Injection Molded Bicycle Tire Lever

This is a guide on how to design, manufacture, and assemble a plastic mold manufactured using a 3 Axis mill. I Made a mold for a bicycle tire lever and so the guide will follow my process and each step I took along the way. This design is intended to showcase the design process I took and the steps you would need to take in order to create any custom mold you wanted. I will not be showcasing the individual Cad Basics in this guide so it is advised you have a basic understanding of fusion 360 when starting the project. There are many guides and video resources online which you can use in order to follow and complete these steps if you need them, and I will link several guides that may help you when we get to the manufacturing section.

Machine & Tools:

I used a Haas VF2 for this project, you can use any cnc mill for this project and if you are lucky enough to have access to a 5 axis mill you will be able to create much more complex molds and it will save an immense amount of time and effort if you model contains complex geometry. I used fusion 360 for my project but you can of course use what ever program you prefer.

I used a 1/2" Flat End Mill for facing operations, a 1/8" flat End Mill for clearing the majority of the stock on the interior of the mold, and a 1/8" Ball End Mill for the 3d smoothing operations in order to create a smoother final finish. A probe would also very useful to set the work coordinate system and tool offsets however it is not necessary by any means as this can be done either manually.

Material:

The metal stock you need will depend on the size of the mold you are making. I used 2 1¨ x 2¨ x 6¨ 6061 Aluminum Square Bars. Generally aluminum should be a great choice for your mold, its easy to machine and should be fully capable of withstanding the pressure of the injection mold.

The first step I personally took was brainstorming different potential designs. I created a concept sketch as seen in image 2 in order to being to lay out the general design and to have a general idea when beginning to design a model in cad. I then 3d printed out several different bike tire levers, one such example is seen in image 1, in order to determine the final design I wanted to go with. I recommend 3d printing out many different designs when designing your own mold as 3d printing is much easier and less costly than the final machining. While brainstorm a design its important to keep in mind that the more overhangs and complex geometry you have the harder it will be to machine out the final mold and it might be entirely impossible depending on the model. In my case I used the prototype on my own bike and it worked well so I moved to the design of the model in fusion 360.

The Bill of materials for a mold is pretty simple, The Bill of Materials for my mold is listed below.

Bill of Materials

Part Material Availability Size Manufacturing Method Quantity

1. Mold Aluminum In stock 2"x1"x6" Cnc Mill 2
2. Bike tire lever plastic In stock 0.982in^3 Injection molded 1
3. Bolts Steel in stock 2 in hex bolt 4
4. Bushing Aluminum in stock 2" Diameter .75" Height Cnc Mill 1

When designing the model for your mold the most important thing is to ensure you design for manufacturing. I spent way to much time on trying to design a complex mold and it ended up delaying my project weeks past when I would've liked to finish it. If at all possible reduce any overhangs or non machinable parts where the tool is not able to reach a face. I also realized too late into designing my mold that parts of the mold I was creating were too small to machine with the tools I had access too forcing me to redesign my mold again.

Once you have the model of the object you are attempting to create a mold for the creation of the actual mold in fusion 360 is relatively simple. First intersect the bodies of your stock and model as seen in image 2. Next use the Combine tool and select the stock as the target body and the model as the tool body(image 3) and use the cut operation. Repeat this process for each part of your mold.

Next I ensured that each part of my mold was machinable on a 3 axis mill using the section analysis tool. Under the Inspect tool menu choose section analysis. Slide the section along each part of your mold (image 4) and ensure there are no overhangs as unless you have a specific tool to cut them out or a 5 axis mill these will make your mold impossible to machine and can make it impossible to pull your finished plastic object out of the mold. I found this to be an incredibly easy to use and valuable tool when designing a mold.

Finally you must not forget to create the cutout for the bushing. I just cut a cylindrical pocket into the back of one of the sides of the mold for the bushing to sit in (Image 5&6). If your part has threads or involves something that must be very precise you can also add alignment pins. My mold did not need to be this exact and so the two sides are aligned with threaded holes in each corner.

For this step I won't be able to go too into depth about how to each individual part of every program as that would be a whole other instructable or two by itself, however I will explain what I did. If you need help with CAM a helpful resource you may be able to use is the CNC Mill resource page on the class website.

I faced both sides of my mold with a 1/2in flat end mill first to square up the stock and in order to ensure the fit together smoothly and so there less inconsistencies on the surface allowing for a tighter seal. I then did an adaptive clearing operation with a 1/8in flat end mill to clear out the majority of the material on the inside of the mold. The 3rd operation was a parallel operation with a 1/8in ball end mill that cleared the rest of the material and smoothed the 3d portions out. Finally I drilled 4 holes so that I could Thread them and connect the two sides of the mold together. The other side of the mold was machined in the same way however I also cut a cylindrical pocket and drilled a hole for the bushing into the top of the stock.

I machined my mold out of 6061 aluminum and I used and would recommend https://app.fswizard.com/ as its relatively simple and intuitive.

This step was relatively simple aside for one of the programs failing at the end. I used four different nc programs to cut out the two sides. I first cut the the mold for the top side using a 1/2in endmill, 1/8in endmill, and a 1/8in ballendmill. I then ran the program for the top of the top side of the mold which cut out the space for the bushing(image 1). I then cut the other side of the mold using the same tools. The only problem I encountered happened when I tried running the program that would drill holes into the top half of the stock. Despite being the exact same NC program as the previous one except for not running the facing or clearing operations for some reason the mill used a wrong tool and when the mill attempted to drill the end mill broke. I tried again this time making sure that the mill used the correct part however unfortunately the drill despite working fine on the previous operation broke again perhaps due to the fact it was drilling the same spot where the previous tool broke. Despite this the rest of the machining turned out great.

While the molds both fit each other perfectly due to an issue when machining the holes on the top half of the mill the drill broke and I was unable to complete the threads in the top half of the mold due to time constraints. A photo attached above however shows the bottom half of the mold which turned out perfectly. If I had not had an issue while drilling the holes on the top half the molds would line up perfectly. When I finish the project next fall all i'll have to do is drill the last 4 holes and then thread the two pieces together. The assembly is incredibly simple and only contains three parts in total as shown in the picture above.

The final build was successful,while their still needs to be 4 more holes drilled the rest of the part came out perfectly.If I had to redo this project over again I would not spend weeks trying to make a really complex mold and instead just design the initial part to be simpler in the beginning. I think In the future I would consider designing for manufacturing more from the very beginning however ultimately it was a learning experience. overall I would say I was successful as I was able to finish the entire mold just not the threading between them. Unfortunately I was not able to mold any tire levers as I ran out of time so that will have to wait for next year. Overall I enjoyed the project and would recommend a mold as it was an interesting and skill enriching experience.