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How to create toolpaths for an aluminum mold

Prototype and mold for a lightweight SPORK: SPOon-foRK-knife

For backpackers and extreme outdoor enthusiasts the weight and size of their luggage is a serious issue. For this target market "Sporks" have been invented (first patented in 1874): this combination of SPOon and foRK is a a lightweight and space-saving alternative to carrying both a fork and spoon.
The spork shown on this page is meant for (semi-)professional use, and even combines three functions as it also offers a knife's cutting edge.

two green sporks on pebble stones
Two green SPORKS. The cutting edge can be seen next to the fork's teeth.

Many sporks are commercially available already, however most of these will easily break during use. So Dutch startup company GreenPolder decided to develop a better product. Their spork is almost unbreakable and by its smart design still weighs only 11 grams. The special PP material allows it to be used from -30 to +100 degrees (Celsius). This material of course fully complies with all food safety regulations.

Sketch on paper
SolidWorks screenshot
The first designs are sketches on paper, later refined using 3D CAD software.

Greenpolder is founded as cooperation of industrial designer Krijn Zuyderhoudt ( and model maker / manufacturer Marcel van Schie (Mascal Design), both located in the Netherlands. Their two professions combined allowed the development process of this product to be completed within a very short time, as in each step the right technology could be applied at the right time.

The process (as always) started with a series of sketches on paper, to outline the basic concept of this new product. After that a 3D CAD model of the spork has been created, in SolidWorks. In this program the geometry has been adjusted step by step for a good balance between robustness and weight. Ergonomics was important as well: adjusting the geometry to make the spork sit comfortably in the hand.

SolidWorks screenshot
DeskProto screenshot
3D CAD model in SolidWorks, and detail of the DeskProto screen showing toolpaths over the knife tip. These are for a 2 mm diameter ballnose cutter, at 0.06 mm toolpath distance.

In this optimization process many computer visualizations (renderings) have been created, which is easy in SolidWorks. In addition a prototype has been machined in acrylic, using DeskProto. Mascal Design operates a Bridgeport VMC 1000 3 axes machine with a Heidenhain iTNC 530 controller, and uses cutting tools made by Fette.

Roughing in acrylic
Finishing the acrylic prototype, side 1
Roughing and semi-finishing side 1 of the prototype, in acrylic.
All toolpaths are calculated using the setting 'Angle with X-axis'.

Testing with a real prototype will find issues that would not have been detected using only computer simulations, so this step cannot be missed. Using a CNC machine was faster than using a 3D printer, and produced a much smoother model that could easily be finished.

Design of the two mold halves
The two halves of the mold, in SolidWorks.

Z-id and Mascal Design have done the complete development process in-house, including mold design, moldmaking and production. The mold as well has been designed in SolidWorks: analysis of the geometry resulted in a parting line, which could be extended to a closing surface for the mold. This is a "ruled surface": swept by a moving straight line. For this first production series a double mold has been created (so with two identical cavities).

DeskProto screenshot
the resulting aluminum mold
Toolpaths for the mold in DeskProto and the resulting aluminum mold.

Mascal Design machined the two mold halves in aluminum, here again using DeskProto to generate the toolpaths. To be honest we do not recommend to use DeskProto for curved closing surfaces of an injection mold, as we cannot guarantee a perfect fit of the two sides. Still this project again proves that a skilled operator can achieve results that amaze us. What helped is that the surface's curves are very gentle: maximum slope far below 45 degrees. And for the finishing toolpaths a very high precision has been used (many toolpaths!.)

presentation photo
The GreenPolder Spork presented.

The total development process for the spork, from sketch to production run, has taken only two weeks!!
This is amazingly rapid, and can only be achieved by skilled developers having all facilities available.

For more information about the spork visit the GreenPolder website.