ENVENTIVE® CONCEPT: AUTOMOTIVE
Driving to Optimal Tolerancing
In the automotive industry, Enventive’s Concept tolerance analysis software is widely used for optimally balancing costs and quality of a vehicle’s mechanical systems. Concept is the only tool for optimization of tolerancing for both assembly fit and meeting performance requirements, such as for forces, gaps, kinematics, deflections, friction, and more.
Designing for mechanical variations
Ensuring that combinations of dimensional and geometric variations do not lead to excessive assembly and product performance failures is a major challenge for mechanical design engineers in the automotive sector.
Enventive Concept empowers engineering teams to rapidly model mechanical designs and then simulate the impacts of variations on assembly and functional performance requirements. Simulation enables engineers to quickly iterate on their design options to ensure functional conditions, such as forces, deflections, motions, and gaps, remain within targeted limits and do so with the largest possible tolerances and lowest costs.
With Concept, users achieve:
- Faster times to market by reducing prototypes, Engineering Change Notices (ECNs), production disruptions, and internal discussions.
- Optimal costs for each function by reliably predicting the impacts of design variations on failure rates.
- Better customer satisfaction with Geometric Dimensioning and Tolerancing (GD&T) designs that meet objectives for product robustness.
Problem: Errors in designs are identified only in production with high rates of rejected assembled products.
Solution: Use Enventive Concept to identify angle of the handle at which the system triggers.
Benefits: Predicting impacts of tolerance variations early in a design process cuts the risks of costly stack up problems during production and in the field.
Problem: The critical stack-up has contributors spread among different views.
Solution: Use a 2.5D projection approach to simulate the impacts of tolerance variations throughout the handle mechanism’s kinematic range of motion.
Benefits: Calculates complex 3D stack-ups and the impacts of variations using a robust approach.
Problems: Control the pressure on the disk. This parameter could be affected by hundreds of possible contributors.
Solution: Build a complete model of the gearbox.
Benefits: Run a tolerance analysis that includes the effect of friction, temperature variation and multi-view combined effects.
Problems: The force delivered by the user on the lever must fall between a minimum and maximum value. In this way, the system provides stability and at the same time avoids excessive wearing of the components.
Solution: Run a Tolerance In Motion study (TIM) combined with a force equilibrium.
Benefits: Understand the range of forces and their tolerance intervals along with kinematics to improve GD&T decision making.
Problems: Control the position of the pedal pad.
Solution: Run a Combined Tolerance Analysis to see the X and Y position of the pedal in a single report.
Benefits: Study multiple stack-ups in parallel to determine the GD&T values that meet requirements for pedal pad position.
Problems: A set of x pins must fit in a set of x holes.
Solution: Build a parametric model of the connector using Concept’s Pin-in-Hole Pattern tool.
Benefits: Quickly design to meet fit requirements by modifying a set of input parameters to simulate the fit pins into the connector.
Use Case Example: Improving product robustness for a switch
See below for an example of how Enventive Concept enables mechanical designers to determine tolerancing that ensures a device robustly performs within its functional limits.
Here is an extract of an Failure Mode and Effects Analysis (FMEA) function involving a turn signal switch:
| Function | Potential failure | Cause | Solution |
| Switch must work within specific forces (30 ± 20%) | 1) Too low means that accidental operation is possible 2) Too high means a) user fatigue b) broken switch 3) Testing cycle over-runs 4) Field failure returns | 1) Manufacturing Tolerance variations 2) Frictional variations | Use Enventive Concept to optimize the impacts of variations on the level of effort to operate the turn signal switch |
Forces target values = between 24/36N with a Cpk = 1.00
As we are at the conceptual design phase we want to identify the maximum dispersions that occur throughout the kinematics so that we pinpoint spot the worst position.
We take into consideration the dimensional, geometrical and physical aspects contributing to the dispersion analysis.
We plot them displaying: the nominal, worst case (WC) and statistical dispersions (RSS) to identify and visualize the expected maximum product variations. Knowing where the maximum variation occurs allows us to focus on and optimize the product design so that fewer parts will be rejected during the inspection process.
We have efforts above the functional upper limit occurring at an angle position of 11° so we run an analysis at this position:
We observe a discrepancy between the actual mean result and the targeted mean result. We also observe a difference between the actual Cpk and the target Cpk (1.00)
Here are the actions we choose to take:
- MEAN IMPROVEMENT: we optimize the stiffness value to bring down the mean value to 30
- CPK IMPROVEMENT: we bring the actual Cpk to 1 by reducing the stiffness variation and the free length. We can further improve the tolerances by reducing the tolerancing profile
After optimizing the tolerance analysis report we run a new “tolerance in motion” study to check by the way of a force vs movement graph that the force value now remains within the 36/24N (30 ± 20%) objective with a Cpk = 1.00
Conclusion:
With the modifications made we now achieve the FMEA functional conditions in a robust way, laying the foundation for optimal GD&T on the drawings after 3D modelling.
