor is required.
Method of Working:
1. Plan out the design of the part
2. Create a 2D CAD design of the parts
3. Fill out a job form and get it attested by project supervisor
4. Submit the above along with the materials in the Central Workshop
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4i Lab facilities:
Laser Cutting :
Acrylic is a very good material for making prototypes or some minor parts that do not
require much of strength . For this first the parts were cut out using the laser cutting
Machine present at the 4i lab. Then the individual parts were then joined together using
chloroform as an adhesive. This technique really helped us a lot in some small parts such
as mount for sensors and some gears.You just need to feed in the 2D sketch file and the
laser will cut the material according to the lines present sketch.
Salient Features :
Light weight and Easily Available
Easy to machine to a desired shape
Cost of Laser Cutting is relatively cheap and operation is fast
Individual pieces are easy to join using chloroform
Disadvantages include less strength and brittleness
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MAKING A U-SHAPE STRUCTURE OF 3 PARTS
Method of Working:
Design the CAD design of the required files on AutoDesk Inventor or any other
software. This design should be preferentially 2D.
If the design is 2D move to step 3. For a 3D design you need to export the face
which has to be machined to a 2D sketch file of DXF extension.
After this the file will be imported on Corel Draw software. Convert the lines to
“Hairline form”. After this just give the print command and define parameters
based on material property.
The Job form for any work done will be made and it will have to be approved by
the supervisor.
The acrylic sheet used must be specifically LASER Cuttable. It is generally
marketed as CAST acrylic and available in different thicknesses and quality
Creating a Sample Object:
Step 1: Create a new Autodesk Inventor file
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Choose Standard(mm).ipt under the Metric tab
Step 2 : Create an object and save it
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Step 3: Right click on the face tp be cut out and select Export Face as
Step 4: Give it a name and save it in dxf format
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Step 5: This file is now ready for machining. Just take it to 4i lab and use Laser
Engraving and Cutting machine. On the system there you will need to import the dxf
file on Corel Draw software.
General Problems Faced:
In Autodesk Inventor(AIP) if you export the 3D structure to DXF instead of a FACE
it may be possible that the file is unable to be imported on Corel Draw. This is
because the entire 3D structure has been exported in wireform 3D format
whereas Corel Draw accepts only 2D files.
If you create a DXF file in AIP by taking the projections of a 3D object ,it will not
be imported correctly because then the diagram will be treated as an image. For
proper working the 2D file should be a set of vector lines
While Designing any object try NOT to have sharp corners. Smooth curved edges
are preferable because they are less prone to crack under an impulse
Limits of Technology:
Not all materials can be laser cut by the ‘EPILOG Laser Cutting machine in the 4i
lab. Even for acrylic there are only some special types of acrylic that can be
machined
There is a width of 0.12mm of the laser beam directed. So if a circle of radius 4cm
is present in the design file, the output will be a circle of raidius 4.12cm. In other
words the width of a line is 0.12mm unlike the ideal case of 0mm.
If the material to be cut is thick(as a rule of thumb>=6mm) the entire drawing
requires 2 passes of cutting
While cutting materials that are thick the front face(where laser strikes) is cut
accurately, while the back face may get slightly distorted
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The above example explains the effect of thickening of line. The figure in the left has
lines of minimal thickness while the picture in the right shows thick lines. As is evident
the output product will have outer dimensions slightly smaller while the inner circle
produced is bigger. The width is approx. 0.12mm.
Abrasive Water Jet Machining:
This technique can be used for a
metal/Plastic/composite to any
desired shape.The output product is
precisely cut by a high pressure jet of
water mixed with sand.We have used
this technique for machining
Aluminium, Mild Steel and Nylon.
This technique can be used for making
gears, rack and pinion mechanisms
out of aluminium and nylon. However
this is a time consuming process.
THE WATER JET MACHINE @ 4I LAB
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basically setting up the tool path for an object takes up time.Once this is done large number of products
can be created at a fast speed.
Method of Working:
Design the CAD design of the required files on AutoDesk Inventor or any other
software. This design should be preferentially 2D.
If the design is 2D move to step 3. For a 3D design you need to export the face
which has to be machined to a 2D sketch file of DXF extension.
The design is then fed into the computer terminal attached to the water jet
machine
After this the tool path is fed into the software. The software basically reads the
lines present in the file and assigns a particular operation to that file. So various
types of operation such as piercing, cutting, non cutting traversal are involved.
After the path has been defined the operation is started and the object is cut
according to the desired path
There are certain limitations to the minimum cut radius , the extent of accuracy
and other practical problems more of which can be known from a guide
Creating a Sample Object:
Step 1: Create a new Autodesk Inventor file
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Step 2 : Create an object and save it
Step 3: Right click on the face to be cut out and select Export Face as
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Step 4: Give it a name and save it in DXF format
Step 5: This file is now ready for machining. Just open it on the terminal attached to the
main machine and define the tool path
Piercing:
The point where the jet starts operation leads toa whide deformed hole to be created.
So the point of Starting is kept away from the main line of cutting. the point of piercing
is at a point which will not be used in the final product.
Inner Cut and Outer Cut
Both the given files have the same dimension circle(the one in blue) to be cut.But the
position of water jet is different in both the cases. So of a hole is to be made choose
inner cut.These options are easily available on the controlling computer.
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Outer Cut
The jet starts cutting from the red blob at centre and then moves outwards to the perimeter.
Blue line indicates the line present in the DXF file and the red area is the removed portion.
General problems faced:
In Autodesk Inventor(AIP) if you export the 3D structure to DXF format it may be
possible that the file is unable to be imported on OMAX(water jet Controlling
software ). This is because the entire 3D structure has been exported in wireform
3D format whereas OMAX accepts only 2D files.
To export as 2D files do this: right click on any of the face and select the ‘Export
face as’ option in the menu
If you create a DXF file in AIP by taking the projections of a 3D object ,it will not
be imported correctly because then the diagram will be treated as an image. For
proper working the 2D file should be a set of vector lines
The software present in the water jet machine is an old WINDOWS 2000
software. So it imports only DXF 2004 format. If you export as DXF format it is not
enough it will have to be converted to the old format . This can be done in 4i lab
itself on AUTOCAD 2012
INNER CUT
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Technological Limitations:
Brittle materials like Glass, acrylic can crack on application of high pressure water
jet
There is an upper limit on the thickness of mild Steel, Aluminium that can be
machined
The machine has an accuracy of 0.05mm in relative position
The thickness of the water jet is around 0.45mm. This makes the lines have a
width of 0.45mm. Appropriate techniques are used by the machine operator to
compensate for this error
There will be some minor problems of burring and tapering that can be
compensated depending on the part formed
