Bush Compression Mold

Bush Compression Mold also called rubber suspension bushing tooling, the mould tooling is used for manufacturing rubber bushings, isolator, suspension, wash basin, bearings, vibration pad, rubber vibration mounts, rear trailing arm bushings, shock absorber, rear shock bush, arm rod, rubber bumper, stopper, leaf spring, widely used in car, bike motorcycle, engine/fuel, transmission, washing machine, door, medical/healthcare devices, etc., as a silencer, in order to protect machine arms, to keep connected components from moving and vibrating, which is necessary to eliminate wear and damage. Rubber suspension bushing is made by compression molding, no matter hole rubber bushings, center bonded natural rubber bushings, conical rubber bushings, equalizer leaf spring, flanged rubber bushing, rubber sleeve bushing, control arm rubber bushing, center bonded rubber bushing with meal center, cylinder rubber bump stop, rubber reducer bushing, rubber step bushing, heavy duty a arm rubber bushing, or medical silicone bushings, compression mold from basic two plates structure to three plates, to sliders more complicated structure. Followings explain silicone rubber compression tooling structure, service life, design guides, silicone rubber materials comparison, and mould surface finishes.

Compression Tooling Silicone Rubber Bush Applications

Rubber suspension bushing is used in vehicles, transport industry, etc.:

Silicone rubber bushes are used in food industry devices, and medical & health care devices, such as self-lubricating sleeve bearings, tribology bearings/bushings, in the medical industry, custom sleeves can be manufactured to meet specific needs, such as precision tolerances, biocompatibility, or resistance to sterilization processes:

Bushing Suspension Compression Mould Structure Design:

Bush mould tooling has different types according to structure of rubber bushes to be formed: compression mould tooling with two-piece construction, and three plates, performs well in step bushing, suspension bush, arm rubber bushing, reducer bushing, cylinder rubber bump stop, bonded rubber bushings, rubber sleeve bushing, flanged rubber bushing, equalizer lead spring, conical rubber bushings, hole rubber bushings, etc. Mould tooling is depended on components parting line / joint line design and tooling cavities, there are three types rubber bushes compression mould structure:

Basic Two Plates Compression Mould:

1) upper plate and lower plate / top plate and bottom plate

2) two plates mold + horizontal bars / keels

Three Plates Compression Mould Tooling: 

upper plate, middle plate, and lower plate, looks like sandwich structure.

Transfer Compression Mold Tooling: three plates + horizontal bars / keels

Compression mould tooling with the middle mold plate that play roles in silicone rubber raw material location pot, material will flow into cavities through holes on the pot after the mold being heated, the transfer compression mould structure is generally used for silicone rubber parts with requirements for thin even wall thickness, and metal mount insert location, such as small pipe, thin grommet, rubber mounting, hot shrink boot, medical silicone bearings, etc.

Four Plates Compression Mold Tooling:

Rubber Bush Mould Structure - Parting/Joint Line Design:

Rubber bushing structure and compression mold struction affect parting/joint line:

1. Mounting Bushes parting line is on top edge and bottom edge, so the bushing body without parting line and looks good.

2. Parting line on side of silicone rubber bushings body, when compression tooling with keels. For rubber parts with thick wall, the side parting line is easy to crack.

Suspension Compression Tooling Service Life Guidelines:

Mold steel material, mold location, and mold maintenance are important for compression mould lifespan, generally is around 30 thousand shots. (For example, if the rubber bushing mold with 10 cavities, then its lifetime is equal to 10*30,000=300,000 pieces rubber bushes.)

Mold Steel

Steel materials of different materials are selected according to product characteristics, and the hardness of quenching is also different. This can also achieve a longer life of the mold. The most important factor that determines the service life of the mold is often the wear resistance of the mold material. The mold is subjected to considerable compressive stress and friction during operation, and the mold is required to maintain its dimensional accuracy under strong friction. There are three main types of mold wear: mechanical wear, oxidative wear and melt wear. In order to improve the wear resistance of mold steel, it is necessary to maintain high hardness of mold steel and ensure that the composition, morphology and distribution of carbides or other hardened phases in the steel are reasonable. For molds that serve under heavy load and high-speed wear conditions, the surface of the mold steel is required to form a thin, dense oxide film with good adhesion, maintain lubrication, and reduce melting wear such as sticking and welding between the mold and the workpiece. It can reduce oxidation wear caused by oxidation of the mold surface.

Based on precision/tolerance requirement, rubber compression mold steel is from 45#, 50#, P20, and 718H.

Mold Tooling Location

Positioning function: Maintain the orientation between the front and rear molds when closing the mold, and maintain the correct shape of the cavity after closing the mold.

Force effect: This situation is mainly in the case of three-plate molds. The positioning guide pillar has to bear the gravity of the push plate and the front template.

Keep the mold movement smooth.

In compression molds, positioning must be considered in many cases, such as sliders, upper and lower mold cores, keels, etc.

