Mold Timing and Terminology

Dry-cycle: The total time required for the (machine) clamp to close and open, or the sum of the mold opening and the mold closing time. Today’s fast machines have dry-cycles in the order of 1–3 seconds. A short dry-cycle is of particular importance with fast-cycling molds. The dry-cycle also depends on the length of the clamp stroke.
Opening time: Usually quite fast. The ejection preferably should take place during this time,to reduce (or to omit completely) any mold open time. Occasionally, mold opening speed may need to be slowed down to suit the ejection method.
Closing time: Usually quite fast, except for the final approach before the mold is fully clamped up, to permit the mold protection system to operate in time before serious damage is caused to the mold.
Mold protection: A system which senses (at the moment of final closing the mold) whether there is foreign material (dirt, plastic pieces, products which failed to eject, etc.) between the mold halves which could cause damage to the mold. A signal from the mold protection system will cause the mold closing to stop before damage occurs and sound an alarm. It usually automatically reopens the clamp so the foreign material can be removed.
There are many types of mold protection systems, such as electric, optical, or pressure activated. Some are more sensitive than others and may not always save a mold from damage.
Mold open (MO) time: This is lost time. This time should be as little as possible. It can be zero.
Mold closed (MC) time: Time from the moment the mold has closed until it reopens. It is the
sum of the following times: Injection time: the time to fill the mold with plastic (usually with high injection pressure).
Hold time: the plastic in the cavities is held under pressure usually lower than the injection pressure to add plastic volume as the plastic shrinks within the cavity.
Cooling time: the time from the moment the injection (or hold) pressure is off until the mold starts opening. (This term is actually a misnomer, since the cooling is always on and starts to remove heat from the plastic as soon as the plastic enters the mold.)
Ejection time: the time required to eject the products from the molding area so that the mold can re-close without catching an ejected piece. Preferably, this should take place during the opening time so as to eliminate the need for additional MO time. In some molds, it is not possible or practical to eject during the mold opening, and the ejection takes place
partly or solely during the MO time.

conclusion
Dry-cycle- Total Time required for the clamp to close and open (sum of mold opening and closing time).
Opening Time- Time it takes to open mold and usually eject part
Closing Time- Time it takes to close mold
Mold Protection- Halts molding operation if a foreign material (dirt, flash, debris) is detected in mold cavity
Mold Open- Time the mold is actually open
Mold Closed- Time the mold is closed and usually includes
o Injection Time, Hold Time, Cooling Time
Ejection Time- Time is takes to eject parts and is a part of Mold Open Time

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Assembly Inspection New Mold

Pre-Assembly Inspection
for a New or Reworked Mold
there are following important point to check list when assembly a new or reworked mold, following pinture below show three plate mold when all parting line open


