Product Design

The outer shell of the ballpoint pen has an entire continuous curved surface to create a sense of integrity. The shape of the fuselage transitions from the circle at the bottom to the triangle at the grip and then to the round shape at the top rotates, forming a streamlined body curve. The triangular shape of the holding part conforms to the way a person holds a pen. Each side is slightly concave to fit the shape of the belly of the finger, and the overall convex angle rotates counterclockwise to adapt to the direction of the thumb and index finger when holding the pen with the right hand.

In terms of size, refer to other ballpoint pens on the market. The overall length is about 138 mm, and the diameter at the narrowest point is about 11 mm. The outer surface of the fuselage is made of mirror-polished aluminum alloy, which is combined with the curves of the fuselage to create a beautiful texture.

Structural Design

Above is an X-ray image of a ballpoint pen, an explosion map, and a structural diagram. As can be seen from the explosion map, the ballpoint pen as a whole consists of five parts, of which 1/2/5 is aluminum alloy and 3/4 is HP PA12 nylon. Part 4/5 divides the fuselage into two segments at a height of 90mm. The overall assembly structure is that part 2/4 clips part 3 in the middle, connected with a clip, and can be rotated. Part 2 is connected to part 1 through an M9 thread, and part 5 is connected to part 4 with a non-rotatable clamping structure (0.5 mm thick).
In terms of the rotating core structure, as can be seen from the structural diagram, part 5 drives part 4 to rotate relative to part 2. Part 4 has an inclined surface. When rotating, the protruding block of part 3 moves downward in the slide rail of part 2, and part 3 pushes the refill (G2 standard) downward, and the pen tip is exposed. When folded, in contrast to the above movement, the spring under the pen pops up, pushes the pen upward, and the nib is retracted.
The overall structure is as shown in the X-ray image. The wall thickness is 1 mm, and reinforced ribs are designed to enhance structural strength. The spring part of the lower half of part 1 is solid, which can reduce the center of gravity of the ballpoint pen and enhance the user's holding experience.

MK I

Iteration 1 is an experiment on the shape and feel of a ballpoint pen. Light-curing printing was used. This technology is characterized by high accuracy, and the high fidelity restores the appearance of a ballpoint pen. Based on this, I was also able to verify the overall feel of the ballpoint pen. The size is quite suitable, and only minor adjustments have been made in the second version of the plan.

MK II

Iteration 2 designed the internal structure. The whole is divided into four parts; in fact, 4/5 of the above parts are combined into one. MJF nylon printing technology is used. Nylon printed with this technology has the characteristics of high accuracy and strong mechanical properties, and is very suitable for making functional prototypes. This version of the design did not consider tolerances enough. There was a problem with the clasp design, and it was completely impossible to assemble, so in Iteration 3, the internal structure was redesigned based on the problems found in Iteration 2.

MK III

Iteration 3 has gone through an internal redesign to separate the rotating structure from the pen cap, and the retractable structure has reached a usable state. Also using MJF printing, Iteration 3 can fully assemble and implement functions. However, at the same time, Iteration 3 also has many problems. The most obvious one is that the length design of the telescopic structure is too short, and the pen tip is still slightly exposed during storage, and the length of the pen tip is not sufficiently exposed when unscrewed, making it uncomfortable to use. In Iteration 4, optimization was made to address these issues.

MK IV

Iteration 4 optimized all the problems of Iteration 3, and the user experience has reached a good level. Also using the MJF process, the surface effect and mechanical properties of nylon mixed with glass fiber are better. After testing, it can already be used as an everyday writing tool. In this edition, the size and specifications of the springs were also tested, and springs of various specifications were purchased. After experience, it was determined that the specifications of 25 mm in length/4 mm in diameter/0.4 mm in spring wire diameter were excellent in terms of feel. In this way, the structural dimensions of Iteration 4 have been completely determined. As a result, I printed and produced the final aluminum version, and obtained Iteration 5, which is the final version.

MK V

Iteration 5 is the final version of the ballpoint pen so far, using SLS metal printing technology. Based on the comprehensive cost, strength and weight considerations of the material, aluminum alloy was selected, and the overall weight can be controlled within 30g. Aluminum 3D printing is similar to MJF nylon in terms of mechanical properties and accuracy. The print was obtained by iterating the print shown in Figure 1. After receiving it, it was found that there was a slight deviation in size, but after a slight polishing, the assembly can be completed.
Since mirrored metal is used in the design, the surface of the metal 3d printing is matte and uneven. Sandpaper was purchased and the outer surface of the ballpoint pen was polished by hand using an electric grinding pen and polishing paste. The number of grids ranged from 60-60,000 mesh, which achieved the mirror appearance in the design to a certain extent (as shown in Figure 2).

Physical Display

The above is a real shot of the final version of the ballpoint pen. The product can already be used normally, but due to manual polishing and lack of experience, the surface effect is still not as good as expected, and the dividing line is too round during polishing, so it's not very beautiful, and there is still room for improvement.