- SPECIAL REPORTS
Manufacturers are always looking for ways to improve quality and reduce scrap to increase their bottom line. One way to do this is by adding process intelligence to your Orbital assembly system. The physical part and or part specification always dictates what type and what configuration is needed.
Forming to a hard-stop is generally the fastest most repeatable orbital riveting configuration, but variations in part thickness and rivet length will affect the final form. Many times our application engineers form coupons in our Assembly Solutions Lab to determine if a good part can be made at the upper and lower limits of variation.
In example 1., even though the hard-stop is the same on both forms the rivet heads deform differently because of variations in rivet length and part stack up. Part testing is required to determine if both these rivets are formed within the customer’s specifications. If both of these rivets are acceptable, forming to a hard-stop may be the best solution.
If the rivet form is outside the customer’s spec, then some type of process intelligence may be required. Factors that can affect the type and configuration of Process Intelligences include:
- Part Geometry and rivet access
- Variations in Parts, Stack-Up, and rivet length.
- Form Spec: Shear, Push/Pull, Torque, etc.
- Material: non-Ferris, mild steel, Stainless, etc.
- Fixturing & Part Stability: The part must be stable
- Head Form shape: reliable datum surface
- Cycle Time: May increase cycle-time
Process Intelligence can occur before, during, and after the forming process. The stages are: Pre-Form Measurement, Process Control and Process Monitoring. They can also be combined, for example pre-form measurement and process control.
Pre-Form measurement occurs prior to forming to verify the part is good to form. Forming a short rivet, oversized part or not detecting a missing component could send an expensive assembly to the rework shop or scrap heap. But this Poka-yoke approach comes at the cost of increased cycle time. The question is, “To scrap or not to scrap?” For high volume inexpensive parts it may make financial sense to form and then scrap assemblies out of spec. Scrapping complex assemblies or components made from expensive materials such as titanium can be costly and well worth the increased cycle time required to measure.
Typical Pre-Form Measurements: (Figure 1.)
- Rivet Height
- Part Stack Up
- Rivet Stick Out (calculated)
Measurements that are out of spec set a machine fault and stop the forming process allowing good parts to be salvaged before they’re permanently assembled. Pre-form measurements can also help isolate production problems upstream, for example a bad batch of rivets or out of spec parts, as well as detecting problems with the assembly equipment such as a broken peen.
Process Control occurs during the forming process to control the force and/or distance. Cycle-time may need to increase as higher forming speeds can affect the ability to accurately hit target parameters.
Typical Process Control Measurements:
- Form to a Force
- Form to a distance
- Form to an offset from a surface
In forming to a distance offset, a height sensing pressure pad is required to establish a surface location. Forming to a force requires a load cell and electronic air regulator. Process control is the more costly of the three process intelligence stages, but for assembling expensive components, the extra cost can be justified.
Process monitoring reports the maximum value of the forming parameters after completion of the forming process. Parts formed out of spec trigger a machine fault alerting the operator. Cycle-time is not effected as passive monitoring happens during forming. Process monitoring is a good fit when quality control is needed and forming and scrapping out of spec parts makes financial sense.
Typical Process Monitoring Measurements:
- Final Form Height
- Peak Force
- Form Collapse
- Touch Point (Rivet Contact)
Depending on the configuration adding Process intelligence to an assembly system requires additional hardware such as a load cell, LVDT, electronic air regulator, clutch brake, and height sensing pressure pad. But the increased machine cost and potential increase in cycle time may be well worth the expense for components or sub-assemblies that are too costly to scrap or require a high level of quality control as in medical and aerospace applications. To improve quality, reduce scrap and increase your bottom line, process intelligence can be a cost effective solution.
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Assembly Equipment for Manufacturing since 1984