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One of the most common questions we are asked is “How much draft do I need for the texture that I want?”

The general rule of thumb is that you allow for 1.5 degrees of draft for each .001″ of texture finish depth. However, there are other considerations that must be taken into account due to the many new resins and polymers, molding improvements, and various other factors that come into play in modern plastic molding. Examples of situations that require additional draft are thin wall part design and high pressure molding.

Some important considerations to keep in mind are:

  • Is the vertical wall in question an inside or outside wall? If it is an inside wall, the part will shrink onto it during molding, so you will need more draft in order to apply a texture, or apply the texture at a lighter depth.
  • Certain plastics have very little shrinkage and will therefore not shrink away from outside walls as easily as other plastics. Thermosets, Ryanite, Glass Filled Nylon, Glass Filled Polypropylene, ABS, Polycarbonate, etc. will usually require more draft in order to mold parts without scuff or drag marks.
  • If the core is very simple, and there is nothing on the core to hold the part in place during ejection, the part will tend to hang onto the cavity, creating scuff marks. The part may require more draft, or perhaps texture could be applied to the core side. This helps hold the part onto the core during ejection. This method has been used very successfully to solve this sort of problem.

I hope you find this information helpful. If you have any questions regarding this or any other injection molding information, please send us an email or give us a call at (770) 901-3200.

 

When it comes to rapidly manufacturing injection molded parts, there are several key factors to consider. Here are a few of the top considerations to start off on the right track:

Design


All successful injection molding programs begin with proper design for the process, and in this case for rapid production. When designing your part for rapid injection molding, the most important factors that contribute to lead time are part size and complexity. Whenever a larger part can be broken down into smaller pieces and then assembled, you will potentially shorten lead time. This is because simple, shallow cavity designs are produced quicker via the CNC machining process. Designing parts that are moldable with a “Straight Pull Mold” is a great place to start. This requires that all the part’s features be designed so that when the two halves of the mold are pulled from each other and the part is ejected, there are no secondary processes required.  This is due to mold material’s tendency to pull through part plastic (this is referred to as an ‘undercut’.) Undercuts require mold pieces to pull out sideways, perpendicular to the direction of the pull. These ‘side actions’ as they are called can require ‘hand loads’ for lower volume projects or automatic/mechanical loads for higher runs.

Material


Ideal quick turn projects should utilize standard, off the shelf materials and colors that are either already on hand or can be quickly sourced from a material distributor. Generally, lack of need for name brand material does not cause issues, but this is not the case for all projects.  When a precise brand and type of material is required, the material can be ordered and shipped while tool cutting occurs simultaneously. Should the material not arrive within the allotted window, a substitute material can sometimes be used in place of the production material to, at the very least, confirm basic design and function of the part. Once production material arrives, a second sample run can take place before proceeding with higher production runs.

Cost


Of course when there is a lead time requirement for parts quicker than the standard, there are cost considerations. These considerations are driven by additional man hours required by the project up front and often result in overtime and extended shop hours to achieve the desired ship date. Those items that can be sped up? Things such as tool design, steel or aluminum delivery to the shop, part material ordering, and scheduling sample production runs.

It is important to remember that in many cases, all the money in the world cannot speed up certain processes. Cutting of the core and cavity, for example, is at the mercy of the almighty CNC machine. So while there are things within a tooling shop’s control, other things will always have a fixed lead time. This is why those factors mentioned become even more important to reduce the number of days to the finish line.

Selecting an appropriate material is, perhaps, the most important factor when implementing a design for injection molding. With literally thousands of different resin grades to choose from, an erroneous choice can prove to be disastrous. Thorough research and consultation is strongly advised, especially for anyone new to plastic part design. A simple web search, along with sites such as www.ides.com and www.matweb.com are invaluable tools for any novice or veteran of injection molding.

