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Injection Molding Process

The mold making process began with the manufacturer sending a detailed scaled blueprint to the master modelmaker to make a wooden master model.  The size of the blueprints varied widely, the largest received at Precise measured 40' in length.  From the wooden master model, the steel injection mold would be made. Some of the model prototypes were also made of cast metal.  A few of the  master models are shown below. 

 

 

Grumman C-2A Master Model above includes a 1/16th blueprint drawing dated October 5, 1966

 


 

 

This master model of the Grumman Hydrofoil boat was shipped from Grumman to Topping Grumman in the box as shown.  The master model mounts on the walnut presentation base and was held securely in the box for shipping.

 

 

 The accompanying correspondence and blueprints dated November 10, 1964 request a quote and price to produce 10 models.  The bluetprints show details for the outboard profile & front view and the main deck. 

 

 

 

Grumman Hydrofoil Gunboat -  November 1964 


Assorted Master Models

 

 

         

        Topping Navajo                           F-5        Quail         Roadrunner                       F-111B                   EF-111

               Wood                                  Wood     Wood            Metal                               Wood               Wood/Metal pins


Grumman 1/240th scale Mini Gulfstream II

 

Gulfstream Mini II Engineering Blueprint & Brass Master Model Signed by Ken Lango 5/19/72

 

 

Mini Gulfstream II - Master model - Blank on Sprue - Finished Model on engineering blueprint


Injection Molds

Buckeye Molding (Joe Goldsmith) had manufactured all of the Topping and Precise Models molds and until his passing,  had a large collection of each model made by both companies. The cost of the cast molds could run well over $100,000 and were returned to the manufacturer after production.  As Precise did not own the molds, they were prohibited to sell models direct to the public. The F-105 mold however was purchased from Republic and Precise could sell the F-105.

The costs of other injection molds included the General Dynamics 1/40th scale F-16 at $112,000 and the F-16XL at $140,000. The McDonnell Douglas YF-17 mold was $70K-$80K of which approximately 50 samples were made by Precise. The Northrop YF-17 Cobra lost in competition to General Dynamics F-16 Falcon.

 

 

Northrop YF-17 Cobra - 1/60th Scale

 


 

An early inventory list of the molds had shown the reference numbers and location of over 120 injection molds that were stored in the warehouse at one time.  The inventory included a mix of Topping and Precise molds for the various contractors.  A roof leak in the early 1990s rusted many beyond use and damaged a portion of the model inventory. The molds weighted from 200 lbs. to over 1,500 lbs., a few are pictured below. 

 

     

   

 

    

 

 

 

 


 

Republic F-105 Thunderchief

Per Gary Schneider, the metal Topping F-105 Thunderchief was the most difficult model to produce. The plane was poured as a zinc die cast metal.  To keep the molten metal flowing thru the mold, blow torches would heat the outside of the mold, causing it to become superheated and unusable in a short period. The sharp metal wingtip edges also frequently caused employee injuries.  A company on the East side of Cleveland refused to sand and buff the models due to employee injuries.  Finally two local buffers agreed to the work at a cost of $25/plane.  Due to the weight, these models had to be shipped with a wooden 2 x 4 in the front and back to prevent the model from punching thru the box during transit.  The manufacture of this model results in > $25,000 loss for Topping and a new plastic injection mold was designed for the 1/48th scale F-105 Thunderchief.

 


The 1/48th scale F-105 Thunderchief model was presented Vietnam pilots

completing 100 missions along with a 3 day trip to Las Vegas


Chance Vought F4U-4 Corsair

 

Ater much work, the Topping F4U-4 Corsair injection mold has been refurbished.  A limited number of 50 were molded in blue gloss ABS and decaled with oversized stars n bars, similar to the original Topping model.  These are available on the Models For Sale page.   Each model will be shipped in a Precise Models Inc. F4U Corsair box that was used in the early 90's with a small run for a 50 year renunion of Corsair pilots.  Also included is a Numbered Certificate of Authentication signed by myself and Gary Schneider, former President of Precise Models, Inc.   The injection mold as it was found and after restoration with the special run is pictured below.

 

 

  
 

                                 F4U-4 Injection Mold                                                 Refurbished Mold - Limited F4U-4     

 

 

 

 

 

      First F4U-4 Production Run                                 Chance Vought F4U-4 Corsair

 


Injection Molding Process

The process cycle for injection molding consists four stages:

     Clamping- Prior to the injection of the material into the mold, the two halves of the mold must first be securely closed by large press. Each half of the mold is attached to the injection molding machine and one half is allowed to slide. The hydraulic powered press pushes the mold halves together and exerts force to keep the mold securely closed while the molten plastic material is injected.

