INTRODUCTION:
Injection moulds play a vital role in the production of qualified quality components. Consistency in the quality of components would also depend on the quality of the mould. Quality deterioration in components by moulds may be fast, which is highly undesirable happening. Productivity in injection moulding works also depends on moulds, apart from other factors. Moulds, which run smoothly and without interruption, would add to higher productivity. Unreliable mould would need frequent adjustment, repairs etc. It is, therefore, necessary that mould should be reliable in its function and moulding of qualified components.In the interest of component quality maintenance and productivity, the mould should have such design and construction features that it can run fully automatically. A mould designer should design in such a manner that a complete shot, i.e., components, runner and sprue, get completely and surely ejected. All factors like the type and specification of the injection moulding machine, auxiliary equipment, robotic specification, etc., would have to be taken into account while designing the mould.
The life of the mould depends on the design features, the steel used, fits and the tolerance of various mould parts and then the quality of the assembly thereof. There may be many other factors apart from the mould itself. For example, the accuracy of the injection moulding machine, upkeep of the mould and the attendant.
UPKEEP AND MAINTENANCE:
It is one of the prime objectives of any moulder that the moulds in use should function well to the maximum possible production quantities. A mould nicely designed and made may not remain necessarily nice unless kept and maintained nicely. Therefore, upkeep and maintenance of moulds are important practical aspects of a moulding shop. Upkeep and maintenance of moulds consist of the following aspects.Specification sheets for all moulds.
History sheets.
Design and construction of storage platforms, racks and pallets.
Moulds handling devices.
Defining, Upkeep.
Defining, Maintenance.
Instruction manual on upkeep and maintenance
SPECIFICATION SHEETS:
Specification may vary from one mould to another. It is, therefore, necessary that the person in charge of mould upkeep and maintenance should be familiar with all moulds.Complete information given in a specification sheet may be stored in a computer, allotting a suitable file number. Whenever needed, specifications can be studied and even a printout can be taken. Sometimes only a portion of the specification is needed for giving to the shopfloor technician or operator. The same can be easily done by taking out a print from the computer. Any maintenance and –upkeep-charges may not feel necessity of having a complete specification of almost all the moulds in the shop. This is good. But it is still better to have specification sheets for the guidance of those who are not familiar with moulds and might have an occasion to handle maintenance and upkeep of moulds. So, from the administration's point of view, it is also desirable to have a mould specification sheet.
Experience has shown that keeping the performance history of moulds is very useful from the technology as well as the management point of view.
On going through the history of a mould, it can be pinpointed as to which defects are occasional, which ones are repetitive and which are ‘chronic’ in nature. The incharge-maintenance-and-upkeep may take appropriate steps to find the reasons for the defects and take corrective measures. Mould history may also reveal to the management a lot of information about the performance and capabilities of the shop floor personnel like the technicians, injection moulding machine operators, etc.
A study of the history sheet reveals that a scratch on a polished surface is a repetitive occurrence and can be attributed to negligence in either mould handling or the operator using the wrong probe to remove the component stuck. Instead of using a copper or hand wooden probe, a steel/iron probe might have been used, which should not have been.
The appearance of flashes at the ejector pins is an indicator of either wrong processing conditions or an increase in the clearance between the pin and its bushing. Now the charge can examine and conclude if the increase in the clearance is premature or expected about the total quantities produced.
STORAGE PLATFORMS / RACKS:
The design of the mould storage pallets and racks varies widely due to variations in mould dimensions and weight. A small mould weighing, say, 200kgs may be handled easily and be kept in the racks. But moulds weighing in tons may be placed preferably on wooden platforms.Pallets of suitable dimensions may be used to facilitate the lifting and placing of the moulds by forklifts.
Once the mould is taken out from the storage place, it can either be further transported to the injection moulding machine by a forklift itself or an overhead travelling crane, which can lift the mould from the ‘pallet’ which is on the forks of the forklift.
MOULD HANDLING DEVICES:
Mould handling devices range from just manual lifting with the help of suitable hangers to fully automatic mould transfer and positioning in between the machine platens. Forklift, overhead cranes are generally used.Manual lifting is used when moulds are not very heavy and two persons can lift and manage to manipulate the mould in between the platens.
The difficulty arises when the injection side half of the mould is manipulated, so that the location ring of the mould enters the bore in the platen. Sometimes wooden support is placed.
