While creating the plastic part drawing, the designer has the best opportunity to decide on the most suitable design for the mold and/or to make suggestions on how the product design might be modified to improve productivity and simplify the mold design; in turn, simplifying the mold design reduces mold costs.
Once the mold design concept has been agreed upon, and as engineering of the mold progresses, the opportunity to make conceptual changes or improvements diminishes and any costs associated with it will increase.
By the time the project reaches completion, the opportunity to make changes is low, and any costs could add up to 150 times the cost of a change in the design phase!
At the beginning of a mold build project, the customer may have only part samples, a CAD model or a 3D-printed model of the part they want to mold. While this may be advantageous to better visualize the product, it is absolutely necessary to have a complete detailed drawing of the product to minimize risk for all parties involved in the final decision. This drawing should show all features, tolerances and specifications.
A complete plastic part drawing should contain the following information at a minimum:
A 3D solid model of the part or a completely dimensioned 2D plan and section view;
Any small or intricate details blown up into additional sections or views, for example, ribs or bosses;
A detail showing any fits to other components;
Engraving, artwork and cavity numbering;
Mold label information (if in-mold labeled);
Surface finishes;
Any stacking details (if appropriate);
Part weight (using an assumed plastic density);
Part volume (if filled and weighed);
Center of gravity (if appropriate);
Identification of plastic or steel sizing;
Identify all split lines and parting lines, including any intentional mismatches.
Once the part drawing is completed, it must be reviewed with the customer and internally at the moldmaker’s facility.
The following checklist can be used as a part drawing critique during the part design review meetings. Embedding a part design critique meeting into your mold design process can save thousands of dollars and weeks of mold build time.
Answering the questions below will ensure that a proper review of the part takes place and that all critical aspects of the part design have been considered and approved by the customer, and are acceptable to the moldmaker.
1) Is the drawing a plastic part drawing or “steel part drawing?” Is this clearly marked on the part drawing? A steel part drawing is the plastic part with shrinkage dimensions applied, so that the mold designer does not need to add shrinkage. This is often used when the shrinkages are not uniform around the part
2) Is the shrinkage defined? Is there one (1) general shrinkage or multiple shrinkages?
3) Are part weight and tolerances clearly shown?
4) Is all geometry defined (radii, angles and so on)? Are complicated details called out in blowups and section views such that the part design is fully understood?
5) Are all negative drafts on the part eliminated? Are all drafts defined, including ribs, bosses and sidewalls?
6) Are there any sharp corners on the drawing? If possible, a minimum radius of 0.25 millimeter (0.010 inch) should be used on plastic parts. A radius of 0.8 millimeter (0.030 inch) is the minimum recommended radii as the stress concentration is mostly eliminated above this.
7) Are the parting lines and all split lines defined? Are all intentional mismatches between core and cavity shown and defined?
8) Has a CAE flow analysis been conducted? Will the part fill and avoid any problematic weld lines and potential voids? Review the L/t ratio (length of flow/thickness) and confirm it is acceptable.
9) Are all venting locations shown and vent sizes defined?
10) Are all potential pinch points to the flow of the molten plastic eliminated? For example, are all thick sections that may cause “race tracking” of molten plastic eliminated?
11) Are horizontal sections (bottom/stack shoulder) 0.05 millimeters thicker to account for stack compression and ease of filling?
12) Are locations where sinks may occur (like at the end of a rib) called out? Are thick-to-thin transitions designed correctly to reduce sinks?
13) Is the gate position defined and an acceptable gate vestige called out? Usually, the acceptable vestige for a valve gate is flush with the molding surface or slightly into the molding surface to prevent interference. Normally acceptable vestiges are around 50–75% of the gate diameter if the gate is a hot tip. Is a dimple needed to hide the gate vestige?
14) Is allowable warpage called out?
15) Do the parts need to stack and de-nest? If so, is the stacking height shown, and is there a diagram showing the stacking of the parts?
16) Are all ribs and bosses shown in plan view, top view and side view?
17) For multi-cavity molds, is the cavity numbering identified?
