Resin or Plastic?

Another explanation would be that injection molding consists of injecting molten plastic, usually Styrene for model kits, into a closed two piece mold at very high pressure. What we call sprues in the kits are actually the runners in the mold that allows the molten plastic to fill all of the parts in the mold. Resin is a casting process where the resin is poured into an open mold, usually made of some form of rubber, and then allowed to cure. The stubs found on the resin parts is the channel that the resin pours through into the mold. Resin castings can deliver more surface detail than injection moldings because the flexible mold allows undercuts that are impossible ( or ungodly expensive ) to achieve with injection molding. The resin molds are only good for a relatively few pours before they wear out & must be replaced from the Master. High tool grade Steel injection molds are good for many thousands of cycles. Some limited run kits use less expensive molds, such as Kirksite, which has a much more limited life & will offer slightly less crisp molding.

Regards, Rick

Ok, from what I remember in college (manufacturing engineering) is that the true difference is by industry definition. Molding refers to making the actual mold, whether it is made of sand, rubber, wood, metal, plaster, or even another type of composite. Casting is the actual process of making a repetative part. The reason why you hear a difference is that the plastics industry refers to all aspects of production as "molding" like injection molding, blow molding, and rotational molding. This is due because many of the processes require other forms of delivery and shaping of the material other than the traditional heat / pour / cast method.

Resin manufacturing still uses the traditional method of making a negative mold, heating a material (AB resin is a thermoset) pouring it into the mold to take shape when the reaction is finished, and releasing the part out of the mold. However, I would not be surprised that some resin model manufacturers are looking at using Centrifugal casting and UV vaccum casting. Which is the same as rotational molding and blow molding but using resin or alloys. However, this two processes are very costly.

Which is the big difference. Cost of material and equipement is far less for working with styrenes than it is for resins.

Scott

QUOTE: Originally posted by echolmberg Sort of a side question here: What's the difference between being "cast" and being "molded"? Thanks, Eric

Sort of a side question here: What's the difference between being "cast" and being "molded"?

Thanks,

Eric

Almost all plastic kits are injection molded in Styrene, which is an easy material to work with. Resin kits are cast, not molded, and while the surface detail can be super, the process has some inherent drawbacks. As noted above, resin dust is toxic, so care must be used when cutting or sanding. Resin can not be glued with conventional hobby glues, so you must use CA or epoxy. Finally, resin is brittle compared to styrene & smaller detail parts are easily broken. If you want to get experience with both media, buy a good quality plastic kit & a resin detail set designed for that kit.

Regards, Rick

The process of producing resin models, however, allows for much crisper detail tahn injection molding can. It also allows for "undercutting" or having detail in areas where injection would not be able to do.

Resin models are very often "home made" limited run, by small one man companies. They often models of very rare/strange subjects. Resin has a drawback: resin dust is toxic! So you must use proper protection.
Secondly, resin kits are often far more difficult to assemble because of their manufacturing proces.
Thirdly, they are very expensive.

If you are a newbie, I would stay clear of them until you some more expirience, first try modelling good kits, then try upgrading them with after market sets, then try resin kits. This way, you won't get dissapointed.

My suggestion would be that you first try some good quality kits, this may cost a bit but they are easier to build.
If you want to improve your skills, try upgrading and building cheap old kits.