Polishing of molding surface - injection molding technology for injection molding factory

        The roughness of the molding surface directly affects the roughness of the surface of the plastic parts.  Due to the increasingly widespread use of plastic parts, customers of plastic parts of the surface quality requirements continue to improve, ordinary mechanical processing and electrical processing to get the shape of the table to the full requirements, so it must be in the injection mold processing or electrical processing after the molding surface processing, in order to improve the roughness of the table.  There are ordinary polishing and mirror polishing, the roughness of ordinary polishing Ra up to 0.2m, the roughness of mirror Ra up to 0.008μm, surface polishing is mainly used to produce transparent plastic parts of the injection mold surface. 

The finished surface also has the following advantages.  

(1) When injection molding production, plastic parts are easy to demoulding.  

② It can reduce the wear of plastic melt on mold production.  

③ The flow resistance of plastic melt can be reduced.  

④ Can reduce the mold production fracture or burst caused by temporary high load or fatigue.  

How to judge the quality of the surface of the injection mold the following points should be paid attention to.  

(1) The surface of the die must have a geometrically correct plane without any convex surface.  

(2) The surface roughness of the mirror polishing of the molding surface is usually judged by the naked eye, and it is often difficult to judge by the naked eye, because a surface judged as smooth by the naked eye may not be a completely smooth plane in the real sense of geometry.  

(3) The surface of the mold must be completely free from scratch marks, such as the small trachoma and local peeling left by the carbonized particles being pulled out.  If the processing quality of the injection mold is strict, the smoothness of the molding surface can be determined by special instruments, such as light refraction method or magnifying glass.  

(1) polishing process and skills polishing process and skills are very important, if the skills are used properly, the effect must be very good, on the contrary, if the skills are poor, not only can not reduce the surface roughness of the molding, and will damage the original surface quality, so that the molding surface becomes more rough.  First of all, engraving injection mold is processed with milling machine, electric spark machine tool or precision casting, if the surface of the mold requires smooth, then the surface of milling must be rough grinding, fine grinding and polishing.  The surface processed by the electrode needs only fine grinding and polishing, and the precision casting mold needs only polishing with diamond plaster.  Fast and good polishing can be polished with a grinding wheel, first of all to remove the knife lines left by mechanical processing.  Whether using mechanical or manual grinding, please observe the following principles:  

① When grinding grinding wheel, a large amount of coolant should be used to avoid overheating and affect the machining hardness of injection mold, so that the formed surface is partially annealed.  

(2) Clean and no scar grinding wheel or grindstone should be selected, the higher the hardness of steel should be selected the softer the grindstone.  

③ When using a fine grinding wheel each time, the workpiece and the palm of the finger must be cleaned thoroughly, so as not to leave a coarse sand and scratch the forming surface. The more fine the grinding wheel, the more attention should be paid.  

④ When choosing a fine grinding wheel each time, the injection mold direction should be changed to 45° with the previous time, and then grind.  When the new grindings completely cover the direction of the previous grindings, add 25% more time to continue grinding to deform a thin surface layer, and then choose a finer grinding wheel.  

The advantage of constantly changing the direction of the stone mill is that irregular patterns can be avoided.  

⑥ When grinding large flat injection moulds, the use of soft hand grinding disc should be avoided as far as possible, and the grinding stone should be selected to avoid the formation of irregular patterns.  

(2) Polishing matters needing attention  

(1) Before trying the mold, it is necessary to check whether the polishing meets the requirements or is completely completed.  

② Whether the fire pattern is correct and whether it can be demoulded.  

③ All mirror polished steel must be ASSAB136 or NAK80 with hardness of 52~54HRC.  

01. Assembly of internal mold inserts  

(1) Type A is not set through, embedded type, fastening with screws. The inner mold insert includes fixed mold insert and moving mold insert. The insert of type A assembly method is not set through, and they are fixed on fixed mold A plate and moving mold B plate respectively by screws.  Number and size of fastening screws  

(2) Type B insert insert, screw fastening.  The holes of fixed inner die inserts of A and B plates are made into through-holes, commonly known as through-holes. At this time, inserts are fixed on the fixed die panel and the moving die bracket respectively by screws. The number, size and assembly size of screws are the same as type A.  

(3) C-type circular insert, fixed step,  

(4) D-type circular insert, fixed with "ten steps of pressing plate",  

(5) Type E on the basis of type A with two wedge blocks, this assembly method is mainly applied to large die frame (die frame width ≥400mm), insert size ≥200mmx200mm occasions, the purpose is to facilitate the assembly and disassembly of internal die insert, and ensure the insert and die position requirements.  Insert wedge size.  Material: 45 steel, heat treatment: quenched to 42~46HRC.  

(1) Both moving and fixed molds should be set with wedges on the two opposite sides of the datum.  

② There can be no gap between the template and the wedge block.  

③ Mark the corresponding position of the wedge block and the template to prevent wrong loading.  

④ The screw locking the wedge block is assembled and removed from the parting surface.  

⑤ In the front of the wedge block to have a screw hole, easy to take out the wedge block.  

02. Core assembly  

(1) Fixed F type step,  

(2)G type screw fastening,  

(3) H-shaped steps are fixed and round pins are anti-rotation. In the design, if the diameter of the round insert is less than 40mm, the height of the steps must be greater than 5mm;  If diameter ≥40mm, step height is 8~10mm. The purpose of this is to facilitate the clamping of parts in turning processing.  

(4) Type core set through, screw fastening.  

(5) The T shaped part is large and the fixed part is small, which is commonly known as mushroom insert.  

(6) K-type inserts are inserted through, and hook is used to replace steps for positioning.