• Check all shutoff areas with spotting blue. Tryout any pieces to be insert molded in assembly, check fit and shutoff
• The cavity & core blocks have 0.002 preload per side (above the mold base plates)
• Cavity surface finish is correct to print. As a rule remove all tool and EDM marks, especially deep ribs.
• Check for nicks, scratches, damaged edges or corners, chipped or damaged pins and damaged or loose pin holes.
• All cavities have been numbered, and have part numbers (if applicable)
• All inserts are numbered to correspond to cavity numbers. Details should be stamped with detail number and material type
• Tool has pry slots (on back side of "A", both sides of "B", & top of "Ejector" plate) and is chamfered in correct areas
• Water line countersink diameter is correct for Jiffy-Tite plug being used. Check plug holes for smoothness, lead in chamfer, & cleanliness. Sealant has been used on all threads. Jiffy plugs, regular plugs, baffles, and bubblers are in place and have been flow and pressure tested.
• Mold Info has been stamped correctly on the Support plate, all water lines are clearly stamped, and stamp "top of mold" and "operator side" on the appropriate sides
• Verify that all cavities have gates and the gates are the same size.
• All sliding parts must have grease grooves, be lubricated, and move easily.
• Verify that slides do not interfere with ejector pins or other moving components. Verify that travel is sufficient to clear molded part
• Check for proper clearance on angle pins, and slides when entering opposite side. Make sure pins don't bottom out. Check if slides lock properly in slide retainer.
• All limit switches must be orientated properly for wiring and function.
• Check hydraulic cylinders for length of stroke.
• K.O. holes are in correct location and tapped to correct dimensions (if applicable).
• Verify that all pins, sleeves and lift cores have the proper hole clearance, head clearance and proper depth clearance. All pins and sleeves must have lead in clearance and lead in chamfer in core insert. Must be a smooth transition.
• All return and ejector pins, and support pillars are the correct length, ejector system moves easily, all pins are in place (and should be marked for proper location), and the entire assembly lubricated
• Push ejector plate forward and check if all pins, sleeves, lift cores and all other moving components spin freely. Wiggle to verify correct clearance and that all components move freely
• Check that ejector plate can use the full length of travel and has spring return if needed. Check if runner & part will clear the core
• Verify that sprue puller design will work as needed
• Open and close tool in assembly to check for any interference. Activate any and all side actions and lifters to check for proper travel and interference of any kind
• All core pins are the correct length, and all pins are in place, do the necessary pins shutoff?
• Runner must be benched smooth with rounded corners and transitions. Gate to Runner transition should be blended smooth. (Parting Line edges stay sharp)
• All runners are vented at every direction change, and part detail is vented directly opposite the gate, at the parts ends & corners, and every 2 inches in between as necessary. Vent all guide pins
• Verify that all plates have eyebolt holes on every side
• Safety strap is attached to mold between A and B halves on the operator side
• Locating ring and sprue bushing are in place, and sprue radius and orifice diameter is correct size. Sprue Busing is rotation locked and retained
• Clamp slots are in place and free from any interference.
• If inserts are fit on surface plate, check fit in assembly also.
• Demagnetize all components.
• All screws/bolts are in place and tight. (Follow a pattern to prevent missing a screw)
• Verify that cavity, core, slides, mold base and all other applicable parts are clean and clear of chips, debris, and benching grit, and spotting blue, especially deep ribs and bosses.
• Check all holes for missing pins by looking in every hole of the assembled mold.
• Verify that parting line locks function properly.
• Open and close mold on bench that everything functions properly. Check if slides clear ejector pins, lift cores and any other moving parts with sufficient clearance and that mold closes freely.
• On hot sprue bushing, check if it is properly installed and assembled, make sure all components are installed and no wires are broken or damaged. Check that wire channel is in mold base and that clamps are in place to hold wires.
• Water lines must be pressure tested with diversion plugs, "O" rings and correct jiffy-plugs installed
• All slides, core pins, angle pins, cam locks and guide pins must be greased.
• For Hot Runner molds check the size and fit of every drop diameter. Check overall lengths and heights to verify heat expansion and proper "crush".
• For Hot Runner molds check that all wiring is in a channel, free from damage, and free from possible "pinches" during assembly. Check continuity all all circuits (compare all zones to the drawing, note any changes or additions)
• For Three-Plate molds, verify that all latches function properly, that they latch and release in assembly, and that plate separation is sufficient to let both the part AND the runner drop through. Also check that all latch dowel pins are secured so as not to come loose during operation.
• Tool is sprayed with WD-40 or equivalent for shipping

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Assembly and Disassembly Mold

The following is a good checklist for disassembly and assembly of a plastic injection mold. Some of our customers to not have trained moldmakers on staff to perform this kind of assembly and disassembly so we have listed a procedure here to help give your tooling room staff a good start, HOWEVER, this must be done at your own risk! We HIGHLY recomend that every molding facility should have skilled moldmaking professionals on staff to perform assemblies, disassemblies, maintenance, and repairs.



the picture at the top show disassembly various parts of mold
Disassembly:
• The mold must be placed on two rails on a clean table with sufficient space. Tools used must be in good condition and should include allen wrenches, aluminum prybars, rubber mallet, duct tape, and some containers.
• Separate mold at parting line carefully and look for any visible damage. If mold is damaged, report it at once. Check for rust in core and cavity and report it at once if found.
• Have containers to put all the parts in and identify it with the proper job number.
• Check for core pins in Ejector Housing (at the bottom clamp plate) and remove the core pins first.
• Remove all necessary screws in the Ejector Housing and remove it.
• Remove screws from the Ejector Plate and remove it.
• Check if all pins are marked, if not mark as necessary.
• Check if lift cores are marked, if not mark as necessary.
• Remove all pins and parts from Ejector Housing. Protect all fragile parts and critical areas with duct tape.
• Remove all water line jiffy-plugs
• Remove all slides assemblies and protect all critical areas with tape or carefully store in container.
• Remove the Sprue bushing, hot sprue, or any hot runner system.
• Remove all screws from cavity and core inserts and install two or four longer screws in cavity and core. Then knock out cavity and core inserts from mold base by hitting screws with a rubber, aluminum, or copper mallet. BE CAREFUL NOT to knock insert out onto the bench or floor and damage it. If you can't bump the insert out into your own hand GET HELP.
• Once the primary inserts are removed, remove all sub-inserts, gate inserts, core pins, etc. and protect all critical edges with tape or carefully store in container.
• Carefully clean all details with a clean, mild solvent and clean towels being careful NOT to damage sharp edges, parting surfaces, shutoffs, or the cavity finish.
• Finally, store all inserts in such a way that the molding surfaces are protected and cannot be accidentally damaged.



