Appearance, Dimension, and Fit of Molded Plastic Shell
No defects on the surface of a plastic shell may exist: material shortage, scorch marks, white lines on top and white line in white line on bottom are allowed as are blisters, whiteness or cracks fractures drying marks and wrinkles.
Welding mark: generally, circular perforation welding marks do not extend past 5mm in length and special-shaped perforations don’t go past 15mm; their strength can pass the functional safety test.
Shrinkage: No shrinkage should occur at obvious parts of the appearance; however, slight shrinkage may occur at less visible parts and no dent can be felt by hands.
Small plastic parts generally fall below 0.3mm for flatness, and must fulfill assembly requirements if there are any.
Plastic shells should be free from air grain and material debris; also, products must not have air pockets within them.
Geometric shapes and dimensions precisions of plastic shell must meet formal die drawing or 3D document specifications for geometry and dimensions precisions. Tolerance should follow tolerance principle; shaft type tolerance shall be negative tolerance while hole type tolerance shall be positive tolerance. If customers have special requests, plastic shell should fulfill them accordingly.
Wall Thickness of Plastic Shell: As a general guideline, average wall thickness for plastic shell is generally desired; any non-average wall thickness must meet drawing requirements, while tolerance can range up to -0.1mm depending on die characteristics.
Plastic Shell Matching: Surface and Bottom Shell Couplings must match within 0.1mm without scraping, with holes, shafts and surfaces meeting specifications to meet matching intervals and usage needs.
Development of Plastic Mould
Plastic mould nameplates must contain clear characters in an organized format.
Nameplate should be secured to the mould foot near its centreline and reference angle, in such a manner that it does not easily come loose. A plastic block water nozzle may be chosen for cooling water applications unless special requirements exist from customers; in such instances it must comply with those needs.
The cooling water nozzle must not protrude beyond the surface of the formwork. A counterbore should be machined for this nozzle with diameters ranging between 25mm, 30mm, and 35mm; its orifice chamfer must remain consistent.
A cooling water nozzle must feature inlet and outlet marks. English characters and numbers should exceed 5/6 in size when placed 10mm beneath the nozzle for legibility and readability. Writing must also be neat, clear, beautiful and evenly spaced for readability.
Plastic mould accessories should not hinder hoisting and storage of molds. Exposed oil cylinders, water nozzles, pre-reset mechanisms and supporting legs must be provided below during installation for protection and hoisting purposes.
Support legs must be secured to the formwork with screws through their support legs; any extra long legs can be fastened via externally threaded columns machined by vehicle.
Ejection hole sizes of plastic molds must conform to the requirements of injection molding machines; with small molds only one center may be ejected at a time.
A locating ring should be installed securely with an outer diameter between 100mm and 250mm and should sit 10-20mm above the base plate unless otherwise required by the customer.
Plastic mold dimensions should meet the specifications for an injection molding machine.
Plastic moulds requiring installation directions shall be identified using an arrow on either the front formwork or rear formwork and marked “UP” next to it, both being yellow with 50 mm text heights.
The formwork surface must be free from pits, rust spots, excessive lifting rings, water vapor inlet/outlet holes and oil holes that might compromise its aesthetic quality.
Plastic moulds should be designed for effortless hoisting and transport. Hoisting should not cause dismantlement of mould components, and lifting rings should not interfere with nozzles, oil cylinders, pre-reset rods etc.
Types of Plastic Mould Material and Their Hardness
Plastic mold frames should adhere to industry standards.
Plastic mold molding parts and the pouring system, including core, fixed die inserts, moving die inserts, moving inserts, flow cone, push rod and gate bushing materials with performance greater than 40Cr are to be utilized.
Molding plastic that easily corrodes is challenging; therefore, when using anti-corrosion materials in molding parts or coating the molding surface with anti-corrosion measures.
Plastic mold molding parts should have a minimum hardness of 50HRC or surface hardening treatments must reach 600HV to be approved for sale.
Eject, reset, insert core and remove part from plastic mould
Ejection should be accomplished without clamping stagnation or an abnormal sound, with polished inclined top surfaces lower than core surfaces.
The sliding parts must feature oil grooves and be subject to nitriding treatment; after which, surface hardness must exceed HV700. All push rods shall feature anti-rotation positioning with numbers assigned per rod.
Ejection distance shall be restricted with a stop block, while standard parts must be used on both ends of the return spring.
The slider and core must both have travel limits; small sliders should be limited by spring; if spring installation proves challenging, corrugated screw may be used instead. Cylinder cores must include travel switches.
Usually, the extracting core for sliding blocks uses an inclined guide post with an angle 2-3 deg less than that of its locking surface angle. Excessive stroke of sliding block will be pulled out using oil cylinder.
