Overmoulding describes the process in which the moulding of parts is split into two or three processes. Overmoulding enables this process without requiring a two or three-shot moulding machine.
Click on our stories below to read more about how the overmoulding process is achieved using Sandretto's moulding machines:
* Daton Tools
* TRW
* Daton Tools
DATON TOOLS DESIGNS AND DELIVERS TOOLS FOR OVERMOULDING - IN EIGHT WEEKS, REGULARLY
As a toolmaker, Daton Tools of Welwyn Garden City consistently proves itself as a more-than-capable contract moulder. Conversely, for a small trade moulder now operating five Sandretto machines from 50 tonnes to 200 tonnes clamp, the company has a remarkably well equipped toolroom with wire-eroding and CNC machining centres, all supported by full CAD technology.
What is particularly significant, states Managing Director Geoff Taylor, is that this toolroom regularly proves wrong the oft-made claims that British toolmakers cannot match the quality, even less, the delivery times offered by overseas companies.
He cites one example after another of six-week and eight-week delivery times for mould tools which, almost without exception, are complex. Most recent example is a suite of six tools for a Prada consumer device designed by IDEO. Ranging from a single-cavity tool for the 180 mm x 80 mm x 35 mm main body moulding, to a 7-cavity family tool for items as small as 4 mm diameter, all six moulds were completed in less than eight weeks from completion of the component drawings. The main body mould tool was completed in six weeks.
ESTABLISHING A REPUTATION
Although its roots as a toolmaker go back 35 years, Daton Tools functioned for some of this time as part of larger organisations until 1998 when it was re-formed under Geoff Taylor and Technical Director Graeme Inge. Together they succeeded in winning back old customers, notably in the field of overmoulding where Geoff was already establishing a reputation for what remains a specialist process.
“SOUND PARTNERSHIP”
The Prada project quoted above is consequently something of an exception as a new project as it can be described as a conventional plastics moulding. It is, however, extremely complex and has to be moulded to within very tight tolerances for which Geoff Taylor relies substantially on his five Sandretto moulding machines. “I’d used Sandretto before we formed Daton Tools and it was an obvious move to specify them in the new factory.
“As far as I’m concerned Daton and Sandretto has become a sound partnership. They’ve never let us down – there’s an engineer here if we need one and we can always rely on first class assistance at Rugby when required.”
QUALITY AND TIGHT TOLERANCES
Overmoulding carried out by Daton Tools is always a two- or even three-part process. Small call-off numbers do not justify the investment in a two- or three-shot moulding machine, states Graeme Inge who maintains that the over-moulding process is ideal to maintain the quality and tight tolerances on the one-piece parts demanded by customers such as Blue Arc, Desoutter and IDEO.
Typical of their work is the range of acrylic lenses moulded in to components such as baby monitors used in hospitals, instrument enclosures for earth-moving vehicles and ocean-going yachts and hand-held industrial data-gathering equipment. All require a guaranteed moisture, oil or weather seal provided by the bond between the acrylic lens and the, typically, ABS or PC/ABS body moulding. Earlier development work has enabled Daton Tools to refine a process which overcomes the inability of techniques such as gluing or welding to create the necessary complete seal.
At the small end of the scale, in a four-cavity mould, Daton produces 5 mm diameter seals comprising a polypropylene core (for flexibility) with a PBT outer to provide the necessary rigidity.
“Materials with different properties inevitably induce stresses, so it’s still not an exact science” states Graeme Inge. However, the regular business of the company is to overmould rubber elastomers and polyurethanes successfully over materials such as nylon, PTB and PC/ABS.
THREE-PART MOULDING PROCESS
All of the suite of tools to produce the Automotive Sander for Desoutter are particularly complex. First, the main body is moulded from glass-filled nylon and then inserted, with threaded inserts, into a second tool and over-moulded with Hytrel.
Other air tool mouldings for Desoutter are manufactured by the elastomeric overmoulding of precision turned or CNC machined aluminium cores. This is where careful mould design is essential to maintain a perfect shut-off between the elastomer and the substrate within the required, confined area.
Specification of a soft-feel elastomer as an overmoulding on these applications is to provide comfort and vibration reduction for the operator and insulation against the effects of the inherently cold compressed air. (Two sentences deleted)
This is one reason why Daton Tools identifies its CAD-based mould design capabilities as a prime reason for remaining busy in a market which is becoming “frighteningly” competitive. The second reason, already mentioned, is short delivery times. Part of a joint development project, completion of the Desoutter mould tools took less than eight weeks from acceptance of the part drawings.
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* TRW
In-Mould Assembly with Flexibly Combined Machine Concepts
The production of a complex three-component injection moulding part demonstrates the compatibility of Sandretto’s and Windsor’s two solutions for the multi-component technology: Series Nove Multi and PlugXPress®. Together with TRW Engineered Fasteners & Components, both companies show how it is possible to achieve a significant surplus value through a combination of innovative solutions for multi-component technology. A three-component moulding cell, consisting of a two-component injection moulding machine Series Nove Multi 220/860/185 and a multi-component retrofit unit PlugXPress WKT 0.6, is the interesting solution proposed by Sandretto and Windsor for the In-Mould Assembly process. Air grilles for the automotive industry made out of several single components, fixed together but movable to each other, can be produced in a 1+1+1 fold mould from TRW Engineered Fasteners & Components in only one manufacturing step, according to the patented In-Mould Assembly process.
For this application three incompatible material components are injected into each other in such a way that a secure movable connection without any external assembly afterwards is produced already in the tool. The manufacturing cell has a cycle time of 40 seconds. This is the time needed to inject into each other the frame, the blades and the gate so that at the end of the cycle the finished part leaves the tool.
The part is manufactured on a hydraulic multi-component machine Sandretto Series Nove Multi with a closing force of 2,200 kN and a screw diameter of 50 mm in the standard injection unit and 33 mm in the second vertically situated injection unit, completed by a Windsor PlugXPress unit with a screw diameter of 20 mm which is also placed horizontally in L-shape on the opposite control side. So the three materials are injected from three different directions. First, the blades out of PBT Celanex are injected from the vertical unit in the first cavity, then the index plate is turned by 120 degrees and the small connecting gate out of PP Noryl is injected from the horizontal PlugXPress unit situated in L-shape in the second cavity. Afterwards the tool is turned again by 120 degrees and the frame is injected in the third cavity out of PP Noryl from the horizontal injection unit of the machine. At last the index plate is turned by further 120 degrees to the starting position and the finished part can be removed. For the production of this application all three injection units work parallel.
By using a standard 2K machine as well as a 2K retrofit unit the manufacturing cell is highly flexible and quickly adjustable to actual production needs in spite of its high complexity, as both systems can also be used independently from each other without problems. These various usage possibilities represent a significant flexibility as well as financial surplus value.
The presented manufacturing cell demonstrates clearly that the concepts of Sandretto’s series Nove Multi and Windsor’s PlugXPress are complementary to one another and can be combined without problems although designed for different needs. All used Windsor and Sandretto injection moulding units are part of the standard machine program. This secures the compatibility of all parts and aggregates and a variety of possible combinations of screw diameters and injection volumes and thus can cover a wide capacity range for both concepts.
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