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Product development teams are facing ever-increasing pressure to provide final specification components quickly and cheaply for performance and customer testing. This demand is fuelled by intense market competition where costs, delivery schedules and product life cycles are under constant scrutiny. Time Compression Technologies such as Virtual Reality, CAD, FEA, CFD and 3D Printing (RP) all aim to help meet these needs and are increasingly utilized within the design and manufacturing sectors. However companies must still test their products by flying, driving or crashing prototypes before selling them. These need to be in final production specification materials and w hile RP technologies can directly produce small to medium component parts, large functional plastic, metallic and composite components (such as car bodywork) still have to be made using mould tools.
Current mold making techniques have been designed for mass production not short runs and cannot easily be re-used. This makes the production of tools for limited volume applications, including research and development, extremely expensive particularly in higher cost regions of the world such as North America, Europe and Japan. This is especially true where even ‘volume’ production is measured in hundred’s and tooling cannot be amortised across high numbers found in other sectors e.g. telecommunications. As such today’s tooling remains fundamentally flawed in the context of rapidly changing business environments, hindering competitiveness and acting as a barrier to entry into as yet untapped markets.
This article examines alternate methods of tooling for large components, with an emphasis on reconfigurable approaches, and introduces a new hybrid reconfigurable tooling process – Subtractive Pin Tooling (SPT TM ) – that has been developed by Surface Generation Ltd.
Traditionally mould tools have been made using a range of well-established technologies, the build strategies of which can be broadly categorised as either additive or subtractive. C onsidered in terms of those routes, which are capable of generating either prototype or production quantities these can be further subdivided into direct (i.e. single stage) and indirect (i.e. multi stage) processes.
Reconfigurable Approaches
While to an extent all moulds are reconfigurable (i.e. by selectively removing material, re-datuming or recycling bolsters), truly reconfigurable tooling is still the panacea of manufacturing. As moulded materials can only ‘see’ the front face of a tool it is possible to temporarily create the mould and still produce highly accurate, functional components. Such an approach is ideal for manufacturers of large and low volume products and the following section outlines the state-of-the-art in reconfigurable tooling which compliments clients who want products not tooling and for whom moulds are only a means to an end.
Flexible Membrane Pin Tools are constructed from elastic sheets, which are deformed by beds of computer-controlled pins, to approximate the tool surface. These systems are attractive in principle as there is no material committed to the mould, and after use the array can simply be re-positioned for the next job. However the faceted surface (a point-to-point interpolation) and maximum aspect ratio of any one feature (which cannot exceed the elastic limit of the membrane) limit resolution and mean that even with fine pins these systems cannot achieve industry cosmetic / functional specifications.
Additionally, highly intricate control systems are required to move each pin in the array and the spaces between the pins (required to let them move past each other) significantly reduces the mechanical strength of the tool. Finally, the perishable nature of the extendable membrane severely limits the maximum operating temperature of the tool and as such no commercial systems have yet been successfully brought to market.
In-flexible Membrane Pin Tools use a sheet of metal, which is deformed to produce large, continuous curved surfaces. The process has been developed for the manufacture of yacht sails and is infinitely reconfigurable within the elastic limits of the ‘membrane’. This means that the process is incapable of even imparting even a modest ridge onto a tool surface but nevertheless within these confines the process is extremely capable and produces accurate compound curve forms.
State Change Systems use the displacement of bulk materials within elastic envelopes to form tools repeatedly without material commitment. Typically the material is ‘fluidised’ (using either air or water) until a vacuum is applied to remove this element leaving a solid. Variants using powders or phase change materials are available and ideal for the manufacture of tooling where patterns exist and processing temperatures do not exceed the membrane thermal limits.
Near Net Shape Pin Tooling systems using beds of square pins, which tessellate to form a continuous surface, have been developed for the stretch forming and casting industries. Large numbers of pins (~2,500 1” square pins on a 3’ by 6’ bed) are used to give a near net shape approximation of the surface and free floating elastic ‘interpolators’ are placed over the top to either seal or smooth the orange peel surface. The systems are infinitely reconfigurable and are also extremely rapid, allowing total surface transformation (i.e. re-formatting) in less than 30 minutes. However the automation cost of having drives under each pin and feature resolution mean that economically viable commercial applications are limited.
Subtractive Pin Tooling (SPT™) is Surface Generation Ltd’s patented technology that uses a hybrid subtractive and additive build strategy to create only the front face of the tool, as opposed to the entire solid mould insert. This is achieved by assembling beds of disposable square pins, which can be moved into a near net position and then machined . This approach addresses the key material commitment issue at the heart of large and low volume product manufacturing while also eliminating the surface resolution issues associated with other reconfigurable tools. The patented SPT process minimises cost by using fewer larger pins (sizes up to 20” square are possible but more typically ~220 4” pins on a 3’ by 6’ bed) and a single height adjustment drive system rather than the dedicated solution used in other processes.
As such the technology can achieve a 90% lead-time and cost reduction for the manufacture of each tool, which translates into a time to market saving of up to 40% . Producing highly accurate tools using pins made from any machinable plastic, metallic or ceramic material, variants can operate across a broad spectrum of pressure, temperature and impact environments in applications including composites and metal forming. The core SPT design is robust, fully scalable and also allows users to maximise efficiency with a number of unique build strategies that enable milling machines to produce previously inaccessible forms (e.g. deep cavities) and parts that exceed the z axis capacity of existing 3 and 5 axis equipment.
The inherent adaptability of this technology allows the precision manufacture of tools and patterns ranging in scale from automotive panels to wind turbine blades. If a tool needs to be modified, or the surface is damaged, the affected region can be selectively re-formed . Once the mold is no longer required it can simply be re-configured permitting immediate recycling of 100% of the array for future use. These combined benefits give a truly disruptive technology, which specifically a ddresses the needs of large and low volume manufacturers in s ectors including Aerospace, Marine, Mass Transit, Automotive, Packaging, Medical and Renewable Energy. Technically there are a wide range of different methods the support the creation of large and short run tooling in today's market all of which have positive and negative features. Selecting the most appropriate is about balancing individual user’s needs on a case-by-case basis. Culturally it is those organisations who embrace the sales, marketing, manufacturing and logistical opportunities of the latest reconfigurable approaches that will derive the greatest competitive advantage - moving towards an economic batch size of one for large components - even in the face of intense global competition.
For more information please contact Jim Gray at 972-699-9976, e-mail