Product category:
Injection moulding
News Release from: Engel Austria | Subject: Injection moulding technology
Edited by the Manufacturingtalk Editorial
Team on 21 September 2001
Engel unveils new injection moulding
technologies
Among a number of new injection moulding process developments from Engel are X-melt for small precision parts, thin wall injection moulding and the Foammelt process for high rigidity.
Georg Steinbichler, Managing Director of Research and Process Technology at Engel, described the latest injectionb moulding developments They include X-Melt for injection moulding small precision parts, thin-wall injection moulding and Foammelt which achieves high rigidity with minimum amount of material
This article was originally published on Manufacturingtalk on 12 Jan 2001 at 8.00am (UK)
Related stories
Automating pulley moulding
An Engel unmanned injection moulding line, conceived with rapid mould change-ocver, is producing a wide variety of automotive drive belt pulleys for the Dutch enterprise Axxicon.
Automation boosts injection moulding quality
The prime aim of the automation of injection moulding systems is not to save high labour costs but to ensure high process and product quality, says Engel.
As a performance-oriented manufacturer of injection moulding machines, Engel offers its customers much more than precision, reliability and cost-efficiency.
Engel * supplies complete production cells comprising component units of its own manufacture which, in their entirety, optimally meet the actual production requirement, * conceives and realizes processing technologies tailored to the customer's specific process requirements, * collaborates with the customer in developing new, hitherto unavailable machines and processes to meet completely new requirements in the injection moulding field.
In order to maintain and extend its lead in these three fields, Engel now channels all related activities through its business division "Research and Process Technology".
Further reading
Expanded versatile standard in elastomer moulding
The Engel ELAST 750/160V Expert injection moulding machine showcased on this years "K" exhibition documents the further improved Expert technology of Engel ELAST machines.
Innovative cell for optical multi-part mouldings
The Engel DUO 5550H/500H/900 Combi (Cleanshot) is a multiple injection unit machine for the production of 2-3 component / 2-3 colour mouldings.
Film-backed thin sections injection moulded
An Engel VICTORY 200/120 injection moulding machine is at work in the production of ready-for-assembly film-decorated thin section housing parts for a cordless telephone.
This division co-operates, world-wide and on an intensive basis, with raw material manufacturers, research institutes and engineering companies.
It is precisely from this development network that Engel's customers can derive enormous benefit: they can, for example, considerably improve their typical, though often uncomfortable, "sandwich position" between the market power of large, influential customers on the one hand and that of large, influential suppliers on the other.
Moreover, innovative processors can now actively exploit those changes which exercise such a decisive influence on this highly competitive market.
Instead of reacting to such changes passively, they can now set the trend themselves.
Besides "time to market", flexibility and service, high efficiency will, to an ever increasing extent, be the success factor of the future in terms of real net output.
Indeed, this is the reason why Engel has, since K'98, been focussing its efforts on further developments in the field of processing technology, for highly specialized, application-related processing technology is a prerequisite for the high efficiency just mentioned.
Achieving precisely this objective for its customers is one of Engel's core competencies.
X-melt is a completely new process for the injection moulding of small, thin-walled parts up to 50 g and microprecision parts.
The basic idea behind this new process is that the pressure of the melt itself can be used for the injection process, waiving the need for a separate hydraulic accumulator for the injection unit.
X-Melt also improves reproducibility, as the machine must no longer perform the difficult task of controlling fast screw movements in conjunction with enormous forces of inertia.
The starting point of this new development was a series of melt front speed measurements carried out on a mould specially equipped for this purpose with sensors.
The results showed that a high screw advance speed generated by a large amount of energy - typical speeds are 1,000 mm/s and over - failed to produce the expected high melt front speed.
On the contrary, a large part of the dynamic energy was dissipated through the compression of the melt under the high injection pressure.
The obvious solution was to divide the injection process into two completely separate operations: "compression" and "expansion".
To this end, the injection unit or the mould must be equipped with a shut-off nozzle.
The usual processes of plasticizing the melt and metering the required volume of melt through screw retraction are followed by the process of building up a high melt pressure of between 1,000 and 2,000 bar prior to injection.
This process takes place with the shut-off nozzle in its closed position.
While a screw advance is required on account of the compressibility of the melt, this is not time-dependent to any critical extent and can be performed by a drive unit without hydraulic accumulator.
The "compression" phase is completed once there is enough energy stored in the melt for the injection process.
The energy and time otherwise needed for accelerating, advancing and decelerating the screw can now be waived - the energy required for filling the cavities is only a third of the usual requirement.
