Mechanical engineering: In your opinion, what are the rules that must be kept in mind while designing castings?

Major points while designing castings:

1. Avoid sharp corners and use curved surface/corners, because at sharp corners stress concentration is very high and can lead to a casting defect.

2. Always provide allowance and tolerances according to the type of metal to be used for casting.

3. Use of riser as per properties of a material such as for grey cast iron we don't require riser due to the conversion of carbon into graphite flakes and there is a possibility of expansion of the material in liquid and solidification state. But in solid state there is a possibility of contraction of the material to overcome this, size of the pattern can be increased by providing shrinkage allowance.

4. Cast surface finish should be very fine because this property will only decide the surface of the freshly cast material and amount of material will get wasted.

5. Casting should always be kept as simple as you can.

I have no expertise in mechanical engineering, as i am an electrical engineer. But i guess the simple rules we must follow are to avoid large flat surfaces, must keep casting as simple as possible, and most minimal too.

1. Cosider draft angle and machining allowences.

2. Minimum thickness for smooth flow of materials.

3. Internal holes and cavities.

4. Sharf edges must be avoided to give strength of the molds.

Rules that must be kept in mind while designing castings:

 

Avoid casting strain

 

Fillet all sharp angles and edges

 

Bring the minimum number of sections together

 

Avoid sharp angles and abrupt section

 

Design all sections in thickness as uniform as possible

 

Design for casting soundness to offset shrinkage

 

Proportion dimensions of inner walls correctly

 

Bosses, lugs and pads shouldn’t be used unless absolute necessity

 

Design ribs and brackets for maximum effectiveness

 

Allow for shrinkage and machine finish in dimensional tolerances

Please find the answer to your Question as follows:

-        The cross section thickness has to be uniform as much as possible.

-        Sharp corners and use of fillet have to be avoided to avoid the concentration of stresses.

-        Curved shapes can be used so as to improve the stress endurance of the casting.

-        The casting has to be designed as simple as possible.

-        Webs and ribs used for stiffening in casting have to be as minimum as possible.

 

-        Abrupt changes in thickness have to be avoided.

Thank you for the invitation. Casting is a very precise process, one defect in the cast may result in a huge failure of the part. So simplicity would give better results. You should avoid any sharp edges to avoid stresses on the part, if you were to cast big parts you should keep the mold heated to so that the molten would be uniformally cooled thus allowing air to escape and form any air bubbles inside the part. The position of the pouring spur, the well and the gate size, as well as the position of the vent/s is very important as well especially if your part doesn’t have a straight or uniform surface, the time of pouring the molten into the cast also is important, it shouldn’t be fast not slow, in order to give time for the molten to settle down and be distributed evenly, of course after the pouring is done and the part is ready, it should go through a process called anealing, which is a process of heating and cooling the part multiple times on different temperatures, this process will help to better form the molecular structure of the part. I should also mention that there are many casting process used for many different parts and applications, each has it’s own parameters to be taken In consideration. I hope my answer was appealing to you.

Thank you for the invitation

This is outside my specialty

Thanks for the invitation. Some of the rules which shall be followed to have good quality of  casting are:

1. To avoid the concentration of stresses sharp corners and frequent use of fillets should be avoided.
2. Section thicknesses should be uniform as much as possible. For variations it must be done gradually.
3. Abrupt changes in the thickness should be avoided at all costs.
4. Simplicity is the key, the casting should be designed as simple as possible.
5. It is difficult to create true large spaces and henceforth large flat surfaces must be avoided.
6. Webs and ribs used for stiffening in castings should as minimal as possible.
7. Curved shapes can be used in order to improve the stress handling of the cast.