What is Press Fit Force?

In engineering terms, a press-fit, also known as force fit or interference fit, is an assembly of two parts mounted tightly thru normal force or friction. For example, when a shaft is inserted tightly into a slightly smaller hole, with the interference holding both parts in place. The inserted part is typically 0.001 to 0.002 inches larger than the mating hole. 

Depending on the amount of interference, the parts may be assembled using a hydraulic cylinder as illustrated in this application note. To avoid damage during joining, critical components may also be cooled significantly below room temperature to shrink one of the components before fitting. Please note that electric and pneumatic press-fit assembly types can also be retrofitted using FUTEK sensors.

Today, press fit technology is widely used in the manufacturing of electronic and electromechanical components. Many parts are assembled with press fits, including bushings, bearings, pins, studs, rotors, gears, pulleys and shaft collars. The technology enables manufacturers to create highly reliable electro-mechanical interconnects without the use of solder.

According to manufacturing industry experts, provided that the components are correctly designed, press fitting is the least expensive assembly method, compared to soldering, fastening or gluing.

Why is it important to monitor press fit force?
Due to its many advantages over traditional assembly methods, press-fit operation is becoming more prevalent in manufacturing plants. However, it is becoming more challenging to inspect press fit defects, since the workpiece dimensions are shrinking and placement density is increasing.

A press fit force monitoring system is designed to catch defects accurately and reliably and perform real-time analysis to continuously improve manufacturing and achieve higher press-fit assembly productivity.

Common quality issues encountered in press force applications:

Part Issues:

• Incorrect Orientation;
• Over-size or Under-size parts;
• Improper insertion;

Machine Issues:

• Bad Alignment;
• Wrong ram speed;
• Loose fixtures;
• Low Hydraulic / Pneumatic Pressure.

The solution is a press-fit force monitoring system that ensures that the press-fit assembly process is monitored properly and quality issues are caught in real-time.  The monitoring system uses force measurement to catch defects accurately and reliably and perform real-time analysis to continuously improve manufacturing and achieve higher press-fit assembly productivity. FUTEK's load cell sensors are ideal for these applications, as they output extremely accurate results through millions of assembly cycles. 

The press fit operation station can also be equipped with a displacement transducer to measure the movement of the press ram during the operation. The data captured by these two sensors, force, and displacement sensors, provides force-displacement measurement for press fit feature checks: Force vs. Time, Distance vs. Time, and Force vs. Distance.