Once the end face of a cylinder core extracting forming part is covered, its cylinder must be equipped with a self-locking mechanism to ensure safe use.
Wear-resistant plate should be added under any large sliding block with width over 150mm, constructed from T8A material and treated to reach HRC5055 hardness after heat treatment. It should be placed 0.050.1 mm above the large surface, with an oil groove available and no movement between push rod and wear-resistant plate. The push rod shall remain stationary.
Add a barb to the top rod in a way that allows it to be removed easily from the product, with consistent direction of barb placement.
The clearance between the top rod hole and top rod, length of sealing section and surface roughness must meet enterprise standard specifications for ease of removal for operators. Furthermore, plastic shell should be designed so as to be user friendly.
Once the plastic shell is released from its protective cover, it is easy to follow its incline jacking, with the top rod becoming grooved or even corroded as soon as it leaves its nest.
The top block must be secure and reliable, with non-formed parts around being processed with an angle ranging from 3 degrees to 5 degrees for processing, and its lower periphery being chamfered. In addition, no scrap iron should be present in the oil circuit hole on the formwork.
End faces of return rods should be smooth without spot welding, without gasket at bottom of blank head and spot welding at spot weld points. A three-plate mould should have gate plates which slide freely while being easily removable for pulling out and replacement of parts.
Three-plate formwork limit pull rods should be placed either on either side of the installation direction for mould installation. Or alternatively, pull plates may be added on mould frames in order to prevent limit pull rods from interfering with operators’s movements.
The oil passage should be smooth, with hydraulic ejection reset in place and air outlet opened at the bottom of guide sleeve; finally locating pin must be secured without any clearance issues.
Air cooling and heating system of plastic mold
Cooling or heating systems must be free from obstruction.
Sealing must be reliable, with leakages from systems below 0.5MPa pressure requiring easy maintenance. Furthermore, dimensions and shapes of formwork sealing grooves must meet relevant standards requirements for efficient sealing performance.
Sealing rings must be fitted with grease when installed and should be higher than the formwork surface once placed. Water and oil flow path spacers made from noncorrodible materials shall also be utilized; additionally centralized water supply shall be adopted for front and rear formworks.
Plastic Mold Casting system
The gate setting should not compromise product appearance and must meet assembly needs.
To maximize forming quality, flow channels must be designed appropriately in terms of their section and length. Process time must be reduced as much as possible while sectional area should be decreased in order to reduce filling and cooling times and losses in pouring systems.
When using three-plate formwork at the rear, its split runner should feature either trapezoidal or semicircular sections.
Three-plate dies feature a material break handle on their gate plate, with diameters under 3mm for gate entrance diameter and 3mm deep steps recessed into its gate plate for ball head operation.
A ball head pull rod must be secured securely to allow easy insertion under the locating ring and pressing plate, or secured using headless screws and pressing plates.
Gate and flow channel must be machined according to the dimensions specified on the drawing; manual polishing machines are not permitted. A point gate must fulfill specification requirements. A cold material storage compartment shall also be added at the front end of each splitter for cooling material storage purposes.
Z-shaped reverse buckle of pull rod must have smooth transition. Diversion channels on parting surfaces must be circular; further, front and rear moulds must not become dislocated from their locations. Ejector pin buried gates must also remain free from surface shrinkage.
Transparent products must adhere to design standards in terms of diameter and depth of cold feed hole, material handle removal ease and appearance free from gate traces as well as assembly without residual material handle residue.
For the hook buried gate, both inserts should be nitrided to reach HV700 surface hardness.
Hot runner system of plastic mould
Wiring layout of hot runners must be suitable, easy and practical to maintain and correspond one-for-one with numbering scheme of other devices in their circuits.
Safety tests on hot runner assemblies must be conducted, with an insulation resistance greater than 2MW to ensure optimal operation. In order to meet safety and efficiency criteria, standard parts should be used in temperature control cabinets, hot nozzles and runners.
The main inlet sleeve is connected with the hot runner by threads, while its bottom surface comes into contact with the sealing surface.
The hot runner must come into good contact with both heating plate/rod and sealing surface. In addition, its heating plate should be firmly fixed to sealing surface with screws/studs so as to provide optimal performance and well-fitting surface conditions.
Temperature Control Gages for Each Group. Every group of heating elements shall be controlled with thermocouples of type J that meet temperature control gauge specifications, and be placed to maximize their effectiveness and meet design requirements. Nozzles must also meet these criteria.
The hot runner must be secured using at least two locating pins or screws, with an thermal insulation pad between it and the formwork for added safety.
