The dry burnishing machine adopts a dual dynamic motion mode of planetary rolling and horizontal rotation. When the sealed drum operates at high speed, it drives abrasives and workpieces to form a continuous three-dimensional circulating movement. Without water medium buffering, all mechanical forces directly act on the workpiece surface. The grinding force is not a single friction force but a composite vector sum of multiple forces, mainly divided into two core acting forces that directly determine the processing effect:
1.1 Normal Extrusion Impact Force
It refers to the pressure perpendicular to the workpiece surface, generated by high-speed centrifugal motion. Its function is to press into the workpiece surface layer, extrude and peel off oxide layers and protruding parting lines. As the core material removal force, it delivers the maximum force value and the deepest processing influence.
1.2 Tangential Shear Friction Force
It is the sliding shear force parallel to the workpiece surface. Through relative sliding and rolling friction between abrasives and workpieces, it polishes and refines surface textures and eliminates micro scratches, determining the final gloss and flatness of workpieces.
The process characteristics of dry burnishing determine that the normal force is 2–4 times greater than the tangential force. This is the fundamental reason why the dry process achieves higher deburring efficiency but may cause edge wear and dimensional out-of-tolerance if not properly controlled. Without medium buffering in the whole grinding process, the stability of force value is completely determined by equipment speed, abrasive attributes and process proportioning.
Abrasive material is the primary core factor determining the strength, stability and action mode of dry grinding force. Plant-based abrasives and synthetic abrasives have vastly different mechanical properties, which correspond to completely different processing scenarios and serve as the core basis for production selection.
2.1 Plant-Based Abrasives: Weak Grinding Force, Flexible Friction, No Impact Damage
Plant-based abrasives are made of natural walnut shell and corn cob substrate compounded with polishing wax, featuring loose texture, low hardness and no sharp hard edges. The overall grinding force is characterized by low impact, pure friction and weak cutting performance.
Its normal impact force is extremely weak, incapable of extruding and peeling hard burrs and thick oxide layers. It only relies on micro tangential friction force to complete surface cleaning, brightening and removal of fine burr flocs. The force value is uniform and soft without local concentrated stress, avoiding edge biting, indentation and deformation of thin-walled and soft workpieces.
However, its grinding force decays rapidly with abrasive wear, leading to poor long-term processing stability. It is only suitable for light polishing, surface cleaning and matte finishing scenarios.
2.2 Synthetic Abrasives: Gradient Strong Grinding Force, High Impact, High Controllability
Synthetic abrasives (brown fused alumina, high-alumina ceramic, resin abrasives) are sintered and pressed with artificial powder at high temperature, featuring dense structure, high hardness and regular particle edges. Their grinding force has the advantages of high strength, good stability and controllable gradient, making them the main consumables for dry mass production.
Brown fused alumina delivers the strongest grinding force with sufficient normal impact force, which can quickly remove parting lines and thick oxide layers. High-alumina ceramic abrasives have moderate and balanced force values, balancing deburring and surface flatness. Resin synthetic abrasives mainly rely on tangential friction for brightening with extremely weak normal grinding force, only used for mirror finishing and texture refinement.
In general, synthetic abrasives have slow force attenuation and high wear resistance, maintaining stable grinding force throughout the process and meeting the requirements of rough, medium and fine full-process processing.
Without water flow buffering and adjustment, dry grinding force is highly sensitive to production parameters. Any parameter fluctuation will directly change the force value and cause processing defects. The core influencing factors are divided into five categories:
3.1 Equipment Rotation Speed (Core Variable)
Grinding force is positively correlated with equipment speed. The higher the speed, the faster the centrifugal movement, and the higher the impact frequency and extrusion strength between abrasives and workpieces, resulting in a multiplied increase in overall grinding force. Low speed produces soft grinding force suitable for slight polishing; high speed brings surging impact force to greatly improve deburring efficiency but easily causes workpiece edge wear. Different speeds are precisely matched for different materials: low speed for soft small parts, medium and high speed for hard hardware parts.
3.2 Abrasive Hardness and Particle Size
Higher abrasive hardness brings stronger normal pressing ability and greater grinding force; larger particle size increases single impact area and strength for better rough grinding effect. Conversely, fine and low-hardness abrasives produce weak grinding force, only applicable to fine polishing and brightening. In addition, worn and broken abrasives cause uneven force and local stress concentration, which easily scratch workpieces and require regular screening and replacement.
