LO3

Be able to set-up and operate a CNC machine to produce components

P5: Set-up and operate a CNC machine to produce components

Control Panel:

Chuck

The chuck is what holds the material stock in place during the manufacturing process. It has to be tightened with a chuck key because its vital that the stock is tightly secured so that it doesn't come out during the machining process as this can damage the material, tools and most importantly, the machine. Because a chuck key has to be used to tighten it, this means that there will be less human error within the process.

Tool Wheel

The tool wheel is what holds all the tools we need to manufacture the part and the tools fit in slot which has a number that links to each tool which is what we refer when writing g-code. The tools we use during the machining process are left-handed turning tool, center drill and the drill. Each tool is used at different stages: LH turning tool is for facing off the stock and to cut the main shape of the part; the center drill is to drill the initial hole into the part; the LH turning tool is also used for the final stage which is parting.

Coolant and Swarf

Coolant is what makes the stock stay cool and is is very important because heat energy is produced from friction of the tool on the stock. If there wasn't any coolant then the tools or machine could become damaged and the tools can be expensive to replace, especially for a good quality carbide tipped tools. Swarf is the product of waste material and coolant mixed, and this is cleared up at the end and is brushed into the swarf tray so that it can be binned because it can't be recycled.

Boxford

Although I have shown my ability to manually write g-code, the Boxford software streamlines this process by creating the g-code for the part ensuring it is accurate. Additionally, the reason this is particularly helpful is because you just have to put the measurements into the software and creates the g-code itself. After this, the software makes a simulation which can show potential errors and problem-solve before physically making a part first.

The first stage of creating simulations using Boxford is to set up the stock. I input the dimensions for the part and ensured the units were metric.

I drew out the dimensions on the software to create a cross-section of the component that was going to be made in the lathe

This is the simulation of the component.

Before tightening the chuck with the chuck key, it had to be measured so that there was 5

Here Dylan put the stock into the chuck and tightened it with the chuck key to make sure the stock was properly secured

Setting stock length correctly is important, because otherwise the tool could collide into the material and cause damage to the machine or parts within. After this Dylan selected the correct toolpath, ensured the machine door was properly shut and started the program.

Boxford software is used to generate the g-code for this operation. The part that Dylan made was made from wax and so it didn't have to be left to cool for as long as you would have to for brass.

Following this the machine was cleaned up using a brush to wipe away any material waste left in the machine.

M3: Prove the accuracy by checking a final result against specification

Important equations:

Range: highest value-lowest value

Uncertainty: range/2

Mean: (1st value2nd value)/quantity of values

Absolute uncertainty: true value-mean value

Absolute % uncertainty: (absolute uncertainty/true value)x100

Accuracy of dimensions:

I measured two inserts, one made of brass and the other made of wax. I used these measurements to compare the inserts against the specification and against each other. Most of the values are close to the specification values; however a notable exception to this is the hole depth which has the highest APU at -70% and was -2.60mm from the spec value. The reason for this is because the drilling tool that was used was curved and so it created a concave hole that was too deep due to the pointed tool head.

The hole should look like the diagram on the right but because of the tool head the cross-section view of it looks like the left instead.

When measured against the spec, the most accurate dimensions were the hole diameter, part length, lip length and dip length; part and lip length were the exact specification value and had no variance, the hole diameter and dip length had slight variance. The manufacturing technique used for this project shows how using CAD/CAM software can provide accurate and precise results in machined parts or components, and this is supported by the measurements. The parts were mostly accurate with the exception of the hole depth which was caused by the drill tool head which was curved rather than flat

D2: Evaluate the effectiveness of the Computer Aided Manufacturing process used to make recommendations for possible improvements

The image above shows a diagram of the actual outcome of the brass component compared to the desired outcome; the actual outcome shows how the drill created a concave hole as the tip of the drill was not a flat bottom. This creates a higher APU and therefore makes the actual results vary from the desired results.

