- SPECIAL REPORTS
Orbital forming is a common cold forming process to permanently join a variety of parts. Proper set-up and routine maintenance will ensure longevity of the machine tool and dimensional consistency of the head form. However, after years of service, part fixtures and tooling have a tendency to wear, which may result in part to part variation of the head form or joint integrity. Other variables, such as material properties of the parts being joined or the rivet itself, may influence the strength of the joint. In most cases, this may have little impact on the end product. What if the failure of the joined part is safety related? Is there a way to instrument an existing machine to verify part quality during the joining process?
In the constant pursuit to improve production processes and quality assurance, a supplier of hood latch assemblies asked Kistler that question. The answer is yes.
Orbital Riveters, like press-fit or other joining operations, can be instrumented with sensors and processing electronics to measure and capture a unique (X,Y) process curve. This measurement curve is then evaluated by a set of criteria or objects positioned along the predefined path of a known curve profile.
Kistler manufactures a variety of direct and indirect force measuring sensors that are suitable for retro-fitting an existing machine. The simplest sensor with the least installation effort is the Type 9232A piezoelectric surface strain sensor. This type is attached directly to the frame of the machine, measuring the strain in the column or structure where the power head or rotational spindle is mounted. Ideally, this should be along the axis of force or in-line with the orbital head.
The strain is proportional to the downward force being applied by the orbital head. Preparation includes removing paint from a small area on the column where the sensor is to be installed. Drill and tap for M6 thread. The sensor is installed with 10 N.m tightening torque on the supplied M6x22 screw. A Type 1631C3 high impedance cable, displacement sensor connected to the Type 5877AK1 maXYmos TL process monitoring device completes the installation.
High Resolution Measurement
During a production shift, the facility lost one of several air compressors supplying the assembly line, thereby reducing plant air. The monitoring device picked up this event and rejected the part due to failing to meet established good part criteria.
The difference is very small, but the subtle change was enough to reject the part and alert production of the potential problem.
The customer was able to use tighter controls on the process and reduce the dwell time. This resulted in a 2-second overall cycle time improvement, quality assurance was achieved and the peen tooling life was improved.