3.3 Workpiece Material and Structure
Hard materials such as stainless steel and iron have strong compression resistance and can withstand high grinding force. Soft alloys including zinc, tin, aluminum and silver have low yield strength, and high grinding force will easily cause edge collapse, over-polished surface and dimensional loss. Furthermore, thin-walled parts, special-shaped dead angles and micro holes suffer uneven stress, requiring reduced overall grinding force to avoid deformation and material deficiency.
3.4 Drum Filling Ratio
Filling volume directly affects the movement freedom and impact strength of abrasives and workpieces. Over-filled drum hinders material rolling and relative movement, sharply reducing grinding force and resulting in uneven polishing and residual burrs. Under-filled drum causes disorderly high-speed impact and overload local grinding force, leading to collision dents and excessive wear. The optimal industrial filling range is 60%–75% of drum volume, ensuring balanced and stable grinding force.
3.5 Processing Time and Abrasive Aging Degree
New abrasives with complete edges deliver the strongest and most stable grinding force at the initial processing stage. With extended processing time, abrasive edges wear and particles refine, leading to gradual attenuation of grinding force and continuous decline of deburring efficiency. Plant-based abrasives age and decay much faster than synthetic abrasives and require frequent refilling and replacement; ceramic and brown alumina synthetic abrasives maintain higher force stability with longer replacement cycles.
Most surface and precision defects in dry burnishing are caused by unbalanced grinding force, which can be accurately matched with abnormal force conditions:
4.1 Excessive Grinding Force: Workpiece edge erosion, thin-walled deformation, dimensional out-of-tolerance, over-polished whitening surface, impact dents caused by workpiece collision.
4.2 Insufficient Grinding Force: Incomplete removal of parting lines and burrs, residual oxide layers, rough surface texture and uneven gloss.
4.3 Uneven Grinding Force: Partial gloss difference, unpolished dead angles and inconsistent batch finished effects, mainly caused by abrasive aging, improper filling and unstable speed.
The core control logic in production:improve force for hard materials to ensure efficiency, reduce force for soft materials to ensure appearance, stabilize force for finishing to improve gloss. Accurate force matching is realized through dual control of abrasive selection and parameter adjustment.
5.1 Hard Metals (Stainless Steel, Iron, MIM Steel) – High Grinding Force Process
Select brown fused alumina and high-alumina ceramic synthetic abrasives with medium and high speed to properly increase grinding force and quickly remove thick burrs and oxide layers. After rough polishing, replace with resin synthetic abrasives to reduce shear grinding force, refine surface texture, and integrate efficient deburring and mirror brightening processing.
5.2 Soft Alloys and Thin-Walled Parts (Aluminum, Copper, Silver, Tin Alloy) – Flexible Low Grinding Force Process
High-hardness brown fused alumina abrasives are prohibited. Low-strength ceramic abrasives are preferred for light polishing to remove fine burrs, followed by plant-based abrasives with ultra-low grinding force for final cleaning and brightening. Reduce equipment speed throughout the process and appropriately increase filling density to lower impact force, completely avoiding scratching, deformation and edge biting of workpieces.
5.3 Electroplating Pre-treatment Parts – Uniform Micro Grinding Force Process
Strong cutting force is not required. Plant-based abrasives are used throughout the process to remove surface oil stains and slight oxide layers through uniform micro friction, without damaging the base material size and surface structure, ensuring uniform and flawless adhesion of subsequent electroplating layers.
The grinding force of dry burnishing machines is a mechanical coupling result of equipment, abrasives and working conditions. Compared with wet polishing, its force is more direct and more sensitive to process parameters. Synthetic abrasives provide gradient controllable strong grinding force, suitable for mass deburring and mirror finishing; plant-based abrasives provide flexible micro grinding force, specializing in cleaning and matte finishing of soft and thin-walled workpieces.
In actual production, accurate matching of abrasive types according to workpiece materials, combined with refined adjustment of speed, filling ratio and processing time, can stably control grinding force, perfectly balance processing efficiency, finished product precision and surface yield, and maximize the water-free, high-efficiency and low-cost process advantages of dry polishing technology.
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