Creep
Creep is the time-dependent permanent deformation of a material under sustained stress or load. In manufacturing, it is most critical in polymers, plastics, and high-temperature metals; in CNC/millwork contexts, it shows up as slow dimensional drift in parts, fixtures, and assemblies held under constant load or heat. This gradual change can compromise tolerances and clamp load even when applied stress is below short-term failure.
On the shop floor, creep shows up as a slow change that is easy to miss until parts start falling out of tolerance. A workholding fixture or polymer component can deform over hours under clamp load, so the first piece may measure fine while later pieces drift. Thermal growth in the machine makes this worse, because sustained heat accelerates time-dependent strain. In polymer-intensive work, nylon, POM, or PEEK spacers can take a set under constant bolt pressure, reducing preload and causing joints to loosen. In metals, elevated temperature is the trigger; even aluminum and brass can creep if stress and heat are high enough. Practical controls include managing temperature, allowing warm-up, reducing heat input, watching tool wear, and checking dimensions repeatedly. In creep-feed grinding, the same word means a slow workpiece feed with deep cuts, a process choice rather than a failure mechanism.
What condition makes creep most severe?
Sustained stress combined with elevated temperature. Creep becomes especially severe above roughly 40% of a material's melting point for susceptible materials, so thermal management is critical for polymers and high-temperature metals.
Is creep the same as elastic deflection?
No. Elastic deflection is recoverable after unloading, while creep is permanent, time-dependent strain that accumulates while the load remains applied. This is why a crept part often does not return to its original dimensions after the fixture is released.
Why do polymers show creep more visibly than metals in many shops?
Polymers generally have lower resistance to long-duration load and temperature, so even moderate clamp forces can cause measurable slow deformation. Metals only show significant creep when operating near elevated temperatures or high sustained stress.