Computer Controlled Machining


Objectives

Let's Go...

BUT Before Starting to get to milling process and designing let's know a bit about what is CNC and machining process.

What is CNC Milling?
CNC milling is a specific form of computer numerical controlled (CNC) machining. Milling itself is a machining process similar to both drilling and cutting, and able to achieve many of the operations performed by cutting and drilling machines. Like drilling, milling uses a rotating cylindrical cutting tool. However, the cutter in a milling machine is able to move along multiple axes and can create a variety of shapes, slots, and holes. In addition, the work-piece is often moved across the milling tool in different directions, unlike the single axis motion of a drill.

~Source- http://www.cnc.com/what-is-a-cnc-mill-and-how-does-it-work/
Basicallyy It's a similar process that we did in Electronics production week using SRM-20 it removed the copper parts but in here we wil be performing those actions on the bigger parts.There is a stock , a bed , a tool which can be moved in x,y,x direction and the tool itself is rotating on the spindle tp to chip off the material.
~Source - Self Understanding
The process involves creating a CAD(Computer Aided Design) file of the desired object. Then a specialized CAM (computer-aided Manufacturing) software is required to convert the 3D CAD file into a set of codes which the machines can understand. CNC machining language, called G-code essentially controls all features like feed rate, coordination, location, and speeds. With CNC machining, the computer can control exact positioning and velocity.

There are certain factors/parameters that must be considered while using a CNC:


Source~ https://www.linkedin.com/pulse/5-factors-should-consider-selecting-cnc-tooling-clara-xiong/
Deep dive into Anatomy Of Bits

Milling is done using a cylindrical milling tool mounted in a milling tool holder that is then mounted in the tool spindle on the machine. Mostly the drill bits are made of Carbide Steel or HSS(High Speed Steel).
Each of the labelled parameter abaove is responible for its specific type of operation.

Source~ http://www.tinkerandfutz.com/a-guide-to-cnc-bits/
http://www.carbideprocessors.com/pages/technical-info/types-of-drill-bits.html

Difference between Drill bit and End Mill
Source~ http://www.amateurcnc.com/viewtopic.php?t=117

The drill mill is the mechanism driving the drill bit into the wood (or whatever material you may have) and enables it to make a hole – usually by rotation with a very high rpm. On the other hand, an end mill has an end bit that enables it to cut in all directions, unlike the drill mill. Noticed“all directions?” You did! Good for you! Except that in some cases, the end mill does not cut axially.

Types of Bits
End Mill
End mills are the most common milling cutters. End mills are available in a wide variety of lengths, diameters, and types. A square end mill is used for most general milling applications. It produces a sharp edge at the bottom of pockets and slots.End mills have cutting surfaces called flutes. The most common end mills have two to four flutes. Generally, fewer flutes evacuate more chips from your material, keeping the bit cool. However, more flutes produce a finer edge finish. There are four basic flute types, each optimized for different materials and edge finish.

Upcut and Downcut End Mill These spiral, flute-shaped end mills either carry chips up and away from the material or down into them.
An upcut will keep the bit cool while quickly evacuating materials when cutting plastic or aluminum, however, it will fray the top surface, and may lift your material so be sure to have adequate hold-downs in place.
Downcut bits ensure a smooth top surface on laminates, assist with holding down your thin parts, and possibly avoiding tabs on larger parts. A single "O" flute is key for plastics like HDPE and acrylic when clearing materials. The flute helps avoid excess heat buildup, which may cause the material to stick to and ruin the end mill and your part.



Ball-Nose Mill These bits have a rounded tip and are ideal for 3D tool paths. When combined with a “roughing” bit to clear large areas of material, this end mill will result in smooth 3D surfaces, especially with two or more passes.
V-bit A 60° or 90° V-bit is great for what’s called V-carving, in which the tip of a V-shaped bit is used to cut into narrow spaces, and the wide bottom is used to cut into larger spaces. V-bits can also create sharp corners that other end mills cannot because of their radiuses.
Source~ makezine.com


Procedure to Follow for milling

  1. Make a 2d Drawing of the design
    -Consider tolerance
    -Put the drawing in layers as per the cutting scheme
    -Arrange pieces to minimize material wastage
    -Leave ample distance between pieces to avoid overlap

  2. Export it in .dxf format

  3. Import it into software that creates tool path(Fusion 360, Aspire etc.) -Choose the type of output(cutting, pocketing etc)
    -Choose the orientation of the bit
    -Check all parameter
    -See the preview in 3D