     Injection - The raw plastic material, usually in the form of pellets, is fed into the injection molding machine and advanced towards the mold by the injection unit. The plastic pellets or granules are heated until melted. The melting point depends on the type of plastic used, but typically ranges from 350-550 degrees F. The molten plastic is then injected into the mold very quickly to fill the mold with the molten plastic. The amount of plastic resin required to fill the sprue, runner and cavities of a mold is called a shot. The injection time can be estimated by the shot volume, injection pressure and injection power. Water is injected through cooling ports to maintain a constant temperature.

     Cooling - The molten plastic inside the mold begins to cool as soon as it makes contact with the interior mold surfaces. As the plastic cools, it will solidify into the shape of the desired part. However, during cooling some shrinkage of the part may occur. The packing of material in the injection stage allows additional material to flow into the mold and reduce the amount of visible shrinkage. The mold cannot be opened until the required cooling time has elapsed.  The mold may contain ports for water to circulate and keep the mold from overheating.

     Ejection -After sufficient time has passed, the cooled part is ejected from the mold. When the mold is opened, a mechanism (ejector pin) is used to push the part out of the mold. To assist in the ejection of the part, a mold release agent can be sprayed onto the surfaces of the mold cavity prior to injecting the material. Once the part is ejected, the mold can be clamped shut for the next shot to be injected.

The larger Precise models such as the A-10 were cooled in water immediately after ejecting to prevent the wings from drooping as it cooled.   


Plastic Material Types

Topping and Precise models were made using three types of material, Butyrate, ABS and styrene.

     Butyrate (cellulose acetate butyrate) was used for manufacture of the early Topping models. This material would shrink slightly as the model cooled, releasing the oils thru the plastic and have a slight odor.

     ABS (Acrylonitrile butadiene styrene) is derived from acrylonitrile, butadiene, and styrene and results in a lightweight, rigid molded product. ABS is a middle-of-the-road type of material with no shrinkage and is preferred for models. Per Gary Schneider, the first Precise model made with ABS was the Lunar Module in the early 1980s. The F-15, F-16 and F-18 were also molded with ABS.

     Styrene, also known as vinyl benzene is a very lightweight thin plastic that is used today for the plastic model kits. The cost of styrene is very low and molded parts can be very detailed with this material. Models made with styrene include the F-101 Voodoo and the Polaris base.

 

 

Samples of Plastic Material Types

 

 

             

 

                                ABS                                                   Butyrate                                                       Styrene

 

 


 

Small Parts Molding

Most of the small parts were included in the larger injection molds, but when Precise needed the small parts in large numbers, a small Arburg molder was used. The Arburg held a small mold of the pars, most were made of steel, however the 4 bladed C-130 prop mold was made of Beryllium at a cost of $2,500. A 6 blade C-130J prop mold was made at a cost of $2,800 but was not accepted by Lockheed. The small arburg and some of the parts molds are shown below.

 

Arburg Mini Molder at Precise Models

The Arburg at left was used at Precise for molding the small parts . Small parts are available and include F-4 narrow & wide Sparrow missiles, F-15 Sparrow missiles, YF-17 & F-18 Sidewinders, C-130 props (4 & 6 bladed), and F-18 tailhook.

 

 

        C-130 Prop                 F-18 Sidewinder & Tailhook

        (Beryllium)                                  (steel)

 

 

These are available on the Model Parts For Sale tab of this site. The mini molder and two of the small molds are shown above.

 


Stand Production

Both Topping and Precise made some of the model stands, cutting the acrylic sheets with a bandsaw, filing, sanding and buffing for a polished finish. Stands were also injection molded for both companies by a Plastics Company located in Cleveland. The dies pictured are part of the original Topping and Precise stamping dies.  Original and reproduction stands are available on the Model Stands For Sale tab.


 

 

 

 

Original Topping and Precise brass imprint stand dies

 

 

 

Agena Space Vehicle Stand stamping dies                     Lockheed Agena Space Vehicle brass stand die

4 1/2" Diameter x 2" Ht.      9.5 lbs. each.                                                  Measures 8" x 5 3/8"  

 

 

 

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