18) Are all molding surface finishes defined?
19) Is all required engraving shown on the part? For example, does the engraving need to be mirrored on the molding surface?
20) Is any geometry to be left off until after the first test (pull rings, engraving)?
21) For critical dimensions, will the dimension be left “steel-safe” for the first run so that the sizing can be adjusted?
22) Have any deviations to standard tolerancing of molding surfaces and fits been noted?
23) Has the part drawing been reviewed with the customer and signed off?
Time for Approval
Once the part design has been critiqued and revised accordingly, the customer must approve it. This step is critical and must never be skipped. Ideally, part approval should take place before a detailed mold design begins so that the mold designer can note any changes in the design and account for the corresponding change costs. However, in today’s fast-paced environment, the mold designer must sometimes work parallel with the customer by completing some of the mold design concept while the part is still being finalized. This approved part drawing, along with the details of the mold design (typically called the mold design order or order confirmation), can now be used to complete the mold design.
Spending the time to critique and carefully evaluate the part before creating a mold design is always a good use of time. If a problem is caught and corrected during the part design review, it can save up to 100 times the cost to resolve the problem at the end of the project. A thorough plastic part design review represents just a small fraction of the time required to design and manufacture the mold, and it ensures that you and your customer have an agreed plastic part for the mold build project.
Although the given example has a simple geometry, there are many other geometrical features that can affect the performance and assembly of a device. This would depend on the material specifications.
The designer does not have to choose a primary material for product design at this stage. However, they can still use flexible materials in case of an unexpected problem later on in the development process, such as during prototyping and production.
It is unlikely that any of these candidates will be able to do the job well.
Materials that are considered for consideration come with their own advantages and disadvantages. Based on past experience, the designer might have a favorite material. When working with familiar materials, it can be helpful, but other materials may be more appropriate.
However, decisions made solely on cost of materials or manufacturing are not based on performance or other advantages.
Candidates should be evaluated on the basis of their processing costs, end use performance, and overall manufacturing characteristics.
Designers can choose the most suitable materials by weighing their properties and characteristics based on an almost unbiased grading system.
Although individual numerical ratings for a house are sometimes arbitrary, I believe they are based on actual numerical data.
After considering all of these factors, a semi-quantitative process will be used to select the best material candidates based on balance.
After the initial design and material have been determined, the design should be modified for manufacturing. The input of process engineers and tooling engineers is invaluable.
Moldability is essential for the part geometry. Designers should consider the effects of different phases of the injection molding process on part design.
Every stage of injection molding, including mold filling, packing and holding, cooling and ejection has its own requirements.
Practically, the part should be modified with draft angles to aid in part ejection and flow (and reduce stress concentrations), radii to help in flow, and surface texture to improve the visual appearance (due to material shatterage) of the sink marks on the wall to the side of the ribs.
These are just a few possible design modifications that may be required from a manufacturing perspective.
You should evaluate the effect of modifications on the part’s end-use performance after they have been made. Because design changes such as adding draft angles to the ribs can have a significant impact on the maximum deflections or stresses caused by service loading,
The prototype of the final part design is usually made at this stage to test both its manufacturability as well as its performance.
Because all the process (e.g. molding simulations) or performance design work (e.g. structural analysis) that have been done up until this point in time are “theoretical”, prototyping is necessary.
This is particularly important for molded plastic parts because many manufacturing-related problems are difficult to predict in advance (weld line appearance and strength, warpage, sink marks, etc. ).
It is important to create prototype parts from the desired production material in order to achieve realistic results. This involves either building a single cavity tool (or a unit) for smaller parts, or soft (often simplified), tools for larger parts.
Prototyping can be costly and time-consuming. However, it is better to detect manufacturing or end use performance issues with a single cavity or soft tool than a multi-cavity hard tool.
To reduce the cost of tool rework, steel safety practices should be observed.
Molded prototypes are useful for verifying engineering functions and manufacturing processes. However, there are other prototypes that can be easily made (rapid prototyping, etc.). They can be made quickly (within hours, or even days) and offer invaluable models for communication and limited functionality well before the prototype tool is built.
prototypye and original part
After the parts and prototype tools have been tested and modified, pre-production tools or production tools can be built.