Mold Maintenance

Mold maintenance is more important than mold repair, because mold and mechanical equipment maintenance are the same. When the mold is repaired more times, the performance of the mold will become worse and worse, which to a certain extent reduces the use of the mold. However, if the mold is maintained regularly, the use time of the mold will be extended accordingly. Carry out internal and external cleaning, cleaning of parting surfaces and anti-rust work on all molds.

Suspension Bush Compression Mould Design Guidelines:

Mold tooling cavity position arrangement

Cavity

Parting line position

Cavity number

Tear/trimming edge design

Compression Moulding Rubber Mounts Bushing Materials:

Compression molded bushings are made from the material according to the bushing working environment, such as whether the bushing bearing contacts with oil, chemical solvents, or will the bushing grommet work at high temperature, extreme low temperature, etc. Our customers always use NR, NBR, EPDM, CR, VMQ, FKM for their compression molded silicone rubber boots bushings.

Suspension Bushing Compression Mold Surface Finish Guide:

Sandblasting or Bead Blasting, or Polishing

1. Sandblasting uses compressed air as power to form a high-speed jet beam, and sprays abrasives onto the surface of the workpiece to be treated at high speed, causing physical changes in the appearance of the outer surface of the workpiece. The surface of the sandblasted workpiece is metallic in color, but because the surface is rough, the light is refracted, so there is no metallic luster and it is a dark surface.

1) Sandblasting is the most thorough, most versatile, fastest and most efficient cleaning method.

2) Sandblasting can arbitrarily choose between different roughnesses, but other processes cannot achieve this. Manual polishing can produce a rough surface, but the speed is too slow. Chemical solvent corrosion will make the surface too smooth.

2. Polishing 

Those with high surface quality requirements can use the ultra-precision grinding and polishing method. Super-precision grinding and polishing uses special abrasives in a grinding and polishing fluid containing abrasives, which are pressed against the machined surface of the workpiece and perform high-speed rotation. Polishing can achieve a surface roughness of Ra0.008 μm.

Mold polishing usually uses oilstone strips, wool wheels, sandpaper, etc. to plastically deform the surface of the material and remove the protrusions on the surface of the workpiece to obtain a smooth surface. Generally, it is a manual operation.

EDM Spark Erosion

EDM (Electrical Discharge Machining), also known as spark erosion. 

The basic working principle of EDM is to use a continuously moving thin metal wire (called an electrode wire) as an electrode to perform pulse spark discharge on the workpiece to erode the metal and cut it into shape. The surface quality of EDM mainly includes surface roughness, surface deterioration layer and surface mechanical properties. The EDM surface is mainly composed of countless non-directional pits and hard convex edges. The calculation of surface roughness is the same as that of machining, using the average arithmetic deviation value Ra of the micro-profile flatness. Since the material removal by EDM relies on the high temperature generated by the discharge between the tool and the workpiece, during the deionization stage, the surface layer of the workpiece undergoes great changes due to the rapid cooling of the working fluid.

It is mainly used to process various complex-shaped and precise workpieces, such as punches, concave dies, convex and concave dies, fixed plates, unloading plates, etc. of punching dies, forming tools, templates, and metal electrodes for EDM processing. Various micro holes, narrow slits, arbitrary curves, etc.

It has outstanding advantages such as small machining allowance, high machining precision, and short production cycle.

Texture/Chemical Texture

Mold Texture is also known as Grain. Some imitate the look of stone, leather or wood grain, while others produce more abstract geometrical designs. These patterns are applied to a mold tool by photoetching. 

Applying texture to a compression mold is more expensive than mold finish mentioned above.

Texturing, also called engraving, refers to a process in which the desired color is chemically etched onto a mold (mostly a concave mold). The principle of rotten skin texture is to use potion to corrode the steel material. For different skin lines, the potion is the same, but the concentration is different.

Principle: This process uses anti-corrosive transfer ink to screen-print decorative patterns on the decal paper. The decorative pattern ink is transferred to the mold using the film lamination method. After drying and trimming, chemical corrosion is performed to obtain a concave and convex pattern on the mold. Decorative pattern. Process flow: base drawing production → photographic plate making → screen printing → ink blending → decal paper printing and decorative pattern → ink drying → mold pre-processing → decal transfer → drying → trimming → corrosion → inspection → cleaning and rust prevention.

Mold grain finish function: 1. Decorate the appearance to make the product more beautiful. 2. Since the glossy product surface is easily scratched and easily stained with dust and fingerprints, skin texture can cover defects on the product surface, making the product more beautiful in appearance and reducing the defective rate. 3. The surface of the product and the surface of the mold cavity can accommodate a small amount of air, preventing vacuum adsorption and making demoulding easier. 4. Anti-slip, anti-rotation, and good feel. 5. Made of matte surface or matte surface to prevent light reflection and eliminate visual fatigue.

Mechanical Finish

Mold mechanical finish mainly depends on 5-axis machining, but the cost is too high, rarely used in silicone rubber bushing compression mold.