  4. Export it as .GCODE

  5. Milling machine -Mount the correct drill bit
    -Turn on the machine
    -Turn on the exhaust
    -Rotate spindle if not used for more than 12hrs to ensure flow

  6. Plug In the USB Flash Drive
    -In my case for SIL Router else in Shop Bit U need to import G-Codes

  7. -Set x,y,z zero(Origin)
    -Do Homing
    -Calliberate the Z
    -Load the file
    -Start Milling

Designing something Big

This is something confusing I alwaysntend to try to get some inspiration for any design but this time it was not strucking in my mind how to proceed.
Just outside the lab there were too many Plant-Pots outside, so I just randomly though to create a flower Pot stand for this week.


This File can be downloaded from here

Now I exported My base and One side Brace as DXF file and Used the Aspire Software to generate the tool path.

Since the Aspire is a Paid tool but Our Lab system has the Licenced Vesrion and We all use from that system I was able to generate the toolpath and I couldn't take the snaps of the screen I would later add the snaps as the system is available to me.

The workflow of using Aspire is as follows-
  • Import the .DXF file and select the stock material dimensions viz width and length.
  • Select all the points and on the left tool bar click on JOIN ALL VECTORS this will join all the vector points leaving nothing left.
  • Now on the right select the toolbar and select the operation, make sure to slect the right bit, here Im using 6mm.
  • Select the pocketing feature, and Add tabs in ur design, TABS are basically while moving the tool skips some part wherever tab is given.
  • Apply DOG_BONE fillet if required, well it's a good practice to have it in the design.
  • Now click on generate tool path u can see it in a 3D view in the next bar.
  • Save the file as .cnc format in the USB flashDrive.
  • Plug the usb drive in the cnc (machine workflow) load the file from usb disk and press the green play button on the teach pendant after doing the homing of the machine and setting of the origin and clliberating the z axis.

Let's do routing

In our LAB we have this SIL 1325 Router
It's X,Y,Z working area is 1300x2500x200 mmm.

A dual Exhaust with vaccum is set up along side it to take away all the husks and wood dust it creates.

It's always adviced to wear protective gloves and eyewear when the machine is running.

It ha ateach pendant with it's controller which basically is used to either manuallly route or to read the files from the USB disk that is attched to the controller.

The teach pendant is required to calibrate and start the opertations.
The stock material is made fixed to the bed using slider clamps that are tightened using the bolts. S

Steps to follow-


Step1-Homing-
Homing has to be done every time the machine restarts basically in homing the machine callibrate the workspace by moving in X and Y direction.
Never be too close to the machine while it's performing some operation and always keep hand on the kil switch so that whenever the machine behaves abruptly press the kil switch to cut-off the supply

There are commands that are written on the back of the teachpendant we were always adviced to refer them before actually giving the command to machine.

Homing from Ahmad Ali on Vimeo


Step2- Now it's time to callibrate Z, for this ther is metal peice attached we just have to put the metal peice blow the bit
and press the command the bit will just touch the metal peice and move up showing the soft limit i.e
Our Z is also caliberated.
basically what it does it makes an electric field and moves till 1mm above and after touching the metal piece it shows 11mm after calliberation.


Now lets's Load the files from the USB disk

Let's Start Milling

Test CNC from Ahmad Ali on Vimeo.



The Output test

The output was not very appealing to me when I routed the base and one side.
Accidently the side brace toolpath generated was less than the actual dimension of the design it
although I kinda liked the small part, but more material of 12mm plyboard were required which was not
available more in lab also I was also not very pretty sure about seeing the design so I thought to change it.

Download the design files from here:


Group Work

Visit the group page from this link

The group work was to test runout, alignment, speeds, feeds, and toolpaths for our machine SIl-1325.
I give much credit to Mr. Ashish who has spend most hours on the machine understanding it to a level that he proposed to make a cnc for machine work much of the work was done by him and due to his experiments we came to know more about our machine limitations.

The CNC we had at our facility was an assembled one, Most of it is imported from china, the bed size is about 8X4 Feet
The feed rate and the spindle speed is controlled by Teach pendant in this machine unlike other ones, in which the feed and spindle speed is given in CAM Software
The metal tool is used to set the Z cordinate of the machine precisely, the X and Y home positions can be set via Teach pendant but the Z cordinate is set 11mm above the surface using this tool


Cutting Speed and Feed

Cutting speed is defined as the speed (usually in feet per minute) of a tool when it is cutting the work. The cutting speed in this machine is mentioned in percentage 10% to 100%, My instructor has asked me not to go beyond 70% due to safety reasons.
The spindle speeds in the machine is denoted by a number followed by S. They are 4S, 5S, 6S, 7S. 4S being the slowest and 7S the fastest.Tha maximum spindled speed at 100% is 3200RPM.