Variance in cutting accuracy lowers the effectiveness of the component as it is less precise. Precision in machining is vital because it ensures that all components properly fit together, if there were to be variance in all components the total cuts then the errors would be much higher overall. Additionally, precision throughout components leads to improved consistent quality which reduces defects and helps to meet design specifications whilst reducing waste and making the design to manufacturing process more efficient overall.

Factors that affect cutting accuracy include: tool selection, workpiece stability, machine wear and tear and cutting tool shape. To decrease the errors we should have used a flat-headed drill bit as this would have made the base of the hole flat and would have met or been closer to the specification measurements. During machining the jaw chucks used to secure the stock could have loosened due to human error which could have been improved by using a torque tool to ensure consistent security. Machine wear and tear refers to how frequently the machine has been used and the effects on the machine/tool parts over time, for example our lathe machine is not brand new and therefore will show signs of wear which can lead to small faults such as inaccurate machining; tool wear can affect the precision of how the stock is cut and can also lead to inaccurate measurements. The shape of the drill bit affected the outcome of the shape of the hole and led to a concave shape, therefore changing this to a flat-headed one would fix the uncut areas of the shape; however, it could also end up decreasing the durability.

One advantage of using CAM in manufacturing is high accuracy and precision provided by compatibility across software/machines meaning that human error is reduced as there is less interference during the machining process and also provides more consistent results because of this. Another advantage is, the accuracy of measurements is close to specification and tolerances (e.g. uncertainty=0% for lip length, part length and hole diameter) because measuring instruments are regularly calibrated to ensure that the correct precision is maintained and that intrinsic error isn’t the cause of inaccurate results. Furthermore, this using digital measuring instruments such as a laser or other electronic measuring equipment provides exact results; this is done in a controlled environment which minimises deviations in results and prevents material expansion or shrinkage when working with materials such as metals or wood.

Despite this, there are some disadvantages to using CAM software in manufacturing such as human error when working with the machines (e.g. not properly tightening the chuck) this is a potential cause as to what created the large deviance in hole depth. However, this was mainly caused by the shape of the tool head, which brings me to my next disadvantage: limitations of machine capabilities. For example, due to the high cost of CNC machines and the software used to power them financial resources can become finite which results in using what resources are available; for our brass component we did not have a flat-headed drill bit which resulted in the concave shaped hole.

Potential Improvements

Solutions to these problems are to use a chuck key or torque tool to ensure that the stock was properly secured before beginning the program; another solution is to get a flat-headed drill bit to prevent the variance from the desired measurements, or, if this were not possible then to use a narrower tool head to clear out the uncut area. However a small issue with using narrower drill bits is that they are more prone to breakage so there are a couple ways to resolve this, the first is to use the narrower drill bits and gradually cut away the material layer by layer.

The second way is to buy drill bits that have carbide tips as these are stronger and less prone to breakage, a set of these may come with a flat-headed one too. These are often more expensive but provide a much higher durability and resistance to warping because of heat. Over time this will be cost effective as the tools will last longer without needing to buy new ones, but also because they will be able to consistently produce higher accuracy parts for longer. The flat bottom drill will also allow for it to make a flat inner face at the bottom of the hole and therefore will create a part that better represents the desired outcome, as shown in the image below.

Another potential improvement would be to use a 3 axis CNC milling machine to work on the brass component created on the lathe. This would allow for the part to have 4 holes drilled for the glass lens which would add to the functionality of the part and allow for it to be closer to the desired outcome. This would be quite a big change to do as ordering the machine would be costly, and then programming the new g-code to create toolpaths for the machine would be time consuming and take more skill as it is working with an additional axis. Furthermore, the machine would also need a specialised fixture making as the brass insert is rounded so using a normal vice would not hold it well enough. This may be produced in house using the 3D printer to make soft jaws or could be done by someone else but this would be at an increased cost again.

The final suggestion I would make is to use deburring to get rid of some of the jagged edges and faces of the finished part. This would create an even better surface finish for the product and make it fit into the final assembly better. If a 3 axis machine is ordered it could be done on this with a tool head on the machine, or if not then it could done by hand with a polishing wheel or hand held tool. This would add more time to making the parts, but they would feel and look much better.

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