Resin Selection Guide

Material selection is often based on the application of the part. While every part is unique, there are some generalities to follow. Click here
for your complimentary Plastic Resin Chart, which includes material names, trade names, abbreviations, descriptions, and most importantly, the most common applications for each particular material.

It is important to note that shrink rates for different materials differ, some more significant than others. Changing a material after a mold has been constructed can lead to inconsistencies in geometry. It’s always a great idea to check with the selected molder before changing materials.

 

Injection Molding

Here at Quickparts, we are in constant contact with engineers, mold makers, machinists, and other self-proclaimed experts of the manufacturing industry. Over the years, our molding lexicon has grown tremendously – to a “molding urban dictionary” of sorts. Listed below are some of the most common terms that frequent our ears daily.

What did we miss? We challenge you to send us your most creative synonyms!

Cavity Refers to the upper half of the injection mold usually the show surface of the finished product but is mainly concave
Core Refers to the side of the tool where the plastic part is injected from; also known as the bottom half of the tool
Gate Refers to where the plastic enters into the cavity of the mold.
Hand Load Aluminum or steel feature in a mold used to create undercuts in molded parts.  They are manually removed from the mold during the part ejection process.
Heel Refers to the portion of an automatic custom injection mold that keeps the slide in the forward position when the molding machine is closed on the mold
Horn Pin Pin used to actuate the slide on an automatic injection mold
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
Side Action Term used for slides and/or hand pulls used in the injection mold build process
Vestige Material protruding from the gate area after gate runner has been removed from the injection molded part. This vestige is usually trimmed by the molding machine operator

We have some great ways to help you save money on your next injection molding project.

:: Top 5 Money Saving Tips

1. When selecting a material for your injection molded part, do not just assume that you need a material that has the best properties. A lot of people overcompensate by selecting materialsthat they don’t really need. Since material is sold by the pound, this drives the piece part price up. Figure out what your needs are, and discuss them with a material representative. These guys will help you select a material that best meets your criteria, and will save you money.

2. Try to minimize secondary processes such as pad printing, custom inserts, painting, etc. All of these processes require extensive setup times and costs which will need to be spread out over the piece part price.

3. Select the right molder. There are many different types of molders out there, some are very large, and some are very small. Keeping in mind the requirements for your parts, select a molder that is capable and has the right size machines for your parts. If your requirements are low, stay away from the big flashy injection molders with lots of machines. Their overhead is too high.

4. Try to order as many parts as you can at one time. This spreads out the setup cost over more parts, thus leaving you with a lower piece part price.

5. Design your part so it is as moldable as possible. Make sure there is plenty of draft to facilitate ejection, and eliminate any thin steel conditions that will cause more mold maintenance down the road.

I hope you find this information helpful. If you have any questions regarding this or any other injection molding information, please send us an email or give us a call at (770) 901-3200.

“Out of which material should you build your mold, steel or aluminum?” This is a very common question that we receive from our injection molding customers and is an important decision to make. The answer is usually dictated by your project requirements, expectations, and what ultimately defines “success” for your project.

QC10 aluminum is an incredible product that machines quite easily (40% faster than those made out of P20 steel). This saves you time and money, with parts in hand in as little as 1-2 weeks. On the other hand, if we were to make a mold out of steel, it will typically run around 100,000 parts while maintaining a polished A2 finish on the cavities.

Will the parts look good if you buy an aluminum mold?

Absolutely, unless you are trying to obtain an optical grade finish, which would likely require a steel mold. Aluminum transfers heat almost 5 times greater than steel, and this gives us a large window for processing. Typically we can run 5,000 to 15,000 parts off an aluminum mold before resurfacing the part line.

So what kind of mold should you buy?

For low volume parts at a reasonable price with a fast lead time, aluminum is the way to go. If you need a few hundred thousand parts, or something that is optical grade, then we would suggest building your mold out of P20 or another grade of steel.

If you have any questions regarding this or any other injection molding information, you can email us at quote@quickparts.com or give us a call at (770) 901-3200.