Playmobil Boeing B-17 "Flying Fortress": The making of. #4

Playmo B17 production process: Techniques employed (II) 

In this final article we will show you the essential component of the Playmo B17 project: the vacuum injection system.

This equipment is the process workhorse.

Without it it would be impossible to manufacture plastic parts with the required quality.

Vacuum injected resin fuselage part.

1.-The vacuum injection system.

This device creates a vacuum in the moulds and injects degassed resin at atmospheric pressure.

It  consists of 2 components:

1.1.- The injection chamber.

It is a 3 mm thick steel box with reinforcement ribs.

Its dimensions (102 x 52 x 35 cms.) allow the chamber to contain the largest Playmo B17 mould : the lower part of the fuselage (87x41x13 cms and 20 kg mass).

Mould loading and unloading is done by removing the upper cover, using a system of pulleys and counterweights.

The chamber has an inclination mechanism to facilitate the concentration of air in the highest points of the mould, where it is eliminated by means of vetilation ducts.

This chamber operates in depression thanks to a suction pump connected to it by a duct.

By means of another duct, the plastic polymer resin (degassed and at atmospheric pressure), is introduced from the pre-chamber into the silicone mould (which in turn is located inside the injection chamber at -0,94 atm.).

One of the biggest unknowns we faced was whether the injection times would be short enough to prevent the resin from setting before completely filling the mould.

As explained previously this forced us to start with a slow-setting resin (more viscous and more expensive ).

Once the mold is filled with resin, it is pressurized to atmospheric pressure and the resin is allowed to set inside the main chamber.

The injection chamber.

The injection chamber: inclined position with big mould inside.

1.2.- Pre-chamber.

This small vessel (a pressure cooker, in fact) is connected both to  the vacuum pump and the injection chamber by means of ducts.

By making vacuum into it, the 2 resin components of the plastic polymer are separately degassed.

Subsequently, the resin components are repressurized at atmospheric pressure, then  mixed together and again subjected to vacuum until bubbling.

Afterwards the mixture is pressurized again. By opening a valve in the duct connecting the 2 chambers, the resin is sucked by the vacuum of the main chamber.

A system of manometers allow us to measure the pressures in both chambers.

Pre-chamber (left)  /  injection chamber (right) connections.
Inclination mechanism in red.

2.- The color problem.

As already mentioned throughout this blog, no stage of the project was easy.

From the beginning it was decided to use dyes in the resin to be injected.

This was so to avoid the cumbersome painting process and to provide the aircraft with a quality as close to Playmobil as possible.

But once the issue of injection times had been solved (by using a slow setting resin on the larger parts) an unexpected problem surfaced:

Color segregation on the resin parts ....2 weeks after manufacturing !!!!.

This puzzled us. A big snowball had just passed over us.

Fed up and discouraged, we stopped everything for several weeks, which would involuntarily turn into several months due to another unexpected and truly dramatic event.

Color segregations 2 weeks after manufacturing

A snowball that nobody saw coming until it was on top of us. One as big as life: Covid-19.

Like most people on this planet, our perspectives and priorities suddenly changed.

Our family was very, very lucky. But with the usual hiccups.

The project was at a standstill for almost a year due to confinements, convalescences, new job obligations and deep discouragement.

As normality was regained, we gradually returned to it.

Relaxed and with level heads after an unexpected time of reflection, we tackled the problem again.

We noticed one fact: Only the parts made with the slow-setting resin segregated the color. None of those injected with fast-setting resins showed any defects (more than a year after manufacturing).

The problem had 2 possible solutions:

•  Painting  the whole Playmo B17.

•  A riskier one: injecting the whole plane with fast setting resin.

We tried both.

Painting involved what we had feared: time and money. A long process of masking, priming, color application and final lacquering. Expensive, slow, uncomfortable but very aesthetic.

Painted details of the Playmo B17.

Painted interior of the Playmo B17.

Injection with fast setting resin found its way by cooling the resin components to make them react as slowly as possible and increasing the sections of the feeding ducts to make it run faster.

We were successful... and even we had time to spare.

We were back in business.

Foreground: Painted Playmo B17. Behind: tinted resin Playmo B17.

3.- Assembly.

Finally the moment of assembly arrived. Another moment of truth. Would the parts  fit?

Well, the previous efforts to provide quality pieces finally paid off. 

The pieces fit well and they were very resistant. They could be manipulated and forced without any problems. They behaved like those of an industrial toy... Bingo!

Then, what adhesive to use? After several unsuccessful tests, we obtained good results with an epoxy adhesive.

Another problem was keeping the parts in place long enough for the adhesive to work. Especially the huge fuselage parts.

The solution adopted is shown below:

Assembly scaffold.

Initial assembly tests: Looking forward to see it assembled.

Almost there...

4.-Final adjustments: The landing gears.

Everything ready to go? No way...

Despite its good looks and consistency, the Playmo B17 had a weak point: the front & rear landing gears.

The Playmo B-17 is a big toy and weighs 4.5 kgs. The initial landing gear did not hold the weight and sagged.

We gave more section to the components. Without success.

We decided to leave the plane under load during a whole hot summer in Madrid and to observe the deformations at the end of it.

After almost 2 months of static loading we saw the problems:

• At the rear landing gear the main cause of  bending was deformation on the bulkhead where the wheel folding mechanism articulated. It was decided to double its thickness

• Regarding  the front landing gear the bending was due to the vertical shaft of the wheels. It was decided to replace it with an aluminum piece. 

Detail of  former rear landing gear bulkhead.

Detail of front landing gear aluminum shaft.

Following a 3-week static load test, everything worked (to our disbelief).

Almost 7 years after the start of the project, it was coming to an end.

5.- Conclusion

Along 7 years  you come across with  lots of people: Playmobil customization fans and people who have nothing to do with the Playmobil world.

Both groups of people proposed us to use the techniques we had  developed for other applications.

During those years we manufactured items ranging from pieces for Playmobil customs to small pieces for industrial equipment.

But that is another story, and perhaps a topic for another posts.

In short, the question is:

Would we do it again?

Most likely not. 

Too much time and money spent. Not to mention the continuous frustrations

Sometimes it pays to forget childhood dreams. Or just keep them at that... dreams. It's cheaper.

As the old curse says: may you get what you wish for.

Still, when we look at the Playmo b17 , we love it.

6.- And now what..?

During such a long and somewhat complex project, new ideas arise. Necessity creates new approaches.

The equipment investment and the know-how acquisition have already been made. 

And there are some people who keep proposing us to take advantage of them. 

There is no shortage of proposals. But there is shortage of money and time.

Within the Playmobil custom field we already have requests for Messerschmitt Bf 109s , Heinkel He 111s, battle tanks, etc. 

There are even proposals for upcycling old Playmobil figures and vehicles.

In any case we do not believe that we will undertake the manufacturing of something as big and complex as the Playmo B17.

One thing is for sure. From now on we will adopt a less dreamy approach.

Another aspect will be the economic management of the new projects. 

Maybe something similar to crowdfunding.

Maybe...