Inputs
Fit diameter DF, required interference Ug, room and inner-part temperature, thermal expansion coefficients of inner and outer part; optionally a different fitting clearance and a permissible maximum outer-part temperature.
Shaft-hub · assembly process
Shrink-Fit Assembly Temperature to DIN 7190-1
The existing interference-fit calculator answers whether a given interference secures joint pressure and load transfer. This calculator answers the other manufacturing-process question: to what temperature must the outer part be heated for that interference to actually be assembled stress-free -- and how large the interference may be at most for a given maximum permissible temperature.
Joint pressure and capacity: Interference Fit (DIN 7190-1).
DIN7190-1
02
Assembly temperature to DIN 7190-1
Enter interference, temperatures and expansion coefficients.
Inputs and method
Calculate the assembly temperature of an interference fit
Determine the outer-part heating temperature required to assemble a given interference.
Calculation
The recommended fitting clearance (Equation 50) and the required interference give the total fitting interference per Equation 51. Equation 52 then calculates the outer part's required assembly temperature; Equation 53 gives the largest still-joinable interference for a known maximum temperature.
Example
DF=100 mm, Ug=80 um, thetaR=thetaI=20 degC, alphaI=alphaA=11x10^-6/K (steel-steel): fitting clearance Usw=100 um per Equation 50, total fitting interference UF=180 um, required assembly temperature thetaA,req=183.6 degC.
Sources and limits: DIN 7190-1:2017-02, clause 8, Equations 50 to 53.
Calculate the assembly temperature of an interference fit in detail
Determine the outer-part heating temperature required to assemble a given interference.
Why doesn't the joint-pressure calculation alone cover manufacturing?
The existing interference-fit calculator answers what joint pressure and transmissible torque result from a given interference -- that's the design question. How that interference is actually overcome during assembly is a separate, independent question: without heating the outer part (or cooling the inner part), an interference of several tenths of a millimetre could only be press-fitted with very high force and a risk of galling. Heating temporarily expands the outer part beyond the required interference so the inner part can be inserted with practically no resistance.
Formula and variables
The recommended fitting clearance (Equation 50) and the required interference give the total fitting interference per Equation 51. Equation 52 then calculates the outer part's required assembly temperature; Equation 53 gives the largest still-joinable interference for a known maximum temperature.
Choose the inputs correctly
Fit diameter DF, required interference Ug, room and inner-part temperature, thermal expansion coefficients of inner and outer part; optionally a different fitting clearance and a permissible maximum outer-part temperature.
How to use the calculator
Enter the fit diameter, required interference (e.g. from the interference-fit calculator), and the starting temperatures and thermal expansion coefficients of both parts. Optionally state a different fitting clearance or a permissible maximum outer-part temperature.
Worked example
DF=100 mm, Ug=80 um, thetaR=thetaI=20 degC, alphaI=alphaA=11x10^-6/K (steel-steel): fitting clearance Usw=100 um per Equation 50, total fitting interference UF=180 um, required assembly temperature thetaA,req=183.6 degC.
What does the result mean for production planning?
The required assembly temperature theta_A,req is not a safety figure but a process specification: fall short of it and the outer part seizes before assembly completes (risk of cold welding/galling); exceed it significantly and the material's microstructure can be damaged -- especially in already heat-treated parts. If a permissible maximum temperature is known and the required temperature exceeds it, the calculator flags this explicitly: in that case, either cool the inner part additionally (dry ice: -78 degC, liquid nitrogen: -196 degC) or reduce the required interference.
Diameters in millimetres, interference and fitting clearance in micrometres, temperatures in degrees Celsius, expansion coefficients in 10^-6 per kelvin.
Typical applications
Setting the heating temperature for induction or furnace heating in shrink-fit assembly, deciding between heating and additional cooling, checking whether a required interference can be joined at all given a material-limited maximum temperature.
Assumptions, limits and common mistakes
DIN 7190-1:2017-02, clause 8, Equations 50 to 53.
Common mistake: Don't swap the inner and outer part's expansion coefficients -- with dissimilar materials (e.g. a steel shaft in an aluminium hub) this materially changes the required temperature. Likewise, don't omit the fitting clearance from Equation 50: without it the standard explicitly warns of the parts seizing before assembly completes.
Frequently asked questions
Must the joint always be heated, or is press-fitting enough?
That depends on the interference and the permissible press force; this calculation assumes the thermal assembly method. For small interferences with sufficient press-force margin (see clause 9.2 of the standard), plain press-fitting is also possible.
Why does the calculator return a larger fitting interference than the actually required one?
The additional fitting clearance from Equation 50 prevents the inner and outer part from seizing before the assembly process is complete -- without it, the outer part could lock prematurely while cooling, before the parts reach their final position.