A method for representation of component geometry using discrete pin for reconfigurable moulds

https://doi.org/10.1016/j.advengsoft.2011.03.004Get rights and content

Abstract

Moulding plays a paramount role in our daily life. Traditional moulding is often dedicated and expensive. As the current market trend moves from mass production towards small batch and large variation production, the demand for a mould that can reconfigure itself for different components is greater than ever. The reconfiguration of mould is often realized through discrete pins. Previous research in that field had focused on the hardware of pin actuation in order to move pins up or down to represent different components and lock the pins at certain positions. Little research has been conducted into support software development that enables rapid reconfiguration of discrete pins to represent component geometry.

This paper addresses a new method of software development for the reconfigurable mould utilising discrete pins. The overall aim of the method is to provide an interface for generic discrete pin tooling in order to enable quick reconfiguration of the mould to represent component geometry. The software is composed of three parts: part discretization, pin matrix construction and adjustment and pin matrix verification.

Introduction

Moulding plays a paramount role in our daily life. Moulding, including Injection moulding, vacuum forming, casting, stamping and forging, is cost effective and is frequently used in mass production. Traditional moulding is often dedicated and expensive. Dedicated tooling means that a mould is made for a single product design and can only be used for production of that particular design. Any design changes lead to the tooling becoming unsuitable for its specific use, and a new one has to be made. Commercial justification for moulds is traditionally based on the amount of production volume required. The current manufacturing trend is moving away from mass production towards small batch and large variation production. Therefore traditional moulds are increasingly becoming both less efficient and less economical for the quantity required. This is simply because of the change-over time for moulds and the cost of designing and building mould used only for a short run. Therefore the need for a technology that is capable of rapid mould redesign and changeover in the same process thus enabling rapid customisation of a component in day to day operations is greater than ever in the manufacturing industry.

The solution is to replace the current dedicated moulds with reconfigurable ones which utilise discrete pins. These pins can be moved up or down in the direction of the central axis to represent the necessary component geometry. In this way, the same batch of pins can be reconfigured and reused many times. Reconfigurable moulding is well suited for components that are not of traditional parametric shapes, as with those commonly seen in industries such as marine, automotive, aerospace, energy and medical. An example of a reconfigurable mould that uses discrete pins for sheet metal forming processing is shown in Fig. 1.

The idea of using discrete pins to produce universal moulds and fixtures is already well over a century old. As identified by Munro [3], the first known US patent relating to pin-type reconfigurable tools was granted to Cochrane [2] in 1863. Since then, many patents regarding discrete pin mould have been granted. Applications have included that of sheet metal forming by using large thin-walled components which have a free-form surface, e.g. the front panel of the high speed train [4], composite forming [5], prosthesis for cranioplasty [6] and rapid prototyping [7].

The key to a configurable mould is the capability for its matrix of pins to move upward or downward to positions determined by the component geometry and to then lock the matrix of pins into position. Therefore, pin actuation is critical for the reconfigurable mould that uses discrete pins. As shown in Fig. 2, according to pin density, there are two types of pin arrangement: close-packed [2] where the pins are put next to each other, support each other, and uniform spaced [2] where pins are evenly distributed, but not in direct contact with each other. Limited by the space available for actuation devices, the actuation of uniform spaced pins is relatively easy compared to that of close-packed ones. For this reason, most early patents [8], [9], [10], [11] of reconfigurable moulds were uniform spaced. However, there are many problems associated with uniform spaced screw-pins: lack of rigidity and there suitability for components with only simple geometry because of the space between the pins as it led to insufficiently supported pins and equally insufficiently represented component geometry from the pins.

Close-packed pin arrangement is better than uniform spaced pin moulds as the pins are engaged with each other, supporting each other to resist loadings from processes and better presentation of component geometry. However, because the pins are engaged with each other, leaving limited space for the actuation system, the whole mould system is far more complicated and expensive. Patents for close-packed screw-pins are reviewed below: Patent [12], [13] described a device containing a matrix of close packed pins for reconfigurable sheet forming. A drive motor and drive shaft were used for each row/column of the pins. Pin motion was controlled by an inline clutch/brake combination through a computer controlled system based on feedback from an encoder attached to the lead screw on each pin. This device is very complicated, as it needs a large number of motors, shafts, worm gears and clutches, etc., which puts it out of reach of wider applications in industry.

Patents [14], [15] were related to reconfigurable moulds and fixtures using interlocking screw-pins. Each of the screw-pins was actuated by computer controlled motors in a serial order. The pins could be adjusted to a pre-determined position by step motors or through use of a servo motor with encoder allowing the pins to stay in position without extra a locking mechanism as it is mechanically locked and supported by the surrounding pins. The actuation of the pins is relatively easy and the mould is rigid.