Temperature control meters must provide accurate readings within +- 5 deg C of what is set on them, with sensitive temperature regulation for accurate cavity and nozzle mounting holes.
Wiring of hot runner must be properly organized and covered with pressing plate. Sockets of equal specification shall be clearly marked.
The control line shall have an undamaged sheath without damages. Temperature control cabinet shall have a solid structure with tight screws so as not to loosen.
The socket shall be secured to a bakelite board and not exceed the maximum dimensions of the formwork. Wires shall not extend beyond the plastic mould. Any contact between hot runners or templates and wires shall feature fillet transition.
Before assembling a template, all lines must be free from open circuit and short circuit conditions, and connected correctly with high insulation performance. After clamping of the template is completed, circuits shall be tested again with a multimeter to verify results.
Plastic Mould Formation Process and Parting Surface Analysis
The front and rear die surfaces must be free from roughness, pits, rust spots or any other defects which obstruct their aesthetic appearance.
Inserts must fit snugly within their die frames, with gaps under 1mm around corners. Parting surfaces must remain clear and undamaged without hand grinding wheel use to prevent voids, while sealing parts should remain undent-free.
Exhaust slot depth should not exceed the overflow value of plastic.
Inserts must be properly matched, placed smoothly, and securely fastened into their positions. Inserts and core inserts should be safely fastened into their places; circular pieces should have rotation stops installed; no copper sheet or iron sheet shall be placed between the inserts for padding purposes.
The end face of an ejector pin must match with its core. Front and rear mould forming parts must be free from such defects as reverse buckleing and chamfering.
Reinforcement position ejection should be smooth. For the products of multi-chamber mould, left and right parts shall be symmetrical; L or R indicators shall be indicated accordingly. If customers have specific demands regarding position and size requirements, these shall be met to the best of our abilities; generally speaking, font size shall not adversely impact appearance and assembly processes.
Locking surfaces must be evenly balanced to cover 75% of the area contacted. A push rod must be installed near sidewall and beside rib/boss and used accordingly with larger pushrod. All similar parts shall be marked accordingly (1, 2, 3 etc).
Collision surfaces, insertion surfaces and parting surfaces must all match. Sealing rubber for parting surfaces must meet design standards; medium molds must fall below 1020mm while large ones between 30-50mm must meet design standard specifications in terms of sealing rubber quality and seal thickness. Vacant spaces in medium moulds will need to be machined out.
Texture and sandblasting must meet customer specifications for products with appearance requirements. When it comes to screws on these products, shrinkage prevention measures shall be implemented on them for appearance purposes.
Jacking Pipe must be chosen for screws with depths greater than 20 mm.
Wall thickness must be consistent and deviation controlled within +- 0.15 mm; reinforcement width shall not exceed 60% of wall thickness of appearance, while inclined roof core insert and sliding block shall be firmly secured.
The front die is placed into the rear die, or vice versa, and each of its four sides must feature bevel locks in order to avoid voids in production.
Injection Mold Production Process
Plastic molds must have the capacity for stable injection molding production and repeatable process parameter adjustment within normal injection molding conditions.
At least 85% of the maximum injection pressure of injection molding machines should be below when producing plastic molds with injection molding techniques.
At injection molding production, injection speed of plastic mold should not fall below 10% of its maximum injection speed or exceed 90%.
Plastic injection molding production should typically use pressure maintaining pressures less than 85% of their actual maximum injection pressure.
Plastic mold clamping force during injection molding production must not exceed 90% of its rated clamping force for that model.
When producing injection molding products, products and nozzle materials must be removed safely and without difficulty (in general no more than 2 seconds should pass).
Plastic molds with insert products must have the insert installed safely and reliably during production, for optimal performance.
Packaging and transportation of plastic mould
The plastic mold cavity should be thoroughly cleaned and treated with anti-rust oil to reduce corrosion, while its sliding parts must be coated in lubricating oil for ease of motion. In addition, its feed inlet shall be blocked with lubricating grease for extra safety.
Plastic moulds should be equipped with locking plates, and meet design specifications. All spare and vulnerable parts must be present and come complete with an inventory list and supplier name attached.
Plastic moulds must be fitted with leak-proof seals for water, liquid, gas and electricity inlets and outlets to prevent foreign objects from entering. Their exterior surfaces must also be painted according to customer requirements.
Plastic mould should be stored and transported according to moisture-proof, waterproof and anti-collision packing specifications, with customers fulfilling any applicable requirements as necessary.
Plastic mold product drawings must include structural drawings, cooling and heating system diagrams, hot runner layout drawings, details of parts and accessories used and mold material suppliers as well as operating instructions, mold test reports, factory inspection certificates and electronic documents.