Sometimes you have inserts that need to be fixed inside your part. You need to consider whether they get molded in or they are presses or welded in after the molding has commenced. With this, both options are viable and come down to the economics of the operation. Do you go for a higher priced tool that can accommodate inserts to be molded over, or do you press them into the part after the fact. If you have a low production run, it might be worth considering a post molding operation. For long production runs, it might be more beneficial to have the inserts molded in. It all depends on the customer’s preference, the viability, and the project’s budget.
Gate location is the area where the material will be entering into and filling the cavity of the part. It is important to keep in mind where you intend to gate your part and possibly make provision. Some questions to consider are: Am I allowed to have a gate mark where I am envisioning my gate? and Is this gate at a location where the material will flow from a thick walled to a thin walled region of the part. You must also account for ejector pin marks that will most likely show up on the underside of your molded part. If ejector marks are not allowed then that must be called out on your print so other ejection alternative can be considered.
The material selection process can be as simple as an internet search for the material of an existing part already on the market, or as complex as identifying every single requirement and material property from the ground up. The first step is to define the requirements needed for your particular application. From there it’s important to narrow the choices b process of elimination. Do you need it to be rigid, flexible, elastomeric etc? Is there a specific application? Medical? What specific property requirements are there? Sometimes the best thing to do is to not reinvent the wheel and do a search history for similar commercial application s if possible, then call up the material supplier for recommendations.
You want to make sure that you try and make the wall thickness of your part as consistent as possible. It’s alright if you don’t have uniform wall thickness to some extent, but uneven wall thickness greatly increases the likelihood of sink marks, warpage, voids, molded-in stress, longer cooling times, and even material flow restrictions. If wall thickness must be uneven, it is best to have smooth transitions that taper over some distance. The size of the part and the ability of the material to fill will determine the minimum wall thickness allowed for your plastic injected part.
All materials shrink at different rates and at varying degrees within the cooling process of your injection molding operation. Shrinkage and warpage are two different phenomena that can occur. Shrinkage occurs where there is a difference between corresponding linear dimension of the mold and the molded part. Warpage is a dimensional distortion in a molded plastic caused by excessive residual stress in the part. There are various things to consider when trying to control either one of these occurrences. Material considerations, part geometry considerations, tooling considerations, and processing considerations all play a part.
Sharp corner are to be avoided at all costs. Sharp edges, such as corners of a square hole, will produce a part with high levels of molded-in stresses. These much of the time result in weak points that lead to part failure and cracking. Adding radii to sharp corners will reduce the amount of molded-in stress. Radii redistributes the stress more evenly and facilitates the flow of the material and ejection from the mold. Stresses rapidly build whenever the inside corner id less than 25% of the nominal wall thickness of the part.
As a product designer you want to minimize the amount of material required to fill your part, while at the same time increasing its structural integrity. Thin walls need some sort of support so that the walls don’t warp or collapse. Ribs are commonly employed on injection molded parts in order to stiffen relatively thin parts. Ribs, bosses and other projections on the piece part wall will greatly strengthen your part while, but if done incorrectly can contribute to other molding issues such as sink marks and non-fills.
Try and imagine your part being molded. It can be difficult for some to think in the “negative”, and by that I mean visualizing the empty cavity space that the liquid plastic will fill in order to mold into a plastic part. Inevitably, once that cavity space is filled, your part will have to be ejected from that space. In order for that to happen, the two mold halves will have to separate, leaving behind your plastic injected part in one side of the mold (preferably the side where you plan on ejecting from). You need to visualize and plan for where this “parting line” will be so as to ensure that your part does not get trapped in the mold.
Undercuts on your part wont necessarily make it more difficult to mold your part, but rather more difficult to demold. The undercut portion of the plastic part will get trapped inside your mold once the part is cooled and hardened, and in turn making it impossible to eject from the mold without other mold actions. Many times, undercuts are a necessity for part function. Side actions and lifting mechanisms will have to be introduced to your tool in order to deal with the ejection of your part. Sometimes this is not avoidable, but if you are looking to save on tooling cost, it might be worth trying to redesign in order to eliminate necessary tooling costs.