Finishing Assembly Picture
Assembly:
• Have all the mold plates, inserts, and components in one place ready for assembly. Have a clean table and two rails to slide plates on. Tools used must be in good condition and should include allen wrenches, aluminum prybars, rubber/copper/aluminum mallets.
• Cleanliness is critical in mold assembly. Make sure all plates, inserts, and components are clean and free from grit, debris, and chips. After you have carefully cleaned all details with a clean, mild solvent and clean towels THEN wipe everything again with your clean, bare hand to remove small grit (Careful NOT to damage sharp edges, parting surfaces, shutoffs, or the cavity finish)
• Install all sub-inserts, gate inserts, core pins, etc. into the primary inserts. Check that all inserts and pins are marked and that they are installed in the correct location and position.
• Mount the B-Plate to the Support Plate
• Install the B-Half insert set, any slide assemblies, and any other B-plate components. Check that all parts are marked and that they are installed in the correct location and position.
• Insert and grease all ejector pins, ejector sleeves, and ejector blades through the pin retainer plate, support plate, and core inserts. Install all return pins and springs. Install and grease any Lifter mechanisms. Bolt on the Ejector plate.
• Assemble the ejector housing, with support pillars, guided ejection pins, etc. Guide this assembly through the ejector & other plates and bolt it to the support plate. Insert any core pins that mount in the bottom clamp plate and fasten their backup plates. Lubricate the entire assembly.
• Verify that the Slide assembly moves freely, is greased, and that the slide retainer is functioning properly.
• Move the Ejector assembly forward and check if all pins, sleeves, lift cores and all other moving components spin freely. Wiggle to verify correct clearance and that all components move freely
• Check that ejector plate can use the full length of travel. Check if runner & part will clear the core when ejected.
• Mount the A-Plate to the top clamp plate
• Install A-Half insert set, heel blocks, angle pins, and any other A-plate components. Check that all parts are marked and that they are installed in the correct location and position.
• Install the locating ring & sprue bushing, check that sprue radius, and oriface are the correct size and verify that the sprue bushing is rotation locked and retained
• If the mold features 3-plate or hot runner system install them at this stage.
• For Three-Plate molds, verify that all latches function properly, that they latch and release in assembly, and that plate separation is sufficient to let both the part AND the runner drop through. Also check that all latch dowel pins are secured so as not to come loose during operation. Lubricate the whole assembly and verify that it moves freely.
• For Hot Runner molds check that all wiring is in a channel, free from damage, and free from possible "pinches" during assembly. Check continuity all all circuits
• Install all jiffy-connectors with teflon tape or suitable thread sealant and water test.
• Check all limit switches
• Spray with WD-40 and close the assembly
• Verify that the mold has a mold strap and that it is fastened correctly

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Hot runner construction and method

Hot runner is a method in plastic injection molding with a mold suitable for use insimultaneous molding of a large number of articles at a time by hot-runner molding technique. The mold has a hot-runner block in which disposed are a plurality of gates through which the molten resin is delivered to the molding cavities formed in a cavity block which is usually kept at a low temperature. The gate area of the hot-runner block is kept in contact with the cavity block, for the safe deliver of the resin to the molding cavities, in the injection step and, therefore, is cooled by the cavity block. Consequently, when the injection is completed, the gate area has been cooled to such a low temperature as to cause a solidification of the resin in the gate area. The hot-runner block is then separated from the cavity block and brought into contact with a hot gate-temperature recovering block, so that the gates are heated to remelt the solidified resin, before the next batch of injection is performed, so as to recover the fluidity of the resin

Types of hot runner systems
There are two types of hot runner systems:

Insulated runners
Insulated runner molds have oversized passages formed in the mold plate. The passages are of sufficient size that, under conditions of operation, the insulated effect of the plastic (frozen on the runner wall) combined with the heat applied with each shot maintains an open, molten flow path.

