Low Cost Automation Tutorial

#181 Production Technology Level-up Course for Machine Designers - 17: Press Fit Assembly

Category : Production Technology

May 9, 2014

Assembly of shafts and holes can be classified into 2 types based on the dimensional relationships of 2 parts parts to be mated.

Assembly of shafts and holes

Here, the terminologies of press fitting that require forces.

[Table 1] Press fit operations and terminology explanations

Press fitting terminology	Terminology explanation and example
Static press fit	Insertion with static forces without impacts. EX.: For press punches on die & mold
Vibratory press fit	Press fitting with vibrations applied. EX.: Light press fitting for easily damaged components, etc.
Impact press fit	Press fitting with impacts. EX.: Press fitting of dowel pins and locating pins.
Push fit	For O-rings, gaskets and springs where the components are push fit along shafts. EX.: E type retaining rings, press fitting of bearings on pillow blocks.
Shrink fit	Fitting shafts into holes by heat expanding the holes. EX.: Press fits requiring high precision and high torque capacities such as shrink press fitting of rotating tools (End mills, etc.) onto tool holders, mounting of drive gear rims onto hubs.
Cold press fit	Reverse of the above where the shafts are made smaller by cooling to be inserted. EX.: ・To avoid the press fitting damage for the large and fragile parts. ・Fitting of bearing bushings.

Explanations of press fitting process

Press fitting is a process where 2 parts are press assembled with a targeted amount of interference between the shaft diameter and the hole diameter.
Insertion forces amounting the surface pressure and friction of creating the interference must be applied. The press fitting can be classified based on how these forces are applied.
Press fitting processes require some preparations with high levels of difficulty such as reliable locating and part holding of the components, but reliable bonding of the parts can be obtained without adhesives according to the press fitting forces applied.

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