Injection is effected simply by opening the shut-off nozzle and allowing the melt to "expand" into the mould.
That this is an appropriate description, is illustrated by the following facts and figures: For the injection moulding of a battery box for a mobile telephone (ABS-PC blend, shot weight 3.2 g, wall thickness between 0.4 and 0.5 mm), the melt is precompressed to a pressure of 2,400 bar.
The injection operation takes only 60 ms (compared with 80 ms using conventional injection moulding technology with an hydraulic accumulator and an injection speed of 1000 mm/s).
Added to this is the fact that X-Melt considerably improves reproducibility: variations in part weight are reduced by half, from +/- 0.07% to +/- 0.03%.
A machine particularly suitable for use with X-Melt is the new "e-motion" all-electric injection moulding machine which will be presented at K'2001.
Its all-electric system enables it to maintain the specified compression and screw position with absolute accuracy after the opening of the shut-off nozzle - this is considerably more difficult in the case of a hydraulic machine.
Important areas of application for thin-wall injection moulding include the manufacture of large-area fluorescent lighting diffusers in polycarbonate, car bumpers and door trim, telephone housings and packagings.
The injection moulding of such parts involves flow length-wall thickness ratios of up to 400:1.
In order that the melt cannot freeze prematurely when moulding parts with a wall or section thickness of less than 0.6 mm, the screw must reach a speed of at least 1000 mm/s within 20 ms after the start of the injection process.
Similarly demanding are the requirements at the end of the injection process, for the mould may be neither overfed nor underfed with melt, meaning that the screw must decelerate within the last 10 ms and reach its end position to an accuracy of within +/- 0.2 mm.
Such high performances cannot be achieved simply by improving the performance of just one component part of the machine.
On the contrary, it is necessary to develop, on the basis of a precise analysis of each individual stage of the process, an overall concept for a production cell which, in its entirety, is capable of meeting these exacting requirements.
The necessary equipment modules are: * a double pump hydraulic system as featured on the new "Victory Speed" series of tiebarless machines, permitting simultaneous movements of the clamping and injection units and hence achieving faster cycling times, * an adaptive, self-adjusting injection control system with two important features: a new 64-bit controller with a clock pulse of 1ms instead of 2 ms and a reaction time which has been reduced from 0.6 to 0.2 ms and a highly dynamic servo valve with accumulator, * an ERS high-speed robot, manufactured by Engel Automatisierungstechnik GmbH in Dietach, permitting extremely fast removal of the moulded part from the mould.
Only through the perfect interaction of the equipment modules mentioned before it is possible to achieve the required quality of part and the necessary degree of economic efficiency.
The thinner the moulded parts are, the more cost-relevant such peripheral operations as demoulding will be.
High-speed robots specially developed by Engel for thin-wall injection moulding technology are capable, through ultrafast communication with the injection moulding machine and the perfect co-ordination of parallel movements, of reliably demoulding a mobile telephone housing, for example, in only 0.29 seconds - that's faster than a free fall! Requirements become even more demanding when the two technologies of thin-wall injection moulding and in-mould decoration are combined in one machine with the aid of Engel's Tecomelt module.
The high injection speed and the high shear forces generated during the mould filling operation must not damage the decorative film.
In the case of simple, large-area parts, the injection-compression moulding process (i.e injection into the partially opened mould) has proved ideal for this application.
When it comes to the moulding of complicated parts, all the individual influencing factors, such as the material, the process control system, the construction of the film, including the printing ink, must in each individual case be optimally adapted to each other.
To this end, Engel has developed the necessary expertise in collaboration with partners from all relevant sectors of the industry.
The use of blowing agents for the injection moulding of foamed thermoplastics is a technique which has now been in existence for a long time.
In recent years, and especially since K'98, the use of chemical blowing agents, which whilst being a relatively simple technique enjoys only limited application, has now been largely replaced by techniques using blowing agents which are physically, not chemically, active.
Expressed in simple terms, "baking powder" has now been replaced by inert gases such as nitrogen and carbon dioxide.
By virtue of its own many years' development work and its cooperation with raw material manufacturers within its "Foammelt" study group, Engel has at its disposal a comprehensive range of processes for the foaming of thermoplastics.
The latest addition to this range is the MuCell process which has been developed at the Massachusetts Institute of Technology (MIT) in the USA.
For this process, which is also suitable for moulded parts having a wall thickness of less than 1 mm, Engel manufactures special injection units in which the blowing agent is uniformly distributed in the melt under a pressure of between 100 and 200 bar.
The melt expands upon entering the mould, generating a high-quality microstructural foam.
