Swiss Point - Engineering Design
Darts is a game of accuracy, and when it comes to darts design every millimetre count and every gram is calculated. The grips, the shape and the dimensions are just some of the factors that need to be carefully considered.
Precision engineering has played a vital role in darts manufacturing for many years, however, what is often overlooked in the industry is the relationships between product design, engineering capabilities and various design techniques. Design thinking practices, alongside constant design for manufacturing (DFM) optimisation can help identify gaps in the market, which opens opportunities for brands like Target to challenge the impossible and for breakthrough innovation.
The replaceable point idea was a solution to a problem.Being able to modify the shaft length and flight shape shifts the centre of gravity(COG) of a dart which has a huge impact on the aerodynamics - specifically its stability when flying through the air. The lack of flexibility in changing point, although understandable given the manufacturing constraints and the nature of the material, presents several problems for dart players especially for those competing at a professional level.
Steel tip darts points are made of special grade carbon steel, extruded to the desired size before being cut and turned to create the taper on the pointy end. It then goes through processes of hardening, plating and coating. Throughout these steps, every small change in the settings can have a big effect on the performance of the point so stringent quality control must be in place to ensure quality consistency. The point is the part of the dart that contacts the board and as a result is subject to enormous stresses and forces from different directions. It is clear why points, being so structurally delicate at only 2.3mm diameter, require such a complex process involving a deep understanding of both material properties and solid mechanics. When we set out to develop a new interchangeable point, we identified 3 major challenges:machining limitation otherwise known as machining tolerance, how to lock the point inside the barrel instead of the traditional interference-fit and how to make sure that in the event of breakage, the point could be easily extracted and replaced.
Machine taper is the primary method of attachment of tools for many machines and a great amount of research has already been done on its locking mechanism. The dart point has such a small diameter that the proportion, the angle and the length on both the point and inside the barrel must be perfect. Via countless tests and trials, we have managed to optimise the right amount of resistance to vibration that a dart goes through during a game at the point it hits the board.
In the project brief, the ability to easily replace the point in the event of breakage has always been priority. Adding a taper, tapping thread and milling a nut affects the machining process and results in a permanent change in the mechanical structure of the point.
The product development stage of this element can be divided into 3 phases; prototyping, stress analysis simulations and testing. During the proof of concept, we noticed that although experimental tests gave us valuable indications on the quality of the design and provided us with comparative data between design variations from an engineering and scientific point of view, the lack of true figures was missing meaning the reliability of the tests could only be trusted to a certain extent. We decided the concept generation process required the support of a more sophisticated engineering tool - FEA (Finite Element Analysis) software.
FEA as applied in engineering, is an advanced tool which provide a computational environment for performing stress analysis simulations. Based on the original CAD 3D models of the point, the software provides an environment in which a material can be assigned to the part, various constrains can be set and the desired amount of load/force is applied in specified direction and magnitude. The software uses triangle mesh generation techniques to divide the part to small elements based on pre-set mesh setting which is dictated by the parts design - the finer the part's details, the greater the number of triangles and the smaller the triangles sizes. Following this meshing generation and once the rest of the analysis conditions are set, the software runs sets of equations to examine how each of these small triangles will perform under stress and identify whether permanent deformation will occur. When the simulation is completed, the software highlights weak areas on the model and provides various heat-maps showing the behaviour of the part under force, the amount of the stress (Von-Mises), the size of the displacement within the part, and most importantly if the safety factor is met.
The first thing to define is the type of the simulation and understand the difference between Linear stress and impact force. Then, in order to set a safety factor for the simulation we needed to find out the volume of the impact force that is applied on the point of the dart when hitting the floor. Using the known factors, I.E the dart mass, the distance it travels, initial velocity and acceleration, we could calculate the velocity of the dart when hitting the floor and the kinetic energy (KE) that it generates.We could then convert the Potential energy (PE) of the impact force which is calculate in energy units (Joules) into a linear constant load which is calculated in Newton force units.
Once the model is fully set within the virtual environment, the point constrained inside the barrel and the contact type is defined(separate but no sliding), the simulation can begin. By running a parametric simulation, parameters of every design feature on the point can be set within a range - for instance the diameter of the point can vary between 2.1mm,2.15mm and2.2mm, and the depth of the groove can be 0.1mm, 0.25mm and 0.4mm. In addition, several restrictions can be specified for the simulation, for example- the safety factor must be kept above 1ul and the maximum allowed stress can’t be more than 100MPa. The software will then simulate applying the loads on every single design configuration and suggest optimised design configurations.
Countless analyses were carried out in order to find the best design configuration. The results were constantly reviewed and compared in order to find the perfect balance between the strongest possible structure that doesn't break too often, and if it did break, it would not occur inside the barrel.
Finally, the point design was tested, physically, in special testing lab equipment, in order to verify the data gathered from the stress analysis simulations. We found a significant correlation between the virtual simulations and the lab testing.
The interchangeable point idea became SwissPoint (SP) and it’s an example of how Target is much more than just a darts manufacturer. We strive on challenging the impossible to perfect the game of dart by driving innovation and technology into the development process. The creation of Swiss Point involved exploring new engineered materials and new manufacturing techniques whilst also using some of the most advance software.We’ve come a long way already, but this is really only the beginning.