Assalamu Alaikom

I think the better one is pressure die casting !

Yes, pressure die casting will give uniformity of metallurgical structures with low segregation. 

in case of custom production the sand casting is easy and cheap

in case of batch production the precision (or lost wax) casting is good, very accurate, but very complicated process

the pressure die casting is good too, but the cating of larger part is problematic, as Mr Mansoor said

Cylinder head is mostly made of Aluminium alloys and this alloys have good fluidity with relatively low melting temperature compared to suitable die material. So pressure die casting will be most suitable with large number of output (production). At the same time repeated production can be achieved.

This is a complex question and not easily answered.

We should perhaps put to one side the option to make the head in a grey cast iron. This traditional material has been used for cylinder heads for many years, but in general is now replaced by aluminum alloys.  Perhaps at this stage we should also limit our considerations to petrol engines rather than diesel.

Only if large quantities of motor cycle heads were required would pressure die casting be a rational option. The high tooling costs and sophistication of use of filling simulation software to reduce air entrainment would then be acceptable costs and might deliver an acceptable product. Even so, the properties of the metal will suffer significantly from the turbulence of the fill, generating oxides and porosity which will limit strength, fatigue resistance, and may cause leakage if the head is water cooled (while acknowledging that the pressure die process cannot usually provide a cored water jacket as required for a water cooled casting). However, for a low duty head this route might be tolerably reasonable and it will have a good surface finish to please the customer.

However, the fact that the question has been asked indicates that the enquirer is not a volume producer, but more likely wanting perhaps only one casting, or at most very limited quantities.  Pressure die casting is now no longer an option.

The option now is for a gravity die casting (permanent cast iron or steel mold) or sand casting. Both can benefit from the lower velocity fill, but the sand casting usually has the greater flexibility for the incorporation of an excellent filling system. Both can, if needed, provide water cooling passages without difficulty.

When considering which variety of sand casting there are many options. The low tooling costs and good accuracy of a core assembly route are commendable and is available from many small and medium sized foundries. The process can use a low velocity well designed filling system which will ensure excellent integrity of the metal, greatly increasing properties, especially fatigue life, corrosion resistance (and leak tightness if water cooled).

However, some greensand options are attractive; a cheap, loose pattern on a bench might be adequate to make one, or even a few, serviceable heads.

Many automated greensand processes can greatly exceed the rate of production of a pressure die casting while producing an accurate, sound and reliable product. A number of heads could, in principle, be made in one mold, and molds require only a matter of seconds to make. Only the surface finish will not match that of the pressure die product. Much depends here on the fickleness of market acceptability.

In addition, if the head is air cooled, its higher operating temperature will require a more appropriate alloy (which are not options for pressure die casting) such as the Al-10Mg alloy or one of the Al-5Cu type alloys. Machinists tend to complain about these alloys because of their extreme ductility, creating continuous machining swarf rather than the easy-to-manage chips produced by such traditional heat treated harder and less ductile alloys with compositions approximating to Al-7Si-0.4Mg.

Whereas the grey iron head had no trouble with valve seating which were merely machined integral with the head material, Al heads require impact and wear resistant seats of steel or high Ni alloy which are shrink fitted at cryogenic temperatures and expand in situ to be held in by compression. However, having only experience with water cooled heads I personally am unsure whether valve seats can be satisfactorily fixed in these high expansion alloys at higher temperatures.

There are plenty of additional questions which require to be answered to achieve a successful head. For instance, the gasket to seal with the cylinder block may be a simple compressible type, or may a metal gasket designed to bite into the two castings, and therefore requiring a specific hardness range in the castings for success. The expansion of the Al alloy head during service operation may cause the casting to creep under compressive stress induced by the reduced expansion of the steel holding down bolts. Thus without adequate accommodation for this differential expansion by special washers or head gasket material the gasket will eventually blow as a result of head distortion,

Pressure die casting will be suitable.

Low pressure die casting (LPDC) or High pressure die casting?

It depends upon 'material'

what is it designed to be made of?

I would want Die Casting of CAST IRON or SG cast iron ( better Compact Graphite Iron).

Usually sand molding are used (DISA / Flaskless molding) for GCI.

For Al, sure use pressure die casting ( Gravity die casting ia also used for 2 wheelers.

Cladded materials are also in vogue with Liners.

I have a paper published on LEAN Manufacturing on Piston manufacturing unit.

I believe that LPDC would be a feasible option, one can rule out HPDC as the sand cores would not be able to sustain the high pressure created in the process of around 1200 bar believe.

The John Campbell's answer (very first reply) was exhaustive and almost complete. This was perhaps reiterated (reposted) by him to draw the readers attention. My call to researchers to enable Die Casting of CAST IRON or SG cast iron ( better Compact Graphite Iron) was a 'wishful' demand.

The LPDC and HPDC differ generally in the direction of metal flow, the former favouring flow back due to gravity. The actual process employed depends more on design considerations.

Squeeze casting

pressure die casting