In order to bring a new plastic product to market and ensure its future industrial viability, it is essential to take into account design, materials, production and processing, as well as managing and/or recovering, this product once its life cycle has ended.
In the initial phase, it is important to be aware of possible legal restrictions, limitations arising from similar developments already on the market and product certification requirements. Product features must also be considered (weather resistance, resistance to chemical agents, resistance to high or low temperatures, chemical incompatibility, lack of mechanical properties, etc.).
Once the viability of the product has been analysed, there are three keys to successful development: design, materials and the manufacturing process. The optimum product will be obtained from the best combination of the three.
A comprehensive and thorough description of specifications and end-use criteria is provided throughout the entire product development process.
Engineers and designers will create the product based on these requirements, which is the first step in the construction process.
It is not possible to use nonconforming products.
A product should be designed according to its intended end-use, rather than its quality.
When defining solid products, terms such as “strong” or “clear” should be used. Because it is not as straightforward, determining how a product should look and what it should withstand is much more challenging.
However, despite all the possible uses of a product, its use can be difficult to measure when considering the potential misuse of that product. In general, it applies to replacing existing products with new ones (e.g. on a conversion to metal basis), but not when producing completely new products.
It can be difficult to anticipate specifications such as these.
The goal of this stage is typically to create prototypes (or models) to ensure that our understanding of the end-use specifications is complete.
A number of factors must be taken into consideration, including structural loading, environment, size specification, and standard requirements.
There are several factors to consider and define when it comes to loading types, speeds, loading time, and loading frequency. Consider the load while mounting, transporting, storing, and using the product. Plastic components are often designed to ensure that when a product is shipped and stored, it is properly packaged.
In addition to assessing typical loading situations for the part, the manufacturer should consider worst-case scenarios as well. It is crucial to determine which side of the load will be most affected if it fails.
Products that are poorly designed are more likely to fail, while products that haven’t taken misuse into consideration will also fail. It is especially important for product designers to ensure that their designs are reliable when failure will cause serious injury.
Because the properties of plastic materials are extremely sensitive to environmental conditions, it is essential to specify the anticipated environmental conditions for use. In addition to radiation exposure and relative humidity, a chemical environment and a temperature are also required.When assembling and storing items, the environmental conditions to be met (ovens for curing paints, acids, adhesives, etc.) should be carefully examined. A temperature high enough for creep or oxidative degradation is not recommended, and a temperature low enough for creep is also not recommended.
Again, the key to preventing misuse is anticipating it, forming worst-case scenarios, and specifying requirements in advance. Chemicals in the product and any risks of UV exposure must be clearly displayed if the product is intended for outdoor use.
The measurements of plastic parts, as well as their surface finishes, are often critical for practical reasons. Tooling and development costs are significantly affected by differences in measurement tolerance.
In certain applications, plastics are regulated by certain agencies. It is important to know which agency is responsible for a given product.
If you follow this step correctly, conforming to these standards should be easy. A material’s grade (flammability, food quality, etc.) or performance standard can be verified (EMI shielding, for example).
Prototypes or pre-production are often required to assess a product.
The maximum cost of the product and the replacement interval are also specified during the first phase of development.
The product development team’s goal is to develop a product that is attractive and affordable (i.e., the most efficient design). Similarly, other restrictions related to the market, such as size, color, and shape, should also be quantified. As aesthetic values are difficult to quantify, models (prototypes without functional components) are a great way to communicate them.
A business must also consider how long the material will last, as well as the type of material to be used.
Designing products and processes to have the lowest possible costs (i.e., the most efficient projects) is crucial. Market-related constraints such as color and size must always be communicated to consumers.
You now have the product that was once a mere idea. Knowing that you’ve gone all the way to this point is a big deal. Remember that not everyone has the ability to actually execute their plans.
