Cad Mold Design

[Su Mcdowall]

Ihave gone through the learning exchange tutorial for mold and browsed the forum for best tools for step by step process for plastic injection, sand cast, and die cast and at this point I am more confused. Learning Exchange Tutorial gives an overview that follows a general sequence but it's not telling me which process they are referring to as far as die cast or plastic injection etc. Once the tutorial get into detail on the commands or tools I lose any step by step process that I was looking for. I understand different companies probably have their own mold process and techniques depending on if it's a complex assembly or just parts. So I think I am searching for a industry step by step process that can work with creo3 mold. If you or anyone know of any industry standards to follow or step by step cheat sheet that coincide with creo would help.

5. The Waterline should be used as a part Feature. The Pattern was completly starnge. This could be done in one sketch in Addition with modifications of end-conditions. Why did they hide this nice Option? In Addition, the Waterline can be done with EMX with the Placement of components.

7. Moldopening: The explode state can be done much easier with the normal Tools. The Moldopening is for checking interfearence with reference part and other cavities. Therefore you should always use small values for the opening! Otherwise the increments are to big and will not detect a collision.

I am running Inventor professional 2018. I am working in an assembly and somehow mold design was turned on. I never use mold design so not sure how this happened. It is annoying because every time I open the file it brings me to the mold design browser which is blank and I want to be in the assembly browser. But more importantly it also creates 5 extra directories in my project file which I do not want. If I delete them and open the file they are re-created. Does anyone know how to delete the mold design from an assembly?.

I didn't start with the mold design template. I actually started with a similar design and did a save as of it. I opened the original design and it doen't have the mold design in it. My design is done so if it can't be deleted then it will remain as it would take a ton of time to redo the design as this part is what everything else is mounted to. I tried copying it into a new assembly file but I could not relink my idw and my top level to it. Inventor said it wasn't the same file and couldn't be used.

Designing plastic parts is a complex task involving many factors that address application requirements. "How will the part be used?" "How does it fit with other parts in the assembly?" "What loads will it experience in use?" In addition to functional and structural issues, processing issues play a large role in the design of an injection molded plastic part. How the molten plastic enters, fills, and cools within the cavity to form the part largely drives what form the features in that part must take. Adhering to some basic rules of injection molded part design will result in a part that, in addition to being easier to manufacture and assemble, will typically be much stronger in service. Dividing a part into basic groups will help you to build your part in a logical manner while minimizing molding problems. As a part is developed, always keep in mind how the part is molded and what you can do to minimize stress.

Plastic injection molding is the preferred process for manufacturing plastic parts. Injection molding is used to create many things such as electronic housings, containers, bottle caps, automotive interiors, combs, and most other plastic products available today. It is ideal for producing high volumes of plastic parts due to the fact that several parts can be produced in each cycle by using multi-cavity injection molds. Some advantages of injection molding are high tolerance precision, repeatability, large material selection, low labor cost, minimal scrap losses, and little need to finish parts after molding. Some disadvantages of this process are an expensive upfront tooling investment and process limitations.

Core Outs

Refers to the portion of a part that is gutted out in order to achieve uniform wall thickness. This portion of the part has no end use function other than lightening the part and reducing warp

Draft

Refers to portion of injection molding part that has some taper to make it easier to remove from the mold. Generally all plastic components should be designed with draft where possible

Gate

Refers to where the plastic enters into the cavity of the mold. The two types of gates are as follows:

1. Automatically Trimmed Gates: Gates that incorporate features in the tool to break or shear the gate as the molding tool is opened to eject the part

2. Manually Trimmed Gates: Gates that require an operator to separate parts from runners during a secondary operation

Line of Draw

The direction in which the two custom injection mold halves will separate from the plastic part allowing it to be ejected without any obstructions from metal creating undercuts

Runner

A channel cut into custom injection molds, in which plastic travels from the injection molding machine, through the sprue, through the runner and then through the gate ultimately filling the part

