High-gloss automobile lights molding

 Case Study    |      2017-02-22

Design and development

Case of normal molding
|—High gloss mold
|—Difficult process by CNC machine
|—Perfect polishing of the cavity and core
|—Extremely sort cycle time
|—Difficult ejection by vacuum air of core

Customer : Volkswagen
Part size: 532.9X210.8X387.7MM
Part material: PC
Cavity Number: 1x1
Cycle time: 75S
Design time: 5 work days
Manufacture time: 40 work days
Manufacture date: 2013.10


Design points
Manufacture requirements
Material
Manufacture requirements
Polishing process
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Part material-PC property

Physical property : No fixed shape, odorless, Inodorous, non-toxic and transparent thermoplastics Polymer.

Specific density: 1.18-1.20.
Glass transition temperature: 140-150.
Melting point: 220-230. With certain chemical resistance and oil resistance. Medium viscosity PC is with high transparency and 180-210℃ heat resistance.

Mechanical property:Good impact resistance, steady dimension. It could keep high mechanical strength in a broad temperature range. Its disadvantage is poor endurance and wearing resistance.

Thermal property: decomposition temperature is above 300℃. Long term work temperature is up to 120℃, with good cold resistance, brittle temperature is as low as 100℃ below. Long term work temperature ranges from -60℃ to 120℃.

Electrical property: low molecular polarity and good dielectric property.Aging resistance and heat resistance property: pretty good aging resistance property. Inflammable, flame is light yellow with black smoke. Oxygen index is only 25%, self-extinguishing away from fire. Normally modified halide, antimonies hydride, magnesium hydroxide, Phosphine acid, red phosphorus are added to raise flammability.

Optical property: Non-crystalline material, pure PC is colorless and transparent with good light transmission.

Application:
     1.High transparency and high impact resistance field, such as CD.
     2.Auto industry, for headlight, sidelight, tail lamp, mirror, glass, interior and exterior decoration parts and instrument.
     3.Electronics, low voltage cubicle connector, insulating plugs, insulating bush, machine tool protection switch, hollow brick housing,instrument box and office automation equipment.
Cost: POF PC material price is about RBM25-35/kg.







Mold temperature and even cooling will directly .

Proportion of cooling diameter, waterline to part distance, cooling space should be strictly under control of 1:2:5:4. Normal cooling diameter is 12mm, waterline to part distance is 30mm, and cooling space is 50mm.
Avoid pool type cooling as much as possible.
Double angled cooling shall be used to keep even cooling in cavity &core when necessary.
Mold temperature with PC material is 100-120℃. Avoid use of rubber seal ring, heat-resistant flu rubber seal could be appropriately used when necessary. Its working temperature: -30~+250 ℃.


















A



Engraving of Lens is different from other mould. The engraving of normal part is reversed in cavity& core, viewing from engravings direction. While core engraving of lens mould is positive direction, cavity engraving is reversed because lens is normally viewed from part visible surface.







Based on PC property: Only a few steel can be use to make transparent lamp mold, mainly DAIDO NAK80,
     ASSAB S136/S136H, Greodiz 1.2344ESR,HITACHI HPM magic. Considering the        
     comprehensive polishing property and steel cost, DAIDO NAK 80 is commonly used.


 

 

 Element  C  Si  Ni  Mn  Mo  Cu  AI  Cr
 Content  0.15  0.3  3.0  1.5  0.3  1.0  1.0  0.3


 Property of NAK80:  Pre-hardened to 37-43HRC. No need for heat treatment. With pretty good optical rotation polishing ability, good cut ability and texturing ability.
 cutting process:  Cutting resistance is bigger than other steel for its high hardness. Suggest to use CNC-M2(SKH9)or super hard alloy-P40 tool to drill.
 Drilling process:  Drill bigger borehole diameter with lower cutting speed. If spiral groove is small and shorter than standard, it will reduce the risk of tool breakage.
 Milling process:  Cutting feed standard 0.06m/l. Big cutting feed will shorten tool life.
 EDM process:  EDM surface will not be hardened and produce hardened layer. Machined surface is smooth and fine. It can replace texturing in some cases as well as wire cutting.
 EDM conditions:  Model: DLAX250 DE 150S/Work current: 2A—4.5A//Hydraulic pressure: 200mmHg//Machine depth: 20mm//Work voltage: 80—100V Electrodes: copper. Electrodes consumption is below 1%. Welding property: welded zone and heat-affected zone will not be hardened. Hardness is slightly lower than base metal (already precipitation hardening) But 500℃*5 hours precipitation hardening after welding could regain the hardness.