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Slide Mold

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  • Member since
    May 2008
Slide Mold
Posted by Tom8321 on Friday, February 4, 2022 2:55 PM

Hi .. can someone explain what a Slide Mold is and how that seems to be a favorable way to mold parts?  It seems to be mentioned when there are better, more detailed parts.

I've seen this reference many times but I can't seem to find a good Google explanation.

Thank you, Tom

PS... So far wonderful information but I want to add to my question... Why are Resin parts desireable for their detail?  In other words, why is Resin able to acheive more detail than regular plastic?

Again thank you for your resposes.   

  • Member since
    March 2007
  • From: Northeast WA State
Posted by armornut on Friday, February 4, 2022 3:59 PM

   Hi, slide molding is fairly new to modeling. The normal or usual way to form parts is to have 2 plates that have been engraved with cavities. The plates are pressed together and molten plastic is injected under high pressure, thus creating out parts.

     The downside of this is items such as gun barrels, intake trunks, exhaust pipes are usually solid requiring drilling ot hollow out.

      Slide molding allows for a 3rdvor even 4th plate to be used to create the parts. As a benefit now our barrels and exhaust pipes are beautifully hollow, and some fine detail can now be made with fewer, better fitting parts.

we're modelers it's what we do

  • Member since
    April 2003
  • From: USA
Posted by keavdog on Friday, February 4, 2022 3:59 PM

Thanks,

John

  • Member since
    September 2012
Posted by GMorrison on Friday, February 4, 2022 4:03 PM

keavdog

really good. The technology has been around for a long time in the foundry to make stuff like bells

 Modeling is an excuse to buy books.

 

  • Member since
    May 2009
  • From: Poland
Posted by Pawel on Friday, February 4, 2022 4:13 PM

Hello!

We're talking about molds being equpped with 3rd, 4th and further parts - so called sliders - that move from side to side if we look at the mold in a way where the main parts move up and down when they open to release the sprue (with parts we want) after it is injection molded. Like has been written before - this sideways movement allows for additional detail on the side of the part - such detail would be impossible on two part mold. The only other way do mold such part with only top and bottom mold would be to divide the part to be molded so that the detailed sides always face up and/or down.

Let's take a tank hull - with a two part mold you would have to make it out of individual plates - bottom and sides, detailed with nuts or rivets to be glued together. With slide molding you could make a mold with two sliders with nut/rivet detail for the sides on them and mold that tank hull with detailed bottom and sides in one part. If you tried to mold this one part in just two part mold it would be impossible to eject the part out of the mold after plastic hardened, because the detailed sides would cause it to lock with the mold.

Hope that helps - thanks for reading and have a nice day

PaweĊ‚

All comments and critique welcomed. Thanks for your honest opinions!

www.vietnam.net.pl

  • Member since
    May 2008
Posted by Tom8321 on Friday, February 4, 2022 4:34 PM

keavdog

Thanks much... using this I was able to find other similar articles and it's really making sense.  

  • Member since
    December 2002
  • From: Fort Knox
Posted by Rob Gronovius on Saturday, February 5, 2022 11:00 AM

If you've been modeling for a while, just about every Monogram car model body was made using a slide mold. That's how the bodies with curved sides are able to get out of the molds.

  • Member since
    August 2005
  • From: Mansfield, TX
Posted by EdGrune on Saturday, February 5, 2022 12:54 PM

Tom8321

PS... So far wonderful information but I want to add to my question... Why are Resin parts desireable for their detail?  In other words, why is Resin able to acheive more detail than regular plastic?   

 
The OPs PS asked about resin pieces.  To cover this really needs a brief understanding of the injection molding process vs resin casting.
 
In the injection process formerly a moldmaker makes a physical model of the subject.   Nowadays the model may be a digital model.  That model is then sent to a die cutter, formerly a craftsman who uses the model and a pantograph cutting tool to grind away the steel die to the shape of the part.   It is now a negative shape.  You made a negative its easy to make a raised panel line by cutting away more.   Its harder to make an engraved panel line as you have to cut away less. Currently it is a CAD/CAM tooling process.   The die cutter works with a plastics engineer who knows the injection molding process.   Knowing the process and limitations of the material he creates the sprue frame and the sprue gates to allow the liquefied plastic to flow into the mold under pressure.   Too fine a part and the plastic may cool prematurely and not fill the part (short shot).   Plastic is viscous and doesn't always flow well.   See the flow marks on some parts - silver plastic seems to show them best.  There are other engineering problems which must be addressed to achieve quality production.   I don't know what the current rate is, but 20-ish years ago it was estimated that a model cost $1000 per piece to produce and bring to the market.   The good thing is that the hard steel tool dies had a production life in 10s of thousands of units and given the economies of scale the model price could be amortized over a longer period.  That is why you see kits from the 50s and 60s still on the store shelves
 
Resin kits and parts are designed and built by a modelmaker.   It may be a home modeler (I have made masters for Iron Shipwright) or a professional modelmaker.   The master is 1:1 to the finished scale where the injection master is usually larger.   The modeler adds detail as needed, in 1:1 scale; wire, plastic shapes, applique PE, etc.   From there the model/part goes to the molding process.   The guys at ISW made the molds from my master, but I have done the process myself.   The model/part is affixed in a mold box.  It may be a one-part/open face mold or a multipart mold.  The piece is imbedded in Room Temperature Vulcanizing (RTV) rubber.   The RTV is viscous, but good coverage is achieved by either vacuum or pressure degassing.   RTV is able to pick up the finest details -- see hatch levers on 700 scale companionway doors.   It also will pick up fingerprints that you left on the master.   When you make your mold box you have to consider how you get the master out as well as how you will get the finished parts out.   A flexible RTV can handle some undercuts, perhaps better than you see in injected parts (engineering the shape and die required).   The RTV hardens in several hours and the master can be extracted from the mold  (can you get it out, can you get it out without tearing?)  The mold is a negative shape.  Next up is mixing and pouring the resin, generally a two-part polyurethane epoxy.   Mixed it is watery thin and it flows into all the shapes, cracks, crevices, fingerprints, and tears in the mold.   The resin reaction is exothermic -- it creates heat.   Big parts make a lot of heat.   Since you got the master out of the mold, I'll assume that you can get the piece out of the mold.   
 
The heat created by the casting process affects the life span of the mold.   The more copies you make, the more degraded the mold becomes.  30 to 50 pulls is about the maximum.   I have a 350 scale Langley by ISW which was one of the first four pulls.  I know because the mold tore on the fifth pull and the master had to be changed and a new mold had to be made.    Economies of scale are working against you with resin.   
 
Often the resin kit will be the only one on the market because the master was created by a modeler/artist who has a passion for the specific, often overlooked, subject.   He has the references.    The model may have been made for his own use and he decided to bring his passion to others.    
 
There are now modelers and companies that are using 3D printing technology to create resin masters.   They print the model, clean it up, and follow the above steps to create a resin model (see Black Cat's new USS Ward kit due later this month)
 
The resin benefit is tooling and material cost, especially for the home/casual modeler.  I've not bought any RTV & resin in the past few years (hey, there is a virus going around).  At Smooth-On, a pound of RTV and a pound of resin in a starter kit cost about 50 bucks.   You could mold & cast a bunch of weapons, wheels, drop tanks, ejection seats, or other items with a pound package.   Smooth-On does have a tool to estimate material quantity requirements based on master size and production run.
 
Different material, different processes, different economies of scale
 
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