The entire process may be tedious. Problems will arise as you travel from point A to B. But it’s all about the way the execution is done that lessens the hassle. Here are a few additional tips that can help you make the process more efficient:
1) Choose the right people
Have the right people in your team will make all the difference. It may be your idea. But other people may show you loopholes you may not have thought of. Usually, we become obsessed with how perfect our ideas are. This makes us miss even the smallest problems in the details. That’s what the other brains in your team is for.
Your team will also help you lessen the load. You can’t juggle it all. There’s a chance that you’re not that familiar with some of the tasks involved. With real experts in your team, the chances of failure are lessened.
2) Take risks
What makes your idea great is the fact that it is yours. Don’t be afraid to take risks. Remember that no one else has the kind of mind you have. This is your dream, so don’t be afraid to experiment. Some of the things you‘re thinking about may not have been done before. But don’t let this stop you.
3) Be realistic
Though you’re open to take risks, don’t overdo it. Accept it when something just isn’t possible. Your team will tell you whether anything is amiss. Trust your gut, but trust your team as well.
4) Be flexible
The more flexible you are, the faster this will be. This is why the moment you hit a wall, be ready to change anything. Don’t be stubborn. If you’ve tried everything and it still doesn’t work, be ready for adjustments right away.
Finally, plan your next steps.
Don’t be too stuck on the creation of the product that you forget what happens after. As early as now, create strategies in terms of sales and marketing. In fact, even before you begin production, you should have a few ideas in place. If it’s a new product no one has ever seen, you can create hype in the market early. Once you release the product, the welcome will be amazing!
Now, all that’s left for you to do is to get started. Good luck, and hope to see your product out on the shelves soon.
Design is a big deal. It’s so big it’s a category with subcategories under it. There’s design for
Manufacturability / Function / Strength / Flexibility / Maintenance / Assembly
Aesthetic (Industrial Design)
Contract manufacturers typically play in all those buckets to one degree or another. This post will deal with plastic injection parts. During the RFQ process, potential customers share their part — either the physical part or prototype, or a set of CAD drawings. The engineer looks at it to get an idea of what they want to make and to see if there are ways the design can be improved for manufacturability.
Every product is different but, as a general rule, engineers will look for three things:
1. Which direction is the tool going to pull?
A plastic part is made in a mold. There are two halves that open and close. All the product features (any details, etc.) should be in one of the two directions of the pull. If there are features in a direction other than the pull of the mold, this will complicate the tooling by requiring the addition of different types of slides — and that means a jump in tool cost. It’s best to avoid this if possible.
2. Are there any undercuts? Are there features that will get trapped?
In the illustration below, you can see where the undercut could get caught in the tool. If your design has obvious features like that, is there a way to change it? Can it be designed without the undercut? You might like the aesthetic, but you won’t like it when your product keeps tearing up in the tool. Sometimes you can get around having undercuts by adding slides, but the mold gets more expensive.
3. Are the wall thicknesses consistent? Are there very thick or very thin areas?
Thick areas were typically designed that way to make the part strong. But thickness dictates cooling time, which can lend itself to areas of sink. Instead, the engineer will determine which direction the maximum force will come from; which direction needs to be stronger. Then they’ll look to see if ribs can be used to reinforce the part. Depending on the part, thicknesses are generally run 3 to 5 mm. What you don’t want to do is go abruptly from a thick to a thin wall section. The part needs to have gradual transitions. If you have a thick section, you can shell — or hollow — it out.
Those are the three easy design issues engineers look for right away. From there they
might also look such things as draft angles. Simply, a draft angle is a slight taper of the sides/walls of the mold to decrease friction when you want to get the part out. Straight walls create friction. But the more draft angle you have, the easier it is to get the part out. Here’s my favorite draft angle illustration: a muffin pan. The sides of the muffin pan cups are slightly angled so muffin comes out easily.
There are plenty of other details a product engineer will look at, but those are the biggies. They’re simple things you can look over BEFORE you send your part/prototype/CAD drawings to the contract manufacturer. The process of product development can be time-consuming, but knowing simple fixes like these might just move things along a little more quickly.