Depending on the actual geometry of the part to be moulded, the user can benefit from the following advantages: * Material saving of between 20 and 50% without any significant reduction in the rigidity of the part.
* Increase in dimensional accuracy and virtually no warpage, this being a particularly important advantage in the case of parts destined for use in high-tech equipment, such as the chassis of a colour inkjet printer to be shown at K'2001, even if fibre-reinforced plastics are also used to increase the strength of the part.
* Thanks to the improved flowability of the melt owing to its gas content, the injection pressure can be reduced by up to 80% and the clamping force requirement by up to 90%.
This means that smaller and hence less expensive injection moulding machines can be used and, by the same token, the operating costs will be lower.
* When combining the two processes of "Foammelt" and "Tecomelt" (in-mould decoration), the reduced injection pressure (on account of the improved flowability of the melt) minimizes the load on the decorative film but also permits the use of more sensitive textiles and films for in-mould decoration.
In the two last-mentioned cases, the tiebarless injection moulding machines from Engel offer the advantage of being readily equippable with larger-than-normal moulds (the platens are totally unrestricted on three sides) and of affording ready access to the mould for film-placing and parts-removal operations.
Gas injection technology (GIT), which has been in existence for over ten years, is a material-saving technology used for producing cavities in thick-walled parts and for eliminating sink marks and warpage in heavily ribbed parts.
Starting out both from its own experience gained with this technology and from a basic research and development project undertaken by the IKV (Plastics Processing Institute) in Aachen, Engel has developed a water injection process named by the name of "Watermelt".
The extremely low compressibility of water compared with gas permits better process control and considerably faster cycle times than with GIT.
Watermelt also produces better shaped cavities with thinner walls and smoother surfaces.
Moreover, crystallization of the inner surface can be controlled by the temperature of the water.
Engel is now collaborating with its raw material suppliers, DuPont, in developing modified materials featuring the necessary media resistance (e.g resistance to anti-freeze) for specific applications.
The capabilities of Watermelt and the many new possibilities will be demonstrated at K'2001 by a machine producing a curved car-engine coolant pipe in PA 6.6 containing 35 % w/w glass fibre.
The demonstration machine is a 1,500 kN tiebarless injection moulding machine of the new "Victory" Series which is additionally equipped with a "Watermelt" module.
After injection of the melt into the mould, water is injected via a second nozzle under a pressure of 150 bar and presses the melt against the cavity wall.
The mould is equipped with a spill-over cavity into which the residual, still liquid core of the melt is forced.
The controlled injection of the water not only ensures optimum reproducibility of cavity shape inside the part but also contributes to the cooling of the moulded part in the mould.
The result: a plastic, vibration-absorbing coolant pipe (25 mm o.d., 3 - 4 mm wall thickness) which is 50% lighter than a steel pipe and can be manufactured in a cycle time of 35 seconds.
"Fibermelt" is the name given by Engel to its technology in the field of long fibre reinforced thermoplastics.
The nucleus of this technology is the reliable, fibre-friendly processing of continuous strand-reinforced rod-shaped pellets.
Parts moulded from continuous strand-reinforced thermoplastics are distinguished by their superior impact strength and energy absorption in crash situations, especially in comparison with parts reinforced with chopped strands.
These continuous strand-reinforced thermoplastics are ideal, for example, for the manufacture of bumper parts and dashboards, and they are also being used to an ever increasing extent in the automotive industry for the manufacture of door modules, spare wheel wells, sound shields and underbodies.
The "Fibermelt" process may also be combined with the "Tecomelt" in-mould decoration process.
A particularly economical way of working with "Fibermelt" is to mix, with the aid of a weigh feeding system, the basic material with a 75% w/w fibre concentrate in the required ratio and to feed this mixture into the feed hopper of the injection moulding machine.
Engel designs plasticizing screws specially for this application.
They ensure the homogeneous dispersion and gentlest possible treatment of the fibres in the melt.
Their decisive feature is their ability to keep shear stresses to a minimum in all sections of the screw while rotating at a peripheral speed which does not exceed the empirical value of 0.2 m/s.
As with the plasticizing unit, gentle treatment of the fibres is also the main criterion governing the design and construction of the mould.
The necessary large flow channels are best obtained with an injection-compression mould.
It is with such a mould that Engel - in collaboration with Illbruck as system supplier, Dornbush as mould maker, Vetrotex as supplier of fibre concentrates and Borealis as producer of polypropylene - will be demonstrating.
• Engel Austria: contact details and other news
• Email this article to a colleague
• Register for the free Manufacturingtalk email newsletter
• Manufacturingtalk Home Page
Search the Pro-Talk network of sites
