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FEA For Bended Pins in Markt&Technik

FEA For Bended Pins in Markt&Technik

Connection and tooling design, as well as its testing have changed dramatically due to FEA (Finite Element Analyses) technology. Markt&Technik (No. 45) weekly magazine for electronics, reports on SM Contact FEA expertise illustrated by PCB & bended pins connector elaboration.

No matter how unique the application and the components are, it is always possible to have a look inside of the processes hidden even from a cross-section research and optimize it in the most cost-efficient way.

FEA has passed its efficiency test when it was used to elaborate connectors and assembly equipment for cutting, bending & simultaneous insertion of four pins into the PCB. The challenge that had almost no equal before.
 


 
 
 
 
 
 
 
 

In general, the success of such a project is owed to FEA solution is two aspects : commercial approach and solution design. The first relates to the fact that with the help of FEA results visualization (3D images and pre-rendered animation) it is possible to secure the customer giving all the solution details. It is the efficient way to tell that you can do something that you have never been doing in the past and to prove your principles by showing a simulation corresponding to your idea. The second issue concerns technical part of the project. Such “blind spots” as pin bending, pin separation from end-to-end line by pulling the material, equipment mechanic reaction depending on the process speed, as well as fatigue test of the spare parts can be elaborated by the means of FEA.
 

CONNECTION AND TOOLING EVALUATION

The main steps for technical solution evaluation with the help of FEA are the following : • to import pins geometry and materials into a discretized computer model ; • to define initial tooling parameters and import them into a discretized computer model ; • to run computer simulation and get visualization of all strains and stresses ; • to improve technical solution according to the first simulation results ; • to check final solution by FEA simulation.

First simulation results defined 4 main problems and ways to solve it :
 

HOW TO SEPARATE THE PINS FROM END-TO-END PIN LINE WITHOUT DAMAGING THE PIN TIP ?
Standard solution implying pressure on the side of the pin and its rotation resulted in pin tip damage. Regarding strains and stresses parameters another option was elaborated and simulated : pins were pulled from each other and separated successfully eliminating any damage.
 


 
 
 
 
 
 
 
 

HOW TO BEND THE PIN WITH SEVERAL ANGLES IN A SINGLE OPERATION ?
This step was the less predictable one as pin bending technology has no profound background today. Thus tooling design was built around the pin parameters and step by step the simulation resulted in unexpected effects : undesirable pin shape, pin damage because of wrong angles and high friction.

With the help of FEA it was possible to determine key factors of this process : pin material and its elastic features, clamp force, friction coefficient, and tooling shape. The last included radiuses, contact surfaces and operation sequence. With a help of computer simulation several combinations were tested. More specifically, clamp force from 10N to 65N and friction coefficient from 0.03 to 0.10 were examined. The optimal force turned to be 40N and works even with the lowest friction 0.03 coefficient, corresponding to oiled surface. As can be seen on the image below the bending tooling shape was improved as well.
 


 
 
 
 
 
 
 

HOW TO TRANSFER THE PIN FROM THE BENDING TO THE INSERTION AREA
How fast could the machine be run keeping required stability ? In the case of pin transfer zero period acceleration, transfer speed and slow down parameters were tested. As the image shows initial solution gave unsatisfactory results unlike final technology. For example the Y-axis acceleration was changed from 2000 to 500 mm/s2 to improve pick-up and transfer processes.
 


 
 
 
 
 
 
 

HOW TO VALIDATE PRESSFIT ZONE ?
This task is much more widespread and traditionally solved by FEA simulation which allows to evaluate press-in force, inner coating and pin deformation, as well as to detect PCB damage. According to the simulation results pressfit zone dimensions can be improved, including its width, depth and eye-of-needle configuration.
 


 
 
 
 
 
 
 

EQUIPMENT ADJUSTMENT

The case study was continued once the machine has been produced and the results were not the expected ones. Pin bending angles were not respected.

The long way to reach the goal was to question simulation efficiency and to readjust tooling randomly on site in order to get the correct pin shape. The fast way was not to improve the parts in hit and miss fashion but to understand why the real result didn’t match the simulation.

Material parameters review showed that customer’s purchasing department had bought material different in terms of hardness. Without changing the tooling design, simulation was run with the new material properties and it resulted in the very same problems that we got during production. The implication is that the simulation proved once again its accuracy.

Measure taken to address the problem was to improve geometry of the tooling parts by the means of simulation using the final material properties. As soon as the new parts were produced and tested, the pin bending angles met the norms.

Thus simulation declared itself not just an engineering tool but also machine adjustment instrument suitable to deal with a human factor.

PRO-ACTIVE ENGINEERING

As can be seen above, Finite Element Analysis is a powerful tool for connection design and troubleshooting. Within the forementioned case study it took three weeks and 35 simulation iterations. After first 10 cycles separation and bending technology was determined. 14 more were necessary to fix the final tooling configuration. After other 11 iterations force was optimized to reduce stress levels.

FEA has changed the design algorithms. Today we can predict the problems before they occur with a prototype or a final product itself. We don’t need costly prototypes, several tooling configuration production and its readjustments. The only thing necessary is to set all the parameters of the potential loads in the computer and FEA software will solve it like a mathematical problem and give a solution : what structure and what components you need to succeed.

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