Heated runners
For heated runner systems, there are two designs: internally heated and externally heated. The first is characterized by internally heated, annulus flow passages, with the heat being furnished by a probe and torpedo located in the passages. This system takes advantage of the insulating effect of the plastic melt to reduce heat transfer (loss) to the rest of the mold. The second consists of a cartridge-heated manifold with interior flow passages. The manifold is designed with various insulating features to separate it from the rest of the mold, thus reducing heat transfer (loss).


hot runner system picture

One of the more important enhancements you can incorporate into your mold to improve molded part quality, reduce production times, and remain price competitive is to equip it with a quality hot runner system. A hot runner-equipped mold can :

• Materials cost savings - no runner to regrind or reprocess
Least expensive cost / piece
Reduction of energy costs
Shorter, faster cycle times - no runners to cool
• Smaller machines - reduced shot volume into runners
Automated processing – runners do not need to be separated from the parts
Gates at the best position for economical design
• No runners to remove or regrind

• Reduces the possibility of contamination
Lower injection pressures
Lower clamping pressure
• Shorter cooling time
Shot size reduced
Cleaner molding process
Eliminates nozzle freeze
Consistent heat within the cavity
There are, however, a few disadvantages to hot runner systems that need to be considered
• Hot runner molds are more complex and expensive to build than cold runner molds
• Higher initial start-up costs than for cold runner systems
• Complex initial setup prior to running the mold
• Risk of thermal damage to sensitive materials
• Elaborate temperature control required
• Higher maintenance costs – more susceptible to:
o Breakdowns
o Leakage
o Heating element failure
o Wear caused by filled materials


other type hot runner system

Lower Cycle Time, Increase Output
The cycle time of any mold is largely influenced by the cooling cycle—how fast the resin can be sufficiently cooled so that the part can be ejected without permanent deformation. In any given mold, the areas that take longest to cool are those with the thickest wall section.
njection time is another component that differs between comparable hot and cold runner equipped molds. The injection time difference will be the extra time required to fill the cold runner.
Close and open stroke of the press is extended with cold runner equipped molds. The travel must be increased to accommodate safe ejection of the cold runner.
Parts molded with hot runners better lend themselves to automated part removal. With no runner to interfere with part removal, secondary mold processing times involving manual labor, including part/runner separation, part trimming and packaging, are reduced or eliminated entirely.
Significantly Reduce Production Costs
Although a more expensive capital investment upfront, a hot runner system is a significantly more cost-efficient means to keep production costs to a minimum over the long run.

Resin Savings
Since there is no cold runner to discard or recycle, resin consumption is reduced. Depending upon the molding application (i.e., medical components or parts requiring FDA approval), the product may require 100 percent virgin material—increasing overall consumption.
Energy Savings
Energy is wasted plasticizing, cooling and regrinding each cold runner that is produced. Increased energy consumption also is a direct result of extended cycle times.
Labor Savings
Secondary operations—such as manual part de-gating and trimming—are eliminated entirely with a hot runner system.
Mold Cost Savings
A smaller cavitation hot runner equipped mold may be able to satisfy production quotas using a smaller number of cavities since it runs at a faster cycle. The smaller mold frame size may enable installation into a smaller press.
Injection Press Costs
Hot runners allow reduced injection pressures during packing, as the system does not have to deal with injecting resin through a cooled runner. Melt in the cold runner may lose heat en route to the gate, possibly requiring higher heats and/or pressures from the injection molding machine. By reducing the injection pressure and clamp tonnage required, it is often possible to run the same part in a smaller tonnage machine as the clamp tonnage required is not as great.


sample heater in hot runner

Benefits for Long-Term
Despite the higher initial cost, the long-term benefits of equipping a mold with a hot runner system can be easily justified. A hot runner-equipped mold can effectively reduce molding costs without significantly increasing the complexity of the mold design. Generally, mold build leadtimes are not impacted as the hot runner is designed and manufactured in parallel with the mold.
It is in the best interests of the moldmaker to continually suggest ways for his/her customer (the molder) to reduce mold operational costs and increase mold output. By demonstrating these initiatives, the moldmaker confirms to the molder that the moldmaker is taking an active role in increasing the molder's overall profitability, which in turn increases the likelihood of repeat business for the moldmaker.

