The one-dimensional calculation of tolerances is usually done using a spreadsheet, but this method can be time-consuming and inaccurate. To make an optimum calculation there are many things to consider:
at the same time consider all the technological requirements of the product
consider clearances around fixing elements and pins, which could cause variations in the position of one part in relation to another
consider that the dimensions and tolerances of parts used simultaneously in several assemblies must be the same
accurately calculate statistical results
Inventor Tolerance Analysis automates not only these tasks but also others, replacing the spreadsheet method.
The parts designed in the CAD system are their own ideal representation. Each manufactured part from the batch has its own unique differences from the rest. The purpose of the tolerance calculation is to account for possible deviations in each part and to determine whether the technical requirements are met during assembly.
To calculate the dimensional chain, overlap or variation in an individual plane must be taken into account. A variation in the constituent dimensions of the parts together results in a change in the closing distance between two different parts in an assembly. For each trailing dimension, an allowable range of values is defined within which parts are manufactured and assembled properly.
Tolerance Analysis in assemblies provides insight into the relationship between dimensional variation and functional requirements.
Tolerance Analysis can solve problems with a one-dimensional overlay, but not with a two- or three-dimensional overlay. With a one-dimensional overlay, the calculated distance and the dimensions affecting the change in distance act in the same linear direction.
Tolerance Analysis and Calculation Methods
Tolerance Analysis contains three methods of analysis: worst case, statistical, and RSS - square root of the sum of squares. RSS is a special case of the statistical analysis method and will be described after the statistical analysis section.
Worst-case" tolerance analysis is the traditional method of calculating an overlap tolerance. The deviating quantities are given a maximum or minimum value to obtain the maximum or minimum overlap tolerance.
The worst-case method does not take into account the distribution of individual variables. It assumes that all parts were produced at the limit value at the time of assembly. This method predicts the possible upper and lower limits of the overlap tolerance.
Parts designed based on the results of the 'worst case' calculation will be assembled without exceeding the maximum permissible values and operate as required. But this method often requires strict tolerances for some components. This can lead to higher production costs and increased scrap rates.
If the use of the worst-case method is not specified in the contractual obligations, the statistical analysis method is often used which, when properly applied, ensures that the required requirements for an assembly (product) with less restrictive component tolerances and, therefore, lower manufacturing costs are met.
The statistical analysis takes advantage of statistical methods, it extends tight tolerances without compromising quality. It assumes that each dimension included in the calculation has a statistical distribution. The statistical analysis predicts the overlap distance distribution without using extreme limits. Statistical analysis provides design flexibility to achieve any level of quality, not just one hundred percent. Statistical analysis, unlike the RSS method, does not assume the same build quality and quality of the part itself.
RSS analysis uses the principles of the general statistical analysis method described above, but with some assumptions that allow the use of tolerances instead of standard deviations.
As a result, with Tolerance Analysis, the manufacturer will be able to
Avoid complex manual calculations
eliminate the use of spreadsheets
ensure the best fit of parts
calculate acceptable tolerances
If you would like to see the Tolerance Analysis tool in action and gain a deeper understanding of the process, watch this webinar on this topic. You will need to answer a few questions to get the link to the recording.
reduce manufacturing costs
increase product quality
track cost variation with dimensional accuracy and generate a full report of the product's bottom line.
Tolerance Analysis is an add-on software built into Inventor for one-dimensional calculation and tolerance analysis in one linear direction. Analysis allows you to determine if components in an assembly conform to mechanical fit and performance requirements based on aggregate dimensional tolerances. Product Design & Manufacturing Collection subscribers can take advantage of this functionality within the Autodesk Inventor environment. Subscribers can download and install Tolerance Analysis from their Autodesk Dashboard. This application is also available to everyone else for a trial period.
What is Tolerance Analysis within Autodesk Inventor?