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In late 2007, CRP Technology took part in a major initiative together with Prince Sports, a leading company in the sports sector and more specifically in the world of tennis. Rapid manufacturing was applied to make functional, yet attractive parts for a new tennis racquet using Windform® materials.
(Published on April 2010 – JEC Magazine #56)
The cooperation between the rapid manufacturing specialist and the sporting goods company focused on the development of functional samples for the inserts/outer clips surrounding the perimeter of the racquet, to be tested in use during the game, and the production of a scale 1:1 tennis racquet prototype as close as possible to the real model to be manufactured subsequently.
The new technology was presented in the USA in late January 2008 as a world preview for the 2008/2009 collection, in anticipation of a series of models that will complete the Prince collections over the next 4 years.
CRP Technology’s rapid prototyping department immediately tackled the insert sample project. The team focused on the choice of materials and any potential problems arising from their use in the field.
The first challenge was to identify a material that would provide sufficient strength, given the thickness involved, the required functionality, and the various stresses on the clips during use.
CRP Technology, a pioneer in rapid prototyping and SLS technology, started in 1996 with an analysis of the RP technology, almost unknown in Italy at that time. CRP has developed cutting-edge materials, including Windform® materials for laser sintering technology. These materials are suitable for wind-tunnel applications as well as production parts for racing cars.
The initial choice fell on CRP’s prototyping material Windform® XT, reinforced with carbon fibre. Its unparalleled dimensional accuracy, definition of detail and maximum breaking-load properties made it the rapid manufacturing material par excellence. This material is also used to create highend functional prototypes and production parts for F1-racing and wind-tunnel applications.
The clips also underwent practical field stress tests in which the component was subjected to normal-use loads. During the tests, the XT insert unfortunately gave way. Subjected to static tension produced by racquet stringing and then to impulsive loads produced by the impact of the ball on the string plate, the grommet support collapsed during the game.
For each single string, the RP team must take into account a static load of around 35 kg and 70 kg if we consider the geometry of the grommet, calculating the tension of two strings and a dynamic load of 100 kg (50 kg for each string, therefore 100 kg for each single grommet). Therefore, it can be said that impulsive loads of 170 kg can be achieved on the single string support element.
Considering such data, CRP Technology’s customer expressed great satisfaction with the results achieved by the insert and the Windform® XT material.
This first test was not an obstacle to the project development, but rather the departure point that prompted the customer to further boost the project and to confirm his desire to use Windform® materials in a second project, with different aims.
Following a careful analysis by CRP’s R&D and RP departments, the customer was presented with Windform® FX, the latest addition to the Windform range. The material’s exceptional resistance to repeated bending and torsion stresses made it a valid alternative to the XT insert, capable of better withstanding the required dynamic and static loads.
A further step forward in the project consisted in updating and implementing the mathematics of the clip to be developed. Prince Sports elongated and extended the insert along the entire racquet perimeter. The design was upgraded and, structure-wise, the experience of the first prototypes was exploited to increase the part’s durability. After studying the updated file and duly verifying feasibility, including from a dimensional viewpoint, the RP department went ahead with the production of the FX clips. This second solution for the production of the surround inserts achieved the success that had been hoped for. In the customer’s opinion too, the samples appeared surprisingly flexible and strong.
Fitting the tested Windform FX inserts inside the complete racquet model (an end result of Prince R&D activities for the new season) was the next step. Here, rather than functional testing, the aim was of a substantially aesthetic and design nature, to which Windform materials adapt well. The parts making up the scale 1:1 model, which were produced by CRP Technology, are the frame structure, the relevant inserts or clips surrounding the perimeter of the racquet (the only ones to be also functionally tested), and a bumper positioned on the racquet head and designed to receive impacts.
The choice of material for the frame took into account two main parameters:
This racquet will be entirely made of carbon fibre and will weigh 240 g (finished with varnishing, plastic parts, strings, etc.). The weight of the raw frame is expected to be around 180 g, even though the accessory parts make it heavier.