Shear

Refers to when plastic enters into the mold and the melt is maintained by friction produced by speed and pressure. Too much shear can cause the plastic material to burn, too little can cause the material to freeze off causing short shot

Shrink Rate

Refers to how much the plastic material will shrink after cooled. This % of shrink is added to the part before the mold is designed. Every plastic material has its own shrink rate ranging from .001 per inch to as much as .060 per inch. Although most fall in between .004" and .021"

Steel Safe

Refers to the amount of metal left on the mold in order to tweak in a dimension. For example, if you have an inside diameter that is supposed to be .500 you may leave the mold at .505 in case you get excessive shrink

Undercuts

Refers to the portion of the designed component where a slide or hand pull is required to create holes, windows or clips that are not in the line of draw (#1 in Figure 1 below)

Warp

Refers to area of a injection molded part that distorts during cooling or molding, causing undesired results in the finished product. Usually caused by un-uniform wall sections

There are tens of thousands of different materials available for injection molding. Most polymers may be used, including all thermoplastics (such as nylon, polyethylene, and polystyrene) and some elastomers. Materials are chosen based on the strength and function required for the final part, but each material also has different parameters for molding that must be considered. Mixing the available materials with alloys or blends of previously developed materials enables product designers to choose from a vast range of materials to find the one with exactly the right properties.

Injection molding machines, also known as presses, consist of a material hopper, an injection ram or screw-type plunger, and a heating unit. Molds are clamped to the platen of the molding machine, where plastic is injected into the mold through the sprue orifice. Presses are rated by tonnage, which is the calculation of the amount of clamping force that the machine can exert. This force keeps the mold closed during the injection molding process. Tonnage can vary from less than 5 tons to 6,000 tons, although higher tonnage presses are rarely used. The total clamp force needed is determined by the projected area of the custom part being molded. This projected area is multiplied by a clamp force of 2 to 8 tons for each square inch of the projected areas. As a rule of thumb, 4 or 5 tons/inch can be used for most products. If the plastic material is very stiff, it will require more injection pressure to fill the mold, thus more clamp tonnage is needed to hold the mold closed. The required force can also be determined by the material used and the size of the part, with larger plastic parts requiring higher clamping force.

The mold or die refers to the tooling used to produce plastic parts in molding. Traditionally injection molds have been expensive to manufacture and were only used in high-volume production applications where thousands of parts were produced. Molds are typically constructed from hardened steel, pre-hardened steel, aluminum, and/or beryllium-copper alloy. Selecting a material for mold building is primarily a question of economics. Steel molds generally cost more to construct but offer a longer lifespan that will offset the higher initial cost over a higher number of parts made before wearing out. Pre-hardened steel molds are less wear-resistant and are primarily used for lower volume requirements or larger components. The hardness of the pre-hardened steel measures typically 38 and 45 on the Rockwell-C scale. Hardened steel molds are heat treated after machining, making them superior in terms of wear resistance and lifespan. Typical hardness ranges between 50 and 60 Rockwell-C (HRC).

Aluminum molds cost substantially less than steel molds, and when higher grade aluminum such as QC-7 and QC-10 aircraft aluminum is used and machined with modern computerized equipment, they can be economical for molding hundreds of thousands of parts. Aluminum molds also offer quick turnaround and faster cycles because of better heat dissipation. They can also be coated for wear resistance to fiberglass reinforced materials. Beryllium copper is used in areas of the mold which require fast heat removal or areas that see the most shear heat generated.

With injection molding, granular plastic is fed by gravity from a hopper into a heated barrel. As the granules are slowly pushed forward by a screw-type plunger, the plastic is forced into a heated chamber called the barrel where it is melted. As the plunger advances, the melted plastic is forced through a nozzle that seats against the mold sprue bushing, allowing it to enter the mold cavity through a gate and runner system. The mold remains at a set temperature so the plastic can solidify almost as soon as the mold is filled.

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