By doing this, a precise up-and-down movement of the mould is possible. Further, the other person is free to manipulate the location ring in the platen bore. Manual mould handling sometimes causes damage either to the mould or the machine tiebars or the platen. Although the damage may not be major, still even minute damage is undesirable.
In the case of mould handling a forklift, lifts off the mould from the storage area, together with its wooden pallet. It is brought near the machine for the overhead crane of the hoist to lift the mould from the pallet and to place it between the machine platens.
Fully automatic mould loading and unloading is generally adopted where two or more moulds are frequently changed as a part of the moulding process.
DEFINING UPKEEP:
The upkeep of a mould means that the mould should be kept well-cleaned. An antirust spray may be used to prevent the rusting of the mould parts. The moulds should be stored preferably at a place where the humidity is low and the ambient temperature is not excessive. Sometimes, moulding shops are situated in the vicinity of other factories or shops having chemical processing or labs. It is practically found that even small traces of chemical fumes do come in contact with mould surfaces. Hence a fine layer of ‘rust’ appears on the cores, cavities and other parts of the mould. This happens if the core and the cavities are not chromium-plated. ‘Rusting’ can be very much minimised if the moulds are kept covered by PVC sheet covers.DEFINING MAINTENANCE:
In General terms, maintenance means to keep the moulds and bring them to production in a worthy condition, some essential aspects of mould maintenance are covered here.Preventive maintenance of the moulds would cover examining the mould for small damages, increase in the clearance of the moving parts, adjusting the locking wedges and cleaning the water channels. Sometimes, any guide pin or cam pin may be found shaky in its holding hole. In that event, as a maintenance action, either a new pin may be put or the existing one may be copper plated at the holding surface.
INSTRUCTION MANUAL:
Upkeep and maintenance actions are almost similar for all the moulds. But some special precautions may be needed for some moulds. It is therefore a good practice to thoughtfully prepare a manual on MOULDS UPKEEP AND MAINTENANCE. Technical personnel involved in upkeep and maintenance can follow it. The usefulness of a manual is that every time one does not have to think of various details of the work to be done. There are chances of one forgetting one action or the other. In the event of the absence of a maintenance man, the manual may help other persons to take up the upkeep and maintenance of moulds. It is useful, both from the technical as well as the administrative angle.Tips for mould cleaning
A Mould is a vital investment that is to be maintained and protected. Keeping a mould clean and properly maintained will pay back efforts on spades. The basic elements of mould cleaning and storage, using basic cleaning methods are given below:MOULD REMOVING, CLEANING AND STORAGE:
Heat the mould to room temperature before removal to evaporate any surface condensation.Using a mild, clean shop safety solvent and soft, clean towels, gently clean internal mould surfaces to remove residual dirt and grime.
More the ejector system fully forward and spray both mould halves with a shop-approved, protective rust preventive before retracting the ejector and closing the mould.
Drain and blow free all residual water to avoid rust buildup. No water should be trapped inside the mould and it is critical.
Make sure all bolts plates and clamps are properly placed and the safety straps are secured and tightened.
Remove mould, check and clean it again, if required.
Bag the last two or four shots to store with the mould (including parts, sprue and runner) as examples of the expected run quality.
Store the moulds on storage racks-notably out of the shop floor.
Don’t let water lines stick out when storing moulds on racks.
Wrap the mould with plastics. Ensure that air is dry when wrapping, or put a desiccant air absorption bag inside so that temperature changes don’t cause condensation inside the wrapping that could form rusting.
LOADING A MOULD FOR PRODUCTION FROM STORAGE:
Open the mould to clean the parting surfaces, cores and cavities.After opening the mould, remove the mould preservative and any dust or particulate with an approved, clean and safe shop solvent. Use a lint-free pad or clean towels. Don’t think the first shop will scrape off the protective coating and clean out the preservative.
Separate and clean all plate faces.
After spraying with cleaning fluid, clean any highly polished surface with uncontaminated facial tissues or cotton balls, not with bushes or rags. Don’t touch them with both hands. Dust on fingertips can scratch the polished surfaces. And dust or rust in the airlines can damage a polished cavity, so be careful when blowing them out.
Lubricate all moving parts, if required. Use lubricant judiciously on moving parts that contact with plastic parts.
Flush all water lines with descaling agents to remove scale build-up.