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Mold part and construction

Many type of mold in the platic industry but generally mold devide in 3 big section there are :

Two plate mold
Two plate mold basically when opening the product after plastic injection process mold just devide in two parts core side and cavity side, this type molding only have one parting line, product parting line with located between core side and cavity side
Look at picture below for more detail


Three plate mold
Basically when product out after injection process this mold type divide in three parts, beside that, this type mold have three parting line, first between top plate and runner stripper plate, second are between stripper plate and cavity plate, the last is parting line product that located between core and cavity (see picture below)


hot runner mold (runner less mold)
this type basically similar with two plate mold but not same, hot runner mold always heating the runner, so runner will not drop out with product, so it is some times called runner less mold, there is two big parts when opening after injection, core side and cavity side. Look at the picture below


Mold Construction
look at the picture, the parts of mold are



1. Top plate (plate 1)
2. Striper plate (plate 2)
3. Runner plate (plate 10)
4. Cavity plate (plate 3)
5. Core plate (plate 4)
6. Spacer Block (plate 6)
7. Bottom plate (plate 9)
8. Ejector plate (plate 7)
9. Ejector retainer plate (plate 8)

other function from all parts will explain in other post

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Polystyrene Injection Process

Polystyrene is one of the best materials for injection moulding. Cycle times with polystyrene are usually short due to ease of melting, fluidity and reasonable set up times. Complex tooling can be used.

The surface finish of the final product is also good, and the low mould shrinkage of polystyrene is a useful factor.
Moreover, due to good inherent thermal stability, polystyrene can easily be recycled.
Finally, polystyrene can be easily compounded or coloured in the melt phase and formulated for specific performance (gloss, anti-static properties,...).

General facts
Total Petrochemicals’s Polystyrene can be processed by every conventional technique used for thermoplastics. The general properties of polystyrene allow for a wide processing window in terms of both temperatures and pressures.

Drying
Polystyrene is not hygroscope, and is delivered in dry pellet form. Drying is not normally necessary. Care must be taken to avoid conditions which can cause condensation, this can lead to the appearance of splash marks on the finished moulding. If necessary, the product can be dried in a ventilated oven for 2 hours at a temperature of about 80°C.

Change of material or colour
All polystyrenes are "compatible", either GPPS or HIPS. The change from one grade to another is straightforward. Polystyrene is not compatible with other polymers such as polyethylene (HDPE or LDPE), PVC (Polyvinyl Chloride), ABS (Acrylonitrile Butadiene Styrene), PMMA (Polymethylmethacrylate), or PA (Polyamides) and, in general, other thermoplastics. This means that the machine has to be purged thoroughly in order to avoid such phenomenon as delamination during molding.
In order to do this efficiently, we advise to let the machine run while decreasing the temperatures, then to feed in the new material, and to start increasing slowly the temperatures. The new material will be more viscous because of low temperature and should "push out" the old material
The change from one colour to another is achieved quite easily by using the same protocol.

Temperature
Standard grades of polystyrene can be processed with a fairly wide temperature range from 180°C to 280°C. Some caution should be exercised when using certain compounds which are heat sensitive e.g. some fire retardant grades.
The choice of temperature to use depends mainly on the component design, the cycle time, and the geometry of the feed system (hot runners, …). Generally an increasing temperature profile from the feed hopper to nozzle should be adopted. The nozzle temperature should be set to a lower value in order to avoid the formation of strings and material leakage from systems without a shut off valve.
In certain cases, where there may be issues relating to plasticising capacity, an inverse temperature profile, where the hottest zone is the feeding section, with an upper limit of 230°C, can be adopted.

Injection speed
The injection speed depends on the machine capacity and general injection parameters e.g. part thickness, hot runners design…. A high speed gives a high level of shear, generating material self heating, which in turn makes it easier for the material to flow by limiting the thickness of the cold layer in the hot runners. Polystyrene, being quite thermally stable, lends itself to this self heating phenomenon. It is recommend to use high injection speeds in order to minimise potential weld line problems. However, there are limits as too high injection speed can cause faults such as material degradation, air inclusion (bubbles), and burn marks due to inadequate tool venting.

Shrinkage
As with every plastic material, polystyrene shrinks during cooling. This value is generally between 0.4 and 0.7% depending on grade, part thickness and issues due to tool design.

Mould Temperature
Generally between 30 and 50°C. For thin wall objects moulded at short cycle times it could be useful to cool down the mould down to 10°C.

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