Spindle speed
Cutting Speed


Testing Kerf and Runout

The tool isn't a perfect straight line, it has some degrees of freedom in the collet, and the collet might also not be straight. So, the reality is your tool wobbles a little bit, jiggles around as it goes around, and so runout is the actual diameter of what's cut. If what's cut is larger than the diameter of the tool, it is because of imperfections in how its held in the collet. And so, one of the things you have to test is the kerf and the runout. To test for runout, we cut holes at 5 different cut depths, and measured their inner diameters. The data is as follows:
runout

So the output was taken on an average of all the values that we got from a 6mm endmill was-
(5.41+5.71+5.72+5.82+5.73)/5
= 5.678mm


Testing Speed & Feed

Feed speed is the rate at which the workpiece moves into the cutter. It is always determined in relation to the spindle speed. Using the wrong feed speed can produce too much dust or burn the workpiece. Basically when the tool is moving into the workspace by what spindle speed and what speed of the axis in that direction, in case where low speed of spindle will cause more husks and chips and it's basically dependant on both parameters you can acyually see the differnce by playing with it.
It's important to know the optimum speed to get the best out of it.

speed and feed

  • The first block- 3S- 60%
  • The second block- 4S- 60%
  • The third block- 5S- 60%


Testing Tool Path

There are two distinct ways to cut materials when milling: Conventional Milling (Up) and Climb Milling (Down). The difference between these two techniques is the relationship of the rotation of the cutter to the direction of feed. In Conventional Milling, the cutter rotates against the direction of the feed. During Climb Milling, the cutter rotates with the feed.
Conventional Milling is the traditional approach when cutting because the backlash, or the play between the lead screw and the nut in the machine table, is eliminated . Recently, however, Climb Milling has been recognized as the preferred way to approach a workpiece since most machines today compensate for backlash or have a backlash eliminator.

Key Conventional and Climb Milling Properties:

    Conventional Milling
  • Chip width starts from zero and increases which causes more heat to diffuse into the workpiece and produces work hardening
  • Tool rubs more at the beginning of the cut causing faster tool wear and decreases tool life
  • Chips are carried upward by the tooth and fall in front of cutter creating a marred finish and re-cutting of chips
  • Upwards forces created in horizontal milling* tend to lift the workpiece, more intricate and expansive work holdings are needed to lessen the lift created
    Climb Milling
  • Chip width starts from maximum and decreases so heat generated will more likely transfer to the chip
  • Creates cleaner shear plane which causes the tool to rub less and increases tool life
  • Chips are removed behind the cutter which reduces the chance of recutting
  • Downwards forces in horizontal milling is created that helps hold the workpiece down, less complex work holdings are need when coupled with these forces
  • Horizontal milling is when the center line of the tool is parallel to the work piece

When to Choose Conventional or Climb Milling

Climb Milling is generally the best way to machine parts today since it reduces the load from the cutting edge, leaves a better surface finish, and improves tool life. During Conventional Milling, the cutter tends to dig into the workpiece and may cause the part to be cut out of tolerance. However, though Climb Milling is the preferred way to machine parts, there are times when Conventional Milling is the necessary milling style. One such example is if your machine does not counteract backlash. In this case, Conventional Milling should be implemented. In addition, this style should also be utilized on casting, forgings or when the part is case hardened (since the cut begins under the surface of the material).

Source ~ https://www.harveyperformance.com/in-the-loupe/conventional-vs-climb-milling/

Designing something again-


So for another design I thought of making a table-
I thought to make a sliding fit table of a polygon shape

Download the design files from here:



Designing Again...


I was not satisfied with my above designs so I decided to make another one
Sticking to the base Idea of table I thought to make a stool more of like a table that is appealing to myself.


Download the design files from here:

Using Aspire to generate Tool path


First select the Job Size which is the peice of wood that you have enter the dimension to save the material in y case it was 16mm plywood with 1090x920 mm dimensions as shown in red box.
Then import your vectors the dxf files that I've save and if there are any open vectors join them manually by selecting the vector and selecting the join vector option from bottom left tool bar. I did not needed it although, it's a good practice.

