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Scottish Plastics and Rubber Association Scottish Plastics and Rubber Association

The Future of Injection Moulding Technology

Peter Kirkham, Managing Director of Billion UK

At the February SPRA technical meeting at Edinburgh Napier University, Peter Kirkham, Managing Director of Billion UK, a long standing SPRA Corporate Member, started his talk with an in-depth comparison of the drive options available on injection moulding machines.  He followed this with a couple of innovative process solutions and ended with a look at new interactive animation software being developed by Billion as a training tool.

1.  Machine Drive Systems

1.1.  Hydraulic systems with a single variable displacement pump.

Hydraulic systems with a single variable displacement pump.
The basic machine drive system for controlling the sequences during an injection moulding cycle (mould open/close, mould lock, injection unit movement, melt injection, suck-back, plasticisation, ejection and core pulling) is a single variable displacement hydraulic pump.  Only one machine function can be operated at a time.  With the proportional valve some distance from each function there is a built in delay (up to 300 ms) with consequences for precision.  Also there is wasted energy during off-load periods.  However these simple drive systems are economic to build (but expensive to maintain) and relatively quiet in operation.

1.2.   Hydraulic systems with two variable displacement pumps
Using one pump for mould open/close and mould lock and a second for all the other functions, allows some parallel operation but the system still lacks precision, is slow to respond and energy efficiency is worse because of the bigger motor.

1.3.  Hydraulic systems with fixed pump and accumulator

Hydraulic systems with fixed pump and accumulator
Building an accumulator into the system and providing proportional valves or servo valves for each function, greatly improves response time (<30 ms) and precision.  The simple vane pump is easier to maintain but the overall system is expensive to build, has a higher noise level and has poor energy efficiency.

1.4. Hydraulic systems with servo motor (stop/start technology)
Using a servo motor on the hydraulic pump to control the speed and volume of oil, gives good energy efficiency because the pump stops during idle periods but there are still questions over precision and cycle time.  However these systems are economic to build and quiet in operation.

1.5.  Hydraulic systems with fixed output pump with accumulator + inverter screw and pump drive
The introduction of an electric motor for screw plasticisation to an accumulator system with proportional and servo valves gives a system capable of parallel operations, good response times and good precision, energy efficiency and quiet operation.  However the system is expensive to build.

1.6.  All-Electric systems

All-Electric systems
Using electric servo motors on each individual function, almost instantaneous response is achieved with high precision.   Energy efficiency is impressive, with 60 – 70 % energy savings compared to comparable hydraulic machines.   All-electric machines have very low noise levels, require no pre-warming (except cylinder heaters) and minimal cooling water requirement, although lubrication systems can be complex and critical.  Manufacturers may have to supply small hydraulic packages for core-pulling for some moulds.  Although all-electric machines have low running costs they are more expensive to build.

1.7.  Hybrid Systems with a combination of hydraulic and electric drives

Hybrid Systems with a combination of hydraulic and electric drives
Using the best of both worlds, hybrid machines can achieve the response, precision, energy efficiency, low maintenance and quietness of all-electric machines.   For larger tonnage machines the hybrid machines are more economic to build and they have a hydraulic supply available for core pulling.

In summary, servo-hydraulic drive systems give good value for money and are suitable for less critical moulding, where precision and cycle times are less of an issue.  All-electric machines offer high precision, optimised cycle times, quiet and clean operation and good energy efficiency but capital costs are high  (although falling).  Hybrid systems are more competitive for larger machines. 

2.  Innovative Process Solutions

2.1. In Mould Assembly (IMA)

In Mould Assembly
Peter described a novel approach to reducing assembly costs by carrying out the assembly operations within the mould, during the mould cycle.  Typically a two-shot machine, with rotary indexing cores, moulds the two halves of the casing in one material and the second material is used to weld the two parts together in an additional cavity. 
Examples of In Mould Assembly
Other options include assembly by plastic rivets, snap-fit or push-fit.  The real benefit of IMA is that the cavities can be robotically filled with filters or electronics within the mould prior to final assembly.  Peter passed round a moulding that had been filled with water before final assembly.

2.2.  Anti-counterfeit technology

Anti Counterfeit Technology: mould insert (left); finished moulding (right)
High value products, such as Swiss watches, use unique identification with nano-level surface details to protect against counterfeiting.  The nanostructure marks are expensive to produce (£300 – 500) and unsuitable for high volume plastics components.  Billion has been working with PEP, the Technical Centre for Plastics Engineering in France, and Mimotec, a company that specialises in microfabrication, to develop an injection moulding process to replicate nanostructures repeatedly on plastics components.  Using an all-electric machine for precision and repeatability, an insert with the nanostructure detail is loaded to the cavity.  After locking, the cavity is evacuated for easier filling.  The mould cavity is subjected to flash heating (180oC) before injection and then super-cooled to 60oC. This ensures a perfect reproduction of the nanostructure, which can be easily read using a standard laser system.

3.   Billion T3D Process Animation Software

Billion T3D interactive animation software
Billion is currently developing software, for Windows and IOS platforms, which has interactive animation of a range of injection moulding machine operations and process technologies.  With no guards to obscure views, the animations provide the user with a clear simulation of the individual steps of various moulding processes, with the opportunity of switching to photographs of actual machine components.

The question and discussion session allowed Peter to elaborate on various aspects of his presentation and this was followed by informal discussions, particularly with the many students present.

Report by  Charlie Geddes, SPRA Member, February 2015.

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