# Thread: Optimizing Cutting Rebars For Least Waste

1. ## Optimizing Cutting Rebars For Least Waste

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I have a global question for excell Gurus , somebody have any IDEEA how is possible to optimize the lenght of rebar for a least waste ?
In my country the standard lenght is 12 meters
For Example I have : 3 position Ø 16 lenght 4 m , 3 position Ø 16 lenght 5 m , 3 position Ø 16 lenght 3 m
the best way it will be to cut from 12 meters 5+4+3
But somebody at building site can cut onother way , which will be uneconomic.
I attach a workbook.
is impossible every time create from bombinations 12 meters lenght but is important to get less waste.
I posted this question also on excel forum , may here is other Ideas
I don't to ofend other guys but I think here are the better mind

2. Fuzzy logic comes to mind

If you draw all the bars and shuffle adding them up and down adding them together until they fit in a 12m length how many times up and down ?

There is software out there that does stuff like this fitting shapes into a rectangle similar approach. Keep repeat till leftover is minimal.

3. I'm probably reading things wrong but:

Is there a coordination break - between drawing and spreadsheet - based on bar position and bar length? The break seems to start somewhere between position 35 (35 or lower all correct) and position 38 (here or higher, doesn't match between files).

4. Yes the documents are different, I attach them ,may be somebody have a idea with lisp , may be somebody with macro excel ...
it doesn't matter in which program it will be done , important ,it should working

5. sergiu,

Your are after the 1d Cutting stock problem.

Here is a link to a page where you can DL an executable that will do it.

http://delphiforfun.org/programs/Cutting%20Stock.htm

ymg

6. If you want to use Excel to solve this optimization problem you can use the Solver feature.

Here I have set up your worksheet to show how to handle the problem for the 3 bar lengths of 25 DIA. The first step is to determine possible ways that the 3 lengths can be obtained from a single 12000 length bar and the amount of waste. Cases A - F show 6 ways and the amount of waste for each. I started with an initial guess of 10 units for each of the 5 cases. The table calculates the waste per bar in column L. Column P shows the total waste (waster per bar times number of bars used). Cell P73 also adds the waste as a result of any extra bars produced beyond what is needed.

You then set up the conditions using Solver.

The objective of the task is to minimize the waste so the Objective cell is the total waste, cell P73. The number of each case used is defined in cells F65:F70, with the constraints as noted specifying that the number of each size must be greater than or equal to the number needed.

Clicking Solve yields the following.

Here's a link for the Excel file with my edits: https://dl.dropboxusercontent.com/u/...iment-lrm.xlsx

What version of Excel are you using? ~ lrm

7. Irm,

This is certainly a correct solution to the problem at hand.

However, using Excel solver you have to setup the patterns
of cut manually before proceeding.

As the number of required length increases the number of
possible patterns out of a bar grows exponentially and
make the method impractical.

ymg

8. I am using 2010 version .
Here is one advice : I need to make a guess for an answer as a start.If your guess is wrong then you make another guess, until/if you can come up with a formula.
Click the button and watch it guess your answer 20 times. It will copy to the range on the right the best guess.
I make little changes in macro and it works but , but does not work for more rebars
If some one have some Ideeas how it possible to make it universal , it will be supper !

9. Solver uses guesses to find a solution. You can automate the process of generating the possible cases for needed possible bar lengths. I am traveling so don't have time for a detailed answer. Good luck.

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sergiu,

I have posted at Theswamp an autolisp solution to your problem.

Here is the link: The Cutting Stock Problem

ymg

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