Green sand casting is a very common method of casting process. Among many manufacturing processes casting process is considered as most economical. Wastage of material is minimum here. Also complex shapes can be manufactured. It is named as green due to moisture content. A mould is prepared by mixing silica sand, clay, bentonite, molasses, water and other additives. Sand can withstand high temperature. It is easily available. It is cheaper than other materials. Therefore still it is used till now. Metal is heated in a furnace known as cupola. Now a day’s different types of heating devices are used. Induction furnace and gas based furnaces are being popular now a days. But there are issues also with this industry. A lot of rejections are observed in this casting process. Mostly this process is used for automotive industry, agricultural tools and general purpose machines. Unskilled labor, improper layouts, poor handling of materials, improper process control, defects in input material caused rejections in this casting.
Many factors are influencing casting process. Some factors are controllable factors while some are uncontrollable. Moisture content, sand grain size, clay content, number of vent holes, mold pressure, permeability, green strength, pouring temperature, pouring time no. of ramming are known as controllable factors. Controllable factors are those factors which can be controlled or varied.
Some factors such as atmospheric temperature, humidity are uncontrollable Factors. Uncontrollable factors are also known as noise factors. So we can do experiments and optimum values of controllable factors can be determined. Experiments can be done in many ways but Taguchi’s design of experiment is considered as best one. Taguchi’s method minimizes no. of experiments. In this way, quality control of casted product can be done.
Taguchi suggested an orthogonal array for experimentation which was able to reduce no. of experiments. Here control parameters have an optimum setting which gives best results. Signal to noise ratio which is log function of wanted output provides an objective function for optimization. There are three signal to noise ratio for optimization of a process for batches.
(1) Smaller the better:
(S/N)_SB= -10* log (〖MSD〗_SB )
Where,〖MSD〗_SB = 1/N ∑_i^N = 1(1/(y_i^2 ))
Examples are vehicle fuel emission, consumption of fuel etc.
(2) Larger the better:
(S/N)_LB=-〖10〗^* log(〖MSD〗_LB )
Where,〖MSD〗_LB = 1/N ∑_i^N = 1(1/(y_i^2 ))
Examples are per shift production in a factory, Mileage per litre of fuel etc.
(3) Nominal the best
(S/N)_NB= -10* log (〖MSD〗_NB )
Where,〖MSD〗_NB = 1/N ∑_i^N = ( yi – yo)2
Examples of nominal the best is air pressure in tyre, gauge location in a panel of instrument
Taguchi method aims improvement in a process, product, material, equipment or a facility. Steps of Taguchi methodology are as follows.
1. Key factors of a process is to be identified
2. Uncontrollable factors or noise factors and testing conditions are identified.
3. For optimization objective function is decided.
4. Main controllable factors and their levels are decided.
5. Orthogonal array matrix is selected.
6. Experiment is conducted.
7. The obtained data is analyzed and best levels of controllable parameters are decided.
8. Confirming experiment is done. Future planning is done.
Taguchi methodology is good for wide sectors such as manufacturing, services sector, medical field or sales &marketing.