First and foremost we must look at the different types of tools that could be used to cut the aluminium into the specified dimensions.
High Speed Steel
This material was invented in the 19th century and was a massive improvement on the standard cutting tools of that time since they can function under higher speeds and hotter temperatures than standard steel tools. Out of all the tools researched this has the lowest range of cutting speeds, however it is still able to cut aluminium to a rough finish, but the life of the tool is significantly small when cutting this material. However the material is the cheapest type of tools looked at.
Cast Alloys
This material is a standard base metal (e.g. iron) which has been augmented with an alloying element (e.g. nickel, tungsten, chromium etc.). The reason for doing this is to improve the metals strength and reaction to heat. This group of cutting tools can operate at higher cutting speeds and temperatures than High Speed Steel, and the tool life is significantly higher. The price of these tools are also quite reasonable.
Carbides
Strong metal such as titanium are part of the this group of materials, and are used in some of the most extreme situations, for example they are used to construct the fuselage of space shuttles which are put under the most extreme temperature any material could be put through. In relation to cutting tools, this material is second only to certain ceramics in cutting speed and operating temperatures. The pieces are highly expensive though.
Price for Cast Alloy cutting tools = approx £20.00 (set of 11 cutting tools)
source: axminster tool centre
Ceramics
As mentioned before this the type of cutting tool that is second to none. Ceramic is the name given to most crystalline oxide structures, such as silicon carbide, saolin, titanium carbide. The strength of this material has been proven through the use in space shuttle re-entry shields, military ballistic vests, and heavy duty abrasives. Yet, as said with the carbides ceramics are very expensive to produce so the tool prices are very dear, but the tool life balances that out quite well.
By looking at this research it can be said that for the current project using Cast Alloy tools would be the most beneficial to the production of the cranes.
area of aluminium = 1.88 m^2
cutting speed = 1.1-1.8 m/sec (66-108 m/min)
life of cutting tool when cutting to a finished result = approx 175 mins
cost per cutting tool = £20/11 = £1.82 per tool
tool cost = £1.8/175mins = £0.01/min
minimum wage of machine operator = £6/per hour = £0.1/min
Machining Cost = Co x tm
Co = operator wage + overhead
overhead = life of tool + material able to be cut by tool per minute
tm = amount of time needed for task to be completed
Machining Cost = £241 per/min
This is quite a reasonable cost seing as the amount of material that can be machined within a minute will make up multiple kits.
source of calculations: Handbook of Material Selection, Myek Kutz, 2002 edition, published by John Wiley & Sons New York.
other sources:
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