Selecting the toolpath- A tricky thing and lot to explore

A good documentation of the tolpaths are described in Aspire's documentation-
https://docs.vectric.com/docs/V9.0/Aspire/ENU/Help/Toolpaths/Basic%20Toolpaths.html

From the toolpath tab you need to slect the proper toolpath for machining, it's basically you are deciding the the tool should move on the stock. Here you give the size of the material you are having and give some offsets and other important things like tabs and all to ensure the safety of the tool as well as the machine.
There are a lot of powerful toolpath options to expore and work upon. It depends what you want as the output so that u select the right toolpath for the purpose.

I will focus on profile toolpath because that's what I've explored the most.

Referenced from- https://docs.vectric.com/docs/V9.0/Aspire/ENU/Help/Toolpaths/2D%20Profile%20Toolpath/2D%20Profile%20Toolpath.html

Profile Machining is used to cut around or along a vector. Options provide the flexibility for cutting shapes out with optional Tabs / bridges plus an Allowance over/undercut to ensure perfect edge quality. Profile toolpaths can be outside, inside or on the selected vectors, automatically compensating for the tool diameter and angle for the chosen cut depth.
If you have vectors which are nested (like the letter 'O'), the program will automatically determine the nesting and cut the correct side of the inner and outer vectors. In addition, the program will always cut the inner vectors before the outer vectors to ensure the part remains attached to the original material as long as possible. As I had a plus inside a circle in my design. So it automatically decide the plus to be inside and circle to be outside.

Here in the image I gave the wrong cut depth i.e 14mm it can be manually adjusted when I maesured the wood it was 19mm so i did all the above procedures with 19mm cut depth earlier I thought the wood piece to be 16mm plywood but it was of 19mm thickness.

Important-If you give more cut depth than the material thickness while generating the toolpath the tool can actually go beyond the material and affect the bed of cnc which should be avoided.

Start Depth (D)-
Specifies the depth at which the Profile toolpath is calculated. When cutting directly into the surface of a job the Start Depth will usually be 0. If machining into the bottom of an existing pocket or stepped region, the depth of the pocket / step must be entered.

Cut Depth (C)-
The depth of the profile toolpath relative to the Start Depth. Tool-
Clicking the Select button opens the Tool Database from which the required tool can be selected. I used a 6mm end mill for my purpose. Pass Depth-
The Pass Depths section at the top of the form shows a list of the current pass depths. It's goofd practice ad it realeased the stress on the bit and it gets less heated in multiple passes rather than one go. I kept 6 number of passed to cut my design completely.
Allowance offset-
An Allowance can be specified to either Overcut (negative number will cut smaller) or Undercut (positive numbers will cut larger) the selected shape. If the Allowance = 0 then the toolpaths will machine to the exact size. After some group test I found out a 0.75 mm allowance was required for perfect snap fit of the assembly.
Tabs (Bridges) Tabs are added to open and closed vector shapes to hold parts in place when cutting them out of material. The Tabs will often allow the machine to run quicker and smoother because it does not have to stop to move in Z at the start and end of each tab.
I included Tabs in my toolpath.

To know more about each toolpath go to this aspire documentation which I referred to understand the toolpath I chose to work upon-
https://docs.vectric.com/docs/V9.0/Aspire/ENU/Help/Toolpaths/Basic%20Toolpaths.html

After that select the calculate to claculate the toolpath and save it as .cnc extension in the USB drive that goes in the contreller of our cnc router.


FinalOutcome

The Outcome was satisfying as the fit was perfect some filing was required to remove the tabs

.

Learning Outcome

  • I learned how to opearte the big cnc router and the commands and about the teachpendant.
  • On the software side a new ASPIRE software was introuced this week to generate tool path apart from ffabmods that I was earlier using it was kind of different also I learned how to add dogbone fillet and necessity of Tabs in our design.
  • On the machine I learned the safety measures and the machine terms for the perfecr design, i tried to learn abouth the feed rate, spindle speed.
    I learne to do homing and also tried to manually rout on the stock material.
  • Although I used only 6mm endmill but I explored the designs that are made using ballnose and v bit and also learned abouth the differneces and their application.
  • During the first time operating the CNC i broke th 6mm bit but that was accidental I learned to be more focussed and cautious while handling big machines.
    Also Mistakes are important in any learning process, I took a lesson from it overall it was another fun week of experimenting with something big.

Contact Me

Location

Ghaziabad, India

Phone

+91 93 152 67 259

Email

ahmd.ali78686@gmail.com

LinkedIn

linked.in.com/ahmad-ali-211030
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