The Reconfigurable Pin Tooling™ technology was developed by Surface Generation plc [16] using patented pin technology [17], [18], [19]. The pin tooling system has a matrix of square shaped pins made of a consumable tool material. When adjusting a pin, the pin rows next to the pin being adjusted can be separated automatically to allow individual pins, which are mounted on screws, to be adjusted vertically by rotating them around the central axis. After adjustment, all the square pins are oriented 45° to allow efficient packing with adjacent rows. Finally, the rough upper surface composed of adjusted pin ends is CNC machined to produce the final tool shape without the need for excessive material waste. In this device, pin tooling is integrated with NC machining, which is considered a breakthrough in comparison with other prior methods.

Academically, the research group led by Prof. D. Hardt at Massachusetts Institute of Technology (MIT) [20], [21], [22], [23], [24] was the original pioneer in the field of reconfigurable pin tooling during the 1980s and 1990s and accordingly conducted systematic analyses into the impact of discrete pins on moulded components and optimization of pin mould design.

Given the importance of the pin actuation method in the field of reconfigurable moulds using discrete pins, the focus of prior research was overwhelmingly centred on hardware development, concentrating on new concepts of pin actuation.

The attention paid to the development of support software is also limited. Indeed, in order for any new concepts of reconfigurable moulds to be applied widely in industry, it is essential for them to be integrated with several other cutting edge technologies, e.g. CAD/CAM, reverse engineering and mould machinery in order to facilitate an automated representation of discrete pins of components that enable rapid mould reconfiguration. This has not been seen in prior research.

This paper addresses a new method of software development for reconfigurable moulds utilising discrete pins. The overall aim of the method is to provide a generic interface for general discrete pin tooling to enable a quick reconfiguration of the mould to represent component geometry. The software is composed of three parts: part discretization, pin matrix construction and adjustment and pin matrix verification. The overall framework of the methodology is demonstrated in Fig. 3. The second part of the software, the pin matrix construction and adjustment, will also be explained in detail in this paper.

Section snippets

Discretization of candidate parts

The candidate parts to be moulded may come from virtual parts created in commercial CAD software (e.g. Fig. 4a) and physical parts (e.g. Fig. 4c). In the case of the former, part geometry is usually continuous and parametric, and the position of a component regarding the individual pins is not available. It is thus essential to divide the continuous surface into many small patches, so that the position of the pins to these small patches can be calculated. Dividing the continuous surface into

Discrete pin construction and adjustment

Visual Basic software is used to develop a user friendly interface to allow users to process the output file based on the previous discretization process to obtain point position, and make a decision about whether a new discrete-pin matrix or previous discrete-pin matrix should be used. If a new discrete-pin matrix is needed, it will be constructed parametrically, otherwise, the previous discrete-pin matrix will be retrieved. After this process, the amount of discrete-pin adjustment will be

Display and verification

After calculating the adjustment of the discrete-pins, it may be necessary to display the discrete-pin matrix within in a CAD/CAM environment in order to verify whether or not the discrete-pins are in the correct position before any physical operations are carried out on the discrete-pin matrix. The geometry and the final position of the discrete-pin matrix after adjustment are generated automatically based on the discrete-pin matrix file saved for retrieval by the programme developed within

Case study

A car model was generated within a commercial CAD software and saved as a neutral file format (∗.igs) as shown in Fig. 13a. The car model was inputted into ABAQUS CAD and discretized as shown in Fig. 13b. The meshed file was processed by the Visual Basic programme using the interface shown in Fig. 12 to calculate the amount of discrete-pin adjustment. The final position of the discrete-pin was saved as a txt file and exported to CAD software Unigraphics using the GRIP programme, and a 3D

Conclusions

Traditional moulds are expensive and dedicated. The demand for a reconfigurable mould is greater than ever in the modern manufacturing environment. The focus of prior research was overwhelmingly placed on hardware development, concentrating on new concepts of pin actuation. The attention of the support software development to enable an automated reconfiguration of discrete pins is limited. A new method of software development can be conducted with the purpose of producing a rapid representation

References (24)

  • Kommineni P, Hollandsworth PE, Jones JW. Method of shaping an antenna panel. US Patent No. 4,731,144;...
  • Sherrill DE, Young KG. Apparatus for constructing a composite structure. US Patent No. 6,298,896 B1;...
  • Cited by (5)

    • Design and development of a rapid prototyping system combining traditional fused deposition modeling and reconfigurable pins platform

      2022, Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering
    View full text