In ultra-precision equipment manufacturing, granite components feature a low coefficient of thermal expansion and excellent vibration damping properties. They are widely adopted as reference carriers for semiconductor inspection equipment, linear motor platforms and metrology instruments. Many equipment manufacturers encounter the same challenge: granite platforms meet precision standards upon delivery, yet their flatness and parallelism gradually degrade after months of on-site operation, resulting in precision drift. The root cause lies in the gradual release of residual stress formed inside the stone and during machining. Residual stress continuously triggers slow deformation of granite, shortening equipment calibration cycles and impairing the stability of optical inspection and dimensional measurement. Drawing on years of experience in the R&D and manufacturing of ultra-precision granite components, UNPARALLELED shares comprehensive solutions to prevent residual stress in granite from five dimensions: raw material pretreatment, machining technology, environmental control, post-processing and inspection verification.
1. Pre-Control of Raw Materials: Native Stone Screening & Multi-Stage Natural Aging to Eliminate Primary Rock Stress
Many people mistakenly believe stress is generated only after granite forming. In fact, natural rock masses carry inherent internal stress formed by crustal movement. Direct machining after quarrying disrupts the internal stress balance of stone, leading to continuous stress release and deformation during subsequent service. Conventional manufacturers simplify aging procedures and grind raw blocks directly, laying hidden risks for precision failure in later application.
UNPARALLELED implements strict screening standards for incoming granite raw blocks. We prioritize high-density black granite with uniform crystal texture and minimal fractures. After rough cutting and shaping, raw blocks are placed in multi-stage natural aging areas for long-term static storage to fully release native rock stress. Our proprietary UNPARALLELED® black granite boasts compact texture and evenly distributed minerals, featuring lower baseline native stress compared with porous stone. Meanwhile, we reject bonded and spliced stone materials, as splicing interfaces easily form stress concentration zones that warp under long-term operating conditions. We eliminate potential stress hazards at the raw material source.
2. Optimize Cutting Machining Technology to Reduce Machining Stress Induced by Mechanical Processing
During mechanical processing including diamond wheel cutting, hole milling and grooving, extrusion and frictional heating from cutting tools generate machining stress on the granite surface. High-speed cutting, excessive single cutting depth and inappropriate feed rates aggravate surface stress accumulation. Mounting threaded holes, positioning grooves and hollow areas on platforms are high-risk zones for stress concentration.
During component machining, we abandon aggressive cutting parameters and adopt a progressive layered cutting scheme. Reasonable machining allowance is reserved for rough processing to avoid impact on the stone substrate caused by one-time heavy cutting. A static buffer period is arranged after rough machining to release surface stress generated by cutting before proceeding to finish machining. For complex structures such as holes and grooves, we optimize tool paths to reduce sustained local extrusion and friction. Machining temperature rise is controlled throughout the process to avoid thermal stress caused by local high temperature, minimizing additional stress introduced by mechanical processing.
3. Machining in Constant-Temperature Clean Workshops to Control Thermal Stress Caused by Temperature Difference
Temperature fluctuation is an easily overlooked source of stress. When stone is processed under alternating high and low temperatures, uneven expansion and contraction occur in different regions of components, forming thermal stress. Ordinary open workshops experience large day-night temperature differences, and components are continuously exposed to temperature variation during machining and transfer, leading to cumulative stress.
UNPARALLELED operates a 10,000 ㎡ constant-temperature & humidity clean production workshop. The whole process including machining, lapping and transfer is completed under stable temperature and humidity to reduce hot-cold alternation of granite components. Rough machining, finish machining and ultra-precision lapping are carried out without cross-environment transfer to avoid uneven deformation triggered by ambient temperature difference. Temperature is controlled gently during lapping to prevent local high temperature from high-speed friction of grinding wheels, avoiding temperature gradients between the stone surface and interior. Thermal stress is eliminated to maintain stable stress status of components. 
4. Stabilization Treatment after Finish Machining to Release Secondary Machining Stress
Static aging after rough machining is insufficient to eliminate secondary stress generated by finish machining and ultra-precision lapping. Reliance merely on natural aging requires an extremely long cycle, which hardly satisfies fast delivery demands of high-end equipment. Granite components without stabilization treatment will suffer gradual precision deterioration as stress releases continuously after delivery to customers.
For high-precision components matched with optical and semiconductor equipment, UNPARALLELED adds exclusive stabilization procedures after ultra-precision lapping. Mild and controllable cyclic environmental treatment slowly releases surface stress formed during lapping and drilling. The whole process will not damage the formed planar precision, yet effectively alleviate surface stress concentration. Final precision inspection is conducted after stabilization treatment to prevent gradual stress release at customers' sites. It guarantees long-term dimensional stability of components and adapts to 24/7 non-stop production line conditions of AOI inspection equipment and wafer inspection platforms.
5. Structural Design Optimization to Avoid Stress Concentration Triggered by Geometric Structure
Improved component shape design can mitigate negative impacts brought by stress. Sharp corners, thin walls, abrupt width transitions and large-area hollow structures tend to form stress concentration under load. Even if the stone itself has low stress levels, deformation preferentially occurs at stress concentration areas under long-term load and temperature variation.
At the project communication stage, we provide structural optimization suggestions for customers: add transition arcs at corners to eliminate sharp right angles; rationally layout hollow areas and control thin wall thickness; optimize supporting point design for large monolithic platforms to disperse bearing pressure. For large components such as linear motor beams and large reference platforms, structural schemes are adjusted according to load conditions to lower risks of stress concentration. Meanwhile, we prefer monolithic integrated solutions and minimize splicing structures to remove assembly stress on splicing interfaces.
6. Full-Item Inspection and Continuous Stability Verification of Finished Products
Stress cannot be observed visually, so stability verification simulating customers' on-site working conditions is mandatory. Many manufacturers in the industry only test static precision without aging stability verification, making it impossible to predict deformation risks in later service.
Before delivery of all high-precision granite components, apart from routine inspection of flatness, parallelism and hole precision, sampling continuous stability testing is implemented. Components are stored under constant temperature for long-term observation of dimensional variation trends to evaluate precision fluctuation caused by stress release. The workshop is equipped with complete sets of world-class metrology equipment including Mahr (Germany), Renishaw (UK) and Mitutoyo (Japan). All test data can be traced to national and provincial metrology institute standards. Equipped with complete ISO triple management system certifications, CE and RoHS certifications, we conduct long-term research on material stability together with Nanyang Technological University and metrology institutions in multiple countries, continuously optimizing the complete set of stress control processes. We adhere to transparent raw material and processing standards, forming a closed-loop stress control system covering design through delivery.